Abstract: The flare system of a new ethanol synthesis project, including pressure relief valves and flare pipe network, is modeled by using Flarenet software, and calculation is carried out respectively according to different discharge scenarios. Based on the calculation result of the Mach number of discharge branch pipes and flare header, the size of pipeline is adjusted and checked, so that the Mach number of all discharge pipes can meet the requirements specified in relevant standards and codes. During the calculation, appropriate size is set for pressure relief valve to meet the relief capacity requirements, and appropriate valve type is selected according to the ratio of total backpressure to set pressure. Using Flarenet software can effectively optimize the pipe size, so as to meet the Mach number requirements of discharge pipes. Also it can accurately calculate the total backpressure of pressure relief valves and has a high value of practical application

Key words: flare pipe network, pressure relief valve, backpressure, Mach number