Optimization of co-production process of cryogenic helium concentration and liquefied natural gas

Abstract

Effective helium recovery is currently one of the major issues in the oil industry. To overcome the bottleneck of the existing single helium extraction process and provide novel coupling and control methods for the co-production process, a process for natural gas helium concentration and LNG coproduction (He-LNG) is proposed. Based on gas from a gas-processing plant in China, key parameters are optimized, and the adaptability is analyzed by the HYSYS and MATLAB software. The optimal pressure and theoretical tray number is 3.8 MPa and 16 respectively, according to an analysis of the two key parameters of the high-pressure concentrator, the key equipment of the concentration unit. When the cold box pinch temperature in the liquefaction unit exceeds 3.0 °C, the counter-current refrigeration process of secondary throttling mixed refrigerant is more cost-effective and energy-efficient than other similar processes. The He-LNG process has a good adaptability to feed gas with different N2 and CO2 contents, and different schemes can be adopted for different N2 contents. The results show that in the co-production process, the reflux flow at the top of the helium concentrator is controlled by temperature, which makes the helium concentration effect very well. The genetic algorithm-optimized mixed refrigerant refrigeration process produces cold energy for liquefaction units with LNG production up to 380 t/d and higher, which is more productive and cost-effective than the single process.