Rashtriya Ispat Nigam Limited Visakhapatnam Visakhapatnam Steel Plant
(A Government of India Undertaking) Visakhapatnam-530031
A PROJECT REPORT FOR THE AWARD OF THE PARTIAL FULFILLMENT OF THE MANAGEMENT TRAINING PROGRAMME
“Various maintenance & repair practices adopted for enhancement of battery life ”
Submitted by: SK IDRISH MOHAMMAD MT (T), CRG
Under Project Guide: Mr. Abhijit Sur (AGM, CAPITAL REPAIR GROUP, VSP)
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Rashtriya Ispat Nigam Limited Visakhapatnam Steel Plant
(A Government of India Undertaking) Visakhapatnam-530031
SK IDRISH MOHAMMAD 2010
122164
MT (Tech).
“Various maintenance & repair practice’s adopted for enhancement of battery life ”
( Abhijit Sur) AGM (Capital (Capital repair group, VSP) VSP)
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Rashtriya Ispat Nigam Limited Visakhapatnam Steel Plant
(A Government of India Undertaking) Visakhapatnam-530031
SK IDRISH MOHAMMAD 2010
122164
MT (Tech).
“Various maintenance & repair practice’s adopted for enhancement of battery life ”
( Abhijit Sur) AGM (Capital (Capital repair group, VSP) VSP)
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ACKNOWLEDGMENT I wish to grab this opportunity to express sincere gratitude and heartfelt regard to my project guide Mr. Abhijit Sur (AGM, CRG, Vizag steel plant). His unmatched skill and cognizance about the subject pave our way with the unprecedented ease to put forth this project named “Various maintenance maintenance & repair practices adopted for enhancement of battery life ”. ”.
I made learned several subtle know-how about the subject that will be building blocks for my industrial career by prodigious and patriarch Mr. Abhijit Sur. His assistance and suggestion will be our lifelong asset.
Moreover, I also wish to convey my gratitude to our seniors MR. C. Ramakrishna (MGR, CRG), Mr. S. Srikanth (AM, CRG) and Mr. G. Malsoor (AM, CRG), for their invaluable assistance and help.
Thanking Sk Idrish Mohammad
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ABSTRACT
Coke oven batteries are very cost intensive and a vital supporting system in a integrated steel plant. All over the world there is an increase in endeavour to prolong the life of coking plants, particularly the batteries in order to reduce investment cost to guarantee coke supply to blast furnaces. In India generally the battery life is 20-25 years, but regularly repair/maintenance can prolong the service life of the coke oven batteries up to 35-40 year.
This project report mentions various repair/maintenance practices and its work procedure & instruction which are generally carried out in a coke oven battery for enhancement of its life.
This project report also covers the possible reasons for damage of silica bricks in heating wall of coke oven battery owing to thermal shock, spalling, expansion, contraction etc. and its remedies. It also deals with measures to be taken in life cycle of silica bricks to enhance its life as well as increasing the life of coke oven batteries.
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CONTENTS Chapter No. 1. 2. 3. 4. 5. 6. 7. 8. 9.
10.
Title
Page no.
Visakhapatnam steel plant over view 6 Department in Visakhapatnam steel plant 9 Coke oven and coal chemical plant 10 Capital Repair Group 13 Refractory 14 Silica brick in coke oven 15 Reason for silica brick failure in battery 30 Various repair method of damage silica brick 34 in heating wall in coke oven battery Work instruction for various running maintenance 37 & Plan repair practices Recommendation
46
11.
Conclusion
47
12.
Remarks
48
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VISAKHAPATNAM STEEL PLANT OVERVIEW
Visakhapatnam steel plant is one of the prestigious steel plants in India which is located 26 KM south of Visakhapatnam city of Andhra Pradesh. Vsakhapatnam Steel Plant, popularly known as Vizag Steel, is one of the major steel producers in India. Vizag Steel Plant has been conferred Navratna status on November 17, 2010. VSP is only shore based steel plant in India. It is of 3 million metric tons capacity per annum with sophisticated technology. It is only integrated steel plant in the country to be certified for ISO 9001-2000, ISO-14001:2004, OSHAS 18001: 1999 and 5S certification for 53 Departments.ERM (Enterprise risk management) and ERP (Enterprise resource planning) are also in implementation stage. It won Prime Minister Trophy for 2 times. Visakhapatnam steel plant is also called “Jewel of Andhra Pradesh”. Foundation stone was laid by late Prime Minister Smt. Indira Gandhi on 20 th Jan, 1971. Consultants were appointed in Feb 1971 and feasibility reports were submitted in 1972. The first block of land was taken over on 7th April 1974. M/s M.N. Dastur & Co was appointed as the consultant for preparing the detailed Project report in April 1975 and in Oct 1977 they have submitted the report for 3.4 mtpa of liquid steel. With the offer for assistance from government of erstwhile USSR, a revised project concept was evolved. Detailed Project Report for a plant capacity of 3.4 Mtpa was prepared by M/s M.N. Dastur & Co in Nov 1980. In Feb 1981 the contract was signed with USSR for preparation of working drawings for Coke ovens, Blast Furnace and Sinter plant. The blast furnace foundation was laid with first mass concreting in the project in Jan 82. The construction of township also started. A new company Rashtriya lspat Nigam Limited (RINL) was formed on 18th Feb 1982. Visakhapatnam Steel Plant was separated from SAIL and RINL was made the corporate entity of Visakhapatnam Steel Plant in April 1982. Silver Jubilee celebrations were conducted in 2007.
Vizag Steel Plant is the only India‟ s shore based steel plant and turnover in 2009-2010 was 10,600Crores and recently on its expansion from 3.1MT to 6.3MT. Its poised to become a World Class Organisation by expanding its capacity up to 20MT.
Visakhapatnam steel plant, the first coastal-based plant of India is located, 16 km south west of city destiny i.e. Visakhapatnam. Bestowed with modern technologies, VSP has installed 6|Page
capacity of 3 million tons per annum of liquid steel & 2.656 million tons of saleable steel. At VSP there is emphasis on total automation, seamless integration & efficient up gradation, which results in wide range of strong & long structural products to meet stringent demands of discerning customers within India & abroad .VSP products meets exalting international quality standards such as JIN, DIN, BIS, BS etc. VSP has the distinction to be the 1 st integrated steel plant in India to become a fully ISO-9002 certified company. The certificate covers systems of all operational, maintenance, services units besides purchase systems, training & Marketing functions spreading over 4 Regional Marketing offices, 20 branch offices & 22 stock yards located all over the country.
VSP by successfully installing & operating efficiently Rs.460 crores worth of pollution control & environmental control equipment and converting the barren landscape by planting 3 million plants has made the steel plant, steel township and surrounding areas into a heaven of lush greenery. This has made a steel township a greener, cleaner & cooler place, which can boast of 3 to 4 o C lesser temperature even in the peak summer compared to the Visakhapatnam city. VSP exports quality Pig iron &steel products to Sri Lanka, Myanmar, Nepal, middle east, USA & South East Asia.(pig iron). RINL- VSP was awarded “Star Trading House” status during 1997-2000. Having established a fairly dependable export market, VSP plans to make a continuous presence in the export market. Having a total manpower of about 17000, VSP has envisaged a labour productivity of not less than 230 per man year of liquid steel which is the best in the country and comparable with the international levels. Steel is one of the most important components that can strengthen the economic backbone of any country. The high versatility of steel allows a vast range of products to use steel as their raw material. Visakhapatnam Steel Plant's product mix consists of Rounds, Reinforcing bars, Squares, Flats, Equal angles, Unequal angles, T-bars, Channels, Saleable billets providing a great variety in the composition as per customer requirements. The plant is designed to produce three million tons of liquid steel per annum to be converted to 2.656 million tons per annum of saleable steel. In addition, Visakhapatnam steel plant will produce annually about 5.56 lakhs tons of pig iron and various by-products and benzyl products for sale.
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MAJOR PLANT FACILITIES: The production facilities in the Visakhapatnam steel plant are most modern amongst the steel industry in the country. The know-how and the technology have been acquired from different parts of the world from the reputed and established sources. Some of the novelties of the Visakhapatnam steel plant are:
Four numbers of 7 meter height coke ovens of VSP are the tallest so far built in the country. Dry quenching of coke has been adopted which not only improves the quality of coke and economics of coke production, but also contribute significantly to the reduction of environmental pollution. Base mix yard for sinter plant was introduced for the first time in the country which helps in excellent blending of the feed material to the sinter machine and production of consistent good quality sinter. 3200 cubic meters two blast furnaces with bell less top charging equipment and 100% cast house slag granulation. The granulation of the entire molten slag arising at the furnace cast house avoids the need to transport molten slag and optimizes utilization of slag. Blast furnace no.3 is under construction. 100% continuous casting of liquid steel into blooms result in less and better quality of blooms. The VSP have three sophisticated and large rolling mills with the latest features of automation and optimization. The operations of blast furnace, steel melting shop and rolling mills have been entirely computerized to ensure consistent quality and efficient performance. The major production departments of Visakhapatnam steel plant are the raw materials handling system, coke ovens, sinter plant, blast furnace, and steel melting shop and rolling mills.
Extensive facilities have been provided for repair maintenance as well as manufacturing of spare parts. There is a Central machine shop, Structural shop, forge shop, foundry, wood working shop and loco repair shop. Visakhapatnam steel plant has got its own Air separation plant for production of oxygen and acetylene plant for production of acetylene gas. A captive power plant has also been provided for power generation with 4 Units, each of 60MW generation capacity.
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DEPARTMENTS IN VISAKHAPATNAM STEEL PLANT:
Coke Ovens & Coal Chemical Plant: Coking coal , after selective crushing and proper blending is subjected to destructive distillation (heating in the absence of air) in the Coke Ovens. After heating for nearly a period of 16-18 hours at a temperature of about 1100 oC, coke is obtained and is used as a fuel as well as reducing agent in the Blast Furnace. The Coke Ovens of VSP are engineering feats by themselves. They are the tallest ovens constructed in the country. The Plant has 4 batteries of 7mtr. tall ovens with each battery consisting of 67 ovens. Another feature is the dry cooling of coke carried out by the inert gas nitrogen thus, reducing pollution considerably. Besides a bio-chemical plant separately undertakes the treatment of effluents. By-products like benzene, toluene, xylene, naphthalene, coal tar, creosote oil, pitch; ammonium sulphate and benzyl products are also recovered from the coke ovens gas. VSP produces, among other by-products, pushkala a prime fertilizer based on ammonium sulphate. Sinter Plant: Iron ore fines, coke breeze, limestone and dolomite along with recycled metallurgical wastes are converted into agglomerated mass at the Sinter Plant, which forms 80% of iron bearing charge in the Blast Furnace. The Sinter Plant comprises of two sinter machines each having 312 square meters of grate area with a total production capacity of 5.256 million tons per annum. Blast Furnace: VSP has two Blast Furnaces with an effective volume of 3200 cu.m. Each of which are the largest in the country. Blast Furnace is charged with coke, iron ore and sinter from the top and produces about 5000 tones of molten iron per day. Its novel circular cast house with four tap holes ensures continuous tapping of hot metal. The annual production capacity of these Blast Furnaces is 3.4 million tones of liquid iron. Steel Melt Shop & Continuous Casting:Three Top blown converters, each of 133 cu.m. Volume, produce a total of 2.7 million tones of liquid steel per annum. This liquid steel thus produced is casted in six-4 strand bloom casters. A special feature in energy conservation is the collection of Converter gas to be used as a fuel in the plant. The entire molten steel at VSP is continuously cast at the radial type continuous casting machines resulting in significant energy conservation and better quality steel. 100% Continuous casting on such a large scale has been conceived for the first time in India. Rolling Mills: The cast blooms from continuous casting department are heated and rolled in the three high speed and fully automated rolling mills namely Light & Medium Merchant Mill, Wire Rod Mill and Medium Merchant & Structural Mill, to produce various long products like Reinforcement bars, rounds, squares, flats, angles, channels, billets, wire rods etc. Technologies adopted at Rolling Mills include world-class Stelmor and Temporal processes. VSP produces steel by employing three numbers of top blown Oxygen Converters called LD Converters. The entire liquid steel is continuously cast in radial bloom casters, which help in energy conservation as well as production of superior quality products.
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COKE OVEN AND COAL CHEMICAL PLANT (CO&CCP)
In our steel plant many departments are there, out of them RMHP, CRMP, CO&CCP, BF, SMS and Mills are important zones. CO&CCP is one of the critical departments in steel plant.In CO&CCP we are having coke dry cooling plant for cooling coke which is pollution free instead of wet quenching. During heating of coal, gas is generated which is sucked by exhauster and treated to get Byproducts like Benzene, Toluene, Naphthalene, Coal tar, Benzyl products and produces Pushkala a prime fertilizer based on ammonium sulphate.
COKE OVEN BATTERY
Coke is manufactured by heating of crushed coking coal (below 3mm) in absence of air at temperature of 1000˚C and above for about 16 to 18 hours. A Coke Oven comprises of two hollow chambers namely coal chamber and heating chamber. In the heating chamber a gaseous fuel such a Blast Furnace Gas, Coke Oven Gas etc. is burnt. The heat so generated is conducted through the common wall to heat & carbonize the Coking Coal placed in the adjacent coal chamber. Number of ovens built in series one after the other form a Coke Oven Battery. At VSP there are four Coke Oven Batteries, 7 Meters tall and having 67 Ovens each. Each oven is having a volume of 41.6cu. Metre & can hold up to 31.6 Tonnes of dry coal charge. The Carbonization takes place at 1000- 1050˚C in absence of air for 16-18 hours. Red Hot Coke is pushed out of the oven and sent to Coke Dry Cooling Plants for cooling to avoid its combustion. There are 4 Coke Dry Cooling Plants (CDCP) each having 4 cooling chambers. The capacity of each cooling chambers is 50-52 TPH. Nitrogen gas is used as the 10 | P a g e
Cooling medium. The heat recovery from nitrogen is done by generating steam and expanding in two back pressure turbines to produce 7.5MW power each. The Coal chemicals such as Benzol (& its products), Tar (& its products), Ammonium Sulphate etc. are extracted in Coal Chemical Plant from C.O. Gas. After recovering the Coal chemicals the gas is used as a by product fuel by mixing it with gases such as BF Gas, LD Gas etc. A mechanical, biological & chemical treatment plant takes care of the effluents.
DETAILS OF COKE OVEN BATTERY: No. of Batteries
4
No. of Ovens/Battery
67
No. of heating wall /Battery
68
No. of Flues/heating wall
32
OVEN DIMENSIONS: Height
7M
Length
16M
Average width
0.41M
Volume
41.6M³
Heating wall thickness
105MM
Dry coal charge /oven
32.4Tones
Gross Coke output/oven
25 Tones
COKE DRY COOLING PLANT: No. of CDCPS
4
No. of cooling chambers / CDCP
4
Coke cooling capacity/chamber
50-52 Tones/hour
Temperature of charged coke
1000- 1050˚C
Temperature of cooled coke
180- 200˚C
Specific steam generation
0.5 Tonne/ cooled coke 11 | P a g e
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CAPITAL REPAIR GROUP – (CRG)
Capital Repair Group (CRG) Dept. has been formed in the year 1998 CRG is look in after running repairs as well as capital repairs. CRG has 2 sections i.e. Mechanical and Refractory. In planned repairs of coke oven batteries heating walls are been changed, sometimes partly or fully. Partly cha nging at ends is called “End vertical repairs”, full heating wall changing is called “Full wall repair”. In planned repairs mechanical activities like flash plate changing, AP changes and CTR (Cross Tie Rod) changing etc. are being done. Regular maintenance and repair activities of CO&CCP so far as refractory is concerned and regular mechanical maintenance and repair activities of all 4 coke oven batteries (except battery machines) are being carried out of CRG.
HIGHLIGHTS:-
1] Carried of partial and full wall repairs of battery 2] Battery no.2 cold repair was completed in a world record time of 11 months. 3] Changing of mechanical anchorage of all ovens in battery no.3.End vertical repairs of all problematic ovens being carried out. Full wall repair of entire battery-3 have started. 4] First department in VSP to get 5 S certification and “ best 5 S sustaining department.” 5] Changing of 2 GCM‟s of battery no.3.
6] Capital repair of 12 CDCP chambers. 7] Capital repair of three (big) and two (small) acid tanks in byproducts area. 8 ]DE platform of batery-1 have changed. 9] All the refractory and mechanical related running repairs are being attended by department.
the
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R EFRACTORY Refractories are inorganic, nonmetallic and heat resistant materials that can withstand the action of corrosive solids, liquids or gases at high temperatures. The various combination of conditions in which refractories are used, make it necessary to manufacture a range of refractory materials with different properties.The refractory range incorporates fired, chemically and carbon bonded materials that are made in varying combination and shapes for diverse applications. Classification of refractories According to the chemical behaviour the refractory materials, which are mainly oxides of metals or non metals or mixtures, are as follows 1)
Acid , 2)Neutral 3) Basic
Acid refratories are those which readily combine with bases .They are materials consisting of silica as their chief constituent greatly in excess of bases present. The important acid refractories are quartz,sand ganister , etc. Acid refractories are of two kinds 1) those composed of sio2 & 2) those composed of aluminium silicate or clay 3) Neutral refractories consists of substances which do not combine either with acidic or basic oxides and for this reason constitute the most satisfactory furnaces lining, e.g., graphite, and chromites. Basic refractories consists mainly of basic oxides without free silica and resist the action of bases .the most common basic refractories are magnesite ,dolomite lime, etc.,but lime , because of dehydrating tendency , is never used as a refractory .
Fireclay Refractories: Fireclay refractories such as firebricks, siliceous fireclay and aluminous clay refractories consist of aluminum silicates with various amounts of silica adding upsio 2 content of less than 78% and containing less than44%ofAl 2o3.Fireclay refractories consist essentially of hydrated aluminum silicates with minor proportion of other minerals. Owing to relative cheapness; this material finds uses in most furnaces, kiln and stoves. Firebrick is the most common form of refractory material. It is used extensively in the iron and steel industry, non-ferrous metallurgy, glass industry, pottery kiln, cement industry and many others. There are 4 standard classes of fireclay: high-duty, medium-duty, low-duty, and also semi- silica. These classes cover the range from approximately 18% to 44% alumina, and from about 50% to80%silica. 14 | P a g e
Silica Bricks in Coke Ovens
Silica bricks constitute a major portion of a coke oven battery and it plays a very vital role in its functioning. The health of a coke oven battery is predominantly dictated by the health of its silica bricks. The performance of carbonization of coal in a battery greatly depends on the condition of its silica bricks. So far, no viable substitute has been invented for silica bricks in spite of its low spalling resistance. The health of silica bricks depends upon various factors spanning from its manufacturing, handling, laying, preheating, heating and operation of the battery.
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Metallurgical coke, undoubtedly, is one of the most important and most expensive raw materials used in iron- making in a blast furnace. Coke plays multiple roles in a blast furnace. As such, coke making becomes a very important aspect insofar as blast furnace route of iron & steel making is concerned. Coke is produced by destructive distillation of coking coal which is carried out in refractory slot chambers named as coke oven. A group of ovens built together constitute a battery. A battery is a monolithic structure of refractory brickwork, largely comprising refractories of silica and fireclay make. In vertical direction, the battery can be divided in five zones; namely, bus flue zone, regenerator, inclined flue, heating wall and oven roofing. The space between two heating walls forms the coking chamber where conversion of coking coal into coke takes place. Excepting bus flue and oven roofing zones, all other zones; viz, regenerator walls, inclined flues, heating walls and coking chambers are all lined with silica bricks. Thus, a major portion of a battery is made up of silica bricks. A 7-mt tall battery of 67 ovens requires nearly 20000 tonnes of refractory bricks, out of which approx. 14000 tonnes are silica bricks.
Coking coal is heated in the coking chamber in oxygen-free atmosphere until all volatile components in the coal get removed. The material remaining in the oven, the residue, is called coke. The coke ovens must remain hermetically sealed under cyclic stress of expansion and contraction. Gas off-take system, located at oven-top on both sides along the length of the battery, remove the gases produced during coal carbonization. Process heat comes from the combustion of gases in the flues of the heating walls. Generally coke oven gas or blast furnace gas is used to heat a battery. The blended coal mass is heated for 16 to 20 hours for production of metallurgical coke. Thermal energy from walls of the heating chamber heats the coal mass by conduction from the sides to the middle of the coking chamber. During the coking process, the coal charge is in direct contact with the heated wall surfaces and develops into an aggregate “plastic zone”. As the additional thermal energy is absorbed, the plastic zone thickens and merges towards the middle of charge. Volatile gases escape in front of the developing zone due to heat progression from side walls. Wall temperatures should stay above 1100 0C during loading operations and actual coking. The maximum temperature attained at the center of the coke mass is usually 1050-1100 0C. Therefore, the bricks, which show sufficiently high refractoriness under load and reliable volumetric stability, are used to construct the chambers.
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Cross section of a Battery
Now, as mentioned earlier, refractory materials for the design and construction of coke ovens are silica and fire clay. They fulfil different duties at different temperature levels at different locations within the coke oven structure. However silica bricks play major role as they occupy larger and critical area of the battery.
Silica brick is a refractory material containing at least 95% SiO 2. Basic materials used for their manufacture are Quartz, Quartzite, Ganister, Sand, Sandstone etc. For their manufacture, the siliceous rock is crushed and ground with 2% lime and water. The thick paste is then made into bricks either by hand moulding or by machine pressing. The bricks are dried in air or in heated rooms and then, burnt in kilns. During heating, temperature is slowly raised. In about 24 hours, to about 1500 0C and this is maintained for nearly 12 hours, so as to allow Quartzite to be converted into cristobalite. Then, cooling is done carefully and it takes about 1 to 2 weeks. During cooling, cristobalite is slowly changed into tridymite, so that a mixture of tridymite and cristobalite results in the final bricks. The polymorphic transformation of the silica determines both the technological process and properties of the product. The most abundant form of SiO 2 in nature is β-Quartz
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Silica can exist in polymorphic modifications. The sequence of polymorphic inversions can be represented as follows:
The inversions indicated by the horizontal arrows are reconstructive transformations (relatively slow), during which the bonds in the secondary coordination sphere are broken and the SiO4 tetrahedra are completely rearranged. The activation energy for the changes are high and as result the high temperature forms can be under cooled without transformation to the stable state. The inversions indicated by the vertical arrows are known as the displacive type of transformations, which proceeds at a relatively fast rate.
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Properties of the different modifications:
Modification
Sp. Gravity
Temp. stability range
0
C
Volumetric effect of transformation At given temp.
β - Quartz
2.65
up to 573
α - Quartz
2.53
573 – 870
+ 0.82
α – Tridymite
2.228
870-1470
+ 16.0
α – Cristobolite
2.229
1470-1713
- 0.6
Quartz Glass
2.203
-
0.9
On the account of the change in volume during the transformation from α to β states, the material cracks.
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Relevant charts / Phase diagrams Olivine‟s linear thermal expansion is lower than silica and relatively uniform over its entire use
temperature range. Low thermal expansion greatly reduces mold wall movement for more stable molds capable of producing castings with closer dimensional control and consistency. This effect is most pronounced in the casting of aluminum alloys where olivine‟ s greatest differential
in thermal expansion compared to silica sand occurs in the 600 - 800°C pouring temperature range of most aluminum alloys. Olivine will stay in the system longer to promote higher green strengths, and maintain those improved properti es through the repeated recycling of the sand and clay mixture. Olivine‟s low thermal expansion also eliminates the need for cushioning additives such as cellulose or cereal for a more easily controlled green sand system of sand, clay and water.
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CaO-Al2O3-SiO2 phase diagram In a ternary phase diagram (Fig 8), each point of the triangle represents 100% of that component. The liquidus point can be easily defined by the composition of the three ash components selected. The solidus point depends on which of the many compounds present will melt first. The diagram shows that an ash with 45% SiO 2, 20% CaO and 35% Al2O3 (composition A) will start melting at 1 170 °C, whereas an ash with 45% SiO 2, 19% CaO and Al2O3 36% (composition B) will start melting at 1 345 °C. Thus a 1% difference in the Al2O3 and CaO content results in 175 °C variation in predicted melting points
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Al2O3-SiO2phasetransformation
Starting from the left at 100% SiO 2 , we first have quartz / cristobalite / tridymite phase (whichever it feels like crystallizing as, or more likely given the "fast" firing rates, a glass). The blue line is the liquidus point, above which all is liquid and below which, at least one phase is solid. (A mixture of liquid and solid is a "mushy state".) The left area is SiO 2 + L, center is mullite + L and on the far right, Al 2 O 3 + L. The areas below these are fully solid, and are labeled. On the left, silica; middle, silica + mullite (a mixture of the two), near right is mullite itself (3 Al 2 O 3 + 2 SiO 2 ) and further right is mullite + alumina. The horizontal lines separating the partially liquid and fully solid zones are solidus lines. Where the liquidus and solidus lines meet is called a eutectic, the lowest melting point composition of any particular combination.
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Properties of Silica Bricks in Coke oven
Silica bricks are used in coke ovens due to the following properties they have:
Excellent mechanical strength at high temperature to withstand the loads of charging car
Excellent thermal conductivity at elevated temperature which enhances the heat transfer rate and ultimately increases the productivity of coke ovens.
High abrasion resistance to reduce damages during pushing and charging
Superb volumetric stability
Exact dimension even for difficult shapes
The brickwork of a battery are subjected to much higher thermal load, greater static and dynamic load due to heavy mobile machines and higher anchorage loads. Also, the pressure exerted by the coal charge on the oven walls during carbonization as well as during pushing is much higher in taller batteries compared to 4.5 M/ 5M tall coke oven batteries due to increased throughput. Silica bricks have excellent thermal conductivity, particularly at higher temperature which is an essential requirement for transferring the heat energy to the coal blend in order to ensure fast carbonization of coal. Silica bricks have low porosity and high bulk density, higher strength, creep and abrasion resistance at operating temperature.
Coke oven are normally operated for a long life span of 30-40 years continuously. So excellent quality, accurate shapes and precise dimensions are strictly required for the refractory used for them. High performance silica bricks, characterized by low thermal expansion rate, good high temperature properties, residual quartz less than 5%, true density 2.31, and high bulk density have been recently developed and produced successfully.
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Specification of silica bricks in coke ovens Technical Specification of Silica bricks for Visakhapatnam steel plant. Wall bricks SNo
Properties
Oven Sole Brick
With coke face
Head bricks and bricks of flooring zone
(a)
(b) *
(c)
Other bricks
(d) Chemical composition weight % 1
SiO2
95 % Min.
95 % Min.
95 % Min.
95 % Min.
Al2O3
1.20 % Max.
1.20 % Max.
1.20 % Max.
1.20 % Max.
Fe2O3
1.40 % Max.
1.40 % Max.
1.40 % Max.
1.40 % Max.
CaO
2.50 % Max.
2.50 % Max.
2.50 % Max.
2.50 % Max.
31 Min. (Seger
31 Min. (Seger
31 Min. (Seger
31 Min. (Seger
cone )
e ) con
cone )
cone )
17 %
20 %
24 %
27 %
16 % Max.
19 % Max.
23 % Max.
25 % Max.
425 kg/cm2
225 kg/cm2
225 kg/cm2
200 kg/cm2
500 kg/cm 2
300 kg/cm2
300 kg/cm2
250 kg/cm2
min.
min.
min.
min.
Pyrometric Cone Equivalent (P.C.E) 2.
PCE
Apparent Porosity 3
No single value to exceed Avg. of 5 results
Cold Crushing Strength (C.C.S) 4
No
single
value
below Avg. of 5 results
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Specifications Oven Sole Brick Properties
(a)
Wall bricks With coke face
Other bricks
(c)
(b) *
5
Head bricks and bricks of flooring zone
(d)
True Specific Gravity No single below
value
2.35
2.35
2.35
2.36
Avg. of 5 results
2.34
2.34
2.34
2.35
6
Residual Quartz content (%)
Below 5.0 %
Below %
7
Refractoriness under load (R.U.L) at 2 kg/cm 2 not less than
Ta 16500C
Ta 16500C
Ta 16500C
Ta 16500C
8
Permanent linear change (P.L.C), % at 14500C for 4 hrs.
+ 0.2 Max
+ 0.2 Max
+ 0.2 Max
+ 0.4 Max
(-) value not allowed
(-) value not allowed
(-) value allowed
9
Reversible thermal expansion (R.T.E) at 10000C
1.3 % Max.
1.3 % Max.
1.3 % Max.
1.3 % Max.
10
Bulk Density (B.D)
1.85 gm/cc
1.79 gm/cc
1.76gm/cc
1.76 gm/cc
Min.
Min.
Min.
Min.
(-) value allowed
not
5.0
Below 5.0 %
--
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not
Design of the Battery The service life of coke oven bricks greatly depends on the inherent stability of the brickwork as well as on the supporting effect of carefully designed Anchorage system. The heating walls of a coke oven are subjected to different loads and stresses during operation. These loads generally result from: Coking pressure Charging car loads Charging procedure Forces from battery bracing Pushing procedure Sudden temperature changes
It is important, however, to recognize that a well designed and sized anchorage system will result in high inherent wall stability and will reduce the deformation of heating wall and undesired opening of joints or the formation of cracks. Cross battery anchorage system consists of the buckstay, the upper and lower cross tie rods, and the spring loaded compression elements located along the oven height. In the longitudinal battery direction, this anchorage system comprises spring loaded longitudinal tie rods, buttress, and the battery foundation system.
Cross anchorage of a Battery Laying Brickwork laying of Coke ovens should be necessarily done with geodetic Survey instruments with permanent bench marks for longitudinal axes, axis of extreme oven and axis of the middle. When laying flues deviations from design dimensions of flues should not exceed the tolerance values (i.e. ± 2 to 5 mm). 27 | P a g e
The number of brick layers in 7 mt tall Battery of Visakhapatnam Sl.no
Basement
Material
Count
1
Pavement zone of Reinforced concrete
Fire Clay
2
2
Sole flue
Fire Clay
5
3
Regenerator
Silica
24
4
Sloping flue
Silica
9
5
Vertical heating flue
Silica
58
6
Flooring of heating flue
Silica
11
7
Flooring of ovens
Silica
1
Laying of Coke oven Brickwork should be carried out only in closed protection shed in order to protect the brickwork from rain, coal & other dust and dirt. Silica bricks are to be laid without wetting by water. When laying the bricks, all the mortar joints should be well filled with the mortar, which should squeeze out along the perimeter of the bricks contacting with the mortar. No cavities are allowed in the joints. All mortar joints on outer sides of the heating walls and heating flues are packed and pointed when laying the brickwork.
Allowable Thickness of Joints in silica bricks 4 mm Max
7 mm
Min
2 mm
Normal
Expansion Joints are thoroughly cleaned off any mortar and filled with dry saw dust. All the expansion Joints are covered with tar paper strips of approx. 1 mm thickness. Top surface of the sliding joints should be made smooth and even. A thick paste consisting of graphite powder and glycerin is applied evenly by brush on the top surfaces of the sliding joints for a thickness of 1.5 to 2 mm.
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Preheating The total expansion of silica bricks for fully heated up VSP coke oven battery is around 1.2%. Thus a battery of oven length 16 M will have a total expansion of about 192 mm horizontally and 169mm vertically. In the course of heating up if the brickwork is not protected properly, it leads to the detachment of the vertical joints and the brickwork will lose its total compactness. As a result, the brickwork becomes extremely weak and due to the cracks developed in the joints, the gases leak from the ovens to the adjacent flues of heating wall. This totally upsets the thermal and hydraulic regime of a battery. During preheating of coke ovens, the volumetric changes take place in the brickwork which are caused by the thermal expansion of the brickwork as well as by structural change of silica refractory at critical temperatures. The aim of drying and preheating is to heat the brickwork to the temperature at which the ovens could be charged with coal for coke making. In order to perform that, it is necessary to ensure gradual and complete removal of moisture from the refractory brickwork of ovens without disturbing their tightness. The brickwork is heated by means of supply of the heat carrier at required temperature, ensuring a minimum temperature gradient over the height of oven body for uniform and steady expansion of the whole coke oven battery brickwork structure. Displacement of some areas of the brickwork can be prevented by keeping minimum temperature gradient in brickwork and by proper regulation of anchorage. The maximum duration of heating-up is 80 to 88 days and oven brickwork temperature is raised to a level of 1100 to 1150 0C. Expansion of the brickwork should be measured for different temperature intervals. If the actual expansion of the brick work is more than envisaged, the rate of temperature rise should be reduced. Schedule of Drying & Heating of VSP batteries: Heating wall temp. 0 C
Maximum % of Expansion in temp. Interval
Number of days
Temp. raise per 0 day C
% of Expansion per day
20 -100
0.280
10
8
0.028
100 -150
0.205
10
5
0.021
150 - 200
0.205
10
5
0.021
200 - 248
0.070
8
6
0.009
248 - 296
0.070
6
8
0.012
296 - 344
0.049
4
12
0.012
344 - 424
0.058
5
16
0.012
424 - 524
0.108
5
20
0.021
524 - 634
0.108
5
22
0.022
634 - 780
0.060
5
25
0.012
780 - 1100
Permanent heating
20
Total
1.213
88
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Reasons for silica brick failure in a battery and measures to be taken:-
THERMAL SHOCK: -
The major reason for silica brick failure in a battery is due to thermal shock. Temperature gradient across a brick or a block causes uneven expansion in the brickwork, which results in spalls or cracks. The reasons for thermal shocks are
Damages in heating wall
Stoppage of heating results in sudden refractory temperature drop and entire battery is subjected to thermal shock. So heating of the battery should be never stopped. The temperature of a battery should never drop below 900 0C.The temperatures at any point should not exceed 1430 0C, otherwise silica brick fuses. 30 | P a g e
More Temperature difference across the flues in a heating wall also causes thermal shock to brickwork. So very smooth temperature gradient should be maintained in flues of a heating wall. End vertical temperature should not be less than 100 0C from the heating wall center temperature . If ammonia liquor, used for cooling of hot coke oven gas, comes in contact with silica brick, it results in sudden cooling of brickwork. Here the brick spalls very fast, and the damage is visible in very next cycle of pushing. So utmost care should be taken in handling of ammonia liquor in a coke oven battery. After pushing if the oven doors remain open for more time, the end vertical bricks get exposed to ambient temperature which causes thermal shock to the bricks. As such, in a battery, deterioration generally starts from end verticals. So, doors of the ovens should be closed in minimum possible time. Improper charging in an oven creates uneven temperature distribution in the flues of adjacent heating walls. This causes thermal shock in brickwork. Pushing delays cause variation in coking periods and result in over heating of ovens. This is not desirable. Timely pushing and uniform coking period enhance the life of brickwork. Wet coal charging with very high moisture content results in cooling of surface of the heating wall bricks. So, for longer life of a battery, moisture in the charge coal should be controlled. Uneven temperature in heating walls across the battery is also a cause of thermal shock. So temperature in heating walls should be maintained within +/- 20 0C Openings in the brick joints and the cracks in the brickwork cause oven gas cross leakages. These leakages increase flue temperature drastically, and create thermal shock to the brick work. Care must be taken to seal/repair joint openings and cracks at the earliest. Calorific value of heating gas should be uniform, otherwise temperature in flues vary erratically.
Anchorage
During the normal operation of the battery, the anchorage system must be properly regulated in order to neutralize the ill effects of mechanical and thermal shocks. In Visakhapatnam steel plant, 12 –15 tons of loads is applied in cross anchorage of each heating wall and 240 tons longitudinally across the battery between buttresses. Anchorage regulation and its proper upkeep are two very vital aspects of a battery. Structural integrity of the whole of the battery brickwork hugely depends on its anchorage system. Lack/failure of anchorage will have its immediate ill-effects on the integrity of the heating walls. A wall failure is a weakness within the battery. If a heating wall failure is not addressed in a timely manner, it can experience a domino effect, causing multiple wall failures. If the anchor loads are more, the jamb bricks of end verticals start breaking and heating walls get deformed. If 31 | P a g e
the anchor loads are less, cracks are formed in the heating wall. Some times it also results in dislocation of bricks. The reasons for anchorage failures are.
The anchorage springs some times get subjected to high temperature due to gas burnings and it loses its property .This weakens the anchorage. So anchor springs are to be protected from higher temperature.
During rains, sudden cooling of anchor tie rods (if it comes in direct contact with water) results in breakage of tie rods. Similarly, sudden release of load from anchor column results in development of cracks and dislocation of bricks in the heating walls.
Anchorage loads also vary due to fluctuations in the battery temperatures and also due to pushing and levelling forces. So these loads are to be timely measured and regulated.
Physical damages
Wrong centring of pusher ram, sharp edges of pusher ram and leveler bar may also cause physical damage to brick work. Poor upkeep of pusher ram‟s carbon shoe and floating shoe can, sometimes, cause serious damages to oven sole bricks.
Improper maintenance of leveller bar may also sometimes create harmful pressures on heating walls during levelling of coal in the oven. This may cause dislocation of bricks in the free space area of the oven.
Wall Pressures -Unbalanced wall pressures that develop during carbonization of coals at different coking periods in the neighboring ovens may sometimes cause slight shifting of oven walls. This may result in many hard pushes and stickers. The basic design of a coke oven battery as well as specific details related to keying or interlocking of shape and their levels strongly influence the distribution and concentration of stresses in a heating wall‟s refractory during flexing of the wall. During flexing, a heating wall is deflected and distorted both vertically and horizontally. Tongue and groove keys of refractory bricks play major role in not allowing the shifting of brick courses. Sometimes heating wall damage is caused by extensive wall flexure, due to excessive unbalanced coking pressure during the coal carbonization.
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HEATING WALL BENDING IN VERTICAL SECTION
Effect of wall pressure
Chemical attack At high carbonization temperature the fusible coal ash in the coal blend may react with silica brick surface and form low melting spots. In such cases the fused refractory surface may be peeled off by coke during pushing. So, all the constituents of the coal blend should have adequate ash fusion temperature.
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Various Repair methods of damage Silica bricks in heating wall of coke oven
It is well known that the breakage of the refractory brickwork of coke ovens begins with the wear out of the head part of coking chamber. This zone operates under the most unfavourable conditions from the standpoint of mechanical, thermal and chemical influences and wears out most rapidly. The process of breakage of the brickwork keeps progressing if timely repair is not carried out. The type and causes of damage in silica bricks in a battery dictate the type and nature of repair work that needs to be taken up.
Flame gunning repair on coke oven wall Flame gunning repair application was developed by Krosaki Harima Corporation. It employs oxygen and propane as fuels, in which fine silica particles are fused instantaneously and transferred in high temperature flame to adhere onto the damaged portions of the chamber wall. This repair gives a life of 8 to 10 years. This repair is characterized by -
Film adhesion of the gunned material on wall brick surface Little rebound/material loss Even surface after application.
Large size cast monolithic refractory repair modules The large size cast refractory modules are monolithic structures which are formed from a castable refractory material having very high dimensional stability over a wide range of temperatures. Each repair module is a rectangular parallepiped having one or more vertically extending flues formed therein, one end of a module being adapted to conform to the end shape of the damaged heating wall, the other end of the module being adapted to inter-fit with existing brick work. The modules are assembled by initially removing damaged brick work from the heating wall and then placing in the new modules which are mortared in place. It is a labour-efficient and quick repair method.
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Ceramic welding This is accomplished by conveying a powder mixture, rich in silica, through a small pipe lance via an oxygen enriched compressed air system. The powdered silica mixture is jetted out of the lance and ignites against the wall of the coke oven. The heat of the reaction penetrates the silica brick creating plastic zone of silica. The reaction also turns the powder silica mixture into a molten mass, which bonds to the aforementioned plastic zone on the silica brick. The appearance is similar to that of a welding rod. The consequent effects are quite similar to that of welding, as new and equally strong material is welded onto the existing worn and cracked silica brick. The process allows to remove a single oven from service and repair cracks and holes. Quickly after repairs, the oven can be immediately returned to production. The average life after this repair is quite high.
Full wall replacement Full wall replacement consists of demolishing and erecting afresh complete heating coke oven wall. This is like an open heart surgery of a coke oven battery. Full wall repairs are the most extensive and expensive and the most complex of all the repairs. In a full wall rebuild, the entire heating wall from coke side to pusher side as well as from oven floor to roof is replaced. In this repair, life of the battery can be extended beyond 10 years.
End flue repair Large damages at ends of ovens necessitate end flue repair. It consists of demolition and replacement of brickwork at the end of the heating walls. End flue repairs can provide a long term solution to deteriorated oven heating walls if the damage is confined to the ends. End flue repairs are generally done for 2/4/6 flues depending upon the extent of damages. It can extend the effective productive life of the battery by five to seven years.
Ceramic welding with zero expansion brick In order to ceramic weld a large hole in the wall, silica brick is cut to fit and slowly heated up to a temperature over 900 o C. This is done to protect the new brick from thermal shock during welding. Success of this repair is limited. Zero expansion brick of fused silica is not susceptible to thermal shock. In the late 1980s, Zero expansion bricks were utilized successfully and the role of ceramic welding for battery maintenance was expanded.
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Guniting The damaged spot of the hot brickwork is sprayed upon, under pressure, with a suspension containing fire clay powder and a solution of orthophosphoric acid in water It is a less time consuming process. Life expectancy of this process is around 6 to 8 months
Spraying and patching Spraying and patching is confined to repairing minor cracks or spalls in the end flue zone. Spraying is carried out using siliceous spray refractory materials with requisite amount of water with help of a spraying machine. To seal wide gaps, patching is carried out with refractory cement with the help of a long trowel. Life expectancy of this repair is only three to four months.
Dusting This helps in sealing the fine cracks or the open joints between the bricks. In this system, fine refractory powder is blown into a closed oven chamber by means of a fan through drilled charge hole cover. The dust while it passes through openings, it deposits there and seals the cracks and minor openings. It is good for preventing cross leakages.
Panel patch repairs In panel patch repair, the damaged brickwork at end verticals is isolated from heating. The damaged silica bricks are removed and replaced with preheated bricks. It is a troublesome repair. It gives a life of 3 to 4 years.
KTM3 welding It is ideal for repairing cracks, spalls and edge damages. An exothermic powder mixture along with water, which is self igniting, is sprayed on the defects. The material catches fire and melts immediately and fills the defects. It also gives a very good life. VSP has been using, depending upon requirement, the above mentioned repair techniques at its batteries excepting „large size cast monolithic refractory repair modules‟ and ceramic welding with zero expansion brick. Disposal of Silica brick The best way of disposing used-silica bricks after repair, in an integrated steel plant, is to use it as quartzite in blast furnace. VSP has been practicing it. Good shaped bricks can be used in building constructions 36 | P a g e
Works instruction for various running maintenance & plan repair practices
a) GUNNITTING
1.Gunniting job of any oven is taken up in consultation with Coke Oven (Operation). It is planned in a matured oven or in an empty oven as per requirement. 2. If the damage is near the Charging Hole, Gunnitng is done from the oven top by putting the Gunniting lance to the Charging Hole. If the damage is in the bottom region i.e up to four metre level Gunniting is done from P/S or C/S depending from which side approach is near. 3. For carrying out gunniting from O/T, if the damaged portion is above thecoke mass then the oven is not pushed. The oven is isolated, the stand pipe caps opened, the required hatch cover is opened and cleaned off graphite by Coke Oven (Operation). 4. The gunnitng machine is placed near the concerned hatch up to two metre away from the charging hole. The gunnitng machine wheels are placed over ceramic blanket to protect it from heat. The electric cable is placed on stands all along the oven top to protect it from heat. 5. Ceramic blanket is also placed around the charging hole for the gunner to stand and do gunnitng. 6.Compressed air, water and power connection are given as per the instruction manual. 7. The area to be gunnited is degraphititsed by blowing compressed air to get a fresh surface. 8. Once the surface is prepared the machine is made ready for gunnitng. Gunniting powder is fed in to the machine. Lance connection is given and the gunner positions himself for gunniting. 9. The length of the lance to be used depends on the position and contour of the damage. 10. The gunnitng machine is switched on and gunnitng is done as per instruction manual so as to get a good quality gunnitng with minimum rebound loss. 11. If the gunniting is to be done from P/S or C/S then the oven is pushed and the oven door is kept opened on the side where gunniting is to be done. The Pusher Car or Door Extractor Car or platform is used for gunniting in the top portion of the oven i.e above four metre level. 12. The oven door frame is covered with ceramic blanket with the help of sodium silicate to avoid the oven getting cooled while gunniting is under progress. 13. Instruction clause no 6 to 10 are repeated, after the gunniting is over the blankets are removed. 14. If the gunning is done in an empty oven, then the oven sole is cleaned. 37 | P a g e
15. Clearance is given to CO (Operation) for pushing / charging of the oven. 16. The details of the job done is recorded by the shift manager in the daily progress log book (QMS/R/CRG/R/02) kept in shift office.
b) HATCH RING CHANGING PURPOSE : To change the distorted and damaged hatch ring of any of the oven
INSTRUCTIONS: 1. As per the requirement hatch ring changing job is taken up in consultation with Coke Oven Operation. 2. It is done in a matured oven so that gassing will be less. The oven is isolated and both the Pusher side and Coke side stand pipe caps are opened. 3. The surrounding bricks of the ring are first removed by dismantling then with the help of chisel and hammer. 4. Once the surrounding bricks are removed the ring is free and it is removed with the help of a crow-bar. 5. A new hatch ring is placed in its position machining with the charging holes. 6. Hatch ring bricks are then positioned and lined as per drawing. 7. After the job is completed the debris is removed with the help of trowel. 8. The job carried out is recorded by the shift manager in daily progress register (QMS/R/CRG/R/02) kept in CRG site office.
C) STAND PIPE BASE CAULKING: PURPOSE: To stop the gas leakage from stand pipe base.
INSTRUCTIONS: 1. As per the requirement stand pipe base caulking job is taken up in consultation with Coke Oven (Operation). 2. It is done in a matured oven so that gassing will be less. The oven is isolated and both the Pusher side and Coke side stand pipe caps are opened. 3. Old burnt out rope and deposited tar is removed from the stand pipe base with the help of an iron hook. 38 | P a g e
4. The base is cleared with compressed air and wire brush. 5. The stand pipe base is then caulked with 25mm unbraided asbestos rope with the help of iron rod and hammer. The asbestos rope is poured in sodium silicate to give it a tight fit and stop all possible gas leakages. 6. Sodium silicate hardens due to heat and a strong leak proof joint is obtained. 7. Over the rope joint fire clay mortar is applied to make it level with the stand pipe base to prevent the rope damage and stop any leakage. 8. After the caulking job is over clearance is given to operation for pushing of the oven. 9. The job carried out is recorded by the shift manager in daily progress register (QMS/R/CRG/R/02) kept in CRG site office. d) OVEN TOP GROUTING: PURPOSE: TO CLOSE THE OVEN BRICK JOINT S BY FIRE – CLAY MORTAR. INSTRUCTIONS:1. THE OVEN TOP IS CLEANED WITH A WIRE BRUSH AND THEN BLOWN CLEAN WITH COMPRESSED AIR .
2. A thick slurry of fire – clay powder with water is made. 3. The slurry is then poured with a mug on the cleaned surface and then applied Uniformly with a wire brush. 4. Brick joints which have opened up more than 3-5 mm is filled with thick fore clay mortar. 5. Around the stand pipe base, hatch ring thick fire clay mortar is applied to arrest gas leakage. 6. The details of the job carried out are recorded by the shift manager in daily progress log book (QMS/R/CRG/R/01) which is kept in CRG site office. e) LINTEL REPAIR: PURPOSE: To carry out the partial or full lintel repair as required on pusher side or coke side. INSTRUCTIONS: 1. Lintel repair is done either Coke side or Pusher side. For doing lintel repair on pusher side, Pusher Car is used and on coke side, Door Extractor car or platform is used. 2. The upper lintel portion is cleaned thoroughly of tar and dust. The bottom lintel area is cleaned after removing the covering plate and damaged bricks are removed.
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3. The gap between the upper lintel and flash plate is cleaned of loose rope and mortar, and caulked with asbestos rope and pointed with mortar. 4. The dismantling of both the upper and bottom lintel is carried out as per requirement and subsequently relined as per the drawings. 5. After lining, the entire face is washed with mortar slurry. After the job is completed the debris is removed, the plate of the bottom lintel is fixed and pointing with castable is done. Clearance is given to Coke Oven (Operation) for charging / pushing. 6. The job carried out is recorded by the shift manager in daily progress register (QMS/R/CRG/R/02) kept at CRG site office. f) END VERTICAL LINING: PURPOSE: To reline the damaged portion of the heating wall of Pusher Side / Coke side as per the requirement, after dismantling the damaged portion and to bring back the ovens in to operating circuit. INSTRUCTIONS: 1. Abbreviations Used: 1) C/S Coke Side 2) D/W Dummy Wall 3) H/W Heating Wall 4) P/S Pusher Side 5) C/S Coke Side 2. The job is carried out at a time on single heating wall either on Pusher Side or Coke side. 3. For carrying out wall repair side ovens on either side are kept loaded with coke as buffer ovens. Then empty the side ovens of heating wall to be repaired one by one with putting bracing dummy walls at the 2nd vertical and front dummy wall at the opposite side of required repair side. 4. Flue disconnection is done as per requirement of the heating wall to be repaired. Stainless Steel screen wrapped with ceramic fibre blanket and asbestos cloth is inserted through the charging hole on C/S or P/S depending up on the location of repair. 5. Removal of the doors of two ovens is done one by one. Ceramic fibre blanket is fixed on side heating walls up to the flues to be repaired. Blanket fixing done along with the scaffolding bench installation. 6. Removal of door frames, stand pipes, sole plate is done by mechanical and ladder fixing is done. 7. Dismantling of heating wall is done as follows: 7.1 Heating wall dismantling is started after putting the asbestos balls in to vertical flues.
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7.2 Dismantling is done up to the roof level with blanket fixing and jack fixing at 81C& 79C. 7.3 Further dismantling is done up to 71C. After removal of 71 course ceramic blanket piece is dropped in to the base of each vertical in order to protect the debris going inside the port holes. 7.4. Further dismantling is carried out with blanketing and jack fixing up to 10
th
course.
7.5. During dismantling, the dimensions of old heating wall of both ovens are taken after a gap of every 10 layers. 7.6. During dismantling following four types of jacks are fixed at six places of one meter height difference at every alternate flue. i) Oven to oven jacks in old heating wall ii) Wall to wall jacks iii) Old H/W to flash plate jacks iv) Flash plate to side heating wall 7.7. Further dismantling of end vertical is done up to the 7th course and in rest portion further dismantling is done as per requirement. Fused and cracked port holes are repaired. 8. Sole dismantling is done as per requirement. If complete sole is to be relined then sole dismantling is done up to the 16th flue. 9. After completion of flash plate alignment, lining is done up to the 9th course.The port holes are cleaned with ejector as wall as manually. 10. The burners are poked from bottom and cleaned. After wards, the burners are grouted with slurry silica mortar mixed with 10% sodium silicate. 11. After completion of al the cleaning activities, the relining is started. The brick work of 10th course is laid on 1mm thick paper so as to give a sliding joint. Dimensions of heating wall and both ovens are measured and adjusted accordingly. 12. After the lining is of 14th course, one metallic plate is kept and asbestos cloth will lifting arrangement (parachute) is placed on the plate. After lining of five more layers one moving metallic plate is provided which will be lifted along with the lining of 10 layers. 13. During lining honey comb dummy wall are erected at alternate partitions and inside dummy walls at the old and new brick work joint and front D/W are erected. 14. After completion of 70th course metal plates are removed and cleaning of all vertical flues from the top. 15. Further lining is done up to 71a course and then a permanite sheet is fixed and further lining is done up to 6b course, again a pemanite sheet is fixed. Further lining up to 9b course is done. 16. The oven is handed over for heating after puncturing the permanite sheets.
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17. After all the flue connections, protective screen is removed and lining is done up to 85th course, door frame is fixed and flash plate grouting is done. 18. Inside bracing dummy wall of opposite end are removed and sole dismantling is done if full sole is to be relined. 19. Honey comb dummy wall is removed one by one oven and sole lining is done as per requirement. 20. After visual joint inspection with operation personnel the ovens are handed over to operation for sole cleaning and charging. Before charging of oven, oven hand over protocol (Ref.QMS/R/CRG/M/05) is made. 21. Regenerator cleaning is done after charging with metal strips and compressed air.
22. The progress of job being carried out is recorded by the shift manager in the daily progress register (Capital Repair – QMS/R/CRG/R/03) kept at CRG site office. f) FULL HEATING WALL LINING: PURPOSE: If full heating wall is damaged then the oven cannot be operated. Then full heating wall lining is being done. INSTRUCTIONS: 1. One heating wall is repaired at a time. It means that two ovens are kept under repair. 2. Dismantling is carried out from the oven top brick work in the area of charging car track,above both side ovens of heating wall to be repaired and bridge fixing is done to support rail track at heating wall on pusher side and coke side. 3. One oven on either side of the ovens to be repaired are kept loaded with coke and the ovens are sealed. 4. After shutdown of the ovens, the stand pipes are removed by the mechanical section. 5. One wall on either side is maintained at a temperature of 800 +/- 50 degree centigrade. 6. Dismantling the deck and fire clay flue pipes is done and jacks at appropriate flue positions are fixed. Before dismantling fire clay flue pipes asbestos plugs are inserted in to the flues. 7. Doors of the ovens to be repaired are removed one by one on both sides and blanketing of side heating walls is done up to 4th flue along with fixing of scaffolding benches. . 8. Door frames of ovens to be repaired are removed and ladder fixing is done. Locking of flash plates is done.
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9. HEATING WALL DISMANTLING IS STARTED FROM OVEN TOP AS FOLLOWS: 9.1 Dismantling is done up to 70th course with blanketing and jack fixing as per the scheme given at table no.1. Blankets are dropped in to the base of all vertical flues. TABLE NO.-1
9.2 Flash plate which needs not to be changed is cleaned along with dismantling. 9.3 Dismantling is continued up to 13th course. Further dismantling of heating wall up to 10th course is done very carefully to avoid debris going in side the inclined flue and checkers. 9.4 Further dismantling below 10th course is done as per requirement. Fused and cracked ports are repaired. Dismantling of both sides i.e 1st and 32 nd flue is done up to 7th course for flash plate alignment. Flash plate is changed as per requirement. 9.5 Sole bricks are dismantled compulsorily. After flash plate alignment, lining is continued. 10. Then lining is done up to 9Th course. Then port holes are cleaned by vacuum cleaner and manually. Burners are cleaned by poking from bottom followed by grouting with silica mortar mixed with 10% sodium silicate. 11. Further lining is continued as per drawing. 12.The brick work of 10th course is laid on 1mm thick paper so as to give a sliding joint. 13. Both sides the brick work at end is kept 65mm (decided after observing the expansion of recently repaired walls away from flash plate in order to keep provision for expansion. Dimensions of the heating wall and oven widths are measured and adjusted accordingly. 14. After every 10 layers lining, honey comb dummy walls are erected at verticals no. 2, 5, 8, 11, 14, 17, 20, 23, 26, 29. Front dummy walls are erected on all four sides. 15. One plate is provided on all the vertical partitions at the 14th course to avoid the debris falling in to the port holes. Asbestos cloth with lifting arrangement (parachute) is placed on the plate. Another moving plate is provided on all vertical partitions which will be lifted along with the lining of every 10 courses and cleaned.
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16. After completion of lining up to 67th course the top plate is removed after cleaning and the bottom plate which was at 14th course is removed after 70 th course lining. All the port holes are cleaned manually from top and position of loose bricks which are kept on 10th course are checked.
17. Lining of 71 and 71a course is done.
18.1 Cleaning of all vertical flues is done with vacuum cleaner from top. 18.2 Permanente sheet is fixed above the flue openings between 71a and 72 courses and again at 6b course. These sheets are punctured from oven top before flue connections. 19. Further lining is completed up to oven roof followed by lining of oven top up to 9b course and charging holes, AP base lining up to 82nd course is done. 20. The oven is handed over for heating. 21. After the connection of all vertical flues to the heating system, the supporting bridge is removed and balance lining of heating wall and oven top lining up to 85th course is done. 22. Door frame erection and alignment is done by mechanical section. 23. Flash Plate grouting is done and pointing between flash plate and brick work, door frame and flash plate are done. 24. Lining of upper lintel and erection of stand pipe and goose neck is done. 25. Honey comb walls are removed through a window on a front dummy wall from both pusher and coke side in both ovens one after the other. 26. After removal of all inside honey comb dummy walls front dummy walls are removed and doors fixed.. 27. After visual joint inspection with operation personnel the ovens are handed over to operation for sole cleaning and charging. Before charging of oven one hand over protocol is made, (Ref. QMS/R/CRG/M/05). 28. Regenerator cleaning is done after charging with metal strips and compressed air. 29.The progress of job being carried out is recorded by the shift manager in the daily progress register (Capital Repair – QMS/R/CRG/R/03) kept at CRG site office.
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g) COKE OVEN BATTERY REFRACTORY INSPECTION: PURPOSE:
To determine the condition of Battery refractory‟s to note the damages and undertake
repairs.
PROCEDURE: 1. Silica brick wall of Coke Oven is inspected after pushing in empty condition. The oven wall and sole condition is noted. Inspection is done as per pushing schedule such that all the ovens are inspected once in a year. 2. Coke oven door inspection is done at door repair station daily for the doors which are brought out from oven for repair. 3. Oven top inspection includes visual inspection of hatch rings, stand pipe and its base, inspection eye blocks and oven top lining. The oven top area is inspected on daily basis along with operation personnel and defects noticed if any are recorded in the daily job plan register of individual batteries. The daily job plan register is kept at respective battery in charge room. 4. Battery buttress wall and upper and bottom lintel brick work inspection is done from 5M platform visually once in a year. 5. Regenerator face walls are inspected for cracks and open brick joints once in a year. If required visual inspection is done with the help of battery operated torch light.
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RECOMMENDATIONS:BEFORE TAKING INTO OPERATION:-
1] Expansion in silica brick has to be taken care of tactfully for enhancing battery life. 2] During laying of Silica brickwork , application of graphite paper and glycerin at the expansion joints has to be done with utmost care. 3] Sufficient gap between heating wall and flash plate has to be provided before heating up. 4] During heating up , the brickwork expands and touches the flash plate on both sides (pusher side and coke side).The load starts increasing on the tie rods and backstays. From this moment onwards, load has to be checked on tie rods and bulk stays at Small intervals to take care on any unwanted stress on brickwork. 5] Once the heating up is completed, final load has to be adjusted. 6] After taking the battery into operation, load checking has to be checked periodically and necessary adjustments to be carried out. IN RUNNING BATTERY:1] Abrupt contraction/expansion of Silica brick work may take place locally either due to sudden temperature fluctuation (external factor) or phase transition (internal factor) leading to thermal shock and premature failure of Silica brickwork. 2] Wet repair methods like semi dry guniting (7 – 9 % water content) and KTM-3 welding ( 50% water content) should be avoided. These may be used in case no other alternative is available. 3] Zero expansion brick (Fused Silica) may be used in place of conventional Silica bricks for lining of end verticals during end vertical/full wall repair. 4] Possibility of incorporating new technologies involving dry methods for welding/guniting may be looked into. 5] Avoid exposure of heating wall to atmosphere for long periods. This can be done by minimizing time interval between door opening and closing. Steps to minimize time interval between lid opening and closing may also be tried out.
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CONCLUSION Coke oven batteries are one of the vital links in the production chain of an integrated steel plant. It is sometimes referred to as the nerve centre for an integrated steel plant . They not only provide coke, a major input for blast furnace but also supply the all important coke oven gas as fuel for the different shop. In view of the above, the health and life of coke oven batteries are very important for attaining high production level in an integrated steel plant. Service life of coke oven battery depends on implementation of systematic preventive maintenance & repair based on inspection report of the battery. Adherence to the maintenance norms can be major contributing factor to ensure trouble free and long service life of the batteries.
So, if we execute regularly all maintenance activities in proper time, based on inspection report and close monitoring & control and follow all instructions of maintenance we can enhance the service life service life of our battery.
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REMARKS
Place: Date:
( Abhijit Sur ) Signature of Project Guide
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