Abstract: During the operation of the selective catalytic reduction (SCR) denitrification unit in coal-fired power plants, part of SO₂ will be oxidized to SO₃, which leads to the air preheater clogging caused by the deposition of ammonium bisulfate. In order to solve the problem of ammonia bisulfate clogging in the air preheater of a power plant, the alkaline adsorbent injection was proposed to remove SO₃ in the flue gas of SCR inlet and outlet flue ducts. To solve the problem of NH₄HSO₄-induced blockage in the air preheater of a power plant, based on computational fluid dynamics (CFD), the SCR and its inlet and outlet flue ducts were modelled and numerically simulated. A variety of arrangement schemes were proposed to quantitatively analyze the degree of mixing homogeneity. Moreover, the effects of the particle size on the mixing homogeneity were also taken into account. The results show that the average residence time of the adsorbent particles in the flue is 9.53 s and 3.41 s for the gun arrangement at the inlet and outlet, respectively. The highest cover rate of the inlet arrangement scheme is up to 50.1%, with the standard deviation of the concentration being less than 1.4. Increasing the total number of spray guns and the spacing between guns is beneficial to the enhancement of gas-solid mixing. The optimal schemes are Scheme F and Scheme K. When the adsorbent particle size is larger than 50 μm, the cover rate of the particles at outlet will be lower than 25%, with risk of inhomogeneous gas-solid mixing and erosion of the flue wall increasing. However, after the particle size is reduced to less than 25 μm, the distribution characteristics of the adsorbent concentration do not change significantly.