Abstract:

In order to fully recover the flare gas in large-scale petrochemical complexes, as well as meet environmental protection requirements and improve economic benefits, the usual practice is to set the pressure setting of the flare gas venting pipeline regulating valve to a higher value (relative to the design pressure of the liquid separation tank), so that the flare gas is temporarily accumulate in the liquid separation tank, and then enter the flare gas recovery system. However, under abnormal emergency conditions such as power failure or fire, the multiple pressure devices are relieved at the same time. The surplus flare gas will cause the flare gas flow to increase transiently, which may cause the Mach number of flare head to be extremely high and the risk of "out of fire". For this reason, a method to determine the best set value of flare gas vent pipeline pressure adjustment is proposed: within the technological allowable range of the set value of flare gas pressure regulating valve, select the value that makes the flare head Mach number meet the safety requirements. Through the flare gas recovery volume and recovery stability to comprehensively measure the economic benefits of flare gas recovery, and finally calculate the best adjustment setpoint. The case shows that by calculating the Mach number of the flare head and analyzing the economic benefits of flare gas recovery, the pressure setting determined by the proposed method can meet the safety requirements of Mach number and maximize the economic benefits of flare gas recovery.

Key words: flare gas, Mach number, risk, safety, recovery, optimization

摘要：

大型石化联合装置为充分回收火炬气，满足环保要求并提高经济效益，通常做法是将火炬气放空管道调节阀的压力给定值设置偏高（相对于分液罐设计压力），使火炬气在分液罐内暂时积聚，随后进入火炬气回收系统。然而停电、火灾等异常紧急工况下多装置同时泄压，富余的火炬气将使火炬放空气流量产生瞬态增高，可能导致火炬头马赫数超高及“脱火”风险。为此提出了一种确定火炬气放空管线压力调节最佳给定值的方法：在火炬气压力调节阀给定值的工艺允许约束范围内，选取使火炬头马赫数符合安全要求的取值，并通过火炬气回收量及回收稳定性来综合衡量火炬气回收经济效益，最终计算出最佳调节给定值。案例表明，通过计算火炬头马赫数和分析火炬气回收经济效益，所提方法确定的压力给定值可以在符合马赫数安全要求的同时，使火炬气回收经济效益达到最高。

关键词: 火炬气, 马赫数, 风险, 安全, 回收, 优化