Optimization of isobaric open refrigeration process for natural gas liquid recovery

Isobaric open refrigeration process is a new NGL-recovery technology. Compared with the traditional direct heat exchange process, this new process requires less equipment, and has lower capital and operating costs. In this study, associated gas from Changqing Oilfield is taken as an example. The process is simulated, and the process parameters affecting C₃⁺ recovery and energy consumption are investigated and optimized. The results indicate that: ①C₃⁺ recovery increases as the feed gas temperature decreases, however when the feed gas temperature is below -30 ℃, C₃⁺ recovery increases slowly; ②refrigerant throttle pressure has little influence on C₃⁺ recovery and de-ethanizer reboiler duty, but a lower refrigerant throttle pressure means a larger mixed refrigerant compressor duty required; ③C₃⁺ recovery increases with the decrease of refrigerant cooling temperature. The optimum operating conditions are as follows: feed gas temperature is -30 ℃, refrigerant throttle pressure is 500 kPa, refrigerant cooling temperature is -30 ℃. Under these conditions, the C₃⁺ recovery can reach 96.1%.