Systems and methods for producing substitute natural gas

A method for producing synthetic natural gas, comprising:

• gasifying a carbonaceous feedstock within a gasifier to provide a raw syngas;
• cooling the raw syngas to provide a cooled raw syngas;
• processing the cooled raw syngas within a purification system to provide treated syngas, wherein the purification system comprises a flash has separator in fluid communication with the gasifier and a saturator;
• converting the treated syngas to synthetic natural has to provide steam, a methanation condensate, and a synthetic natural gas;
• introducing the methanation condensate to the flash gas separator;
• indirectly exchanging heat from the raw syngas to the steam to provide superheated steam;
• and
• introducing the superheated steam to a steam turbine connected to an electric power generator to provide power and a condensate.

A method for producing synthetic natural gas comprising:

• gasifying a carbonaceous feedstock within a gasifier to provide a raw syngas comprising particulates;
• cooling the raw syngas within a syngas cooler to provide a cooled syngas and a first process condensate;
• recycling the first process condensate within the syngas cooler;
• removing at least a portion of the particulates from the cooled syngas within a particulate control device to provide a filtered syngas;
• adding moisture to a first portion of the filtered syngas within a saturator to provide a saturated syngas;
• shift converting the saturated syngas within a shift converter to provide a shift converted syngas;
• cooling the shift converted syngas within a gas cooler to provide a cooled shift converted syngas and a second process condensate;
• hydrolytically treating a second portion of the filtered syngas within a carbonyl sulfide hydrolysis device to provide a carbonyl sulfide lean syngas;
• ammonia scrubbing the carbonyl sulfide lean syngas with water within an ammonia scrubber to provide scrubbed syngas and waste water comprising ammonia;
• combining the second condensate with the waste water to provide a combined condensate;
• introducing a first portion of the scrubbed syngas to the gasifier;
• combining a second portion of the scrubbed syngas with the cooled shift converted syngas to provide a mixed syngas;
• treating the mixed syngas to provide a treated syngas;
• converting the treated syngas within a methanator to provide steam, a methanation condensate, and a synthetic natural gas;
• compressing the synthetic natural gas to provide a compressed syngas;
• separating the combined condensate and the methanation condensate within a flash gas separator to provide a flashed gas and a condensate;
• introducing the flashed gas to the gasifier;
• introducing the condensate to the saturator;
• indirectly exchanging heat from the raw syngas to the steam within the syngas cooler to provide superheated steam.