Cross current staged reverse osmosis

A purification system comprising at least one reverse osmosis stage, wherein the at least one reverse osmosis stage includes:

• a liquid feed stream that is separated into a first feed input stream and a first feed bypass stream;
• a first reverse osmosis module having a high pressure side and a low pressure side;
• and
• a second reverse osmosis module having a high pressure side and a low pressure side;
• wherein the first feed input stream is pressurized to a pressure higher than a pressure of the liquid feed stream, and then received by the first reverse osmosis module high pressure side, and the first reverse osmosis module high pressure side outputs a yield stream;
• and
• wherein the first feed bypass stream, having the same pressure as the liquid feed stream, is received by the first reverse osmosis module low pressure side, and the first reverse osmosis module low pressure side outputs a first exit stream that is purified compared to the liquid feed stream;
• wherein the yield stream is split into a second feed input stream and a second feed bypass stream;
• wherein the second feed input stream is received by the second reverse osmosis module high pressure side, and the second reverse osmosis module high pressure side outputs a concentrate stream;
• and
• wherein the second feed bypass stream is received by the second reverse osmosis module low pressure side, and the second reverse osmosis module low pressure side outputs a second exit stream that is purified compared to the liquid feed stream;
• and
• wherein the first exit stream from the first reverse osmosis module low pressure side and the second exit stream from the second reverse osmosis module low pressure side are directly combined with each other to form a diluted stream;
• wherein the system further comprises a pressure retarded osmosis stage having a high pressure side and a low pressure side;
• wherein the high pressure side of the pressure retarded osmosis stage receives a high pressure concentrate stream and outputs a high pressure diluate;
• wherein the low pressure side of the pressure retarded osmosis stage receives a dilute solution and outputs a concentrated solution;
• wherein the high pressure concentrate stream is produced by pressurizing the concentrate stream of the at least one reverse osmosis stage using a pressure exchanger and a pump downstream of the pressure exchanger, so that the high pressure concentrate stream has a higher pressure than the concentrate stream of the at least one reverse osmosis stage;
• and
• wherein:
• (i) the high pressure diluate feeds the pressure exchanger that produces the high pressure concentrate stream;
• and
• (ii) the high pressure diluate feeds an energy recovery device.

A method for purifying a liquid feed stream to obtain an exit stream that is purified compared to the liquid feed stream, comprising:

• separating the liquid feed stream into a first feed input stream and a first feed bypass stream;
• pressurizing the first feed input stream to a pressure higher than a pressure of the liquid feed stream, and then sending the first feed input stream to a high pressure side of a first reverse osmosis module of a reverse osmosis stage;
• and
• sending the first feed bypass stream to a low pressure side of the first reverse osmosis module, wherein the feed bypass stream, having the same pressure as the liquid feed stream, received by the low pressure side;
• wherein the first reverse osmosis module low pressure side outputs a first exit stream having a first salinity and the first reverse osmosis module high pressure side outputs a yield stream;
• splitting the yield stream into a second feed input stream and a second feed bypass stream;
• sending the second feed input stream to a high pressure side of a second reverse osmosis module of the reverse osmosis stage and sending the second feed bypass stream to a low pressure side of the second reverse osmosis module;
• wherein the second reverse osmosis module high pressure side outputs a concentrate stream and the second reverse osmosis module low pressure side outputs a second exit stream having a second salinity;
• wherein the first exit stream from the first reverse osmosis module low pressure side having the first salinity and the second exit stream from the second reverse osmosis module low pressure side having the second salinity are combined to obtain the exit stream that is purified compared to the liquid feed stream.