Synthetic natural gas (SNG) liquefaction processes with hydrogen separation

The fact that synthetic natural gas (SNG) contains hydrogen has a great impact on its liquefaction process. Aiming to produce liquefied natural gas (LNG) from SNG, hydrogen separation from SNG through cryogenic processes is studied. A new separation method combining distillation and flash is developed, resulting in higher liquefaction rate than that of distillation under same operating parameters. Process simulations are performed by combining one liquefaction part (a nitrogen expansion process or a mixed refrigerant one) and one distillation part (direct flash, atmospheric distillation, pressurized distillation or the new separation method). Compared to direct flash, distillation can reduce the hydrogen content of products to a very low level, increasing the temperature of products by 8 °C and reducing the unit power consumption by 3%; and, compared to the other three separation ways, the new separation method reduces the unit power consumption by 7-10%. Both nitrogen expansion and SMR liquefaction processes can be integrated with hydrogen separation, but power consumptions for SMR processes are less than those for nitrogen expansion ones.