System for controlling water content of an air stream

Abstract

A system for controlling water content in an air stream (7) comprising a contact device (3) for transferring thermal energy and water vapor between a liquid desiccant (5) and the air stream (7) flowing through the contact device. The system comprises further a regeneration part (11) for removing water from the liquid desiccant (5) and a recirculation part (21) for recirculate the liquid desiccant, wherein the system further comprises at least one liquid desiccant temperature restoring device 31a, 31b provided in the regeneration part (11) and / or in the recirculation part (21), where said liquid desiccant temperature restoring device 31a, 31b comprises an air-to-liquid heat exchanger (33) and a fan (35), wherein said air-to-liquid heat exchanger (33) is connected in the system such that liquid desiccant 5 passes through the air-to-liquid heat exchanger for being tempered by ambient air and wherein said fan (35) is positioned in the system such that the ambient air is directed by the action from the fan to flow towards the air-to-liquid heat exchanger.

Description

[0001] System for controlling water content of an air stream

[0002] TECHNICAL FIELD OF THE INVENTION

[0003] The present invention relates to a system for controlling water content in an air stream by use of a liquid desiccant.

[0004] BACKGROUND

[0005] Control of water content of an air stream is for example desirable for dehumidifying the air in cold, chilled and frozen facilities, such as cold storage and warehousing. This improves the working environment and avoids damage from moisture to equipment in the facility and on the facility itself. In other environments, such as temperate rooms, there may instead be a need for humidification of the air. A typical example of the need for controlling minimum humidity levels is to avoid static discharges (ESD) in manufacturing of electronic components and PCBs.

[0006] One type of system for controlling water content of an air stream which can be used both for dehumidification and for humidification of the air stream uses a liquid desiccant for absorbing water vapor from the air or adding water vapor into the air. Often the temperature of the air stream also needs to be controlled. This can be done by separately heating the air stream after it has passed via the liquid desiccant. However, in WO2022 / 203573 it is described how both temperature and water content of the air stream can be adjusted simultaneously. There is a need to optimize capacity and energy consumption for such systems.

[0007] SUMMARY

[0008] It is an object of the present invention to provide an improved system for controlling water content of an air stream. This is achieved in system for controlling water content in an air stream according to claim 1.

[0009] According to the invention a system for controlling water content in an air stream is provided. Said system comprises:

[0010] - a contact device for transferring thermal energy and water vapor between a liquid desiccant and the air stream flowing through the contact device, said liquid desiccant flowing through the contact device from a liquid desiccant inlet to a liquid desiccant outlet and said air stream flowing through the contact device from an air stream inlet to an air stream outlet, the contact device being configured to allow a contact between the liquid desiccant and the air stream in which contact thermal energy and water vapor is transferred;

[0011] - a liquid desiccant collecting tank which is positioned for receiving liquid desiccant from the liquid desiccant outlet of the contact device, said liquid desiccant collecting tank comprising a regeneration inlet, a regeneration outlet and a recirculation outlet;

[0012] - a regeneration part connected to the regeneration inlet and the regeneration outlet of the liquid desiccant collecting tank such that liquid desiccant expelled from the liquid desiccant outlet of the contact device can be circulated through the regeneration part from the regeneration outlet to the regeneration inlet, said regeneration part comprising a regeneration device for removing water from the liquid desiccant; and

[0013] - a recirculation part connected to the recirculation outlet of the liquid desiccant collection tank such that liquid desiccant expelled from the liquid desiccant outlet of the contact device can be recirculated via the recirculation part and reintroduced to the contact device via the liquid desiccant inlet, wherein the system further comprises:

[0014] - at least one liquid desiccant temperature restoring device provided in the regeneration part and / or in the recirculation part, where said liquid desiccant temperature restoring device comprises an air-to-liquid heat exchanger and a fan, wherein said air-to-liquid heat exchanger is connected in the system such that liquid desiccant passes through the air-to-liquid heat exchanger for being tempered by ambient air and wherein said fan is positioned in the system such that the ambient air is directed by the action from the fan to flow towards the air-to-liquid heat exchanger.

[0015] Hereby a system for controlling water content of an air stream is achieved, which will utilize a temperature difference between the liquid desiccant and the environment where the system is positioned in order to optimize capacity and energy consumption of the system. For example, if the system is positioned in a cold facility where the system is to be used for dehumidifying the air stream, the cold temperature of the ambient air is utilized, as a type of free energy, for improving the capacity of the dehumidifier. Hereby also energy consumption for operating the dehumidifier is lowered. In the liquid desiccant temperature restoring device, air from the cold surrounding is directed by the fan to flow towards the air-to-liquid heat exchanger in which the liquid desiccant is flowing. The liquid desiccant has at this position a higher temperature than the surrounding air because of the treatment in the regeneration device whereby a cooling is provided to the liquid desiccant in the air-to-liquid heat exchanger. By lowering the temperature of the liquid desiccant the temperature of the air passing the liquid desiccant in the dehumidifier will also be lowered. Air of lower temperature contains a lower amount of water at the same relative humidity as air of higher temperature. A dehumidifier using a liquid desiccant of the type described in this invention can achieve a certain degree of relative humidity of the air passing the dehumidifier and hereby air of lower temperature will contain a lower amount of water after having passed the dehumidifier than air of a higher temperature thus increasing the adsorbed humidity.

[0016] Even further, thanks to the lower temperature of the liquid desiccant as achieved by the invention when the system is used in a cold environment for dehumidification, a temperature increase of the air stream when dehumidified in the system will be lower. The dehumidifying process has a consequence of raising the temperature of the air stream. However, with a liquid desiccant of lower temperature this effect will be smaller. Hereby a cold temperature in the room can be maintained with use of less energy. Even further, the dehumidifier will hereby contribute to the distribution of cold air in the room, i.e. a cooling effect provided from a cooling device in the room will be better distributed in the room thanks to the distribution via the dehumidifier.

[0017] If the system according to the invention on the other hand is used as a humidifier in a temperate room the liquid desiccant will instead thanks to the invention be warmed up by ambient air in the air-to-liquid heat exchanger and with a liquid desiccant of comparatively higher temperature a capacity for adding water in the humidifying process is increased. Furthermore, a temperature of the room can be maintained with use of less energy.

[0018] Hereby the liquid desiccant temperature restoring device according to the invention improves capacity and optimizes energy consumption for the system both when the system is used as dehumidifier in cold environments and as humidifier in warm environments.

[0019] Thanks to the invention the temperature in the room is utilized better as a kind of free energy, for restoring a temperature change of the liquid desiccant. The temperature of the environment is utilized for improving capacity and energy consumption of the system by directing air to a specific position according to the invention.

[0020] The system of the invention utilizes energy from the environment, in a way which is readily available and easy to implement. Existing systems can in a convenient way be configured with this new liquid desiccant temperature restoring device.

[0021] In one embodiment of the invention the regeneration part further comprises a liquid-to- liquid heat exchanger via which liquid desiccant is transferred both on its way to the regeneration device from the liquid desiccant collecting tank and from the regeneration device back to the liquid desiccant collecting tank, whereby heat from the regeneration process can be used for heating the liquid desiccant on its way to the regeneration device. In one embodiment of the invention the liquid desiccant temperature restoring device is positioned between the liquid-to-liquid heat exchanger and the regeneration inlet of the liquid desiccant collecting tank.

[0022] In one embodiment of the invention the regeneration device is a boiler.

[0023] In one embodiment of the invention the liquid desiccant is a salt such as Lithium Bromide, LiBr, Calcium Chloride, CaCL, Magnesium Chloride, MgCL , Potassium Sulfate, K2SO4, or Potassium Formate, HCO2K.

[0024] In one embodiment of the invention the contact device is an evaporator pad.

[0025] In one embodiment of the invention the contact device is a liquid to air membrane energy exchanger, LAMEE.

[0026] BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 is a schematic drawing of a room comprising a temperature controlling system and a system for controlling water content of an air stream according to the invention.

[0028] Figure 2 is a schematic drawing of a system for controlling water content of an air stream according to one example of the invention.

[0029] Figure 3 is a Mollier diagram illustrating the difference when using the invention.

[0030] DETAILED DESCRIPTION

[0031] A system for controlling water content of an air stream is disclosed. The system according to the invention uses a liquid desiccant and can be used both for dehumidification and for humidification of the air stream. The liquid desiccant absorbs water vapor from the air or adds water vapor into the air.

[0032] Figure 1 is a schematic drawing of a room 201 comprising a temperature controlling system 101 and a system 1 for controlling water content of an air stream according to the invention. The temperature controlling system 101 can be a cooling device and in that case the system 1 is used as a dehumidifier. In another example the temperature controlling system 101 is a heater and in that case the system 1 is used as a humidifier. According to the invention the cooling or heating provided by the temperature controlling system 101 is utilized efficiently by a temperature restoring device 31a, 3 lb in the system 1 such that air from the surroundings is directed by a fan 35 towards an air-to-liquid heat exchanger 33 in which the temperature of a liquid desiccant 5 is restored, which will be further described below with reference to Figure 2.

[0033] Figure 2 is a schematic drawing of the system 1 for controlling water content of an air stream 7 according to one example of the invention. The system 1 comprises a contact device 3 for transferring thermal energy and water vapor between a liquid desiccant 5 and the air stream 7 flowing through the contact device 3. The liquid desiccant 5 flows through the contact device 3 from a liquid desiccant inlet 9a to a liquid desiccant outlet 9b and said air stream 7 flows through the contact device from an air stream inlet 10a to an air stream outlet 10b. The air stream 7 is in this example pushed towards the air stream inlet 10a by an air fan 51 provided in the system 1. However, another alternative would be to pull the air stream through the contact device 3 by a sucking device positioned in connection with the air stream outlet 10b. The contact device 3 is configured to allow a contact between the liquid desiccant 5 and the air stream 7 in which contact thermal energy and water vapor is transferred. When the system 1 is used as a dehumidifier the liquid desiccant 5 will adsorb water vapor from the air stream 7 and when the system 1 is used as a humidifier the liquid desiccant 5 will add water vapor into the air stream 7. The system 1 comprises further a liquid desiccant distributor 6 which is connected to the liquid desiccant inlet 9a and configured for distributing the liquid desiccant into the contact device 3.

[0034] The system 1 comprises further a liquid desiccant collecting tank 41 which is positioned for receiving liquid desiccant 5 from the liquid desiccant outlet 9b of the contact device 3. The liquid desiccant collecting tank 41 comprises a regeneration inlet 42a and a regeneration outlet 42b to which a regeneration part 11 is connected. The liquid desiccant collecting tank 41 comprises further a recirculation outlet 42c to which a recirculation part 21 is connected. The regeneration part 11 is connected to the regeneration inlet 42a and the regeneration outlet 42b of the liquid desiccant collecting tank 41 such that liquid desiccant 5 expelled from the liquid desiccant outlet 9b of the contact device 3 and collected in the liquid desiccant collection tank 41 can be circulated through the regeneration part 11 from the regeneration outlet 42b to the regeneration inlet 42a. The regeneration part 11 comprises at least one regeneration pump 17 for pumping the liquid desiccant 5 through the regeneration part 11. In the example as shown in Figure 1 two regeneration pumps 17 are provided, however only one regeneration pump 17 may be provided in another example. The regeneration part 11 comprises a regeneration device 13 for removing water from the liquid desiccant 5 when the system is used for dehumidification of the air stream 7. The regeneration device 13 can be for example a boiler, a vacuum boiler or a second contact device which is driven in regeneration mode, i.e. opposite mode compared to the contact device 3. When the system is used as dehumidifier the desiccant is treated in the regeneration device 13 such that water is removed from the liquid desiccant 5 and the temperature of the liquid desiccant 5 will increase.

[0035] The recirculation part 21 is connected to the recirculation outlet 42c of the liquid desiccant collection tank 41 such that liquid desiccant 5 expelled from the liquid desiccant outlet 9b of the contact device 3 and collected in the liquid desiccant collection tank 41 can be recirculated via the recirculation part 21 and reintroduced to the contact device 3 via the liquid desiccant inlet 9a. The recirculation part 21 comprises at least one recirculation pump 27 for pumping the liquid desiccant 5 through the recirculation part 21. A filter 28 is suitably also provided in the recirculation part 21.

[0036] According to the invention a liquid desiccant temperature restoring device 31a, 3 lb is provided in the regeneration part 11 and / or in the recirculation part 21. In the example as shown in Figure 2 two liquid desiccant temperature restoring devices 3 la, 3 lb are shown however, only one of these are needed. Hereby at least three different examples are included in Figure 2, where two examples comprise one each of the two liquid desiccant temperature restoring devices 3 la, 3 lb and one example comprise both liquid desiccant temperature restoring devices 3 la, 3 lb. The liquid desiccant temperature restoring device 3 la, 3 lb comprises an air-to-liquid heat exchanger 33 and a fan 35, wherein said air-to-liquid heat exchanger 33 is connected in the system such that liquid desiccant 5 passes through the air-to-liquid heat exchanger 33 for being tempered by ambient air and wherein said fan 35 is positioned in the system 1 such that the ambient air is directed by the action from the fan 35 to flow towards the air-to-liquid heat exchanger 33.

[0037] Hereby, if the system 1 is positioned in a cold facility where the system 1 is to be used as a dehumidifier for dehumidifying the air stream 7, the free energy from the cold ambient air, free cooling, is utilized for improving the capacity of the dehumidifier. Hereby also energy consumption for operating the system is lowered. In the liquid desiccant temperature restoring device 3 la, 3 lb, air from the cold surrounding is directed by the fan 35 to flow towards the air-to-liquid heat exchanger 33 in which the liquid desiccant 5 is flowing. The liquid desiccant has at this position a higher temperature than the surrounding air because of the treatment in the regeneration device 13 whereby a cooling is provided to the liquid desiccant 5 in the air-to-liquid heat exchanger 33. By lowering the temperature of the liquid desiccant 5 the temperature of the air stream 7 passing the liquid desiccant 5 in the contact device 3 will also be lowered. Hereby both capacity of the system 1 is increased and temperature of the air stream 7 passing the contact device 3 will be kept lower which was described in further detail above in the summary. Hereby, energy consumption of the system 1 can be reduced.

[0038] In some examples, but not necessarily for the invention, the regeneration part 11 further comprises a liquid-to-liquid heat exchanger 15 via which liquid desiccant 5 is transferred both on its way to the regeneration device 13 from the liquid desiccant collecting tank 41 and from the regeneration device 13 back to the liquid desiccant collecting tank 41. Hereby heat from the regeneration process can be used for heating the liquid desiccant 5 on its way to the regeneration device 13 and hereby energy consumption can be reduced. In such an example the liquid desiccant temperature restoring device 3 la is suitably positioned between the liquid-to-liquid heat exchanger 15 and the regeneration inlet 42a of the liquid desiccant collecting tank 41. With this position of the liquid desiccant temperature restoring device 3 la a cooling effect from ambient air can be utilized efficiently since a temperature difference between the liquid desiccant 5 at this position and the ambient air is comparatively large. The temperature of the liquid desiccant when leaving the regeneration device 13, for example a boiler, can for example be between 110- 150 °C and after having passed the heat exchanger 15 the temperature of the liquid desiccant is between 60-80 °C. In the liquid desiccant collecting tank 41 the temperature of the liquid desiccant 5 is somewhere close to the temperature in the room where the system 1 is positioned.

[0039] As discussed above in the summary and in relation to Figure 1, the system 1 can as well be used as a humidifier in a heated room. In that case the liquid desiccant 5 adds water vapor to the air stream 7 in the contact device 3. Hereby a water adding device 45 is needed in the system 1. The water adding device 45 is for example configured and positioned for adding water to the liquid desiccant collecting tank 41. When the system 1 is used as humidifier the regeneration part 11 is not necessary for removing water from the liquid desiccant 5. However, if the liquid desiccant temperature restoring device 3 la is positioned in the regeneration part 11 the liquid desiccant 5 can still be circulated through the regeneration part 11 such that the temperature of the liquid desiccant 5 can be restored in the liquid desiccant temperature restoring device 31a. The temperature of the liquid desiccant 5 will in this example be lowered by the process of humidification in the contact device 3 and it is advantageous to increase the temperature of the liquid desiccant 5 in the liquid desiccant temperature restoring device 3 la by blowing warmer air from the surroundings by the fan 35 towards the air- to-liquid heat exchanger 33. Hereby, the temperature of the liquid desiccant 5 will increase and the effect of temperature decrease of the air stream 7 during humidification in the contact device 3 will be decreased whereby energy consumption for humidification and for keeping the temperature up in the room can be reduced. As in the first described example the liquid desiccant temperature restoring device 3 lb can alternatively or additionally be positioned in the recirculation part 21. The fan 35 of the liquid desiccant temperature restoring device 3 la, 3 lb can be controlled to operate at specific intervals. In the example where the system 1 is used in cold environments as a dehumidifier, the fan 35 can for example be controlled to operate at the same time as the regeneration device 13 is operating.

[0040] The system 1 can be based on a controlled vapor pressure technology, CVP, where the vapor pressure in the liquid desiccant is controlled to match desired air output quality. This is described in more detail in WO2022 / 203573.

[0041] The liquid desiccant may be a salt such as Lithium Bromide, LiBr, Calcium Chloride, CaCL, Magnesium Chloride, MgCL , Potassium Sulfate, K2SO4, or Potassium Formate, HCO2K.

[0042] The contact device 3 may be an evaporator pad. The contact device 3 may also be a liquid to air membrane energy exchanger, LAMEE.

[0043] Figure 3 is a Mollier diagram showing the difference when using the invention according to one example of the invention compared to using the same type of system for controlling water content of an air stream but without the temperature restoring device 3 la, 3 lb according to the invention. Numbers from the diagram of Figure 3 are collected in table 1 below. In this example the temperature of the air provided into the contact device 3 is 10°C and water content is 6g / kg, as illustrated at point 1 of the Mollier diagram. Point 2 in the diagram illustrates the change of temperature and water content of the air stream after having passed a contact device of a similar system without the use of this invention, i.e. without the use of a temperature restoring device 3 la, 3 lb in the system. Point 4 in the diagram illustrates the change of temperature and water content of the air stream after having passed the contact device 3 of the system 1 according to the invention, i.e. with use of the temperature restoring device 3 la, 3 lb. By cooling the liquid desiccant 5 in the temperature restoring device 3 la, 3 lb, the temperature of the air is kept to 10°C also after passing the contact device 3. Hereby more water has been removed from the air stream, According to this example the capacity of the dehumidification is increased by around 30% by use of the invention. Table 1:

Claims

CLAIMS1. A system (1) for controlling water content in an air stream (7) comprising:- a contact device (3) for transferring thermal energy and water vapor between a liquid desiccant (5) and the air stream (7) flowing through the contact device (3), said liquid desiccant flowing through the contact device (3) from a liquid desiccant inlet (9a) to a liquid desiccant outlet (9b) and said air stream (7) flowing through the contact device from an air stream inlet (10a) to an air stream outlet (10b), the contact device (3) being configured to allow a contact between the liquid desiccant (5) and the air stream (7) in which contact thermal energy and water vapor is transferred;- a liquid desiccant collecting tank (41) which is positioned for receiving liquid desiccant (5) from the liquid desiccant outlet (9b) of the contact device (3), said liquid desiccant collecting tank comprising a regeneration inlet (42a), a regeneration outlet (42b) and a recirculation outlet (42c);- a regeneration part (11) connected to the regeneration inlet (42a) and the regeneration outlet (42b) of the liquid desiccant collecting tank (41) such that liquid desiccant (5) expelled from the liquid desiccant outlet (9b) of the contact device (3) can be circulated through the regeneration part (11) from the regeneration outlet (42b) to the regeneration inlet (42a), said regeneration part (11) comprising a regeneration device (13) for removing water from the liquid desiccant (5); and- a recirculation part (21) connected to the recirculation outlet (42c) of the liquid desiccant collection tank (41) such that liquid desiccant (5) expelled from the liquid desiccant outlet (9b) of the contact device (3) can be recirculated via the recirculation part (21) and reintroduced to the contact device (3) via the liquid desiccant inlet (9a), wherein the system further comprises:- at least one liquid desiccant temperature restoring device (31a, 3 lb) provided in the regeneration part (11) and / or in the recirculation part (21), where said liquid desiccant temperature restoring device (3 la, 3 lb)comprises an air-to-liquid heat exchanger (33) and a fan (35), wherein said air-to-liquid heat exchanger (33) is connected in the system such that liquid desiccant (5) passes through the air-to-liquid heat exchanger (33) for being tempered by ambient air and wherein said fan (35) is positioned in the system such that the ambient air is directed by the action from the fan (35) to flow towards the air-to-liquid heat exchanger (33).

2. System according to claim 1, wherein the regeneration part (11) further comprises a liquid-to-liquid heat exchanger (15) via which liquid desiccant (5) is transferred both on its way to the regeneration device (13) from the liquid desiccant collecting tank (41) and from the regeneration device (13) back to the liquid desiccant collecting tank (41), whereby heat from the regeneration process can be used for heating the liquid desiccant (5) on its way to the regeneration device (13).

3. System according to claim 2, wherein the liquid desiccant temperature restoring device (3 la) is positioned between the liquid-to-liquid heat exchanger (15) and the regeneration inlet (42a) of the liquid desiccant collecting tank (41).

4. System according to any one of the preceding claims, wherein the regeneration device (13) is a boiler.

5. System according to any one of the preceding claims, wherein the liquid desiccant (5) is a salt such as Lithium Bromide, LiBr, Calcium Chloride, CaCh, Magnesium Chloride, MgCL , Potassium Sulfate, K2SO4, or Potassium Formate, HCO2K.

6. System according to any one of the preceding claims, wherein the contact device (3) is an evaporator pad.

7. System according to any one of the preceding claims, wherein the contact device (3) is a liquid to air membrane energy exchanger, LAMEE.5

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