Interactions of high temperature H₂S and HCl cleaning sorbents with biosyngas main components and testing in a pilot integrated biomass gasifier SOFC system

Abstract

High temperature biosyngas cleaning is more efficient when the end user operates at elevated temperature, as in biomass gasifier solid oxide fuel cell systems. However, there is not much experience with this technology and low temperature gas cleaning is usually adopted. This paper advances current knowledge by presenting the results from the investigation of side reactions catalysed by commercially available sorbents involving biosyngas main components, and the results obtained with the pilot plant developed within the Horizon2020 project “Flexifuel-SOFC”. K₂CO₃, used for HCl removal, appeared catalytically active towards the water gas shift reaction. Under conditions representative of a real system, the residence time was not sufficient for the gas composition to reach thermodynamic equilibrium. ZnO–CuO, used for H₂S removal, showed a catalytic activity significantly higher. Both sorbents seemed not active towards the methanation reaction. The pilot plant tests confirmed the occurrence of the WGS reaction in the HCl removal reactor. The sorbents decreased H₂S and HCl below the target value of 1 ppmv for H₂S and 5 ppmv for HCl. The catalytic activity of sorbents and the heat released by these reactions should be carefully considered in the design phase of high temperature gas cleaning units.