Chemical hot gas cleaning concept for the 'CHRISGAS' process

The aim of the CHRISGAS project was the development of a gasification technique to produce clean hydrogen-rich synthesis gas from biomass. In order to improve the process efficiency, this work presents a gas cleaning concept, which combines chemical hot gas cleaning with hot (1 MPa, 900 oC) and warm (1 MPa, 300 oC) filtration. As the focus is set on the removal of H2S, HCl and KCl, calculations on chemical gas cleaning for the hot and warm gas filter were done using a thermodynamic process model using SimuSageTM (GTT-Technologies). The calculations show that Ca-based and Fe-based sorbents are not suitable H2S sorbents under the conditions of the hot gas filter. For Cu-based sorbents, H2S concentration below 100 cm3 m-3 is achievable, if the temperature is reduced below 810 oC. Additional calculations of KCl sorption on alumosilicates under the conditions of the hot gas filter show that the alkali concentration in gasifier-derived gases can be limited to 100 mm3 m-3. Thus, the condensation temperature of KCl can be decreased down to 580 oC. The results of HCl sorption calculations show that Na- and K-based sorbents are only suitable for temperatures below 600 oC. Therefore, the HCl sorption is transferred to the warm gas filter. The KCl sorption results were confirmed by experiments using bauxite, bentonite, kaolinite and naturally occurring zeolite as sorbents. -- Highlights: → Chemical hot gas cleaning for pressurized fluidized bed gasification of biomass. → Laboratory experiments and thermodynamic model calculations. → Aluminosilicates limit alkalis at 800 oC to < 0.1 cm3 m-3. → Cu-based sorbents reduce H2S at 800 oC to < 100 cm3 m-3.