Reasons for the high temperature in the roof space of 6m coke ovens

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Reasons for the high temperature in the roof space of 6m coke ovens: High temperatures in the roof space of our company’s JN6O–82 type coke ovens were detected as soon as they came online. When using blast furnace gas for heating, the coking time is 18 hours, and the temperature in the roof space reaches around 920°C. The high temperature in the furnace roof area affects the yields of tar and crude benzene, and graphite grows rapidly on the furnace roof. This paper analyzes the reasons for the high temperature in the roof space of 6m coke ovens. 1 Temperature conditions in the roof space of 6m coke ovens: The characteristics of the temperature in the roof space of 6m coke ovens are as follows: (1) The temperature in the roof space is relatively high. At the same coking time, it is about 40–60°C higher than that of a 5.5m coke oven. (2) As the coking time increases, the temperature in the top space of the furnace gradually decreases. The degree of decrease is as follows: for a coking time of x hours, the temperature drop for blast furnace gas is y °C/h, and for coke oven gas it is z °C/h – 18–20, 10–15, 10 for x ≥ 20, and 5–2. When the coking time is the same, the temperature in the top space on the coke side is 20–30 degrees higher than that on the machine side℃ ； Heating with blast furnace gas results in a temperature that is 15–25°C higher than when using coke oven gas. 2 Reasons for the high temperature in the furnace roof area 2.1 Top heating: The uniformity of top heating in 6m coke ovens is better than that in 5.5m coke ovens. Heating is carried out using blast furnace gas, with a coking time of 18 hours. The temperature difference between the upper and lower parts of the coke cake is 10°C on the machine side and 5°C on the coke side; whereas in a 5.5m coke oven, at a coking time of 1 hour and 30 minutes, this difference is 40°C on the machine side and 30°C on the coke side. Whether heated with blast furnace gas or coke oven gas, the temperature difference across the coke cake is always lower on the coke side than on the machine side. At the same coking time, blast furnace gas with higher vertical heating uniformity is superior to coke oven gas. As the coking time increases, with the same type of gas used for heating, the temperature difference between the coke cakes in 5.5m coke ovens and 6m coke ovens shows an increasing trend. The temperature difference between the upper and lower sections when heating a 6m coke oven with coke oven gas is similar to that in a 5.5m coke oven heated with blast furnace gas. 2.2 Furnace structure: (1) The area of the exhaust gas circulation holes in 6m coke ovens is 37% larger than that in 5.5m coke ovens; the area of the cross-over holes is 46% larger. As a result, the amount of exhaust gas circulated increases. (2) The area of the flue shaft decreased by 6%, while its height increased by 0.5 m. This increased the buoyancy difference between the ascending and descending air currents. If the temperature difference between the ascending and descending air currents in a 6-m coke oven is the same as that in a 5.5-m coke oven, then the buoyancy difference between these air currents would increase by 12%, and the air flow velocity would increase by about 17%. As a result, the combustion center moves upward, reducing the temperature difference between the exhaust gases at the top and bottom. (3) The time it takes for the raw gas from a 6m coke oven to pass through the hot coke is about 9% longer than that in a 5.5m coke oven; therefore, the temperature of the raw gas is higher in the 6m coke oven. (4) The roof of a 6m coke oven is thicker than that of a 5.5m coke oven, and its rising pipe is higher (4.7m), whereas that of a 5.5m coke oven is only a little over 2m; as a result, heat dissipation and ventilation at the roof are poor. It has been determined that the ambient temperature at the top of a 6m coke oven is about 10°C higher than that of a 5.5m coke oven. (5) The heating level is low. Our factory uses spiral feeders for coal feeding in the 6m coke ovens; the shrinkage of coal is relatively high, typically at 8%. Therefore, at the late stage of coking, the distance from the coke line to the crossing hole is only 98 mm, which is a very small difference. 2.3 Heating gas: The calorific value of heating gas is relatively low. Generally, the calorific value of blast furnace gas is 3250 kJ/m³, while that of coke oven gas is 15370 kJ/m³. Due to the low calorific value of gas, it facilitates flame elongation, resulting in better heating of the upper part of the carbonization chamber. 3 Measures to reduce the temperature in the furnace top space (1) Increase the n coefficient. Heating is carried out using blast furnace gas. The coking time is 20 hours; after α increases from 1.10 to 1.45, the temperature difference between the upper and lower parts of the coke cake is 5.5°C. In 6-m coke ovens, this difference is 45°C, while in 4-m coke ovens it is only 30°C. The temperature in the roof space decreases by about 15°C. Therefore, it is impossible to reduce the temperature in the furnace roof space to below 850°C by simply increasing the α coefficient. Therefore, α should generally be kept between 1.25 and 1.35. (2) When heating is carried out using blast furnace gas and the proportion of coke oven gas added increases to 8%, the temperature in the roof space can be reduced by 15–20°C. (3) Increase the coal loading capacity. The original design specified a coal charging line of 350 mm; in order to reduce the temperature in the roof space, the amount of coal loaded into the carbonization chamber was increased. It was found that when the coal charging line was set at 277 mm, the temperature in the roof space was 858°C on the machine side and 866°C on the coke side, resulting in a reduction in the roof space temperature of approximately 20–25°C. Therefore, the coal loading line should be controlled at 200–300 mm. (4) Optimize the heating schedule. When the coking time is 18 hours, the standard temperature is reduced by 5°C while ensuring uniform maturation of the coke. The temperature in the furnace top space was measured to be 887 ℃ on the machine side and 903 ℃ on the coke side; it decreased by 3 ℃ on the machine side and by 26 ℃ on the coke side, for an average decrease of 14.5 ℃. (5) Strengthen coal loading and leveling operations to ensure the coal is fully loaded, evenly spread, and compacted. Optimized management in terms of production and thermal operations can be implemented, making it possible to reduce the temperature in the furnace roof area to around 850°C. Last edited by Lawlessness on 2009-3-20 17:10]