PURPOSE: To reduce steam consumption remarkably by adding H2SO4 to the supernatant liquid discharged from a gypsum separation stage, to adjust the concn. to 0.5W5%, introducing the supernatant liq. to an acid decomposing tank where the COD component is decomposed without forcibly degassing generated SO2.
CONSTITUTION: The supernatant liquid 22 from a gypsum separation stage 4 is led to a sulphuric acid mixing tank 11 where H2SO4 is added to attain 0.5W5% H2SO4 concn., then the liquid is led to a steam mixing device 12 where the liq. is heated with steam 32 to 95W130°C. The hot supernatant liquid 22 contg. added H2SO4 31 is led to a sufficiently insulated decomposing tank 13 where it is decomposed under a pressure above the saturated vapor pressure of the supernatant liquid 22. COD components contained in the liquid such as dithionic acid, S-N compds., etc. are removed in this stage without degassing generated SO2 forcibly from the decomposition tank 13, and the treated liquid 22' in the acid decomposition stage is then cooled to ≤ca.80°C. Then, it is led to a cooling stage where it is reused for replenishing water of the cooling stage 1.
SAWAI TOORU
FUNAKOSHI TOSHIO
KAKIMOTO AKIRA
FUJIWARA ISAMU
SATOU MOTONARI
