Experimental study on the ash deposit thermal conductivity for ammonium bisulfate and fly ash blend with an in situ measurement technology

Abstract

Ammonium bisulfate (ABS) deposition is a severe problem in economizers and air preheaters, since it will result in the blockage of preheater, decreasing the efficiency and the corrosion of downstream devices. The blend deposition characteristics of ABS and fly ash blend, including thickness, effective thermal conductivity and heat flux through the probe surface, are investigated with an in situ measurement technology. The low flue gas temperature and high blending rate could promote the growth of blend deposit. The stable thicknesses of the blend deposits at different flue gas temperatures are 10.20 mm, 7.64 mm and 5.21 mm for different furnace temperatures (Case A, B and C, respectively). The stable thicknesses of the blend deposits with different blending rates are 10.20 mm, 5.52 mm and 3.36 mm for different blending rates (Case A, D and E, respectively). The effective thermal conductivities of blend deposits at the stable stage are 0.413, 0.397, 0.387, 0.357 and 0.28 W/m/K for Case A, B, C, D and E, respectively. In order to clarify the mechanism of the blend deposition, XRD and SEM-EDX are applied to analyze the blend deposits. The results indicate that the ABS content in blend deposit decreases with the increasing flue gas temperature and increases with the increasing blending rate. Meanwhile, the blend deposit with high ABS content has a more compact microstructure, a higher strength and a greater effective thermal conductivity. The results contribute to an insight into the ABS deposition characteristics in economizers and air preheaters.