NOVELTY - Methanation stage comprises at least one methanation reactor holding an amount of methanation catalyst, heat providing means for a heat exchange (122) configured for heating the feed gas upstream the methanation reactor, and a heat collecting means for a heat exchange configured for cooling the gas rich in methane downstream the methanation reactor. The reactor has inlet for stream of a feed gas rich in hydrogen and a carbon oxide, such as carbon monoxide or carbon dioxide, where the reactor further is configured for directing the feed gas to contact the methanation catalyst.    USE - The methanation stage is useful in process plant (claimed).    ADVANTAGE - The two means for heat exchange are thermally connected by heat transfer medium with the associated benefit obtained by use of heat transfer medium avoiding risk of leakages from the feed gas to the methane rich gas. The heat exchange medium (heat exchange medium circuit) is configured for independent heating of heat exchange medium, which provides benefits during startup and other situations with fluctuating conditions.    DETAILED DESCRIPTION - Methanation stage comprises at least one methanation reactor holding an amount of methanation catalyst, heat providing means for a heat exchange (122) configured for heating the feed gas upstream the methanation reactor, and a heat collecting means for a heat exchange configured for cooling the gas rich in methane downstream the methanation reactor. The reactor has inlet for stream of a feed gas rich in hydrogen and a carbon oxide, such as carbon monoxide or carbon dioxide, the reactor further is configured for directing the feed gas to contact the methanation catalyst, and comprises outlet for a stream of a methane rich gas having higher temperature than the feed gas. The two means for heat exchange are thermally connected by a heat transfer medium. INDEPENDENT CLAIMS are also included for:    (1) process plant comprising the methanation stage and reactor for gasification of carbonaceous materials, including coal, petcoke, waste or a renewable fuel; and    (2) methanation process comprising preheating a feed gas rich in hydrogen and carbon oxide, such as carbon monoxide or carbon dioxide by heat exchange with heat exchange medium in presence of a material catalytically active in methanation, reacting the feed gas to form a methane rich gas having a higher temperature than the feed gas, and transferring heat from the methane rich gas to the heat exchange medium.    DESCRIPTION OF DRAWING(S) - The figure illustrates methanation process with three adiabatic methanation reactors and a heat exchange with steam as heat exchange medium.    Synthesis gas (102)    Heat exchanger (118)    Heat exchange (122)    Cooler (124)    Boiler (144)