Validation of Double Wall Reactor for Direct Biogas Upgrading via Catalytic Methanation

Abstract

Actively cooled fixed bed reactors for catalytic methanation provide the opportunity for stable operation as temperature hotspots and thermal runaways occur in existing multi-stage fixed bed set-ups in commercial scale. This short paper reports on the experimental investigation of three cooled double wall reactors for direct biogas upgrading via catalytic methanation. The inner diameter (14, 18 and 27.3 mm) of the reactors has been significantly reduced to evaluate the improvement of the thermal management. The reactors have been tested in an existing pilot plant under varying operation parameters such as pressure and gas hourly space velocities (GHSV). As validation parameters, the CO₂ conversion rate and the measured temperature profile in the catalyst bed are considered. The thinnest reactor with an inner diameter of 14 mm performs best regarding the CO₂ conversion rate at all operating points, and the CO₂ conversion ranges between 99.7 and 97.6% at GHSV of 4,000 and 20,000 h⁻¹, respectively. Also, the maximum catalyst temperature of 510 °C is not exceeded at high catalyst loads (15,000 and 20,000 h⁻¹) to ensure long stability and activity of the catalyst. In comparison, in a reactor with an inner diameter of 27.3 mm far lower conversion rates (98.5% and 88.5% at 4,000 and 20,000 h⁻¹, respectively) can be achieved in one reactor stage while the maximum measured temperature in the catalyst bed lies around 600 °C. The most favorable reactor design for biogas upgrading at high catalyst loads corresponds to the reactor with the thinnest inner diameter. Beside well performing, a thin cooled reactor is characterized with a reduced system complexity and low investment costs. Furthermore, an easy scale up is possible while ensuring simplified operation.