(268a) Carbon-Negative Production of Hydrogen from Biomass and Waste – Opportunities and Challenges

Global interest and investment in hydrogen as a carbon-free energy carrier for power generation, transportation and industrial use has seen a recent upsurgence. Electrolysis based on renewable power from wind and solar is the standard approach for fossil-free production of hydrogen. However, biomass and waste can also be used to produce hydrogen with the potential to incorporate capture and sequestration of atmospheric CO₂ (via vegetation), thus achieving carbon-negative hydrogen production. Several gasification-based approaches are possible. Sorption-enhanced gasification (SEG) involves the use of two interconnected fluidized beds that circulate a mixture of bed material such as olivine and limestone/lime particles. Biomass is 80-85% converted in the steam-fluidized gasifier reactor. High-hydrogen synthesis gas is produced via a combination of steam reforming, water-gas shift, and in-situ sorption of resultant CO₂ by CaO particles. Unconverted char travels with the bed particles to the combustor reactor, where fluidizing air burns the char, thus heating up the bed particles and calcining the CaCO₃ to release CO₂ and regenerate CaO. Operating the combustor as an oxy-fuel reactor generates flue gas that is nearly pure CO₂. Another technology involves pressurized oxygen-blown, entrained-flow gasification of biomass or sorted MSW that has been pre-liquefied by flash pyrolysis. High carbon conversion can be achieved in a few seconds to produce a very clean syngas. Deep water-gas shift to convert the gas to H₂ and CO₂ followed by pressure swing absorption results in product streams of pure H₂ and CO₂. This presentation discusses the principles and chemistry of the two technologies, describes the designs of pilot-scale process development units at the University of Utah, and shares results of lab- and pilot-scale investigations.