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Analysis of the reasons for smoke emission from coke oven chimneys. The chimney is an auxiliary device of the coke oven and one of the iconic structures in a coking plant. Its main function is to generate suction to draw in air and gas from the basement for combustion, and to properly expel the exhaust gases produced by the combustion from the furnace. During normal operation of the coke oven, the exhaust gases emitted from the chimney are colorless; therefore, we generally do not see smoke coming from the chimney. However, sometimes smoke does appear, and it is not of a single color – there can be black smoke, yellow smoke, white smoke, and occasionally blue smoke as well. First, let’s talk about black smoke – it is the type of smoke we least want to see, and it also poses the greatest threat to coke ovens. The fundamental cause of black smoke coming from chimneys is the incomplete combustion of gas, which leads to the decomposition of methane and unsaturated hydrocarbons in the gas into graphite; this graphite then remains suspended in the exhaust gases and is eventually discharged from the chimney after passing through the regenerator and flue. When flue gas passes through the checker bricks in the regenerator, some graphite gets deposited, thereby reducing the void spaces between the bricks and increasing the resistance of the regenerator. This, in turn, affects the normal heating of the coke oven and causes black smoke to be emitted from the chimney. The specific reasons for this are as follows: 1. During the initial stage of the coke oven’s operation, the brick joints or drying holes used during oven drying are not properly sealed; as a result, raw gas from the carbonization chamber leaks into the combustion chamber, leading to incomplete combustion of the gas and the emission of black or even yellow smoke. 2. Due to production requirements, the timing of heating is changed; poor management of iron components leads to unreasonable expansion or contraction of the furnace body, resulting in leaks and black smoke emission. 3. Leakage occurs due to the furnace being left empty for a long time as a result of an accident, or because the furnace door remains open for an extended period, which causes the graphite in the brick joints to burn away. 4. Incomplete combustion occurs due to an unstable heating regime, such as unstable or unreasonable collector duct pressure and a low air excess coefficient. 5. Faults in the heating system, such as switch failures, insufficient air exchange, or malfunctions in the suction adjustment mechanism, can lead to incomplete combustion. To address the black smoke caused by the leakage of raw gas, it is common to increase the pressure in the gas collection system; this helps to decompose the carbon deposits that form as a result of the leakage of raw gas into the combustion chamber, thereby providing a sealing effect. At the same time, it is necessary to properly measure and adjust the iron components used to protect the furnace, so as to ensure uniform and proper expansion or contraction of the furnace body. Once the smoking stops, the pressure in the carbonization chamber is measured (it should be maintained at 5 Pa toward the end of coking), and a suitable pressure level is established to be maintained constant. Regarding smoking caused by poor heating procedures or failures in the heating system, it is generally necessary to have a stable heating procedure, as well as to carry out proper maintenance and inspection of the heating equipment to ensure its proper operation. In addition, adjustments to the heating equipment must be made according to seasonal changes. Secondly, white smoke is also a type of smoke that often comes from chimneys; the white smoke emitted from chimneys is actually a form of \"vapor\". When exhaust gas is discharged from a chimney, white smoke is formed when its diffusion rate is slower than the condensation rate of the water vapor in the exhaust gas. When exhaust gases contain high levels of chlorine dioxide and sulfur trioxide, they combine with water vapor to form white acid mist, which also causes the chimney to emit white smoke. The main reasons for white smoke coming from chimneys are: 1. Water accumulation in the flue, which is carried away by the hot exhaust gases, increasing the water vapor content in those gases. 2. Steam from the gas preheater leaks into the gas system. 3. Poor drainage of condensate from the gas pipeline leads to gas containing water. 4. When the temperature drops suddenly, the water vapor in the exhaust gases condenses rapidly. 5. The temperature of the regasified gas itself is too high. 6. When the switch fails and there is no reversal for an extended period, the chain breaks. Due to these reasons, it is necessary to carry out effective flood control and drainage measures for the flue ducts, conduct regular inspections of the water seals for gas condensate, and perform checks on the preheaters as well as routine inspections of the exchange equipment. The last type of smoke is blue smoke. The exhaust gases contain nitrogen oxides (nitric oxide and nitrous oxide), which, when mixed with other gases in the exhaust gases such as carbon monoxide and sulfur dioxide, cause blue smoke to be emitted from the chimneys under the influence of sunlight and ultraviolet rays. Treating blue smoke is a complex process that requires control at various stages, including coal blending, coke oven heating, and gas purification and recovery, in order to reduce the levels of nitrogen and other nitrogen-containing compounds in the gas and thus eliminate blue smoke.