SE538623C2 - Device and method for adsorbing water from a gas where the hygroscopic material is regenerated using a pump and a heat exchanger - Google Patents

Description

DEVICE AND METHOD FOR ADSORBING WATER FROM A GAS WHERE THE HYGROSCOPIC MATERIAL IS REGENERATED USING A PUMP AND A HEAT EXCHANGER FIELD OF THE INVENTION The present invention relates to a device for adsorbing water from a gas and a method of adsorbing water from gas where water adsorbing material is regenerated using a pump and a heat exchanger.

BACKGROUND There are many ways of extracting water from air but many of them are struggling with efficiency.

By using a hygroscopic material the vapour in the air may be adsorbed and stored in the material. The amount of water that may be stored in a hygroscopic material depends on the materials ability to adsorb at different humidity. In order to use the same hygroscopic material to adsorb new vapour the hygroscopic material needs to be regenerated. When the hygroscopic material is heated the vapour pressure in the hygroscopic material increases. When the vapour pressure in the hygroscopic material becomes higher than the surrounding vapour pressure the adsorbed water is vaporised. In this way hygroscopic materials may be regenerated and reused. The amount of water,m,that may be adsorbed/desorbed per second can be described by: Image available on "Original document" where^is the amount of water adsorbed/desorbed per second,kis a material constant,Ais the area of the hygroscopic material andPmis the vapour pressure in the hygroscopic material and P«is the vapour pressure in the gas surrounding the hygroscopic material.

Hence, to achieve a high regeneration flow a high vapor pressure in the hygroscopic material and a low vapor pressure in the gas surrounding the hygroscopic material is required. To get a high vapor pressure in the hygroscopic material during the regeneration, the hygroscopic material is conventionally heated. However, in order to avoid damage on the hygroscopic material and to reduce the rate of aging the regeneration temperature has to be limited. These issues sets a natural limit for the magnitude of the regeneration flowMoreover,when the regeneration is made, the hygroscopic material are in equilibrium with the surrounding, e.i.Pm= Paand^ = 0.Since the vapor pressure in the hygroscopic material depends on the temperature, the lower the regeneration temperature, the more water is confined in the hygroscopic material after the regeneration.

In order for the adsorbed water to leave the hygroscopic material it needs to be vaporized and for that vaporisation energy is needed. This energy is taken from the heat and creates cooling. This cools the hygroscopic material resulting in a lower vapour pressure in the hygroscopic material when the water is vaporized. More heat needs then to be added in order to keep the material warm.

Several methods for dehumidify air using a vapour compression system have been invented. WO2011/062554 discloses a device for adsorbing water or moisture from air using water adsorbing material. The water is removed from said material by heating the material evaporating the water and letting the formed steam condense on the walls of the device.

However, prior art there is a need for a more energy efficient way of regenerating the hygroscopic material. Overcoming these issues would lead to more efficient methods to control air humidity and to condense water vapour.

SUMMARY OF THE INVENTION The object of the present invention is to provide a device which overcomes the drawbacks of prior art.

In a first aspect the present invention relates to a water adsorption device comprising: a first housing having a first sealable inlet and a first sealable outlet; a container within the housing, separating the housing in a first and a second compartment respectively wherein the first compartment and the second compartment has a second and a third sealable outlet respectively; wherein the container has at least one inlet and one outlet, wherein the inlet of the container communicates with the first sealable inlet of the housing and the outlet of the container communicates with the first sealable outlet of the housing; a water adsorbing material confined within the container; whereby the device is configured to allow a gas to flow from the first sealable inlet of the housing through the container in contact with the water adsorbing material in the container to the first sealable outlet of the housing; a heating device arranged in the container and / or in thermal contact with the water adsorbing material and/or the container; a heat exchanger configured to heat the water adsorbing material in the container; a second housing, having a first inlet, a first sealable outlet, and means for removing collected water; at least one pump configured to reduce the pressure in the first and the second housing and to compress steam; wherein the second and third sealable outlet communicates with the pump; said pump communicates with the heat exchanger and the heat exchanger communicates with the first sealable inlet of the second housing; whereby gas can flow from the first and the second compartment of the first housing via the second and the third sealable outlets of the first housing, via the pump in order to be compressed, to the heat exchanger and into the second housing via the first sealable inlet of the second housing.

In a second aspect the present invention relates to a method of adsorbing water from a gas comprising: a. providing a device according to the present invention; b. bringing a gas flow into contact with the water adsorbing material; c. letting the water adsorbing material adsorb vapour or water from the gas; d. sealing the housing; e. reducing the pressure in the first housing; f. heating the water adsorbing material in order to form steam; g. letting the steam exit through the second and third sealable outlets; h. compressing the steam using the pump i. letting the steam condense in the heat exchanger during heat transfer to the water adsorbing material; and j. collecting the condensed water in the second housing.

In a third aspect the present invention relates to a dehumidifier comprising the device according to the present invention.

In a fourth aspect the present invention relates to a machine for drying timber comprising the device according to the present invention.

The embodiments presented below are applicable to both aspects of the present invention.

BRIEF DESCRIPTION OF THE FIGURES Figure 1 a schematic view of a cross-section of the present invention, lb a schematic view of a cross-section of the container comprising water adsorbing material, 1 c discloses a schematic view of the means for removing collected water. Figure 2, flow chart of the method according to the present invention.

DETAILED DESCRIPTION OF THE INVENTION In the present application the wordings "water adsorbing material", "water adsorption material" and "hygroscopic material" are used interchangeably.

The present invention is based on the fact that a water adsorption material confined in a container adsorbs, and to some extent maybe also absorbs, water from the surrounding gas, preferably air, and for example to the point of saturation. Thus, after having allowed the water adsorption material to adsorb water, the housing is sealed using a lid or any suitable cover and the water adsorption material is then heated using the heating device, and later also the heat exchanger. The process of releasing the water from the water adsorbing material is driven by the difference in vapour pressure of the water in the gas and the water adsorbed in the water adsorbing material. The amount of water released from the water adsorbing material to the surroundings can be, as mentioned above, described by Eq. [1].

The present invention facilitates an energy efficient way of regenerating the water adsorption material by using formed steam to heat the water adsorbing material. The device according to the present invention is designed so that the pump controlling the pressure in the device should not work more than necessary in order for the water in the steam to condensate in the heat exchanger.

The device according to the present invention is designed for water adsorption from a gas, for example from air. The device may be integrated into another device or may be a standalone device.

Referring now to figures la, lb and lc. The water adsorption device 10 according to the present invention comprises a first housing 20 with a first sealable inlet 22 and a first sealable outlet 24 and where said inlet and outlet are both sealable using any suitable means to close and seal said inlet and outlet. The housing comprises a container 26 separating the housing in a first and a second compartment27aand27brespectively. The container has at least one inlet 28 and at least one outlet 30 which both are in communication with the sealable inlet 22 and the first sealable outlet 24 of the housing respectively. In one embodiment the container is heat insulated and may be made of stainless steel. The container comprises a water adsorption material 32 which may be any suitable material for example molecular sieves, active carbon, zeolite, silica gel, LiCl, CaCl, NaNCh, wood, sulphates or any suitable material known to a person skilled in the art or combinations thereof. The water adsorption material may be in shape of particles, powder or solid.

The inlets and the outlets of the housing and the container are arranged so that gas 33 may flow from the first sealable inlet 22 of the housing into the first compartment27aand into the container 26 via inlet 28 of the container so that the gas comes in contact with the water adsorbing material 32. The gas will then exit the container 26 through the outlet 30 and into the second compartment 27b and then out through the sealable outlet 24 of the housing 20. The dotted arrows in figure 1 represent the gas flow. A heating device 34 is arranged in thermal contact with the water adsorbing material 32 and/or the container 26, figure lb. The container may be in the form of a net, a cage or a perforated surface and may be made of for example a metal or a metal alloys, for example aluminium. The housing comprises at least a second and a third sealable outlet36aand36brespectively where the second outlet 36a is arranged in the first compartment 27a and the third outlet 36b is arranged in the second compartment 27b. The device further comprises a second housing 42 having a first, preferably sealable, inlet 44 and a first sealable outlet 46 and a means for removing collected water 48.

A pump 38 is configured in order to reduce the pressure in the first and the second housing 20 and 42 respectively and to compress steam exiting through the second and third sealable outlets36aand36b.A heat exchanger 40 is arranged in the container 26 and/or in thermal contact with the water adsorbing material 32 and/or the container 26. The heat exchanger 40 communicates with the pump 38 that compresses the steam and the first inlet 44 of the second housing 42. The different parts (first housing, pump, heat exchanger and second housing for example) of the device 10 are connected via suitable tubing 58. The tubing 58 should preferably be insulated in order to minimize energy losses and to avoid condensation in the tubing.

The pump 38 may constitute of one or more pumps or only one pump, or may constitute of one pump and one compressor. In one embodiment the device according to the present invention comprises at least two pumps. The pump 38 should reduce the pressure in the first housing from an initial pressure PI to a pressure PI'. In one embodiment the pump reduces the initial pressure P2 in the second housing 42 to a pressure P2'. In one embodiment the pump reduces the pressure P2 in the heat exchanger and the tubing connecting the heat exchanger 40 and the pump 38 and the tubing connecting the heat exchanger 40 and the second housing 42 to P2'. In one embodiment the pressure is reduced such that PI' is lower than P2'. In one embodiment the initial pressure of P2 is lower than PI. PI is usually atmospheric pressure, i.e. 1 bar. P2 may also be atmospheric pressure but may be 1-3 bar. For example PI' may be 1 bar or lower, or lower than 0.7 bar for example in the range 1 mbar to 0.95 bar, such as 0.01 bar to 0.3 bar, but PI' may also be 0.8 to 0.95 bar. When P2 is reduced P2' may be lower than 1 bar for example lower than 0.5 bar, or lower than 0.1 bar in the range 0.05 to 0.9 bar, such as 0.1 to 0.8 bar. The initial pressure P2' may be lower than PI, for example P2' may be lower than 0.2 bar, or lower than 0.08 bar, or lower than 0.01 bar. By having P2 as low as possible (below PI) prior to start, or prior to start collecting condensed water, the device may be free from air and is instead filled with steam by letting steam formed in the first housing fill the first housing 20, tubing 58, heat exchanger 40 and the second housing 42. Without being bound by theory it is believed that this will make the device and the method more efficient.

When the pump 38 acts as a compressor it compresses the steam coming out from the first housing 20 and pushes the compressed stream towards the heat exchanger 40 and the second housing 42. In one embodiment the pump 38 may be one or more of a linear pump, diaphragm pump, piston pump or a rotary vane pump. The selection of pump or pumps is dependent on the wanted pressure. The COP value (Coefficient of Performance) should be as high as possible.

The device may further comprise valves (50, 54 and 56) in order to control the flow of air and steam in the tubing 58 during pumping and evacuation. Any suitable type of valve may be used.

The first sealable inlet 44 of the second housing 42 may be arranged at a point below (in a vertical direction) the heat exchanger 40 in order for the condensed water to easier flow into the second housing 42.

The method according to the present invention is schematically shown in figure 2. The method starts with that the first sealable inlet 22 and first sealable outlet 24 are opened bringing the gas flow in contact with the water adsorbing material 32 (step 100) and letting the material adsorb water (step 102). After for example a predetermined amount of time or when the adsorbing material has adsorbed a predetermined amount of water the first housing 20 is sealed by sealing the inlet 22 and the outlet 24 (step 104). The pressure in the first housing 20 is then reduced to a pressure PI', optionally the pressure of the second housing is reduced to a pressure P2'. In one embodiment PI' is lower than P2' (step 106).The reduction of the pressure in the first and second housing may be done simultaneously or in sequence using valves at the sealable outlets(36a, 36band46).In one non-limiting embodiment, during the pressure reduction of the second housing valves 44, 56 (besides 50 and 46) are opened reducing the pressure to P2 in a part of the device from the pump 38 and downstream to the heat exchanger 40 and to the second housing 42. During or after the pressure in the first housing 20 has been reduced to PI' the water adsorbing material is heated in order to vaporize the adsorbed water and forming steam (step 108). The temperature of the heating device is dependent on the pressure PI' but the temperature may be below, at or above the boiling point of water at the reduced pressure. After for example a predetermined time or after a predetermined amount of steam has been formed the second and third outlets36aand36bopen letting the steam exit the first housing 20 (step 110). The steam is transported to the pump 38 and compressed using the pump 38 resulting in an increase in steam temperature (step 112) where after the steam is transported using the pump to the heat exchanger 40 where the water is condensed during heat transfer to the water adsorbing material 32 (step 114). The condensed water is then collected in the second housing 42 and removed using the means 48 (step 116).

The pressures PI', P2 and P2' as well as the compression of the steam should be adjusted so that the steam condenses in the heat exchanger and not in the tubing for example. Also the pressures PI', P2 and P2' should be adjusted so that a minimum of compression is needed.

In order to make the device even more efficient, i.e. condensing more water per energy unit, the device is first filled with steam. This may be accomplished by letting the steam initially produced in the first housing 20 flush the tubing 58 and the second housing 42 before sealing the device. The device is then filled with steam and any removal of water should be done without ventilating the system. This may be performed prior to compressing the steam.

The heating device 34 may be manoeuvred using electricity, fuel cells, solar energy or in any other suitable way and the heat could be supplied via electricity, microwaves (for example via the microwave oven principle) or via solar energy. In order to minimize the energy needed to vaporize the water in or on the water adsorption material 32 the heating device 34 and the pump 38 may be regulated using a regulating device 68 in such a way that the heating device heats the water adsorption material 32 just enough in order for the water to vaporize at the present pressure. In this way a shift in the pressure PI affects the amount of heat needed to vaporize the water. The regulated device may also control the pressure PI and P2.

The heating device 34 may also be connected to a sealing control mechanism to optimize the process of when the sealable inlet and sealable outlet should be opened and closed and when the heating procedure of the water adsorption material should start. Additionally, the housing is preferably constructed in such a way that the gas volume inside a sealed housing remains substantially constant during heating of the water adsorbing material. This may be accomplished by securing or locking the sealing after closing or using a check valve as a sealing.

In order to increase the flow of gas or air into and through the first housing a fan or a pump 66 may be arranged in or near the first inlet22and/or the first outlet 24 of the first housing20.

The walls of the container and/or the housing may be made of but not limited to metals or metal alloys. However walls made of a heat insulation material will reduce thermal losses and therefore a non-limiting list of suitable materials are glass wool, plastic, cellular plastic, rubber, cellular rubber or combinations thereof. Therefore, the walls of the first and / or the second housing are preferably made of a heat insulation material. The inner surface70aof the first housing, and optionally also second housing70b,may have a heat insulation value of less than 1A (Wm-'K-<1>), preferably less than 0.5 A. In one embodiment the first housing is thermally insulated. In one embodiment the first and/or second housing has a heat insulation material on the inside (the inner surface facing the water adsorption material) and a metal or metal alloy on the outside. Furthermore, the housing (first and/ or second housing) may have a thickness so that the thermal conductance is less than 0.02 Wm<1>, preferably less than 0.005 Wm<1>.

The housing may be constructed such that the inner surface of the housing70afacing the water adsorption material is heat conductive so that it is heated during the evaporation phase and thereby minimizes the risk of condensation on the surface but the housing is thermally insulated in order to minimize energy losses.

The container 30 may have an emissivity value of more than 0.5, preferably more than 1. The outside of the housing(72aand/ or72b)may have an emissivity value of less than 0.5 or less, for example 0.45 or less, or 0.30 or less, or 0.20 or less, or 0.10 or less, or 0.05 or less. Examples of ranges may be 0.5-0.01, or 0.30-0.01, or 0.30-0.05, or 0.20-0.01, or 0.20-0.05, or 0.10-0.05. In one embodiment the outer surface may be painted, anodized or coated to obtain an emissivity value of at least 0.70. By painting the outer surface preferably with a pale paint, for example black or pale black the emissivity value may be 0.80 or more, or 0.90 or more.

The first and second housing 20 and 42 may be thermally insulated from the container 26 with the water adsorbing material 32 and heating device 34 so that the housing is not heated during heating of the water adsorbing material. The housing may be made of a non-transparent material, in one embodiment the housing has a small window for inspection. The first housing may also comprise means for removing collected water.

The temperature of the heating device 34 may be below, at or above the boiling point (i.e. temperature) of the adsorbed or absorbed water which is dependent on the pressure PI. In one embodiment the temperature is 20°C below the boiling point or higher, or 10°C below the boiling or higher. In one embodiment the temperature is at the boiling point or higher. In one embodiment the temperature is between 60-200°C, such as 80-160°C.

The walls and the bottom of the housing 42 may be constructed in such a way that the liquidized water is assembled. This may be accomplished by having grooves, trenches, channels or the like in or along the walls of the housing or condensation surface, they may further continue along the bottom plate of the housing towards an assembling spot. These grooves, trenches or channels could be made of or covered with hydrophobic material. The bottom plate could be constructed in such a way that all the water from the walls and from the hygroscopic material is assembled. This could be achieved by having the bottom lean into one or more spots. The housing has a means for removing the collected water 48 for example a draining element which could be but is not limited to a tap, faucet or an outlet, or the housing may contain a removable tray where the condensed water is collected and could be discharged from. In one embodiment, figure lc, the means 48 is a lock comprising a container 60, a check valve or a sealable inlet 62 at one end facing the second housing 42 and a second sealable opening 64 in the other end. The collected water will enter the container 60 through the check valve 62 where after the check valve (or sealable inlet) 62 is closed and the sealable outlet 64 is opened to remove the water. In one embodiment not all water is removed from the container 60 in order to prevent air from coming in to the container 60 through the outlet 64. In this way the collected water may be removed without ventilating the second housing or the rest of the device.

The present invention is aimed at extracting water from gas, preferably air, to either produce water or remove the water from the gas. The latter could be used for example, but not limited to, for dehumidification of indoor environments or in air-conditioning devices. The present invention may also be used for drying of substances such as wood or timber.

Claims (17)

1. A water adsorption device comprising: a first housing (20) having a first sealable inlet (22) and a first sealable outlet (24); a container (26) within the housing, separating the housing in a first (27a) and a second compartment (27b) respectively wherein the first compartment and the second compartment has a second (36a) and a third sealable outlet (36b) respectively; wherein the container has at least one inlet (28) and one outlet (30), wherein the inlet (28) of the container (26) communicates with the first sealable inlet (22) of the housing (20) and the outlet of the container (30) communicates with the first sealable outlet (24) of the housing (20); a water adsorbing material (32) confined within the container (26); whereby the device is configured to allow a gas to flow from the first sealable inlet (22) of the housing through the container (26) in contact with the water adsorbing material (32) in the container to the first sealable outlet (24) of the housing; a heating device (34) arranged in the container (26) and/or in thermal contact with the water adsorbing material (32) and/or the container; a heat exchanger (40) configured to heat the water adsorbing material (32) in the container; a second housing (42), having a first inlet (44), a first sealable outlet (46), and means for removing collected water (48); at least one pump (38) configured to reduce the pressure in the first and the second housing and to compress steam; wherein the second (36a) and third sealable outlet (36b) communicates with the pump (38); said pump communicates with the heat exchanger (40) and the heat exchanger communicates with the first inlet (44) of the second housing (42); whereby gas can flow from the first and the second compartment of the first housing via the second and the third sealable outlets of the first housing, via the pump in order to be compressed, to the heat exchanger and into the second housing via the first sealable inlet of the second housing.

2. The device according to claim 1 wherein the housing is made of a non-transparent material.

3. The device according to any one of claims 1 or 2 wherein the temperature of the heating device is 80-200°C.

4. The device according to any one of claims 1 to 3 wherein the inlet of the second housing is arranged at a point below the heat exchanger.

5. The device according to any one of claims 1 to 4 wherein the container is made of stainless steel.

6. The device according to any one of claims 1 to 5 wherein the device comprises at least two pumps.

7. The device according to any one of claims 1 to 6 wherein the water adsorbing material is selected from molecular sieves, active carbon, zeolite, silica gel, LiCl, CaCl, NaNCh, wood or sulphates.

8. The device according to any one of claims 1 to 7 wherein the first housing is thermally insulated and optionally wherein the second housing is thermally insulated.

9. The device according to any one of claims 1 to 8 wherein the outer surface of the first housing has an emissivity value of less than 0.5.

10. The device according to any one of claims 1 to 9 wherein the inner surface of the container has an emissivity value of more than 0.5.

11. A method of adsorbing water from a gas comprising: a. providing a device according to any one of claims 1-10; b. bringing a gas flow into contact with the water adsorbing material; c. letting the water adsorbing material adsorb vapour or water from the gas; d. sealing the housing; e. reducing the pressure in the first housing to PI'; f. heating the water adsorbing material in order to form steam; g. letting the steam exit through the second and third sealable outlets; h. compressing the steam using the pump i. letting the steam condense in the heat exchanger during heat transfer to the water adsorbing material; and j. collecting the condensed water in the second housing.

12. The method according to claim 11 wherein PI' is in the range of 0.01 to 0.3 bar.

13. The method according to claim 11 wherein the pressure in the second housing is reduced to a pressure P2' in the range of 0.1 to 0.8 bar.

14. The method according to claim 11 wherein PI' is in the range of 0.8 to 0.95 bar and the pressure in the second housing P2 is in the range of 1 to 3 bar.

15. The method according to claim 11 wherein the device is filled with steam prior to step h.

16. A dehumidifier comprising the device according to any one of claims 1 to 10.

17. A machine for drying timber comprising the device according to any one of claims 1 to 10.