Operational Office: 4575115, Onkar House, Room No. 3-4, Ground Floor, Darya Ganj, New pelhi-110002 Phone: 23243042 Fax: 23243043 Despatch Office: 11, Community Centre, Ashok Vihar, Phase 2 Delhi-110052. Phone : 27224179 Regd. Office: 2-B, Nath Market, Nai Sarak, Delhi-110006. Ph. 23912380
KHANNA PUBLISHERS
ASSISTANT PROFESSOR DEPARTMENT OF CHEMICAL ENGINEERING HARCOURT BUTLER TECHNOLOGICALINSTITUTE,
B.E.(HO~S.),M.Tech., Ph.D.
Dr.RAM PRASAD
PETROLEUM REFINING TECHNOLOGY
, ,
Published by : Romesh Chander Khanna for KHANNA PUBLISHERS 2-B, Nath Market, Nai Sarak Delhi- 110 006 (India)
Q All Riehfq,Regerv,ed
This book orpart thereof cannot be tmnslated or reprodued i n any form (exceptfor review or criticism) without the written permission of the Author and the Publishers.
First Edition Fifth Reprint :2008
Price :Rs. 185.00
Computer Typeset and Figures designed by : Steps Computers, D-2/77, Dayd Pur, Delhi 110 094 Ph. 218-1367
Printed at.. Print India. Delhi-95
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It givesme a great pleasure in presenting the book on "Petroleum RefiningTechnology' .The relvant topics for working Chemical/Petroleurn Engineers in Petroleum-Refineries have.",, been covered.
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The first chapter gives an account of theories of oil and gas formahon, methods f o p , exploration and drilling for oil and gas. It highlights the development of petroleum refininB industry in India. ,.
The knowledgeof chemisty and compositionof crude oil isessentialin the selectionof the refining processes. The characteristics, constituents and classification of crude coils have been. discussed.in chapter 2.
Indian crudes such as Bombay l-hgh,Assam are waxy in nature. These require sped; method for transportation. The problems related to the handling of waxy crude oils and their -feasible solutions have heen discussed in chapter 3.
Quality control of petroleum-productsisa necessity if the products are to give satisfactory wrformance to the customers. Bureau of ,lndian~Standard; New Delhi sfandaLdizes ~rocedure ind issues specifcationsfor eachpetroleumproducts.~efktion,methodandsignifi-eof the various laboratory tests have been given in chapter 4.
Chapter 5discusses manufacture,properties and uses of petroleum products. Thischapter covers LPG, naphtha, gasoline, kerosine, ATF, diesel fuel, fuel oil, hydrocarbon solvenk " ' lubricating oils, petroleum waxes, bitumen and petroleum coke.
Petroleum refining processes have been discussed in six chapter (611). Crude ou distillation is the first unit in the refinery and carried out in two stages-atmosphericand vacuum, Before discucssing these processes the removal of impurities by electrical desalting process ha, been discussed.The influenceof the process variables on the opera tion of a fractionatingcolumn ?.* and the scope for improvement have been discussed in Chapter 6.
Crude oil distilltion produces reside which is to be upgraded. Thennal conversio~~.. processes for this purpose include visbreaking and coking. These processes have been discussea in chapter 7. lh
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Catalytic conversion processes use catalyst and either change carbon number or carbon/ hydrogen ratio. The most important processes include fluid catalyticcracking, catalytic reforming,hydrocracking,catalyticalkylation, isomerizsltion and polymeriza tion Catalytic isom& tion neither changes carbon number nor carbon/hydrogen ratio. These processes have been dis-,. cussed in chapter 8.
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Finishing processes are necessary to make the petroleum products suitable for use with respect to performance,corrosivity, suitabilityon storage,odour etc. Various finishing processes such as hydrogen sulphideremoval processes, sulphur recovery processes, sweeteningprocess-,,. es, solvent extraction processes and hydrotreating processes have been discussed in chapter 9.
-Ram Prasad K ~ ~ P W
I will be highly grateful, if short comings of this edition inform of contents, errors are highlighted to me.
It is hoped that this book in its present form will be useful for the students of chemical engineering.
Chapter 14, highlights, designs and operation of pebbleurn processing equipments.
Air, water and soil are vital of life on this planet. These resources are to be protected and used wisely. Chapter 13 discusses air pollutions, water pollution and sludge treatment and disposal.
Generationof process engineershave accepted corrosion as a fact of life, an incurablevirus whose progress may be slowedbut never stopped. Corrosioh can reduce the lifeof refinery units. Chpater 12 disucsses typk and forms of corrosion and their control in crude oil distillation, thermal cr?cking, fluid catalyticcracking,amine gas processing,and steamand condensatelines.
Chapter 11discusses the manufatture of bitumen from crude oil.
(iv) L@~&&@p@b*ould possess and maintain proper viscosity, flow as liquid at thehandling and operatingtemperature and have good thermal and oxidation stability. Lubricating oils of various grades are manufactured by mixing of the selected lubricating oils base stock and additives. A modem lube oil complex consists of vacuum distillationunit, solvent deasphalting unit, solvent extraction unit, solvent dewaxing unit and hydrofinishing unit. These processes have been discussed in chapter 10. The details on the manufacture of petroleum waxes have also been presented ir\ this chapter.
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3.1 INTRODUCTION 3.2 PIPELINE TRANSPORTATION 3.3 WAXY CRUDE OILS 3.3.1 Definitions of Rheological Parameters 3.3.2 RheologicalClassification of Fluids 3.4 FLOW PROPERTIES OF WAXY CRUDE OILS 3.5 PUMPABILITY CHARACTERIS~CSOF WAXY CRUDE OILS 3.5.1 Temperature 3.5.2 Yield Stress-Model Pipeline Test 3.5.3 Flow at Restart 3.5.4 Effective Pipelie Viscosity 3.6 METHODS FOR PIPELINE TRANSPORTATION OF WAXY CRUDE OILS 3.6.1 Use of Pow-Point Depressants/Flow Improvers 3.6.2 Mechanism of Flow Improvement 3.6.3 Point of Additive kijection 3.6.4 Pour point Reduction by Additives 3.6.5 Effect of Flow Improvers on Yield Stress and Viscosity 3.6.6 lncorporation of Low Pour Point Crudes in Waxy Crudes 3.6.7 Crude Oil Conditioning
3 TRANSPORTATION OF WAXY CRUDE OILS
2.1 INTRODUCTION 2.2 CHARACTERISTICSOF CRUDE OILS 2.3 CONSTlTUENTSOF CRUDE OILS 2.3.1 Hydmarbons 2.3.2 Non-Hydrocarbons 2.4 CLASSIFICATION OF CRUDE OILS 2.4.1 Characterization Factor 2.4.2 Correlation Index 2.4.3 Method of Structural Group Analysis
2 CRUDE OILS CHEMISTRY AND COMPOSITION
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1.1 INTRODUCTION 1.2 FORMATION OF OIL AND GAS 1.3 OIL AND GAS EXPLORATION 1.4 DRILLING FOR OIL AND GAS 1.5 PRODUCTION OF CRUDE OIL AND NATURAL GAS 1.6 PETROLEUM REFINING, OPERATION AND OPTIMIZATION 1.6.1 Selection of Processes for Optimization 1.6.2 Optimization in a Running Refinery 1.6.3- Refining Capacity in India
1 PETROLEUMEXPLORATION,PRODUCTION AND REF~NING
29-44
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15-28
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4 --Q~~&JTY~ONTR OF OPETROLEUM L PRODUCTS
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4.1 INTRODUCTION 4.2 CLASSIFICATION OF LABORATORY TESTS 4.3 DISTILLATION 4.4 VAPOUR PRESSURE 4.5 FLASH POINT AND FIRE POINT 4.6 OCTANE NUMBER 4.7 PERFORMANCENUMBER 4.8 CETANE NUMBER 4.9 ANILINE POINT 4.10 DIESEL INDEX 4.11 CALCULATED CETANE INDEX 4.12 CALORIFIC VALUE 4.13 SMOKE POINT 4.14 CHAR VALUE 4.15 VISCOSITY 4.16 VISCOSITY INDEX 4.17 PENETRATION TESTS 4.18 FREEZING POINT 4.19 CLOUD POINT AND PQUR POINT 4.20 DROP POINT OF GREASE 4.21 MELTING AND SEITING POINTOF WAX 4.22 SOFENING POINT OF BITUMEN 4.23 INDUCTION PERIOD OF GASOLINE 4.24 THERMAL STABILITY OF JET FUELS 4.25 GUM CONTENT 4.26 TOTAL SULPHUR 4.27 ACIDITY AND ALKALINITY 4.28 COPPER-STRIPCORROSION TEST 4.29 SILVER-STRIPCORROSION TEST FOR AVIATION TURBINE FUELS 4.30 ASH 4.31 CARBON RESIDUE 4.31.1 Conradson Method 4.31.2 Ramsbottom Method COLOUR DENSITY AND SPECIFIC GRAVITY --. GAS CHROMATOGRAPHY OF PETROLEUM GASES AND LIQUIDS REFRACTIVE INDEX OF HYDROCARBON LIOUIDS --LEAD IN GASOLINE WATER SEPAROMETER INDEX (MODIFIED) (WSIM) DUCTILITY
4.32 4.33 4.34 4.35 4.36 4.37 4.38
S PETROLEUM PRODUCTS 5.1 LIQUEFIED PEIROLUEM GASES 5.1.1 Composition of LPG 5.1.2 Properties of LPG 5.1.3 Production of L K 5.1.4 Uses of LPG NAPHTHAS 5.2.1 Methods of Manufacture of Naphthas 5.2.2 Composition of Naphthas
45-64
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(vii)
5.2.3 Usesof Naphthas 5.3 MOTOR SPIRIT 5.3.1 Spark-Ignition Engine 5.3.2 Composition of Gasolines 5.3.3 Properties of Gasolines 5.3.4 Types of Additives Used in Gasolines 5.3.5 New Gasoline Blending Components 5.3.6 Alternative Gasoline Fuels 5.4 KEROSINE 5.4.1 Manufacture of Kerosines 5.4.2 Composition of Kerosines 5.4.3 Properties of Kerosines 5.4.4 Uses of Kerosines 5.5 AVIATION TURBINE FUELS 5.5.1 Composition of ATFs 5.5.2 Properties of ATFs 5.5.3 ATF Additives 5.5.4 Storage and Handling Problems
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5.6.1 Compression-Ignition FUELS (Diesel) Engine 5.6.2 Composition of Diesel Fuels 5.6.3 Properties.of Diesel Fuels 5.6.4 Additives for Diesel Fuels 5.6.5 Alternative Diesel Fuels T,~NELOILS 5.7.1 Nature and Composition of Fuel Oils 5.7.2 Properties of Fuel Oils 5.7.3 Combustion of Fuel Oils 5.7.4 BumersCharacteristics and Applications 5.7.5 Storage, Handling and Preparationof Fuel Oils 5.8 PETROLBUM HYDROCARBON SOLVENTS 5.8.1 C~ppositionof Hydrocarbon Solvents 5.6.2 Classificationof Hydrocarbon Solvents 5.8.3 Manufacture of Hydrocarbon Solvents 5.8.4 Properties of Hydrocarbon Solvents 5.8.5 Uses of Hydrocarbon Solvents LUBRICATING OILS ,, 5.9.1 Mineral Oil-Based Lubricants vt!'d 5.9.2 Synthetic Lubricants 5.9.3 Basic Functions of Lubricants 5.9.4 Automotive Engine Oils 5.9.5 Indushial Lubricating Oils 5.9.6 Electrical Insulating Oils 5.9.7 Jute Batching Oils 5.9.8 White Oils 5.9.9 Steam Turbine Oils 5.9.10 Metal Working Oils 5.9.11 Miscellaneous Oils 5.10 PETROLEUM WAXES 5.10.1 Types of Petroleum Waxes 5.10.2 Properties of Petroleum Waxes 5.10.3 Manufacture of Petroleum Waxes 5.10.4 Uses of Petroleum Waxes 5.10.5 Quality Requ~rements-Industry-wise/End-use wlsr
7.1 INTRODUCTION 7.2 THERMAL CRACKING REACTIONS 7.3 THERMAL CRACKING 7.3.1 Process Description 7.3.2 Typical Operating Conditions 7.3.3 Typicak Yield Pattern 7.4 VISBREAKING 7.5 CONVENTIONAL VISBREAKING 7.5.1 Process Description 7.5.2 Process Variables 7.5.3 Typical Operating Conditions 7.5.4 Typical Yield Pattern 7.5.5 Decoking of Furnace Tubes
'4. THERMAL CONVERSION PROCESSES
6.1 INTRODUCTION 6.2 IMPURITIES IN CRUDE OILS 6 3 NEED FOR DESALTING OF CRUDE OILS 6.4 ELECTRICAL DESALTING OF CRUDE OILS 6.4.1 Process Description 6.4.2 P r o m Variables 6.4.3 Typical Operating Conditions 6 5 CRUDE OIL DrsTnLATION 6 6 ATMOSPHERIC DISTILLATION OF CRUDE OIL 6.6.1 Process Description 6.6.2 Prefractionation 6.63 Typical Yield Pattern 6.7 VACUUM DISTILLATION OF REDUCED CRUDE OIL 6.7.1 Process Description 6.8 OPERATION OF FRACTIONATING COLUMNS 6.8.1 Temperature 6.8.2 Column Pressure 6.8.3 Flow Rates 6.8.4 Reflux 6.8.5 Reboiler/Stripping Ste? . 6.8.6 Stability of Column Ope; hon 6.9 IMPROVEMENTS IN FlZACTIONATINGCOLUMNS
6 CRUDE OIL DISTILLATION
A 1 BITUMENS 5.11.1 Asphalts 5.11.2 Petroleum Bitumens 5.113 <y Specificstiow of Bitumens 5.1 1.4 Physical and Chemical Characteristicsof Bitumens 5.11.5 Uses of Bitumens 5.12 PETROLEUM COKE 5.12.1 Types of Petroleum Cokes 5.12.2 Properties of Petroleum Cokes 5.12.3 Storage and Transportation of Petroleum Cokes 5.12.4 Uses of Petroleum Cokes
193 194 195 195 1% 196 196 197 138 199 200 200
192
192-221
177 177 178 178 178 180 181 181 182 182 184
177-191
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8.2.1 Development of Fluid Catalytic ~ r a c h g 8.2.2 Technological Aspects of Fluid Catalytic Cracking 8.2.3 Principles of Operhtion 8.2.4 Process Description 8.2.5 Process Variables-Reactor Section 8.2.6 Process Variables-Regeneration Section 8.2.7 Feedstock Characteristics 8.2.8 Typical Operating Conditiow 8.2.9 Typical Yield Pattern 8.3 CATAI.YTIC REFORMING 8.3.1 Reforming Reactions 8.3.2 ReformingCatalysts 8.3.3 Process Description 8.3.4 Process Variables 8.3.5 Typical Operating Conditions 5.3.6 Typical Yields and Product Quality 8.3.7 Pretreatment of Catalytic Refomer Feedstock 8.3.8 Catalytic Reforming For Aromtics Production 8.4 HYDROCRACKNG 8.4.1 Applications of Hydrocracking 8.4.2 Types of I-lydrocracking 8.4.3 Hydrocracking Reactions 8.4.4 Hydrocracking Catalysts 8.4.5 Process Description 8.4.6 Typical Operating Conditions
8.1
8 CATALYTIC CONVERSION PROCESSES
7.5.6 Maximization of Diesel Oil Production 7.6 SOAKER VISBREAKING 7.6.1 Conventional Soaker Visbreaking 7.6.2 High Conversion Soaker Visbreaking 7.7 COKINC 7.8 DELAYED COKING 7.8.1 Process Description 7 8.2 Process Variables 7.8.3 Typical Operating Condi tions 7.8.4 Typical Yield Pattern 7.8.5 Needle Coke Processing 7.9 FLUIDCOKINC 7.9.1 Rocess Description 7.9.2 Typical Operating Conditions 7.9.3 Typical Yield Pattern 7.10 REXICOKING 7.10.1 Process Description 7.10.2 Dual Gasification Flexicoking Process 7.10.3 Comparison of Conventional and Dual Gasification Proresses 7.11 OTHER COKING PROCESSES 7.12 CALCINATION OF GREEN COKE 7.12.1 Process Description 7.12.2 Typical Calcination Data
222-266
(4 8.4.7 Typical Yield Pattern 8.5CATALYTIC ALKYLATION 8.5.1 Alkylation Reactions 8.5.2 H,SO, Alkylation Processes 8.5.3 HF Alkylation Processes 8.5.4 Process Variables 8.5.5 Typical Operating Conditions 8.5.6 Comparison of %SO, and HF Alklation Processes 18.6 CATALYTIC ISOMERIZATION 8.6.1 Chemistry and Catalysts of the Process 8.6.2 UOP Butamer Isomerization Process 8.6.3 UOP Penex Process 8.7 CATALYTIC POLYMERIZATION 8.7.1 Chemistry and Catalysts of the Process 8.7.2 UOP Catalytic Polymerization Process 8.7.3 IFP Dimersol Process
9.1 9.2 9.3
19.4
9.5
9.6
INTRODUCTION HYDROGEN SULPHIDE REMOVAL PROCESSES 9.2.1 Absorption by Regenerative Solvents 9.22 Adsorption on Solid Beds SULPHUR CONVERSION PROCESSES 9.3.1 Claus Process 9.3.2 Selective Oxidation Processes 9.3.3 Wet Oxidation Based on Aqueous Solutions 9.3.4 Thermal Cracking of Y S SWEETENING PROCESSES 9.4.1 Caustic Treatment 9.4.2 Solutizer Process 9.4.3 Doctor Treating Process 9.4.4 Copper Chloride Sweetening 9.4.5 Hypochlorite Sweetening 9.4.6 Air and Inhibitor Treating Process 9.4.7 Merok Processes 9.4.8 Sulphuric Acid Treatment 9.4.9 Clay Treatment SOLVENT EXTRACTION PROCESSES 4.5.1 Edeleanu Process 9.5.2 Udex Process 9.53 Sulfolane Process HYDROTREATING PROCESSES 9.6.1 Applications of Hydrotreating 9.6.2 Hydrotreating Reactions 9.63 Hydrotreating Process for Distillate Desulphurization 9.6.4 Hydrotreating Process for Smoke Point Improvement
10 LUBE OIL MANUFACTURING PROCESSES 10 1 INTRODUCTION 10.2 EVALUATION OF CRUDE OILS FOR LUBE OIL BASE STOCKS MANUFACTURE
296-319 296 296
(xi)
10.3 VACUUM DISTILLATION 10.3.1 Process Description 10.3.2 Typical Operating Conditions 10.3.3 Typical Yield Pattern and Product Quality 10.4 SOLVENT DEASPHALTING PROCESS 10.4.1 Process Description 10.4.2 Process Variables 10.4.3 Typical Operating Conditions 10.4.4 Typical Yield Pattern and Feed/Product Quality 10.5 SOLVENT EXTRACTION OF LUBE OIL FRACTIONS 10.5.1 Comparison of Furfural, NMP and Phenol 10.5.2 Process Description 10.5.3 Typical Operating Conditions 10.5.4 Typical Yield Pattern and Feed/Product Quality 10.6 SOLVENT DEWAXWG PROCESS 10.6.1 Process Description 10.6.2 Typical Operating Conditions 10.6.5 Typical Yield Pattern and Feed/Product Quality 10.7 HYDROFINISHING PROCESS 10.7.1 Process Descrition 10.7.2 Typical Operating Conditions 10.7.3 Feed and Prod:lct Quality 10.8 MANUFACTURE OF PETROLEUM WAXES 10.9 WAX SWEATING-PRINCIPLESAND APPLICATIONS 10.10SOLVENT DEOILING 10.10.1Fundamentals of Solvent Deoilig 10.10.2Process Description 10.10.3Process Variables 10.10.4Typical Operating Conditions 10.10.5F i s h i n g of Waxes
11 MANUFACTURE OF BITUMENS
11.1 INTRODUCTION 11.2 SELECTION OF CRUDE OIL 11.3 METHODS OF MANUFACTUREOF BITUMENS 11.3.1 Distillation 11.3.2 Solvent Precipitation 11.3.3 Air Blowing 11.4 AIR BLOWING PROCESS 11.4.1 Process Description 11.4.2 Process Variables 11.4.3 Typical Operating Conditions 11.5 TYP!CAL REFINERY PRODUCTION 11.5.1 Cutback Bihunens 11.5.2 Bihunen Emulsions 11.6 HANDLING AND DISTRIBUTION
12 CORROSION CONTROL IN REFINING PROCESSES 12.1 TYPES OF CORROSION 12.2 FORMS OF CORROSION
320-327
328-338
PETROLEUMRERNlMp TECHNp4OQY
Oil exploration is a complex process. It begins with prognostication and involves au entire gamut of activities. m e hunt for the hydrocarbons is focused at the favourable or promising areas based on geological considerations. Geological survey aims at selection 'and mapping of such areas which satisfy the criteria of being sedimentary rocks preferably of marine origin with the presence of anticline structures of Mesozoic (50 percent of oil produced belongs to this era), Cainozic (40 percent of oil produced belongs to this era) and Paleozic (10 percent of oil produced belongs to this era) periods.
1.3 OIL AND GAS EXPLORATION
There are two theories of the genesis of petroleum: the organic theory and non-orgMc theory. The former holds that petroleum is of an organic origin and is the currently favoured proposal. It predicts limited reserves worldwide; moreover Indian reserves are predicted as minimal. The latter maintains that it is of non-organic genesis, supposedly of primordial origin. On the basis of this theory, oil reserves would be much larger than those predicted by the organic theory. India, oil-poor in the organictheory, is predicted to be oil-rich in the non-organic one. The non-organic theory that was much prevalent earlier suggests that oil is formed by the action 'of waikr on metallic caibides or by atmospheric radioactivity or by cosmic radiation. ?he rme occurrence of oil in,meteorite~,igneous dykes and in petrozoic rocks weighs in favour of the non-organic theory. The organic theory which is the most prevalent today, suggests that the petroleum was formed from remains of plants and animals that died millions of years ago and accumulated on ocean floors. Tiny, minute marine animals and plants comprising mainly algae, fungi, diatoms and foraminifera used to float on the surface of the sea and were abundant during the Mesozoic (about 225 million years back) and Cainozoic (about 65 million years back) period. On the other hand, rock surface and land are continuously getting eroded. Broken pieces of material like sand, clay, lime are carried away by rain and subsequentJy depamted on beds of oceans. In millions of years the sediments pile up to a great height (several thousands of metres) and subsequently, pressure and temperature continue tq rise in *ose rocks. Shells and skeletons of dead planktong, sponges and jelly fish sublime.on sea bed and subsequently get buried under the piling sediments. Aerobic bacteria present infie ocean flgor and sediments act as scavengers and attack the organic patter. Some complex chemical bansformation takes place that is facilitated by the enormous overburdeq,:pressure, rising temperature and the absence of oxidizing agent. The process continues through various complicated stages and chemical reactionsforming fats, amino acids, lipids and finally into oil and gas. Oil is produced within the temperature range of 100-200DC. Source rock when subjected to greater overburden pressure and temperature beyond 160°C for a long period does not generate liquid oil but gas. Amongst the different sedimentary rocks like sandstones, shales, clays and limestones, the clays are more suitable for formation of oil and serve as 'source rocks'. With the piling up of sediments, lower sediments get progressively compressed and the fluids in them are squeezed out. Oil formed in the clay rises up or sideways and if the rock above is,like a sandatme with pore spaceo, fissures and fractures, the oil tends to get accumulated in such a reservoir, provided this upward and sideways migration is prevented by the intervention of an impervious layer of rock known as cap rock from moving further. This layer traps the oil. In a normal oil pool gas remains at the top, oil below i t and water further below. These pools remain intad till disturbed by earth.
1.2 FORMATION OF OIL AND GAS
2
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The drilling equipment (shown in Fig. 1.1)consists of a tall huge tower called 'derrick' anchored to the ground, engines, Qd pumps, water tanks, draw-works and many other modules. The travelling block is suspended from the crown block (a large pulley at the top of the derrick). The swivel, attached by a large hook to the travelling block, can rotate freely, and the kelly is fitted onto this. Rotary table at the centre of the derrick floor holds the kelly (which has a square or hexagonal cross-section) and can be rotated at a desired speed by the engine. To begin drilling, the kelly is hauled up the derrick, its bottom is fitted with a drill bit and lowered through the rotary table until that bit is resting on the earth. With the starting of the engine, the rotary table rotates the kelly and the drill bit which is pressed hard against the earth by the weight of the drill string above, cuts and penetrates the rock at the bottom. Much of the success of drilling depends on the quality of mud which is a specially prepared slurry of water, various chemicals and adhesives like barytes, bentonites, xanthanite. It is pumped through the drill column to carry out several important functions such as removing cuttings to the surface, cooling the bit (heat generated is due to friction), lubricating the bit, providing buoyancy to the drill string to reduce the hook load, retaining the side wall of the well from caving in, allowing to examine the hole by lowering' a variety of instruments and balancing the formation pressure that prevents the formation fluids from running into the well. With the increase in depth of the open hole, the side walls of the well tend to collapse. To avoid this, a casing pipe is introduced into the hole. The annular portion between the hole and the casing pipe is cemented. M h e r drilling is carried out with smaller diameter bit, and at a certain depth a smaller diameter casing is introduced and cemented in the same manner.
1 1~ Q L ~ NFOR G OIL AND GAS
Owing to the presence of fault planes and fissures, a seepage of oil to ihe surface may take place. The analysis of surface samples of soil, water and oil or gGy'in such cake$'; for detection of oil and gas is known as geochemical prospecting. Magnetic surveys are then done. Magnetometer survey is carried out either on the ground or from the air by air-borne magnetometer. It is based on the principle that the magnetic attraction on the surface depends on the magnetic intensities of the rocks and their distance from the surface. It helps to delineate the nature and possible dip angle of the subsurface rocks. Dip is the angle that a geological stratum makes with a horizontal plane (the horizon): the inclination downward or upward of a stratum or bed. The same principle can be applied to the measurement of the gravitational attraction at the surface by a gravimeter. These two methods together help in demarcating areas having thicker pile of sediments with better chances of oil. The seismic method of oil and gas exploration involves generation of a series of shock waves in the subsurface and picking up the reflected waves by sensitive geophones which are laid along a line on the surface. The time taken for the return signifies the velocities through the subsurface rocks and these can be interpreted to assess the nature of rocks and their angle of dip. The field studies are supported by an e q u d y elaborate testing of samples in the laboratory. Sophisticated modern equipment like Electron Microscope, Mass Spectrograph, X-rays Chromatograph, Nuclear Magnetic Resonance (NMR),Spectroscopy, Infia-red, Ultra-violet and Differential Thermal Analysis (DTA) are indispensable aids. On the basis of all these studies, the most suitable places where oil is likely ta be found is selected for drilling.
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Miscible hydrocarbon displacement (LPG enriched gas & lean gas) Carbon dioxide injection Inert gas injection (Nitrogen, air, etc.)
Selection of a suitable EOR method requires a careful analysis of reservoir configuration and the oil properties. Trapping and release of fluids from porous media is a complex phenomena. For a spe.cific system, trapping behaviour is controlled by Ci), the pore geometry of rock matrix, (ii) fluid-rock properties, in particular, wettability and (iii) fluid-fluid i n t e r a ~ o n sincluding viscosity, rock density difference, interfacial tension and, partition coefficient. The general properties of pore system, its shape, size and distribution in the rock plays an important role in trapping of oil. It is established that (1) Trapping of fluids occurs in unique and reproducible patterns which are controlled by capillary forces, (2) Nearly complete networks of interconnected equal size pores exist throughout the pore size distribution, (3).individual pores have good accessibility with adjacent pores, thereby allowing alternate paths of flow around igolated immobile phases, (4) Fluids can be trapped at pore constrictions for all degrees of wetting. Non-wetting pqases are trapped in discontinuous masses whose lengths are largely determined by interfacial tension and potential gradient. For selection of suitable EOR methods laboratory investigation under simulated conditions of reservoir are necessary. Mathematical models (3 phase, 3 dimension) are used to analyze the reservoir geometry. The past performance of the reservoir is matched to predict the performance of reservoir under different operating conditions. Based on these modelling studies, the most suitable EOR methoais selected for maximum~productionof the oil in place. In India, the increase in crude oil production is not significant during the last 4 5 years. No new oil fields with substantial reserve is discovered. The percentage of primary recovery in the total oilgroduction is gradually decreasing. Rate of production from Bombay High is reported to have already shown the declining trend. Some of the old oil fields of Assam and Gujarat under prevailing price structure have already reached their economic limit. On economic terms, both ONGC and OIL may prefer to plug the well, pull
Suifactant$olyrnei injection Polymer injection Alkaline flooding
(c) Chemical flooding processes
( b )Thermal recovery processes Steam stimulatibn Steam flooding (including hot water) In-situ combustion
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pores. Second limitation is,$hat,the advapcing. water f q n t :bypaqsessjgpif~qt.~rt$n?~~of the reservoir due to difficult :wellplacements and wexpe+g:.,geologi+ c d g u r a t i ~ n s . This lack of a perfect!sweep efficiency is responsible for leavingbehind crude oil'$ -!as not reached by water.flood. ,. Anumber of methodsltechniques are employed to recqver the rem&ing oil. The diffkrent techniques may be ,broadly classified into three categories:
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; ~ t o ~ A n o ~ ; ~ ~ bAND ~ uRERNING cno~
7
Crude production in the country has been going through fluctuating fortunes. From a high of 34.09 million tomeu in 1989-90, it dipped to 26.95 million tomes in 1992-93 and stayed a t that level in the following year also. But in the past couple of years there has been a recovery and the crude production was 33.865 million tomes in 1997-98. The offshore reserves account for about 63 percent of total oil produced in the country. This reveals how poor the country is in on shore oil reserves and how much it is dependent on Bombay High. The production of natural gas in the country is currently about 74 million standard cubic metres per day and the total gas availability for sale is about 61 million standard cubic metres per day.
the pipe and abandon t h e lfield. It is beWr ts use EOR meth6da after primary recovery. It is imperative that proper assessment of EOR potential in the country is required for making recovery plans. The successful application of any EOR process depends on its viability. The price of oil is the most important factor for how much will be produced and when. Gas injection may not find wideapplication in India. It is true that natural gas or associated gas, propane, enriched gas and lean gas are available in India. But the pressure required to liquefy the gas is high and it may not suit the shallow Indian reservoirs. So is the case with air and nitrogen gas injection. But in some reservoirs carbon dioxide could be injected. Again it depends on the availability of low cost carbon dioxide in plenty. It is estimated that about 4-6 million cubic feet of CO2 is required to recover a barrel of crude oil, Although thermal methods predominate as most successful EOR processes, they may not be applicable on a large scale in India. Depq of the Indian reservoir and API values of 28 - 45 restrict the injection of steam or hot water for additional recovery because of apparently unattractive cost benefit ratio. Of course in Western sector it may be successful in some reservoirs. In-situ combustion is the most difficult method to predict properly. Moreover, it is economical and successful in heavy oil recovery only. It appears that the chemical flooding viz. polymer flooding or surfactant-polymer flooding may prove successful in India. For alkaline flooding, acid number of the crude must be high which is not so with Indian crudes. Polymer flooding method may become more popular in India not only for its easy handling but also for the economic returns. Surfactant/polymer flooding is required to be assessed properly, particularly the non-compatible nature of surfadant to various monovalent and bivalent metal ions and in Indian reservoimkhese metals are plenty. The production of crude oil in India is given in Table 1.1.From a meagre 0.5 million tonnes of oil produced from one of the oldest oilfields in the world-Digboi in Assam, the indigenous crude production is expected to go up to 44.45 MMTPA (million metric tonnes *r d u r n ) by the turn of the century. Till 1947, India used to produce around 0.5 to 1.0 MMTPA of crude oil from Digboi and Naharkatia fields of Assam. After independence in 1947, two public sector companie~wete formed by Government of India, namely Oil & Natural Gas Commission (ONGC)and Oil India Limited (OIL)to explore and produco oil and liatural gas in India from both onshore and offshore fields. Up to 1960, India was practically depending on imported crude oil. ONGC first struck oil in Cambay in 1958-59 and in Ankaleahwar fields (Gujarat)in 1960, followed by oil finds in other pmta of Gujarat such as Nawagam, Ahmedabad, Mehsana, Gandhar, Kalol, Tapti basin, 'etc. Biggest oil field struck by ONGC was Bombay High r offihore fielda in Arabian sea in 1974. In 1976, ONGC found a large sour gas r e s e ~ o i at South Bassein, south of Bombay High offshore fields. Also, gadoil was found in smaller quantities a t Heera, Panna, Ratna and Neelam offshore fielda in Arabian sea.
''
ptliwUk,
Table 1.1 Production of Crude Oil4n &dia
*
1.6 PETROLEUM REFINING, OPERATION AND OPTIMIZATION Crude oil in its raw form has got very limited use. By adopting various refining processes in the refineries, crude oils are separated into a number of fractions which are suitable for various uses. Crude oils received from oil fields are stored in refinery storage tanks. .From these takes crude oil is fed to the atmospheric distillation unit. All the crude oils are basically mixture of hydrocarbons which can be physically separated in groups of different boiling range by the conventional process of distillation. The fractionation of crude oil yields the following streams in the order of rising boiling ranges : Methane, Ethane and Propane mixture Liquefied Petroleum Gas (LPG) NaphthasfGasoline fractions KerosindAviation Turbine Fuel (ATF) High Speed Diesel Oil (HSD) and Light Diesel Oil (LDO) Reduced crude oil (RCO) Depending upon the crude oils properties and impurities present in them, the above products are further treated to meet the required specification. Reduced Crude Oil is further distilled under vacuum to recover some more lighter fractions. This process produces light vacuum gas oil (LVGO),heavy vacuum gas oil (HVGO) and vacuum residue (VR).In order to meet the viscosity specification of fuel oil, heavy residues such as HVGO, RCO and VR are processed in visbreaking unit to reduce their viscosity. To produce bitumen, the vaccum residue is air-blown in Bitumen Blowing Unit. To maximize the production of middle distillates, heavy residues such as HVGO are processed in fluid catalytic cracking (FCC) unit, hydrocracking unit and coking unit. Straight-run naphtha of low Octane Number is processed in catalytic reforming unit to enhance its Octane Number. Reformate rich in benzenhluene
L
I
J
~FTR[31;ELlM,~ERPTORATION~~ODUCTION AND REFINING
a
r9
-
is used as feedstock-fonUdex unitito prPduce benzene an& toluene. Kerosine fkacti~nsfrom certain crudes such as Assam crude do'not meet specification on amoke point due to higb aromatic content. To improve smoke point of these fractions, Edeleanu process is usually employed.
1.6.1 Selection of Processes for Optimization Optimization is the process of determining the best poseible way of selecting the proces. scheme and fixing the unit capacities etc. The selection of procesdprocessing scheme is to be optimized considering all the objective functions. The following factors would influence + . decision making in the selection of processes and process scheme for a given refinery : Type of crude Product slate Product specification ~nve*tme;t and operating costs Merits/demerits of alternative processes. Type of crude. The tyRe of c v d e to be processed in a refinery yill have a bearipg on t; process scheme? For example, crudes containing high sulphur require the iqstallation of desulphq+ation processps/sweeteningprocesses for streams. Kerosine from Aghajari c n has a peculiar problem of colour dekrioragon on ptorage which cannot be corrected by treating in an Merox upit apd hence desulphurieatiop w i t would be req%ed. Some crudes are I suitable for m&ing lubricabg oils, a n d , q p ~are e not suitable for making bitumen. In some cases the prodpcts do not require any tieatment like some of the in9genous crudes e+Therefore, each and every stream from the crude distillap?,n unit has to be evaluated tol making a suitable scheme of treatmentdsecondq processing facilities. e o d u c t slate. The capacity of the refiney, the type (lube or non-lube) and size oft., secondary groceseiffgwjb is largely governed by the product slate which jn turn is decided by the dem,pd of petroleum,~roducts,The process scheme is selected so as to match with tproduct slate. b Indiq, generally the yaximization of middle distillates is,the main criteria. In U.S.A., the production ,of light djetillateq particularly, motor spirit is maximized in F r ' unit by keeping high severity operations, If the objective is to maximize HSD in a refinery processing high sulphur crudes, it would be advantageous to provide an FCC unit with 9 desulphurisation unit either for straight-run gap oil or cycle oils so as to,upgrade the heavl-. ends to the maximum poaeible extent as limited by sulphur specifications. For extreme maximization of middle distillates, a hydrociacker can also be considered which upgrades t heavy ends to the middle distillates (ATFkerosineiHSD)better than any other knownprocess. Yield of kerosin$HSD from a hydracracker is of the order of 80 to 85 percent as compared about 50 percent from FCC unit. Product specifications. Geaerally the treatment processes are governed by tF specifications of the products. Depending on the type of crude processed and the quality or streams, a judicious selection of treating processes has to be made from a simple chustic wash Merox sweetening units to a hydro=deeulphurisation unit. The flash point of the midc.distillates are often relaxed, with a view to m-ize these products. Therefore, to take advantage of such relaxed specifications, it would be desirable to provide a naphtha splitt column inthe process scheme, sa that heavy naphtha can be injected into kerosinddiesel cuts. Investment and operating aosts, This is a very important point to be kept in view whilfixing the refrnery capacity, selecting the processes and sizing the unit capacities. However, the selection of process technology at times may entirely be'governed by the products demand rather than by investment cost limitations. Investment costs are function of refinery size ar.-
OF
i
,I-
1.6.2 ~ ~ t & i ? h t iin ~ an R ~ n n i n Refinery g dPtimization ofthe operition bf a runxi&;! refineiy is sutij&d to the influence of various factors. There are, some factors which are beyond refinery's control. These include : I (a) c h h e mixture (b) Type of processing units (c) Demaqd pattern (d) Movement constraints (el Product specifications E a r n a l streams (g) Industrial relations. Those factors which are within refinery's control are given below. (a) To investigate the possibilities of improving over processing capacities not only for crude oil but also for secondary processing units. (b) To adopt various effective measures of controllingthe erosion/corrosionin processing units to improve their service factors.
..
i t & a s n p ~ ~ ~ ~ y t ~ f ~ h ltihe e tm'1~1wmp1~xityi~ze6ults :fox~ as!the capa@f increases. ~ n v 8 8 k r n ~ n ~ p e m ~ r w e s s i n g , c a p progressively acity go,down.h some cas$s,,apartidar planh~siree~~~eomeieW~miud~md k s o m e othea w e e it maypot be.ecoaomie;JI. For example; some oil companies do not consider it economical to provide FCC Unit of less than 0.6 MMTPA capacity. Similarly, the latest trends are to provide single crude distillation unit of 8 to 10 MMTPA capacity. , i .-$Qxp~f$he,plants*tveconsuming high amount of fue1,ahd utilities. This aspect has to be kept i P ~ X i e w ~ ~ w ~ ~ s e 3 eacprocess-For ting. example, inxase ofhyQrgcracker, thetotal energy c ~ n s ~ p t ' i bo spr ~ b ~ $ u.6 t times than that of Fluid catalytic cracker. Fufiher, a substantial quantity,q&p~pSlthai~ copsumed to meet the hydrogen, requirelpent of h y & g c ~ ~ & n gThe . total energy consumption in a fuel refinery would.be of the order of 10 to 11percent. One has to be cautious in the selection of new process technology keeping in viey the situation, location and availability of local expertise. Some of the technol~giesfor upgradation of the heavy residues may not be straight way made applicable @ Indian conditions. Develop ments like continuous catalyst regeneration may not be verJ;atractive to refineries which upqaSI&qaphthaf?r #e production of motor spirit ?f bqder*te o c h k q u m ~ t . ' ~ e s u l P h ~ s a tio~iof Gel oil which i s $ow being practiced elsewhere with7 the okijedive df rMucing$ollution in concd+qa$ed @au$+al flrei-i? rimy-not &e appli,cable+@s?in_e other situations, y h e p p:ol$t$m - h @ s a$$ow. HydroqackinP ddugb a "e$j yitd pmck$s fo; h&hiking'niiddle distillates h p a soEh@dcatkdmi!llurgy and ikgu+ea szecid operatibnd &d rnewnqnce c a i e : ~ o c e s , o , w a@ted,forJFct hydiocrack@g"ofreeidu'es abuld call yo; s f i & q t high i'?vestm~tsand Gg'hop,perqkirig costs becaube df the hjrdrdgen rkquirementh,,pa&~ularlykor high
[email protected]&des'.'R.eddced d v d e oil; fiod indigent& crucY$d because oftheir low ?ulpRur and metal conbl;t$ &ohla dre better suitedto thiktype of te&ology. Me$ta/demqets alterqdivq pyoces&ir: There may be more than qne prvess to do the '&me m e OF operatidin. Fbr exhljk, th'e'r~are various'types of swebtenihgl$hce~sfor naphtha@and ultihat&ly chohh has to be & b e on the meritk &&demerits of aeihdiyidual processes, opkrating cpqp t+d quality of t&e pfoduct etc. Fo* extractipn of aromatics:fiom kerosine, apart from conventional Edelead~prdcess one coqd possibly choose shlfolane process or &d,hydr"dgenation in orddr to irp~rovethec'amoke'poiht. For the extraction of arqmatics f r ~ m t h lube e oil distillates either furfural or phenol extraction could be adopted.
rw
1.0
7.5 0.65
Guwahati Barauni Gujarat Haldia Mathura Digboi*
IOC
3.75
3.3 9.5
CapacityMMTPA (as on 1.4. 1997),
Refinev
&p +!
Company
Table 1.2 Refining Capacity i n India
l'hd total xefm$g.i{payjty
1.6.3 RefJning Capacity in India in I?$+ as' on,\.Qi1997 stands at 61.55 MMTPA of which 58.55 MSd'I'PA is a c c b u n ~ dfor by the puljlic sector refineries @able 1.2). ~ ' ~ R P accduhts L for the btlbce. ~jt$'the ~ngoi~~gcomh$,~ioning of IOC'a Pqnipat re@ery,,+e,~@re~in$capacity wh ri?ach k~67.55 ~lk'&~.'~e"el'alexpansion projectk ahd grassfoot ikfineries hive been planned to enhance the,rehipg capaqity in the c o m S . About 31 myion tonnes of adqtional &.dIAi%k 'capacityi s li~e1Ptb bki cr'@~d'ibB e ?omtry 1b9 Ftii'th: commi&i6:n$k of a li&ge ~riv@f$sector refine'rj. a$d completion'of the eXli+dion, p~dq-es Public s&&r/jdint sector r'efineries. Thi'major con9biition is e,xpected to c6rne4fi6h riiinery being set up at Jamnagar'by Reliance: The compii(y has heeled up thd capacity #%refine* to 27 MILITPA from the-earlier plan of 15,MMTPAreFnery. Among the public secp~!efineries, IdC's Gujarat refinery has undertaken a h.749 crore programme to exband its ~apacityby 3 MMTPA. HPCL's Visakhapatnam refinery has undertaken a Rs. 998 crore programme to expand its capacity by 3 MMTPA. MRPL, the joint venture between HPCL and the Aditya Birla group is expanding itsccapaditYbjr 8 MMTPAat'&e'stirhatedlcost of Rs.3490 crore. IOC Barauni refinery has an installed capaciwof3.3 MMTPA. The capacity is primarily limited due to crude supply constraints from Assam oilfields. Now, the Haldia-Barauni crude pipeline Iins been laid and is under commissioning to supply imported crude to Barauni. Apart from these capacity additions in 1999, Essar's refinery atrJamnagaris likely to be commissioned in Xinrch 2G02. The refinery was planned with a 9 MMTPA capacity, but Essar has since scaled u p the capacity to 12,MMTPA.
1
consqmptions. ,,I,, (d) Various streams obtained f ~ diffvrent m pftcesslirg units a i 6
(c) To.plan(shut downs of vari6us unitsratoptimum time tu avoid the&@?&ed htiiitieb
P E 7 R r % g E U M f E X W a ~ ~ ~ E I M : T lAND O N REFINING
*AOC,Digboi was taken over by the government in October 1981 and merged with IOC
.::....,
'
'
. .
.. ..
The refinery production and consumptionof petdeqm+productsi s giyen$Tables 1.3-1.4. In In$a the consumption of light.and heavy distillateshave beensfagnatkdgver t$epe.eod of last Siie years. How+, the demand foi midd1,e ,&atjljates'ia'~'&ei$big's@ong'50 .ip h$ r e c k t times. In order to meet :the' increasing d.em?d for, middle disFla%s:!60-65%),'the second& and tertiary processink f@$ilities' . &e . becoming$& bf1;1.bd.y~ yelink$ . . cpmplqxts.
3. ,
I
[
1001 7371 1108 7907 4041 2079
1,
1636 18289 1453 13389 6358 ,
4044
'
4550
1801 $j85 1609 18196 4879 . ... .
4164
1519 14624 1177 10016 3791
Tablg 1.3 Refinery Production in India (In Thousand Tonnee)
HSD LDO Heavy ends Furnace oil LSHSHSHWRFO
ATF
H 4 t o pmqesscrud? bib,?= gpttihgg+temati&awti6n:L d$&l?*%~+&<~j$?s ki+ couM 'increase i h e r e f i n e ~ efficienqies.'@e n,eedto co'nv* bottomcif:?+eb,arrelil:iii$ocleiitofuel as~~mes,si~ific.mtim~;twce, ipIn,$a p@icul,+lyj@ 09pool 4aficit,c?nt$etddb$lwh a&d India costiflues to dep,pnd feafly on impoited crude 'oil. '&e.,e$sting refineries skbuld therefore upgrade,t&eirtechnologies, o p ~ i z e s n e r g y : c @ s ~ p*dt i ~fmpro+e&fficiencyof furnaces and process equipmeritsto kclude the f1exib;iQt.yt;d p+c&g the broad spect,mm . . .c ~ d e oil.
.-
P p , Q L E U W E v b P R w Q M ; PblQpUGTION AND REFININ0
Table 1.4 Consumption of Petroleum Products in India (In Thousand Tonnes)
..
1.S. Abbas, p e noxi-orgapic theory of the genesis of petroleum, Current Science, Vol. 71, NO,9, ppF877-684 (1996X, " 2. P. Dutia, The oil refining industry in India, Chemical Industry Digest, pp. 103-110 (hhrch 1997). 3. A. Borthakur, K.V. Rao and B. Subrahmanyam, Recent trends in enhanced oil recovery by chemical methods, Chemical Engineering World, Vol. XXXII,No. 4, pp. 83-86 (1997). 4. A.X'~r0r.a:Status. &projectionsin the oil refining sector, Chem. Engg. Progress, Vol. XXXE.N,o. 4, pp. 87-88 (1997). 5. Aqonymous. India still lagging potential as major player on worid energy markets, Oil & Gas J., pp. 19-22 (Feb. 12,1996).
PETRQLCUM1REFINING TECHNOLOGY
G
I
!
I
I
I
!
2.2 CHARACTERISTICSOF CRUDE OlLS Crude oil has been defined as a naturally occurring mixture, consisting predominantly of hydracarbons andor of sulphur, nitrogen andor oxygen derivatives of hydrocarbons, which is removed &om the earth in a liquid state or is capable of being removed. Crude oil is commonly accompanied by varying quantities of extraneous substances such as water, inorganic matter and gas. The removal of such extraneous substances alone does not change the status of the mixture as crude oil. If such removal appreciably affeds the composition of the oil mixture, then the resulting product is no longer crude oil. Crude oils range widely in their physical and chemical properties. Typical properties of several crudes are given in Table 2.1. Crude oils are brownish (light oils having large amounts of distillates) to brownish black (heavy oils) in colour. Heavy oils have an unpleasant odour (garlic like) due to the sulphur compounds, while the light crudes have pleasant aromatic like smell. Though general, this is-not $ways true. Data for a considerable number of crude oils indicate the specific gravities between 0.73 id' 1.02; most crudes gaving specific gravities lying -&tween 0.80 and 0.95. These values are for surface conditions of temperature and pressure. The kinematic viscosities vary from 0.7 to 1300 cSt a t 37.8"C; the bulk of the values being in the range of 2.3-23 cSt. In terms of elements, crude oils are composed principally of carbon and hydrogen. Of the other elements present, sulphur, nitrogen and oxygen appear as heteroatoms in hydrocarbon derivatives, some of which occur as petroporphyrins, i.e. complexes involving traces of metals (mainly vanadium and nickel). Carbonthydrogen ratio is usually between 6 and 8. A wide range of metallic elements have been found, generelly as traces, in the small amount of ash obtained by burning many crude oils. The elemental composition of crude oils is given in Table 2.2.
2.1 INTRODUCTION Petroleum, etymologically, means rock oil. It is natural organic material composed principally of hydrocarbons which occur in the gaseous or liquid state in geological traps. The liquid ,part obtained after the removal of dissolved gas is commonly referred fto as crude petroleum or crude oil or simply crude. Crude oil o c m in many different parts of the world, and its structure and composition variestaccording to its source to such an extent that each producing area, and field, and reseryoir bears its own profile just as individually as finger prints identify man.
-
CRUDE OlLS CHEMISTRY AND COMPOSITION
16
( 12.0
-
1
11.8
(
1
PETROLEUM REFININGTECHNOLQGY
11.7
0.0047
(
(
-
0.006
(
Table 2.1 Typical Properties of Crude Oils
(
Amount, w f 8
0.004
1
-
2.3 CONSTITUENTS OF CRUDE OILS The main constituents of crude oils are hydrocarbons. The proportions of the different types of hydrocarbona vary from one crude oil to another. Many members of each type are presegt. Naphthenic acids, complex nitrogen compounds, and mercaptans account for some of the-yxygen, nitrogen and sulphur present in crude oils. In additioq, the resinous and asphaltic substances present in some crudes contain oxygen and sulphur. Inorganic sulphur can be present as hydrogen sulphide (HzS) dissolved in the oil. Crude oil also contains trace elements suth as metals, mostly in -small quantities-some contained in water impuritieg and some existing as complexes in the hydrocarbon phase.
(KUOP
Element
11.0-14.0 0.06-8.00
83.9-86.8
S
0.02-1.70
C
N
0.08-1.82 0.0-0.14
0 Metals
H
Table 2.2 Elemental composition of crude oils
15. ( ~ econtent, h wt. % 16.
-
---
----
I
:
,tif
H H H H I I I I H-C-C-C-C-H I I I I H H H H butane
I,
~ h l b r b i ,pi,iphyrin&,a+e ~~~. tj.eeII'1y$,d8 &.sinam,;af d @ + ~ . ~ # & ~~.. ~ & -. l... & l A,%. ~ P %C.$ $ e compoun$s indicate a contributio? from,plant 6Ou,Kei3, a ~ o ~ ~ ~ pr $!uk ~ ~ ~ Hi$tp~ji,dnd hob$ljly B ~'ed$cin&eriiri~iiibnf: @&l$pi iio@hynnshm%%dn i.a *&&: bd+it.i$b0$ b o w n h b t c61p"hli $~vh~s':inkP+$~<&{~&~#&, &egikihblebomilaht tjbdrees: 1 s o j x i d hy&r:,brbo$s 8'iG been r.e~<&~ed:th'e'~:bFdd$&%ai have structurkri tjrpital of substaixes'formea biologically: Other hydrocarboiii'st~u~tu~es~~ith . biol'dg;icali*ni&, li'a"sbeen.detecb'd. .', . ,- <;:: :, . ; : . , ;: . <.;; <:.; :;:<.Th& w&&p, &#b&ted .with ?oil:ma.gas & c c u m y l ~ t ~$8: o :usually n~ - jn&&$aljris~lifiB)i and appears Mmany fnstmces to' be modified$eaWater,tkepnncipa1:diKere'nc~s~bei~ a'deficiency in sulphates, relatively less magnesium and commonly.,greaterconcentration than normal sea water. Traces of hydrocarbons andorgrtllic acids are pksent.
'
I
H H ethane
H H H I 1 I H-C-C-C-H I l l H H H propane
2.3.1 Hydrocarbons Hydrocarbons are compounds composed solely of hydrogen (H) and carbon (C). The main types of hydrocarbons present in crude oils are alkanes, cycloalkanes, arenes and hybrids involving combination of these types. They range widely in boiling point, and many cannot be distilled under atmospheric pressure without breakdown. Alkanes.These are open-chain saturated hydrocarbons. They are also known asparaffins. They can be divided into two types: Straight chain alkanes - x~ormal Branched chain alkanes - iso or neo When carbon atoms are connected in a straight chain, they are known as straight chain alkanes. When carbon atoms are connected in a branched fashion,they are known as branched ' chain alkanes. Alkanes have a general formula Cn H2n + 2, where n is the number of carbon atoms. The names ofthe alkanes end in -me. The first four alkanes have specialnames (methane, ethane, propane, butane) related to their histories H H H I I I H-C-C-H
I
H-C-H
H methane
CH3 - CHz - CHz - CHz - CH2 - CHz - CHz - CH3 n-octane ,
From pentane (C5 Hlz) onwards, Latin or Greek numerals are used to reveal the number of carbon atoms per molecule. A few examples are given below:
CH3 - CHz - CHZ- CHZ- CH3 n-pentane
I cH3
From butane (C4Hio) onwards, alkanes may exist in two or more forms (isomers)differing in structure. For example, butane may exist in two forms as follows:
n-butane
isobutane
Ill
I
7
.......f......
Blphenyl
~tgn&~
Naphthalene
,
Anthracene
m4;'th *t{a%ahe;. CiH,, e i e l y i:A, fe : *e., we .' '.. iS( ; .GoS
'
d&&rh:!b. ona; T
Phenanthrene
The moat common mononuclear ammatics found in crude oils,are toluene and m-xylene. The possible constituents of crude oils. include polynuclear species containing up to a t least eight condensed rings. Many polycyclic aromatic hydrocarbons present in petroleum are carcinogens. Alkenes. ,These are openchain unsaturated hydrocarbons,c o n w g a carbon-cirbon the ~ : , chbbn-h,+ddi6h ~ pr!op,c~~hk.xrPi.it:~'d 'driabsgj,cli,c eak.e)i :, ,an.d,,:& ?-1;'d;a:vi8r
..
*em
rs o C ~ Wl ~ l pF&, .Ad $ & . & 6 4 ?' , le;&:,6f .$&.&;::hd& $ ,p& *ivLfds&dtutai,is&h&&:&po8diti1;,d'e ped&g,,od ,&ei'&Pti:bh' s;i hl,&Ij:6$d hainmu.& , for =hpr8', . ~ 6 : i t i ~ g h c ~ w & ' b ~ & n nljre~ ~ 6 . a ~
within the basic expected, as follows:
H H H H I l l 1 C=C-C-C-H but-2-ene
H H H H I I I I H-C-C=C-C-H I I H H
,
..
,
,
I '
I
.
I
, :
;j,
.-8
,.: :
.;
,.
VC,,.
The number indicates the number of the first of the doubly bonded carbon atoms, numbered from the end nearer the double bond. In addition, the typical side-chain isoniei is . . . ... . . . . . > I ! ; , ; , . ,,. .,:, , expected, that.is
' '
H3C H I C=C I H3C H isobutene (2methylpropene)
The two possible geometrical isomers of but-2-me are the foliowing: H-C-CH3 CHR-C-H
These isomers are classified by the Latin preiixes cis (on this side) and trans (across) indicating the relative locations of the two end methyl groups. Coneequeptly, there are four isomeric butenesin all.
,;
, , ~ m & ~ , . p e ! m n ~ ~ i n ~ b t ' ; s....~ ~- ...~ ~ ; d i i ~ b ~ ~ b ~ ~5 ~,: 3F.j ~ ~ I w
;,
:
!
.:;
.,
I
H % HI -C-H
: . l;'3-butadl@ne:
:
v.
'
...
.
. . . .
.,
.
.
.
H
:I ,:&penWeriw
I
t
7
L.
-..:. .I3, ;b'he~ttiine
,
.k(~ln.~Cio,H,2).. .. ...,,. . ..
(1,2, 3, Ctetrahydmnaphaalene)
.
-
..
.
.
.
,
. .
...
amY1um for ine f B h ~ i i ~ ~ ~ O ~ ~ ' b ~ f i v ~ ~ t i ' 6 ~ . nsmr ~di.;~! pentylenes may supersede this. For the higher members of the series the IUPAC system is used. For example, 'H
p,@adlene . . . . .
-
!
.
,. ':. .. ; , ,<, ;,! 2 ! : .: :' ' . . . . ; ,!. .'; ; ; . < !.:. .' A l ~ e e ~ ~ e e . a r e o p e n - c h a i n ~ h y d r o e a rcboo~ntsa h i n onecarbon-ctybon g triple bond. The fin&.member:o$thi~~s~eesi~acetylene, Cfia,:wbich,appe~~8;injexten44 f o h ' l a as:the linear molecule: H-CGH. Additional members of the alkyne seriea:.comphe,-open-chain molecules somewhat similar to the higher alkenes but with each double bond replaced by a t r i ~ l ebond. The.IWAC system of nomenclature.ri~pliesthroughout t h e series as with the alcenes, but t h e des&tem treats tho!~~htah&abers. as d&vativee,:of acetylene. Thus, .I: for example,. H.arnWfijjcbuld . be d e s d & d !& .&itherbut-l--ge' b i s&ylacetylene. The and relative densities of the alkynes are slightly higher than those of the boiling , corresponding alkanes. Cycloalkanoarenes. These, also called naphthenoaromatics, are mixed polycyclic hydrocarbons and possess structures involvingfusion of aromatic with alicyclic rings, and may carry aliphatic side chains. These h y $ ~ ~ & ~ ~ ; ~ Q appearing u$ in the kerosine fraction, increasing in concentration in the higher-boiling dbtillaticn fractions and residues. Bicyclic ~?!p~t$enp~~m~$c.. $nee.tu.prn~ti-~ r h g . &dfpop alicxy&c).ingee.?:p.$+in and..theic,alkyl 4$vativ$ 3;" r'la!jiy$~.+&dadt' .9,keroeifte..apd:h& . . ......<... gas ,oi4, ..... ,Ew , . -pl of+ , C:Q ~ P O ~ W & present . are. . . giyen.belpw : ... . . I. . . . . . . . . >
i.,.
I n ~ a n O ' ( ~ ~ " ,'::o"~
~.
d '
:<,..
,
"
.,<
.,,!
QHGHzSH
(ethyl,merw~tan)
, e@anethiiol
'(CHsh Ck SH ~sopropanethlol (~sopmp$imercaptan)
>.,v.-
.?C,..
..
I
..
in low concentration, however, and they are often used as odourants iii LPQThe ibwer thibls are the inost malodourous..One part in 50 million of ethanethiol can be detected in air by the human nose. The odour is strong at 0.6 ppm arid distinct at 0.03-0.07 ppm. In high concentrations, the odour ohanges to something like that of chloroform. Thiols are stronger acids than alcohols, and use is made of this to remove low molecular weight thiols from light gasolines with caustic soda solution. Hydroprocessingtechniques are employed to desulphurise other oil fractions and here combined sulphur is eliminated as hydrogen sulphide from all type of-compoundcontaining this heteroatom.
'.
'The #resence of thiols:'in the.~~etr~~c!u~il"hattions ca;i+ies -cofp5sioR,I!rcibkems, c'talyit p&sdin& an.d ~ple'&*t'i~60rata~,&d pf& oaouis. mbjg:a'te n& bMc:h&lj; poi*oi;d&
CH3 SH methapethld (methyl mercaptan)
'.
geological beds. The other origin is the biogenic reduction ~f'"dil$h'&.~'&de oil* "&-y considerably i n their sulphur content ranging from a few hundredths by weight to as ;puch #rceht OT sdbhdi. ~ u l b h u ycokedf of 13.95% foddd $ d a d p o i n t (inetah State in Ui$.;Aj?.is #e,&ghkst . I :.. record& . sulphur cdptent of any cqde:oil. . . .,.. I'. . . , * . The * u l p h ~com~~unds~'~re'se'nt in c k d e oils can' be dividedlinto thiolq, &on& and . . . Wlphides and thiophenes. (':
[email protected] mercaptans,-are&hesulphur ana1ogues:ofthe alcohols (i.d.thiodcohols) and characterized by the presence of the sulp-hydryl group, -SHd which takes the place of a hydrogen.atom in,an alkane-p~:cycloalk.ane molscule.;Thiols:are.t&amain;sul$hur.compo~ds of lower~boiling.(.petroleum~~fraotioh~ (blow 200°C). Etamples uf.this'dltrss ohaul~hurCOWpounds are givep belaw:
.;<,
Crude oils contain appreciable amounts of organic compounds with structures incorporating one or more (the same or different) atoms of sulphur, nitrogen, or oxygen in addition to carbon and hydrogen and some of these are associated with metals such an vanadium and nickel, i.e. they are organometallic in nature. Sulphur compounds. Sulphikr'is th8 mast.abundant atomic constituent of &de oils, otherthan carbon and hydrogen. One of the origins of sulphur compo.ydsin the c v d e oils is ~~&~~tcird:kulphiw~h-*~i;it .dtigs;siie$.bf&e.filarit and'mirriLl $&&;ns'd;po&ted,&
2.3.2 Non-Hydrocarbons
m ~ h e x a n a m w p h l d e )
-
A
CHs 2-memyC3!<hiehuxane ~ a ~ ~ . d l s u l p h I d e )
2-emytthlophene
benzo(b)thlophene
Thiophene and its alk$ dNvativee are n o ~ y , r ~ l a t i v ~ I y . sconstituents c~ce of crude oils, but condensed system-benzothiophenes, dibenzothiophenes, and higher polycyclics (e.g. benibnaphth~thio~henes) are impartant component8ofall high aulphur crudes. Thiophene derivatives are p d c u l a r l y abundant in erude oils containing high proportions ofmmatics, resins and asphaltenes.
thlophene
Some examples of thiophenes found in crudes are given below:
23-dlthlabutane (methyl dlsulphlde)
As in the case of thiols, the sulphides are generally very malodouroue. Afew low molecular weight disulphides (dithiaabnw) have also beenshownto be present in crude&.The accurrence of disulphides in;prudeoile may be owing to the secondary reaction of thiols with tln olriaant such as air or free sulphur. Organic disulphides are isologs of the organic peroxides, ROOR, but are much morestable. Examplea are given below:
(CHI CHdz S 3-thiap'entane (dlethyl sulphlde)
CH3 CHSCHCH3 I I CH3 CH3 2,4-dlmethyl-3thiipentane (dhwrwyl sulphide)
syao~spaaj jo d0n)Fse nam se .-a 'leaq ag!aads 'queqsuoa blpad-bq!soasr~ 'ququo3 uaSorp6q s-e qans savadord i a q o pue d0nx u a a w q pado~a~ap suo!+81auoa Lxequaura~duroaaqq u! saq lo33ej a w j o etlaqnJasn u y u r a q , 'uo!qaeq a w u! suoqieaolplCqjoadLq ~ep!+%d re jo aaueu!uropa~da w q e 3 ! p ~03 pasn aq trea suogaeq wna~oqadjo donxjo sanIea aq? ' m u sa!lamoxv 0'11 - 0'6 sauayqqd8~ 0'zT - 0.11 sugsisd O'ET - 9'ZT
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.
o
? K J ! ? ~R ~ SY
~ P a q d ~ g ~?F q EI!O;aP!v . 30 uoRe~J!$m % ?I.! W+:(PUO!TW. Xaq, s y ~ ~ ? ~ , ? ~ , ; ~ ~ ) , j o ~ ~ & y e ~ Wp a s ~ w .ys a u ! m ~ n e a m psn
,
:uqskdi& B p o n d J ap7 q ' 8 r @ p ~ o m'k+efi~gaads ' q q y $$dd Z q o q &qqa.uoa IWBJ '(*03~s?sn~q'E@ti,61arimn) sodidq p&~aAap%! 'donx 'i$$b& u o ~ e ~ ~a bu q' j I i o ~ ~ ~ 1 . ~v ~ ~
1
(TIZ)---
:shio~~oj SB am su0q~eoo"pbqjosassel:, p a r a m 103dbnx j o f ~ ~ r i p A .s!sap.jq+am E uo angppe SF l g a e j uoge5pajSs.req3 s m spuqq LO s a q q x rod .pa,ws!p s3tim1onguaarad (jdp w ( ~ '09 i "0s '01 qF! samqe&&&q' ~*'I@BX$AB Kq ahma u o r p m s i ~ ~ N J , u10~~~paqe$4ds~~1oga~rg ~ rtrna~oiqada 9 3 0 qqod ~Utfi0~'&833~%? aqL . 3 ; g 9 a 9 ~ / 3 0 ~ b ' g 3~ ~ ~ ~ ~ ~ ? qij & p~s :7 ~ p'P :yo 'F& xZ;!~:dq a s e ~ a ~a w e r! u a:?qm
910aplu3 JO uo!pa&ssa13 j o - p o q l a ~ go d npamg ~ Sn p.g e l q ~ ~
., ..,.
.
: .., ..
: ,:I.,: ;
:
2.4.2 Correla$inqJn~@xi .. .,;:, . . - ~c~oe~ F index p ((311, developed by US Bureav of ~ i n e s is , Biven by the following empiiiical eqfiation:; 11
,.
.
.
,
where fi ie'the average boiling point, OR ,'determined by the standard-BureaU8'dfMbes distillation method and G is the specific gravity at 15.56°C/15.560C. CI values of a petroleum fraction between 0 and 15 indicate that the components of the fraction are'predominantly paraffinic in nature. CI values between 15 and 50 indicate a predominance either of naphthencs or of mixtures of paraffins, naphthenes a d qomatics in the p&roleum fraction. CI values above 50 indicate a predominance of aromatics in the , I , fraction.
,
p..,
Parec Parfinic-naphthenic
Denomination of crude oils
%C, 2 72 %CP 2 50; %CP + %CN 2 90
-
-
Class delimitation by structuml in& values
-
Table 2.15Denomination and Classification of Crude Oil Classes
2.4.3 Method of structural Group Analysis The methodi?f.siyctyd group analysk.,deseribq?the .ch$ajier; qf.the fraction in terms of elements constituting a h theticalaverage molecule2Pavingthe chemical and pbxeiqal ..! . . . I . . . ' properties of the eumof ' e .indiiridual comporien&..,p;f;@2:Bacti,on,. awprdb..to .thek concentration.This methodclarjsifiesthe crude.oilsinto:.sev& Classes (Table 2.7).
Class I I1
1. 2. 3. 4.
5. 6.
G.D. Hobson (ed.), Modem Petroleum Technology, Part 1(Chapter 91, 5th edition, John Wiley & Sons, New York, (1984). L.F. Hatch and S. Matar, From Hydrocarbons to Petrochemicals, ~ u lPubyishing f Company, (1981). L.F. Hatch, A chemical view of refining, Hydrocarbon Processing, Vol. 48, No. 2, 77-78 (1967). B.B. Agrawal and I.B.Gulati, Trace metals in petrolem and petroleum products; Part I - Occurrence, nature & significance, Petroleum and Hydrocarbons, Vol. 6, NO.4, 193-197 (1972). B.B. Agrawal and I.B. Gulati, Trace metals in petroleum and petroleum produds ; Part 11 - Individual constituents and their significance. Petroleum and Hydrocarbons, Vol. 6, No. 4, 198-202 (1972). P. Jones, The presence of trace elements in crude oils and allied substances, The Institute of Petroleum, 73-76 (AprilJ u n e 1988).
I
1
i
I I
I
1
I 1
, i',.
,u
TRANSPORTATION OF WAXY CRUDE OILS
3.1 INTRODUCTION Crude oils contain a mixture of light and heavy hydrocarbons. Typically, a stabilized oil may contaitl paraffinic, naphthenic and aromatic components as heavy as Cso. In addition, poli& ahd asphaltenes M& also be'present. The lighter componentsin the crude oil kdep the he&d& toxhpohents in solution. This solubility depends very strongly on the temperature. If the temperature of the oil is decreased, the soldbility of the h e a w hjkirocarbons atiy be sufficientlyreduced to cause precipitation of these components in the form of solid wax crystals. The polars and asphaltenes may also co-precipitate with wax crystals. The phenomenon of wax separation from petroleum fluids at low temperatures has been a problem to users of petroleum products for a long period. It can occur in lubricating oils, residual fuels and crude oils. ' The presence of wax crystals changes the flow behaviour of the crude oil from Newtonian to non-Newtonian. The wax crystals usually lead to higher viscosity with increased energy consumption for'pumping and a decreased capacity. In addition, if the oil is cooled during transportation, the wax crystals tend to deposit on the colder pipe wall. Wax deposits can lead to increased pipeline roughness, reduced effective diameter, more frequent pigging requirement and potential blockage. If these deposits get too thick, they can reduce the capacity of the pipeline and cause problems during pigging. Wax deposition in process equipment may lead to more frequent shutdowns and operational problems. In extreme cases, wax crystals may also cause oil to gel and lead to problems of restarting the pipeline. Great potential savings can be derived from accurate prediction of wax formation. The knowledge of the magnitude of wax deposition can lead to reduction of insulation requirements for production and transportation systems. Conversely, problems with wax can be addressed in an early stage of a project so that sufficient thermal insulation is planned for instead of expensive chemical injection and loss in capacjty or loss of availability. Process heat loads can be reduced by increasing efficiency of heat transfer. Capacity reduction in heat exchangers can be overcome.This reduction results from blockage or vibration problems. The size of export pump8 and flow lines c+ be reduced by an accurate knowledge of the effect of,waxformation on crude viscosity. The minimum pigging frequency can be estimated. In addition, problems related to start up and shutdown can be solved cost effectively. The crystallization of wax in crude oils causes severe difficultiesin pipelining and storage. The crystallization of waxes at low temperature causes reduced liquidity of waxy crude oils which considerably w p e r s the transportation of crude oils through long distance pipelines. Several methods exist for handling waxy crudes for ease of transportation. For example, pigging the pipeline is useful for removing thin layers of wax only. A highly waxy crude may
The crude oils pumped in pipelines up to the early sixties generally showed normal characteristics in respect of pumping conditions such as viscosity'and low pour point. nowever, the opening up of remote oil fields in North Africa and India in the 1960's to exploit the low sulphur (but waxy) crudes in these locations, and the need to pump tKese oils through the much colder pipelines has led'oil producers to study the pumpability of waxy crudes at temperatures below the pour point limit. The advantages of these crude'oils in respect of high reserves, low sulphur content, good distillate product yield and its low dscous flow under fair temperature conditions are, however, partly compensated by the disadvantage of high wax content, which results in a high pour point and under certain conditions of low temperatures could create operational difficulties after a long-term shutdown of the pipeline. Worldwide, one can distinguish about 1500 varieties of crude oil of which 10 to 20 percent are considered
3.3 WAXY CRUDE OlLS
~.$+~P~~~U~~'~R~NSPORTATION For the transportation of large quantities of crude oils, pipelines are the most economic means. Under safety aspects, transportation by pipeline guarantees the best protection for the environment. Further, there is no handling of other traffic and no disturbance by noise or air pollution. A continuous supply to the refineries is normally assured and this is not endangered by weather conditions such as fog, icy roads, or traffic conditionsalong inland waterways, such as high or low water level, ice, etc. However, each pipeline system requires very high investment which should be used most economically. The most economical and efficient operation of a pipeline could be reached by maintaining a continuous constant flow rate without any interruption. Also, ip respect of a reliable and continuous supply to the refineries, a steady-state throughput, with some seasonal fluctuations due to market requirements, should be envisaged. Otherwise, additional storage volume has to be provided for large quantities of crude oil and this would be very expensive. Interruptions by shutdown of a pipeline are by no means desirable. However, a shutdown may occur due to the following operational reasons: (a)There ia an inadequate stock of oil in the terrnind. This could be caused by distribution in tanker schedules, for instance, due to weather conditions. (b) There are no delivery requirements by the refineries fed by pipeline. This could be caused by disruption in operations sf one or more of the processing units of the refineries, for instance, due to equipment breakdown. (c) A pressure test for leakage control of the pipeline has to be performed. ( d ) Repair, maintenance work on the pipeline system including pumps is required. (e) The pipeline might be shutdown automatically by exceeding the operational safety limits. These shutdowns are not expected to last longer than 3-4 day. Under extreme conditions one could think of extraordinary long shutdowns. The reasons might be government action, earthquake, strike, war, etc. However, under normal conditions, they are'not expected. I n e n transporting waxy crude oils, these operational points of view'are of considerable importance.
,\,
require fiequent.piggingtokeep the wax accumulation manageable. Apigging operation often rattires significant amounts of costly offshore man-hours. Taking into consideration all the &o-economic aspects additive treatment is reported to be the most suitable method for the t k w o r t a t i o n of waxy crude oil, which can depress the pour point and improve the flow characteristics at low temperatures.
PETROLEUM'REFININGTECHNOLOGY
1
1
I
I
31
acceleration), the sum of these two forces is zero. Therefo;e, w6 can write
3.3.1 Definitions of Rheological Parameters SHear stress. Consider the steady flow of a fluid in a horizontal pipe of circular cross-section. The fluid flows with an average velocity of U in apipe of inside diameter D. The pressure difference between two points 1 and 2, separated by a distance of L is (Pi - P2). q e decrease in pressure in the fluid reflects the applied force causing the fluid to flow and if the flow is steady (i.e. no change in the flow and hence velocity), this force must be counter-balanced by a shear force of equal magnitude at the wall of the pipe. If r, is the shear stress at the pipe wall, then force acting on the fluid at the wall must be - 71 DL rw.The negative sign indicates that this force acts in a direction opposite to the direction of flow. The (Pi - P2). In steady state (no force acting upon the fluid due to pressure difference is
able 3.1 Characteristics of Waxy Crude Oils
to be the:waxy. Such a,classificatioo~wasbased-on the wax content.oEthe,cmdeaad itspour point; The,characteristics of some of these crudes are given in-Table3:l. In-contrast,mos$of the MiddleEast crude oils have a pour pointbelow 0 OC and wax contentless than 7wt.kand therefore pose no problems in pipeline transportation even at low temperatures. Waxy crude oils exhibit non-Newtonian behaviour a t temperatures below about 10°C above the pour point. The wax can crystallize as the crude is cooled to form gel or a partial gel. Under static conditions a rigid gel is formed, but if the crude is cooled while in motion, the apparent viscosity will increase but the material remains fluid: Therefore, the rheological properties are functions of temperature, shear rate, shear stress and past history. Problems in pumping these crudes will occur if the temperature drops and the fluid becomes non-Newtonian and if gel formation occurs after a shutdown. The pipeline facility must be designed to recover from these problems or prevent them. A realistic approach should be developed based upon an extensive evaluation of the rheological behaviour of the crude oil under representative temperature and shear conditions. The two rheological parameters of which knowledge is indispensable for transporting waxy crude oil through pipeline are viscosity and yield stress. Before we go further into rhealogical behaviour of the crude oils, a few relevant terms that will be frequently used are defined below.
TRASPORTATIQNQR WAXY,CRUDE OILS
The above eQUatibh rneteliy shews thaCthe,sheaps&ss at-thepipe w l i@jUsti&pther ~ e a n of s e*@&ioh bP"dti%n~losd.-~rbin E1$,3j1, itfdlfowru that.avddab1e~hear'strgSs~or a particular pipeline depends,on the leligtbd the line between twa,pump stations! and the pressure difference. The availdble sheatj $tress can
Pressure drop
Density of crude at pumping temperature
:. Inside diameter of line Line length Shear strees
= 0.000339 psi
= 23.4 dynes/m2
3
If the available shear stress is equal to or more than the. forcp peeded to overcome the shear streas at the.innersqfape of the pjpe, $hen tbe,flow l$e initiated. Shear rate. consider two p&allq;lplanes of area A, separated by &:d~erqntiai&jtance dr. The space between the two planes is filled with a fluid. The lower plane is fixed. A small force F applied to the upper plane wiv give it a velocity dU in the direction of the force. If there is no slip between the wall and the flGd, the fluid adjacent to the upper plane or wall &q also have a velocity dU in the direction of the applied force and the fluid next to the lower plane or whll will have a zero velocity. Thus, a unifoy velocity gradient of magnitude dU/&ris set up in the fluid since the shear force F is uniform across the distance dr;The velbcity gradient, dU/cir, is commonly referred to as the rate of shear. The shear force per unit area, F/A, is called the shear stress. Viscosity. It measures the ability of fluid to flow during steady state condition. It is the property of a fluid that resisp a shear force. It can be thought of as the friction resulting when one layer of fluid moves relative to another. Viscosity, p, can be defined as the ratio of the shear stress to the rate of shear.
I
I
/
TRA&&RYAT~ON /
OF WAXY CRUbE OILS
L
-(PI = -P2)
o2
-
.
.
/
2
[(PI P2)DI4LI -- TW (8UD) -(8UD)
Rate of shear = 8U/D
'=
,For laminar flow in pipes, friction loss ie given by 32 p U
&.
which can be rearranged in the form
Therefore, for laminar flow,
.
J3.3)
and for turbulent flow, *..(3.4) Rate of shear = (SU/D) Cr where Cri3 correction factor which depends upon Reynolds number. Yield stress. It measures the ability of fluid to restart its flow aRer shutdown of the transportation system. The yield stress of an oil, at a given temperature is defined as the shear stress required to initiate flow. It can thus be directly compared with theshear stress available or allowable in a pipeline. The yield stress of waxy crudes ie influenced by-ite temperature history, shear history, aging and composition.
I
3.3.2 Rheological Classification of Fluids There exists a rate of shear and shear stress at each point in a flowingfluid. In determining the rheology of fluids, any one of the following b a i c behaviour patterns (fluid types) may be found upon agitation of the fluid a t constant temperature. Newtonian fluids.A Newtonian fluid is one whose visco~itya t a given temperature ie independent of the rate of shear. There is a linear rdationship between the shear streas and the rate of shear for a Newtonian fluid. The viscosity of a Newtonian fluid a t a given temperature is constant regardless of the velocity, previous agitation or shearing of the fluid.
Purely viscour flddr
Fluids
P Time dependent
P
Flg. 3.1 RheologlcalclasslficaUon of lulds.
With pseudoplastic behaviour, the fluid displays increasing viscosity with decreasing shear rate. This means that there is a non-hear relationship between shear stress and shear rate. Curve number 3 represents pseudoplastic behaviour. Dilatent beheviour is depicted by curve number 4. Most waxy crude oil gels exhibit thixotropic or occasionally rheopectic behaviour. When a waxy crude oil is allowed to cool below its pour point under static condition in a pipeline, the paraffins will crystallize causing the entire mass of crude to gel. To initiate flow again, a finite pressure is required. For waxy crudes, yield stress is an inverse function of temperature and increases with decreasing temperature. With the crude oil that is below its pour point, the wax crystal structures in the oil start to breakdown as flow begins. This breakdown depends both on the time and rate of shear. Start up pressure depends to a large extent on whether the oil is cooled under static or dynamic condition. For instance, the additional restart pressure will be substantially higher
.,-.-,
Figure 3.2show8 thevariation of viscosity with shear rate for different types of fluid. Curve number 1 is typical of the response of a Newtonian fluid. A Bingham-plastic fluid is characterized by a flow curve 2 which is a straight line having an intercept b on the shear stress axis. The stress is called the yield stress which must be exceeded for flow to commence. The flow behaviour is described by an equation
Non-Newtonian fluids. A non-Newtonian fluid is one whose viscosity at a given temperature is dependent on the rate of shear. A fluid having a viscosity greater than 20 Pa.s is likely to be non-Newtonian. The viscosityof non-Newtonianfluids may increase or decrease with the rate of shear, depending on the type of fluid. The classification of non-Newtonian fluids is depicted in Fig. 3.1. Time-independent non-Newtonian fluids. A non-Newtonian fluid is said to be timeindependent if the shear stress at any rate of shear is constant with time. The properties of such fluids dependonly on the magnitude of theimposed shear stresses and not on theduration of the stresses. If the viscosity decreases with increase in the rate of shear, the fluid is known as a pseudoplastic fluid. This behaviour,is generally restricted to a certain range of shear rates. At a very low or high shear rate, fluid,maybe Newtonian. If the viscosity inkeases with increase in rate of shear,the fluid is known as dilatpnt fluid. Bingham-plastic fluids exhibit a definite yield stress below whith no flow occuis (the behaviour is that of a solid). A finite force must be applied to produce movenlent. The line* relationship between the rate of shear and shear stress for Bingham-plastic fluids does not pass thmugh the origin. Time-dependent non-Newtonian-fluids, A non-Newtonian fluid is said to be time-dependent if the shear stress changes with the duration of shear. In other words, the viscosity of such fluids at any time depends on the amount of previous agitatidn or shearihg of the fluid. A fluid whose viscosity decreases with time at a given shear rate is called thixotropic.'If the viscosity of a fluid increases with time at a given shear rate, We fluid is called rheopectic. 1) Viscoelastic fluids. These exhibit many characteristics of solids. Their resistance to deformation is proportional to the usual viscous effect, plus an elhticeffect that is a a c t i o n of time. When the rate of strain of such a fluid is suddenIyincreased, there is a relaxation time during which the stress changes from its origidal to a new steady-state value. Equations developed for pseudoplastic fluids can be applied to the steady-state flow of viscoelastic fluids.
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35
The viscosity of crude oil is perhaps it. most important physical property. For most crudes, at sufficientlyhigh temperature, the viscosityat a given temperahue is constant and the crude, is reduced, although chemicallyverymmpl?~,is a simple N e v however, the flow properties of a crude oil can readily change very complex flow b e h a w due to the crystallization of of asphaltenes. The waxes basically consist of . crystals Can form an interlocking structure of plates, needle or malformed ~ s t a l sThese entrap the oil into a gel-like struehue that is capable of forming thick deposits in pipes and
3.4. FLOW PROPERTIES OF WAXY CRUDE OILS
for a statically cooled pipeline (the fluid was above the pour point while flowing and allowed to cool during shutdown of the pipeline) than for one that has been dynamically cooled (the fluid was already below pour point when pipeline was sl~utdown),i.e. the cooling occurred due to the flow of the crude in the pipeline. --
Shear rate
/ 2
fig. 3.2 Typical non-~ewtionionfluids.
WRASPORTATIONOF WAXY CRUM,OILS
3.5.4.Effective Pipeline Viscosity For determining pressure gradients in the pipeline, effective pumping viscosities have to be determined. Using these viscosities, the conventional formulae can be used for calculation of pressure dmp. The effective pipeline viscosity for calculating frictional pressure drop at various flow rates and temperatures can be predicted by rotational viscometer tests. Due to wax crystallization at low temperature, the conventional capillary tube viscometers cannot be used. Moreover, for non-Newtonian fluids viscosity is dependent on shear rate. For this service as also for other sluny services, rotational viscometers are used. The sample is taken in a double w d e d cup (a refrigerant flowid in between the two walls). The outer cylinder is rotated by a variable speed motor. The &er cylinder is suspended from a torsion wire consisting of a stainless steel tube, the deflection being measured by a balanced pointer. The rpm of the outer cylinder multiplied by the instrument constant gives the shear rate. The deflection reading of the pointer multiplied by another instrument constant gives shear stress. The ratio of shear stress to shear rate gives the viscosity of the fluid. When the oil is at such a temperature that flow is non-Newtonian, the Reynolds number is a function of viscosity which itself is a function of the effective rate,of shear. Therefore, an intermediate calculation is required to arrive at the appropriate pipeline viscosity for calculating pressure drops. Viscosity of the oil to be pipelined is determined at various temperature and rate of shear by rotational viscometers. These are used to plot-viscosity versus temperature curves for various rate of shear. This plot can be used to determine the temperature below which the oil will behave as non-Newtonian fluid. It is required to find the effective viscrosities of the oil for pumping at'different flow rates a t various temperatures. The f i s t step is to use the plot of viscosity versus temperature-and plot curves of viscosity versus rate of shear for different temperatures.
3.5.3 Flow a t Restart kc At the time of restart of the pipeline because of very high viscosity,the flow rate is ejrpected to be low. This, however, depends on available shear stress as compared to thejrield stress. In any case, the minimum flow conditioris of the pumps have to be investigated. If a pump is operated at a very low flow rate, additional wear due to unbalanced flow is expected. Further, due to the poor efficiency,the oil will be heated and, after a short while, the allowable maximum temperature will be exceeded. This limits the allowable time for the operation of the pumps with low flow. If the restart flow rates do not meet the pump requirements, gpecial pumps with appropriate characteristics h i g h head, low flow) have to be used for restart of the pipeline.
Correlation of the model pipeline test results for actual pipeline d e s i p ie tlormally based on the previous experience. Some of these correlations are developed by the designers by pilot plant tests simulating the field conditions in a test loop. A general equation for calculating restart r e q ~ r e m e for h a cooled line is p=-YLC A ...(3.6) where P is the pressure required, Y is the yield stress of gelled crude (thitr value must be determined in laboratory tests and is different for static and dynamic cooling), L is the line length, C is the circumference of inside pipe wall and A is the cross sectional area of pipe.
i
I
I
Pipelining the crude as an oil in water (Om) emulsion reduces the flow properties to nearly the viscosity of the continuous water phase. An O N emulsion pipeline handling 40000 barrels of oil per day (265 m3 h-l) of 70 vol.% crude oil has been operating in Kalimantan (Borneo) in Indonesia since 1962. Blending with a less waxy crude oil or distillate improves the flow properties by altering the wax solubility relationships. Both of these methods have the disadvantage of reducing the crude oil carrying capacity of the pipeline. Note that separation at the well head to include more condensate in the crudepjl (if available) has the same effect as dilution. There is one interesting case of a shear and t e ~ p e r a t u r treatment e being used to favourably alter the flow properties of waxy crude oils in (Assam (India). More recently, pour
One of the following methods for pipelining waxy crude oils may be considered: (a) Select pumps to allow a paralleYseries arrangement, whichcouldtransport at slower rateg and higher pressures when required. The piping could be manifold so that parallel arrangement would be accommodated by repositioning of valves to handle higher flow rates. (b) Use of separate low flow, high head pumps for restarting. Side traps at frequent interval? to allow short s6&ons to be started separately. Reverse pumping to create back and forth pumping sequence which prohibits static cool down. Use of pour point depressants/flow improvers. Adding hydrocarbon diluent such as a less waxy crude or light distillate. Iqjection of water to form a layer between pipe wall and crude. Mixing water with crude to form an emulsion. Displacement with water or light hydrocarbonliquid in case of shutdown of pipeline. Separation at higher than normal pressure to allow as much gas and light hydrocarbons as possible to remain in the crude. Conditioning the crude before pipelining to change the wax crystal structure and reduce pour point and viscosity. Further sub-division of pipeline into smaller segment or reducing batch length of waxy m d e to increase maximum shear stress available. Combination of the above methods.
3.6 METHODS FOR PIPELINE TRANSPORTATION OF WAXY CRUDE OILS
The .second step is to plot curves of viscosity versus rate of shear for different pipeline throughput as follows: For a given flow rate, an equivalent shear rate is determined by Eq. 3.3. Assumin$ the value for viscosity, the Reynolds number is calculated. If the flow is in turbulent region, the correction factor for rate of shear is read from the plot of the correction factor for shear rate versus Reynolds number. Using this factor the effective rate of shear is obtained. By repeating this for different values of viscosity, a curve of viscosity versus effective rate of shear for a flow rate can be superimposed on the plot of viscosity versus rate of shear for various temperature. The intersection of the constant throughput curves with the constant temperaturecurves$ves the appropriate viscosities to be used for these conditions. An effective viscosity versus temperature curve can be plotted for the various Chroughputs.As mentioned earlier, using these values of effectiveviscosity, pressure drops in the various sections of the pipeline can be calculated.
TRASPORTATION OFWAXY CRUDE OILS
40
PETROLEUMREFININGTECHNOLOGY
point depressantdflow improvers have been developed that, in small concentration, affect the crystal growth, and as a result improve the flow properties. Of the various methods developed, the use of pour point depressantdtlow improvers is found to be more attractive. The main attraction of this method is its relative cheapnees and variability of dosage with respect to the temperature and desired viscosity requirements. 3.6.1 Use of P o u r Point DepressantslFlow Improvers The injection of pour point depressantfflowimprover additives appears to hold the greatest ( promise of achieving the desired overall objectives of operational safety and operating economy. Now improvers should have the capacity to reduce the pour point, viscosity and yield stress under dynamic conditions; and restart the pumping after a shutdown with the available shew stress. Chemically pour point depressantshlow improvers are ashless polymeric additives which when added into the crude oil a t 300-600 ppm level reduce the pour point and viswsity of the crude oil. Polymeric materials.widely used as pour point depressantdflow improvers are (a) alkyl acrylate polymers and cdpolymers, (b) o l e h alkyl maleate copolymers, (c) vinyl ester polymers and copolymers, and (dl alkylated polystyrene. Normally, the average molecular weight of the commercial available pour point depressants for crude oils is between 2000 to 20000. Various flowimprovers developed a t RRL, Jorhat (India) are SWAT-104, SWAT-106, FIR1 and FIRI-B. These are polymerdcopolymers,easily soluble in crude oil around 4M5OC and non-corrosive. They are used in pipelining crudes of Bombay High and Asssm (India). 3.6.2 Mechanism of Flow Improvement When a waxy crude oil is cooled below its cloud point, the wax crystals form and begin to agglomerate and with further temperature reduction crystal agglomerationreaches a point a t which a gel structure is formed below the pour point due to interlocking of the growidg crystals and dependent on constituents like resins, asphaltenes, asphalts, paraffin and microcrystalline waxes, etc., their molecular weight, structure and quantity and also on the rate of cooling and degree of agitation during cooling. When the additives or flow improvers are added, they alter the wax crystal size and shape in some manner and prevent the tendency to interlock. l'he'flow improvers or pour point depressants act by retarding the growth of the wax crystals in the XY crystallographic plane, thereby producing smaller crystals of higher volume/surface ratio. It appears that the flow improvers cocrystallizewith the growing wax crystal, leading to the formation of a fault in the otherwise compact regular wax crystal and resulting in diminished gel strength, so that by coating on to a growing wax crystal the flow improvers reduce the tendency of wax crystals to interlock. 3.6.3 Point of Additive Injection As a general rule, the additives should be injected into the crude above or around its cloud point and also a t a temperature of some 20°C above the pour point of the additive. The additive pour point could be depressed considerably by cutting (diluting) the basic component with kerosine, or aromatic solvents. The preferred location of iqjection should be a t a point where No heating of the oil is required (utilize the heat of formation) Subsequent external application of heat can be avoided or minimised. The maximum benefit can be derived in the system downstream.
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TRASPORTATION'OFWAXY CRUDE OILS
41
All of the above considerations point to additive injection into the crude stream at well head.
3.6.4 P o u r Point Reduction b y Additives Pour point measurements on crude oils have been used to detect low temperature handling problems. However, as mentioned already, they do not necessarily predict the field performance. Pour point can at best be used for preliminary screening of various additives for their potency with a particular crude oil. These studies were carried out in the Salaya-Koyali-Mathura crude pipeline by Oil & Natural Gas Commission, India. The line was originally designed for transportation of low pour point Middle East crude oils (Light Arabian and North Rumaila). With the discavery of the Bombay High crude oil, it was decided to process this crude too at these refineries. Efforts were made to find a suitable solution to the problem of pipeline transportation of this high pour point (30°C) Bombay High crude oil to these refmeries during winter. It was reported by model pipeline tests that the line will not be able to take a restart after cooling statically to low winter temperature of around 16OC. A number of flow improver additives were tested for their effectiveness on Bombay High crude. born preliminary tests, Shell-swim-5Tand Esso Paradyne-80 were reported to be the most effective additives in lowering pour point. Further tests by rotational viscometers indicated that, for similar level of dosage, both effective viscosity and yield stress were reported to be lower in case of Shell-swim-ST as compared to Esso Paradyne-80. It was therefore concluded that shell-swim-5T is superior to Esso Paradyne-80. Subsequently, Shell-swim-5T was used for transportation of the Bombay High crude to Uran terminal through the submarine pipeline from the production platform. Extensive studies were subsequently done at IIP, Dehradun and Gujarat Refinery to determine the optimum doping conditions for Shell-swim-5T in Bombay High crude. k o m these.studies the optimum doping levels were reported to be 250-300ppm of the Shell-swim-5T.The effect of doping temperature on the pour point was reported to be negligible.
Yield stress @ 160 C
'45.0 45.0 42.4 41.0
CP
Viscosity @ 160C
3.6.5 Effect of Flow Improvers on Yield Stress a n d Viscosity Significant reduction in yield stress and effective viscosities can be achieved by doping waxy crude oils with flow improvers. The following results were reported for the effect of Shell-swim-5T (flow improver) on Bombay High crude oil. Doping level
dyneslcm2
330.0 62.5 62.5 45.8
PPm Nil
250 300
400
These results show significant reduction in yield stress with 250 ppm doping. Further improvement with higher doping levels is, however, marginal. In fact in some cases the trend was reported to be reversed with higher doping levels, as shown below by the following model pipeline tests conducted by ONGC.
/
.
1
1000
750
400
Nil
CNde
sant in Bombay High
pintDePres-
I
27.5
on n 1u.I.
21.2
I
I
589 at 45 dynedcm2 966 at 45 dynes/cm2
435 at 45 dynes/cm2
Test was as oil could not be transferred to model pipeline - abandoned due to congealingat 18OC.
Yield stress at 1kc,d y t w s ~ c m ~ Viscosity at 16°C at flow deueIop. ment, cP
-
PETROLEUMRWNINQ TECHNOLOGY .
5.0
62.5
330.0 J
.
E
point depressant 90% Bombay High + 10% Basrah with 300 ppm pour point depressant 90% Bombay High + 10% Basrat point depressant
. - 250 ppm pour Basrah with 90% Bombay High + 10% Basra1
Crude blend
I
I
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I
5.0
5.0
5.0
50°CDoping 50°C Doping
I
)
25.0
25.0 25.0
25.0
30°C)Doping 3O0C)Doping
Yield stress at 16"C, dynes/cm2
I
I
1
1
The doping temperature is quite important as far as yield stresses are concerned. The blends of Basrah with Bombay High crude doped at 50°C is reported to give better results as compared to temperature of 30°C. This is s h o w by the following experimental results reported.
de~resaant.
100% Bombay High with 250 ppm of pour point depressant 90% Bombay High + 10% Basrah with 250 ppm pour point
100%Bomhnv Hioh -I-.
problems of wary crudes provided the lowpour p i n t cmde is easily available for blending and no problems are expected to be encountered in processing the cmde blend as far aa product specificationsare concerned. Once again B e example of Salaya-Koyali-Mathurapipeline can be cited here. The Gujarat spd Mathura refineries fed by thispipeline (Gujaratpartly) are to p m n n partly Bombay High crude and partly low pour point Middle East crude. A small percentage of tbP Middle East cmde mixed with Bombay High cmde will not result io any serious processing problems. The reported results of laboratoq studies on blends of Middle E u t crude with Bombay High m d e indicate that the incorporation of Basrah cmde in doped Bombay High cmde shows no further reduction in pour point. I b i q could be due to reduction in percentage of n-parfins when Basrah cmde is mixed, the effect of pour point depre~sant being more predominant on n-paraffins as compared to iao-parafiins. However, a significant reduction in the yield stress of the blend is reported, as shown below.
Aa mentioned earlier, this can be one of the probable solutions to pipeline transportation
3.6.6 Incorporation of Low Pour Point Crudes i n Waxy Crudes
Hence, optimum doping levels by extensive laboratory studies must be determined before starting additive injection.
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42
.
6.
5-.
4
3.
2.
265-279 (1986). 12, pp. 1937-1942(1.988). S. ~angul~,Ftheological~arameteraand s o l u t i o ~ e m of waxy cmde oil, URJh vol. 26, No. 2, pp. 33-34 (1989). P. Datta, H. Dubey and K.L.Pate1, Pipeline transportation of waxy crude oil from the oil fields, Chemical Engineering World, Vol. XW, pp. 43-45 (1990)., -. R. Prasad. Waxy crude oils, In PIPING DESIGN HANDBOOK J.J. Mcketta, Ed.. Marcel ~ikker,il992). S. Naik, C.K Pathak, and V.P. Sharma, Effecte of our p i n t dep"essant8 on WaXY Indian crude oil, IE(1) J., Vol. 69, Part CH2, p p 60-63, (1989).
NO.
A ther-
modvnamic --- -" model for predicting wax formation in crude oils, AIChE J, Vol. 34,
J.H.Hansen, A. Fredenslund, K.S.Pedersen and H.P. Ronningsen,
-
1 K. W. won, Thehodynamics for solid solution liquid - vapor equilibria :Wax phase formation from heavy hydrocarbon mixtures, Fluid Phase Equilibria, Vol. 30, pp.
This process is developed by Oil India Limited. The crude oil conditioning is a unique process in which the cmde oil is first heated to melt and dissolve the wax in it. Thereafter, on dynamic cooling and wbrkbg t b u g h the p m p the crude oil is subjected to static cooling at a predetermhed rate. The result is the conditioned crude oil which has much improved physical properties than the virgin crude oil. The conditioned crude oil remains fluid at much lower temperature and possesses satisfactmy physical properties so far as transportation of crude oil through the pipeline to refineries during the winter monUs is concerned. This has been employed for transporting wary crude oils from Assam (India). I,the actual process the crude oil is heated to a temperature of lCO°C in tube heater. Before entering into the tube heater, the crude oil passes through heat exchanger and exchanges heat with the outgoing oil from the heater, bringing down its temperature to 65OC by dynamic cooling.The crude oil at 65OC is stared in a tank from where it passes thmugh a pump to static cooling vessels, commonly called conditioning vessels, These vessels are essentially sheU andtube heat exchangerd'in which crude oil is taken in the shell side and cooling water is passed through tubes. The con&oning vessels follow a batch time cycle of 208 minutes to achieve coaling of crude oil &om 65OC to l8.S0C (this includes h ~ & time g of cmde oil and its emptying outtime also). The coolirigof the crude oil in the conditiohg vessels is effected by circulating watets, namely intemediate and relrigerated waters. Intermediate water is maintained in a closed circuit through a pump and heat exchanger in which cooling medium ia tbs cooling water. The refrigerated w a t u is also maintained in a closed circuit though a pump and absorption refrigeration machine. The c i r ~water t while f l o i n g paat evaporator chamber of absorption refigeration machioe though tube bundles gets chilled. h the temperature of crude oilis brought down to the desired level of 18 - 2g°C, the cmde oil from conditioningvessels is emptied out automatically into conditioned oil storage tanks. T h e conditioned oil from these tanks flows pipeline pumps through a booster pump and this .------completes the process of conditioning.
3.6.7 Crude Oil Conditioning
TRASPORTATIONOF WAXY CRUDE OILS
s
4
PETROLEUM REflNlNG TECHNOLOGY
7. M. N. Sunil Kumar, Reviews on polymeric and copolymeric pour point depressants for waxy crude oil, The Institute Of Petroleum, 0ct.-Dec., pp. 47-71 (1989). 8. B. Smith, Steps for finding crude properties, The Oil and Gas J., Vol. 77, No. 23, pp. 150-152 (1979). 9. L. T. Wardhaugh and D.V. Boger, Measurement of the unique flow properties of waxy crude oils, Chem. Engg. Res. Des., Vol. 65, pp. 74-83 (1987). 10. B. Smith, Heat transfer explored in pipelining high-pour-point crude oil, The Oil and Gas J., Vol. 77, NO.25, pp.110-lll(1979). 11. B. Smith, Restart of heavy crude lines probed, The Oil and Gas J., Vo1.77, No. 27, pp. 105-106 (1979). 12. B. Smith, Design of heavy crude facilities explored, The Oil and Gas J., Vol. 77, No. 29, pp. 69-70 (1979). 13. B.M.A. Rao, S.P. Mahajan and K.C.Khilar, A model on the breakdown of crude oil gel, The Can. J. Of Chem. Engg., Vol. 63, No. 1, pp. 170-172 (1985). 14. T.Viswanathan and KC. Khilar, Hydrodynamically induced gel breakdown in pipes, The Can. J. Of Chem. Engg., Vol. 67, No. 3, pp. 353-360 (1989). 15. 3. Sestak, M.E. Charles, M.G. Cawkwell and M. Houska, Start-up of gelled crude oil pipelines, Journal Of Pipelines, Vol. 6, No.1, pp. 15-24 (1987). 16. M.G. Cawkwell and M.E.Charles, An improved model for start-up of pipelines containing gelled crude oil, Journal of Pipelines, Vol. 7, NO. 1, pp. 41-52, (1987). 17. A. Majeed, B.Bringeda1 and S. Overa, Model calculates wax deposition for N. Sea oils, The Oil Gas J , Vol. 88, No. 25, pp. 63-69 (June 18,1990). 18. R.A. Vora and D.P. Bharambe, Polymeric flow improvers, Indian J. Techol., Vol. 31, No. 9, pp. 633-635 (1993). 19. L.T. Wardhaugh and D.V. Boger, Flow characteristics of waxy crude oils :Application to pipeline design, AIChE J., Vol. 37, No. 6, p. 871 (1991). 20. J.A. Svendsun, Mathematical modelling of wax deposition in oil pipeline systems, AIChE J., Vol. 39, NO.8, pp. 1377-1388 (1993). 21. T.F. Al-Fariss, Effect of wax on oil behaviour, Indian Chemical Engineer, Vol. .=I, NO.2, pp. 8-12 (1990). 22. G.P.van Engelen, C.L. Kaul, B. Vos and H.P. Aranha, Study of flow improvers for transportation of Bombay High crude oil through submarine pipelines, Journal of Pet. Tech., Vol. 33, No. 12, pp. 2539-2544 (1981). 23. T.R. Sifferman, Flow properties of difficult-to-handle waxycrude oils, Journal of Pet. Tech., Vol. 31, No. 8, pp. 1042-1050(1979). 24. C.A. Irani and J. Zajac, Handling of high pour point west African crude oils, Journal of Pet. Tech., Vol. 34, No. 2, pp. 289-298 (1982). 25. R.N. Tuttle, High-pour-point and asphaltic crude oils and condensates, Journal of Pet. Tech., Vol. 35, No. 7, pp. 1192-1196(1983). 26. E.D. Burger, T.K. Perkins and J.H. Striegler, Studies on wax deposition in t h e h a n s Alaska Pipeline, Journal of Pet. Tech., Vol. 33, No. 6, pp. 1075-1086(1981). 27. C. Chang, D.V. Boger and Q.D. Nguyen, TLEyielding of waxy crude oils, Ind. Eng* Chem. Res., Vol. 37, No. 4, pp. 1551-1559 (1992).
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~ O D U C T I O N
QUALITY CONTROL OF PETROLEUM PRODUCTS
Qunlity control of petrolcum products 1s ;I n(bc(bssilq.il't hc protlucls ilrt! to give sillisii~ctory pedormance to the customcra. Keeping in view 11~.ascli~in(~ss of mlch prlxluct. fi)r sp(*(:ilic purpose, standnrd urganisations have t n f L r l md\v)(lsol'trsl.~and s~cciticdinnc.Bur\.;iu I* Indim Standard @IS), New Delhi is onc sc~chor~;rnis;~lion in lndia which stantlnrdihcs procedures and issues specilations. 111stiluteof Pctroleun~(ll').1J.K and Anlvrican S(aic1y for Testing & Materials (ASl"l'), U.S.A. ;IIX thc other two i ~ ~ ~ ~ ) organisiltions o r l i ~ ~ ~ t wllosc' methods and specifications are widely followed. Apart from BIS sl)ccifications, I!cntral Board Of Revenue, New I)elhi has certain othcr specifications tbr the purpoxc ol'cxcisc Ic!vy. Some of the important limits set by them are for carbon residue, flame height,fli~sh[mint. a ~ visajsity. ~ d
4.2 CLASSIFICATION OF LABORATORY TESTS Most of the laboratory tests can be broadly classified into seven groups 11;lst:tl 011 t11(' followingcharacteristics: Volatility Combustion e Viscosity and consistency e Melting point e Oxidation Corrosion and protection e Miscellaneous tests Volatility is the major dcterminant ofthc tendency of a hydrocarbon to produce polontially ex~losivevapours. I t is also critically important to an cmgine's start and warm-up. Volatility is gssessed by the following tests: (a) Distillation (b) Vapour pressure (c) Flash point and fire point The combustion properties of petroleum products are evaluated by the following tests: (a) Antiknock quality-Octane number, Performance number (b) Ignition quality-Cetane number, Aniline point, Diesel index, Calculated cetanc index (c) Calorific value ( d )Burning quality-Smoke point, Char value
PETROLEUM REFlMlNGTECHNQLQGY
The laboratory distillation test comprises a simple process in which 100 ml sample is vaporised in a suitably designed flask fitted with a thermometer, and condensed in an ice-cooled tube and collected in a measuring cylinder. Whereas an individual hydrocarbon would exhibit a single boiling point, commercial fuel blends boil over a range of temperatures. Corresponding readings of vapour temperature and condensate recovered are made at prescribed intervals and the results are plotted in the form of distillation c w e . The initial boiling point (IBP) is taken as the temperature observed at the fall of the first drop of condensate, and the final boiling point (FBP) as the maximum temperature reached during
4.3 DISTILLATION
The determination of viscosity and consistency of petroleum products is done by the following tests: (Q) Kinematic viscosity (Redwood, Saybolt, Engler) (b)Viscosity index (c) Penetration tests The tests designed to ascertain the tendency of certain petroleum products to melt or liquefy,,tosolidify or to precipitate wax-like materials are: (a)'k8ezing Point (b) Cloud point and pour point (c) Drop point of grease (d) Melting and setting point of wax (el Softening point of bitumen Methods have been devised for the evaluation of storage stability and resistance to oxidation for gasoline and aviation turbine fuel. These include: (a) Induction period of gasoline ( b )Thermal stability of Jet fuels (c) Gum content Most crude oils are corrosive to greater or lesser extent, frequently due to the presence of sulphur compounds, organic acids (mainly naphthenic acids) and traces of brine. Therefore, test methods have been designed to evaluate the corrosive poteqtialities of the petroleum products which are obtained by processing of crude oils. The following methods are available: (a) Total sulphur (b) Acidity and alkalinity (c)Copper-strip corrosion test (dl Silver-strip corrosion test for Aviation Turbine Fuels The misceJlaneous tests include: (a) Ash (b) Carbon residue (c) Colour (d) Density.and%pecific gravity (el Gas ckpmatography of petroleum gases and liquids (f) Refractive index of hydrocarbon liquids (g) Lead in gasoline (h)Water separometer index (modified)(WSIM) ( i ) Ductility The definition, method and significance of tests mentioned above are given below.
46
4.5 FLASH POINT AND FIRE POINT Flash point and fire point can be taken as indirect measureof the product. The flash point is the lowest temperature at which application of test flame causes the vapour above the oil to ignite. The fire point is the lowest temperatwe a t which the oil ignites and continues to burn for 5 second. The determination of flash point of petroleum products consists of heating a given volume of liquid at a standard rate of temperature rise until vapour is produced to such a degree as to give a flammable mixture with air in an enclosed space (i.e. closed flash point temperatye) or with air in an open cup (i.e. the higher open flash point temperature), ignition resulting
Vapour pressure of a liquid fuel may be defined as the pressure exerted by the vapour above the free surface of the liquid at the given temperature. For volatile, nonviscous petroleum products, it is determined by Reid method. This is the pressure exerted by vapollr when it is in equilibrium with the liquid under the conditions of test. For liquefied petroleum gas, the procedure is different and the determination should be done at 65%. The conditions under which vapour pressures are determined give results which are not true because of the ' air which is invariably present in apparatus. n e true vapour pressure is higher than the Reid vapour pressure by about 5 to 9 percent but this relationship varies widely. The standard Reid apparatus consists of a fuel chamber comectea to an air chamber of four times volume, and fitted with a pressure gauge. This test is important with ,no-x vzan.oort,pzur&&jg-the gdsoline *types of storage tanks employed and the starting characteristics of motor hels. High t storage and transportation. In case of motor vapour pressure entails loss of the ~ r o d u cin spirit, it may cause vapour lock in the gasoline engines.
4.4 VAPOUR PRESSURE
the test. Due to small losses of vapour a t the connections and openings in the apparatus and the residue remaining in the flask on compfetion of the test, the total recovery does not generally exceed about 97 percent. A maximum distillation temperature limit of 370% has to be set, otherwise the heavier hydrocarbon molecules are liable to suffer from cracking into lighter molecules causing the distillation characteristics to change duringtheir measurement. Thus fiels heavier than gas oils cannot be tested completely for distillation behaviour. The distillation characteristics give a broad indication of fuel type. Being a measure d volatility, they determine the system of fuel metering required (wick feed, carburation or atomization), and are indicative of the vaporisation behaviour of fuels instorage (vapour loss and vapour lock), and in piston-engine manifolds (uniformity of distribution to cylinders). The extent of the distillation range for any given fuel is representative of the availability of that fuel from the parent crude oil. For a fuel with a high demand, the aim of the supplier will be to extend the distillation range as far as practicable. However, due to the interrelationship between properties and the associated problems, minimum and maximum limits, respectively, may need to be set for the initial and final boiling points. The significance of this test varies from product to product. In case of crude oil, the ASTM distillation data give some idea of the frwtions that could be collected below 300°C. If it is a true boilkg point (T.B.P.) distillation, the TBP curve reveals a lot of characteristics that are useful for the design of the refinery. The 10vol.% of distillation for motor spirit is an indication of the ease with which the engine can be started. Too high a FBP will cause crankcase oil dilution.
QUALITY CONTROL OF PETROLEUM PRODUCTS
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48
PETROLEUMREFINING T E ~ H N O ) ~ ~ & ~
tiom the applicalion of'a small flame. At firc point, not only will the vapour-air mixture'fir)8h but the liquid will continue to burn. Abcl apparatus is used for determiningthc closed cup flash point of' petroleum products h ; t v i n ~tlash points between 19°C and 49°C. Pcnsky-Martens a p ~ a r a t u a iused s for deteymining the flash point of fuel oils and lubricating o h , bitumcn other than cutback bitumen having ilaxh point :~br>vc 49OC. Clcvcland appariltus is used for determining the flash and fire points products having an open cup flash point below
;I
79°C.
of pctroleun~products cxccpt l'uucl oils and those
Ylirsh p u n t measurcs thc tcntlcncy of the fuel to form a flammable mixture with air under conlrollcd laboratory conditions. This is tho only propcrty that must be considered in assessing the ovcrull tlammability l~azartlof a mntcrial. I t is used in shipping and safety regulations thnldcfinc flttmmable and combustible n~uterials.Petroleum products having low flash points irrlb~~otential to fire hazards. Flash point can indicate the possible presence of highly volatile ant1 tlan~n~ablo materials in rclativoly nonvolatile or nonflammnble makrial. 4.6 OCTANE NUMBER
This is a n important test for measuring the antiknock quality of the gasoline (petrol or motor spirit). The knocking of the motor fuelsis compared using blends of reference fuels. The standard reference fuel8 used foroctanenumbers below 100areiso-octiineand normal heptwe which arc assigned valuerr of100 and 0, respectively, on the octane number scale. The octane number of thc fucl is defined atl the volume percentage ofiso-octane t2,2,4-trimethyl pentane) in a blcnd with n-heplanc which is equal to the test fuel in knockintensity under standardised and closely controllcd conditions of test in a single-cylinder, variable cbmpression ratio enbines, known as CFli cnginerr. Thus, a fuel of 87 octane number has a CFR engihe performance matching that obtainable with a blend of 87 volume percent iso-octane and 13 volume percent n-heptane. Thc rating can be done by either Research mcthod or Motor method. The differences in the two methods are as follows:
Octane numbcr rcquirc~ncntsof gasoline engines depend on their compression ratio. If the fuel meets the minimum requirements in respect of octane number it ensures trouble Bee ol~cration.Apart fiom being a nuisance, the knocking in an engine may result in loss of energy : ~ n da t times may cause severe damage to the engine. 4.7 PERFORMANCE NUMBER
This is used to estimate knoekihg characteristics of aviation gasolines of octane number highcr than 100. The standard reference fuels for knock ratings above 100 octane number are iso-octane and its blends with tetraethyl lead (TEL). The ratings of aviation gasoline above 100 octane number are normally expressed as performance number. The performance number scale is based on engine power output. The performance number of an aviation fuel represents approximately the maximum knock-free power output. The
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QUALITY CONTROL OF PETROLEUMPRODUCTS
49
onrformance number shows the percentage increase in aipcrafi engine power for addition of r------TEL to iso-octane and is given by Performance number - 100) Octane number = 100 + ( 3 -
On the performance number scale, 100 octane number equals 100 performance number. The ratings of aviation gasoline above 100 octane number can be done by (a)Aviation method (lean mixture rating); ( b )Supercharge method (rich mixture rating); and (c) xie ended motor method. I n aviation method, the rating is done a t 1200 rpm by comparing the combustion chamber temperature for the fuel with those of the blends of known performance number. This lean mixture rating gives us an idea of the availability of knock limited power in spark ignition type aircraft engines when the aircraft is under cruising conditions. In supercharge method, the rating is done a t 1800 rpm by comparing the h o c k limited power of the fuel with those for blends of iso-octane and isooctane plus TEL. This is done a t constant compression ratio by measuring indicated mean effective pressure a t enough points to define the mixture response curves for the sample and the reference fuels. When the knock limited power for the sample is bracketed between those for two adjacent reference fuels, the rating is cakulated by interpolation. The rich mixture rating indicates the a v d a b z t y o f b o c k limited power when the plane is under take-off conditions. In extended motor method, the rating is done in a CFR engine normally used for rating of motor gasolines by motor method (rpm=9OO). The knocking intensity of the fuel is bracketed between reference fuel prepared from iso-octane and TEL and the performance number is calculated by interpolation.
Cetane number is related to the ignition delay of a fuel in a diesel engine, i.e. how rapidly
4.8 CETANE NUMBER
to lower cetane numbers. Cetane number of diesel fuels is determined in a single cylinder CFR engine by comparing the ignition delay characteristics of the diesel fuels with that of reference blends of known cetane number. Cetane number of a diesel fuel is defined as the whole number nearest to the value determined by calculation from the percentage by volume of normal cetane in a blend with h e p t a m e t w nonane which matches thdignition quality of the test fuel when compared bv this method..The matching blend percentages to the fiist decimal are inserted in the following equation to obtain the cetane number: ... (4.2) Cetane number = % n-cetane + 0.15 (% heptamethyl nonane) The shorter the ignition delay period, higher is the cetme number of the fuel. Cetane number is the index of ignition quality of a fuel. High cetane number fuels will facilitate easy starting of compression ignition engines, particularly in cold weathers, and faster warm up. These also result in increased engine efficiency and power output, reduced
,,
-
Diesel index = Aniline point, OF x OAPI 100 Diesel index = Aniline gravity constant 100 Diesel index = Cetane number 10 0.72 J4.6)
...(4.5)
...(4.4)
where
G = specific gravity at 15OC
Tlo = 10 percent distillation temperature, OC T ~ O=NTm - 260, OC Tso = 50 percent distillation temperature, OC T ~ O=N2'90 - 310 OC T90 = 90 precent distillation temperature, "C B = - 3.5(G-O.85) - 1
0.00049 [(T~oN)~ - (T~oN)~] + 107B+ 6 0 ~ ~ TION= Ti0 - 215 ,OC J4.6)
4.1 1 CALCULATED CETANE INDEX Calculated Cetane Index (CCI) is based on specific gravity and the 10 percent, 50 percent and 90 percent distillation temperatures of the fuels and it gives numbers that correlate with the engine-testing method. The relationship is given Ly the following four-variable equation: CCI = 45.2 + 0.0892 TION+ (0.131+0.901B)T ~ O+N(0.0523 - 0.428)Tgo~ +
(c)
(b)
(a)
Diesel index is an indication of the ignition quality of a diesel fuel. This is dctemined by calculation from the specific gravity and the aniline point of the sample. Although it is ofthe same order as the cetane number, it may differ widely from the cetme number. Higher the diesel index, better is the ignition quality of the diesel i e l . It is normally used aa a guide to ignition quality of the diesel fuel in the absence of test engine for the direct measurement of cetane number. The diesel index is calculated as follows:
4.10 DIESEL INDEX
.
4.9 ANILINE POINT Aniline is a poor solvent for aliphatic hydrocarbons and excellent one for aromatics. This propertg is used in the aniline point test. Aniline point of an oil is the e t u r e & l & f & J - a W - . .. Equal volumes of the sample and aniline (5 ml each) are heated or cooled with stirring in a jacketed test tube and temperature at which complete miscibility occurs is noted. High aniline point indicates that the fuel is highly paraffmic and nence has a high diesel mdex and very good ignition quality. In case pf ar~maGc&he-milanilhe point is low u e ._+,-.-" ~.rrc.-.n-.ro-i
exhaust smoke and odour and combustionnoise. In the absenceoftesten&e,the diegel index or the calculated cetane index will give an approximate idea ofthe ignitiofi quai* ofthefdcl. Cetane number can also be roughly assessed by the formula: Cetane Number = 0.72 x Diesel Index + 10 ... (4.3)
38
The amount and nature of the deposits (char) produced on a wick during combustion depend on the hydrocarbon composition of the fuel and also on the design of the appliances in 'which it is used. Char occurs as a result of the breakdown and decomposition of the kerosine under the local conditions existing at the wick surface, and these conditions will also determine what proportion of the decomposed products remains on the wick.
4.14 CHAR VALUE
Smoke point is the maximum flame height in mm at which the fuel will b u m without smoking *hen determined in a smoke point apparatus under specified conditions. Smoke point apparatus comprises four main parts-lamp body, candle socket, candle and stand. The lamp body with chimney is fitted on the inside with a polished black engraved scale which is marked in white. A gallery is secured in the lower part of the body. The candle socket assembly is designed to give a smooth rise and fall over the total distance of travel. To ensure interchangeability the candle is finished to close tolerances. The assembly is mounted on a stand. The sample is burned in a standard lamp with a specified wick for five minutes. The height of the flame is read when it leaves no smoky tail. This is an important test for evaluation of illuminating oils (kerosines) for their ability to bum without producing smoke and the assessment of the burning quality of aviation fuels. Higher the smoke point better is its domestic use. I t also serves as a guide to assess the aromatic content of kerosines.
4.13 SMOKE POlNT
Calorific value is a measure of the energy available in a fuel. Thus a knowledge of the calorific value of the fuel, and the efficiency of the heating equipment, is essential to compare the merits and running costs of different fuels and energy costs. It is a critical property of fuel intended for use in weight-limited vehicles.
in which calorific value is in caYgm and p is density at 15OC in gm/crn3.
-
This is the quantity of heat released per unit quantity of fuel, when it is burned completely with oxygen and the products of combustion returned to ambient temperature. This quantity of heat will include the heat of condensation (latent heat) of the water vapour formed by the ' combustion of the hydrogen in the fuel, as it cools to ambient conditions. It is called the @ calorific value" or "hi~hercalorific yalue". Most h z t i n g applications cannot recover the heat of the water vapour; it simply escapes with the vapoui out of the chimney. The potential heat content is therefore more nearly indicated by subtracting this latent heat from the gross calorific value, and the resultant value is called the net calorific value, or lower calorific value. A weighed quantity of the sample is burned in a bomb calorimeter under controlled conditions. The calorific value is calculated from the weight of the sample and the rise in temperature. I t can also be calculated from the formulae J4.7) Calorific value = 12400- 2100 p2
CALORIFIC VALUE
Thirr CCI ia useful for estimating cetane numbers when a test engine is not available for direct measurement, and it may be convenientlyemployed for estimating cetane number when the quantity of sample available is too small for an engine rating.
Q U A M Y CONTROL OF PETROLEUMPRODUCTS
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4.15 VISCOSITY
PETROLEUM REFININGTECHNOLOGY
Kinematic viscosity is defined ris the mearidre of the r e d s t h i &to gravity flow of a fluid, the pressure head being proportional to the density. The time of flow of a fixed volume of fluid is directly proportional to its kinematic viscosity. The unit of kinematic viscosi$ is, cm2/s or Stoke. The unit most usually used in measurement of the kinematic viscosity of ~etioleum fuels is the centistoke (cSt) which is Stoke. Dynamic viscosity, also known as absolute viscosity, is the ratio of applied shear stress to rate of shear and thus a measure of the resistance of a fluid to flow. The unit of dynamic viscosity is gm1cm.s or Poise. Dynamic viscosity may be obtained from kinematic viscosity by multiplying it by the density of the fluid at the temperature at which measurement was made. Kinematic viscosity may be measured as an absolute property of the fuel, or alternately as a conventional property that is'dependent on the instrument and the method used. Both approaches depend on the efflux time of a given volume of sample flowing under its own head through a restriction. This follows because the force acting the laminar (low speed) flow of a fluid through a restriction is approximately proportional to the dynamic viscosity, whereas the force promoting the flow is that due to gravity, and is proportional to the density of the fluid. Hence the time taken for the gravity flow of a given volume of sample through a restriction is approximately proportional to the kinematic viscosity. The conventional methods, which are generally simpler but less accurate, are represented by the Redwood instrument in the UK, Saybolt in the USA and Engler in continental Europe. They each comprise a sample cup fitted with a standard-sized oriiice in the base and surrounded by a waterjacket containing a heating device. When the temperature reaches the test level, the orifice is unsealed and the time of flow is determined for the given volume of sample. The result is reported as Redwood or Saybolt universal second or as Engler degree, given by the efflux time ratio for the sample and for water. When the efflux time exceeds a specified maximum-for example 2000 s-due to high viscosity, use is made of a Redwood No. 2, or a Saybolt Furol (fuel and road oils) instrument, incorporating a larger diameter orifice. The absolute determination of kinematic viscosity'generally employs a glass U-tube viscometer with a capillary tube built into one leg. The length-diameter ratio is such that end effects are negligible and the precision is therefore higher. The instrument is suspended vertically in a thermostatically controlled water bath, and the time is measured for a given volume of sample to flow d o u g h the capillary. This measured time period is inserted into an \ equation to give a direct measure of the kinematic viscosity in centistokes. v=At-B/t ...(4.8) where A = instrument calibration constant; B = instrument type constant, depending on the capillary diameter; and t = efflux time, s (Engler degree for Engler viscometer) Table 4.1 gives the values of A and B for Redwood, Saybolt and Engler viscometers. Viscosity is an important characteristic of a fuel and it is used for the pump design. Pump clearance are aGusted according to the viscssity and if i t is out of the range, it will result in pump seizer. Pump operation of an engjne depends on the proper visesity of the liquid fuel. The viscosity of liquid fuel is important to its flow through pipelines, injector nozzles, and orifices, and for atomization of fuel in the cylinder.
Table 4.1 Instrument Constant Values
OUAUTY CONTROL OF PETROLEUMPRODUCTS
4.1 6 VISCOSITY INDEX
L-H
v1=L-Ux100
Viscosity index (VI)is the most widely used way of characterizing the effect of change of temperature on the viscosity of any oil. Proposed by Dean and Davis, viscosity index is an empirical concept based on the behaviour of mineral oils. In this concept, an oil whose viscosity changes rapidly with change in temperature has a low VI. An oil with a minimum change in viscositywith change in temperature has a highVI. In this system, Pennsylvanian (paraffinic) oils of a selected type which show a desirable, relatively small change of viscosity with change in temperature, were assigned a VI of 100, while selected Texas Coastal oils showing less desirable viscosity-temperature characteristics were assigned a VI of O.VI is governed by the type of hydrocarbons in the oil. Dean and Davis prepared tables giving the kinematic viscosities a t 40°C and 100°C of the Texas Coastal oils (L) and the Pennsylvanian oils (HI. The values of kinematic viscosities of L and H are given in Table 4.2. The VI of an oil can be calculated from the equation
where
U = kinematic viscosity at 40°C of the oil whose VI is to calculated L = kinematic viscosity at 40°C of an oil of 0 VI H = kinematic viscosity at 40°C of an oil of 100 VI .17 PENETRATIONTESTS
1
Several standard grades of bitumen are comlqercially available, which are normally ssified into different grades by p e n e t r a t i o n p e sample of bitumen is plzced in a suitable container and brought to a temperature of 25OC in a water bath. The weighted needle is brought to the surface.and at the end of 5 seconds interval, the penetration the needle into the bitumen, in units of UlO mm is t e ~ v o nofthe ' b $ The penetration at 25OC and the softening point, or penetrations a t two di erent temperatures (for example, 25OC and 10°C) can be used to define the extent to which the consistency of a bitumen changes with temperature. This an important characteristics for bitupens, and determines the type of bitumen used for a particular application. Various factors have beexi
.,
i
.,
,
.
L = Kinematic viscosity at 40 OC of an oil of 0 VI, cSt)
Table 4.2 Values of H. L and D for Kinematic Viscosity at 100 O C (H = Kinematic viscosity at 40°C of an oil of 100 VI, cSt,
used to define temperature 'dependence. The most commonl~used factor,.however, is the Penetration Index (PI),which is defined as follows :
QUAUTYCONTROLOF PETROLEUMPRODUCTS
55
56
PETROLEUMREFININGTEFHNOLQGY
QUALITY CONTROL OF PETROLEUMPRODUCTS
57
r
-?
--
4.20 DROP POlNT OF GREASE The standard drop point tests indikte that the temperature at which the thickener is so soluble in the base oil that the grease becomes substantially fluid. Clay and dye thickened greases have no measurable drop points. The drop point can be used to assess whether a grease of known formulation has been properly made or to obtain an indication of the type of thickener which has been used in a
Cloud point of petroleum products is the temperature at which a cloud or haze of wax crystals appears at the bottom of the test jar when the oil is cooled under prescribed conditions. It is generally determined for products that are transparent in a 43-mm thick layer and have cloud points below 49°C. The cold filter plugging point test is used to determine the extent to which diesel fuel or gas oil will flow, even though the temperature is below that at which wax crystals normally appear, i.e. cloud point. Cloud point gives a rough idea of the temperature above which the oil can be safely handled without any fear of congealing or filter clogging. Pour point is the lowest temperature expressed in multiple of 3°C at which the oil is observed to flow when cooled and examined under prescribed conditions. Pour point is a well-established test to estimate the temperature at which a sample of oil becomes sufficiently solid to prevent its movement by pumping. The pour point temperature depends to a large extent on the thermal history of the sample. Also, the pour point indicates the waxy nature of the oils.
4.19 CLOUD POlNT AND POUR POlNT
Freezing point is the temperature at which crystals of hydrocarbons formed on cooling disappear when temperature of fuel is allowed to rise. This method covers a procedure for the detection of separated solids in aviation reciprocating engine and turbine engine fuels at any temperature likely to be encountered during flight or on the ground.
4.18 FREEZING POlNT
where TRBis the ring and ball softening point of the bitumen in "C. etration of a bitumenat the softening point temperature is about 800. Bitumens less n fected by temperature change have positive values of PI and those ?ore affected by temperature change negativ'e values.
-
log (800) - log (PEN25°C) - 20 - PI 1 TRB 25 - [i?Gx][SO]
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4.23 INDUCTION PERIOD OF GASOLINE Induction period of gasoline is the time elapsed between the placing of the bomb in the bath and break point at 100°C. Break point is the point in the pressure-time CUNe that is preceded by a pressure drop of exactly 2 psi within 15 minute and succeeded by a drop of not less than 2 psi in the next 15 minute. Fifty millilitre of the sample is enclosed in a bomb with oxygen a t 100 psi and heated in a water bath at 100°C. The pressure is then recorded either on a chart or read every 15 minutes
standard disc of bitumen confined in a metal ring softens to such an extent, when heated at a rkteif 5"~/minute,that it deforms under the loading imposed by a small steel ball which falls a distance of 2.54 cm. The determination of the softening point of bitumen is regarded by some as an indication of viscosity, although from the point of view of the application of bitumen its use is limited to that of its title. The softening point is used in the designation of hard bitumens and oxidized bitumens.
2 The ring and ball test for softening point measures the temperature in OC at which a
d
point is defmed as the temperature at which a substance attains a particular under specified conditions of tes A steel ball of specified weight is placed upon a disc of sample contained within a metal ng of specified dimensions. The assembly is heated at a constant rate anct the temperature at which the sample becomes soft enough to allow the ball, enveloped in a bitumen, to falld distance is taken as the softening
Bituminous materials do not change from the solid state to the liquid state at any definite temperature, but gradually become softer and less viscous as the temperature rises. For this reason, the determination of the sofbning point must be made by a fixed arbitrary, and closely
4.22 SOFTENING POlNT OF BITUMEN
421 MELTING AND SElllNG POlNT OF WAX The cooling curve method is used to determine the setting point of waxes. Molten wax is allowed to cool in a specified apparatus and the temperature is recorded at frequent intervals The point at which the temperature remains within a range of O.l°C for one minute is taken as the setting point. This method is not suitable for microcrystalline or intermediate waxes, or blends of paraffin waxes with these or any additives. The congealing point of a petroleum wax or petrolatum is determined by applying a drop of molten wax to a thermometer bulb, and noting the temperature at which it congeals when the thermometer is rotated under standardised cooling conditions.This method is suitable for all waxes. The drop melting point of wax or petrolatum is determined by recording the temperature at which a drop of the sample falls from the bulb of a thermometer when heated under standard conditions. These are considered to be suitable for checking the constant quality of wax output in refineries.
grease' of an hknown formulation. It cannot be used to measure the upper operating temperature limit for a grease.
60
PETROLEUMREFINING~TECHNOLOGY
The test is continued until the break point is reached. The test result is reported as induction period in minute. This test is conducted to assess the stability of gasoline in storage. This test indicates the presence,of unsaturated hydrocarbons in the fuel and hence its gum forming tendency. Higher the induction period, better is the storage stability of the fuel. An induction period of 360 minute under laboratory conditions ensures storage stability of at least six month. However, this correlation may vary with different gasolines under different conditions. 4.24 THERMAL STABILITY OF JET FUELS
Jet fuel thermal oxidation tester (JFTOT) is used to measure the high temperature stability of gas turbine fuels. This subjects the test fuel to conditions which can be related to those occumng in gas turbine engine fuel systems. The fuel is pumped at a fixed volumetric flow rate through a heater after whichit enters thestainless steel filter whert! fuel degradation products may become trapped. The apparatus requires 600 ml of test fuel for a 2.5 hour test. The essential data derived are the amount of deposits on an aluminium heater tube, and the rate of plugging of filter located just downstream of the heater tube. In the JFTOT a charge is placed in a reservoir and the whole system is pressurized to 3.45 MPa with nitrogen. This ensures a single-phasereaction in the heated section. The fuel passes from the reservoir through a 0.45 micron filter, to remove trace particulate matter, and into the reactor section, where it passes upwards in an annular space over iyaluminium tube and out via a 17 micron stainless steel filter through a heat exchanger, to cool it, and back to the top of the reservoir. The used and unused fuel in the reservoir are separated by a floating piston. The fuel is rated by a visual tube rating or by placing the tube in a Tube Deposit Rater. In this the tube is rotated at a constant speed and its surface scanned by two light sources reflecting off the tube on to a photocell. The photocell gives a signal to a meter. Also, the differential pressure across the 17 micron filter is measured. The test results are indicative of fuel performance during gas turbine operation and can be used to assess the level of deposits that can form when liquid fuel contacts a heated surface. 4.25 GUM CONTENT
The gum compounds which can be present or produced in the fuel are classified into two types for test evaluation. Existent gum may be already formed in the fuel and can be deposited from solution as the fuel evaporates. Potential gum may be formed under extended storage conditions during which unstable hydrocarbonsare thereby polymerized and oxidized to form gums. Existent gum is the amount of nonvolatileheptane insoluble residue left when the sample is evaporated in a jet of hot air at 160°C. For jet fuels, the evaporation is camed out in a jet of superheated steam at 232OC. Potential gum is the amount of gum formed afier the sample is aged in an oxidation stability bath and evaporated under specified conditions. Gum is always troublesome in any fuel and it may cause piston ring sticking and deposits on engines. The amount of gum points to the presence of olefins which have very poor storage stability. The existent gum test is claimed to measure the amount of gum or gum-forming compounds existing in the fuel, while the potential gum test attempts to predict the tendency to form gum on storage and use. These gum tests are usually used as refinery control methods.
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QUALITY CONTROLOF PETROLEUM PRODUCTS
4.26 TOTAL SULPHUR
g1
.: .
This is determined by lamp method or wickbold procedure for volatile petroleum Products and by bomb method for heavier products. Sulphur in the sample is oxidized by combustion , and is estimated volumetrically after absorption in Hz02 or by gravimetric methods after converting into barium sulphate. Sulphur compounds pose a dual problem: they not only cause environmental pollution from their combustion products, but these products are also naturally corrosive and cause severe physical problems to engine parts. A knowledge of the sulphur content of petroleum products is therefore of importance to both refiner and user. d c l D I T Y AND ALKALiNln
New and used petroleum products may contain acidic constituents present as additives or as degradation products, such as oxidation products, formed during service. Total acidity is a measure of the combined organic and inorganic acidity. The acids in the sample are extracted in neutral alcohol andthen titrated against standard alcoholic potassium hydroxide under hot conditions. Total acidity is an indication of the corrosive properties of the product. Inorganic acidity is a measureof the mineral acid present. Organic acidity is obtained by deducting the inorganic acidity from the total acidity.
ER-STRIP CORROSION TEST
7
products contain sulphur compounds, most of which are removed during refining; Of the sulphbr compounds remaining in the petroleum product, however, some can have a corroding effect on various metals. This corrosivity is not necessarily directly related to the total sulphur content. The effect can vary according to other chemicals and types of sulphur compounds present. which is then A cleaned and smoothly ~oli$hedcopper strip is irnmerse&&hsm@& mamtained at the specified temperature for the specified length of time. This strip is removed L a m p l e , washed with aromatic and sulphur free petfoleum spirit and examined for evidence of etching, pitting or discolouration. It is then compared with F T M copper-strip corrosion standkd colour code. Th_eclass%cation cbde indkates that the numbers 1 , 2 , 3 and 4 designate slight tarnish,'moderate tarnish, dark tarnish m d corrosion,kespectively. Sub-scripts-a-e describe a standard colour reproduction'in the standard chart. For example, the classification code l a indicates slight tarnish with a light orange colour. C ~ h itest s serves as a measure of possible difficulties with copper, brass, or bronze parts of the fuel systems.
4.29 SILVER-STRIP CORROSION TEST FOR AVIATION TURBINE FUELS
A Polished silver strip is completely immersed in Aviation Turbine Fuel at 45 f 1°C for a period of 16hour. At the enctof this period, the silver strip is removed from the sample, washed and evaluated for corrosion against the set of standard. Since some parts of the fuel pumps in aircraft are made of silver, the corrosive tendency of the he1 for silver assumes special significance.The cumulative effect of corrosion on such a vital component in the aircraft is hazardous.
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-h~ji{:!:*;:~ : p > 5 ~ z :.b,,:;.7!t$; ~ y ~j !;,;~ : ;.,:,.t;.3: ... c ,~:.., ~ ~ ~. ~.. ~
3
Density of a fluid is its mass per unit volume. It is measured over a range of temperatures. usually for convenience a t the temperature at which the fuel is to be stored.
4.33 DENSITY AND SPEClFlC GRAVITY
Colouris an indication of the degree of refining of the products. Various test methods used for the measurement of colour of petroleum products along with their main items equipment and product application range are given in Table 4.3.
4.32 COLOUR
e sample S t e r being weighed into a special glass bulb having a capillary opening is 'plackd. in"&metdfurnace maintaihed a t 550°C for 20 i I'minute. Thesampleie thus quickly '1heatedytothe point, atwhich all volatile Matter i~evaporatedout of the bulb with or without decompositionwhile the heavier residue remaining in the bulb undergoes cracking and cqking reactions. Aftek a specified 20 minate heatingperiod, the bulb is removed from the bath, cooled in a desiccator and again weighed. The residue remaining is calculated as the percentage of the original e m p i e and reported as ramsbottom carbon residu of a fuel oil when C?+on ;&due gives a measure of h$ated in a buI6 under prescribed conditions. While not directly correlating with engine deposits, *s property is considered as an approximation. For example, carbon residue value of die& h e 1 corielates with the amount of carbonaceous depmits the fuel will form.& the combustion chamber of the engine. The expected carbon deposits in the combustion chamber is greater for higher value of the carbon residue. Carbon residue is also used in design calculation of vessels.
Method
quantity of sample is placed in a crucible and subjected to destructive distill$tion. The residue undergoes cracking and coking reactions during' fixed period of severe heating. At the end of the specified heating period, the crucible containing the carbonaceous residue is, cooled in a desiccator and weighed. The residue remaining is calculated as the 'percentage of the original sample and reported as conradson carborl residu
onradson Method
w r b o n residue can be defined as the amount of carbon residue left after evaporation and pyrolysis of an oil and is intended to provide some indication of relative coke forming tendency. Either Coriradson method or Ramsbottom method can be used to determine the carbon residue of petroleum products.
A b ~ w l e d g eof, the amount of a product's ash forming material can provide information on whethemthe-product is suitable for use in a given application.
di&qj&+s$,~.:~~:~. . , . .. 'A kqom'p~,ogn$:.qf 3aible is ignited and the c a r b o n a ~ i oresidue ~s I&€ib . heated .. to 800°C in a muffle hrnace, cooled and weighed as ash.
.,&h.@n!~esultfr0.p oi1,water-solpble metallic cqpounds, or extraneous solids, such as
4.30 ASH
t
I
Name
.
Colour of dyed aviation gasoline Colour by the Lovibond tintometer
ASTM Colour
I
..;.,,:<,< % * , ( ...(,.... .rll..-.. . ~ . .. I. I
Oto8
Colour scale I +30to - 16
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. ,
.
.
-
-
.,
Heavy petroleum products, lubricating oils Dyed aviation gasoline
Applt'catlon White products petroleum
.
Permanent colour glass disc Lovibond tintometer Colour standards of dif- A11 petroleum products ferent rating for red, yel- except black oils and low, blue and neutral tint bitumens -J
Colour comparator
Calorimeter
Chromometer
Main equcpment
i
Table 4.3 ColourMeasurementmethods, -. :.-;- , .!l:.,,.:. ... , ,: . - . . .. .
Refractive index is defined as the ratio of the velocity of light (of specified wavelent$) in air to its velocity in the substance under examination. It may also be defined as the sine of the
4.35 REFRACTIVE INDEX OF HYDROCARBON LIQUIDS
fi measured volume of the gas sample is introduced into a chromatographic column and transported through the column, the sample is split into various components, either by adsorption or partition, depending on the column packing. The composition of the sample is determined from the chromatograms by measuring the area under the peaks. An identification of the components is done by noting the elution time. - .
4.34 GAS CHROMATOGRAPHY OF PETROLEUM GASES AND LIQUIDS
The specific.gravity is an indication of thetype of hydrocarbon present, being highest for aromatics and lowest for paraffins. The API gravity reverses this relationship. The most accurate method of determining the specificgravity of an oil is to weigh a known volume in a specific-gravity bottle at 15.56OC. A correction may be applied by measuring the 'specific gravity at some conventional temperature near 15OC and adding or subtracting 0.00063 per O C above or below 15OC. ' Another method for determining the specific gravity of the oil is by means of a set of hydrbmeters. A hydrometer is placed in the 6il sample at 15.56OC and allowed to come to rest. The specific gravity is shown on the scale at the point coincident with the surface of the oil. Accurate determinations of the density, specific gravity and API graliity-of petroleum products are necessary for the conversion of measured volumes to volumes a t standard temperature of lb.56OC. When the volume of oil is known, its mass can be calculated. These factors govern the quality of cmde petroleum. These properties, however, are uncertain indications of fuel quality, unless correlated with other A correlation of fuel density with particulate emissions indicates increasing particulate emissions with increasihgdensity.
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Specific gravity is the ratio ofthedensity ofafluidtothatofwaterat the same temperature. The temperature usually specified is 15.56OC. In the USA, specific gravity of an oil is often - e , ~ ~ e s s as e ddegrees kP1.API gravity is an arbitrary figure related to the specific gravity of jytroleum products in accordance with the formula: 141.5 . , Degrees API = - 131.5 Specific Gravity at 15.56°C115.560C . .(4.11)
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angle of incidence divided by sine of the angle of refradion, as light passes from air into the substance. The refractive index of liquids varies inversely with both wavelength and temperature. Refractive intercept is calculated by
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Refractive intercept = n - 2 ...(4.12) where ri is the refractive index at 20°C and p is the density at 20°C,gm/cm3. ' ~ i ~ h t h e content ne in naphthas can be easily calculated by knowing the refractive index and density of the saturates fractions as determined by the refractive intercept method. There is a relation between the molecular weight, aromatics and refractive index of hydrocarbons and hence the determination of refractive index gives an indication of the content of aromatics in the hydrocarbon fractions. 4.36 LEAD IN GASOLINE The lead alkyl is converted to lead chloride and extracted from the gasoline by refluxing with concentrated hydrochloric acid. The acid extract is evaporated to dryness. Any organic material present is removed by oxidation with nitric acid and the lead is determined gravimetrically as lead chromate. The method covers the gravimetric determination of the total lead content of gasoline and other volatile distillates blended with lead alkyls (tetraethyl lead or tetramethyl lead, etc.). ! Tetraethyl lead is added in gasoline to improve the octane number but it is highly poisonous. Hence, its concentration in gasoline is restricted and its handling is done with utmost precaution.
4.37 WATER SEPAROMETER INDEX (MODIFIED) (WSIM) This is carried out with a water separometer. It~measuresthe water separation characteristics of fuels expressed in terms of WSIM. An emulsion of water and fuel is prepared and passed through a cell containing a standardized 'fibreglass' coalescer.~Theeffluent from the cell is examined for entrained water by light transmission. A numerical scale (0-100) rates the case with which the fuel releases gxpu!sified water. :,,WSIMis a measure of fuel cleanliness relative to its freedom from surfactant materials. A higher WSIM rating indicates that the fuel is cleaner relative to surfactant materials. -7
4.38 DUCTlLlPl Bituminous surfaces exposed to varying temperature conditions undergo a great deal of elrpansion and contraction. Therefore an important characteristic of the Kinder is its ductility and the degree of ductility has an effect on the cracking of bituminous surfaces caused by traffic stress. The ductility of bitumen is expressed as the distance in centimeter to wfich a standard briquette can be elongated before the thread formed breaks under the specified conditions. A molten bitumen sample is poured into a standard mould, allowed to coal to room temperature and then placed in a water bath so that the briquette can be brought to test temperature before mounting in the testing machine. Ductility testing machine consists of a moving carriage moving over a lead screw.An electricmotor driven reduction gear unit ensures smooth constant speed and continuous operation. The temperature is controlled thermostatically.
Bitumen having high ductility may be more temperature susceptible.
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,&&2 Composition of Naphthas . is a complex mixture of hydrocarbons. Its mmpositiopdep&ds o&+e crude oil proce sed and the conversion.proce~gemployed. For the composition o q b a p h v , two types of analyses a i e usually carried out. These are: ~vdrocarbontype analysis . Individual component wise analysis he hydrocarbontype~alysisdeterm~n~~thepercenta~~of ~ ~ @ m olefi&naphthenes s , and aromatics. Gfferent tj$es of c o ~ p o ~ n found d a inpaphtba fracti~nsfmv v uses are given in Table 5.bThe approximat&cdrbon dumber range of the p r d d u is ~ slap 8 v e n in the same table. In Table 5.5, a summan, of quality+of the naphtha-fiqctions porn various , indigenous and certain imp~rtedand worldWidqyailable cmde);&h respecQ9 the para!' , fidnaphthendar~maticc~ntentso f q e i r na$hth@fracGons $re given. The vque indicated 1s for the full ranggnaphthd (C5 - 140°C). -~ h ~ h y d r o c a r b type o n composition of naphthas fionl Indian crudes is @en in Table 5.6 for boiling ranges of 60 85OC, 110 l2O0C, 120 130"~' and 130 - 14o0C:
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1d'fldi~~Mtkl~ie~h8'c~fig1(~~~) uiifir the Yeed~&sfi&\ffb$W"hi'&xddp &-fed SU-+& j f l r- ; v v C Q ~ ~ ~ ~ to U the O Ureactor B \ ~ tower, fmm which, a t thetsamet&e,kk8alyhtia k&5&jw1@h&nf combus$on .< ed&es, it is e&emely to a regenerator where coke deposited on the catalys6is burnt & ~ ~ h ' & n t k a d f f l ~ $ o h ~ t h e h g and hardening, steel;utting e t c h f u e for i n . I reactor is fractionated in main fractionating column into so called light endq;mf~dkb&t~late good, but it has yet ta l e c o m e p o p u1 l ~ . and heavy fraction#. Uncondensed overhead gases and catalytically c r a o k & i q g ~ e l ~are e , ik routed for LPG recovery. The uncondensed gases are compressed, moledaq~pha&$&uqces5,2 NAPHTHAS sively to two absorbers which employ cracked gasoline and light cycle oil respectively as name give? td light hydrocarbons bgilin&$he:ge.gasoline range. I t is , Naphtha is a absorbents to increase hgbt ~ ? ~ r ~ ~ ~ v e w ~ , ~ ~ fmm h g aabsmber s o l i p is45tfi8p&,d, e off its refipwg of crude:~il. y e bo~lingfiiages of various types of -, kfedto a debpta?iger ~ ~ l ~ ~ , ~ ~ b , & ~ i a c k e datlight distillate obtaine4,frop lighter ends in a stripperjl'he stripped g~sol$ne naphthas produced include: C5 - 85OC. Cs 118C, C5 140°d, CS; ~ ~ O O C C5 , 1 7 5 0 and ~ LPG is taken as overhead producp. L P q q 4:yerhead product from debptahipfr ,$oJu+n is . t treated further to conform to required specikations. C5 - 200°C. In these iiitial boilink point (IBP) is c o n s t s n t . ~ ~ t ~ ~ - b oranges i l i n ~can be -. Coker gases are compressed in two stage compressor and routed to the bloi~&$$&k~~orber 60 - 85Oc, 85 - llo0C, p + l l p - 140",~.w a s are u s u a l l ~classified a s light.hterme&ate ~ $ @ d f ? ~ ~ ;is $used, ? ~as~absorbing ~ medium. Gases from ap$tha a sorber to are and heavy naphthas. I t t h h a p h t h a fraction ~ lbe1ovk1000($, s it ii,"c1bsified as l g h t naphtha. ~k'& interniediate naphtha ~ k b @ % $ & ~ ~ g < ? ibetween es ;&aer a sqrbe, ,,,y coker'kerpsi$, ~L%"kerosifibkord kerdsine a!sor~& % d ~ ~ ~ R the 'v H~~~ naphgaboils above 150°C. For Imw$$a$tidnating,k71mnnb,!the ,ckkii;~*li8?%ighte'rrehds (C1 and-cijkre s,thr&qdffG o d * 4 '3 Ti)OPC. ' rich nabhka in a $ l p $ y r ?ndtc$&et'riom' ?,' / stri$eP$re ??
.&pGisbweda q a domestic fuel, 8 fuel internal copbustionLPG engine anQa feydstopk for themanufacture of various chemicals andfor olefins (by pyrolysis.). supplied for,dbmestic P U Y Y ~ S is~ysually, ~ a mixture of propane and butane, butanes predominating in warmer countries and propane being in greater proportion in colder countries. LPG' has many industrial applications. It is used for portable blow-lamps, soldering, brazing, welding, anneal-
2 3 Uses of Naphthas The major end-uses of naphthas are listed in Table 5.7. The use of naphthas in fefland petrochemical industries and as gasoline is discussed below.
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a b l e 5.7 Mqjor End-Use*of Naphthas -
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/volatility characteristice The volatility of gasoline affectstha Q ~ & af ~ the ~ $ ~ . . ecengine i s a number of ways, which ~reaey$~,o~-,~gr~ng, r$p:;!f warm;yf3 vapour lock, carburetor icing and crankcase d i l ~ t i o n r ( ~ , & , ~ ~of, ~the,.~~p~.e.~Iub~.~.a~~~~g.~.oil $i~n with the higher boiling constituents of the gasoline): The fuel must be sufficiently volatilc to give easy t i opnr o q r ,d.E$.ribution bctyeen*the starting, rapid warm-up, and a ~ e q ~ g t e ~ g a p o r i ~for cylinders; Conversely, it must n ~b:b'&'"ol&ti~&tli~t t ',kipour losses fibm the'fud @hk are !, ' '. .exccssivear that-vapourisforme&i-t@ ffibf%ficcausing vapouf'#&k'rnich dj%&&d the flow of fuel to the carburetor. To som&&kf'6fil%hcsec o n f l i c t i ~ @ i i ~ l ~ ~ &can;6?ibet cnts by , usinga nibre volatile gasoline in wintcr than in summer, but some dcgrce of .compfomise is . . . : . . . .<'i. . . . . . . .' ... / :.. :.. ..l ..: .. . obvi~usl~~~ecessar~. J o x i d a t i o n Stabilit~ or gasolines. ~hi~d~pg~d~stori\ge!g~s:o!irlps undf.pg~~&a)y.but progressive oxidatibn dcterioration. Thc rcsult of' this is formation of n ~ n - v d a t ~ ! ~ ~ ~ , m m y residues. If present in the gasolincs, thc gummy residucs can causc multiplc Gouble, such as deposit formation in thc carburctor parts,p&pPr&~,~ifA1d~o.f$~~t~jpluIji$~p&~p-+i~ the
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~:~@00mbu6tion~qlixalb&~s$i~:~~ @ ~ ~ a i ~ y ~ h ~ : s p & i g n i t i &m& ~ ~ @ gmj nw~ , On en&nddes&ad ~ ~ ~ 4 ~ ~ l i h r ~ ~ , ~ ~ i d B a 1 i C b n i l i t M n . 8 ~ ~ e ~ ' ~ i n ~ d f R d r a . ~ x C f ; ; g ~ ~ ~ p ~ ~ g ~ p ~ ~ ~ d k l p a ~ o & h ~ "nfi~a1~khe:gasP1i~a&ii&bs8;.~~&;r~e ~ ~ b i i . & i ~ ~ ~ ~ , . Y e r e f j s & i ~ t e ~ po aa ~u rg~e & b ~ ~ h 6 ~ r d ~ g ~ f t h B f l ~ ~ , & & U 1 ~ s' & , a $ ~ ~ ~ ~ ~ & i h grmssurc in the end gas zone, which is thatpart:of the p s o l i n s a i r mixturewher~theflame h@ mtyet reached. T h @ l s c m o s e h ~ P L p e ~ ~ ~ ~ p ~ ~ $ u ~ a ~ ~ t b ~ ~ ~ & ~ ~ ~ . ~ n ~ ~ ~ ~ ~ ~ ~ t h 6 ~ ~ & s b l i ~ e ~ t 0 undergoprc+me reactions: Amongst-themyn preflamepriducts are the:highly temperature (Heavyends contamination ~ ,\',,:.:,.xTl. e ~ .,;:~,i: ~ t ~ v e ~ ~ ~ " ,rtain d ~ ~c.itical ~ ~ t ~d& 'b ~~~ : fe ~~f i ~ ~ ~h t r~athe t& i oend:gas n~, ~ $ ~ & ~ 1 ~ $ Preformed gum i~purities ' . I win';pontaneo";,$ ;ini& >.": ,.,:";.:'. . . e arrival pf the flame f r ~ n t e m a n a t i n ~ f r o.the m sparking Improper volathiti coir&b%r . , r: Pobr cold starting plug: this causes detonation or' knocking. If, on the other hand, the flame fmnt , end Water contamination sasEone before the @$d UPof th$@$&fi, t&reshold:per6~ideconcentrati~n,~~ co@JJ&ion ;;. .:!, , of the gasoline-air m ~,x. ,t u r \?fiI.k-be.w~t&jut e kbock. Hot fuel problems .Improper-volotilityeontro1.-. . .t. .:;.,, , !. < :,, , , . .. .. ........ ~ e ~ ~:
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The phenomenon of preignition is encountered in gasoline engines. The deposits in the combustion chamber are supposed to be resppnsible far hot spots which are responsible for preignition. Some of these deposits arise from tail ends of fuel and lube oil aaumulating,in the combustion chamber. These form carbonaceous deposits which may trap lead salts also. The build up of such deposits affects the octane requirement of the engine. When lead halides or sulphates get deposited on the spark plug they cause low shunt resistance (short circuiting).
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Detergents. . . , , , . + . . . The ,,. . control of deposit build-up in carburetor; fuel, injection equipment and ., ) , inlet system.canbffer significant performance benefits. These include: ,, exhaust:eniissions, :,:: . .. :.., ,..!.,.- ,xi; . . (bl!mp=$$id fuel e ~ o n c & ~ , (c) Improved-vehicle driv'eabi~it~, and (d)Reduced maintenance costs. The use of.;low levels of carburetor detergents typically amides; fatty amines and imidazolines can,give good control of carburetor deposits. Combustion improver*. A range of additives for combustion improvement have been used. These intluae: (a)h a d appreciytoyisuch as tertiary but$ acetate which were effective a t extonding the anti-knock effectiveness of leqd alkyls a t high additive concentraticins. (b),;Qepgs~,mbdifiprs sych a s the phosphorus and,bp~n,compbundsextensively used to . . increase the g1oW:pointof engine deposits. . ,: , (c) ' m e catalytic approach where the ?atalyst is added to the fuel which ,appeaia , , . 4.,, t o . be . . . increasingly considered. 5 k ; ~ e Gaso1ine!Blendinggc~mpopent8 w ,
In recent times, pollution, from automobileexhausts: has increased toalarming~li.Velsi Starting from April 1, 1995, new c ~ r s ~ ~ in o lfour d metropolitan cities of India, i.e. Dclhi, Mumbai, Calcutta, Chennai are fitted with a catalytic converter on their exhaust pipes. Catalytic ,. .~.! , . . converter is an anti-~llutiori'devicetittcdto the exhaustsygtcm o f ~ e h ~ d & ~ I t ~ ~ c l p s prevent em~ssio~of'noxious gasds i n t the ~ atmosphere. ~ t . i s - t u ~ u l : & i n . s h&id. a ~ ec0nipAse.a hoiit?'jico~lj.hetallicor ccrariii'cd'i'Sc coated With 'noble metals like p l ~ t i n ~ ' ~ & h d i p a l l a d i u m . ~o!k&Febl~jAiy B e ' i 6 l l ~ o f ~ a t a t a in l ~ ~ii:lractibn 1 which wridbis exhaust;eonponents ltke. carbbfit"monoxideand hydro'carbons Bafrn~ess~by converting. thcminto carbon. dioxide 'and, wat'e%:Thcse inetals are spread over a Inrgb surfaccto proddeihbimatc.wntact between exhaust gases and catalysts.Catalytje corivdrtcrs n i e rcquirgd.::to simultnne&sly :remove tdfg~0Eeil'pal~utants,~rc6ist.'Cahlyst:poisoning bycontam'irrants;md:~~tJlo~g~~~~Ofa.a.~two t ~ e ~ ~ o f . ~ a ~ ~ ~ y t i t ~ c oTwo-way n v e r t c systems rs. using.plabinum and:palladi~,:.yhich.remove o~'1~'c~~b~n~m~nbxideand~hydrdcnrbons~ leavingnitrogen oxidcs unchwgd.:~he~latt'cr.,is o%idf~ed-th,rm&h..air,: pump; Threc-way catalytinysbms. Oqplpy plati~mGipall~diY$;!~ayd rhodium to remove all thrcepollu~ananbsimultnne~uoly.,had-i.n-,thegawli~~:issj~ju~ious tha..honeycomb disc of the:conu~rterand poisons the noble m e t a l . ~ , i n , ~ h ~a",r+uc~s d~@~~ its potency; . . .,. , ' . . ... .,. . .. -Bheiaquirement olprod~cingunleaded gasoline will result in octane s$ortages qt many manufacturing sites.!The use of oxygenates in gasolines is made for raising thc gasolinq pool volume and its octane level, especially in the critical front-end ran* The excellent byming properties of oxygenated compounds result in increased operating cficicncy of. the engines, thus compensating for the loww calorific vrlucs of the oxygcnatw. Simultaneously, 11.wer
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5 h ~ e Gasoline w BlendingComnonenta - . . . .. In recen't:times,:pul.lutian:from autpmobile.lexhausts! .has incr Starting from April 1, 1995, new c&++"ild-?~ fo0.f metrepditan ci$cs of :Iodia, i.e. Dclhi, Mumbai, Calcutta, Chennai are fitted with a catalytic convcrter on their exhaust pipes. Cat&l@ideonwrter is an s"ti:p6llutibi d&ice fiftdiJ.td the eih.aust s y ~ ~ c ~ o f & e ~ . ~ ~ . ~ ~ ~ t . ! ~ c ] P S $&&df , , . & ~ i ~ & n ~ o f n o ~ i o u s ' ~ a k ~ s & ' d p h e r & , ig,ahla$in ,shapL*.and ', :'~m.p&ae:a. h d f i ~ ~ b ~ b . h ~ ce~amic l i ~ od%+& r coatcdwittnoble met& hke pl&tjfil&.~ndi~&l]&jum: hlibbekal$'$&f Bi&?&;d$cataly+tib a:rea&i&n.which rendcf;i!exh~~bcomponM~9'1ijke hydr~arij&s n.h&mta*r jay wnvhDinLzithrm:..intoJc'~rbon::.di~xide,-.and $&~@~r",r&ehe5fiet;a1~. a*C s . read iver;-a large sgifac@;-to.provide &timqtctcon.tact b e t w e n e*ust gases and catl~stsiCatalyticconverb~s a r e ruquir~d':~t!simuhnebUsly :remoue t.pght'~awh~ nts,~cxsf~t,Ida~l~st~poisoning~~by.eon~ami~.~ . ati+la~tJo~~~$el..a.~two t ~ 6 ~ , 6 ~ h ~ ~ i k ~ c ~ n ~ b r t '~jrbtemsusingpldinum dr~.~~o+wap nn~alladiynj~~~c,h.~mov~ ~''~$s$&>~. . uf~cturqd by,fepentqt@n,9f,i!@fg:, tvra12~mduc,@. . :: ., ,. >,.: @ r ~ ~ ~ o x i d o ~ a . d ; ~ h y d r d ~ al cra W v i nnb~n i b m n oiidca h,nchq$.::T.he !l$t$.;ib ::;*5gjhflpltJ$&;mm.\, .,,.,?, ,., , i L '<. r. ,' .:: . , I : ,iofiw@ng 5 +.reen; ethanol by volume are sold in Sdhth kihxica 9.W~!>, %;RF~: ., & J : ~ " . .th - . BY?d?i!~d"'$h~iiQgh-oir. pump;:Thr&woy .catil@c systems, crnpluy , @ & i n . m J p d l a d i , pand ~ p p r t i q such.as better w a M .:. ~ . i ~ $ ~ ~ ? O . rhodium to remove ill,thre6pollutdnts ~irnnltaneuusly;laad:inth~.g@ig~ia.ir\ju~iou~t'o, ' t i~e*~,& $J& $$f$ ; 14biahi=gidsponent . . 'pithout . .. . kh0nev-b discof the: conxocter, gndpoirma ,&henoble m a t n l s,. i f i 3 ~ h y ~ d ~ v j ~ ~ apdre$uces . its pobnpy,;..:.-!.!;.: :.., i o v m m & subsidies its price is currently u n a t t r a c ~ v e/nm*~,~$*tnes-:, ;; . ;. !,: , r:: . . .. ., ..:. p#3B.,Lpia pro,du!e$,b~ ,a simp! , ~ ~ ~ ~ y ~ ,,, ~ ~ a i"he&quiremnttor p.rod~cing:un'loaded~asolioe will re"$, i n &tqo s&~.a@ceqt many "e~faetiatin~;sites:~The use of.ixygcnntcsin gasolincs is made for rai$.i.ng.ihc gaio~ind.. joo] repre? nts a way,to use metbanpl rn Feltber t q r : gfrom F o l mFCC ? (fluid eiit&lpialytiscrackyg) o&-gples ar is available 3 volumeandits octane ,level, cspecialb in. tho critical front-end range. The r.&ell& bUrohg steamcrackers. ~~t the amount of isobutylene available fmm these sources Is very 'lrnlted' . . Propertie? of oxygcnatcd compounds result in increased operating,cfficicney of thc 'on$nes, The isobut.lene content in the c4fractions from steam cracker varies from 4' to 45.Prcent . thus compensating for the lower ealoritir valucs of tho oxypcnates. ~ i ~ u i t ~ n e o ulbwcr sl~, ;
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cffective~Thesui(aekactive c ~ ~ ~ o h ~ ~bysfo~ming&fi~MB~~~i~~&j&over,~bk~Fatal ~ f ~ n ~ t i , ~ ~ surfaces& the carburetor and prcventihjj Mherine to them. ~~h~ c h ~ ~ ~ ~ ~ j c ~ ~ ~ $ o u n ~ ; ' ; ~ n be as surface a ~ t ~ ~ " Q ~ ! f j n ~ b $+@,thqp..c$ten ~ ~ ~ ~ u @ , dinclude ~ the compounds ~ s e a?.carburetor d detergents orenginec~eanlinessadditives which are discussed below. Dete?$$~t). "P control of deposit build-UPin carburetor, fkekinjectioneguipmentand inle,bSyst.eb$?hXFb:
[email protected]~6kn&fits.These include: : :. :. .> &$'~ed~dd~e~ha"~t: , . (:,. &h5kiions, ...,. ,,. ..,. ! . . it ::; ($1!:mpr{+df~el econo&y, (c) Improved vehicle driveability, and (dl Reduced maintenance costs. The use of,-bw levels of carburetor detergents typically amides, fatty amines and imidazolines can give good control of carburetor deposits. Combustion improvers. A range of additives for combustion improvement have been used. These include: (a)cad ~ @ ~ ~ & i ~ ~ ~ s . ~ ~ c ~ : abbtil-&tiitit@ s t e r t i ~ which r y were eBertive a t extending the. anti-knock e&?~+venessoflead alkyls a t high additive coqoenhativnsi ( ~ @ ~ . ~ ? $ , m ? ~ i f s.$+ i , y s aq.the p h o s p h o ~and ~ boion,compaunds extensively used to .:.. . ,: ,. .. . . ., .. increase the glow:point of engine depoiib. - . , .: . d ? ~ ~ i ~ . ~ p p r ?where. , a c h thecatalyst in addid b, the fuel which a p p e a r ~ t o be ,. . . . , '",.:". *. . . . .. increasingly constdefid.
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7 @&wed to typkalpsolioe, metha1ial~~uiretr44% as m u ~ l a - a i r ~ f o 1 1 ( 1 0 m b - ~ ~ & ~ &@~asnhacii -BF& and .equirbs3!7 timesas much heat f o r v ~ ~ o r i z ~ t i ~ n ~ ~ ~ h e i w ~ e s ~ n ~ ) comparisons fop ethanol are: 6lY'aamuch air, 66% as much energy, and-2.6timea thbh~etld. vaporization. The ratios of heat of vaporization to heat of combwtion show that fn.a Weh
i~ii~~&ri'~~~~~b~~~h~r~&hno~and~thand11h2t~ f u e ~ ~ f d r s ~ ~ k ~ iengines. ~ n i t i o nethanol and ethanol differ m y k r a & ~ ~ m g h ~ b ~ b ~ ~ b a d t i ~ t i c s i t h a J ; , wimporkant e to t h e i f i d i s t r i b ~ t i ~ ~uselas r n d a &el-fon w=k+i&on &$-&Pf.,Ql2 &~$a~
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station costa of CNG are very high. Bgnfuel~.Synthetic fuels (synfuels) can be produced from coal, cil shale and tar sands. A co'pmy, sasol, in south &a is producing synfuels froid ctgltWgfnatr@is th%+kQrAp1ete
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dc!1 ~ ~ ~ 'iz .x(%o':? .Ll'll " amylede%4~&~k%&6E, prg$kiice of acidic~r~i4ctio $9 9" t " ~ ~ ""8w~.:)ii 74 [vb; .':cd "11flf4' ' ~ E~ , I,a s-(it a~slightly fighera*g $ i h h ~ s o m e i v h a t l ~ w eoctane r val& ~ M T B E~ . AT M f u & ~ ~ ~ ~ ~IF,~y;@p $ j &&ib(i&a&,qd'mdrgfggtlltzp:>~:~~ ~ \ ~ With ~ ! i o f " h x z l r ~ ~ e p d s . Abi&;'&x~e~@Q$b ~ e ~ @ & o f & ~ ~ ~ ~ @ a d ~ r f $ t j ~ ~ l @ @ ~ & t r b I 'g,~ s ' d b ~ s n o t r ~ i W h w e [email protected] as a t i - h o t k eLbrqmndntbas2h ~ ? @ ; ~ ~ t ~ ~ i @ + & b ~ g ~ & .~i&j$%&kii-$ ,11h b u ~ p t~o&&b~:-lifit l s h i n ef r a a . 1.. I , -- l,x)fsv,,, *ne:t L 1,. !zLv :I!;~CI~,~;;xx d $%!6" ii T A S T Q ~ sift -. , 5 - ~ ~ e m a t i ~ e i h l ~ a ~ & d 1 ~
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uther extra t' Qce qes for the sep atipn of aromatics a d o n - o atics use solvents with much highBr'?fk'B$$biiie$ ~H&"~%B~~$'~I~~W&~BQ&S#~~'~~G"&Q~~~ very in that rafthates with very low, as.well as extracts with very high arpmatics contentr can be -- ..-made, Of the processes ayaJpRIe? the Shell%.ulfi&e extra<$i<< p G e & i. wide$ u b d , especial1y.for the aromatics from hydrocarbon mirtlires h u o r e piqduction of low-aromatic!solvents. . -+irrq;:ltnz.~-t, . -% 5.5 AVIATION TURBINE FUELSA
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A potentialfuel for'the gas turbine engines usedin alcr~Fe~tlir~s8highl~~mdstabi1itY, high heat content, low vapour pressure, good combustion charakt+ris$di zodd kis-tytemperature relationship, hi&, density, high specific heat, a u # J o ~ t ~ 7 # y ~ g ~ + ~ q d l i n g charac$ngtics. The combustion properties of aviation turbine fiiet ( A g J i l f i ~ y t i ~ e l a f i controlled using several of the following five tests: smoke point, l u m i d ~ m e t a ~ u ~ b e r . 7 aromatics content, aniline point.and mavitv. ,. lr , The heat of combustion ishormally ,calculated f~~~-,-@j9aP~t~ad@g~tYYY &)ely hvb basic types ofATFs, the k ~ m s i n etype and U e wide-cut$; ,$jnek&,a$hgmira\18ed worldwide+ The kerosine t y p "of ~ ATF is a much modikC&f@R@+;&l&iTR~gpr kernsin; oeginally used in gas fYrbine engines, whilst the mde-cdFap my ~JJ AT is a wider bGiling range fuel incl~dibdsomegasoline fraction. h $8&&:idird$e+ r eeia'Ij?ed fuel grades are required for limited military use, as irl su~db!oriidaFr$r'affv ' tk ?'-;' The properties that control ATF quality are listed in Table 5.14. ~ohb&fi$g'*&alit~ relates those properties which directly affect the ability of a fuel to ignite properly. With g ~ s turbine engines, the volatility factor assures delivery of fuel~ta~b~e+tb~bi~e~~hb;bpIe~~ith satisfacto~ignitionand flame propagation characteristics. Ioturbin&engines,the Liishduld mt allow deposit. to form in fuel nozzles, fuel control systems, turbine blades, cpatings and wale, all of which will degrade performance.
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The volatilityaf ATPa is contfdled to minimize the]oS8 off&f&$ &$$&uri;ided.&,.raR tanks due to boiling-off at high i1ditude8. Fop this the "&&i&$ '#k;$Ji$he .tn, ATF is desirable. Distillatioq apeiifirntjon reguire~at l e s t 20 vol,c r&dJ$e'&~$.~~,&jt+~The 20 p r c e n t point control8 hvnt-e~d.w]ati]ity, and ensures ~ ~ k & : f ~ & ~ g j j j ~ + ~ a ~ i ~ y : $ ~ w & 001d atadbg and limit evaparaWon losses s t high altitudes,, .,' i . .. *uh-igniti?n of ATF can happen with a alght leak of fu&'from the engine .h&&: ifter ~h~f!b~!A!::"~.f?pa he1 line fracture during aperation. T ~ : ~ ~ & ~ r BU$ e , f.&i%n W ~ ~ cw ~~a i n ec r e a s in e ~vapour ~ proe?Un, ~ &.the atmOspherii ~~eBB,uiB;i-a~'d<~e.2fb-~yam\1i ~rew",""duel increaa,ldao tho ~ut~-,gnjtion tempe&"&j in;&&&, '. , . Thermal properties. Jet engines require the use of fuels which ha*Lowfreezin~poinh , and maintain their flow properties. A high degree of thermal stability of fuels is nqbirea t.a
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