System and Method for Purification of Water by Membrane Distillation

Abstract

The invention relates to an autonomous system for purification of water by membrane distillation. The invention also relates to the use of a membrane distillation module in a system. The invention furthermore relates to a method of operation a system for purification of water by membrane distillation.

Claims

1. Autonomous system for purification of water by membrane distillation, comprising: at least one main water supply for supplying water to the system, at least one membrane distillation module, the membrane module comprising: at least one retentate channel for flow-through of a heated water stream, which retentate channel is at least partially defined by at least one vapour selective membrane allowing vapour of the heated water stream to flow via pores of the membrane to a distillation side of the membrane facing away from the retentate channel, at least one distillate channel at least partially defined both by said distillation side of the membrane and by a non-porous condenser wall separating said the distillate channel from a coolant channel for flow-through of a cold water stream to cool the condenser wall to condense vapour present in the distillate channel to give a distillate stream within said distillate channel, a coolant channel inlet, for supplying cold water with a first temperature to the coolant channel, a retentate channel inlet, for supplying heated water with a second temperature to the retentate channel, wherein the second temperature is higher than the first temperature, a coolant channel outlet, for discharging water from the coolant channel, a retentate channel outlet, for discharging water from the retentate channel, at least one distillate outlet for discharging distillate created in the distillate channel, at least one distillate receiving unit for receiving at least a fraction and preferably substantially all distillate discharged via the distillate outlet of the membrane distillation module, at least one heat pump comprising: a condenser configured for heating water to said second temperature before feeding this heated water into the retentate channel inlet, and an evaporator configured for cooling water to said first temperature before feeding this cooled water into the coolant channel inlet, preferably a renewable power supply, for powering the system, in particular said at least one heat pump, and at least one first buffer tank, connected to the main water supply, for storing water to be led through the evaporator of the heat pump into the coolant channel inlet, which first buffer tank is configured for receiving water discharged from the retentate channel outlet, wherein the system is configured for recirculation of at least a fraction of water from the first buffer tank via the evaporator of the heat pump, via the coolant channel of the membrane distillation module, directly or indirectly via the condenser of the heat pump, via the retentate channel of the membrane distillation module, back into the first buffer tank.

2. System according to claim 1, comprising multiple membrane distillation modules, wherein each membrane module comprises: at least one retentate channel for flow-through of a heated water stream, which retentate channel is at least partially defined by at least one vapour selective membrane allowing vapour of the heated water stream to flow via pores of the membrane to a distillation side of the membrane facing away from the retentate channel, at least one distillate channel at least partially defined both by said distillation side of the membrane and by a non-porous condenser wall separating said the distillate channel from a coolant channel for flow-through of a cold water stream to cool the condenser wall to condense vapour present in the distillate channel to give a distillate stream within said distillate channel, a coolant channel inlet, for supplying cold water with a first temperature to the coolant channel, a retentate channel inlet, for supplying heated water with a second temperature to the retentate channel, wherein the second temperature is higher than the first temperature, a coolant channel outlet, for discharging water from the coolant channel, a retentate channel outlet, for discharging water from the retentate channel, at least one distillate outlet for discharging distillate created in the distillate channel, #Said membrane distillation modules are fed by the same heat pump.

3. System according to claim 2, wherein said membranes modules are arranged in parallel.

4. System according to claim 2 or 3, wherein each membrane module comprises an individual channel through the condenser of at least one heat pump for heating water to said second temperature before feeding this heated water into the retentate channel inlet of the respective membrane module. #in order to equal flow on both the cold and hot side of the membrane module (83).

5. System according to any of claims 2-4, wherein each membrane module comprises at least one control valve configured to obtain an equal pressure and flow per membrane module.

6. System according to any of the preceding claims, comprising at least one second buffer tank, preferably connected to the main water supply, for storing water to be led through the condenser of the heat pump into the retentate channel inlet, which second buffer tank is configured for receiving water discharged from the coolant channel.

7. System according to any of the preceding claims, wherein the main water supply is provided with a main valve to selectively either (i) to allow water to flow from the main water supply into the first buffer tank and/or the second buffer tank, or (ii) to prevent water to flow from the main water supply into the first buffer tank and/or the second buffer tank.

8. System according to any of the preceding claims, wherein at least one buffer tank is provided with at least one sensor to measure at least one water related parameter, wherein said sensor is preferably selected from the group consisting of: a level sensor, a temperature sensor, an electrical conductivity sensor, a flow sensor and an optical sensor, and/or wherein the system comprises at least one sensor to measure at least one water related parameter both at the retentate channel inlet, the retentate channel out, the coolant channel inlet, and the coolant channel outlet, wherein said sensor is preferably selected from the group consisting of: a level sensor, a temperature sensor, an electrical conductivity sensor, a flow sensor and an optical sensor.

9. System according to claim 8, wherein the system is configured to retain the circulation until at least one sensor measures at least one water related parameter value meeting and/or exceeding a predefined critical parameter value.

10. System according to claim 8 or claim 9, wherein the system is configured to remove water from the first buffer tank and/or the second buffer tank in case at least one sensor measures at least one water related parameter value meeting and/or exceeding a predefined critical parameter value.

11. System according to any of the preceding claims, wherein the system comprises a discharge pump for displacing water from the first buffer tank and/or the second buffer tank to a water waste outlet for discharging water from the system.

12. System according to any of the preceding claims, wherein the distillate receiving unit is provided with at least one sensor, preferably a conductivity sensor.

13. System according to any of the preceding claims, wherein the system comprises a control unit for controlling the system, in particular one or more controllable components, such as a pump, sensor, or valve, of the system.

14. System according to one of claims 8-10, and claim 13, wherein the control unit is preprogrammed or programmable to compare a measured water related parameter value with at least one predefined parameter value.

15. System according to claim 11 and claim 14, wherein the control unit is preprogrammed or programmable to activate the discharge pump in case the measure water related parameter value meets and/or exceeds at least one predefined parameter value.

16. System according to claim 11 and claim 14, or to claim 15, wherein the control unit is preprogrammed or programmable to open the main valve to fill the first buffer tank and/or second buffer tank with new water.

17. System according to any of the preceding claims, wherein the first buffer tank comprises a level sensor for sensing the liquid level of water in said first buffer tank.

18. System according to any of the preceding claims, wherein at least one membrane distillation module is an air gap membrane distillation module.

19. System according to any of the preceding claims, wherein at least one membrane distillation module comprises at least one spirally wound membrane, and an adjacent spirally wound condenser wall

20. System according to any of the preceding claims, wherein at least one the membrane of the membrane distillation module is made of polytetrafluoroethylene (PTFE), preferably stretched PTFE.

21. System according to any of the preceding claims, wherein at least a part of at least one condenser wall is made of a thermally conductive material, preferably metal, in particular aluminium.

22. System according to any of the preceding claims, comprising at least one additive supply for supplying at least one additive to the distillate.

23. System according to any of the preceding claims, wherein the system is configured to operate at a pressure below 1 bar, preferably below 0.75 bar, more preferably below 0.5 bar.

24. System according to any of the preceding claims, wherein the heat pump is an ammonia heat pump.

25. System according to any of the preceding claims, comprising at least one pump for displacing water within the system, and in particular between the first buffer tank and the second buffer tank via at least one membrane distillation module.

26. System according to any of the preceding claims, wherein the condenser is configured for heating water to a temperature of at least 40 degrees Celsius, preferably at least 50 degrees Celsius, more preferably at least 60 degrees Celsius.

27. System according to any of the preceding claims, wherein the evaporator is configured for cooling water to a temperature below 30 degrees Celsius, preferably below 20 degrees Celsius, more preferably below 15 degrees Celsius.

28. System according to any of the preceding claims, wherein the first buffer tank and/or the second buffer tank has a volume at least 500 litres, preferably at least 1000 litres.

29. System according to any of the preceding claims, comprising at least one filter for filtering water, preferably before said water is supplied to the system.

30. System according to any of the preceding claims, wherein the main water supply is connected or connectable to an external water reservoir, such as a water well or surface water, such as the sea.

31. System according to any of the preceding claims, wherein the system is configured to pass the heated water stream through the retentate channel in counter-current with the cold water stream led through the coolant channel.

32. System according to any of the preceding claims, wherein the system comprises a plurality of membrane distillation modules, preferably arranged in parallel, wherein each membrane distillation module is connected, either directly or indirectly, to the first buffer tank.

33. System according to any of the preceding claims, wherein the system comprises a single heat pump.

34. System according to any of the preceding claims, wherein the main water supply comprises a prebuffer tank for storage of water taken from an external water source and to be fed to the first buffer tank and/or second buffer tank.

35. System according to any of the preceding claims, wherein at least a part of the system is accommodated in a container, preferably a twenty-foot equivalent unit (TEU).

36. Use of a membrane distillation module in a system according to one of claims 1-35.

37. Method of operating a system for purification of water by membrane distillation according to one of claims 1-35, comprising the steps of: A) filling the first tank with water by using the main water supply, B) leading water originating from the first buffer tank through the evaporator, and subsequently through the coolant channel of at least one membrane distillation module and directly or indirectly through the condenser, and subsequently through the retentate channel of at least one membrane distillation module and into the first buffer tank, wherein distillate will be created within the distillate channel of the membrane distillation module, together forming a chain of components, and C) receiving distillate created in the distillate channel in at least one distillate receiving unit for receiving.

38. Method according to claim 37, wherein during step B) water will be circulated in said chain of components a plurality of times.

39. Method according to claim 37 or 38, wherein steps A), B) and C) are performed as batch process.

40. Method according to any of claims 37-39, wherein during step B) at least one water related parameter, in particular the electrical conductivity, is measured.

41. Method according to claim 40, wherein at least one measured parameter value is compared with at least one predefined parameter value, and wherein, in case the measured parameter value meets and/or exceeds the predefined parameter value, the execution of step B) is interruption, and preferably at least a part of water present in said chain of components is discharged from the system, more preferably by using a discharge pump.

Description

[0123] The invention will be elucidated on the basis of non-limitative exemplary embodiments shown in the following figures.

[0124] FIG. 1 shows a schematic view (process scheme) of a first possible embodiment of an autonomous system (1) for purification of water taken from an external source, in particular to produce potable water, according to the present invention. The system (1) comprises a main water supply (2) for supplying non-potable water to the system, and a membrane module (3) or membrane unit (3) for distillation of non-potable water. The membrane unit (3) comprises at least one, and preferably multiple vapour selective membranes, a coolant channel inlet (4), for supplying water with a first temperature T1 to the membrane unit (3), a retentate channel inlet (5), for supplying water with a second temperature T2 to the membrane unit (3), a coolant channel outlet (6), for discharging water from the membrane unit (3) which was supplied at the coolant channel inlet (4) and a retentate channel outlet (7), for discharging water from the membrane unit (3) which was supplied at the retentate channel inlet (5) and a distillate outlet (8) for discharging distillate D which is distilled from water supplied at the retentate channel inlet (4) via the at least one vapour selective membrane. The system (1) furthermore comprises a distillate receiving unit (9) for receiving at least a fraction and preferably substantially all distillate D discharged from the membrane unit (3). The system (1) comprises a heat pump, such as an ammonia heat pump, the heat pump at least comprising a condenser (10) for heating water to a second temperature T2 before the water is fed to the retentate channel inlet (5) of the membrane unit (3) and an evaporator (11) for cooling water to a first temperature T1 before the water is fed to the coolant channel inlet (4) of the membrane unit (3). The system (1) furthermore comprises a first buffer tank (12) and a second buffer tank (13) for storing water. The first buffer tank (12) receives water from the retentate channel outlet (7) of the membrane unit (3) and supplies water to the coolant channel inlet (4) of the membrane unit (3). The second buffer tank (13) receives water from the coolant channel outlet (6) of the membrane unit (3) and supplies water to the retentate channel inlet (5) of the membrane unit (3). The system (1) is configured for circulation of at least a fraction of water and preferably substantially all water via the first buffer tank (12), the membrane unit (3) and the second buffer tank (13) till at least a fraction of the water reaches a predefined conductivity. The system (1) preferably comprises a stand-alone power system (SAPS) or remote area power supply (RAPS), for powering at least the heat pump. This can be any of the known off-the-grid electricity systems. The system (1) according to the invention is configured such that the second temperature T2 is higher than the first temperature T1.

[0125] The system (1), and in particular the second buffer tank (13) comprises a conductivity sensor (14) for determining the conductivity of water, preferably the conductivity of water in the second buffer tank (13). Based upon the conductivity of the water in the second buffer tank (13) the degree of saturation of the water can be determined. This is useful in order to determine whether the water should be removed from the system, such that the system (1) can subsequently be refilled with non-potable water to be used in the distillation process. The system (1) therefore comprises a liquid waste outlet (15) for discharging water from the system (1). The liquid waste outlet (15) may possibly be configured to supply the waste water to a further waste buffer (19). The main water supply (2) is configured to supply non-potable water to at least the first buffer tank (12). However, it is also possible that the main water supply (2) supplies water to the second buffer tank (13) either directly or indirectly. This can for example be done via an overflow (16) of the first buffer tank (12). At least the first buffer tank (12) comprises a level sensor (17) for sensing the liquid level of water in said first buffer tank (12). It is however, also possible that any of the further tanks comprises a liquid level sensor and/or a conductivity sensor and/or any further sensor such as for example a temperature sensor. In a preferred embodiment the system (1) comprises a control unit (not shown) for controlling the main water supply (2) based upon the level sensed by said level sensor (17) such that a minimum and/or maximum liquid level is maintained in the first buffer tank (12). The system (1) furthermore comprises an additive supply (18) for supplying at least one additive A to the distillate D. The additive A generally comprises sodium hypochlorite (NaOCl). It is a benefit of the system (1) that the system (1) is configured to operate at relatively low pressures, such as a pressure below 1 bar, preferably below 0.75 bar, more preferably below 0.5 bar. The system (1) also comprises a filter (20) for filtering water before it is supplied to the circular water system. As can be seen in the figure, the filter non-potable water is collected in a buffer tank (21) before it is supplied to the system (1). The system (1) comprises multiple pumps P for the transfer of water.

[0126] FIG. 2 shows a schematic view (process scheme) of a second possible embodiment of an autonomous system (51) for purification of water taken from an external source, in particular to produce potable water, according to the present invention. The system (51) comprises a main water supply (52) for supplying non-potable water to the system, and a membrane module (53) for distillation of non-potable water. The membrane module (53) comprises at least one, and preferably multiple vapour selective membranes, a coolant channel inlet (54), for supplying water with a first temperature T1 to the membrane module (53), a retentate channel inlet (55), for supplying water with a second temperature T2 to the membrane module (53), a coolant channel outlet (56), for discharging water from the membrane module (53) which was supplied at the coolant channel inlet (54) and a retentate channel outlet (57), for discharging water from the membrane module (53) which was supplied at the retentate channel inlet (55) and a distillate outlet (58) for discharging distillate D which is distilled from water supplied at the retentate channel inlet (54) via the at least one vapour selective membrane. The system (51) furthermore comprises a distillate receiving unit (59) for receiving at least a fraction and preferably substantially all distillate D discharged from the membrane module (53). The system (51) comprises a heat pump, such as an ammonia heat pump, the heat pump at least comprising a condenser (60) for heating water to a second temperature T2 before the water is fed to the retentate channel inlet (55) of the membrane module (53) and an evaporator (61) for cooling water to a first temperature T1 before the water is fed to the coolant channel inlet (54) of the membrane module (53). The system (51) furthermore comprises a first buffer tank (62) for storing water. The first buffer tank (62) receives water from the retentate channel outlet (57) of the membrane module (53) and supplies water to the coolant channel inlet (54) of the membrane module (53). Water which is discharged at the coolant channel outlet (56) is led through the condenser (60) and subsequently into the retentate channel inlet (55) of the membrane distillation module (53). The system enables water circulation till at least a fraction of the water reaches a predefined conductivity. The system (51) preferably comprises a stand-alone power system (SAPS) or remote area power supply (RAPS), for powering at least the heat pump. The system (51) according to the invention is typically configured such that the second temperature T2 is higher than the first temperature T1. The system (51), and in particular the first buffer tank (62) comprises a conductivity sensor (64) for determining the conductivity of water. The system (51) comprises a liquid waste outlet (55) for discharging water from the system (51). The liquid waste outlet (65) may possibly be configured to supply the waste water to a further waste buffer (69). The main water supply (52) is configured to supply non-potable water to at least the first buffer tank (52). The first buffer tank (62) comprises a level sensor (67) for sensing the liquid level. The system (51) furthermore comprises an additive supply (68) for supplying at least one additive A to the distillate D. The system (51) also comprises a filter (70) for filtering water before it is supplied to the circular water system. As can be seen in the figure, the filter non-potable water is collected in a buffer tank (71) before it is supplied to the system (51). The system (51) comprises multiple pumps P for the transfer of water.

[0127] FIG. 3 shows a schematic view (process scheme) of a third possible embodiment of an autonomous system (81) for purification of water taken from an external source, in particular to produce potable water, according to the present invention. The system (81) has overlap with the system (51) as shown in FIG. 2. However, the shown embodiment comprises a series of parallel positioned membrane distillation modules (83). Said membrane distillation modules (83) are fed by the same heat pump (95). The heat pump (95) comprises a condenser (90) for heating water to a second temperature T2 before the water is fed to each retentate channel inlet (85) of the membrane modules (83) and an evaporator (91) for cooling water to a first temperature T1 before the water is fed to the coolant channel inlet (84) of the membrane modules (83). Each membrane module (83) comprises a control valve (99) configured to obtain an equal pressure and flow per membrane module (83). Water which is discharged at each coolant channel outlet (56) of each membrane module (83) is led through the condenser (90) and subsequently into the retentate channel inlet (85) of the membrane distillation module (83) it was discharged from. In particular, each membrane module (83) comprises its own channel through the condenser (90), in order to equal flow on both the cold and hot side of the membrane module (83). A main water supply (92) for supplying non-potable water to the system (81), in the shown embodiment originating from the non-potable water buffer tank (97). Each membrane module (83) comprises at least one, and preferably multiple vapour selective membranes, a coolant channel inlet (84), for supplying water with a first temperature T1 to the membrane module (83), a retentate channel inlet (85), for supplying water with a second temperature T2 to the membrane module (83), a coolant channel outlet (86), for discharging water from the membrane module (83) which was supplied at the coolant channel inlet (84) and a retentate channel outlet (87), for discharging water from the membrane module (83) which was supplied at the retentate channel inlet (85) and a distillate outlet (88) for discharging distillate D which is distilled from water supplied at the retentate channel inlet (84) via the at least one vapour selective membrane. The system (81) furthermore comprises a distillate receiving unit (89) for receiving at least a fraction and preferably substantially all distillate D discharged from the membrane modules (83). The system (81) furthermore comprises a first buffer tank (82) for storing water. The first buffer tank (82) receives water from the retentate channel outlets (87) of the membrane modules (83) and supplies indirectly water to the coolant channel inlets (84) of the membrane modules (83).

[0128] It will be apparent that the invention is not limited to the working examples shown and described herein, but that numerous variants are possible within the scope of the attached claims that will be obvious to a person skilled in the art.

[0129] The verb “comprise” and conjugations thereof used in this patent publication are understood to mean not only “comprise”, but are also understood to mean the phrases “contain”, “substantially consist of”, “formed by” and conjugations thereof. Where the term ‘membrane module’ is used, also the term ‘membrane unit’ can be used, or vice versa.