Opportunities for Low-Grade Coals and Biomass for Producing Hydrogen Using Iron Oxide-Based Direct Chemical Looping Combustion with Effec- tive CO2 Separation

Coal and biomass are abundant in supply but contain carbon which, to avoid greenhouse gas emissions, needs to be sequestered after the primary energy conversion. A comparison is reported here of the performance of four different coals and biomass in an iron oxide-based direct chemical looping combustion system. The principal aim is to identify the coal and biomass with the highest H2 to CO2 ratio for a given amount of fuel, based on the resources (air and iron oxide) used. The impact of fuel blend (mix of coal and biomass) on hydrogen production is compared, and the effect of moisture content of the source fuel on hydrogen production is investigated. Simulation results suggest that low-grade coal can also produce the same amount of hydrogen as high grade coal, but with additional energy requirements. In achieving maximum hydrogen production, the final 20 to 30% of hydrogen production consumes the same amount of energy required by the initial 70% of production. When biomass is blended with 20% coal by mass, 10% additional hydrogen is produced. A 10% moisture content in the source fuel reduces the hydrogen production by 10% for high-grade coal while it eliminates the possibility for low-grade biomass to produce hydrogen within the available energy region. Potential improvements of the energy requirement to achieve maximum hydrogen production from low-grade solid fuels are also reported.