Collector pressure

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Factors Affecting the Pressure in the Gas Collecting Pipe and Improvement Measures Gao Mingli (MCCC Coke & Refractory Engineering Co., Ltd., Anshan 114002); Qian Rugang, Li Fazhu (Shagang Coking Plant, Zhangjiagang 215625). The gas collecting pipe of a coke oven is one of the key devices used for conveying raw gas from the coke oven; proper control of its pressure is an important factor for ensuring the stable operation of the coke oven. Addressing the issue of large fluctuations in the pressure within this pipe has become a common challenge in the coking industry. The gas collection pipe pressures of coke ovens 1 to 4 at Shagang’s coking plant remain relatively stable, staying within ±20 Pa of the set value for over 90% of the time. However, ovens 5 and 6 experience significant fluctuations in gas collection pipe pressure; even with the automatic DCS control systems in place, stability cannot be maintained, with pressure variations ranging from –70 to 300 Pa. In some cases, negative pressure persists for extended periods or the rising pipes are overpressured, leading to leaks, which has an impact on safe production as well as environmental protection and energy efficiency. 1 Analysis of factors affecting the pressure in the gas collection pipe. The main factors that influence the stability of the pressure in the coke oven gas collection pipe include the adjustment sensitivity of the coal intake pipes, the uniformity and stability of the coal charging process, the proper use of high-pressure ammonia water, the adjustment of the suction force before the blower, the stability of the pressure behind the machine, and the uniformity of the direction changes in the heating system. Shagang’s coke ovens are operated at a high level, with the K3 coefficient remaining above 0.9. Only ovens No. 3 and No. 4 use coke oven gas for heating, while the other ovens utilize blast furnace gas for heating. As can be seen from the comparison of Figure 1 and Figure 2, the process layout differs between Recovery 1 and Recovery 2: Recovery 1 is located at a relatively greater distance from the coke ovens, and it is connected to the associated gas holder after the gas purification system. The gas pressure after the benzene washing tower is less than 500 Pa, while the gas pressure after the crude benzene output from Ovens 1 to 4 is typically 7.5–7.8 kPa. Due to geographical factors, the second recovery unit is located relatively close to the coke oven, while the gas holder associated with it is several kilometers away from the coking plant. Moreover, there are direct users connected to the gas pipelines leading to the gas holder, which results in pressure fluctuations in the gas after passing through the benzene washing tower often exceeding 1 kPa. The pressure of the gas after crude benzene processing in Furnaces 5 and 6 is usually between 8.5 and 9.2 kPa, which affects the stability of the pressures before and after the gas blower. The suction pressure before the primary cooler is affected by the recovery systems before and after the blower, such as changes in the resistance of the gas systems in various sections of the recovery workshop, as well as the effects of coke oven exchange on the gas returning to the furnace; all these factors ultimately impact the stability of the collector pipe pressure. II. The suction pressure before the recycler’s pre-cooler experiences significant fluctuations, which are mainly adjusted manually through a large-scale circulation; the fluctuation range is between 600 and 1600 Pa. Since the pressures in the collector pipes of coke ovens No. 1 to 4 are relatively stable, while ovens No. 5 and 6 experience significant fluctuations in these pressures, comparative analysis shows that the main factor affecting the stability of the pressures in the coke oven collector pipes is the stability of the pressures before and after the gas blowers. 2 Solutions: (1) There should be no users between the coking plant and the gas holder, and the gas holder must be located near the coking plant in order to function as a pressure stabilizer and ensure stable pressure behind the equipment. (2) Maintain stable suction in front of the machine. Stability of the suction pressure in front of the machine is maintained by adjusting the speed of the blower or the control flap for the large-scale circulation of gas; for example, the blower’s speed can be adjusted using frequency conversion, or via a hydraulic coupling for automatic control, or the flap controlling the large-scale circulation of gas can be used for automatic adjustment. (3) Consider the adjustment of the pressure in the coke oven gas collection pipes and the suction pressure before the blowers, which belong to two different systems, as a unified process. The automatic control valves for adjusting the pressure in the coal intake pipes and the speed of the blowers, or the automatic control valves for the large-cycle operation of the blowers, are adjusted in coordination with each other, thereby avoiding any interference that might occur when each is adjusted separately. (4) Chemical production operations must be stable; constant attention should be paid to the gas resistance in various sections to prevent fluctuations in the gas system resistance from affecting the pressure stability before and after the blower. 3 Conclusions The causes of pressure fluctuations in the coke oven collector pipe are multifaceted. Pressure control of the coke oven collector pipe can be achieved by comprehensively considering the relationships among the pressure-regulating flaps of the collector pipe, the pressures before and after the gas blower, adjustments to the large circulation pipeline, and the reversal of the gas returning to the furnace. To maintain stable pressures before and after the gas blowers in coking plants and reduce fluctuations in the pressure in the gas collection pipes, the best approach is to install gas storage tanks with a sufficient capacity between the gas purification system and the users. These tanks help stabilize the pressure in the gas system, serve as a storage facility, reduce gas leakage caused by short-term malfunctions on the part of users, improve the efficiency of gas utilization, and enhance economic benefits.