NOVELTY - Preparing a methane enriched product gas flow from a carbon oxide and hydrogen containing synthesis gas-fresh gas flow, comprises (a) contacting the synthesis gas-fresh gas flow with a recycle flow to obtain a synthesis gas-input flow; (b) heating the synthesis gas-input flow and feeding to a main reaction zone; (c) converting hot synthesis gas-input flow to a methane enriched intermediate product-gas flow in the main reaction zone; and (d) deducting a partial flow of methane enriched intermediate product-gas flow after the main reaction zone as recycle flow.    USE - The process is useful to prepare methane enriched product gas flow.    ADVANTAGE - The process sets the target pressure before the main reaction zone and/or before or in the post-reaction zone, hence the energy can be saved.    DETAILED DESCRIPTION - Preparing a methane enriched product gas flow with defined target pressure from a carbon oxide and hydrogen containing synthesis gas-fresh gas flow, comprises (a) contacting the synthesis gas-fresh gas flow with a recycle flow to obtain a synthesis gas-input flow; (b) heating the synthesis gas-input flow and feeding to a main reaction zone; (c) converting hot synthesis gas-input flow to a methane enriched intermediate product-gas flow in the main reaction zone under methanization conditions, where the main reaction zone contains at least a methanization catalyst containing catalyst bed; (d) deducting a partial flow of methane enriched intermediate product-gas flow after the main reaction zone as recycle flow, where recycle flow is recycled using a conveyor before introducing into main reaction zone and combined with synthesis gas-fresh gas flow to obtain synthesis gas-input flow; (e) feeding remaining portion of methane enriched intermediate product-gas flow to a post-reaction zone; (f) converting intermediate product-gas flow supplied to a methane enriched product gal flow in the post- reaction zone under methanization condition, where the post-reaction zone contains at least a methanization catalyst containing catalyst bed; and (g) deducting the methane enriched product gas flow at target pressure, where the adjustment of the target pressure takes place by condensing before the main reaction zone and/or before or in the post-reaction zone.    DESCRIPTION OF DRAWING(S) - The figure shows a schematic view of a methanization device for preparing methane enriched product gas flow.    Methanization device (100)    Pipes (101, 103)    Heat exchanger (104)    Methanization catalyst containing reactor (106)    Compressor. (117)