Basic situation
The 4# and 5# coke ovens of Steel Coking Plant in this article are JN60 60-hole reheating coke ovens, with a designed annual coke production capacity of 1.2 million tons. The two coke ovens were put into operation in September 2003. In May 2011, when pushing coke, it was found that the bottom of the small side furnaces of the two coke ovens had different degrees of wear. After multi-directional measurement and analysis, the root cause of the problem was never found. As the production progressed, it was found that the wear parts continued to expand, and then part of the furnace bottom bricks fell off, which has threatened normal production. In view of this, after careful research and repeated demonstrations, the factory technicians finally decided to use fused silica bricks to heat repair the 505# carbonization chamber with more serious problems.
The choice of silica brick
Since ordinary silica bricks need to be slowly heated according to the expansion law of the oven, the time requirement is very urgent in actual production. The temperature rises from tens of degrees to about 1000 ℃ in just a few hours, and the heating speed is too fast. This leads to inconsistent expansion of the inside and outside, which can easily cause the brick to break. In addition, the heat repair treatment is adopted this time, and the temperature in the furnace reaches about 850°C. Generally, the thermal shock resistance of silica bricks cannot meet the requirements, so higher quality requirements are put forward for the silica bricks to be replaced. After many arguments, a zero-expansion fused silica brick was finally selected, which has less residual quartz and has a very small thermal expansion rate at 1000°C. The physical and chemical properties of fused silica bricks are shown in Table 1 and Table 2.
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Table 1 Fused silica brick chemical index (mass fraction)
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Table 2 Fused Silica Brick Physical Index
Ready to work
Braising oven and buffer oven settings
(1) Because the furnace room 505# to be repaired is in the empty state, the adjacent furnace room must be cooled. 504# and 506# are braised, and the 503# and 507# carbonization chambers are used as buffer furnace chambers to cause coking. The time is controlled at 24h, and other carbonization chambers are the normal coking time. If the demand for output is not high, a buffer furnace chamber can be added, which will be more beneficial to the furnace body.
(2) In order to ensure the heating speed, switch the blast furnace gas used for heating 5# coke oven to coke oven gas in advance.
(3) When the 505# carbonization chamber is emptied, close the riser flap, open the riser cover, and seal the riser with a hanger to ensure that raw gas does not flow back. For 504# and 506#, due to the implementation of the braising furnace, the amount of raw gas generated at the end of coking is extremely low, and the above-mentioned measures have also been taken to cut off the raw gas.
Tools and materials preparation
(1) Refractory materials: 40 zero-expansion bricks, refractory mud, water glass, ceramics, fiber felt.
(2) Tools: special brick supporting board, special brick pushing rod, special pouring trolley, air pipe, heat insulation baffle, ash trough, mud bucket, water pipe, straw handle, shovel, rake, brick cutter for cleaning the bottom of the furnace , Electric welding machine, etc.
Figure 1 Special brick support board, Special brick push rod，Special grouting trolley, Air duct, Heat insulation baffle
(3) Labor protection supplies: anti-high-temperature radiation mask, hand stuffiness.
Combustion chamber cooling treatment
(1) Cooling needs to be carried out two days in advance, and the cooling frequency is reduced by 10% per hour: to 850~900℃.
(2) During the cooling process, the standard temperature of 505# and 506# combustion chambers is controlled at 1100~1200℃, and the standard temperature of other combustion chambers remains normal.
(3) Arrange the fire control personnel to measure the horizontal temperature every 4 hours and make a record.
(4) Cool down as planned, and ensure that other furnaces have even temperature and the coke cake is mature.
(5) Measure and pressurize the spring of steel column according to the temperature drop.
(6) It is planned that when the wall temperature of 505# carbonization chamber drops to about 850 °C, the door will be opened for repair.
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The actual cooling process data is shown in Table 3.
The actual cooling curve is shown in Figure 2.
Table 3 Actual cooling data sheet
Figure 2 Actual cooling curve figure
Bottom brick thermal repair
(1) After emptying the 505# carbonization chamber according to the normal coke pushing sequence, sweep the bottom of the furnace with a straw until there is no coke at the bottom of the furnace, and remove the old brick stubble at holes 2 to 12 until the new bricks and the old bricks When the faces are the same, sweep again with a straw handle until there are no tail burns or broken bricks. Use compressed air with blowing to ensure that the posture remains flat when falling bricks.
(2) Close the coke-side furnace door to prevent heat loss and cold air from corroding the furnace head, and implement heat preservation measures.
(3) After the heat preservation is over, open the machine side furnace door (the coke side furnace door does not open), the furnace wall, and the furnace door frame are insulated with ceramic fiber felt and water glass to prevent the furnace wall from being damaged due to rapid temperature changes.
(4) This repair is about 5 m long with 2 holes and 12 holes on the machine side. About 30 new fused silica bricks are needed. The rest of the original furnace bottom is not damaged and will not be repaired.
(5) Build from the inside to the outside. Use a special tool (pallet) to send the new bricks to the junction of the carbonization chamber and the old brick surface, and place them seamlessly in sequence. Before placing the new bricks, you need to smear the clay fire mud around the brick body (such as If the concave surface is over the bottom, it needs to be leveled with mud bottom). During the operation, it is required to find the reserved mortar joints on both sides, and the masonry is required to be flat and there must be no misalignment. The actual masonry process is shown in Figure 3.
Figure 3
(6) After placing the new bricks, use a grouting trolley to pour the clay fire mud on the joints of the bricks. After pouring, clean the surface of the bricks to ensure that the surface of the bricks is clean and tidy.
(7) During the operation, pay attention to water to the tools to cool down in time, and at the same time spare the brick cutter to make special-shaped bricks. In addition, prepare the electric welder and welder to adjust and repair the tools in time.
(8) During the thermal repair process, attention should be paid to monitoring the temperature inside the furnace chamber, and measures such as closing the door for heat preservation if necessary.
To resume production
(1) After the repair work is completed, close the 505# furnace door (before closing the door, the vertical seam of the furnace head on the side of the machine should be re-painted and shotcrete).
(2) Pull out the hanger after 2h, and close the rising pipe cover.
(3) 4 hours after the maintenance is completed, 505# is loaded with coal. The coal loading should be controlled for the first time, and the amount of coal should be reduced appropriately.
(4) The coking time of the first cycle of 505# is 48 h. After the first coke discharge monitoring furnace bottom is normal, the coking time will be gradually shortened. During this period, the heating work should not be too rushed. It should be carried out in accordance with the heating plan. Table 4 below is the actual heating situation of the combustion chamber: 504#—507#
(5) 504#, 506# wait 2 hours after 505# has been loaded with coal, and then continue to push coke to load coal, and gradually follow the normal coke push sequence.
(6) The coking time of 503#, 507# is 24 hours, and after the repair is completed, the coking sequence will be pushed step by step to the normal coking sequence.
(7) After the repair, the coal is added and the coke is produced until the normal coking time, the workshop arranges fire control personnel and professional and technical personnel to monitor the bottom of the furnace and the current of the coke pushing, and the amount of coal added should be properly controlled during this period.
Table 4 Actual cooling data sheet
Figure 4 Actual cooling curve
Conclusion
(1) Using molten silica bricks to thermally repair the bottom bricks of the carbonization chamber, instead of ordinary silica bricks, can avoid uneven expansion caused by cold repairs, shorten the repair time, and extend the life of the coke oven.
(2) The price of fused silica brick is relatively high, which is suitable for units with tight production tasks.
(3) The masonry can be built by dry pendulum and then grouting during thermal repair, which saves time and manpower compared with ordinary plastering and masonry.
(4) After a period of operation and observation of the repaired carbonization chamber, the bottom bricks of the furnace are flat and firm, and the coke pushing current is stable and normal.
