Hydrogen production from biomass gasification; a theoretical comparison of using different gasification agents

In the present paper hydrogen production from biomass gasification using various agents is investigated and compared theoretically, from the viewpoints of the first and second thermodynamics laws. Gasification of wood and paper, as two types of common biomass feedstocks, is assessed using four gasification agents namely: air, oxygen-enriched air, oxygen and steam. Thermodynamic equilibrium model is employed to simulate the gasification process, the results of which are validated using available theoretical and experimental data in literature. The NOx and SOx emissions from the biomass gasification are also considered in the model and a sensitivity analysis is performed to determine the accuracy of the results regarding to the uncertainties of the input data. A parametric study is conducted to assess the effects of key operating parameters on the hydrogen concentration and calorific value of producer gas, energy and exergy efficiencies of the process and exergy destruction rate at different operating conditions. The results indicate that the higher values of hydrogen production is associated respectively with using steam, oxygen, oxygen-enriched air and air as the gasification agents. Also, it is concluded that for the gasification process the highest value of sensible energy efficiency is obtained for air gasification, while the highest exergy efficiency, as a rational criterion, is obtained for steam gasification for which the calorific value of the producer gas can reach to higher than 11 MJ/Nm3.