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(Reprinted from the Coal Coking Network) Heating system and operation of the 7.63m coke oven of the Kaiserstuhl Coking Plant in Germany. At the end of 1992, the new Kaiserstuhl Coking Plant in Dortmund, Germany, which has the largest coke oven in the world, finally went into production after about 35 months of construction in close cooperation with Krupp Hess Metallurgical Company. This installation has comprehensive equipment and can * * The environmentally friendly plant can also be considered the most modern coking plant in the world. This article will introduce the coke oven heating system and its operation of the coking plant. 1 Overview of the Kaiserstuhl Coking Plant The Kaiserstuhl Coking Plant (belonging to Ruhr Coal AG) is located in the center of the Krupp Hess Steel Works complex in Dortmund, closely connected to the blast furnace and rolling mill. The metallurgical plant is the largest user of coke and coke oven gas produced by the Kaiserstuhl coking plant. The blast furnace gas and some other media (N2, natural gas and water) from the metallurgical plant are in turn supplied to the Kaiserstuhl coking plant. The Kaiserstuhl coking plant has an annual design capacity of: 2 million tons of coke, 1 billion m3 coke oven gas, 1 million tons of high-pressure steam, 200 million kilowatt-hours of electricity, 25,000 tons of crude benzene, 85,000 tons of tar, and 9,000 tons of sulfur. Steam is produced by a coke dry quenching unit (CDQ), while electricity is produced by an attached power station. 2 Coke oven system The coking plant consists of 2×60 hole coke ovens. It is equipped with 1 coal tower (2,700 tons), 2 sets of coke oven machinery and 1 set of the world's largest dry quenching device (250t/h), including 1 thermal power station. Each coke oven requires approximately 28,000 tons of refractory materials. The coke oven operation adopts 2-1 coke pushing sequence. At full load, the turnaround time is 25h. The coke oven can be heated by either coke oven gas or mixed gas. The mixed gas is composed of blast furnace gas, residual gas from dry coke quenching and coke oven gas. The calorific value of the mixed gas is adjusted by the amount of coke oven gas added. Coke oven No. 1 can only replace the heating gas for the entire furnace, while coke oven No. 2 can be divided into two sections, that is, the 30-hole carbonization chamber in each section can be heated by different types of gas. Combustion air is not sucked in by flue suction, but sent through fans, so that it is not affected by changes in the atmosphere. Fans are also used in coke oven basements for forced ventilation. According to the requirements of the environmental protection department, the smoke coming out of the furnace door must not be discharged into the atmosphere. To meet this requirement, the carbonization chamber must be connected to a leakage gas extraction device during the first hour of carbonization time. In this way, once the furnace door leaks, the leaked gas can be collected into the fixed cover located above the furnace door, and the solid matter in it is separated in the bag filter. The gas discharged from the bag filter is sent into the combustion air and burned in the combustion chamber. After the first hour until the end of coking, the suction devices on all hoods, even at half capacity, are sufficient to eliminate smoke. 3. The specifications of the coke oven of the carbonization chamber system are as follows:: Number of coke oven seats 2 Number of carbonization chambers 2 × 60 holes Carbonization chamber length 18 m Carbonization chamber height 7630 mm Furnace top space height 450 mm Effective height of carbonization chamber 7180 mm Effective volume of carbonization chamber 78.84 m3 Carbonization chamber width 610 mm Carbonization chamber taper 50 mm Fire channel temperature is about 1330°C Furnace top thickness 1750 mm Carbonization chamber center distance 1650 mm The thickness of the furnace wall is 95 mm, the thermal conductivity of the furnace wall is 2. 2 W/(m·K), the allowable load value is 1106 kg/m2, the effective volume of the carbonization chamber is about 78.84m3, its coal loading capacity is about 67 tons, and the amount of coke pushed out of each hole is about 49 tons. The center distance of the carbonization chamber of 1650mm enables the coke oven's allowable load value to reach 1106 kg/m2. Such a carbonization chamber is quite stable and can withstand high internal gas pressure. In addition to the use of height-adjustable flat coal rods to adapt to different coal loading heights, the so-called differential heating method is also used to adapt to furnace coal loading with greatly different vertical shrinkage (see Figure 1). Under normal circumstances, when refining coal with little or medium shrinkage, the waste gas passes through two crossing holes (one above the other) located at the upper part of the vertical fireway partition wall and then enters the descending fireway from the ascending fireway. A circular groove with a sliding plate is provided between the two spanning holes to close the upper fire channel. When refining coal with large shrinkage, the differential heat channel is closed, and less heat enters the furnace top, the furnace top space and the coal material. In this way, graphite is less likely to accumulate on the furnace top. Figure 1 Schematic diagram of heating fire channels (rich gas) Figure 2 Layout of regenerator (mixed gas) 4 Each combustion chamber of the heating system is equipped with 36 fire channels. Two adjacent fire channels form a double fire channel. The ascending fire channel and the descending fire channel alternate air flow with each other. The regenerator is located below the carbonization chamber and combustion chamber and is used to preheat the mixed gas and combustion air. The regenerator is arranged longitudinally along the coke oven. The regenerator is separated by special-shaped brick walls (see Figure 2). The mixed gas or combustion air enters the ascending fire channel for combustion and heating of the coke oven through the ascending regenerator. The combustion exhaust gas is discharged from the descending fire channel into the descending regenerator, and then enters the separate flues on the machine side and coke side from the small flue at the bottom of the regenerator. The adjustment of various gases that need to be preheated is carried out by an adjustable orifice plate (grate brick) located in the lower part of the regenerator. When heating with mixed gas, the mixed gas preheated to 1000°C in the regenerator is fed through the chute opening at the bottom of the fire channel (see Figure 3). Each fire channel is divided into three sections to supply combustion air. The air inlet of the first section is located at the bottom. The second air inlet is located on the partition wall about 2.5m away from the bottom of the fire channel. The third air inlet is located on the partition wall 4.5m away from the bottom of the fire channel. When using coke oven gas for heating, the gas is supplied through the lamp holder brick, and the gas outlet of the lamp holder brick is 364mm away from the bottom of the furnace. Since all regenerators connected to the rising fire channel preheat combustion air when using coke oven gas for heating, the two bottom holes of each fire channel and the two holes on the partition wall are used for air supply. In order to supply hot air to each section respectively, partition walls are used to separate the air regenerators longitudinally and connect them to their respective small flues. Some regenerators send combustion air into the chute opening at the bottom of the fire channel, while other regenerators supply air into the holes in the partition wall. The amount of air supplied can be accurately adjusted outside the furnace, and can be adjusted back at any time when the type of gas changes. The exhaust gas generated by the coke oven is discharged from one end of the coke oven through the exhaust gas flap located on the coke side, and is discharged into the atmosphere through the 164m high chimney. The geometric dimensions of the air outlets of each heating section in the heating fire channel are determined based on the cold model flow test done before the construction drawing design. After adopting the three-stage air supply, it is not only beneficial to multi-stage combustion to achieve uniform heating in the high direction of the carbonization chamber, but also conducive to greatly reducing the generation of nitrogen oxides. This is because the lower combustion zone is burned at a low flame temperature with less than the theoretical air volume, and the internal and external recirculation systems of the exhaust gas ensure further reduction of the formation of NOx. The internal return flow of exhaust gas refers to that part of the exhaust gas in the descending vertical fire duct enters the rising fire duct from the double fire duct. Two holes are provided in each intermediate partition wall. If necessary, these two holes can be plugged with a roller-shaped brick that can be moved along the bottom of the fire channel. In addition to the exhaust gas from the descending fire channel returning directly to the ascending fire channel, the cooler exhaust gas and its mixture from the chimney are returned to the combustion air in the form of "external flue gas return". This process technology requires the combustion air to be forced into the regenerator, which can achieve a return rate of 30% of the waste gas generated by coke oven gas heating. The combustion air sent to the coke oven under pressurization is a mixture of the following three parts of gas, namely fresh air directly inhaled, exhaust gas after coke oven leakage is inhaled and bag filtered, and exhaust gas from the coke oven chimney. The communication to each combustion chamber is located in the exhaust valve, and the air supply is controlled by a single reciprocating rod and live handle linkage (with corresponding cock). If there is a problem with the combustion air supply system, a feasible solution is to open the valve on the exhaust valve and change the combustion chamber to automatically inhale combustion air. However, in this case, the suction above the furnace door and the return operation of the external flue gas cannot be performed. Changing the gas type (mixed gas to coke oven gas or vice versa) is carried out by automatic switching of the relevant cork and valves. Various changes in coke oven heating and all controls and adjustments are carried out in the coke oven operation control station. The reversing tractors installed in the coke oven area are unmanned. Equipment operators can use the keyboard to input all set value data to the video display device, and check all measured values and control values on this device. For example, the use and status of various coke oven machinery, coal supply and coke screening stations are all inspected here. The automation system structure of the entire coking workshop is shown in Figure 4. Each operating area is equipped with a programmable logic control system and is connected to each other via a bus system for control, regulation and measurement data collection. “The coke oven group control station is also included in this system. Figure 3 Schematic diagram of heating fire channel (mixed gas) Figure 4 Structure of automation system 1 - PG750 programmer ； 2-Power plant (4×PLC S5-155U) ； 3-Chemical production workshop ； 4-Dry quenching ； 5-Coal processing ； 6-Coke oven ； 7－Coke oven machinery ； 8-Screen coke ； 9-SINEC H1. Since the control station is located at a high location, everything happening around the coke oven can be observed with the naked eye through several large windows. In order to achieve optimal heating, if the gas type is changed, the flow rate sent to all parts of the coke oven can be automatically adjusted. 5. Operation of the coke oven system. After the coke oven is put into operation, each operating area will gradually reach full capacity, and at the same time, it will be adjusted according to the optimal operating mode. In order to achieve good distribution of the medium in the regenerator, the adjustment of the grate bricks and the adjustment of the rich gas nozzles must be constantly improved. Figure 5 shows the temperature distribution curve of the combustion chamber when the grate bricks are "non-optimally adjusted" based on experience in the early stages of production. The optimal adjustment results when heating with mixed gas are shown in Figure 6. Figure 5 Combustion chamber temperature distribution curve at the initial stage of production Figure 6 Combustion chamber temperature distribution curve under optimal conditions At the same time, using this adjustment method, the heating state in the high direction of the fire channel also reaches the standard, that is, △T is about 40K. The temperature difference of 50K from the machine side to the focal side is close to the ideal value. The situation when heating with rich gas is similar to the above. Since the shrinkage rate of coking coal is 6% to 8%, the differential heat channels are all open, and a large amount of carbon deposits are not formed in the furnace top space. Even the roller bricks used for internal flame channel gas return are open. The NOx value in the exhaust gas fully meets the limit of 500mg/m3. The composition of exhaust gas when heating with rich gas: NOx