Abstract: In this paper we present our investigations on biomass used as renewable energy. The numerical study of biomass gasification and methanation in fluidized bed was carried out in the framework of the GAYA project supported by ADEME (French Agency For Environmental Protection and Energy). We have developed a sharp expertise in the modeling of the hydrodynamic of single or multiple phase fluidized beds. Indeed, specific sub-models have been developed to represent particles/particles and fluid/particles interactions. Our tools are now able to help improving an industrial scale gasifier and methanation reactor unit design by defining optimal operating conditions and instrumentations location.