Abstract: The stable control of coke oven gas collecting pipe pressure is not only related to the lifespan of the coke oven, but also directly affects the quality and output of coal chemical products. Therefore, the stable regulation of coke oven gas collecting pipe pressure has always been a common concern for coking plants. Controlling the gas collecting pipe pressure of multiple coke ovens of different sizes and outputs is a headache for many coking enterprises. After adopting the multi-coke oven gas collecting pipe pressure stepless fuzzy control system from Xi'an Zhongcheng Automation Engineering Co., Ltd., Dazhou Steel Group Coking Company has greatly improved this problem. Keywords: Multi-coke oven gas collecting pipe pressure control, fuzzy control system. Dazhou Steel Group Coking Company has three JN4.3-80 type mechanized coke ovens, with an annual output of 1 million tons of metallurgical coke and nearly 100,000 tons of coal chemical products. Due to the different construction times of the three coke ovens, the process pipeline lacks rationality. Previously, when two coke ovens were in production, the control of the gas collecting pipe pressure using a DCS system was basically able to meet the process requirements. However, after the third coke oven was put into operation, the original control scheme could no longer meet the production needs. Despite numerous discussions and efforts, no significant improvement was achieved. After extensive research and evaluation, the multi-coke oven gas collecting pipe pressure stepless fuzzy control system from Xi'an Zhongcheng Automation Engineering Co., Ltd. was finally adopted, and the smoke and fire problems of the coke ovens were basically controlled. I. Analysis of Factors Affecting Gas Collecting Pipe Pressure Control 1. Strong Coupling Effect Between Gas Collecting Pipe Pressure Regulation Loops. The gas collecting pipes of the coke ovens are interconnected with the pipes before the primary cooler. Pressure fluctuations in the gas collecting pipes of any one coke oven will affect the pressures of the gas collecting pipes of other coke ovens. Under conventional regulation methods, the pressure of each gas collecting pipe is regulated independently without communication or coordination. The regulation process of the gas collecting pipe pressure of any one coke oven will inevitably affect the stability of the gas collecting pipe pressures of other coke ovens, thus triggering the action of their regulation mechanisms. The regulation processes of different coke oven gas collecting pipes influence each other, thus forming a typical parallel coupling oscillation phenomenon in the gas collecting pipes. This oscillation is more severe during coke pushing, coal charging, and high-pressure ammonia spraying. Due to the large number of coke ovens, the instability factors of the entire system are further increased. Without effective control measures, the system will inevitably be in a continuous oscillation state for a long time, and the regulation quality will be severely deteriorated. 2. Unstable Suction Before the Primary Cooler. The drastic fluctuations in gas pressure after the blower cause continuous changes in the suction before the blower, which in turn directly affects the pressure and regulation process of the coke oven gas collecting pipe through fluctuations in the suction before the primary cooler. If the suction before the primary cooler is unstable, it will directly induce pressure fluctuations in the gas collecting pipe and trigger oscillations. Currently, the suction before the primary cooler is only roughly controlled by the opening of the blower inlet flap, and the actual suction is still in a state of continuous and large-amplitude fluctuations, which undoubtedly seriously disrupts the stability of the gas collecting pipe pressure. There are many factors that disturb the suction before the primary cooler, such as coke oven heating reversal, use or discontinuation of high-pressure ammonia water, changes in pressure after the blower, changes in coke oven gas production, changes in primary cooler resistance, and changes in gas consumption by users, etc. 3. Previously, the gas collecting pipe pressure control used a DCS system with single-loop control, which was isolated and lacked mutual consideration and coordination. Later, program control was adopted for the gas collecting pipe pressure control, using different control methods for different situations, but the effect was minimal. Pressure regulation after the blower, changes in suction before the blower, and monitoring of suction before the primary cooler are all important factors in controlling the gas collecting pipe pressure. However, these three parameters themselves vary greatly and influence each other, making it impossible to guarantee stable control of the gas collecting pipe pressure. 4. The suction before the blower is entirely regulated by the opening of the in-muffle flap. To ensure stable blower operation and prevent blower malfunctions caused by rapid airflow changes, the in-muffle flap cannot be adjusted quickly. When there are significant changes in pressure after the blower, it becomes difficult to stabilize the suction before the blower by adjusting the in-muffle flap, leading to violent fluctuations in suction before the primary cooler. Therefore, it is impossible to quickly overcome instantaneous fluctuations in the gas volume of the gas collecting pipe system. These fluctuations in gas volume will worsen the pressure regulation of each coke oven gas collecting pipe and may cause the gas collecting pipe regulating flap to quickly enter the insensitive zone, losing its regulating function. II. Process Layout III. Process Improvements Due to the significant time gap between the construction of the three coke ovens at Dagang Coking Plant, and the geographical limitations, it was difficult to standardize the gas pipelines to facilitate the DCS system's control and adjustment of the gas collecting pipe pressure. This was challenging due to safety concerns and construction difficulties. Therefore, improvements could only be made through small-scale modifications. The gas collecting pipes of coke ovens #1 and #3 were connected, and valve openings were controlled according to production conditions. An adjustment mechanism was added to the original large circulation pipeline to regulate the suction before the primary cooler, keeping it within a relatively small fluctuation range. The gas collecting pipe flap adjustment mechanism was replaced to improve adjustment accuracy. Simultaneously, the management of process adjustments was strengthened to minimize large fluctuations in gas pressure after the blower. IV. Improvements in Control Methods The original coke oven DCS system only regulated the suction of the main gas pipes and the machine and coke side flues of the three coke ovens, and controlled the exchange time of the gas exchangers. The control of the gas collecting pipe pressure, the suction before the primary cooler, and the large circulation flap is completed by a dedicated fuzzy system. To ensure the stability of the fuzzy system database, the fuzzy system does not record the pressure and suction change curves; the pressure and suction change trend recording is completed by the DCS system. Stable control of the suction before the primary cooler is an important means of stabilizing the gas collecting pipe pressure; therefore, the control of the large circulation flap is particularly important. The sensitivity of the gas collecting pipe flap actuator is required to be controlled within ±0.6 – 0.8%. V. Effects Before and After the Control System is Implemented [align=center] Gas collecting pipe pressure trend before fuzzy system implementation [align=center] Gas collecting pipe pressure trend after fuzzy system implementation[/align] VI. Experience Using the Fuzzy System The core program of this fuzzy system is written in VC language, and the target code is provided to the user after compilation. Although the openness of this control system to the user cannot compare with PLC and DCS, it effectively solves the coupling effect between multiple coke ovens, and utilizes the large circulation to quickly adjust the suction before the primary cooler, thereby stabilizing the gas collecting pipe pressure. The overall control effect is quite good.