Process for the production of biomethane

The present invention relates to a biogas process for producing from hydrocarbon feedstock (200) comprising at least the following steps: - Gasification (201) of the feedstock to produce a synthesis gas in a gasification reactor, - waste (204) the syngas produced in the biomass gasification step in a purification unit, - methanation (206) the purified synthesis gas in a methanation reactor, - setting the specifications (207) of the gaseous mixture obtained in the methanation step synthesis gas for obtaining biogas. During the step of the specifications, a flux composed of at least carbon monoxide excess is recycled (208) into the gasification reactor. The invention also relates to a device for carrying out the method according to the invention.