Chemistry: fischer-tropsch processes; or purification or recover – Liquid phase fischer-tropsch reaction
Reexamination Certificate
1999-08-05
2001-06-19
Barts, Samuel (Department: 1621)
Chemistry: fischer-tropsch processes; or purification or recover
Liquid phase fischer-tropsch reaction
C518S702000, C518S703000, C518S704000, C564S065000, C423S359000
Reexamination Certificate
active
06248794
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a process for converting light hydrocarbon gas to a heavier hydrocarbon liquid, and, more particularly, to a gas conversion process employing a thermal reformer and a Fischer-Tropsch reactor.
Natural gas is often plentiful in regions where it is uneconomical to develop the reserves due to the lack of local markets for the gas or the high cost of transporting the gas to distant markets. An alternative is to produce the natural gas and convert it locally to a liquid hydrocarbon product for more cost-effective transportation. Processes for converting light hydrocarbon gases, such as natural gas, to heavier hydrocarbon liquids are generally known in the prior art. Such processes typically involve the indirect conversion of methane to synthetic paraffinic hydrocarbon compounds, wherein methane is first converted to a synthesis gas, commonly referred to as syngas and comprising hydrogen and carbon monoxide, followed by conversion of the synthesis gas to synthetic paraffinic hydrocarbon compounds via a Fischer-Tropsch catalyzed reaction. Inefficiency of the Fischer-Tropsch process is a drawback in that the value of the conversion products may not justify the cost associated with building and operating the conversion process. Therefore, a need exists for a more efficient process for the conversion of gas to liquid hydrocarbons. Integration of a Fischer-Tropsch process with other process units in accordance with this invention greatly improves the overall economics of converting gas to liquid hydrocarbons by reducing capital and operating expenses.
SUMMARY OF THE INVENTION
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 boiler 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.
REFERENCES:
patent: 5733941 (1998-03-01), Waycuilis
patent: 6011073 (2000-04-01), Agee et al.
Atlantic Richfield Company
Barts Samuel
Parsa J.
Scott F. Lindsey
Yassen Thomas A.
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