ES2565014B1 - Brackish water desalination system with zero discharge - Google Patents

Abstract

Brackish water desalination system with zero discharge. It comprises, properly interconnected with each other, a pressure steam generating device (13) configured to provide water vapor at a pressure comprised between 3-10 bars, a brackish water pressurization device (12) comprising at least a set of a steam engine (5) and a volumetric pump (7) configured so that the exchange of energy between them is carried out by means of a piston (9) which also acts as a physical separation barrier between them, a device desalination by reverse osmosis (14) and a brine concentration subsystem (15) that includes embodiments in which a dry brine residue is produced.

Description

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DESCRIPTION

Brackish water desalination system with zero discharge FIELD OF THE INVENTION

The present invention relates to a brackish water desalination system and more particularly to a system in which water desalination is carried out by a reverse osmosis process.

BACKGROUND OF THE INVENTION

Brackish water desalination systems are known, both from seawater and inland waters with significant salt concentrations. In the latter case, steam pumps are usually used, powered especially by solar energy.

WO 2011/161432 describes a desalination system that includes a steam pump to feed a reverse osmosis desalination device comprising two cylinders (one in which the steam expands and another in which the water is pressurized) with their respective pistons, which are joined by a coupling mechanism (a crank-crank system) through which the energy exchange between steam and water is carried out. That coupling mechanism provides a relatively low mechanical advantage when the pump volume is relatively large and a relatively high mechanical advantage when the pump volume is relatively small.

However, the energy yields of known systems are low, so there is still a demand for more efficient desalination systems. The present invention is oriented to the satisfaction of that demand.

SUMMARY OF THE INVENTION

The present invention provides a brackish water desalination system comprising, properly interconnected with each other, a pressure steam generation device configured to provide water vapor at a pressure comprised between 3-10 bars, a pressure pressurization device brackish water comprising at least one set of a steam engine and a volumetric pump configured so that the exchange of energy between them is carried out by means of a piston that also acts as a physical barrier of separation between them, a desalination device by reverse osmosis and a brine concentration subsystem.

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In one embodiment, the brackish water pressurization device comprises several assemblies of a steam engine and a volumetric pump arranged in parallel so as to provide a substantially constant pressurized brackish water flow.

In one embodiment, the brine concentration subsystem comprises a thermal brine concentrator, coupled to a refrigeration device, connected to the steam engine / s of the brackish water pressurization device to receive the wastewater vapor generated in he / they and the pressurized steam generation device to send the condensed water produced in it. Advantageously, the brine concentration subsystem includes a brine feedback circuit concentrated in the thermal brine concentrator.

In one embodiment, the brine concentration subsystem also comprises a crystallizer connected to the thermal brine concentrator to produce a dry brine residue as well as, advantageously, a concentrated brine feedback circuit produced in the crystallizer.

In one embodiment, the brine concentration subsystem comprises two or more thermal brine concentrators, coupled to refrigeration devices, arranged in series so that each brine concentrator (except the first one) is fed with concentrated brine produced in the previous concentrator thermal brine, as well as, advantageously, a brine feedback circuit concentrated in each of the thermal brine concentrators.

In an embodiment with two or more thermal brine concentrators, the brine concentration subsystem also comprises crystallizers connected to the thermal brine concentrators to produce a dry brine residue and, advantageously, concentrated brine feedback circuits produced in the crystallizers.

In one embodiment, the brackish water desalination system also comprises an electric power generator coupled to the brine outlet conduction of the reverse osmosis desalination device.

In one embodiment, the brackish water desalination system also comprises an electric power generator coupled to the brackish water pressurization device.

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Other features and advantages of the present invention will be apparent from the following detailed description of illustrative embodiments of its object in relation to the accompanying figures.

BRIEF DESCRIPTION OF THE FIGURES

Figure 1 is a schematic diagram of the brackish water desalination system of the invention.

Figure 2 is a schematic diagram of the brackish water pressurization device.

Figures 3a, 3b and 3c are schematic diagrams of the basic configuration of the brine concentration subsystem.

Figure 4 is a schematic diagram of an embodiment of the brine concentration subsystem that produces a dry residue.

Figure 5 is a schematic diagram of an embodiment of the brine concentration subsystem that produces a dry residue in two stages.

Figure 6 is a schematic diagram of another configuration of the brine concentration subsystem.

Figure 7 is a schematic diagram of an embodiment of the brackish water desalination system with two power generators.

DETAILED DESCRIPTION OF THE INVENTION

Components of the brackish water desalination system These are the following (see Figure 1):

- A pressure steam generation device 13. The pressure must be between 3-10 bar. It can be, for example, a boiler of any fossil fuel value, a biomass boiler or a device that uses solar energy (for example, parabolic trough solar collectors, Fresnel linear solar collectors or flat ford high solar collectors).

- A brackish water pressurization device 12 connected to a brackish water supply circuit 32 and the pressurized water vapor generating device 13. It is formed (see Figure 2) by a steam engine 5 and a pump

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volumetric 9. The steam engine 5 is constituted by a cylinder, within which a piston 7, symmetrical cylinder heads located at both ends of the cylinder and a rod that crosses the whole assembly moves. The cylinder heads are provided with the intake and exhaust valves, which are moved by a system of cams and springs. The entire system works without lubrication, which prevents contamination of the exhaust vapor. The volumetric pump 9 is composed of a cylinder, the symmetrical cylinder heads containing the intake and impulsion valves and the piston 7 anchored to the rod. The whole device works without lubrication. It also comprises a crank crank mechanism that only fulfills the function of storing kinetic energy in a flywheel that is necessary to make smooth transitions in the lower and upper dead spots, in addition to compensating for the different behavior of the steam engine 5 and the volumetric pump 9. The essential feature of the device is that the exchange of energy between the steam engine 5 and the volumetric pump 9 is carried out by means of the piston 7 which, in addition to transferring the steam energy to the brackish water, acts as a physical barrier of separation between both. The device can accept different configurations (with single or double piston, with one or several stages for greater use of steam to pressurize water) and also with several steam-volumetric pump motor assemblies arranged in parallel so that they perform alternately , in pairs, the steam intake / escape cycle to provide a substantially constant pressurized brackish water flow. At the same time, it can have means to self-regulate the pressure of the water produced according to the osmotic pressure requirement.

- A reverse osmosis desalination device 14 connected to the brackish water pressurization device 12 to produce desalinated water and brine. The brackish water pressurization device 12 uses the water vapor produced by the pressurized water vapor generation device 13 to provide the brackish water with the osmotic pressure necessary to carry out the desalination.

- A brine concentration subsystem 15 connected to the reverse osmosis desalination device 14, the brackish water pressurization device 12 and the pressurized water vapor generating device 13 to produce desalinated water and concentrated brine from the brine produced by the reverse osmosis desalination device 14.

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System operation

The water vapor formed in the pressurized steam generation device 13 flows through the conduit 31 to the brackish water pressurization device 12 whereby the steam inlet is transferred to the brackish water for the purpose of providing the necessary pressure to feed the desalination device by reverse osmosis 14. For this it is necessary that the brackish water be previously sent to the brackish water pressurization device 12 through the feed circuit 32 provided, typically, with a pump of low pressure (not shown in Figure 1).

The brackish water that is introduced into the pressurization device 12 through the feed circuit 32 is pressurized thanks to the exchange of steam / water pressure that is produced inside, obtaining a pressurized brackish water that is sent to the desalination device by reverse osmosis 14 through conduction 33. Upon exchange of pressure from steam to water, a low pressure vapor is obtained which is extracted from the brackish water pressurization device 12 by conduction 40 (see also Figure 2) .

In the reverse osmosis desalination device 14, the reverse osmosis membranes are installed, semipermeable membranes that allow the passage of water through them, leaving the salts retained by the membrane. In this way the desalination process itself is produced, in which a desalinated water is obtained that leaves the desalination device by reverse osmosis 14 through conduit 34.

The brine resulting from the desalination process, with high salt content and high pressure, is conducted to the brine concentration subsystem 15 through the conduit 35. Thanks to the action of the steam coming from the brackish water pressurization device 12 , through line 40, in the brine concentration subsystem 15, evaporation of the water contained in the brine and its subsequent condensation occurs on the one hand, obtaining a desalinated water that is extracted through line 36 and a brine concentrated which is extracted through conduit 37. In turn, the vaporization of the brine in the brine concentration subsystem 15 causes condensation of the low pressure steam introduced in the subsystem and thus a condensate is obtained which is sent to the pressurized water vapor generating device 13 through conduit 41 for pressurization and subsequent reuse.

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The brine concentration subsystem

In the embodiment illustrated in Figure 3a, the brine concentration subsystem 15 comprises a thermal brine concentrator 16 (such as a single or multiple effect watt evaporator, a membrane distillation device, a thermal compression evaporation device or steam mechanics) connected to an internal refrigeration device 17 and a concentrated brine feedback circuit.

In the thermal brine concentrator 16 the brine is introduced through the conduction 35 and the residual steam from the brackish water pressurization device 12 through the conduit 40 and heating and subsequent evaporation of the brine occurs, obtaining a water vapor that condenses on the same device thanks to the internal cooling device 17 producing desalinated water on the one hand that is extracted through conduit 36 and a concentrated brine that is extracted through conduit 37, part of the which is recirculated to the thermal brine concentrator 16 through conduit 38, in order to increase the conversion of the process and the other part is purged by conduction 39. Vaporization of the brine in the thermal brine concentrator 16 produces the condensation of the steam of the low pressure steam introduced into it. In this way, a condensate is obtained which is introduced back into the pressure steam generating device 13 through the line 41 for pressurization and subsequent reuse. In the event that the steam introduced into the thermal brine concentrator 16 is higher than the one necessary to produce the vaporization of the brine, at the outlet of it a low pressure steam will be obtained which will be necessary to condense before introducing it back into the pressurized water vapor generation device 13. In this case, appropriate refrigeration device will be used for this, which in any case will be external since it will only be required in the event that the steam is higher than necessary and does not produce evaporation condensation

The concentration of the brine in the thermal brine concentrator 16 allows more desalinated water to be produced per unit of energy used.

In the embodiment illustrated in Figure 3b, the brine concentration subsystem 15 uses an external cooling device 17 'to condense the desalinated water leaving the thermal brine concentrator 16 in the form of steam through line 44 and then in liquid form by conduction 36 after the corresponding heat exchange with the external cooling device 17 '.

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In the embodiment illustrated in Figure 3c, a second external cooling device 17 '' is added to the subsystem illustrated in Figure 3b to condense the outlet steam through conduction 45. After the heat exchange the resulting liquid is taken to the storage device. steam generation through conduction 41.

In the embodiment illustrated in Figure 4, the subsystem illustrated in Figure 3a is complemented with a crystallizer 19 to obtain a dry residue.

The part of the concentrated brine that is not recirculated to the thermal brine concentrator 16 is carried by line 48 to a crystallizer 19 (after brine purge by line 49 in order to avoid the precipitation of salts inside the concentrator thermal brine 16).

When the concentrated brine is introduced at high temperature in the crystallizer 19 crystallization of the salts present in it occurs. The salts formed during crystallization, or dry residue, are extracted from the crystallizer 19 through conduit 50. The system may include the recirculation of the concentrated brine to the thermal brine concentrator 16. For this purpose the concentrated brine is extracted from the Crystallizer 19 by conduction 51 and sent to the thermal brine concentrator 16 together with the portion of the recirculated concentrated brine mentioned.

In the embodiment illustrated in Figure 5, the subsystem illustrated in Figure 3a is complemented with means to perform a fractional precipitation of the salts in two stages (and similarly it could be done with the subsystems illustrated in Figures 3b and 3c). For this purpose, the subsystem comprises two thermal brine concentrators 16, 20 with their corresponding external cooling devices 17, 21 and two crystallizers 19, 23 arranged in series. In this way, a part of the concentrated brine recirculation of the first stage is recirculated through conduit 38 to the first thermal brine concentrator 16 and another part is conducted to the second thermal brine concentrator 20 via conduit 53.

The steam supply to the two thermal brine concentrators 16, 20 from the residual steam from the brackish water pressurization device 12 that is extracted by the conduit 40, can be carried out in two ways (for simplicity in Figure 5 it is possible use line 40 as a residual steam inlet line to both devices):

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- The steam at the exit of the brackish water pressurization device 12 is distributed to the thermal brine concentrators 16, 20. Upon evaporation of the brine in them, condensation of the steam provided for the process occurs, obtaining condensed water at the output thereof that is returned to the conduction 41 from where it is led to the water value generation device under pressure 13 for pressurization and reuse. If the steam does not condense, the process would be complemented with refrigeration means to condense the steam before introducing it back into a pressurized steam generating device 13.

- The steam at the exit of the brackish water pressurization device 12, which is extracted by conduction 40, is progressively conducted to the thermal brine concentrators 16, 20 passing from one to the other. If the steam does not condense in the last one, the process would be complemented by a refrigeration system to condense the steam before introducing it back into the pressure steam generating device 13.

In the second thermal brine concentrator 20, concentrated brine 53 is received through the conduit 53 and desalinated water is generated on the one hand, which is extracted through the duct 58 thanks to the second cooling device 21 (the cooling device 17 of the first could also be used stage) and on the other a brine of higher concentration that is extracted through conduit 59. As in the first stage, at the exit of the second thermal brine concentrator 20, part of the brine is recirculated back to the a through conduit 65 to achieve greater efficiency in the process, and part is sent to the second crystallizer 23 through conduit 61. In addition, the process is completed with a brine purge prior to crystallization through conduction. 62

In the second crystallizer 23 the crystallization of the salts present in the concentrated brine takes place, obtaining a dry residue that is extracted by the conduit 63. The system can include the recirculation of concentrated brine to the second thermal brine concentrator 20. For this Concentrated brine is extracted from the second crystallizer 23 via conduit 64 and sent along with the pre-concentrated brine recirculation to the second thermal brine concentrator 20 via conduit 65.

The brine concentration subsystem can also be configured (see Figure 6) so that the refrigeration device 17 uses the refrigerant itself

brine from the reverse osmosis desalination device 14 before introducing it into the brine thermal concentrator 16 itself.

In the case of the two-stage brine concentration subsystem shown in Figure 5, the brine that feeds the two thermal brine concentrators 16, 5 20 could also be introduced into them through the cooling devices 17,

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Means of electric power generation

The system may include electric power generation means that take advantage of available energy in the system and in particular (see Figure 7) a first electric generator 25 coupled to the brackish water pressurization device 12 that takes advantage of its cycles for the production of electric power (and can serve as a means of regulating the outlet pressure of the water vapor) and a second electric generator 29 (for example, a micro-turbine) installed at the outlet of a reverse osmosis desalination device 15 that takes advantage of the energy stored in the pressurized brine stream coming out of it.

Although the present invention has been described in connection with various embodiments, it can be seen from the description that various combinations of elements, variations or improvements can be made therein and that are within the scope of the invention defined in the appended claims.

Claims (19)

5 10 fifteen twenty 25 30 1. Brackish water desalination system comprising: - a pressurized water vapor generation device (13); - a brackish water pressurization device (12) connected to a brackish water supply circuit (32) and the pressurized water vapor generating device (13); - a reverse osmosis desalination device (14) connected to the brackish water pressurization device (12) to produce desalinated water and brine; - a brine concentration subsystem (15) connected to the reverse osmosis desalination device (14), the brackish water pressurization device (12) and the pressurized water vapor generating device (13) to produce desalinated water and concentrated brine; characterized in that: - the pressurized water vapor generating device (13) is configured to provide water vapor at a pressure between 3-10 bar; - the brackish water pressurization device (12) comprises at least one set of a steam engine (5) and a volumetric pump (9) configured so that the energy exchange between them is carried out by means of a piston (7) that It also acts as a physical barrier of separation between them. 2. Brackish water desalination system according to revindication 1, in which the brackish water pressurization device (12) comprises several assemblies of a steam engine (5) and a volumetric pump (9) arranged in parallel so that alternatively carry out, in pairs, the steam intake / escape cycle to provide a substantially constant pressurized brackish water flow. 3. A brackish water desalination system according to any one of claims 1-2, wherein the brine concentration subsystem (15) comprises a thermal brine concentrator (16), coupled to a refrigeration device (17), connected to the steam engine (s) (5) of the brackish water pressurization device (12) to receive the waste water vapor generated in it and to the pressurized water vapor generation device (13) to send the condensed water produced in it. 5 10 fifteen twenty 25 30 4. The brackish water desalination system according to claim 3, wherein the brine produced in the reverse osmosis desalination device (14) is introduced directly into the thermal brine concentrator (16). 5. A brackish water desalination system according to claim 3, wherein the brine produced in the reverse osmosis desalination device (14) is introduced into the thermal brine concentrator (16) through the cooling device (17). 6. A brackish water desalination system according to any of claims 4-5, wherein the brine concentration subsystem (15) includes a feedback circuit of part of the brine concentrated in the thermal brine concentrator (16). 7. Brackish water desalination system according to any of claims 4-5, wherein the brine concentration subsystem (15) also comprises a crystallizer (19) connected to the thermal brine concentrator (16) to produce a dry residue brine 8. A desalination system according to claim 7 wherein the brine concentration subsystem (15) also comprises a feedback circuit of part of the concentrated brine produced in the crystallizer (19). 9. A brackish water desalination system according to any one of claims 3-8, wherein the thermal brine concentrator (16) is one of the following devices: a single or multiple effect vacuum evaporator, a distillation device by single or multiple stage membranes, an evaporation device with thermal or mechanical steam compression. 10. A brackish water desalination system according to any one of claims 1-2, wherein the brine concentration subsystem (15) comprises at least two thermal brine concentrators (16, 20) coupled to a cooling device (17, 21) arranged in series so that the second thermal brine concentrator (20) is fed with concentrated brine produced by the first thermal brine concentrator (16) and each being connected to the steam engine (s) ( 5) of the brackish water pressurization device (12) to receive the wastewater vapor generated in it and the pressurized water vapor generation device (13) to send the condensed water produced therein. 5 10 fifteen twenty 25 30 11. Brackish water desalination system according to claim 10, wherein the brine feed to the first and second thermal brine concentrator (16, 20) is carried out directly from, respectively, the reverse osmosis desalination device (14) and the first thermal brine concentrator (16), 12. Brackish water desalination system according to claim 10, wherein the brine feed to the first and second thermal brine concentrator (16, 20) is carried out through the cooling devices (17, 21). 13. Brackish water desalination system according to any one of claims 1012, wherein the brine concentration subsystem (15) includes a feedback circuit of part of the brine concentrated in each of the thermal brine concentrators (16, twenty). 14. Brackish water desalination system according to any one of claims 1013, wherein the brine concentration subsystem (15) also comprises crystallizers (19, 23) connected to the thermal brine concentrators (16, 20) to produce a dry brine residue. 15. Brackish water desalination system according to claim 14, wherein the brine concentration subsystem (15) also comprises a feedback circuit of part of the concentrated brine produced in the crystallizers (19, 23). 16. A brackish water desalination system according to any one of claims 1015, wherein the thermal brine concentrators (16, 20) are one of the following devices: a single or multiple effect vacuum evaporator, a device for distillation by membranes in single or multiple stage, an evaporation device with thermal or mechanical steam compression. 17. Brackish water desalination system according to any one of claims 116, which also comprises a first electric power generator (25) coupled to the brackish water pressurization device (12). 18. A brackish water desalination system according to any one of claims 116, which also comprises a second electric power generator (29) coupled to the brine outlet conduit (35) of the reverse osmosis desalination device (14). 19. Brackish water desalination system according to any of claims 118, wherein the pressure steam generating device (13) is one of the following: a boiler of any fossil fuel value, a biomass boiler , a device that uses solar energy.