Effect of pre-treatment of herbaceous feedstocks on behavior of inorganic constituents under chemical looping gasification (CLG) conditions

Abstract

Biomass chemical looping gasification (BCLG) is a promising key technology for producing carbon neutral liquid biofuels. However, various ash-related issues, such as bed agglomeration, fouling and slagging, or high-temperature corrosion may cause significant economic and ecologic challenges for reliable implementation of BCLG. Biomass pre-treatment methods, such as torrefaction, (water-)leaching and combination of both approaches may significantly improve ash-related characteristics and therefore provide a promising approach for enabling the use of herbaceous residues. This study deals with essential lab-scale investigations under well-defined, gasification-like conditions at 950 °C, joint with thermodynamic equilibrium calculations. Fundamental knowledge on the influence of pre-treatment methods on the release and fate of volatile inorganics as well as on the ash melting behavior of the residual ashes was gained. Molecular Beam Mass Spectrometry (MBMS) was applied for in situ online hot gas analysis of (non-)condensable gas species during gasification of pre-treated feedstocks. Both ash composition and behavior were characterized particularly by X-ray powder diffraction method and hot stage microscopy (HSM). The results obtained by chemical characterization were taken into account for thermodynamic modelling. Based on the results, conclusions were drawn on how different pre-treatment technologies can help to improve and solve ash-related issues during thermochemical conversions. It has been demonstrated that (combined) pre-treatment methods can counteract the above-mentioned problems and have a noticeable effect on the principal inorganic constituents (e.g. K, Ca, Si) originating from the ash by shifting their proportions.