The original reflux plate is arranged on the tower wall of the upper outlet area of the absorption tower, which results in the reflux of solid particles in the flue gas, further increases the retention time of particles, and strengthens the mixing between gas and solid. At the same time, the height of the tower body is increased, so that the reaction time between the absorbent and the flue gas in the tower is longer, and the residence time of the flue gas can reach more than 5S.