NOVELTY - A co-production of superheated steam and methane comprises reacting gas containing carbon monoxide and hydrogen in series of methanation regions to produce product gas containing methane; and cooling first and second internally cooled methanation region with water, which water is vaporized in first internally cooled methanation region to produce steam and which steam is subsequently superheated in second internally cooled methanation region to produce superheated steam.    USE - Method is used for co-production of superheated steam and methane. The superheated steam is subsequently used to generate power. The product gas containing methane is used as substitute for natural gas (all claimed).    ADVANTAGE - The method neither need any adiabatic reactors nor any expensive construction materials for superheating steam, thus it is cheap.    DETAILED DESCRIPTION - Co-production of superheated steam and methane comprises reacting gas containing carbon monoxide and hydrogen in series of methanation regions to produce product gas containing methane; and cooling first and second internally cooled methanation region with water, which water is vaporized in first internally cooled methanation region to produce steam and which steam is subsequently superheated in second internally cooled methanation region to produce superheated steam. The gas containing carbon monoxide and hydrogen flows, in passing through series of methanation regions, successively through at least first internally cooled methanation region and second internally cooled methanation region. The internally cooled methanation regions comprise tubes filled with methanation catalyst and space surrounding the tubes. The gas containing carbon monoxide and hydrogen and/or product gas flows through tubes and water flows through space surrounding the tubes.    DESCRIPTION OF DRAWING(S) - The drawing is a schematic diagram showing a co-production of superheated steam and methane.    Coal gasification unit (101)    Stream of coal (102)    Oxygen containing stream (103)    Synthesis gas stream (104)    Steam stream (105)