Repair of the lining in the small flue of the coke oven

Thread Content

Repair of the lining in the coke oven flue: The coke oven flue is located at the bottom of the regenerator and serves as a passage that connects the regenerator to the waste gas tray. Its main function is to distribute air or blast furnace gas using the grating bricks when air flows upward, and to collect and discharge waste gases when air flows downward. The quality of the small flue structure not only affects the normal coke oven production schedule, but also reduces the yield and quality of coke; it can even impact the service life of the coke oven. 1. Problems with the small flue: (1) Erosion of the lining. The burner area is severely eroded, with the lower lining being more eroded than the upper one. (2) The detachment of the lining occurs mainly in the small flue at the gas outlet, and it is primarily the upper layer of the lining that detaches; this detachment extends about 3 meters inward from the burner ； Part of the lining in the small flue at the air inlet has fallen off, extending about 1.5 meters inward from the burner. (3) The grate bricks on the machine side broke and collapsed, falling into the small flue where severe ash accumulation occurred ； The grate bricks on the coke side showed signs of looseness and cracking, but there was no collapse or ash accumulation. (4) As a result of the peeling off of the interior walls, the main walls, individual walls in those areas, as well as some of the walls at the furnace end also showed varying degrees of corrosion and pits caused by peeling. 2. Cause analysis: In small flues with low temperatures, SO2 and SO3 in the exhaust gases react with water to form sulfurous acid and sulfuric acid, which are the main factors causing the erosion of the lining. Since the temperature in the small flue at the gas inlet is lower than that at the air inlet, the corrosion at the gas inlet is more severe than at the air inlet. The leakage of coke oven gas from the brick gas channels into the small flue where it burns is also a factor contributing to the detachment of the lining. The reason why the damage to the burner area is severe while the damage inside the small flue is mild is that as the air flows upward and enters the small flue, it is continuously preheated by it; as a result, the temperature of the air inside is higher than that at the inlet (the burner area). Therefore, the temperature difference across the internal lining before and after direction reversal is smaller compared to that in the burner area. Furthermore, the cumulative expansion resulting from furnace heating and actual production also concentrates mostly in the furnace head area; as a result, cracks and lining damage in this area are more severe than those inside. The main reason for the detachment of the upper lining in the small flue is its loss of support from the lower lining. The main and single walls of the small flue lose their protective layer due to the peeling off of the lining inside the flue, which exposes them over time to large temperature differences in both directions as well as corrosion from sulfides in the exhaust gases; as a result, they gradually develop peeling and pits. 3. Repair methods: (1) Repair of the lining inside the small flue. During construction, this method involves using a special shovel and the help of spotlights to remove the detached lining and debris, and then locating the areas where the lining has come loose in order to patch and repair them. Due to the special location of the small flue, this method is not only inconvenient to use, but the mud applied or the repaired lining exists only on the surface; over time it will fall off as well, failing to address the root problem. This method is only suitable in the early stages of liner peeling. (2) Method of removing the lining of the regenerator for repair. According to this method, before construction, it is necessary to arrange the insulation work with coke for the carbonization chamber that is connected to the maintenance regenerator (small flue). During construction, first stop heating the combustion chamber that is connected to the maintenance regenerator, remove the partition wall of the maintenance regenerator, and lift out the exhaust gas tray at the bifurcated section; thereafter, manually or with specialized tools, remove the grid bricks and grate bricks until the lining area is intact. Rebuild and clean the small flue; during construction, it is necessary to follow the original design specifications, and at the same time repair and seal the main walls as well as the side walls. We applied this method in 1997 and 1998 to repair the liner of the small flue on the coke side of Unit 1, and at the same time replaced the waste gas tray at the bifurcated section on the coke side. Practice has shown that this method can completely repair the lining of small flues, but it also presents problems such as long construction time, an impact on coke production, and the need for multiple types of workers to carry out the work. 4. Effect of the repair: After the repair, the horizontal temperature in Row 1 of Coke Oven No. 1 returned to normal levels, meeting the production requirements. The suction at the top of the regenerator on the coke side of Unit 1 has returned to normal, and there is room for adjustment in the suction in the small flue. The temperature of the small flue gas duct on the machine side has increased slightly, but it remains low ； The temperature of the flue gas on the coke side has returned to normal. Before the repair, Chamber 1 of Coke Oven No. 1 experienced 7 instances where the low furnace temperature prolonged its coking time, affecting the normal coke extraction schedule. After the repair, with the furnace temperature remaining normal and no occurrences of furnace failure or delays, both the coke production volume and the quality of the coke improved. It created favorable conditions for the long service life of Coke Oven No. 1. 5. Conclusion (1) The consistently low temperature in the small flue is the fundamental cause of liner erosion. (2) In small flues with lower temperatures, sulfurous acid and sulfuric acid formed when SO2 and SO3 in the exhaust gases come into contact with water are also the main factors causing erosion and detachment of the lining in these small flues. (3) The repair method for the small flue is only applicable in the early stage when the lining has begun to peel off ； The scraping and regenerative chamber repair method is practical for flues with significant liner detachment, but it has issues such as long construction time.