CO2 gasification in a dual fluidized bed reactor system: Impact on the product gas composition

The use of CO₂ as gasification agent in the 100 kW_th dual fluidized bed gasification pilot plant was investigated at TU Wien. For this purpose, steam as gasification agent was replaced stepwise by CO₂. Softwood was used as fuel and olivine as bed material. Starting from 100 vol.-% steam as gasification agent, substituting it by 32, 45 and finally 68 vol.-% CO₂. All loop seals were fluidized further with steam, which resulted in these volume percentages. Additionally, a CO₂ gasification test campaign converting softwood with a mixture (90/10 wt.-%) of olivine and limestone was investigated. For this case, the gasification agent was composed of 65 vol.-% CO₂ and 35 vol.-% steam. The use of CO₂ as gasification agent led to changes of the product gas. Instead of a H₂-enriched product gas, which was produced during steam gasification, CO and CO₂ occupied the major share of the product gas. Consequently, the H₂/CO ratios as well as the lower heating values decreased when substituting steam by CO₂. Tar contents were lower for CO₂/steam gasification compared to pure steam gasification.