With the application of selective catalytic reduction (SCR) technology, the operation of rotary air preheaters is faced with a challenge, the fouling problem caused by ammonium bisulfate (ABS). In previous studies, within the operational temperature range of the preheater, the gaseous ammonia and sulfur trioxide (or H2SO4) in the flue gas can react to form ABS and ammonium sulfate (AS). The initial condensation temperature of ABS might be over predicted due to the effect of the formation of AS, which has a higher initial formation temperature than ABS. In this study, the effects of the deposition temperature, ammonia-sulfur molar ratio and molar product of inlet flue gas on the deposition characteristics of inducing ash deposition compounds were experimentally studied to provide guidance to prevent fouling and corrosion of rotary air preheaters. The results show that the main path to generate ABS is the reaction between H2SO4 and NH3. With the increase in the deposition temperature, the contents of NH4+ and SO42− in the sediments decrease continuously, and the proportion of AS deposition increases. On the contrary, with temperature decreasing, more ABS is deposited. When the molar ratio of ammo-sulfur in the inlet flue gas increases, the proportion of AS in the sediments increases, and the deposition rate also gradually increases. When the ammo-sulfur product in the inlet flue gas increases, the concentrations of both NH4+ and SO42− in the sediments increased in a nearly consistent trend. The variations of the ratio and deposition rates of the two ions in the sediments were not obvious. The ratio of NH4+ and SO42− remains at about 1.2, and the sediment is mainly ABS.

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