Multi-stage seawater desalination apparatus and operation control method of multi-stage seawater desalination apparatus

A multi-stage seawater desalination apparatus comprising:

• a high-pressure pump that is mounted on a raw water line through which raw water is supplied, and increases pressure of the raw water to a predetermined high pressure;
• a high-pressure reverse osmosis device that includes a high-pressure reverse osmosis membrane for concentrating a salt content in high-pressure feed water whose pressure is increased by the high-pressure pump;
• a first drain valve that is mounted on a permeated water line through which permeated water that has passed through the high-pressure reverse osmosis device is supplied downstream, and temporarily drains the permeated water of an initial start-up;
• a low-pressure pump that is mounted on the permeated water line provided downstream of the first drain valve, and reduces pressure of the permeated water to a predetermined low pressure;
• a low-pressure reverse osmosis device that includes a low-pressure reverse osmosis membrane for concentrating a salt content in low-pressure feed water whose pressure is reduced by the low-pressure pump;
• and
• a second drain valve that is mounted on a discharge line on a concentrated water side of the low-pressure reverse osmosis device, and temporarily discharges the low-pressure feed water of the initial start-up supplied to the low-pressure reverse osmosis device.