In-situ production, separation, and combustion of hydrogen in a monolithic-structured membrane reactor: Process modeling and reactor scaling

In this study, a novel intensified membrane reactor of monolithic square-channel structure is investigated, considering steam methane reforming, H₂ separation, and H₂-air combustion for power generation and sustaining autothermal operation of the membrane reactor. The work introduces an integrated approach that combines hydrogen production by steam methane reforming, selective permeation, and in-situ combustion within a single monolithic configuration, enabling direct thermal coupling between the combustion and reforming zones to enhance compactness and support autothermal operation. A three-dimensional CFD model is employed, incorporating a reduced H₂–air mechanism for combustion, a steam methane reforming model, and NOₓ formation model. The simulations first consider a non-reforming configuration in which a reformed gas mixture containing CH₄, H₂O, CO₂, and H₂ is supplied to the feed side. The effect of gas reactor temperature, feed gas compositions, operating pressure, and flow configuration (co-current vs counter-current) are analyzed to determine the optimal reactor operating conditions and NO_X emissions. Subsequently, a reforming configuration is examined, in which a feed stream containing methane and water is reformed. The reforming configuration results show that combustion on the permeate side slightly increased the average hydrogen flux compared to the case without permeate-side combustion, due to the higher permeate-side temperature that enhances membrane permeation. The equivalence ratio is on the lean side for the reforming case (φ ≈ 0.15–0.20) with extended flame compared to the non-reforming case (φ ≈ 0.5–3), due to early flame quenching by permeated hydrogen. Upscaling the reforming-with-combustion design to 5–10 MWe yields a plant-scale reactor requiring ≈ 3.2–6.3 × 10⁴ total channels.