In Situ CO2 Capture in a Dual Fluidized Bed Biomass Steam Gasifier – Bed Material and Fuel Variation

Abstract

AbstractThe AER (absorption enhanced reforming) process, based on the dual fluidized bed steam gasification process, uses a bed material which, apart from its function as heat carrier, acts as a CO2 transporting agent and selectively transfers CO2 from the gasification reactor to the combustion reactor. Thus, a hydrogen‐rich gas is produced (H2 55...70 vol.‐%db, CH4 8...13 vol.‐%db, CO 5...11 vol.‐%db as well as CO2 7...20 vol.‐%db). Seven different CaO containing bed materials were tested for their principal applicability to the AER process with special focus on their influence on tar production. The amount of tars was generally found to be five times lower than with conventional gasification (at 850 °C) despite the low gasification temperatures (600–700 °C). Due to these low gasification temperatures, biomass with high alkali contents (e.g., straw), indicating a low ash melting point (< 800 °C), can be used under AER conditions. In summary, the AER process is very effective owing to the integration of the heat of the chemical reaction of CO2 with CaO and the water‐gas shift reaction, which are both exothermic, into the gasification and the internal reforming of primary and secondary tars, which cuts off the formation of higher tars.