PURPOSE: TO prevent the deposition of solid in the main pipe and the clogging of the spray nozzle, when the solid slurry from the wet system waste gas desulfurization plant, etc., is sprayed from the branch pipe of the main pipe, by arranging this branch pipe along the tangential(normal) line for the lowest point of the main pipe.

CONSTITUTION: The waste gas including SO2 is cooled and is introduced to the absorption tower 2, and is contacted with the absorbent solution like as the limestone slurry being sent through the branch pipe 8 and the spray nozzle 9 from th e main pipe 3 for recycling the absorbent solution; hereby, the waste gas is desulfurized. Hereupon, the branch pipe 8 is being arranged along the normal or tangential direction for the lowest point of the diameter ring of the main pipe 3. According to this method, the solid slurry arriving at the spray nozzle 9 from the main pipe 3 is not retained in the main pipe 3 when the operation is stopped; therefore, the deposition of solid in the main pipe 3, the clogging of the nozzle 9, etc., are prevented.