Two-step numerical procedure on the removal process of gaseous potassium chloride generated from waste incineration via the injection of sulfate-based additives

Gaseous potassium chloride (KCl) that constitutes a relatively large portion of the combustion gas of municipal solid waste can condense on the surface of boiler heat exchanger tubes, causing severe corrosion attacks. To reduce the chlorine-induced high-temperature corrosion, sulfate-based additives have been used. In this study, a two-step numerical procedure is proposed to quickly predict the effect of the injection of sulfate-based additives on the removal of gaseous KCl. A computational fluid dynamics (CFD) simulation is first carried out to obtain the temperature distribution. Then, the thermal decomposition of sulfate additives, sulfation of gaseous KCl, and condensation of K₂SO₄ are calculated to predict the species concentration profiles at the temperature conditions given by the CFD simulation. After validation with a laboratory-scale experiment using NH_{4 2}SO₄, the procedure is applied to a pilot-scale boiler to examine the effects of NH_{4 2}SO₄, Fe₂SO_{4 3}, and Al₂SO_{4 3}. The calculation results show that each additive has an optimal injection temperature range: approximately 800 °C for NH_{4 2}SO₄ and 1000 °C for both Fe₂SO_{4 3} and Al₂SO_{4 3}, which are consistent with the values reported in the literature. The expressions for the stoichiometric KCl removal efficiency of each additive are derived and compared with the calculated efficiencies.