Double mixed refrigerant liquefaction process for natural gas

Abstract From the Canadian patent

A process and system are set forth for precooling liquefying and subcooling a methane-rich feed stream such, as natural gas, with two closed circuit multicomponent refrigerant cycles in which the first refrigerant comprises a binary mixture of propane and butane in a flash refrigeration cycle and the second refrigerant comprises a mixture of nitrogen, methane, ethane, propane and butane in a subcool refrigeration cycle. The first refrigerant preferably cools the feed stream in a plate and fin heat exchanger.