Ash deposit formation during the combustion of pulverized grape pomace in a drop tube furnace

This article concentrates on the ash deposit formation during the combustion of pulverized grape pomace in a drop tube furnace. All experiments were conducted for a wall drop tube furnace temperature of 1200 °C. Initially, axial measurements of temperature, major gas species concentrations and particle burnout were obtained for a representative drop tube furnace operating condition. These measurements allowed to establish the drop tube furnace axial position to place a deposition probe, fitted with a removable stainless steel capsule, to study the ash deposit formation. Subsequently, detailed data on ash deposit formation rates were obtained for seven probe exposition times between 2 and 14 h. Finally, deposit samples for all exposition times were analysed on a scanning electron microscope equipped with an energy dispersive X-ray detector. Important distinct features of the present study include the examination of the temporal evolution of the deposit characteristics, such as their sintering degree, which is critical to assess the need for boiler cleaning, and the method of analysis of the deposits chemical composition. It is concluded that the sintering degree of the deposits increased with the probe exposition time and for exposition times above 8 h, the deposits are very difficult to remove. It is also observed that the impact of the probe exposition time in the concentrations of potassium, phosphorus and magnesium is marginal, and that the oxygen concentration decreases as the probe exposition time increases, while the opposite behavior is observed for calcium and silicon. Overall, the results reveal that the use of this biomass residue in industrial combustion systems may pose severe operational and maintenance problems, requiring frequent boiler cleaning.