PRECIPITATION SYSTEM AND PRECIPITATION METHOD
A precipitation system for precipitating the target component is provided. The precipitation system includes: a reverse osmosis module; a precipitation device; a membrane separation device that includes a semipermeable membrane module including a first chamber and a second chamber separated by a semipermeable membrane, and that makes the feed solution after precipitation of the target component in the precipitation device flow to each of the first chamber and the second chamber and pressurizes the feed solution in the first chamber to transfer water into the second chamber via the semipermeable membrane and thereby concentrate the feed solution in the first chamber and dilute the feed solution in the second chamber; first return means for returning the feed solution concentrated in the membrane separation device to the precipitation device; and second return means for returning the feed solution diluted in the membrane separation device to the reverse osmosis module.
1 . A precipitation system for, from a feed solution in which at least one type of target component is dissolved in water, precipitating the target component, the precipitation system comprising:
a reverse osmosis module that separates water from the feed solution, pressure of the feed solution being raised to a predetermined pressure, via a reverse osmosis membrane to concentrate the feed solution;
a precipitation device that cools the feed solution concentrated in the reverse osmosis module to a stipulated temperature to precipitate the target component;
a membrane separation device that includes a semipermeable membrane module including a semipermeable membrane, and a first chamber and a second chamber separated by the semipermeable membrane, and that makes the feed solution after precipitation of the target component in the precipitation device flow to each of the first chamber and the second chamber and pressurizes the feed solution in the first chamber so that pressure of the feed solution in the first chamber becomes higher than pressure of the feed solution in the second chamber to transfer water contained in the feed solution in the first chamber into the second chamber via the semipermeable membrane and thereby concentrate the feed solution in the first chamber and dilute the feed solution in the second chamber;
first return means for returning the feed solution concentrated in the first chamber of the semipermeable membrane module in the membrane separation device to the precipitation device; and
second return means for returning the feed solution diluted in the second chamber of the semipermeable membrane module in the membrane separation device to the reverse osmosis module.
2 . The precipitation system according to claim 1 , wherein the feed solution after precipitation of the target component in the precipitation device is supplied to the membrane separation device after the feed solution is heated.
3 . The precipitation system according to claim 1 , wherein:
the feed solution contains a concentration component that is a component other than the target component; and
the target component precipitates, and the concentration component is concentrated.
4 . The precipitation system according to claim 3 , wherein if a concentration of the concentration component in the feed solution becomes equal to or exceeds a normal concentration, a part of the feed solution is recovered.
5 . The precipitation system according to claim 1 , wherein a precipitate containing the target component precipitated in the precipitation device is recovered after the precipitate is rinsed using a part of the feed solution, water discharged from the reverse osmosis module or the feed solution diluted in the second chamber of the semipermeable membrane module as a rinse liquid to an extent that the target component is not dissolved.
6 . The precipitation system according to claim 5 , comprising third return means for returning the rinse liquid after use for the rinsing to the reverse osmosis module.
7 . The precipitation system according to claim 1 , wherein the semipermeable membrane of the semipermeable membrane module is a hollow fiber membrane.
8 . The precipitation system according to claim 7 , wherein in the semipermeable membrane module, a space on an outer side of the hollow fiber membrane is the first chamber and a space on an inner side of the hollow fiber membrane is the second chamber.
9 . The precipitation system according to claim 1 , wherein:
the membrane separation device is a multi-stage membrane separation device including a plurality of semipermeable membrane modules each including the semipermeable membrane module;
the plurality of semipermeable membrane modules are connected in series in a flow direction of the first chamber;
the plurality of semipermeable membrane modules include a final module that is the semipermeable membrane module located on a downstream-most side in the flow direction of the first chamber, and at least one upstream module that is the semipermeable membrane module other than the final module; and
the feed solution flows through the first chamber of the upstream module, a part of the feed solution that has flowed through the first chamber of the upstream module flows through the first chamber of the final module, another part of the feed solution flows through the second chamber of the final module, and the feed solution that has flowed through the second chamber of the final module flows through the second chamber of the upstream module.
10 . A precipitation method for, from a feed solution in which at least one type of target component is dissolved in water, precipitating the target component, the precipitation method comprising:
a reverse osmosis step of separating water from the feed solution, pressure of the feed solution being raised to a predetermined pressure, via a reverse osmosis membrane to concentrate the feed solution;
a precipitation step of cooling the feed solution concentrated in the reverse osmosis step to a stipulated temperature to precipitate the target component;
a membrane separation step of, using a semipermeable membrane module including a semipermeable membrane, and a first chamber and a second chamber separated by the semipermeable membrane, making the feed solution after precipitation of the target component in the precipitation step flow to each of the first chamber and the second chamber and pressurizing the feed solution in the first chamber so that pressure of the feed solution in the first chamber becomes higher than pressure of the feed solution in the second chamber to transfer water contained in the feed solution in the first chamber into the second chamber via the semipermeable membrane and thereby concentrate the feed solution in the first chamber and dilute the feed solution in the second chamber;
a first return step of returning the feed solution concentrated in the first chamber of the semipermeable membrane module in the membrane separation step to the precipitation step; and
a second return step of returning the feed solution diluted in the second chamber of the semipermeable membrane module in the membrane separation step to the reverse osmosis step.