Supercritical water gasification of biomass for H₂ production: Process design

The supercritical water gasification (SCWG) of biomass for H2 production is analyzed in terms of process development and energetic self-sustainability. The conceptual design of a plant is proposed and the SCWG process involving several substrates (glycerol, microalgae, sewage sludge, grape marc, phenol) is simulated by means of AspenPlus™. The influence of various parameters - biomass concentration and typology, reaction pressure and temperature - is analyzed. The process accounts for the possibility of exploiting the mechanical energy of compressed syngas (later burned to sustain the SCWG reaction) through expansion in turbines, while purified H2 is fed to fuel cells. Results show that the SCWG reaction can be energetically self-sustained if minimum feed biomass concentrations of 15-25% are adopted. Interestingly, the H2 yields are found to be maximal at similar feed concentrations. Finally, an energy balance is performed showing that the whole process could provide a net power of about 150kWe/(1000kgfeed/h).