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

Abstract

The 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 CO 2 transporting agent and selectively transfers CO 2 from the gasification reactor to the combustion reactor. Thus, a hydrogen-rich gas is produced (H 2 55...70 vol.-% db , CH 4 8...13 vol.-% db , CO 5...11 vol.-% db as well as CO 2 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 CO 2 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.

Steam gasification of various feedstocks at a dual fluidised bed gasifier: Impacts of operation conditions and bed materials

“…Despite the low gasification temperature, the tar levels are significantly lower than for standard gasification (bed material: olivine, gasification temperature: 850°C). Details on the AER process can be found in several publications [26,28,39]. Different limestones applying the AER process have been investigated by Soukup et al [39] and Höftberger [40].…”

The calcium looping cycle for CO2 capture from power generation, cement manufacture and hydrogen production

“…The CO 2 Acceptor Process consisted of two bubbling fluidised beds with solid system with a gasifier / carbonator operating at 600-700 C at atmospheric pressure and a combustor / calciner, which can handle 100 kWth fuel power. Much work has been done on suitability of sorbents for the process, with a focus on finding a sorbent with a suitable mechanical strength and reactivity without susceptibility for melt formation (Pfeifer et al, 2007;Soukup et al, 2009). AER operation can increase H 2 production from biomass -in comparison to an analogous process without CO 2 sorbent, which has been scaled up and is available commercially -from ~ 40 % to ~ 75 % v/v -while allowing a lower gasification temperature and producing lower tar emissions (due to catalytic cracking by CaO) .…”

Air–steam gasification of biomass in fluidized bed with CO2 absorption: A kinetic model for performance prediction

“…A separate reactor has to be provided for the purpose of CaO regeneration [6]. An innovative technique for this regeneration was reported in the form of a dual fluidized bed -absorption enhanced reforming (AER) process by the researchers [5,[15][16][17][18] at the Institute of Chemical Engineering, Vienna Institute of Technology. Instead of mixing the biomass with CaO sorbent or providing a separate reactor for CO 2 absorption, CO 2 affinity bed material was used in the study resulting in more than 75% H 2 purity.…”