HYBRID DESALINATION SYSTEM

Abstract

The hybrid desalination system (10) includes a reverse osmosis filtration system (14), a forward osmosis filtration system (18), and a multi-effect distillation system (16). A condenser (12) receives seawater (S) and produces cooled seawater (CS). The cooled seawater (CS) is filtered by the reverse osmosis filtration system (14), which outputs a first brine reject stream (BR1) and a permeate stream (P). The multi-effect distillation system (16) outputs a second brine reject stream (BR2). A feed side (20) of the forward osmosis filtration system (18) receives the first brine reject stream (BR1), and the second brine reject stream (BR2) is received by the draw side (22), which outputs diluted brine (DB). The multi-effect distillation system (16) is in fluid communication with the forward osmosis filtration system (18) and recycles the diluted brine (DB). The multi-effect distillation system (16) outputs a return condensate (RC) and a pure water distillate (D).

Claims

1. A hybrid desalination system, comprising: a condenser having: a seawater inlet port adapted for receiving seawater; a vapor inlet; a seawater outlet port adapted for producing cooled seawater therefrom; and a condensed water outlet; a reverse osmosis filtration system having an inlet side connected to the outlet port of the condenser for receiving the cooled seawater, a brine outlet, and a permeate outlet, the brine outlet being adapted for producing a first brine reject stream therefrom; a multi-effect distillation system having: a steam inlet adapted for receiving steam from an external source; a brine inlet; a distillate outlet connected to the permeate outlet of the reverse osmosis filtration system to form a combined desalinated water output conduit, the condensed water outlet of the condenser being connected to the combined desalinated water output conduit; a vapor outlet connected to the vapor inlet of the condenser; a brine outlet adapted for outputting a second brine reject stream; and a return condensate outlet; and a forward osmosis filtration system having a feed side and a draw side, the feed side having a brine inlet connected to the brine outlet of the reverse osmosis filtration system for receiving the first brine reject stream and a brine outlet adapted for outputting a third brine reject stream, the draw side having a brine inlet connected to the brine outlet of the multi-effect distillation system for receiving the second brine reject stream and a brine outlet connected to the brine inlet of the multi-effect distillation system for transferring dilute brine from the forward osmosis filtration system to the multi-effect distillation system.

2. A hybrid desalination system, comprising: a reverse osmosis filtration system having a seawater inlet port adapted for receiving seawater, a brine outlet port adapted for outputting a first brine reject stream, and a permeate outlet port; a condenser having: a brine inlet port connected to the brine outlet port of the reverse osmosis filtration system for receiving the first brine reject stream; a vapor inlet; a cooled brine outlet port adapted for outputting the first brine reject stream as cooled brine; and a condensed water outlet; a multi-effect distillation system having: a steam inlet adapted for receiving steam from an external source; a brine inlet; a distillate outlet connected to the permeate outlet of the reverse osmosis filtration system to form a combined desalinated water output conduit, the condensed water outlet of the condenser being connected to the combined desalinated water output conduit; a vapor outlet connected to the vapor inlet of the condenser; a brine outlet adapted for outputting a second brine reject stream; and a return condensate outlet; and a forward osmosis filtration system having a feed side and a draw side, the feed side having a brine inlet connected to the cooled brine outlet of the condenser for receiving the first brine reject stream and a brine outlet adapted for outputting a third brine reject stream, the draw side having a brine inlet connected to the brine outlet of the multi-effect distillation system for receiving the second brine reject stream and a brine outlet connected to the brine inlet of the multi-effect distillation system for transferring dilute brine from the forward osmosis filtration system to the multi-effect distillation system.

3. A method of desalinating seawater, comprising the steps of: processing the seawater in a condenser to produce a stream of cooled seawater; filtering the seawater in a reverse osmosis filtration system to produce a first brine reject steam and a permeate stream; filtering the first brine reject stream through a forward osmosis filtration system to obtain a stream of dilute brine; inputting the stream of dilute brine to a multiple-effect distillation system to obtain vapor output and a distillate output stream; processing the vapor output of the multiple-effect distillation system through the condenser to output condensed water; and combining the permeate stream, the distillate output stream, and the condensed water in a common conduit to provide a combined desalinated water output.

4. The method of desalinating seawater according to claim 3, further comprising the step of recycling a second brine reject stream from the multiple-effect distillation system through a draw side of the forward osmosis filtration system.

5. The method of desalinating seawater according to claim 3, further comprising the step of outputting a third brine reject stream from a feed side of the forward osmosis filtration system.

6. The method of desalinating seawater according to claim 3, further comprising the step of supplying the multiple-effect distillation system with steam from an external source.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0013] FIG. 1 is a schematic diagram of a hybrid desalination system operating in a first mode.

[0014] FIG. 2 is a schematic diagram of the hybrid desalination system operating in a second mode.

[0015] FIG. 3 is a chart showing specific energy consumption as a function of recovery ratio, comparing multiple-effects distillation with reverse osmosis, and with the hybrid desalination system.

[0016] Similar reference characters denote corresponding features consistently throughout the attached drawings.

BEST MODES FOR CARRYING OUT THE INVENTION

[0017] The hybrid desalination system 10 combines a reverse osmosis filtration system and a forward osmosis filtration system with a multi-effect distillation system. FIG. 1 illustrates the hybrid desalination system 10 operating in a first mode, which is configured to be operated in an environment with cool temperatures (i.e., a winter mode). As shown, the hybrid desalination system 10 includes a condenser for receiving seawater S and producing cooled seawater CS therefrom. A reverse osmosis filtration system 14 is in fluid communication with the condenser 12 for receiving the cooled seawater CS and producing a first brine reject stream BR1 therefrom. Preferably, the cooled seawater CS is chemically treated prior to input to the reverse osmosis filtration system 14, as is well-known in the art. A multi-effect distillation (MED) system 16 receives steam ST from an external source and outputs a second brine reject stream BR2.

[0018] A forward osmosis filtration system 18 is in fluid communication with both the reverse osmosis filtration system 14 and the multi-effect distillation system 16. The first brine reject stream BR1 is received by a feed side 20 of the forward osmosis filtration system 18 and the second brine reject stream BR2 is received by a draw solution side 22 of the forward osmosis filtration system. The feed side 20 of the forward osmosis filtration system 18 outputs a third brine reject stream BR3 and the draw solution side 22 of the forward osmosis filtration system 18 outputs diluted brine DB. In the forward osmosis filtration system 18, due to the osmotic pressure difference between the highly concentrated brine (i.e., the second brine reject stream BR2) and the feed side 20 (i.e., the reverse osmosis reject brine BR1), pure water transfers from the feed side 20 to the draw solution side 22. The draw solution, which includes sodium chloride (NaCl), is used with synthetic salts to reduce the solute back flux from the feed side 20 to the draw water side 22.

[0019] The multi-effect distillation system 16 is in fluid communication with the forward osmosis filtration system 18 and recycles the diluted brine DB from the draw solution side 22, such that the multi-effect distillation system 16 outputs a return condensate RC and a pure water distillate D. Since the forward osmosis filtration system 18 selectively retains the divalent ions from the feed side 20 and allows pure water transport to the concentrated side (i.e., draw side 22), when compared against conventional distillation and/or filtration systems, the top brine temperature (TBT) is able to be increased to a temperature greater than 65 C. The increase of the TBT consequently increases the MED unit distillate production and increases the overall recovery ratio.

[0020] The multi-effect distillation system 16 is also in fluid communication with the condenser 12, such that the condenser 12 receives water vapor V produced by the multi-effect distillation system 16. Condensed water CW produced by the condenser 12 is mixed with the pure water distillate D output from the multi-effect distillation system 16. A permeate P produced by the reverse osmosis filtration system 14 is mixed with the pure water distillate D to yield a final water product. By mixing the MED distillate D and the reverse osmosis permeate P, the system 10 is able to make use of only single pass reverse osmosis, compared to conventional double pass reverse osmosis filtration, thus reducing operational costs.

[0021] FIG. 2 illustrates an alternative embodiment of the hybrid desalination system 10, which operates in a second mode (or the hybrid desalination system 10 of FIG. 1 configured to operate in the second mode by the use of valves, pumps, or the like to alter flow through the system 10). The second mode is configured to be operated in an environment with warm temperatures (i.e., in summer mode). The reverse osmosis filtration system 14 of the hybrid desalination system 10 receives the seawater S and separates the seawater S into a first brine reject stream BR1 and a permeate P. Preferably, the seawater S is first chemically treated prior to input to the reverse osmosis filtration system 14, as is well-known in the art. The condenser 12 is in fluid communication with the reverse osmosis filtration system 14 for receiving the first brine reject stream BR1 and producing cooled brine CB. The multi-effect distillation system 16 receives the steam ST from the external source and outputs a second brine reject stream BR2.

[0022] The forward osmosis filtration system 18 is in fluid communication with both the condenser 12 and the multi-effect distillation system 16, such that the cooled brine CB is received by the feed side 20 of the forward osmosis filtration system 18, and the second brine reject stream BR2 is received by the draw solution side 22 of the forward osmosis filtration system 18. The feed side 20 of the forward osmosis filtration system 18 outputs a third brine reject stream BR3, and the draw solution side 22 of the forward osmosis filtration system 18 outputs diluted brine DB. In the forward osmosis filtration system 18, due to the osmotic pressure difference between the highly concentrated brine (i.e., the second brine reject stream BR2) and the feed side 20 (i.e., the cooled brine CB), pure water transfers from feed side 20 to the draw solution side 22. The draw solution, which includes sodium chloride (NaCl), is used with synthetic salts to reduce the solute back flux from feed side 20 to the draw water side 22.

[0023] The multi-effect distillation system 16 is in fluid communication with the forward osmosis filtration system 18 and recycles the diluted brine DB from the draw solution side 22. The multi-effect distillation system 16 outputs a return condensate RC and pure water distillate D. Since the forward osmosis filtration system 18 selectively retains the divalent ions from the feed side 20 and allows pure water transport to the concentrated side (i.e., draw side 22), when compared against conventional distillation and/or filtration systems, the top brine temperature (TBT) is able to be increased to a temperature greater than 65 C. The increase of the TBT consequently increases the MED unit distillate production and increases the overall recovery ratio.

[0024] The multi-effect distillation system 16 is also in fluid communication with the condenser 12. The condenser 12 receives water vapor V produced by the multi-effect distillation system 16, and condensed water CW produced by the condenser 12 is mixed with the pure water distillate D output from the multi-effect distillation system 16. Additionally, a permeate P produced by the reverse osmosis filtration system 14 is mixed with the pure water distillate D to yield a final water product. By mixing the MED distillate D and the reverse osmosis permeate P, the system 10 is able to make use of only single pass reverse osmosis, compared to conventional double pass reverse osmosis filtration, thus reducing operational costs.

[0025] In order to test the effectiveness of hybrid desalination system 10 (and the alternative mode of hybrid desalination system 10), simulations were run using visual design and simulation (VDS) software, comparing the present hybrid desalination system against single pass reverse osmosis (RO) filtration alone and multi-effect distillation (MED) alone. For the simulated single pass RO filtration system, the following parameters were used in the simulation. The seawater was fed through the RO filtration system at a fixed rate at 16,000 tons/hour and with a salinity of 45 g/L. This matches expected feed of cooled seawater CS into the RO filtration system 14 of the hybrid desalination system 10. The simulated RO system recovery ratio was 30%.

[0026] The RO brine had a salinity of 63 g/L, which, in the present hybrid desalination system 10, would be directed to the feed side 20 of the forward osmosis filtration system 18. The residual chemicals in the brine (beside the available pressure at 5.8 bar) would assist the FO process. The electrical consumption was 3.6 kWh/m.sup.3. The low recovery ratio of the RO system alone would decrease the boron effluent in the permeate. The permeate of 4790 tons/hour (25 MIGD) and a salinity of 450 ppm would be blended with the MED distillate in the present hybrid desalination system 10. A pressure exchanger assists the simulated RO high pressure pump and recovers 50% of the brine energy. The simulated RO section included six trains, with each train containing 180 vessels. Each vessel contained seven elements. The RO element was simulated to be 8 inches long with a surface area of 37 m.sup.2.

[0027] Overall, for the RO system alone, the simulated recovery ratio was 0.3, the electrical energy consumed was 5.9 kWh/m.sup.3, and the total energy consumption was 5.9 kWh/m.sup.3. For a simulated two-pass RO system, such as that described above, the recovery ratio of the first pass was 30% (as in the single pass RO system) and the recovery ratio of the second pass was 90%. The salinity of the final permeate was 25 ppm.

[0028] For the simulated MED system, the simulated recovery ratio was 0.3, the electrical energy consumed was 1.73 kWh/m.sup.3, the thermal energy expended was 6.2 kWh/m.sup.3, and the total energy consumption was 7.93 kWh/m.sup.3. By comparison, for the present hybrid desalination system 10, the simulated recovery ratio was 0.43, the electrical energy consumed was 3.0 kWh/m.sup.3, the thermal energy expended was 1.2 kWh/m.sup.3, and the total energy consumption was only 4.2 kWh/m.sup.3. Thus, the recovery ratio of the present hybrid desalination system 10 is up to 43% higher than the standalone RO desalination plant or standalone MED system. The specific total energy consumption of the present hybrid desalination system is also 45% lower than that of the simulated MED plant, and 30% lower than that of the simulated RO desalination plant.

[0029] For the simulated hybrid desalination system 10, a distillate of 1940 tons/hour (10 MIGD) was simulated as the product from the MED system. The top brine temperature (TBT) increased to 85 C., and this temperature range allowed the use of 16 effects in the MED system, as opposed to a conventional 10 effect MED plant. As the number of effects increases, the gain output ratio (GOR) increases from 8.7 to 13.3 (i.e., 53% higher). The specific heat transfer surface decreases in area by 10%. The steam flow rate consumption was 146 tons/hour, which is 53% lower than that of a conventional MED plant (i.e., 221 tons/hour). Due to a significant reduction in the heating steam, the equivalent thermal energy decreased by 34%.

[0030] In FIG. 3, the data corresponding to the hybrid desalination system 10, which is a hybrid of reverse osmosis (RO), forward osmosis (FO) and multi-effect distillation (MED), is labeled as RO-FO-MED, and is compared against the data taken from the simulated RO system alone, and the simulated MED system alone. Specifically, FIG. 3 plots the energy consumption variation at different values of recovery ratio. As shown, as the recovery ratio increases, the specific energy decreases. As the recovery ratio increases, the capital cost of intake operation and construction will decrease up to 50%, since common intake is used. Further, as noted above, by mixing the MED distillate D and the reverse osmosis permeate, the present hybrid desalination system is able to make use of only single pass reverse osmosis, compared to conventional double pass reverse osmosis filtration, thus reducing operational costs. Additionally, since the RO permeate is diluted by the MED distillate, a concentrated brine waste product is not an issue with the present hybrid desalination system.

[0031] It is to be understood that the hybrid desalination system is not limited to the specific embodiments described above, but encompasses any and all embodiments within the scope of the generic language of the following claims enabled by the embodiments described herein, or otherwise shown in the drawings or described above in terms sufficient to enable one of ordinary skill in the art to make and use the claimed subject matter.