Concentration plant, plant for producing fresh water by concentration and for generating electric power, concentration method, and method for operating plant for producing fresh water by concentration and for generating electric power

A desalination device operated by a membrane method and a concentration device operated by a vaporization method are used in combination to thereby stably concentrate water containing a salt, such as accompanying water, at a low equipment cost and separate the water into fresh water and the salt. Accompanying water (20) is treated in pretreatment equipment (3) to remove solid substances and dissolved substances therefrom to thereby yield pretreated water (21). The pretreated water (21) flows into reverse osmosis membrane concentration equipment (4) and is separated into filtrate water (22) and membrane-concentrated water (24). The filtrate water (22) is utilized as fresh water. The membrane-concentrated water (24) flows into a precipitation part (10), in which an alkali is mixed therewith to precipitate insoluble matter. Thereafter, this membrane-concentrated water flows into a storage tank (5) together with discharge water (23) resulting from the pretreatment and sent from the pretreatment device (3), giving supply water (25) for vaporization concentration. The supply water (25) flows into vaporization concentration equipment (6) and is separated into condensed water (26) and vaporization-concentrated water (27). The condensed water (26) is utilized as fresh water. The vaporization-concentrated water (27) is stored in a concentrated-water tank (7). In the vaporization concentration equipment (6), the concentration is conducted using, as a heat source, steam generated in a waste heat recovery boiler (2).