WO2017021884A1

WO2017021884A1 - Water distillation system

Info

Publication number: WO2017021884A1
Application number: PCT/IB2016/054646
Authority: WO
Inventors: Huy TON THAT; Issam EL BAKKALI
Original assignee: Nereid Sa
Priority date: 2015-08-03
Filing date: 2016-08-02
Publication date: 2017-02-09

Abstract

The water distillation system of the invention includes first and second humidifiers (1, 21), first and second dehumidifiers (2, 22), a first closed gas circuit (3) crossing the first humidifier (1) and the first dehumidifier (2) and in which a first gas is circulated, a second closed gas circuit (23) crossing the second humidifier (21) and the second dehumidifier (22) and in which a second gas is circulated, a feed water circuit (14) carrying feed water and successively crossing a first feed water heater (15), a second feed water heater (16; 16'; 16''; 16'''), the second humidifier (21) and the first humidifier (1), a closed cooling water circuit (18) carrying cooling water and successively crossing the second dehumidifier (22), the first dehumidifier (2) and the first feed water heater (15), and a unit (29, 10, 11) for recovering, as product water, excess water from the cooling water. The first and second humidifiers (1, 21) are arranged to respectively humidify the first and second gas by direct contact between the feed water and, respectively, the first and second gas. The first and second dehumidifiers (2, 22) are arranged to respectively dehumidify the first and second gas by direct contact between the cooling water and, respectively, the first and second gas. The first feed water heater (15) is arranged to transfer heat from the cooling water exiting the first dehumidifier (2) to the feed water.

Description

WATER DISTILLATION SYSTEM

BACKGROUND OF THE INVENTION

The invention relates to distillation systems.

More particularly, the invention is a low cost, low maintenance, closed-air open water distillation system that can be utilized on a commercial scale to produce distilled water.

Distillation is a thermal separation, that is, a purification process that yields pure water from a solution or from a vapor. As for all thermal separation processes, non-equilibrium conditions are required as a driving force for the process.

Evaporation of liquid mixture or cooling are the most frequent means employed to establish the required non-equilibrium conditions.

The main feature distinguishing distillation from other separation processes is the fact that it mainly uses thermal energy.

The main distillation technologies are the Multiple Effect Distillation (MED),

Multistage Flash Distillation (MSF), Vapor Compression (VC) and Humidification- dehumidification (HDH).

In MED, the water vapor generated by brine evaporation in each effect flows to the next effect, where heat is supplied for additional evaporation, at a lower temperature. There the vapor condenses, giving up its latent heat to evaporate an additional fraction of water from the brine.

Multi-stage flash distillation (MSF) is a process that distills feed water by flashing a portion of the water into steam in multiple stages of what are essentially

countercurrent heat exchangers.

Vapor compression (VC) refers to a distillation process where the evaporation of feed water is obtained by the application of heat delivered by compressed vapor. Since compression of the vapor increases both the pressure and temperature of the vapor, it is possible to use the latent heat, rejected during condensation, to generate additional vapor.

The humidification-dehumidification method (HDH) is based on evaporation of feed water and subsequent condensation of the generated humid air, mostly at ambient pressure. This process mimics the natural water cycle, but over a much shorter time frame. An improved version of the HDH is the Multiple Effect Humidification (MEH). It uses multiple evaporation-condensation cycles at separate temperature levels to minimize the total energy consumption of the HDH process.

However, all of the known prior art distillation methods described above suffer from one or more of the following problems/shortfalls: a) they are expensive to build b) they are expensive to operate c) they consume a substantial amount of energy d) the cost of product water is expensive and/or e) they are bulky.

Accordingly, there is a need for an improved distillation system which overcomes the aforementioned problems/challenges in the prior art.

SUMMARY OF THE INVENTION

The present invention provides a water distillation system including:

first and second humidifiers,

first and second dehumidifiers,

- a first closed gas circuit crossing the first humidifier and the first dehumidifier and in which a first gas is circulated,

a second closed gas circuit crossing the second humidifier and the second dehumidifier and in which a second gas is circulated,

a feed water circuit carrying feed water and successively crossing a first feed water heater, a second feed water heater, the second humidifier and the first humidifier,

a closed cooling water circuit carrying cooling water and successively crossing the second dehumidifier, the first dehumidifier and the first feed water heater, and

- a unit for recovering, as product water, excess water from the cooling water, wherein:

the first and second humidifiers are arranged to respectively humidify the first and second gas by direct contact between the feed water and, respectively, the first and second gas,

- the first and second dehumidifiers are arranged to respectively dehumidify the first and second gas by direct contact between the cooling water and, respectively, the first and second gas, and

the first feed water heater is arranged to transfer heat from the cooling water exiting the first dehumidifier to the feed water.

By "gas" is meant a gas or gas mixture. The first and second gas may be identical or different. The first and second gas are e.g. air. The feed water is typically an impure or saline water to be purified or desalinated by the water distillation system of the invention.

The water distillation system of the invention may further include a third humidifier, a third dehumidifier and a corresponding third closed gas circuit, and still further sets of humidifier-dehumidifier-closed gas circuit if desired.

Preferably, the first feed water heater is a heat exchanger.

Typically, the second feed water heater is arranged to be powered by an external heat source.

The second feed water heater may be a heat exchanger arranged to transfer heat from the external heat source to the feed water.

Alternatively and preferably, the second feed water heater is a heat pump powered by the external heat source. More preferably, the heat pump is an absorption heat pump.

The cooling water forms a cold source for the heat pump while the feed water forms a warm source for the heat pump.

In a variant, the feed water exiting the first humidifier forms a cold source for the heat pump while the feed water exiting the first feed water heater forms a warm source for the heat pump.

In another variant, the cooling water and the feed water exiting the first humidifier each form a cold source for the heat pump while the feed water exiting the first feed water heater forms a warm source for the heat pump.

Thus, the invention is primarily based on a humidification-dehumidification process where feed liquid mixture (or feed water) between 80 and 90 degrees Celsius is evaporated in a humidification tower by direct contact with a carrying gas. Vapor is then directed to a dehumidification tower where it condenses by direct contact with a volume of cooling liquid mixture (or cooling water, or condensate at ambient temperature at spray outlet) circulated in a closed loop. Excess condensate is recovered as product water. The direct contact between liquid and gas in the humidification and dehumidification towers allows a significant reduction of the size of the towers.

The latent heat of condensation gained by the condensate during the

dehumidification process is exchanged with the feed liquid mixture through an external heat exchanger. In order to enhance the gained output ratio (GOR), the system includes multiple stages of humidifier-dehumidifier where feed liquid mixture is sequentially preheated by the heat exchangers of the multiple stages or by at least one such heat exchanger. The system also preferably includes an absorption heat pump which recovers the residual heat from the brine and/or the condensate.

An advantageous feature of the invention is the recovery and transfer of the latent heat of condensation to the feed liquid mixture by means of the combined use of a counter-current direct contact condenser (dehumidifier), an external heat exchanger and an absorption heat pump.

Another advantage of the invention is the use of off the shelf structured packing material for the direct contact condenser as well as commercial off the shelf heat exchangers and absorption heat pumps in order to reduce dramatically the system's overall costs.

BRIEF DESCRIPTION OF THE DRAWINGS

Figure 1 shows a water distillation system according to a first embodiment of the invention.

Figure 2 shows a water distillation system according to a second embodiment of the invention.

Figure 3 shows a water distillation system according to a third embodiment of the invention.

Figure 4 shows a water distillation system according to a fourth embodiment of the invention.

DETAILED DESCRIPTION OF THE INVENTION

Briefly, in accordance with the invention, an improved method of distillation is provided. The method includes the steps of providing a self-contained distillation system.

Evaporation is achieved at warm temperature (between 70 and 90 degrees Celsius) in a closed air circuit evaporator where a constant airflow is maintained. The feed liquid mixture (or feed water), raised to a temperature between 70 and 90 degrees Celsius, is sprayed through a liquid distributor over a bed of structured packing in the evaporator.

Un-evaporated liquid mixture is constantly discharged out of the system or circulated in a subsequent evaporation phase in order to increase recovery rate. The vapor generated in the evaporator is directed towards the condenser, where it is refrigerated by direct contact thermal exchange with a volume of cooling liquid mixture (condensate at ambient temperature at the exit of liquid distributor) flowing in counter-current in the condenser.

The condensate (or distilled water) produced by the process is mixed altogether with the mass of cooling liquid mixture and pools at the bottom of the condenser. This condensate, still warm, is circulated in a counter-current heat exchanger to transfer the condensation latent heat to the feed liquid mixture. The feed liquid mixture is therefore pre-heated from feed temperature to approximately 60 to 80 degrees Celsius.

In order to reach the operating temperature of the evaporator, the feed liquid mixture is further heated in order to reach approximately 70 to 90 degrees Celsius at the entry of the evaporator's liquid distributor. This subsequent heating may be provided by a heat exchanger or, preferably, by an absorption heat pump powered by an external heat source such as industrial waste heat or thermal solar energy. The cold source of the heat pump is the brine exiting the evaporator and/or the condensate exiting the counter current heat exchanger. The warm source of the heat pump is the warm pre-heated feed liquid mixture exiting the counter current heat exchanger. It is noted that the use of an absorption heat pump in this configuration can enhance the overall performance (GOR) of the system by a factor of approximately 1 .5 x.

The air exiting the condenser circuit is re-injected into the evaporator in a closed loop mode. It is to be noted that evaporation warms and humidifies the air, while condensation cools and dries the air as it releases the latent heat necessary for the condensation. Therefore the recycled dry air re-injected into the evaporator can maintain a level temperature.

The energy required to operate the system comprises:

a) Thermal energy to drive the evaporation-condensation system, b) Power to operate the axial fan and the water pumps.

The thermal energy required for the water heating can be provided from an array of sources, including thermal solar panels provided by third party suppliers, waste heat from an industrial source, geothermal or bio waste.

The axial fan and water circulation pumps can be powered by an array of photovoltaic solar panels, power generator or local grid power.

The electrical consumption of the present invention is substantially reduced compared to conventional distillation technologies. There is also to be noted that besides the axial fan's drive, the only other moving parts in the system are the water circulation pumps. The invention is therefore optimized for low energy consumption, enhanced reliability and low cost construction.

Turning now to the drawings, which illustrate the presently preferred embodiments of the invention,

FIG. 1 illustrates a water distillation system constructed in accordance with a first embodiment of the invention and including a humidifier (or evaporator) 1 and a dehumidifier (or condenser) 2 and an additional set of humidifier 21 and

dehumidifier 22. It is noted that an indefinite number of sets as described above can be added to the system in order to improve the performance.

The carrying gas (such as air) circulated between the humidifier 21 and the dehumidifier 22 in conduits 23 in a closed loop circuit is independent and separated from the carrying gas circulated between the humidifier 1 and the dehumidifier 2 in conduits 3 in a closed loop circuit.

The gas is humidified in the humidifier 21 , by direct contact, using the hot liquid mixture (i.e., feed water, impure aqueous saline solution withdrawn from water body 7), which is sprayed from a liquid distributor 24 at the top of the humidifier 21 through a bed of structured packing 25 while the gas moves in a counter flow direction (up through the humidifier 21 , as shown), thereby increasing the water vapor content in the gas via evaporation of water from the liquid mixture into the carrier gas flow. The remaining portion of the liquid mixture that is not evaporated in the humidifier 21 , pools at the bottom of the humidifier 21 and exits through a liquid-mixture output conduit, to be finally transferred to humidifier 1 and sprayed from the liquid distributor 4 through a bed of structured packing 5 while the gas moves in a counter flow direction (up through the humidifier 1 , as shown), thereby increasing the water vapor content in the gas via evaporation of water from the liquid mixture into the carrier gas flow. The remaining portion of the liquid mixture that is not evaporated in the humidifier 1 , pools at the bottom of the humidifier 1 and drains through a liquid-mixture output conduit 6 to water body 7.

The humidified carrier gas exiting humidifier 21 is directed through the conduit 23 to the dehumidifier 22, where the carrier gas is dehumidified, by direct contact, using the dehumidifier cooling liquid mixture (such as pure condensate) which is sprayed from a liquid distributor 26 at the top of the dehumidifier 22 through a bed of structured packing 27, allowing for heat transfer from the carrier gas to the cooling liquid mixture inside the dehumidifier 22. The water vapor in the carrier gas therefore condenses and mixes to the cooling liquid mixture which pools at the bottom of the dehumidifier 22. The carried gas can be circulated between the humidifier and dehumidifier in conduits 23 naturally by convection or by using a fan 30 powered by an electric motor or alternately by renewable energy. Simultaneously, the humidified carrier gas exiting humidifier 1 is directed through conduit 3 to the dehumidifier 2, where the carrier gas is dehumidified using the dehumidifier cooling liquid mixture (such as pure condensate) exiting the bottom of dehumidifier 22 which is sprayed from a liquid distributor 8 at the top of the dehumidifier 2 through a bed of structured packing 9, allowing for heat transfer from the carrier gas to the cooling liquid mixture inside the dehumidifier 2. The water vapor in the carrier gas therefore condenses and mixes to the cooling liquid mixture which pools at the bottom of the dehumidifier 2. The carried gas can be circulated between the humidifier and dehumidifier in conduits 3 naturally by convection or by using a fan 12 powered by an electric motor or alternately by renewable energy.

The liquid mixture passed by pump 13 via liquid mixture conduit 14 to humidifier 21 followed by humidifier 1 is preliminarily heated in sequence through heat exchangers 15 and 16, which may be plate heat exchangers. The heat exchanger 15 recovers the latent heat of condensation contained in the cooling liquid mixture passed in a loop mode through the dehumidifiers 2 and 22 by pump 17 in the conduits 18. The heat exchanger 16 may use a solar energy source (e.g., the heater may be in the form of a solar collector) and/or may use any waste heat source (e.g., use waste heat generated by other nearby machinery or by a power generating apparatus) passed in a loop mode by pump 19 in the conduits 20 to further heat the liquid mixture before its spraying in the humidifiers 21 and 1 .

Product water (pure condensate) is removed from the system by level overflow in the cooling liquid mixture buffer tank 29, and then transferred to the product water tank 1 1 via the product water output conduit 10.

As an option, a water chiller 28 can be installed on the cooling mixture line 18 in order to enhance the cooling of the liquid mixture prior entering the liquid distributor 26.

FIG. 2 illustrates a water distillation system constructed in accordance with a second embodiment of the invention and including a humidifier (or evaporator) 1 and a dehumidifier (or condenser) 2 and an additional set of humidifier 21 and dehumidifier 22. It is noted that an indefinite number of sets as described above can be added to the system in order to improve the performance.

The carrying gas (such as air) circulated between the humidifier 21 and the dehumidifier 22 in conduits 23 in a closed loop circuit is independent and separated from the carrying gas circulated between the humidifier 1 and the dehumidifier 2 in conduits 3 in a closed loop circuit. The gas is humidified in the humidifier 21 , by direct contact, using the hot liquid mixture (i.e., feed water, impure aqueous saline solution withdrawn from water body 7), which is sprayed from a liquid distributor 24 at the top of the humidifier 21 through a bed of structured packing 25 while the gas moves in a counter flow direction (up through the humidifier 21 , as shown), thereby increasing the water vapor content in the gas via evaporation of water from the liquid mixture into the carrier gas flow. The remaining portion of the liquid mixture that is not evaporated in the humidifier 21 , pools at the bottom of the humidifier 21 and exits through a liquid-mixture output conduit, to be finally transferred to humidifier 1 and sprayed from the liquid distributor 4 through a bed of structured packing 5 while the gas moves in a counter flow direction (up through the humidifier 1 , as shown), thereby increasing the water vapor content in the gas via evaporation of water from the liquid mixture into the carrier gas flow. The remaining portion of the liquid mixture that is not evaporated in the humidifier 1 , pools at the bottom of the humidifier 1 and drains through a liquid-mixture output conduit 6 to water body 7.

The humidified carrier gas exiting humidifier 21 is directed through the conduit 23 to the dehumidifier 22, where the carrier gas is dehumidified, by direct contact, using the dehumidifier cooling liquid mixture (such as pure condensate) which is sprayed from a liquid distributor 26 at the top of the dehumidifier 22 through a bed of structured packing 27, allowing for heat transfer from the carrier gas to the cooling liquid mixture inside the dehumidifier 22. The water vapor in the carrier gas therefore condenses and mixes to the cooling liquid mixture which pools at the bottom of the dehumidifier 22. The carried gas can be circulated between the humidifier and dehumidifier in conduits 23 naturally by convection or by using a fan 30 powered by an electric motor or alternately by renewable energy.

Simultaneously, the humidified carrier gas exiting humidifier 1 is directed through conduit 3 to the dehumidifier 2, where the carrier gas is dehumidified using the dehumidifier cooling liquid mixture (such as pure condensate) exiting the bottom of dehumidifier 22 which is sprayed from a liquid distributor 8 at the top of the dehumidifier 2 through a bed of structured packing 9, allowing for heat transfer from the carrier gas to the cooling liquid mixture inside the dehumidifier 2. The water vapor in the carrier gas therefore condenses and mixes to the cooling liquid mixture which pools at the bottom of the dehumidifier 2. The carried gas can be circulated between the humidifier and dehumidifier in conduits 3 naturally by convection or by using a fan 12 powered by an electric motor or alternately by renewable energy.

The liquid mixture passed by pump 13 via liquid mixture conduit 14 to humidifier 21 followed by humidifier 1 is preliminarily heated in sequence through a heat exchanger 15, e.g. a plate heat exchanger, and an absorption heat pump 16'. The heat exchanger 15 recovers the latent heat of condensation contained in the cooling liquid mixture passed in a loop mode through the dehumidifiers 2 and 22 by pump 17 in the conduits 18. The absorption heat pump 16' further heats the liquid mixture before its spraying in the humidifiers 21 and 1 . The absorption heat pump 16' may use as a power source thermal solar energy (e.g., the heater may be in the form of a solar collector) and/or any waste heat source (e.g., use waste heat generated by other nearby machinery or by a power generating apparatus) passed in a loop mode by pump 19 in the conduits 20.

The cold source of the absorption heat pump 16' is the cooling liquid mixture exiting the counter current heat exchanger 15 through line 18. The warm source of the absorption heat pump 16' is the pre-heated liquid mixture exiting the counter current heat exchanger 15 through line 14. One of the benefits of using the absorption heat pump 16' is to further cool the cooling liquid mixture exiting the counter current heat exchanger 15 by capturing and transferring its residual heat to the pre-heated liquid mixture exiting the counter current heat exchanger 15 through line 14. It is noted that the use of an absorption heat pump in this configuration can enhance the overall performance (GOR) of the system by a factor of approximately 1 .5 x.

FIG.3 shows a water distillation system constructed in accordance with a third embodiment of the invention. The water distillation system according to this third embodiment is identical to that of the second embodiment except for the cold source for the absorption heat pump.

In FIG.3, indeed, the cold source of the absorption heat pump 16" is the brine liquid mixture (i.e. concentrate) exiting the bottom of the humidifier 1 through line 6. The warm source of the absorption heat pump 16" is the pre-heated liquid mixture exiting the counter current heat exchanger 15 through line 14. One of the benefits of using the absorption heat pump 16" is to capture and transfer the residual heat contained in the brine liquid mixture exiting the bottom of the humidifier 1 through line 6 to the pre-heated liquid mixture exiting the counter current heat exchanger 15 through line 14. It is noted that the use of an absorption heat pump in this configuration can enhance the overall performance (GOR) of the system by a factor of approximately 1 .5 x with respect to the embodiment of FIG.1 .

FIG.4 shows a water distillation system constructed in accordance with a fourth embodiment of the invention. The water distillation system according to this fourth embodiment is identical to that of the second or third embodiment except that it has two parallel cold sources for the absorption heat pump 16"'.

In FIG.4, indeed, the cold sources of the absorption heat pump 16"' are

simultaneously the cooling liquid mixture exiting the counter current heat exchanger 15 through line 18 and the brine liquid mixture (i.e. concentrate) exiting the bottom of the humidifier 1 through line 6. The warm source of the absorption heat pump 16"' is the pre-heated liquid mixture exiting the counter current heat exchanger 15 through line 14. In the event that the absorption heat pump 16"' cannot take two simultaneous cold sources, an intermediate fluid circuit with a dedicated heat exchanger for each source (line 6 and line 18) will capture the residual heat of each source and merge it at the cold source inlet of the absorption heat pump 16"'.

Claims

1 . Water distillation system including:

- first and second humidifiers (1 , 21 ),

- first and second dehumidifiers (2, 22),

- a first closed gas circuit (3) crossing the first humidifier (1 ) and the first dehumidifier (2) and in which a first gas is circulated,

- a second closed gas circuit (23) crossing the second humidifier (21 ) and the second dehumidifier (22) and in which a second gas is circulated,

- a feed water circuit (14) carrying feed water and successively crossing a first feed water heater (15), a second feed water heater (16; 16'; 16"; 16"'), the second humidifier (21 ) and the first humidifier (1 ),

- a closed cooling water circuit (18) carrying cooling water and

successively crossing the second dehumidifier (22), the first

dehumidifier (2) and the first feed water heater (15), and

- a unit (29, 10, 1 1 ) for recovering, as product water, excess water from the cooling water,

wherein:

- the first and second humidifiers (1 , 21 ) are arranged to respectively humidify the first and second gas by direct contact between the feed water and, respectively, the first and second gas,

- the first and second dehumidifiers (2, 22) are arranged to respectively dehumidify the first and second gas by direct contact between the cooling water and, respectively, the first and second gas, and

- the first feed water heater (15) is arranged to transfer heat from the cooling water exiting the first dehumidifier (2) to the feed water.

2. Water distillation system according to claim 1 , wherein the first feed water heater (15) is a heat exchanger.

3. Water distillation system according to claim 1 or 2, wherein the second feed water heater (16; 16'; 16"; 16"') is arranged to be powered by an external heat source.

4. Water distillation system according to claim 3, wherein the second feed water heater (16) is a heat exchanger arranged to transfer heat from the external heat source to the feed water.

5. Water distillation system according to claim 3, wherein the second feed water heater (16'; 16"; 16"') is a heat pump powered by the external heat source.

6. Water distillation system according to claim 5, wherein the cooling water forms a cold source for the heat pump (16') while the feed water forms a warm source for the heat pump (16').

7. Water distillation system according to claim 5, wherein the feed water

exiting the first humidifier (1 ) forms a cold source for the heat pump (16") while the feed water exiting the first feed water heater (15) forms a warm source for the heat pump (16").

8. Water distillation system according to claim 5, wherein the cooling water and the feed water exiting the first humidifier (1 ) each form a cold source for the heat pump (16"') while the feed water exiting the first feed water heater (15) forms a warm source for the heat pump (16"').

9. Water distillation system according to any of claims 5 to 8, wherein the heat pump (16'; 16"; 16"') is an absorption heat pump.