PROCESS TO INCREASE NATURAL GAS METHANE CONTENT

摘要

PROCESS TO INCREASE NATURAL GAS METHANE CONTENT of the Invention The present invention is directed to a process for purifying natural gas to provide a liquified natural gas product which is substantially pure methane. In the process, a natural gas feed stream is introduced into indirect countercurrent heat exchange in a first heat exchanger to cool the natural gas to below the dew point of ethane and higher hydrocarbons so as to separate the feed stream into a gas which is substantially pure methane and liquid which contains the ethane and higher hydrocarbons. The liquid/gas mixture is transferred to a separator where the gas occupies the head space of the separator and the liquid occupies the bottom of the separator. A gas friction is removed frm the top of the separator and is introduced into countercurrent heat exchange with liquid nitrogen in a second heat exchanger so as to liquefy the substantially pure methane gas. Liquid nitrogen is introduced into a third heat exchanger where the liquid nitrogen is mixed with a recycled portion of nitrogen vapor is mixed with a recycled portion of nitrogen vapor exiting from the second heat exchanger to provide a liquid nitrogen feed stream for the second heat exchanger. The nitrogen vapor exiting from the second heat exchanger is divided into a recycle portion for introduction into the third heat exchanger and a heat exchange portion for introduction into countercurrent heat exchange with the natural gas feed stream in the first heat exchanger. A liquid fraction containing C2 and higher hydrocarbons is removed from the bottom of the separator. The liquid fraction removed from the bottom of the separator is introduced into indirect countercurrent heat exchange with the natural gas feed stream in the first heat exchanger.