coking furnace

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Introduction to Coking Ovens: The typical service life of a coking oven is around 25 years; with proper operation and maintenance, it can last more than 30 years. 　　 Before the 1930s, the volume of the carbonization chamber in coke ovens generally did not exceed 20 cubic meters. In 1927, the first large-capacity coking oven in Germany was put into operation, with a carbonization chamber height of 6 meters and an effective volume of 30 cubic meters. Starting in the 1960s, many **successively built large-volume furnaces. The large coke ovens that are widely used today have a carbonization chamber height of 6 to 7.5 meters, a length of 15 to 17 meters, an average width of 0.4 to 0.46 meters, with an effective volume of around 50 cubic meters. China’s first modern coking ovens were built and put into operation in Anshan in 1919, followed by the construction of such ovens in Shijiazhuang, Shijingshan, Benxi, Dalian, Jilin, and other places. Due to the prolonged war, most of them were damaged. Between 1949 and 1959, 11 old coking ovens with 448 chambers were restored; 24 new or renovated coking ovens with 1,239 chambers were built. Starting in 1957, he designed coking ovens independently, and from 1965 he began researching and designing large-capacity coking ovens. In 1970, the first coke oven with 36 chambers, a height of 5.5 meters, and an effective volume of 35.4 cubic meters was put into operation, achieving good levels in all key performance indicators during production. 　　Structure of a coking oven: A modern coking oven consists of a carbonization chamber, a combustion chamber, a regenerator, an incline zone, a furnace top, a foundation, flues, and so on. In the carbonization chamber, coal is heated in an air-free environment to turn into coke. A coke oven has dozens of carbonization chambers and combustion chambers arranged alternately, separated by refractory materials (silicon bricks). Each combustion chamber has 20 to 30 vertical flues. The preheated gas from the heat storage chamber (high-calorific-value gas is not preheated) and air meet at the bottom of the vertical flame channel to burn, providing heat to the carbonization chamber from the side. The regenerator is located at the lower part of the coke oven, and it uses high-temperature waste gas to preheat the gas and air used for heating. The chute area is an inclined passage that connects the regenerator and the combustion chamber. The part of the furnace above the carbonization chamber and combustion chamber is called the furnace roof, and its thickness is determined based on the strength of the furnace body and the need to reduce the surface temperature of the furnace roof. The roof area contains coal loading holes and riser tubes that lead to the carbonization chamber, used for loading coal and removing the raw gas generated during the carbonization process. There are also fire viewing ports leading to each flame channel, used for temperature measurement and checking the flame; based on the results of these checks, the temperature and pressure are adjusted. The entire coke oven is built on a solid and level concrete foundation; each regenerator is connected to the flue gas ducts via exhaust gas plates, with these ducts being located within or on either side of the foundation, one end of them connecting to the chimney. Main parts of the coking oven: The main parts of the coking oven are constructed from silica bricks; to ensure good sealing, special-shaped bricks are used for construction. Typically, a large coking furnace requires more than 400 types of bricks, or even over 1,000 types. A coking oven with 36 chambers and a volume of 35.4 cubic meters requires approximately 8,400 tons of refractory materials. Construction must be carried out in accordance with strict quality standards, and the properties of silica bricks should be fully considered during furnace drying to ensure proper operation and extend their lifespan. After heating the coke oven, the expansion in the carbonization chamber area is nearly 200 millimeters. The daily expansion rate of the drying furnace is generally set at no more than 0.035%, with a drying period of 50 to 60 days. Due to the significant expansion that occurs during the heating up of coke ovens, certain equipment and structures connected to the oven body must be connected, fixed, and sealed only at the end of this process, once the expansion of the oven body has essentially come to an end. Coke oven temperature control is aimed at maximizing the production capacity of the coke oven and achieving optimal thermal efficiency. Temperature regulation is divided into three stages: at the beginning of operation, the furnace temperature experiences significant fluctuations; the main task in this phase is to ensure that the temperatures in all the combustion chambers remain balanced, by adjusting those chambers whose temperatures are too high or too low. When the coking time is gradually reduced to 16–18 hours, the formal temperature adjustment phase begins. At this stage, based on the uniform carbonization of the coke cake (the entire coke mass in the carbonization chamber) in both the vertical and horizontal directions, as well as on the fact that the temperature at the center of the coke cake reaches 950–1050°C, the temperature and pressure of the entire furnace heating system are adjusted to establish a reasonable heating regime and maintain it stable. The temperature adjustment process at this stage takes about half a year. Thereafter, it transitions to a regular temperature regulation phase, during which heating is adjusted in a timely manner based on changes in factors such as the coal feed, the heating gas, and atmospheric conditions, so that the coke cakes in each carbonization chamber can be uniformly converted into coke within the specified coking time, both in the longitudinal and vertical directions. The heat consumption of a coke oven is an important indicator for evaluating the thermal management of the coke oven. Generally, when using coke oven gas for heating, the heat consumption per kilogram of dry coal is approximately 550 kcal ； When heated with blast furnace gas, it is about 630 kilocalories. Coking oven drying: During the drying phase of the coking oven, due to the nonlinear expansion of silica bricks, the expansion rates at the upper and lower parts differ, which may lead to the formation of stepped cracks. During normal production, due to the periodic loading of coal and removal of coke from the carbonization chamber, the furnace temperature fluctuates significantly, causing the masonry to undergo certain degrees of expansion and contraction. Furthermore, the impact of various mechanical devices on the masonry can all lead to deformation and cracking of the masonry. Therefore, it is necessary to utilize the adjustable spring potential energy to apply a sufficient amount of protective pressure to the masonry in a consistent manner, through specialized equipment, so that the masonry remains intact and secure throughout the entire process from furnace heating and startup to normal operation. This protective pressure should be maintained even after the coke oven stops operating, with regular inspections and adjustments carried out. The total load exerted on the coke oven by the furnace-supporting iron components is, calculated based on the oven height, 1.5 to 2.0 tons per meter. Due to the residual expansion of silica bricks and the cracks that inevitably occur, the length of the furnace increases over time. The normal annual expansion rate should not exceed 10 millimeters; in coke ovens with well-maintained furnace protection equipment, this annual expansion rate can be below 5 millimeters after two or three years of operation. The total expansion of the furnace head is one of the indicators of furnace aging. Types of coke ovens: A carbonization chamber is also known as a furnace hole, and a coke oven consists of dozens of such furnace holes. Depending on the structure of the heating system, modern coking ovens come in various types, which can be roughly classified as follows: ① Dual-chamber type, where ascending airflow chambers and descending airflow chambers are combined in pairs, with the entire combustion chamber consisting of several such dual-chamber sets ； ②Two-zone flame path design: on one half of the combustion chamber, the flame paths follow an upward airflow pattern, while on the other half, they follow a downward airflow pattern ； ③It features an overlying flame channel design; the various flame channels in the entire combustion chamber are divided into several groups, which are connected to the flame channel groups of adjacent combustion chambers through overlying flame channels. The production capacity of a coke oven is determined by the size of the carbonization chamber and the coking time. Bituminous coal high-temperature coking ovens: Due to its complete lack of bindability, bituminous coal is classified by countries around the world as a coal unsuitable for coking; it can only be used as domestic fuel or as a raw material for producing gas in the synthesis of ammonia. Bituminous coal is characterized by a high fixed carbon content, low volatile matter (10% or less), a high true density of pure coal (1.35–1.9), no cohesion at all, a high ignition point (380–420 degrees), and smoke-free combustion. Continuous coking furnace: A continuous coking furnace has a carbonization chamber, which is divided into a first direct-heating zone (2A ； 2A'”), an exhaust port (3) is installed on the feeding side within the zone ； Radiant tube heating zone (6 ； 6'”), the area is equipped with several coke oven gas outlets (8) ； and the second direct heating zone (2B ； 2B’), the discharge side within the zone is equipped with an exhaust port (3). In the first (2A ； 2A') and second (2B ； 2B') The direct heating zone is equipped with several burners (5) to enable combustion under low excess air conditions. In such a continuous coke oven, the coal molded therein is carbonized during continuous transport.