Integrated process for converting hydrocarbon gas to liquids

Abstract

The present invention is an integrated process for converting light hydrocarbon gas to heavier hydrocarbon liquids. In each embodiment, a Fischer-Tropsch (FT) process comprising a thermal reformer and a reactor containing an FT catalyst is combined with one or more additional processes to achieve operational synergies. In a first embodiment, an FT process is integrated with a cryogenic liquefied natural gas (LNG) process wherein tail gas from the FT reaction is used to drive a refrigeration compressor in the LNG process. The tail gas, optionally supplemented with natural gas, may be fed directly to a gas turbine or may be combusted in steam boiler, which in turn provides steam to a steam turbine. The natural gas may be processed prior to its being fed to the LNG process and the FT process in order to remove any impurities and/or condensate. The process may be further integrated with a fertilizer production process comprising an ammonia synthesis process and a urea synthesis process. To produce ammonia, hydrogen separated from synthesis gas produced in a primary and/or secondary reformer in the FT process is combined with nitrogen produced in the LNG process. Nitrogen may also be supplied to the ammonia synthesis process from an optional air separation process, which also provides oxygen enrichment to the thermal reformer in the FT process. To produce urea, the ammonia is subsequently reacted with carbon dioxide removed during processing of the gas prior to its liquefaction. The integrated FT/LNG/Fertilizer process may be further integrated with a carbon dioxide removal process which separates flue gas from a gas turbine or steam generator driving the refrigeration compressor in the LNG process into nitrogen which is used in the ammonia synthesis process and carbon dioxide which is used in the urea synthesis unit. Alternatively, the FT process may be integrated directly with the fertilizer production process, in the absence of an LNG process. In an alternative embodiment, an FT process is integrated with a methanol synthesis process wherein tail gas from the FT reaction is used to fuel burners in a secondary thermal reformer.