Abstract: In engineering design, safety valve sizing calculation must be based on the physical parameters of the relieved medium. Due to the relatively low critical pressure of C4 hydrocarbon systems, they are prone to reaching supercritical states. However, research on physical property simulation and safety valve sizing methods for supercritical mixed C4 hydrocarbons remains scarcely documented in existing literature. Through screening and comparative analysis, it is found that only the equation of state is suitable for the calculation of supercritical system. Three typical equations of state were selected to simulate the phase diagram of the mixed C4 system. According to the boundary pressure in the phase diagram, the method with the least error was selected. Finally, the conventional calculation, calculation methods for safety valve relief design of supercritical fluids in API 521 and SH/T 3210-2020 are compared by theoretical calculation. Simtech Relief and Aspen safety analysis were used to verify the calculation results, which were proved to be reliable.

Key words: supercritical, mixing C4 system, equation of state, physical method, safety valve calculation