DESULFURIZATION OF WASTE GAS

摘要

PURPOSE:To prevent the lowering in the activity of a limestone absorbing liquid in an absorbing tower, by injecting a soluble aluminum salt and an alkali agent in a gypsum slurry to remove impurities such as fluorine dissolved in the slurry while solidifying the same. CONSTITUTION:Exhaust gas (a) is subjected to dust removal, desulfurization and removal of impurities in an absorbing tower 1 by using a limestone slurry. The slurry from the absorbing tower 1 is oxidized in an oxidation tower 2 while the treated slurry is guided to a neutralization tank 3. An alkali agent such as NaOH is supplied in the neutralization tank 3 through an automatic control valve 13 so as to maintain the pH in said tank 3 to 7-8 and a soluble aluminum salt 22 such as aluminum sulfate is injected in said tank 3. The residual fluorine in the slurry is solidified by the flocculation action of aluminum sulfate and precipitated and removed along with gypsum. The supernatant liquid of a thickener 5 is re-utilized while returned into the absorbing tower 1. By this mechanism, it is prevented that fluorine is refluxed into the absorbing tower 1 through supernatant liquid and the lowering in the activity of limestone in the absorbing tower 1 can be prevented.