A method of producing substitute natural gas (SNG) includes providing at least one steam turbine engine. The method also includes providing a gasification system that includes at least one gas shift reactor configured to receive a boiler feedwater stream and a synthesis gas (syngas) stream. The at least one gas shift reactor is further configured to produce a high pressure steam stream. The method further includes producing a steam stream within the at least one gas shift reactor and channeling at least a portion of the steam stream to the at least one steam turbine engine.