HOT REPAIRS OF COKE OVEN BATTERIES AT CHINA PLANTS OF HANGZHOU AND TANGSHAN

Hot Repair of Coke Oven Battery № 2 at Steel Plant of Hangzhou Iron & Steel Group Company in Hangzhou, Zhejiang

Works on coke oven battery №2 were conducted in two stages: November 2008 - May 2009 and September 2009 - January 2010. Battery № 2 was constructed in 1976, i.e. at the start of repair its service life was 33 years. Battery inspection was conducted by the specialists of LLC "OKOS" A.A. Vinnikov and V.P. Petryakov in December 2006 together with the engineers of the Chinese company "Zhong Hong Xin". General specifications of coke oven battery №2 at Steel Plant of Hangzhou Iron & Steel Group Company are as follows:

There is only one collecting gasmain on the battery from the machine side. Collector for smokeless ovens charging is located on the coke side, very massive, like collecting gasmain.

Coke oven battery with CO under firing, but with non-drawer type regenerators. Such coke oven batteries are most repairable and maintaining of the desired temperature in the repair zone is achieved without any problems. By construction, coke oven battery is almost the most common of China, built in the 70s of the last century. Many plants in China have similar batteries with small differences. Since 1995, repairs of heating walls brickwork were executed by method of replacing of defective sections with new silica brick by the efforts of the plant. Repeatability of repairs at some ovens reached 11 times in 10 years. There has been a shift of repairable sites from the 1-2^nd heating flues up to the 6^th and even the 11^th to the depth of chamber in the process of repairs. Repairs were carried out mainly from the machine side in 1-20 courses.

High level of the battery operation is worth mentioning. Coke ovens pushing schedules are observed, after each oven’s charging all gas leakages from the doors are sealed. The amperage level during pushing of coke, as well as time of pushing and charging are fixed properly and clearly. Coke ovens pushing schedule observance coefficient amounted to K1 = 0.99, K2 = 1.0, K3 = 0.99.

Significant non-uniformity of coke ovens pushing amperage was observed at the battery prior to repair. Normal amperage of ovens pushing 140-150 A was observed at certain ovens only. Excess graphite on the walls of oven chambers interfered with coke passage at its pushing, creating severe load on the chambers’ wall and destroying them intensively. Average mean of coke pushing amperage from the ovens amounted to 225A with a minimum value of 120 A and maximum 500A (scale on the ampere meter 500A).

There has been massive coke "sticking" at ovens pushing. The main reason for coke "sticking" being the excess graphite on the walls of oven chambers. Practice shows that deep bricks destructions occur under the large plaque – shaped graphite deposits. In the presence of such defects long-term performance of coke oven battery without overhaul maintenance can not be guaranteed.

Refractory brickwork of heating walls had serious defects common to all ovens from coke and machine sides of the battery:

- Cracks up to 15 mm in 1-6 heating flues;

- Cracks up to 10 mm in 25-28 heating flues;

- Local deformations of heating walls;

- Cracks with brickwork displacement and formation of counter ledge;

- Chippings and bricks flaking to the depth of 40 mm at 1-6 heating flues;

- Net cracks of large areas of chambers’ walls;

- A large cleavage of all roofing brick shapes and chippings of charging holes roofing brick shapes;

- Destruction of 3-5 charging holes brickwork courses and their withdrawal to the chamber up to 50 mm in the zone of 1, 2, 3 charging holes;

- Through holes on the 1-11 heating flues;

- Leakages of raw coke oven gas in the inspection holes of many heating flues;

- Large deposits of graphite on the surface of brickwork.

Condition of regenerators and sole level channels brickwork was good enough allowing further long operation. Cleaning and replacement of 1-2 upper courses of checker brickwork. Most anchor columns were in emergency condition and required immediate replacement.

Virtually all anchor columns had significant deflection and deformation. Deflection of anchor columns and load spring reinforcement nodes are represented in the table.

Pitch of Anchor Columns Deflection and Load on the Spring Units of Anchorage

Some inconformity between high level of operation and emergency condition of anchor columns was clearly conspicuous. The reason for this were disorders in China and at the factory in 1989, when the plant did not work for a few days, the workers left the shop. Coke oven gas burning at the doors began, leading to deformation of anchor columns.

Earlier the plant discussed complete rebricking of the battery and the project of such repair was prepared. Hot repair was made out of the following considerations.

1. Coke oven battery will not be shut for repair in its full scope which in cold variant lasts about 12 months. Only worn out oven chambers are taken for repair,  the rest of the chambers are involved in coke production.
2. Great economic effect is achieved by reducing the need in refractories, materials and equipment for hot repair in comparison to cold repair. Depending on the scope of repairs and standard size of coke oven battery, the cost of hot repair makes 30-40% of the cost of similar cold repair.
3. The plant is located near the residential area of Hangzhou, which has cultural and touristic value. City officials planned to eliminate the coke production completely within five years, in this case it was inexpedient to spend much money on a new battery.

The personnel of the technical department initially tried to interfere with the process of repair actively, which was not always well-matched creating necessity to justify repair methods in practice making it a specific nature of repair at Hangzhou Plant. Thus, the technical department personnel demanded verticality of oven chambers’ walls as with the new brickwork, although the heating walls inclination at the buttresses was ~ 50 mm. So we had to prove that in this case it was not possible to make perfectly vertical heating walls. Shop superintendent personally supervised repair works without days off throughout 10.5 months.

In the period from November 2008 to May 2009 - 11 heating walls were repaired completely, 8 heating walls were rebricked up to the depth of 6 heating flues from machine and coke sides (Fig.1). Within the period of September 2009 - January 2010 - four heating walls were completely rebricked, 20 heating walls were rebricked to the depth of  6 heating flues from machine and coke sides. All in all the battery was completely renovated (all 43 heating walls), 708 (58.8 %) heating flues of 1204 were rebricked: 15 heating walls were completely rebricked, 28 heating walls were rebricked to the depth of  6 heating flues from machine and coke sides.

Complete rebricking of walls was carried out by one heating wall, the temperature in heating flues of neighboring heating walls  being maintained within 750-850°C. Coke ovens adjacent to the repair site remained with coke throughout the repair. Semi buffer ovens were pushed for periods of 24 and 21 hours. Continuation of rebricking of one heating wall was 28 days within the first months of repair due to low-skilled mechanics and refractory-men and was later reduced to 18 days. Chinese experts involved in repairs did not have any experience of such work hence their training was necessary. Training began only with the beginning of repair and included theoretical course as well as (classroom training). The quality and the speed of work improved after training. However, the workers contingent periodically changed in the course of repair (by 10-15 people partially) that had to be trained again. Rebricking of the end heating flues by method of hot-repair was made up to the depth of 6 heating flues, two heating walls being repaired simultaneously. Bracing dummy walls (jacks) "flash plate - brickwork" were installed at dismantling. Ovens adjacent to repair site were left with coke, semibiffer ovens being pushed on the 24 and 21 h coking period, the mean average duration of repair being 10-12 days.

Warming of renovated brickwork as in the case of complete repair and in the case of rebricking up to the depth of six heating flues was carried out due to heat conduction and radiant heat exchange from the adjacent heated heating walls and the rest part of repaired heating walls.

Joint of new and old brickwork was performed with bonding of bricks in each course. Though, in some heating walls bonding was not always possible in each course, but in general, this condition was met. After heating the joint was not sealed, gas leakages  at the junction disappearing after 2-3 ovens’ pushings.

At rebricking to the depth of six vertical flues all repaired heating walls were included into heating in two days, at complete rebricking of the heating wall - in three days. After removal of spacer joints from the chambers  the renovated ovens were charged. The first charging was not full - the first and the second hopper of charging car were charged. Subsequent charging increased and full charging was made after 3-4 ovens’ turn overs. First ovens’ turn over was 24 hours, subsequent turn overs - 21 hour and at that period of coking ovens were set into series. Furthermore, two upper courses of regenerator’s checker brickwork were replaced to the depth of 3 to 6 m from the front.

Buttress walls were rebricked together with silica buttresses,  though on fireclay buttresses only facades were renovated. Reinforcing beams were fixed on to the facades of buttresses after heating of end heating walls.

Defective flash plates, frames, anchor columns, (upper part of servicing platform) were replaced during repair of heating walls. Totally 19 anchor columns were replaced. Temporary supports on columns adjacent to anchor columns subject to replacement were mounted and removed at each replacement. Frames were replaced with the use of frame lifter on coke machines, armor and columns changed using hoists.

The number of mechanics in the group was seven people. Repairs on the battery were performed on two sites simultaneously. There was one group dismantling the old brickwork (23 people), one group of refractory – men – layers amounted to  42 persons (12 refractory – men and 30 flunkey workers), divided into two shifts. Disassembling of brickwork was executed at one site – brickwork laying and heating on the other site. Layers could be allocated to help mechanics and dismantling workers to help layers and mechanics. As per the safety requirements dismantling of brickwork was conducted during daylight hours only, though laying of new brickwork was made round the clock..

All repairs were carried out under the direct supervision of the Chief of Repair V.F. Bogdanov and round the clock supervision of LLC "OKOS" specialists: four shifts-in-charge, four instructors-refractory-men and mechanical engineer (at the initial stage of repair).

Special attention was paid to safety requirements at the plant. Battery №2, was working in tandem with Battery №1, each battery having 42 ovens. Pushing schedule was general, in other words, both batteries worked as one battery with one set of machines. Repair could be carried out only during the pushing of ovens on the Battery №1 and cyclic pauses of pushing. At transfer of pushing into Battery №2, repair was stopped. It was somewhat inconvenient at first as it took time to adjust and plan the work in accordance with the schedule of pushing. It was approximately 1.5-3 hours of work and 1.5 hours of break.

Particular attention at the plant was paid to the environmental problems. Batteries are located close to the uptown whereas Hangzhou itself has touristic value. Coke shop is small, only two batteries. Battery №1 is comparatively new, about 5 years old. Smokeless charging system works effectively almost with no emissions. Collector of charging gases exhaustion and installation of gases purification are mounted on the anchor columns from the coke side for smokeless charging. It should be added that dust free coke pushing and  smokeless charging system work rather effectively. The territory of  the shop is kept clean the amount of coke and coal dust being rather insignificant.

Good quality of refractories should also be noted as practically no rejection was required. The quality of thermal insulation material (mullite siliceous roll felt 25 mm) used for pasting of walls of the repair area, was also perfect. All materials were of PRC production.

Repair of Coke Oven Batteries № 1, 2 at HBIS Steel Plant, Urban District of Tangshan, Hebei Province

Repairs at  the HBIS Steel Plant were also performed in two stages : July 2009 - May 2010 and November 2011 - January 2012. Inspection of coke oven batteries was performed by the specialists of LLC "OKOS" in November 2007 in conjunction with the Chinese engineers of " Zhong Hong Xin" company.

General characteristics of the batteries are the following:

There is only one collecting gasmain on the batteries. Massive collector for ovens’ smokeless charging is located on the coke side. The batteries are with bottom supply of coke oven gas, design coking chamber charging is - 30 tons. Commissioning of the battery №1 - 29.01.1987 g, № 2 - 05.07.1988.

Among the design features of coke batteries fireclay ovens roofing can be outlined (show itself to good advantage to silica), which supports the CCC rails (in comparison to supporting heating wall Giprokoks design).

At the time of the inspection  two coke oven chambers of Battery№1 were backfilled and two worked with 28 hours coking period. All chambers of coke ovens at the battery №2 were in operation no information on repair was available. Major defects of oven chambers brickwork – displacement of inspection holes of heating flues, raw gas leakages, inclined flues jamming with bricks’ debris. There were out-of-operation heating flues with complete lack of combustion. Some incurvations and convexities of chambers brickwork, chips and cracks on the head heating flues were marked. Brickwork facades above the flash plates were in unsatisfactory condition, especially around the charging holes and ovens’ heads. Regenerator checker brickwork was is littered up to the height of the top two courses (bricks debris, litter).

Severe deflection of anchor columns was noted (up to 75 mm), which had a negative impact on the safety of brickwork of coke oven batteries. Columns having deflection of 60 mm or more, do not fulfill their reinforcement functions.

Operation level at the plant was modest. Unsatisfactory work of machine room was also noted due to the fact that it was not extended at construction of new coke oven batteries at the plant: it was originally designed for four coke oven batteries, though later two more were built.

All repairs were carried out under the direct supervision of the Chief of repair A.M. Pos and round the clock supervision of LLC "OKOS"  specialists numbering to nine people: four shift supervisors, four instructors - refractory-men and mechanical engineer. Brigade of Chinese workers on average consisted of 30-40 dismantling workers, 65-70 layers, 13-15 mechanics. Layers could be allocated to help mechanics and dismantling workers- to help layers and mechanics.

In the period from July 2009 to May 2010 18 heating walls were fully renovated and 5 heating walls rebricked to the depth of six heating flues from machine and coke sides. For the period of November 2010 - January 2012 34 heating walls were completely renovated, 16 heating walls rebricked to the depth of six heating flues from machine and coke sides.

Thus, during this time the batteries were fully repaired (all 74 heating walls). 52 heating walls were completely rebricked, 21 heating wall was rebricked to the depth of six heating flues from machine and coke sides (Fig.2). Totally 1928 heating flues were rebricked out of 2368 (81.4%).

All flash plates, columns, anchor tie rods and stand pipes were replaced at both batteries. The quality of refractories and materials supplied for repair was good.

It should be noted that good, friendly relations were formed with shop workers in the process of repair based on every assistance from their side.

Currently the first stage of hot repair of coke oven batteries № 1, 2 at Xuanhua Steel Plant (September 2012 - March 2013) has been successfully completed under the supervision of A.M. Pos’. This is the first hot repair of coke oven batteries with the height of ovens chambers 6 m performed by LLC "OKOS" in China.

Thus, LLC "OKOS" together with "Zhong Hong Xin" and "Hua Chen" Ltd. carried out extensive hot repairs of 13 coke oven batteries at seven steel plants of China. Plant specialists praised the quality of repairs. Chief of repairs V.F. Bogdanov was awarded the Honorary Award of Liaoning Province for worthy contribution to the economic and social development of Liaoning Province on the 27^th of September, 2010.