Bioenergy Via Char Gasification with Carbon Capture and Storage: An Alternative to Beccs

IPCC techno-economic models suggest that staying below the 2^oC limit set forth by the Paris Agreement will require negative emissions technologies, with a majority of models incorporating bioenergy with carbon capture and storage (BECCS). However, there are several limitations to the most commonly described BECCS approach such as competition for water, land, and energy resources as well as difficulty in separating CO₂. We propose a novel BECCS alternative which uses biowaste and pyrolyzes it into biochar. This biochar would then be gasified at a larger power plant in CO₂ to generate syngas as a fuel for a solid oxide fuel cell (SOFC). The fuel cell would produce a stream which is almost all H₂O and CO₂, easily separated through condensation into a CO₂ stream for sequestration.

The biochars we have derived experimentally were from food waste (walnut shells, pistachio shells, corn cob, and pumpkin seeds). Several pyrolysis conditions such as ramp rate, moisture content, and purge atmosphere were investigated to understand reactivity in gasification. Chars with high ash content (e.g. corn cob) were most reactive with CO₂, perhaps from the inorganics present in ash. Fast pyrolysis yielded a more reactive biochar and biowaste drying before pyrolysis made the biochar less reactive in gasification. We will present both a techno-economic analysis of the alternative BECCS scheme and experimental data on pyrolysis and biochar gasification. We performed ASPEN simulations to compare our data to traditional BECCS models. [Fajardy, M; Dowell, N. Energy Environ. Sci., 2017, 10, 1389-1426].