Biomass gasification under external heating and using steam as a gasifying agent: Numerical analysis

Gasification using an external heat source is considered as a high potential alternative to take high moisture content biomass into a fuel gas. This gas could reach energy densities close to 12 MJ/Nm3, which allows its use as a fuel in conventional thermal machines or as a precursor for higher fuel gases. Given this, in the present work allothermal gasification for a 50 %w.t. moisture content biomass was analyzed computationally aiming to yield a high hydrogen content syngas. Using a power supply of 8 kW, the dry tar-free gas yield was around 51.9 mol/kg of biomass with an average concentration of 45.7% CO, 44.8% H2, 4.8% CH4 and 4.6% CO2. A peak temperature of 1,070 K and 33% for chemical efficiency were achieved. In spite of using homogeneous heating along the reactor wall, the process temperature decreases near the gas outlet. This is due to solid material depletion decreasing the process thermal inertia. During the final stages, H2 and CO concentration also record an increase due to the endothermic carbon gasification as well as water-gas shift and methanation reactions.