Objective In order to reduce the equipment investment and energy loss of extracting helium from natural gas by using a single low-temperature method, a new natural gas helium extraction combined with LNG production process is provided.

Methods Based on the data of low helium feed gas from a domestic gas field, the characteristics and adaptability of this new process have been simulated and analyzed, and the refrigeration cycle of the mixed refrigerant has been optimized by genetic algorithm.

Results (1) Characteristic analysis shows that the lower the temperature before throttling and the higher the throttling pressure, the better the concentration effect of the flash tank on helium gas. At the same time, nitrogen products with a purity of 99.9 mol% can be produced, and liquid nitrogen products can be produced by itself; (2) The new process has strong adaptability to changes in nitrogen and helium content in the feed gas, as well as the pressure of the feed gas. The higher the feed gas pressure and the lower the nitrogen and helium content, the lower the compressor shaft power; (3) Through analysis of characteristics and adaptability, as well as optimization of mixed refrigerant refrigeration process parameters, it can be obtained that the temperature before throttling in the flash tank is -150 ℃, the throttling pressure is 350 kPa, the pressure of the helium extraction tower is 3 200 kPa, the number of plates in both the denitrification and helium extraction towers is 12, the optimal boost pressures for the first and second stages of the mixed refrigerant compressor are 1 341 kPa and 2 767 kPa, respectively, and the circulation rate of the mixed refrigerant is 1 722.67 kmol/h, the total compressor shaft power is 3 765 kW, the cooling water consumption is 6 474 t/d, the comprehensive energy consumption and unit energy consumption are 1 097 216.00 MJ/d and 3.66 MJ/m³, respectively.

Conclusions The helium recovery rate is more than 98%, and the crude helium purity is higher than 70 mol% for the new process. It can produce refrigerants by itself and obtain high-purity nitrogen and liquid nitrogen products, and has good adaptability to the gas quality conditions of the feed gas.