PURPOSE: To perform the treatment of waste gas with good efficiency by utilizing products in a circulating manner in which products formed in the washing of waste gas with an alkaline solution containing a denitrifying catalyst are decomposed by heating under a controlled temperature and then used in denitrification reactions.
CONSTITUTION: When the waste gas 21 containing SOx, NOx, and O2 is introduced into the absorption tower 6 and washed with an alkaline aqueous solution containing a denitrifying catalyst, desulfurizing, denitrifying, and oxidizing reactions occur to form crystallized products composed primarily of dithionic acid salt, sulfate, and imidedisulfonic acid salt. Then, after separating the crystallized products, the alkaline aqueous solution is sent to the gas stream thermal decomposition tube 3 where it is treated with the high-temperature gas 23 of a temperature above the thermal decomposition temperature of dithionic acid salt but below the decomposition temperature of imidedisulfonic acid salt. And, the SOx gas generated is sent to the absorption tower 6 and high-temperature solids are reduced to convert them into alkaline salts and then usedas washing agents. Thus, the products formed can be effectively used in the treatment of waste gas.
ANDOU KOUICHI
HIYOUDOU SUSUMU
