Residual chlorine concentration control system and process method for purified water preparation

The invention provides a residual chlorine concentration control system and process method for purified water preparation, a source water tank, a source water pump, a heat exchanger, a pretreatment device, a reverse osmosis device and an EDI purified water device are connected in sequence, the pretreatment device comprises a filtering unit and a softening unit, the filtering unit can be an ultrafiltration or multi-medium filter, and the softening unit can be a reverse osmosis device or an EDI purified water device. A chlorine-containing medicament adding device is arranged on a passage between the source water tank and the source water pump, and a residual chlorine detector is arranged on a passage between the source water pump and the pretreatment device; the output end of the source water pump is connected to the source water tank to form a first circulation loop; and the output end of the pretreatment device is simultaneously connected to the source water tank and the pretreatment device to form a second c