PECULIARITIES OF RENDERING TECHNICAL ASSISTANCE AT VISAKHAPATNAM STEEL PLANT (INDIA) BY LLC «OKOS»

Roizen Leonid Semenovich, Ch. Engineer

Chemarda Nikolai Alexandrovich, Tehn. Advisor of General Director

Cooperation between LLC "OKOS" and Visakhapatnam Steel Plant (VSP) started in the late 1998 with the arrival of a group of specialists to the plant for inspection and issuing of recommendations for normalization of condition and stabilization of operation of Coke Oven Batteries № 1-3, 67 ovens each, with chamber volume of 41.6 m3, underjet system, combined heating - 9, 7 and 6.5 years correspondingly.

All three coke oven batteries worked unsatisfactory due to low operating level of Coke Oven Batteries № 1-3 and critical conditions emerged by the end of 1998.

Cross and longitudinal anchor tie rods and battery reinforcement panels were ineffective that led to formation of cracks damage of the flash plate, divergence of flash plates from refractory brickwork of "shoulders" up to 30-60 mm and subsequent mass destruction of refractory brickwork of head paired heating flues; appearance of a large number of disabled and poor working heating flues and as a consequence complete caving of some heating flues throughout the whole length and taking a large number of ovens out of operation. The number of non-operating ovens by the end of 1998 amounted to 65 (136 working of 201) and the situation continued to be deteriorating.

Deformation of buckstays and brackets of collecting gasmain caused sinking and sludging of collecting gas main on all batteries, which further increased the flows of raw gas into the firing system and its unregulated burning:
In regenerators - fusing of inclined flues zone and regenerators checker brickwork; in the sole channels and flues - with bringing of gas-air valves out of operation and through all leakages of doors, inspection holes and gas risers.

Complex program of a large scope of maintenance and repair work was developed as a result of inspection work to improve the level of operation and prevent further drop in production and destruction of coke oven batteries.

The program consisted of three main stages.

1. The main objective of the first stage –elimination of destructive burning of raw coke oven gas through the cracks and doors’ destruction, stand pipes, "heads" of oven chambers, charging holes of coke oven batteries №1-3, for which a program "Fighting Against Fire" was worked out.

Strategy of repairs, allowing to stop the drop in production and gradually build it up to the level of needs of the plant (VSP) was developed after implementation of the program based on the assessment of the actual state of refractory brickwork and equipment of coke oven batteries and included the following:

- performing of mass-replacement of inoperative elements of reinforcement, door frames, doors, gas take off stand pipes, frames and charging hole lids, gas-air valves of Coke Oven Batteries №1-3 first at working and then on the stopped ovens in proportion to repair of refractory brickwork within a short period of time;
- performing of necessary repairs of the head portion of heating walls with minimal volume of defective chambers rebricking, at batteries №1-3 (repair of the head portion of heating walls on the battery №1 began in March and ended in December 1999);

- performance of complete rebricking of destroyed heating walls on the battery №1;

- replacement of collecting gas main on the coke side of the battery №1 on the area of ​​oven chambers №101-133 with parallel cleaning,  partial repair and lifting of collecting gas main on the machine side.

2. At the second stage of repair a full cold repair of the upper structure of Coke Oven Battery №2 with partial repair of inclined flues zone, regenerators zone and flues of the sole level was performed within 11 months. Flash plates, half-columns, reinforcement units, were selectively changed prior to heating walls lining. Upper cross and longitudinal anchorage was completely replaced. Structural changes increasing the strength of anchorage elements and protection from fire exposure and high temperatures were implemented in the process of repair, as well as changes aimed at improving the technological mode of operation of the battery top equipment: gas take off stand pipes, collecting gas mains and outlet pipelines of direct coke oven gas.

Development of coke oven battery production capacity №2 was carried out under the accelerated schedule. First coke was pushed by March 31, 2001.

3. The third stage of repairs began in August 2001 with hot rebricking of the head part of heating walls to the depth of 4-10 heating flues on coke oven battery №3. The process of destruction and deformation of heating walls on coke oven battery №3 was slowed down by the improvement of maintenance level and performance of preventive maintenance at the first stage, but was not stopped completely. At the same time to the beginning of 2002 condition of refractory brickwork under the middle charging holes on coke oven battery №1 began to deteriorate dramatically.

Schedule of repairs allowing to complete the full rebricking of all the rest heating walls by method of hot repairs under the methodology of LLC "OKOS" was composed and implemented in order to maintain the production at the required level and to improve the condition of brickwork fund of coke battery №1 (at least 250 pushings per day). Flash-plates, half-columns, anchor ties, risers and gas-air valves were replaced selectively during repairs. Repair of one heating wall throughout the entire length in hot climatic conditions of India took 32-33 days.

Management of the plant took a correct view of the current situation and adopted the program of repairs, mobilizing human and material resources for its implementation. Today, it can be noted that such strategy of repairs was chosen correctly. Restoration works began in March 1999, after signing the contract between VSP, TPE "Tyazhpromexport" and LLC "OKOS". Increase of coke production began already in July 1999 with the commissioning of the first repaired oven chambers of the battery №1 and replacement of worn out reinforcement on battery №3.

Successful implementation of the planned technical and technological activities in all stages allowed to recover technical condition of coke oven batteries at a minimum losses of coke production. (For more information, see report of: Chemarda N.A., A.A. Vinnikov, P.K. Singh, N. Saho, Rao D.N. Joint operation of the specialists of Visakhapatnam Steel Plant and LLC "Ogneuporkoksservis" // Coke and Chemistry /Magazine/. 2003. № 3. Pp. 24-31).

Signing the contract for technical assistance on coke production №VSP/WC/CO & CCP/57086-0./2008-09/13227 dated 26.04.2008 became the next milestone in the development of relations between LLC "OKOS" and Visakhapatnam Steel Plant (VSP).

Duration of the contract was two years (from the 24 July 2008 up to 24 July 2010). The period of this contract coincided with the construction of the third blast furnace complex at the plant, new, second sinter plant, as well as with the construction and commissioning of the fourth coke oven battery with chamber volume 41.6 m3, lower supply of heating gas and combined heating.

At this time, coke production work was relatively stable, but the reserve factor received during the years of 1998-2005, began reducing the campaign. The age of coke oven batteries №1, 2 and 3 was 19, 17 and 16 years correspondingly.

Coke Oven Battery №1. Condition of ovens fund  was operative despite of the fact that the average working life of heating walls rebricked by method of hot repairs of LLC "OKOS" approached to ten years, and for 16 heating walls even exceeded this warranty period (under the contract). Ovens’ chambers №116, 117, 133, having deformation of heating walls due to coke sticking, were not fully charged  (2.5 bin). There was a need for urgent replacement of support beams under the tracks of door extracting car throughout the entire length of the service platform from the coke side  threatening a major accident though the battery reconstruction was planned by VSP only in 2014.

As site preparation required considerable time and money the specialists of LLC "OKOS" together with the Capital Repairs Group (CRG) developed and implemented a multistage program envisaging the following:

- temporary reinforcement of support beams of door extracting car tracks at minimal costs;

- full replacement of service platform throughout the entire length of the site, taking into account the above-level deformation of anchor columns in some areas of the battery from the coke side.

Complexity of the platform replacement was accounted for selective rebricking of heating walls having maximum deformation and fracture, with adjustment of their sizes (length) under the dimensions of the adjacent old heating walls tolerances with temperature rise tolerances (carried out not by production line method with observation of the design dimensions). Otherwise flash plates matching, connecting the old and new heating walls, was impossible. In the course of time new heating walls got additional and uneven growth, whereby door extracting car tracks had to be changed in a complex curved line avoiding outstanding  anchor columns at some areas (up to 60 mm or more) to prevent contact with anchor columns.

Service platform had to be moved aside to solve this problem within the limits not interfering with the travel of coke car, along with the strengthening of supporting structures of anchor columns and frame walls.

The preparation of each new site for platform replacement at 10 ovens took 1-2 days. The works on  removal of constructions of the old platform and installation of new sections were performed with a stop of coke pushing at coke oven battery №1 from 10 to 18-20 hours (8-10 hours). As a result of careful preparation and precision of new sections the platform was replaced within 23 days.

Coke oven battery №2. Condition of ovens fund was operating. There were no "sick" and non-serial ovens. Condition of gas collecting main, service platforms and anchorage was quite satisfactory. The most stable unit of the old batteries.

Coke oven battery №3. Condition of supporting beams of servicing platform and support beams of door extracting car was unsatisfactory. Complete replacement of service platform was performed in August - September 2009.

Condition of collecting gasmains was unsatisfactory. Specialists of LLC "OKOS" carried out a supervision over replacement of collecting gas mains №1 and 2 with platforms, communications and gas take off stand pipes from the coke side and major overhaul of collecting gasmains and stand pipes from the machine side with straightening of crossover gas mains. Specific feature of these works was inevitable loss of production.

For example, during October 2009 collecting gasmain №2 was prepared for stop from the coke side of battery №3 for its complete replacement and collecting gasmain №2 from machine side for straightening and repair. Work was carried out with shut down of oven chambers № 334-367. All chambers at site 334-367 were previously discharged from coke, sole level was cleaned. All ovens’ doors were removed and "face walls" installed (front spacers) of fireclay normal. Brick spacer walls were installed in buffer ovens 334 and 335 on holes and additional spacer walls  at 2, 4, 29 and 30 heating flues. Temperature in control heating flues of the repair site was maintained within the range of 1000-1100°C.

Thorough replacement of all brackets and trolleys of door extracting car was carried out at the same site additionally. Works were carried out only at day shift at six-day working week. All dismantled doors were repaired.

Collecting gasmains were stopped at 18.11.2009 and re-commissioned on 28.12.2009, after 40 days. Works were carried out professionally and efficiently.

CRG refractory group performed unhurried repairs on rebricking of head heating flues (up to six), from machine and coke sides (and reached 100% up to August 2010) despite the fact that beginning of complete rebricking of coke oven battery №3 at VSP was planned to start in October 2008.

Coke oven battery № 4. Coke oven battery № 4 was commissioned in April 2009. A number of significant problems requiring immediate resolution appeared with its start up.

One of the main problems of coke production was the excess (10-12 times higher than normal) content of phenol in wastewater after biochemical plant (BCP). The excess content of phenols decreased down to 1.5-3 times from the normal content and reduction of ammonia water consumption by coke oven batteries № 1-4 (up to 25 m3/h) took place as a result of solution to the problem worked out and proposed by LLC "OKOS".

Normalization of ovens charging level of coke oven battery № 4 with blend and optimization of temperature mode allowed obtaining the required parameters on the content of phenols in wastewater.

A positive role was also played by gradual adaptation of phenol-destructing cultures of biochemical plant to new conditions and increase in degree of purification, which allowed to strengthen achieved results despite the fact that the BCP worked beyond its capacity. Construction of the second part of BCP designed for fundamental solution of this problem was carried out with a long delay.

The second problem was limited capacity of gas treatment plant (by-product recovery shop) on coke gas 120000 m3 / h taking into account a 20% power capacity - 144 000 m3/h. At daily discharge of 308 ovens and content of volatile substances in the blend ~ 26.8% by-product plant operated at its limit capabilities. Specialists of LLC "OKOS" studied the problem of maximum performance dependence of coke production from the volatile content in the blend supplied to coking, issued recommendations on the distribution of coke for each battery separately in accordance with their technical condition and a need to develop capacity of coke oven battery № 4.

The main problem for coke oven battery № 4 proper was the regulation of buildups and maintaining of the set pressure in gas collecting mains.

The buildup of pressure occurred within 11 - 28 mm of water column (110-280 Pa) at rated 14 mm of water column (140 Pa), that is, 17 versus ± 1 mm of water column according to operational regulations. Pressure control system in gas collecting mains and the buildup of pressure between pusher and coke sides functioned unsatisfactorily. All these factors gave rise to the following new problems:

- de-carbonization of refractory lining and appearance of unregulated cross leakages of raw coke oven gas in head heating flues of heating walls;

- significant gassing through the doors, which in turn caused great claims to doors, not providing the required gas sealing and loosing in this indicator to doors of the old design, having besides a double frame with asbestos rope sealing gasket.

By joint efforts of LLC "OKOS" and VSP instrumentation service, the limits of pressure buildup were  decreased to 5 mm of water column (50 Pa), but the required by operational regulations parameter ± 1 mm of water column was not achieved. However, even this improvement did not allow to reduce the refractory lining decarbonization. The battery switching on to heating with a mixture of blast furnace and coke oven gases allowed to increase the temperature of the under roofing space, which is usually observed with the "poor" gas. Already after one month under roofing and suspended graphite was obtained, which eliminated cross leakages of raw gas in end heating flues.

Gassing of doors decreased, but was not completely eliminated. Besides the mentioned reason (the buildup of pressure in the gas collecting mains) it was necessary to solve the problem of proper regulation of load distribution on the door membrane sealing knives.

Although the design of doors of Simplex system with a membrane sealing frame set on coke oven battery № 4 was exceptionally successful, but no door was regulated according to the requirements of the instructions. Regulation was carried out unskillfully, in a hurry before commissioning. As a result, almost all doors had up to 50% compression springs, which completely or partially lost their elasticity properties. Massive replacement of springs and skilled regulation of each door were required. However, VSP coke production specialists wanted to obtain the effect without changing anything in their method of regulation and not spending on buying new springs.

The lack of calorimeter at coke oven battery №4 did not allow to regulate the temperature mode taking into account changes in gas calorific values, which is especially important when switching the battery on to heating with a mixture of blast furnace and coke oven gases.

The next difficulty faced by LLC "OKOS" specialists, management of coke oven and by-product plant was a problem of accelerated  destruction of refractory lining of head heating flues of coke oven battery №4 after four months of operation. Based on the survey two main reasons for the occurrence of lining defects were discovered.

The first defect was abrasions of smooth top layer of wall bricks, the so-called "jacket" - by different parts of the pusher ram, mostly by the lower part of the pusher ram head and the top edge of the pusher ram gear rack. Traces of the pusher ram head were basically met at the first jamb bricks. Most notably their devastating impact was observed on the material vertical joints between the first and second jamb bricks (25-30 mm). Abrasions from the rack were mostly found in 9-10 courses from its lower part  and 18-20 courses from the top of the rack. The length of such horizontal abrasions was from the beginning of the second to the third, sometimes the fourth jamb brick, with depths ranging from 3 to 7 mm and width from 10-15 mm to 50 mm.

Traces from mechanical impact of pusher ram on oven lining were found out only from the pusher side. Such defects were not observed from the coke side. The causes of these defects were as follows:

- incorrect installation (positioning) of pusher ram against discharged oven.

- significant deviations from the vertical position of  (+20 ÷ -35 mm ) of the head and the rack of the pusher car during coke discharge and ram return. Reduction of these deviations can be regulated by front guides, side and supporting rollers, where there were significant gaps. The measures for adjustment of pusher rams, brake mechanisms, movement of pushers and straightening of tracks used at some areas of the battery were suggested.

After the detection of defects (abrasions) of wall brick lining, inflicted by pusher rams at coke oven battery № 4 by specialists of LLC "OKOS" a random inspection of the status of refractory brickwork was conducted at coke oven batteries № 1-3 (6-10 ovens at each battery).

Traces of mechanical effect of pusher ram on the lining of heating flues were found at all coke oven batteries.

It should be noted that the degree of destruction of the lining was primarily dependent on the technical state of the pusher ram and then from its accurate setting by the axis of the discharged oven. Thus, for example, the head of the pusher ram №2 had a significant inclination to the left, locating  almost diagonally across the doorway and the main task of the coke pusher operator was to submit a pusher ram in the oven without hitting the door frame or flash plate with lower or upper part of pusher ram head. Installation of the pusher ram by the oven axis was out of the question.

A thorough inspection of the technical condition of coke pushers № 1-6 was performed; conclusions and suggestions to eliminate the identified defects were sent to the HOD of Coke Oven and By-Product Plant.

The second type of defects was the presence of hairline cracks in jamb bricks (1 -2- and 31st - 32nd ), followed by their subsequent opening up to 10-15 mm and more with the formation of chips and cavities.

The observations showed that the rate of development of this type of defects was considerably ahead of the four - month age of coke oven battery № 4 and corresponded to 3 -4 -year battery life.

In all inspected cells vertical cracks were observed (sometimes oblique) on the first jamb bricks in quantity from one to three located mainly from the first to the seventh course from the oven’s sole  with the opening of edges from hair cracks (0.3 mm ) to 7-10 mm. The presence of cracks of the second jamb bricks in the same courses of lining was observed, but their number and width of edges opening was considerably less. The top of the oven also had similar cracks in the courses from the first to the fourth from oven’s roofing.

With further development of cracks the chipping and cavities of various sizes up to 35 mm depth took place. Such cracks and chippings were also observed from the coke side, though their depth  was much more significant (up to 80 mm), but due to the absence of lining defects caused by coke pusher ram, the end heating flues from the coke side looked more attractive. Causes of development of jamb brick cracks:

- air leakages due to poor sealing of face walls ("face walls"), installed in doorways, at long operation of  the battery in a constant heating mode without charging with blend practically being at hot conservation (more than 2 months.)

- sudden temperature fluctuations at end heating flues at switching on to the permanent heating regime;

- low-quality refractory bricks;

- unsatisfactory operation of regulators maintaining the predetermined pressure in gas collecting mains and differential pressure regulators between gas collecting mains from pusher and coke sides.

Lack of benchmarks for measuring the expansion and battery lining growth in the area of units F4 (at the level of oven soles) did not allow to analyze the situation fully and causes of the formed mass defects of lining. For several months, much effort had been concentrated on regulation of the load level and reducing gassing and dust emissions during charging of blend in the ovens of COB № 4. Permanent underchargings of oven chambers at high temperatures in oven under roofing led to intense pyrolyses of raw coke oven gas and affected the quality of tar.

The main reason for undercharging was the human factor. At coke pusher №6 a bin for under leveling bar racking was mounted three times less than usual due to the presence of joint automatic program of exact dosage of blend by charging car and coke pusher leveling bar operation.

This program, except for the rare cases, did not work, and the whole process was carried out manually. In order not to travel often to SKIP, coke pusher car operator simply reduced the number of leveling bar strokes (often one long and one short). Therefore, underchargings between holes and "racks" in holes themselves took place. At full connivance of engineers at all levels there was only one solution - to engage and debug the automation system.

Improved nozzle design suggested by the specialists of LLC "OKOS" allowed to increase the efficiency of hydro injection operation and reduce gassing and dust emissions during charging of blend to the required levels of environmental indices, and reduce the pressure of ammonia water after booster pumps by 7 psig ( 0.7 MPa) to 18 versus 25 psig ( 1.8 vs. 2.5 MPa).

Common problems that influence negatively on operation of all coke oven batteries

Frequent violation of the level of charging of oven chambers of COB № 1-4 in the conditions of coal blend high humidity due to monsoons and heavy rains.

Cutting of blast furnace gas supply for heating of batteries for a long time and switching of coke oven batteries №3 and 4 for heating with coke oven gas and back to mixed gas due to unscheduled (emergency) shutdowns of blast furnaces.

Violation of temperature and hydraulic modes of coke oven batteries and frequent insignificant changes of coking periods at low blend balance at coal yard. The system for determining the silo filling of the Coal Preparation Plant and coal towers of coke oven batteries had been erected long ago, but was not brought to operating condition. Measuring of the level of blend in the coal towers with a rope often gives a distorted result.

Frequent shutdowns of discharge caused by strikes of the operation personnel.

Low technological and performance discipline of operation personnel.

Frequent failure of equipment and coke  machines due to mechanical and electrical reasons, because of the failure of current and capital repairs.

Democracy, which VSP is so proud of, frequently was the cause of unsatisfactory work of the personnel. The administrative officer is not entitled to demand from the executor to perform this or that particular job. Control can only be realized through multiple convictions or explanation that do not always bring the desired results. In the presence of a huge number of workers the most necessary technological operations of charging, planning, removal of coke falls can not be performed or performed with considerable violations.

For example, on 25.11.2009 at coke pushing in the area of coke ovens №434-460 occurred large falls of coke on to the platform at pusher side of the battery №4. In the presence of the personnel the burning coke was not removed from the backstays, but was abandoned for a long time waiting for its removal by scraper conveyor, which was out of order. As a result, all backstays in this area were significantly burned near units D1. The disassembly of intermediate anchor units D1 was required on all these backstays, checking their status in unloaded condition and selective replacement of springs having a residual deformation.

Successful cooperation of JSC "OKOS " and Vizakhapatnam Steel Plant CO&CCP had continued signing the contract № VSP / WC / AGT/4969/2010-2011 dated 30.11.2010 for relining of top structures of heating walls of coke oven battery № 3 by the method of hot repair.

In the period from 18.01.2011 to 16.11.2012 at coke oven battery № 3 thirty eight heating walls were repaired throughout the entire length. Works were carried out by two fronts: one front was from the buttress to the middle of the battery, the second one - from the middle to another buttress. Heating walls were repaired one by one. By the Customer’s decision took on 20.11.2012 the work at battery № 3 was temporarily suspended to provide repair of 16 heating walls for the entire length and two end-flues at coke oven battery №1 and then it was planned to continue repair at coke oven battery №3