Biomass gasification using low-temperature solar-driven steam supply

A numerical modeling study on the low-temperature steam gasification process is presented to outline the possibility to drive the process with an integrated Concentrated Solar Power (CSP) plant, which provides low-temperature steam, with the aim of preserving a comparable efficiency of the new plant with traditional high-temperature biomass gasification processes. To meet this, the effective parameters and operating conditions are assessed and determined for low-temperature biomass gasification by means of sensitivity analysis, in order to find out the optimal design of the new gasifier. Crucial parameters comprise the residence time of the solid fuel and of the gas phase (leading to efficient gas-solid interactions), as well as the amount of injected oxygen and steam. Moreover, several operative parameters such as content of moisture in the biomass feedstock, size of the solid particles, equivalence ratio and structural components amount in the biomass feedstock are taken into account to optimize the operation. The molar ratio of H2/CO has been selected as a benchmark of efficiency in the process because the produced syngas would be applied in the methanol synthesis process, which needs a molar ratio of H2/CO close to the value of two. The percentage of the solid residue (weight % of the solid feedstock) has been evaluated along with the molar ratio of H2/CO in the low-temperature process to guide the re-design of the solar driven gasifier, in terms of reactor volume and amount of required oxygen and steam, which are necessary to sustain the process. The modeling and simulation to design the process have been accomplished by a comprehensive modeling package (GASDS), which includes kinetics of biomass devolatilization and pyrolysis, gasification, and secondary gas phase kinetic schemes. The gasifier, owing to its intrinsic multi-scale nature, is simulated describing both the particle and the reactor scales.