Biomass-waste gasification with CCUS

Gasification is a thermochemical process in which a feedstock (in this case biomass or waste) is heated to high temperatures in the presence of an oxidant (oxygen, air and/or steam) under non-stoichiometric conditions to avoid complete combustion. Depending on the operating conditions, such as temperature, catalysts and oxidant, a flue gas is produced consisting of varying percentages of H2, CO, CO2, CH4, CxHx and tars. The flue gas is upgraded and conditioned in a water gas shift (WGS) reactor in which steam reacts with CO in the presence of a catalyst to generate H2 and CO2. The gas leaving the WGS typically contains 65-70 vol% hydrogen, which can be purified by pressure swing adsorption (PSA), resulting in a high purity (99.9%) hydrogen stream. The CO2 is separated into a concentrated waste stream as an integral part of the process, thus providing a favourable source for CO2 capture and storage and, consequently, negative CO2 emissions. Biomass has an inherent low (< 1) hydrogen to carbon ratio, so the hydrogen yield from this feedstock is fundamentally lower than methane (100 g of H2 per kg of biomass as opposed to 300 g of H2 per kg of methane) requiring a higher intake of (limited) biomass if the goal is to produce a fixed hydrogen amount, but representing an attractive option if the goal is to sequestrate CO2 (although production of power and heat might be more attractive). Biomass gasification to obtain hydrogen offers great opportunities for process integration. Surplus heat can be used in other industrial processes or for district heating. The process can also generate other valuable products in addition to hydrogen, such as methane, biochar and food-grade CO2.