Desalination apparatus and desalination method
View Patent ↗A desalination apparatus includes a pretreatment device 13 having a pretreatment membrane 13 a that filters suspended matters in raw water 11 with added chlorine-containing water 12 , a reverse osmosis membrane device 17 having a reverse osmosis membrane 16 that removes a salt content from filtrate water 14 supplied from the pretreatment device 13 to produce permeated water 15 , and a reducing-agent injection device 30 that neutralizes the added chlorine on an upstream side of the reverse osmosis membrane device 17 . The reducing-agent injection device 30 extracts a part 14 a of the filtrate water 14 , adds metering SBS solution 18 to the part, obtains a maximum change point (equivalence point) of the oxidation-reduction potential of a reducing agent and chlorine, obtains reducing-agent additive concentration (Csm) corresponding to the equivalence point, and supplies the SBS solution 18 corresponding to the concentration to the filtrate water 14 to thereby neutralize the chlorine.
1. A desalination apparatus comprising:
a line for flowing raw water with added chlorine-containing water;
an extraction line for extracting a part of the raw water from an extraction position of the line as an extracted water;
a reducing-agent tank for adding a reducing agent solution to the line downstream of the extraction position so as to neutralize chlorine of the raw water;
a control valve provided between the line and the reducing-agent tank, for controlling an additive amount of the reducing agent solution in response to a flow regulation signal;
a reverse osmosis membrane device including a reverse osmosis membrane that removes a salt content from the raw water to thereby produce permeated water, the reverse osmosis membrane device being provided downstream of a supply position of the reducing agent solution;
a metering reducing-agent supply tank that supplies a metering reducing agent solution to the extraction line;
a sequencer that supplies a metering reducing-agent supply signal having a pattern of change;
a flow-variable metering pump provided between the extraction line and the metering reducing-agent supply tank, for changing a supply flow rate of the metering reducing agent solution in response to the metering reducing-agent supply signal;
an oxidation-reduction potential (ORP) meter that measures an oxidation-reduction potential of the extracted water of the extraction line downstream of a supply position of the metering reducing agent solution and produces a ORP signal; and
an arithmetic device configured to:
receive the metering reducing-agent supply signal and the ORP signal;
based on the metering reducing-agent supply signal and the ORP signal, obtain an equivalence point which is a maximum change point of the oxidation-reduction potential of the metering reducing agent solution and chlorine of the extracted water;
obtain a reducing-agent additive concentration (Csm) corresponding to the equivalence point;
obtain the additive amount of the reducing agent solution corresponding to the reducing-agent additive concentration (Csm); and
output the flow regulation signal to the control valve.
2. The desalination apparatus according to claim 1 , further comprising a pretreatment membrane that filters suspended matters in the raw water, the pretreatment membrane being provided on the line.
3. The desalination apparatus according to claim 1 , wherein the pattern of change of the metering reducing-agent supply signal is configured so that the supply flow rate of the metering reducing agent solution is changed in a stepwise manner.
4. A desalination method implemented by using a reverse osmosis membrane device including a reverse osmosis membrane that removes a salt content from raw water to thereby produce permeated water, the reverse osmosis membrane device being provided on a line for flowing the raw water with added chlorine-containing water,
the desalination method comprising:
adding a reducing agent solution to the line so as to neutralize chlorine of the raw water;
extracting a part of the raw water from the line as an extracted water;
controlling an additive amount of the reducing agent solution in response to a flow regulation signal;
removing a salt content from the raw water downstream of a supply position of the reducing agent solution and producing permeated water;
adding a metering reducing agent solution to the extracted water;
supplying a metering reducing-agent supply signal having a pattern of change;
changing a supply flow rate of the metering reducing agent solution in response to the metering reducing-agent supply signal;
measuring an oxidation-reduction potential of the extracted water and producing an ORP signal;
receiving the metering reducing-agent supply signal and the ORP signal;
based on the metering reducing-agent supply signal and the ORP signal, obtaining an equivalence point which is a maximum change point of the oxidation-reduction potential of the metering reducing agent and chlorine of the extracted water;
obtaining a reducing-agent additive concentration (Csm) corresponding to the equivalence point;
obtaining the additive amount of the reducing agent solution corresponding to the reducing-agent additive concentration (Csm); and
output the flow regulation signal to the control valve.
5. The desalination method according to claim 4 , wherein the pattern of change of the metering reducing-agent supply signal is configured so that the supply flow rate of the metering reducing agent solution is changed in a stepwise manner.