Green Hydrogen from Biomass Through Gasification—A Carbon Negative Route for Hydrogen Production

Nature fixes hydrogen as an element in only two compounds: water and biomass. Biomass, a typical CXHYOZ compound produced naturally through the process of photosynthesis, on a specific basis, contains about 520 g of carbon and about 61 g of hydrogen with the balance being oxygen. In the process of gasification, under sub-stoichiometric auto thermal conditions, biomass is converted to hydrogen-rich synthetic gas when using superheated steam and oxygen as the gas phase reagents. Operating in the stoichiometry range of 0.25 to 0.30 and steam to biomass ratio of 2.0 to 2.5, hydrogen-rich syngas, of typical composition 45% H2; 15% CO; 5% CH4; 10% N2 and 25% CO2, is generated which contains close to 135 g of H2 per kilogram of biomass. It is important to note that while biomass contains only about 61 g of H2 the enhanced yield in syngas is due to the contribution by both biomass and steam. The patented gasification system is configured to leverage the carbon present in the biomass to act as a reducing agent for steam and thereby generate additional H2. The syngas so generated is subjected to swing adsorption-based separation adopting a patented configuration and operating on an adapted Skarstrom cycle. The separation system generates bio-hydrogen of desired quality and has been tested exhaustively over a range of capacities to generate ISO 14687-2019 Type I Grade D quality H2 at recovery factor of over 75%. On the realized recovery basis, every kg of dry biomass yields 85 g of ISO 14687 quality H2. It is important to mention that every kg of H2 generated through the gasification route fixes close to 300 g of solid carbon in the form of char, which on equivalent basis amounts to about 1.1 kg of carbon dioxide. Thus, the system is inherently carbon negative and coupled with carbon capture technologies, and it is possible to capture close to 12.5 kg of carbon dioxide per kg H2. Learning objectives