PURPOSE: To make SO2 concn. constant, to increase denitration performance and to obtain stable denitration performance by introducing SO2 in the waste gas in case of catalytically reducing NOx with NH3 under existence of denitration catalyst in flue-gas denitration process.
CONSTITUTION: SO2 concn. contained in the wast gas sent from a boiler or a combustion apparatus is measured and a control valve 5 is actuated on the basis of load signal outputted from an SO2 concn. controller 3 and the necessary amount of gaseous SO2 2 is fed in the waste gas to maintain the SO2 concn. at constant value. The waste gas wherein SO2 has been fed is supplied to a denitration reactor 4 and subjected to catalytic reduction effectively under existence of NH3. The degree of denitration is improved by means of feeding SO2 and the change of denitration performance due to the change of fuel can be prevented.
MITSUOKA SHIGEAKI
IIDA KOUZOU
