Research on safety requirements of critical safety instrumented function in coke oven gas to methanol process using aspen simulation

Abstract

As an important part of the protection measures, safety instrumented systems are widely used in process industries, especially in coal chemical industry. The setpoint value and process safety time (PST), which are contents of safety requirements, of the safety instrumented function (SIF) directly affects whether the safety function can correctly protect a specific scenario. In this paper, the setpoint value and PST of the SIF of “low coke oxygen ratio” is studied. The HAZOP-LOPA method is used to analyze the deviations and the possible cause and consequences. Steady-state model of coke oven gas (COG) to methanol is established based on Aspen Plus to research the effect of the coke oxygen ratio on the high-temperature gas temperature and oxygen concentration in syngas under different working conditions. Based on the simulation results, combined with the sensor working principle and signal processing, the setpoint value is determined. The PST is determined by using Aspen Dynamics. It is found that the smaller the coke oxygen ratio, the higher the high-temperature gas temperature, and the higher the oxygen concentration in syngas; for controlling the coke oxygen ratio, controlling oxygen flow is more critical than controlling COG flow; the setpoint value should be set to 3.78; the PST should be or less than 3.4s.