India's largest coal handling agency - Mjunction

More documents

Recommendations

Info

Expert Speak Internal lining work of bridge pipe is in progress in coke oven plant bricks started coming out one by one and the castable, which took support from these bricks, collapsed gradually, thereby exposing the ceramic fibre board layers as well as the lower metallic edge of the cast iron door to direct heat. The lower edge and some portion of the exposed rib started melting down. The molten iron falling on the lower doors started damaging them in turn. 2) Lower Oven Doors The damage and melting down of the upper oven doors spread extensively to the lower oven doors also. The molten iron falling on the refractory lining of the lower oven door first damaged the refractory, which gave way, thereby exposing the lower door metal to direct heat. The ribs of the lower door melted down. Thus, a large number of lower doors also got heavily damaged and became unserviceable. The first replacement activity of Lower Oven Doors was started in March 2008. free space below the arch roof and the rest of the unburned gas, along with the hot burnt flue gas, travels down to the sole flue which is divided into four linked arches below the oven sole. Additional combustion air known as secondary air is introduced in the sole flue to complete the balance 20 percent combustion and the hot inert flue gas, devoid of any combustible constituent, is allowed to go up the uptakes to the bridge pipes, the branch header and finally to the chimney via the waste heat boiler, for recovery of waste heat from the hot flue gases for generation of power. The damage of bridge pipes commenced from the early days of commissioning. The commissioning of battery nos.7 and 8 started towards end of December 2007. Thereafter, sequentially other batteries were commissioned in January 2008(nos. 5 and 6), March 2008 (nos. 3 and 4) and May 2008 (nos.1 and 2). The damage of bridge pipes started in the months of January to February 2008 and the first replacement was done in Oven no. 86 coke side (Battery no. 8) on February 13, 2008. It meant that the damage of the bridge pipe had commenced within a month’s time of the first commissioning. During subsequent months, replacement of damaged bridge pipes went on as follows: March 2008-3 nos., April 2008- 3 nos., May 2008-6 nos., June 2008-7 nos., July 2008-8 nos., August 2008-5 nos., September 2008-5 nos., Oct 2008-7 nos., November 2008-6 nos., December 2008-10 nos., and so on. Translated year–wise, the bridge pipe replacements were as follows: 2008-61 nos., 2009-147 nos. and 2010 (till July)-66 nos. There was a time when bridge pipes got damaged within a few days of installation. Observations and Remedial Actions Upper Oven Doors The first action with regard to the upper oven doors was to make some changes in the design of the liner. The L-shaped bricks were replaced with dense castable LC-45, cast on L-shaped ss-anchorage. Ceramic Fibre castable of the main 3) Bridge Pipes Bridge Pipes are breather pipes for ovens and serve as nostrils for the oven chambers. Each oven, therefore, has two bridge pipes connected to two separate branch headers – one at the pusher side and the other at the coke side. These create the necessary suction inside the oven uniformly from both ends for inhaling combustion air into the free space above the coal cake. The inhaled air helps in burning of volatile substances ejected out of the coal cake and creates a fire ball which radiates heat in all directions. The arched oven roof serves as a concave mirror and reflects the radiations in parallel vertical rays falling on the coal cake. The entry of air into the oven should be so controlled that 80 percent of the combustion is completed in the oven top Chart showing gradual decline of damaged upper doors vis-à-vis increasing nos. in good condition COAL INSIGHTS 56 October 2010
Expert Speak Refractory lining work for lower oven doors in progress in COP body was replaced with insulating castable Insulite-15. Top surface was finished with 70 mm LC-45 dense castable. About 78 upper oven doors have been replaced with the new lining since September 31, 2009. None of these freshly lined doors have failed so far. There is a proposal to use ceramic fibre modules for upper door lining. Orders have already been placed for imported and indigenous modules, particularly for the upper door lining, the results of which can be seen only after installation. Lower Oven Doors The first instance of damage of lower oven door commenced almost within two to three months of the first start-up of coke oven battery nos. 7 and 8. Similar to the upper door lining, changes were made in the lower door lining also, mainly the peripherals, which receive maximum external abrasions. These were lined with dense LC-45 castable on top of Hysil boards. A pictorial representation of the extent of repairs done almost over a year after September 31, 2009 is given herewith. None of these freshly lined doors have failed till date. Bridge Pipes It was observed that the ceramic fibre lining of the bridge pipes was failing repeatedly and fallen refractory material was blocking the suction ports. It was also observed initially that the temperature inside the bridge pipes was shooting up as high as 1450°C leading to fusion and melting down of not only the refractory material, but also the mild steel body of the bridge pipes, thereby creating gaping holes. It was also observed that certain amounts of combustibles were being carried over to the bridge pipe region. The operating procedure being followed at that point of time (before September 31, 2009) had a flaw, although it was as per the instructions given by the Chinese suppliers. The two primary air windows provided in the upper oven doors were completely closed for the initial three hours after charging of ovens. Since the plant was being operated almost at full load, one oven was being pushed and charged every 45 minutes. As a result, unburnt volatiles escaped continuously to the bridge pipe and branch headers. Another mistake which further aggravated the problem was that a tertiary hole was made by some agency at the bottom of the uptake just after the fourlinked arch, which provided additional combustion air to the unburnt volatiles. A third observation was that when bridge pipes were being changed, flue hole cleaning was overlooked at times and bridge pipes were also being changed only on one side, that is, either the coke side or the pusher side, ignoring the condition of the other side. This resulted in more flow of gas through one of the bridge pipes leading to higher temperature and meltdown. The following steps were undertaken to overcome the problem of bridge pipe failure: a) Immediate plugging of tertiary holes with strict instructions to never open them in future. b) Keeping the primary air windows open right from the time after charging, closing it fully only when the oven is ready and regulating it in between as per combustion requirement. c) Keeping the levels of the combustibles in flue gas, particularly carbon monoxide and hydrogen at trace levels. d) To take up bridge pipe replacement either simultaneously on both the coke side and the pusher side or at a small gap of maximum one week. e) Use of dense castable LC-45 in the top layer in contact with the hot gas. f) To do compulsory suction port cleaning with every bridge pipe replacement. The above mentioned steps have brought in drastic improvements in the condition and life of the bridge pipes and their lining. Over the last one year, more than 100 out of a total of 192 bridge pipes have been replaced, none of which have failed as yet. With full load operation at 36 pushing per day, some damages temporarily resurfaced but were quickly controlled. The key to the solution to the problem was basically lowering the temperature of the flue gas to about 1100°C to 1150°C which is as per the design and the liner material can withstand the same. The author is working as Vice President in the coke manufacturing unit of Bhushan Power and Steel Limited, Jharsuguda, Orissa. Right from its inception in 2007, the plant has been facing problems of massive failure of refractory lining of bridge pipes, upper oven doors, lower oven doors and branch headers. Many trial and error processes were carried out with different material and massive maintenance work was taken up to combat the failures, but fruitful results were not coming up. Finally after doing an in-depth study of various operational and maintenance aspects, a viable solution to this endemic problem could be found with the combined efforts of all related disciplines. The author is grateful to M/s K. Vijayan, S. Mukherjee, Sanjeev Srivastav, Sanjit Kumar and the entire coke oven team for their relentless efforts in bringing about the improvements in the operation and maintenance of the coke oven plant. COAL INSIGHTS 57 October 2010
Page 3 and 4:
Chief Editor Rakesh Dubey, Tel: +91
Page 5 and 6: India’s largest coal handling age
Page 8: Cover Story INDUSTRIAL GROWTH INDIC
Page 12: Cover Story India, China lead globa
Page 16: Cover Story Beml plans to double tu
Page 20: Cover Story complete longwall minin
Page 23 and 24: coal market fundamentals Coking coa
Page 25 and 26: Feature Competitive bidding: Will i
Page 27 and 28: Feature allotment of captive coal b
Page 29 and 30: Feature Coal ministry puts illegal
Page 31 and 32: Feature Coke shortage may hamper st
Page 33 and 34: Feature How coke making evolved Tho
Page 35 and 36: Feature Cement makers to hike price
Page 37 and 38: Feature increased imports, which is
Page 39 and 40: Feature Forestry clearance delays m
Page 41 and 42: Feature embarked on a massive affor
Page 43 and 44: Feature India misses Sept power gen
Page 45: government Coal ministry firm on pr
Page 49 and 50: INTERNATIONAL Forum seeks Canada-In
Page 51 and 52: INTERNATIONAL UAE 269,462 331,688 1
Page 53 and 54: INTERNATIONAL EIA raises 2010 US co
Page 55: Expert Speak Heat recovery chinese
Page 59 and 60: Expert Speak and in a hard copy for
Page 61 and 62: CORPORATE We have already commissio
Page 63 and 64: CORPORATE Cil in top league after i
Page 65 and 66: CORPORATE Banks not tapped for capt
Page 67 and 68: Logistics down rates and increased
Page 69 and 70: Power sector update PROGRAMME AND P
Page 71 and 72: Power sector update CAPACITY ADDITI
Page 73 and 74: Power sector update Northern WESTER
Page 76: SnapShot Chile mine rescue - a marv
Page 80: Snap Shot It was finalised that the
Page 84: E-Auction data Month Details of e-A
Page 88 and 89: All India coal data - August 2010 N
Page 90: port DATA Major Ports Through Which
show all

India's largest coal handling agency - Mjunction

You also want an ePaper? Increase the reach of your titles

Delete template?

Save as template?