Alkaline sorbent injection is an important method to remove SO_3 from coal-fired flue gas

while SO_2 in the flue gas may also react with the alkaline sorbent

which reduces the SO_3 remove efficiency of alkaline sorbent. In order to study the reaction rate and mechanism of reaction between SO_2/SO_3 and CaO at different temperatures

a corrosion-atmosphere-resistant absorption reaction device was designed and a reaction rate control model was established. The key reaction kinetic parameters were calculated. The results show that

the average reaction rates of SO_3 and CaO are 3.2 times

4.2 times and 4.0 times of that of SO_2 respectively at 350 ℃

400 ℃ and 450 ℃within 20 min. When CaO reacts with SO_2

the control step of the reaction rate is interface reaction. When CaO reacts with SO_3

the control step of the reaction rate is external diffusion. On this basis

a method is proposed to improve the removal efficiency of SO_3 by alkaline sorbent injection

namely reducing the external diffusion resistance from the sorbent side

such as fine grinding of the sorbent

atomization spraying after the sorbent is dissolved

and optimization of the flow field. In addition

decreasing the reaction temperature appropriately can reduce the consumption of sorbent by SO_2.