CONTROL METHOD FOR CHLORINE INJECTION IN WATER PURIFYING PLANT

PURPOSE:To perform the controlling of chlorine injection that can deal with the abrupt change in water quality of determining the chlorine injection percentage from the detected values of the ammonia concn. and COD concn. of raw water and injecting chlorine until the residual chlorine at arbitrary points attain the prescribed value. CONSTITUTION:The ammonia concn. N and COD concn. of C raw water are measured with densitometers 6, 7 respectively, and are inputted to a chlorin injection rate operator 8 which operates chlorine injection percentage Y from the respective chlorine consumptions incorporated therein and outputs the same. The chlorine treated water flowing out from a mixing basin 2 is fed to a residual chlorine meter 9, by which the residual chlorine RCL is measured. The deviation DELTARCL of the residual chlorine RCL and the target value RCL0 is operated by a residual chlorine deviation operator 10 and is outputted therefrom. The deviation DELTARCL in excess of the permissible value is outputted from a decision device 11. In a chlorine injection percentage correcting operator 12, the corrected chlorine injection percentage Y1 is operated from the chlorine injection percentage Y and the deviation DELTARCL, and is outputted together with the inflow rate F from the flowmeter 4 to a chlorine injection percentage operator 13. Here, the chlorine injection percentage FY is operated, and a chlorine injection 14 injects chlorine in accordance with the chlorine injection percentage FY.