Method for reducing monovalent ions in concentrate of nanofiltration system and the nanofiltration system
This specification describes a method for lowering the content of monovalent ions in a final concentrate of a nanofiltration system relative to a brine and a corresponding nanofiltration system. The nanofiltration system comprises at least three stages of nanofiltration, wherein the concentrate from each segment flows into the next segment. A feed stream is sent into one stage to generate a concentrate stream, and a first portion of the concentrate stream is recirculated to the one stage. The pH of the feed stream is controlled in a range of 2-7. The temperature of the feed stream is in a range of 20-60° C. The feed stream includes the recirculated concentrate stream and at least part of a concentrate generated from an upstream stage. The method and the system described herein can reduce the concentration of monovalent ions in the final concentrate during a nanofiltration separation process.
1. A method for operating a nanofiltration system, the nanofiltration system comprising at least three stages of nanofiltration with concentrate staging between the stages, the method comprising:
introducing a feed liquid to one stage and producing a concentrate;
recirculating a first portion of the concentrate to the one stage;
controlling the feed liquid in a pH range of 2 to 7 and a temperature range of 20° C. to 60° C., and,
controlling a permeate flux of the nanofiltration system to be 20 L/m 2 ·h or less
wherein the feed liquid comprises at least part of a previous concentrate produced by a previous stage and the first portion of the concentrate and wherein the recirculating is carried out with a recirculation rate of about 1 or more.
2. The method of claim 1 , further comprising:
recirculating a first portion of the previous concentrate to the previous stage.
3. The method of claim 1 , wherein the one stage is the last stage, and the previous stage is the last but one stage.
4. The method of claim 1 , wherein the feed stream is controlled in a pH range of 3 to 7 and a temperature range of 20° C. to 50° C.
5. The method of claim 1 , wherein the recirculation rate is 2 or more.
6. The method of claim 1 , wherein the recirculation rate is 5 or more.
7. The method of claim 1 , wherein the feed liquid further comprises a deionized water stream.
8. The method of claim 7 , further comprising:
controlling a flow rate of the deionized water stream to be 20% to 300% of a flow rate of the at least part of the previous concentrate.