Study on the effects of the surface temperature on the formation of ammonium chloride and fly ash deposits

The selective catalytic reduction technology has the potential hazards of NH3 escape while catalytically reducing NOx. The HCl in the flue gas can react with the NH3 under certain conditions to form NH4Cl and deposit in the appropriate temperature range. In this study, the deposition behavior of fly ash and NH4Cl was studied by a charge‐coupled device (CCD) camera in a drop tube furnace under the condition of the NH4Cl atmosphere. To investigate the effect of surface temperature on the deposition characteristics, we set the surface temperature at 363 K for Case 1, 373 K for Case 2, and 383 K for Case 3, respectively. The CCD camera monitored the morphology of ash deposit growth, and two type‐K thermocouples measured the temperature of the inner and outer surfaces of the deposition probe. Collected deposit samples were analyzed by scanning electron microscopy and X‐ray diffraction. The results showed that the primary substance of the deposited sediments was salammoniac (NH4Cl). The crystal granules of NH4Cl in the deposited sediment were disconnected, and they were denser under the lower surface temperatures. The deposited layer caused a declination in the heat flux through the deposition probe, and the lower surface temperature was more conducive to the growth of the deposition. This work contributes to a deeper understanding of the characteristics of NH4Cl deposition, which has practical utility in preventing the formation of the NH4Cl deposition in the precipitator and induced draft fans.