The Power and Biomass to Methane (P&BtoM) technology is a key sustainable solution that combines electrical power and biomass to produce methane, playing a crucial role in ensuring a sustainable future. Funded by the European Union’s Horizon Europe research and innovation program, the METHAREN project aimed to develop an integrated system composed of an anaerobic digestion system, a biowaste gasification system, a solid oxide electrolyzer, and a syngas methanation to convert renewable electricity into e-biogas. The METHAREN pilot plant operates in various modes, leading to significant fluctuations in gas compositions and flow rates due to the intermittency of renewable energy sources. CEA designed an innovative orthoradial methanation reactor, featuring a tube and shell design with staged gas distribution and product collection, which was validated through an interactive experimental and numerical approach. Experimental results demonstrated 100% CO conversion and over 96% CO₂ conversion, with the numerical model validated against experimental data, enabling the confident design of the demo-scale methanation reactor.