Method of recycling brine from a multi-stage flash desalination plant

Abstract

The method of recycling brine from a multi-stage flash desalination plant recycles the high-salinity, high-temperature brine output from a multi-stage flash desalination plant to produce diluted brine suitable for reinjection back into the multi-stage flash desalination plant as a makeup stream. The high-salinity, high-temperature brine output from the multi-stage flash desalination plant is diluted with water extracted from treated wastewater effluent output from a wastewater treatment plant, thus providing further recycling of the treated wastewater effluent. Following osmotic transfer of the diluting water from the treated wastewater effluent to produce the diluted brine, the remaining concentrated treated wastewater effluent passes through a secondary filtration system to yield a solid product and a volume of permeate water. The volume of permeate water may be further mixed with the diluted brine.

Claims

1. A method of recycling brine from a multi-stage flash desalination plant, comprising the steps of: injecting brine output from a multi-stage flash desalination plant into a membrane filter system; injecting treated wastewater effluent output from a wastewater treatment plant into the membrane filter system; diluting the brine in the membrane filter system through osmotic transfer of water from the treated wastewater effluent to produce diluted brine and concentrated treated wastewater effluent; and outputting the diluted brine from the membrane filter system and mixing the diluted brine with condensed steam output from the multi-stage flash desalination plant to produce twice-diluted brine.

2. The method of recycling brine from a multi-stage flash desalination plant as recited in claim 1, wherein the membrane filter system comprises a pressure retarded osmosis filter system.

3. The method of recycling brine from a multi-stage flash desalination plant as recited in claim 1, wherein the membrane filter system comprises a forward osmosis filter system.

4. The method of recycling brine from a multi-stage flash desalination plant as recited in claim 1, wherein the membrane filter system comprises an assisted forward osmosis filter system.

5. The method of recycling brine from a multi-stage flash desalination plant as recited in claim 1, further comprising the step of mixing the diluted brine output from the membrane filter system with water from an external source.

6. The method of recycling brine from a multi-stage flash desalination plant as recited in claim 1, further comprising the step of outputting the concentrated treated wastewater effluent from the membrane filter system.

7. The method of recycling brine from a multi-stage flash desalination plant as recited in claim 6, further comprising the steps of: mixing a portion of the concentrated treated wastewater effluent with raw sewage entering the wastewater treatment plant; and injecting a remainder of the concentrated treated wastewater effluent into a secondary filter system to produce a solid product and a volume of permeate water.

8. The method of recycling brine from a multi-stage flash desalination plant, as recited in claim 7, further comprising the step of mixing the volume of permeate water with the twice-diluted brine to produce thrice-diluted brine; mixing a portion of the thrice-diluted brine with seawater input into the multi-stage flash desalination plant as a makeup stream for the multi-stage flash desalination plant; and outputting a remainder of the thrice-diluted brine.

9. A method of recycling brine from a multi-stage flash desalination plant, comprising the steps of: injecting brine output from a multi-stage flash desalination plant into a membrane filter system; injecting treated wastewater effluent output from a wastewater treatment plant into the membrane filter system; diluting the brine in the membrane filter system through osmotic transfer of water from the treated wastewater effluent; outputting diluted brine from the membrane filter system and mixing the diluted brine with condensed steam output from the multi-stage flash desalination plant to produce twice-diluted brine; outputting concentrated treated wastewater effluent from the membrane filter system; mixing a portion of the concentrated treated wastewater effluent with raw sewage entering the wastewater treatment plant; injecting a remainder of the concentrated treated wastewater effluent into a secondary filter system to produce a solid product and a volume of permeate water; mixing the volume of permeate water with the twice-diluted brine to produce thrice-diluted brine; mixing a portion of the thrice-diluted brine with seawater input into the multi-stage flash desalination plant as a makeup stream for the multi-stage flash desalination plant; and outputting a remainder of the thrice-diluted brine as a final brine discharge stream.

10. The method of recycling brine from a multi-stage flash desalination plant as recited in claim 9, wherein the membrane filter system comprises a pressure retarded osmosis filter system.

11. The method of recycling brine from a multi-stage flash desalination plant as recited in claim 9, wherein the membrane filter system comprises a forward osmosis filter system.

12. The method of recycling brine from a multi-stage flash desalination plant as recited in claim 9, wherein the membrane filter system comprises an assisted forward osmosis filter system.

13. The method of recycling brine from a multi-stage flash desalination plant as recited in claim 9, further comprising the step of mixing the diluted brine output from the membrane filter system with water from an external source.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The sole drawing FIGURE diagrammatically illustrates a method of recycling brine from a multi-stage flash desalination plant according to the present invention.

(2) Similar reference characters denote corresponding features consistently throughout the attached drawings.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

(3) The sole drawing FIGURE illustrates a method of recycling brine from a conventional multi-stage flash (MSF) desalination plant 12. As described above, a typical MSF desalination plant 12 includes a series of stages 16a, 16b, 16c, 16d, 16e, 16f, 16g, 16h, each containing a heat exchange portion and a condensation collection portion. After the hot end (i.e., after stage 16a), brine heater 14 receives the brine from the heat exchange portion of stage 16a and reinjects it back into the condensation collection portion of stage 16a. The heat added in the brine heater 14 comes in the form of hot steam from an external industrial process co-located with the desalination plant 12. It should be understood that the MSF desalination plant 12 shown in the sole drawing FIGURE is shown for exemplary and illustrative purposes only, and that the present method of recycling brine from a multi-stage flash desalination plant may be used with any suitable type of MSF plant which produces desalinated water from seawater using a conventional MSF process.

(4) As shown in the sole drawing FIGURE, the method includes injecting the high-salinity, high-temperature brine output from the multi-stage flash desalination plant 12 into a membrane filter system 18. At the same time, treated wastewater effluent (TWE) output from a wastewater treatment plant 20 is also injected into the membrane filter system 18 on the other side of the membrane filter. It should be understood that wastewater treatment plant 20 may be any suitable type of plant for treating raw sewage. Further, it should be understood that membrane filter system 18 may be any suitable type of membrane filtration system, such as a reverse osmosis filter system, a pressure retarded osmosis filter system, a forward osmosis filter system, an assisted forward osmosis filter system or the like.

(5) The high-salinity, high-temperature brine is cooled and diluted in the membrane filter system 18 through osmotic transfer of water from the treated wastewater effluent. Both diluted brine and concentrated TWE are then output from the membrane filter system 18. The diluted brine retains all chemicals previously added during the desalination process and is cooler than the concentrated brine. The diluted brine is then mixed with condensed steam output from the brine heater 14 of the multi-stage flash desalination plant 12, as well as water from an external source such as recycled cooling water from a power plant, for example, to produce twice-diluted brine.

(6) Simultaneously, a portion of the concentrated treated wastewater effluent is recycled by mixing the concentrated TWE with the raw sewage entering the wastewater treatment plant 20. A remainder of the concentrated TWE is injected into a secondary filter system 22, which may be any suitable type of filtration system, to produce a solid product and a volume of permeate water. The concentrated TWE is rich in nutrients, thus the solid product, which is typically in crystalized form, may be used as fertilizer or the like. The volume of permeate water is mixed with the twice-diluted brine to produce thrice-diluted brine. At least a portion of the thrice-diluted brine can be used as a makeup stream, as is conventionally known, for the multi-stage flash desalination plant 12 by mixing the portion of the thrice-diluted brine with the seawater being input into the multi-stage flash desalination plant 12, thereby forming a closed loop system. A remainder of the thrice-diluted brine can be output as a final brine discharge stream.

(7) It is to be understood that the present invention is not limited to the embodiments described above, but encompasses any and all embodiments within the scope of the following claims.