CONTROLLING METHOD FOR INJECTION RATE OF CHEMICAL IN WATER SUPPLY SYSTEM OF BOILER

摘要

PURPOSE:To stably and certainly control an injection rate of a chemical by a method wherein the rotational speed of an injection pump is controlled according to the deviations between given specific electric conductivity and electric conductivities of water to be treated on the upstream and downstream sides of the ammonia injection point, and the stroke of the injection pump in proportion to the flow rate of water to be treated. CONSTITUTION:Specific electric conductivity detectors 2 and 6 are furnished between a condenser demineralizer 1 and condenser pump 3 and at the upstream side of a deaerator 7 to detect specific electric conductivities at the upstream and downstream sides of the ammonia injection point. Deviation signals between a specific electric conductivity at a given pH and the detected specific electric conductivities are obtained by a PID controller 13 and a proportion setting device 14, and a variable speed driving motor 15 of an ammonia injection pump 10 is controlled by a rotating speed controller 11. The flow rate of water to be treated is detected at the downstream side of a low voltage heater 4 by a water flow meter 5, and the stroke of the ammonia injection pump 10 is controlled by a stroke controller 12 via a driving unit 16 so that the injection rate of ammonia becomes proportional to the flow rate of water to be treated. Therefore, controls of the rotational speed and stroke of the ammonia injection pump 10 result in stable, certain control of the injection rate of ammonia even when a sharp change in pH.