System and method for producing LNG from contaminated gas streams

摘要

A system and method for removing nitrogen and producing liquefied natural gas (“LNG”) from methane without the need for external refrigeration. The invention also relates to a system and method for removing nitrogen from methane and for producing liquefied nitrogen in addition to LNG. The system and method of the invention are particularly suitable for use in recovering and processing comparatively small volumes of methane from coal mines or from flash gas captured at an LNG loading site.

主权项

1. A system for removing nitrogen and for producing liquefied natural gas (LNG) from methane gas comprising other gaseous components, the system comprising:
a source of methane gas disposed proximally to a processing site, the source being accessible to the site without transport through an external pipeline; a nitrogen removal section configured to remove nitrogen gas from the methane gas and to liquefy a substantial portion of the methane gas to produce LNG without use of a recirculated refrigerant, wherein the nitrogen removal section comprises a plate fin cooler and a nitrogen fractionation tower; wherein the nitrogen fractionation tower discharges gaseous nitrogen and LNG; wherein the gaseous nitrogen is expanded and cooled; wherein the expanded and cooled nitrogen is used to subcool the LNG; wherein the nitrogen used to subcool the LNG is recirculated to the plate fin cooler; wherein the recirculated nitrogen cools the methane gas; wherein the recirculated nitrogen is vented after cooling the methane gas; an LNG subcooler section comprising at least one separator wherein cold but unliquefied methane gas is separated from the LNG and is recirculated to the plate fin cooler in the nitrogen removal section, wherein the recirculated methane gas cools the methane gas entering the nitrogen removal section; at least one compressor that compresses the recirculated methane gas exiting the plate fin cooler, which compressed recirculated methane gas is then recycled, and apparatus that splits the recycled compressed recirculated methane gas into a first part and a second part; a receptacle for LNG received from the LNG subcooler section; apparatus for combining the first part with the methane gas entering the nitrogen removal section upstream of the plate fin cooler and upstream of the nitrogen fractionation tower; and a conduit through which the second part flows through the plate fin cooler and then into the LNG subcooler section, where the second part is received into at least one expander and cooled sufficiently to liquefy at least a portion thereof.