CONTROLLING METHOD FOR CHLORINATION IN WATER PURIFICATION PLANT

PURPOSE:To maintain the residual chlorine in treated water accurately to a target value in controlling of chlorination to raw water by correcting the target value of the residual chlorine in accordance with the pH of the raw water, and correcting the rate of chlorination according to the deviation between the corrected target value and the residual chlorine. CONSTITUTION:In a water purification plant, raw water is fed to a chlorine demand meter 9, by which its chlorine demand K2 is measured. The value thereof is fed to a chlorination rate operating circuit 10, which determines a basic chlorination rate CL in accordance with a residual chlorine target value K1. The treated water injected with chlorine from a chlorinator 14 is conducted to a residual chlorine concn. meter 16, by which the residual chlorine RCL is measured and this is inputted to a comparator 29. The pH of the raw water is measured with a pH meter 17, and is inputted to a consumption rate operating circuit 18, which determines a chlorine consumption rate CCL in accordance with a residence time Tn. This is inputted to a residual chlorine command operating circuit 19 which determines a residual chlorine command value K3 in accordance with he chlorination rate DCLT before the time Tn. The value K3 is applied to the comparator 20, which compares this with an actual residual chlorine value RCL and determines a deviation DELTARCL. This deviation is inputted to an operation circuit 11 which corrects the rate CL from the circuit 10.