A method of producing substitute natural gas (SNG) includes providing a gasification reactor having a cavity defined at least partially by a first wall. The reactor also includes a first passage defined at least partially by at least a portion of the first wall and a second wall, wherein the first passage is in heat transfer communication with the first wall. The reactor further includes a second passage defined at least partially by at least a portion of the second wall and a third wall. The method also includes coupling the cavity in flow communication with the first and second passages. The method further includes producing a first synthetic gas (syngas) stream within the cavity. The method also includes channeling at least a portion of the first syngas stream to the first and second passages.