NOVELTY - Producing substitute natural gas (SNG) involves providing at least one steam turbine engine (130); providing at least one gas shift reactor (212); producing a steam stream within the at least one gas shift reactor; channeling at least a portion of the steam stream to the at least one steam turbine engine; providing at least one heat transfer apparatus; and channeling at least a portion of a first condensate stream at a first predetermined temperature to the at least one heat transfer apparatus.    USE - For producing substitute natural gas (claimed).    ADVANTAGE - The method reduces capital and labor costs associated with constructing IGCC and SNG production systems.    DETAILED DESCRIPTION - Producing substitute natural gas (SNG) involves providing at least one steam turbine engine (130); providing at least one gas shift reactor (212); producing a steam stream within the at least one gas shift reactor; channeling at least a portion of the steam stream to the at least one steam turbine engine; providing at least one heat transfer apparatus; channeling at least a portion of a first condensate stream at a first predetermined temperature to the at least one heat transfer apparatus; transferring heat from at least a portion of a shifted synthesis gas (syngas) stream to at least a portion of the first condensate stream, to form a second condensate stream at a second predetermined temperature that is greater than the first predetermined temperature; and channeling at least a portion of the second condensate stream to a syngas scrubbing and quenching assembly. INDEPENDENT CLAIMS are included for following:    (1) gasification system comprising at least one gas shift reactor configured to receive a boiler feed water stream and a syngas stream, where the at least one gas shift reactor is further configured to produce a high pressure steam stream; and    (2) an integrated gasification combined-cycle (IGCC) power generation plant (100) comprising at least one gasification reactor configured to generate syngas stream; at least one gas shift reactor coupled in flow communication with the at least one gasification reactor (208), where the at least one gas shift reactor is configured to receive a boiler feed water stream and at least a portion of the syngas stream, the at least one gas shift reactor is further configured to produce a high pressure steam stream; and at least one steam turbine engine coupled in flow communication with the at least one gas shift reactor, where the at least one steam turbine engine is configured to receive at least a portion of the high pressure steam stream.    DESCRIPTION OF DRAWING(S) - The figure shows schematic view of integrated gasification combined-cycle power generation plant.    Integrated gasification combined-cycle power generation plant (100)    Steam turbine engine (130)    Gasification reactor (208)    Gas shift reactor (212)    Conduit (228)