PURPOSE: To give a reducing agent in the minimum necessary amount constantly by computing the necessary amount based on flow rate of water to be treated and the dissolved oxygen concn., measuring the dissolved oxygen concn. after a reducing agent addition., and adding the reducing agent in a specified necessary amount when the measured amount is either more or less than a predetermined value.
CONSTITUTION: When sea water 1 is made fresh water 4 through a reverse osmosis membrane 3, a reducing agent 5 is added to the sea water 1 in a pipeline 2 so as to remove oxygen dissolved in the sea water. To do it, the flow amount of the sea water 1 and dissolved oxygen concentration (SO) are detected and the sufficient amount of the reducing agent 5 to meet prescribed volume to the permissible (SO) is computed. Then, the open degree of a valve 7 to meet the prescribed injection amount is automatically set and the reducing agent is injected. When (SO) in the sea water 1 suddenly becomes more than the permissible value, (SO) after addition of the reducing agent 5 is detected by a (SO) detecting terminal 11. If the detected (SO) is higher than a short-term permissible value, the injection amount of the reducing agent 5 is corrected and increased, and when (SO) becomes less than the short-term permissible value, the correction is stopped and the amount is returned to the original amount.
YAMANAKA ZENKICHI
YAMATANI TOSHIO
SAITO KOICHI
SAWANO TAKASHIGE
