Petroleum Refining Crude Evaluation and product characterization
Contents About Crude oil oil Common Refinery Units
Crude Distillation Secondary Refinery Processes Residue processing
Opportunity crudes and its compatibility Crude Evaluation and characterization
About Crude oil
Composition by weight Element Percent range Carbon 83-87% Hydrogen10 - 14% Nitrogen0.1 - 2% Oxygen0.05 - 1.5% Sulfur0.05 - 6.0% Metals < 0.1% Four different types of hydrocarbon molecules appear in crude oil. The relative percentage of each varies from oil to oil, determining the properties of each oil Composition by weight Hydrocarbon Paraffins 30%; Naphthenes49%: Aromatics15% Asphaltene 6%
Common process units found in a refinery
Atmospheric distillation unit distills crude oil into fractions. Vacuum distillation unit further distills residual bottoms after atmospheric distillation. Naphtha hydrotreater unit uses hydrogen to desulfurize naphtha from atmospheric distillation. Must hydro treat the naphtha before sending to a Catalytic Reformer unit. Catalytic reformer unit is used to t o convert the naphtha-boiling range molecules into higher octane reformate (reformer product). The reformate has higher content of aromatics and cyclic hydrocarbons). An important byproduct of a reformer is hydrogen released during the catalyst reaction. The hydrogen is used either in the hydrotreaters or the hydrocracker. Distillate hydrotreater unit desulfurizes distillates (such as diesel) after atmospheric distillation. Fluid catalytic cracker (FCC) unit upgrades heavier fractions into lighter, more valuable products. Hydrocracker unit uses hydrogen to upgrade heavier fractions into lighter, more valuable products
Common process units found in a refinery
Visbreaking unit upgrades heavy residual oils by thermally cracking them into lighter, more valuable reduced viscosity products. Merox unit treats LPG, kerosene or jet fuel by oxidizing mercaptans to organic disulfides. Alternative processes for removing mercaptans are known, known, e.g. doctor sweetening process and caustic washing. Coking units (delayed coking, fluid coker, and flexicoker) process very heavy residual oils into gasoline and diesel fuel, leaving petroleum coke as a residual product. Alkylation unit produces high-octane component component for gasoline blending. Dimerization unit converts olefins into higher-octane gasoline blending components. For example, butenes can be dimerized into isooctene which may subsequently be hydrogenated to form isooctane. There are also other uses for dimerization. Isomerization unit converts linear molecules to higher-octane branched molecules for blending into gasoline or feed to alkylation units. Steam reforming unit produces hydrogen for the hydrotreaters or hydrocracker.
Common process units found in a refinery
Liquified gas storage vessels store propane and similar gaseous fuels at pressure sufficient to maintain them in liquid form. These are usually spherical vessels or "bullets" (i.e., horizontal vessels with rounded ends). Amine gas treater, Claus unit, and tail gas treatment convert hydrogen hydrogen sulfide from hydrodesulfurization into elemental sulfur. Utility units such as cooling towers circulate cooling water, boiler plants generates steam, and instrument air systems include pneumatically operated control valves and an electrical substation. Wastewater collection and treating systems consist of API separators, dissolved air flotation (DAF) units and further treatment units such as an activated sludge biotreater to make water suitable for reuse or for disposal. Solvent refining units use solvent such as cresol or furfural to remove unwanted, mainly aromatics from lubricating oil stock or diesel stock. Solvent dewaxing units remove the heavy waxy constituents petrolatum from vacuum distillation products
Addressing the concerns to process Opportune crudes
Blending of Lighter Crudes, Condensate etc for transportation Modifying existing configuration and pipeline of refinery for receipt and processing Opportune crudes
Opportune Crudes could be of High TAN, high pour, Heavy crude of high density
Opportune Crudes and Compatibility Structure of Crude Oil A R A S
= = = =
Asphaltenes (Solute) Resins (Dispersant) Aromatics (Solvent) Saturates(Nonsolvent)
Cause of Instability-Asphaltenes Polyaromatic in nature with alkyl substitution usually contain heteroatoms such as oxygen, nitrogen, sulfur and metal atoms Dispersed in the oil with the t he resins and this asphaltene-resin dispersion is dissolved into petroleum oils with aromatics (solvent) but opposed by saturates (non-solvents).
Opportune Crudes and Compatibility Methods For Determination Conventional Process
P- test Spot test- Insolubility & Solubility Approach Colloidal Instability Index (CII) Stability Number (Turbiscan) Microscope Tests, etc . Limitations in the study of Blend Compatibility C ompatibility of Asphaltenic/waxy Crude Crude oil is a blend containing both saturates and Asphaltene Compatibility of saturate and asphaltenic crudes depends on their content and type Structure property correlation not explored much and is of complex nature
High TAN Crudes
Corrosion due to Naphthenic acids 0 • Less than 200 C not a problem since NAs are heavier compounds 0 • Greater than 420 C not a problem because NAs breaks down lighter acids. 0 0 • Problem for streams in the range 200 C – 420 C (Kero, HSD, and VGO
Difficulties while processing HAC
Desalting (high calcium crude oils) Naphthenic acids can form stable emulsions, foaming problems, formation of calcium naphthenates are particularly bad factors
Rapid corrosion with higher fluid Velocity & dual phase flow
Rapid corrosion due to more physical contact between fluid & metal, Transfer line
Crude Distillation Unit Furnace, Overhead, Column, Side-cut piping etc Points of vaporization or condensation Vacuum towers and tower internals
Problem in Product Streams Diesel and ATF cuts (Higher TAN)
RCO, LVGO, HVGO and VR circuits,
Furnace tubes and transfer lines,
Secondary Processing Units (FCC feed… etc)
Accumulation of NAs are more in boiling ranges 2000C to 4200C
Methods of Processing HAC Crudes S.N
APPROACH
REMARKS
1.
Blending/dilution with low TAN crude oils
Diminishing the value of low TAN crude oils
2.
Caustic treatment
Effluent and emulsion problem
3.
Changing the hardware/plant metallurgies
Higher capital cost
Processing High TAN crudes without any hardware change
Small size Refineries like in China, Dismantle the plants after making profits
4.
5.
6.
Processing high TAN crudes with the use of corrosion inhibitors & continuous monitoring Crude TAN Removal
Not commercialized at larger scale
New Approach
Processing Opportune Crude Oils What Determines Average Average Crude Prices and Hence Differentials Specific gravity – API – a positive factor Sulfur (% by weight) – a negative factor Acidity (TAN) (TAN) – a negative factor High Pour
:Distillate yields :Cost of Refining :Corrosion & Fouling :Transportation/pumping :Transportation/pumping
Advantages of Processing Opportune Crudes Ability
to process low cost crudes - Crude constitutes more than 80% of input costs of a refinery e.g., For a 15 MMT capacity refinery, refinery, processes 1/3 of opportune crudes costing 1$ less would make over 100 crores additional profit which is substantial. Enlarging crude basket – reduced dependency dependency of specific crudes i.e., ability to process wide variety of crudes
Each ° API per $ of Brent is worth w orth +$0.00969. Each % of sulfur is worth w orth -$1.979 Each unit of TAN is worth -$1.435
Crude oil evaluation and product characterization
Detailed Crude Evaluations Crude Characterizations • Density/SG/API • SUL • KV • PP • CCR • Nitrogen • Asphaltene • Salt • Metals • BS&W etc.
Product Characterizations • LPG • NAPHTHA (IBP-140) 60-70;70-90;110-140 etc.
KERO (140-240 &140-290) • HSD (240-360 & 290-360) • VGO (360-565) • LR (360+) • SR (530+ & 565+) •
Objectives of Detailed Crude Evaluation Given the crudes, identifying the suitable crudes for blends through scientific studies. Characterize the individual crudes in terms of :
Assay Corrosivity Fouling and emulsifying species
Assess the compatibility of blends Simulate the deslater performance Impact of Corrosion in atmospheric and vacuum units Assess fouling tendencies of the identified crude blends Suitability of products to meet Euro (III)/(IV) norms. Evaluate economic impact of processing opportune crude blends
THE CHEMISTRY OF CRUDE OIL
Crude oils are organic in nature and are made up of carbon and hydrogen (hydrocarbons) with lesser amounts of sulphur, nitrogen, oxygen and traces of different metals such as cobalt, nickel, potassium, calcium, sodium, silicon, copper vanadium etc Elemental composition of crude oil can be summarized thus: Element/Component Percentage Weight Carbon 85.0 Hydrogen 12.0 Sulphur 0.8 Nitrogen 0.6 Oxygen 0.6 Trace metals (e.g. Fe, Al, Ni, Ca etc) 0.2 Sediments 0.8 The hydrocarbon contents of crude oils are complex but are principally: 1. Paraffins (Alkanes) 2. Napthenes (Cycloparaffins) 3. Aromatics The predominance of one group gives the petroleum certain properties valuable in formulating a general idea i dea of the usefulness of the crude in producing p roducing various refinery products.
Crude Characteristics Density , API, Specific Gravity Flow properties – Viscosity, Pour Point Sulfur Residue – CCR, Ramsbottom Total Acid Number Mercaptans Basic Nitrogen content Asphaltene content Distillation Profile – SIMDIST, D86, D1160
Properties of Fuels and their significance
Density
Essential for quantity calculations, setting purifier, indicates specific energy and ignition quality. Density is the absolute relationship between mass and volume at a stated temperature and the SI unit is kg/m3. The standard reference temperature used in international trade for density calculation of petroleum and its products is 15°C. Knowledge of density is required for quantity calculations. Its value also needs to be known in order to select the optimum size of gravity disc for the centrifuge. In addition the density gives an indication of other fuel characteristics, including specific energy and ignition quality. Specific gravity of a substance is the ratio of the mass of a given volume to the mass of an equal volume of water at the same temperature. As it is a ratio there are no units. API gravity (degrees) = (141.5 / Relative density @ 60 / 60 °F) 131.5
