Heat integration aspects of exothermic biomethanation ─ A pilot reactor with shell-and-tube heat exchange capability

• An integrated reactor-heat exchanger is demonstrated for high rate biomethanation. • Feed gas pre-heating and tube-side heat exchange reduces axial thermal gradients. • Operation at 70°C is optimal for reaction conditions and external off-takers of heat. • Improvement in CH 4 production capacity to 13.4 NL CH4 L R -1 d -1 . • Full-scale utilization of up to 27.14% of the energy input is possible as heat. Biomethane (CH 4 ) production from green hydrogen (H 2 ) is a renewable replacement for fossil natural gas. As in the case of other hydrogenation reactions, the methanation of CO 2 for biomethane production is an exothermic process, which produces heat equivalent to 23% of the converted H 2 ′s heating value (HHV). During the scaling and advancement of technology readiness of trickle-bed biomethanation, exothermic heat production has become apparent and needs addressing via suitable experimental development to achieve stable thermal operation. This work presents the integration of an internal heat exchanger into a pilot-scale trickle-bed reactor for the biomethanation of raw biogas as CO 2 source. Without heat integration, the performance of the reactor tested was limited to a specific CH 4 productivity of 6.9 NL CH4 L R -1 d -1 , with a severe axial temperature gradient not optimal for stable thermal operation. With the active use of the heat exchanger and a feed gas pre-heating stage, the CH 4 productivity was enhanced up to 13.4 NL CH4 L R -1 d -1 , with a much smaller temperature gradient (48–71°C). In the future, other external off-takers that utilize the produced reaction heat will contribute to higher overall biomethanation efficiencies. This paper therefore also presents three energy balance scenarios (i.e. theoretical, pilot experimental, and future industry-scale) that exemplify the requirements and opportunities of heat-integrated biomethanation.