Optimization studies of hydrogen production via biogas steam reforming

DEL PÓPOLO GRZONA M. VICTORIA; IZURIETA, EDUARDO M.; ADROVER, M. ESPERANZA; BORIO, DANIEL O.; LÓPEZ, EDUARDO; PEDERNERA, MARISA N.

Simposio; 8th Symposium on Hydrogen, Fuel Cells and Advanced Batteries; 2022

Although hydrogen is produced from many different raw materials and using diverse methods, hydrogen production from biogas/biomethane is identified as an interesting alternative in a process with low/zero fosil CO₂ emissions. Anaerobic conversion of organic raw materials into biogas provides not only a clean and renewable fuel, that consists almost exclusively of a mixture of methane and carbon dioxide (50-70% CH₄), but also a nutrient-rich digestate for land applications. Biomethane with up to 97% CH₄ can be obtained through biogas purification[1].In order to maximize H2 production, catalytic steam reforming of natural gas is preferred as it leads to the highest H2/CO ratio. This reaction is strongly endothermic and presents equilibrium limitations, which determines that the choice of the reactor results highly dependant on the process scale. For large-scale operations, a reactor with radiant heat transfer is prefered, while, at smaller scales, convective-type designs become convenient. In the latter reactors, heat is supplied through a stream of hot gases from a combustion chamber. The temperature of the hot gases is preferably selected under 1300 °C to preserve the mechanical integrity of the the reformer tubes assuring long life operation. The combustion chamber could be fed by fuel cell output stream, PSA stage rejection or the retentate stream of H₂ purifying membranes [2]. In order to improve energy integration and reduce reactor volumes, the implementation of two reactors showing different types of process intensification are proposed: biomethane steam reforming is conducted in a bayonet-type reactor while the water was shift reaction is performed in parallel with H2 purification in a membrane reactor. The design of bayonet reactors provides internal countercurrent heat recovery [3]. Although the using of convective heating implies lower heat fluxes when compared with radiant heating, the internal heat recovery and the absence of the radiant box lead to an overall simpler and smaller reactor design, with enhanced dynamics [3]. These facts point out the preference of this compact design for small-scale instalations, specially where a suitable fuel is available. Membrane reactors are an interesting intensification strategy as they combine in the same unit, the reaction and separation process. The membrane selectively removes one of the products of reaction and shifts the equilibrium towards products in equilibrium-limited reactions. In particular, if the removed product is H₂, constitutes a method to purify the desired product. In the present study, an autothermal process to produce ultrapure hydrogen from biogas is presented and analyzed. In order to maximize pure H2 production, optimization studies were performed over the integrated process.