Ash melting temperatures for biomass fuels: Effect of fuel sample preparation by ashing at different temperatures

Abstract

In the discussion on biomass as a renewable energy source, its benefits are repeatedly recognised: - reducing greenhouse gas emissions by substituting fossil fuels; - increasing energy security by diversifying the energy mix and reducing dependence on imported fuels; - creating economic prospects by promoting rural development, job creation and valorisation of waste streams. However, the utilisation of biomass in combustion processes faces some challenges. This article emphasises one of them: the ash problem due to the pronounced tendency to form deposits on the heating surfaces. In order to properly design or select a biomass combustion system, the indicators of the tendency of biomass ash to form deposits on the heating surfaces must be adequately determined. Determining ash melting temperatures for biomass is crucial for understanding combustion behaviour and potential problems such as slagging and fouling. Biomass ash melting temperatures are typically determined at 550 °C for biofuels and 815 °C for solid mineral fuels. Some established certification schemes and national regulations favour the preparation of biomass samples by ashing at 815 °C. In this paper, the question is answered whether and how the ashing temperature of the biomass sample influences the characteristic points of the ash melting temperatures. The characteristic ash melting temperatures were determined for different types of biomass (wood chips, soybean and maize straw), where the ash sample was obtained by ashing at three different temperatures (550, 710 and 815 °C).