Effect of Different Pretreatment Methods on the Mineral Transformation and Ash Behavior of Biomass in Co-Utilization with Coal

Abstract

The reduction of climate-relevant emissions, particularly CO2, can be easily achieved by a partial replacement of coal by biomass. This co-utilization of biomass and coal has an important effect on the ash composition and ash behavior. In the present study, two kinds of biomass of wheat straw and chili straw have been pretreated by different methods (kaolinite addition, acid washing and water washing) to prepare them for trouble-free operation in industrial applications. The mineral transformation and ash behavior of these blends are compared for the three pretreatment methods and the untreated biomass by several analytical techniques, including X-ray fluorescence (XRF), ash fusion temperatures (AFTs), X-ray diffraction (XRD), thermogravimetric analysis (TGA), scanning electron microscopy with energy-dispersive X-ray spectroscopy (SEM-EDS) as well as different key figures for ashes/slags, deposit formation and process-related behavior. The results indicate that the pretreatments have a recognizable effect on the ash composition and mineral transformations, which can noticeably modify ash melting temperatures and deposit formation in industrial-scale plants. The impact of the different pretreatment methods is unequal for the two studied biomasses. Finally, an assessment of the suitability of the differently pretreated biomasses blended with coal is performed for fixed-bed, fluidized-bed and entrained-flow plants.

Keywords: biomass, kaolinite addition, acid/water washing, ash behavior, mineral phases, key figures