Research on adhesion mechanism of ash particles and ammonium bisulfate on the metal wall in coal-fired boilers

摘要

The blockage of air preheater caused by ammonium bisulfate (ABS) associated with SCR denitration is serious, closely related to the adhesion of ABS and ash particles on the wall of the air preheater. This paper established an experimental platform to investigate the adhesion rate of ABS and ash particles on the mental wall, and the influences of the temperature, the particle size and the mass ratio of ABS to ash on adhesion rate were considered. To analyze the coupling mechanism of ABS and ash particles, the tests on micro characterization, pH/conductivity and BET were undertaken of the adhesive. The results show that liquid ABS is the root cause of ash particles sticking to the wall, and different condensation modes of ABS form different ash deposit layers. The strength of direct adhesion of ABS to the wall is greater than that of ABS and ash particle mixture, but the adhesion rate of the latter is significantly higher than the former. We found that the existence of ABS enhances agglomeration between particles and transforms the original morphology of ash particles. In addition, there exist physical adsorption and chemical reaction between ABS and ash particles, which change the adhesion rate of the mixture on the wall. The increase of temperature can promote the degree of physical adsorption and chemical reaction. Therefore, this work contributes to a deeper understanding of the adhesion mechanism of ash particles and ABS on the metal wall, providing guidance for the subsequent effective prevention and reduction of blockages in air preheaters.