Interest in the gas-to-liquids (GTL) process using Fischer-Tropsch (FT) reactors has increased recently due to the drop in the price of natural gas relative to liquids fuels. The commercial application of microchannel reactors for this application has also decreased the capital investment required for GTL plant construction, making GTL accessible to more companies. The energy conversion efficiency for the GTL process is mainly determined by the approach used to prepare the synthesis gas fed to the FT hydrocarbon synthesis reactor. The current most efficient and cost effective synthesis gas generation approach uses autothermal reforming (ATR) technology, at a low steam to carbon ratio, in combination with some form of heat exchange reforming (HER). A 2007 Exergy analysis compared the ATR + HER approach to ATR alone. It found a significant energy efficiency benefit when the HER is installed in a series arrangement. Large commercial GTL facilities have used non-catalytic partial oxidation (POX) reforming (combined with some smaller steam methane reforming (SMR) duty) or ATR to prepare the synthesis gas. In all cases some form of integration with the residual tail gas after the FT hydrocarbon synthesis is used. These integration approaches are described in the patent literature. For the ATR + HER approaches, there is a need to recycle some portion of the FT tail gas to the reforming unit and there is a need to purge inert gas components in the FT tail gas, particularly nitrogen. The purged portion of the FT tail gas is typically either used as a fuel gas or as feedstock for the production of hydrogen. The purge approach depends on the composition of the gas fed to the GTL process. Options considered in the patent literature to separate useful components in the FT tail gas are discussed with the emphasis on their applicability to the ATR + HER approach. The preferred approach depends on the infrastructure available at the selected site. Examples are provided of preferred approaches for different situations.

Review of patent literature relating to synthesis gas production and Fischer-Tropsch tail gas processing aimed at the cost effective enhancement of the GTL process efficiency

249th National Meeting (2015)

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