Biomass fly-ash deposition: Dependence of deposition rate on probe/particle temperature in 115–1200 °C range

Abstract

Seven biomass fuels were fired to determine the relationship between the ash deposition rate and the probe/ash-particle temperature varied in the 115–1200 °C range. The experiments were carried out at deposition-probe Reynolds number in the 40–60 range and Stokes number in the 0.8–1.9 range. The relationship between the deposition rate and probe/ash-particle temperature was determined to have a U-shape with the largest rates occurring at the largest (in excess of 1100 °C) and the lowest (115 °C) temperatures. When both the flue-gas and probe temperatures were in excess of 1100 °C, inertial impaction was the mechanisms of deposit build up; a correlation between the sticking propensity and (K + Na + Ca)/(Si + Al + Fe) ratio was observed. Thermophoresis was identified as the primary mechanism of deposit build up at 600 °C probe temperatures and 978 °C flue-gas temperature. At probe temperatures around 115 °C, condensation of Potassium salts was substantial, and so was thermophoresis both forming a sticky layer on the deposition surface. Thus, condensation, inertia impaction and thermophoresis have contributed to the deposit build-up at 115 °C probe temperature although in different proportions depending on the fuel combusted.