Patent Description:
Air dehumidification systems are generally used for processes, process areas or residential buildings which require the supply of dry air with a lower or more stable humidity ratio than available from outside. Humidity control is indispensable in many locations, such as for the wellbeing of humans in offices and commercial buildings, for certain industrial drying processes, in process areas where condensation and mold growth should be eliminated and to avoid the formation of snow at low temperature freezing processes.

Desiccant dehumidification processes utilize a hygroscopic desiccant material to absorb moisture or water vapour from air, thereby lowering the humidity level in the air to the desired value. Desiccant materials can be a solid (e.g., silica gel, molecular sieve) or a liquid (concentrated salt solutions such as lithium chloride, calcium chloride, or lithium bromide). The energy required for desiccant dehumidification processes is less than for conventional vapour compression systems.

Dehumidification of air by a liquid desiccant is known to be carried out in a packed column, with liquid sprayers above the column and the entrance of air at the bottom. Solid desiccants are usually applied as a surface layer on porous materials through which the air stream is directed. The use of solid desiccants can have the disadvantage that it is costly for larger air flow rates. Another disadvantage of using solid desiccants can be that high temperatures are required for desiccant regeneration. Lastly, a disadvantage can be that known conditioners using solid desiccants are generally not suitable for extra functionalities being incorporated in the conditioner, such as air cooling or scrubbing, to mitigate air borne microorganisms.

<CIT> concerns a liquid desiccant dehumidifier and a liquid desiccant air conditioner including an absorption air conditioner and a liquid desiccant dehumidifier. The dehumidifier includes a liquid desiccant absorber for absorbing moisture contained in ambient air entering the dehumidifier and passing through the desiccant absorber. <CIT> provides a liquid desiccant air conditioner which does not require a compressor.

<CIT> discloses methods and control systems for operating a liquid desiccant air-conditioning system to efficiently maintain a target temperature and humidity level in a space, the system discharging relatively hot moist air during operation.

<CIT> discloses a heat pump in a dehumidification air conditioner system, wherein a compressor is connected with a first condenser, a second condenser and an evaporator through refrigerant pipelines. The first condenser and the second condenser are also connected with the evaporator (through refrigerant pipelines). The condensers are arranged for condensing refrigerant. The evaporator is arranged for chilling liquid water, conducted via a chilled water circuit. During operation, dilute solution of the regenerator is pressurised by a solution pump and is heated by a first condenser, and then sprayed in a packing plate of a regenerator. The regenerator and dehumidifier are arranged in different locations, wherein moist air, leaving the regenerator, is discharged outdoors.

It is an object of the invention to provide a system for dehumidification of air, and/or a method for dehumidifying air, that obviates, or at least diminishes the disadvantages mentioned above. More in general, it is an object to provide an improved air dehumidification system and/or method for dehumidifying air. Herein dehumidifying can also be defined as demoisturising, and vice versa.

Thereto, according to the invention an air dehumidification system according to claim <NUM> is provided. The air dehumidification system comprises a conditioner configured for absorbing moisture from air into a liquid desiccant. The conditioner can e.g. include a packed column. The liquid desiccant can comprise concentrated salt solutions such as lithium chloride, calcium chloride, and/or lithium bromide. The air dehumidification system further comprises a desiccant dryer configured for evaporating the absorbed moisture from the liquid desiccant to become evaporated moisture. The desiccant dryer can include a shell and at least one heat transfer tube, or a packed column. The air dehumidification system comprises a condenser configured for condensing the evaporated moisture (in particular condensing evaporated water into liquid water). The condenser includes at least one heat transfer tube. The air dehumidification system comprises a heat transfer medium flow circuit arranged such that heat removed from the evaporated moisture during condensation thereof in the condenser is absorbed by the heat transfer medium, and such that said absorbed heat is used for the evaporation of the absorbed moisture from the liquid desiccant. The temperatures, volumes and/or pressures in the air dehumidification system can be chosen such that the absorbed moisture evaporates from the liquid desiccant in the desiccant dryer, and/or such that the evaporated moisture condensates in the condenser. The temperatures, volumes and/or pressures in the heat transfer medium flow circuit can be chosen such that the heat transfer medium condenses in the desiccant dryer or in a heat exchanger, e.g. associated with the desiccant dryer, and/or such that the heat transfer medium evaporates in the condenser. Heat can be transferred to and from the heat transfer medium using convection, conduction and/or radiation. The air dehumidification system can be more energy efficient due to its use of heat from condensation during evaporation (wherein the system in particular does not discharge moist air during operation, but -in particular liquid water).

The condenser comprises at least one cooling tube forming part of the heat transfer medium flow circuit and having a first surface for condensation of the evaporated moisture thereon. The first surface can be an outer surface of the cooling tube. The cooling tube can in use be internally cooled by the heat transfer medium.

The heat transfer medium flow circuit comprises a compressor downstream of the at least one cooling tube. The compressor can be positioned upstream of the desiccant dryer and/or upstream of a heat exchanger. The compressor is arranged to increase a pressure of the heat transfer medium.

Optionally, the condenser is arranged for discharging condensed moisture in liquid form. The condensed moisture can comprise, or be, water.

Optionally, the pressure in the desiccant dryer is, in use, substantially equal to the pressure in the condenser. In use, the pressure at which moisture is removed from the desiccant in the desiccant dryer can be substantially equal to the pressure at which this moisture condenses in the condenser.

Optionally, the pressure in the desiccant dryer differs, in use, from the pressure in the condenser by less than <NUM> Pascal. The pressure of the moisture and the liquid desiccant in the desiccant dryer can e.g. differ, in use, from the pressure of the moisture in the condenser by <NUM>-<NUM> Pascal. The pressure at which moisture is removed from the desiccant in the desiccant dryer differs from the pressure at which this moisture condenses in the condenser by less than <NUM> Pascal, such as <NUM>-<NUM> Pascal.

Optionally, the pressure in the desiccant dryer and/or the pressure in the condenser is subatmospheric. The pressure of the moisture and/or the liquid desiccant can in, use, be subatmospheric.

Optionally, the system is arranged such that the mechanical power of the compressor contributes to the heat used for evaporation. The energy imparted by the compressor to the heat transfer medium can be transferred to the desiccant dryer e.g. by condensation of the heat transfer medium in the desiccant dryer or in a heat exchanger associated with the desiccant dryer.

Optionally, the compressor is arranged for pressurizing the heat transfer medium such that said heat transfer medium changes from vapour to liquid. The phase change from vapour to liquid of the heat transfer medium can take place in the desiccant dryer or in a heat exchanger.

Optionally, the desiccant dryer comprises at least one heating tube forming part of the heat transfer medium flow circuit and having a second surface for evaporation of the absorbed moisture from the liquid desiccant thereon. The pressure of the liquid desiccant at the first surface can be substantially equal to the pressure of the liquid desiccant at the second surface. The second surface can be an outer surface of the at least one heating tube.

Optionally, the at least one heating tube is arranged such that the liquid desiccant flows, in use, along the outer surface of the at least one heating tube in a falling film. The desiccant dryer can comprise a vertical shell and tube heat exchanger.

Optionally, the at least one heating tube is further arranged such that the heat transfer medium condenses inside the at least one heating tube. The at least one heating tube can be positioned vertically.

Optionally, the heat transfer medium flow circuit further includes a heat exchanger upstream of the desiccant dryer for allowing transfer of heat from the heat transfer medium to the liquid desiccant. The heat exchanger can be positioned downstream of the compressor in the heat transfer medium flow circuit.

Optionally, the desiccant dryer and the condenser are arranged in a common enclosure. The desiccant dryer can be arranged next to the condenser inside the common enclosure. The desiccant dryer can be placed below the condenser in the common enclosure. The condenser can have an access port for evaporated moisture on a top side thereof. The condenser can be placed on top of the desiccant dryer, or vice versa.

Optionally, the desiccant dryer comprises a packed column. The packed column includes a vessel filled with a packing material, as is known in the art. The packed column can have a desiccant spraying section above it.

Optionally, one or more parts of the desiccant dryer are corrosion resistant against the liquid desiccant, or wherein the construction of the desiccant dryer is arranged to withstand the pressure of the heat transfer medium.

The heat transfer medium comprises a refrigerant. Optionally, the heat transfer medium is arranged such that the pressure ratio and suction volume flow rate for the compression of the heat transfer medium are minimized,.

Further according to the invention, a method for dehumidifying air according to claim <NUM> is provided.

The method comprises absorbing moisture from air into a liquid desiccant. The method comprises evaporating the absorbed moisture from the liquid desiccant to evaporated moisture. The method comprises condensing the evaporated moisture, wherein heat released during condensation of the evaporated moisture is absorbed by a heat transfer medium, and wherein said heat is used in evaporation of the absorbed moisture from the liquid desiccant. Thus, the added energy required for demoisturising the liquid desiccant, i.e. evaporating the absorbed moisture from the liquid desiccant, can be minimized.

The method further comprises discharging condensed moisture from the liquid desiccant in liquid form.

The method further comprises compressing the heat transfer medium subsequent to condensing the evaporated moisture.

The heat transfer medium is pressurized such that said heat transfer medium can change from vapour to liquid.

Optionally, the mechanical power used for compressing the heat transfer medium contributes to the heat used for evaporation.

Optionally, the heat transfer medium is compressed such that the pressure and temperature of heat release required for evaporation of the moisture from the liquid desiccant are reached.

Optionally, the absorbed moisture evaporates at a first pressure, and the evaporated moisture condenses at a second pressure, wherein the first pressure is substantially equal to the second pressure.

Optionally, the first pressure differs from the second pressure by less than <NUM> Pascal.

Optionally, the first pressure and/or the second pressure is subatmospheric.

Optionally, the liquid desiccant flows along an outer surface of at least one tube in a falling film during evaporation of the absorbed moisture from the liquid desiccant, and optionally the heat transfer medium condenses inside the at least one tube.

It will be appreciated that any of the aspects, features and options described in view of the air dehumidification system apply equally to the method for dehumidifying air, and vice versa. It will also be clear that any one or more of the above aspects, features and options can be combined.

Embodiments of the present invention will now be described in detail with reference to the accompanying drawings in which:.

<FIG> shows an illustration of an air dehumidification system. The air humidification system of <FIG> has some disadvantages associated therewith which the present invention seeks to alleviate. The system includes a conditioner <NUM>. The conditioner <NUM> contains a packed column <NUM> with a liquid desiccant spraying section <NUM> above it, a liquid pump <NUM> to circulate the desiccant <NUM> over the packed column <NUM>, a fresh air supply connection pipe <NUM> and a discharge fan <NUM> to remove the dehumidified air <NUM> from the conditioner <NUM>. The packed column <NUM> includes a vessel filled with a packing material. In the Figure, the packing material is schematically indicated as a hatched portion. In use, the desiccant <NUM> will take up moisture from the fresh air <NUM> inside the packed column <NUM>. The moisture containing liquid desiccant <NUM> can gather at the bottom of the vessel. The supply temperature of desiccant to the spraying section <NUM> is controlled by a cooler <NUM> to a sufficiently low temperature, such that the vapour pressure of the air entering the vessel is greater than that of the desiccant <NUM> in the packed column <NUM>. The desiccant cooler <NUM> is for this purpose connected to a cooling circuit <NUM>, <NUM>, which can use cold water or an evaporating refrigerant from a refrigeration system.

The system further includes a regenerator <NUM>. The regenerator <NUM> contains a packed column <NUM> with a desiccant spraying section <NUM> above it, a liquid pump <NUM> to circulate the desiccant over the packed column, a fresh air supply connection pipe <NUM> and a discharge fan <NUM> to remove the wet air <NUM> from the regenerator <NUM>. In use, the air takes up moisture from the desiccant inside the packed column <NUM>. Hence, in this system, the moisture is removed from the regenerator in vapour form. The supply temperature of desiccant to the spraying section <NUM> is controlled by a heater <NUM> to a sufficiently high temperature, such that the vapour pressure of the desiccant is greater than that of the air <NUM> in the packed column <NUM>. The desiccant heater <NUM> is for this purpose connected to a heating circuit <NUM> and <NUM>, which can use hot water or steam, from a hot water system or steam boiler.

After taking up water from the air in the conditioner <NUM>, the diluted desiccant <NUM> is transferred from the conditioner <NUM> to the regenerator <NUM> via a connection line <NUM> and heat exchanger <NUM>. In a similar fashion, after discharging water inside the regenerator <NUM>, the concentrated desiccant <NUM> is transferred from the regenerator <NUM> to the conditioner <NUM> via a connection line <NUM> and heat exchanger <NUM>. The function of heat exchanger <NUM> is to preheat the relatively cold diluted desiccant <NUM> by the transfer of heat from the relatively warm concentrated desiccant <NUM>. An open communication line <NUM> guarantees that possible desiccant liquid level differences between the conditioner <NUM> and the regenerator <NUM> are equalised.

Although wet desiccant dehumidification processes are generally considered to be relatively energy efficient as compared to traditional chillers applied for this purpose, the energy use of these systems is still significant, for the following reasons. Apart from some electricity for the circulation pump <NUM> and discharge fan <NUM>, the conditioner <NUM> requires energy to cool the cooling circuit <NUM>, <NUM> for sensible cooling of the air stream <NUM> from the supply temperature of the fresh air to the desired, generally lower injection temperature of the dried air stream <NUM>. Another contribution to the energy use is the latent heat associated with the condensation of vapour from the to be dried air stream <NUM> to the desiccant <NUM> which is typically <NUM>-<NUM> kJ per kg condensed vapour. Besides this latent heat, also the enthalpy of dilution (typically <NUM> to <NUM> kJ/kg dissolved vapour) is transferred to the desiccant. The mentioned contributions to the heat load are to be discharged via the cooler <NUM> to the cooling circuit <NUM> and <NUM>.

The moisture absorbed by the desiccant <NUM> in the conditioner <NUM>, has to be removed again from the desiccant in the regenerator <NUM>. This regeneration process also consumes energy. Apart from some electricity for the circulation pump <NUM> and discharge fan <NUM>, the regenerator <NUM> requires thermal energy via the heater <NUM> from the heating circuit <NUM>, <NUM> for sensible heating of the air stream <NUM> and <NUM> from supply to discharge temperature. Besides this, latent heat associated with the evaporation of the moisture from the desiccant is required, typically <NUM>-<NUM> kJ per kg of evaporated vapour. Furthermore, the enthalpy of dissolution (typically <NUM> to <NUM> kJ/kg of water extracted from the desiccant) has to be supplied to remove the dissolved moisture from the desiccant. The sum of these mentioned contributions is to be supplied by the heating circuit <NUM>, <NUM> through the heater <NUM>.

The energy use of wet desiccant dehumidification processes is hence considerable and consists of energy requirements for the discharge of heat from the conditioner <NUM> to a cooling system <NUM> and the supply of heat to the regenerator <NUM> from a heating system <NUM>. More specifically, the latent heat and energy for dilution associated with the absorption of a unit mass of water by the desiccant have to be transferred twice: first via the cooler <NUM> to the cooling circuit <NUM>, <NUM> and secondly via the heater <NUM> from the heating circuit <NUM>, <NUM>. On top of this, there are losses associated with unwanted sensible heat exchange between the desiccant and the airstreams through the packed columns <NUM>, <NUM> inside respectively the conditioner <NUM> and in the regenerator <NUM>.

Various attempts have been described in the literature to reduce the energy requirements of wet desiccant dehumidification processes, for example by integrating a heat pump to cool the fresh air stream <NUM> to the conditioner <NUM>, the energy of which is used to heat the airstream <NUM> to the regenerator <NUM>. This solution can additionally be combined with a solar collector, to supply solar energy to the heater <NUM>, Another option is to install a so-called twin coil system, which indirectly heats the fresh supply stream <NUM> to the conditioner <NUM> by heat from the discharge stream <NUM>. It is also possible to pre-dry the airstream <NUM> with a traditional chiller with high efficiency, or to partially recirculate exhausted air from the process area to reduce the moisture charge on the desiccant dehumidification system.

The above mentioned solutions have in common that the above mentioned sensible and latent energy requirements remain in place, although to a somewhat lesser extent. Other known disadvantages of known wet desiccant dehumidification processes are carry over of expensive desiccant from the regenerator, entrained with the wet air discharge steam <NUM>; the pollution of the desiccant by substances from. the fresh air <NUM> to the regenerator <NUM>; the sensitivity of the regeneration process for external climate influences: higher desiccant temperatures and higher air flow rates through the regenerator are necessary in wet climates, when humidity ratios of stream <NUM> are relatively high, with consequential higher thermal losses from the regenerator <NUM> and higher energy demands of heater <NUM>; and the requirement of floor space at a location outside the building, to guarantee free air supply and discharge to and from the regenerator. For certain climates, the outdoor installation requires measures for frost protection of the regenerator.

<FIG> shows an example of a diagram of an air dehumidification system according to the present invention. In this example, the air dehumidification system includes a dryer and a condenser. Here, the dryer and condenser are provided in separate enclosures. The to be demoisturised desiccant is supplied at <NUM> to a desiccant dryer <NUM> which comprises a shell 40A with internally heated tubes <NUM>. The desiccant is demoisturised inside the shell space of the desiccant dryer <NUM> at a certain, in this example subatmospherical, pressure, whereby the formed water vapour (i.e. moisture) is discharged via a connection pipe <NUM> to a condenser <NUM>. The moisture subsequently condenses at virtually the same, in this example subatmospherical, pressure on the outside of the internally cooled tubes <NUM> inside the shell of the condenser <NUM>. A pressure difference between the vapour in the dryer <NUM> and in the condenser <NUM> is preferably less than <NUM> Pascal. In this example, the pressure difference is <NUM>-<NUM> Pascal. The formed condensate is discharged from a condensate outlet <NUM>. Here, a condensate pump <NUM> pressurises the condensate from the subatmospherical pressure to atmospherical pressure. The condensate (i.e. liquid water) is discharged via a condensate drain <NUM>. Thus, in this example the moisture is discharged in liquid form.

The latent heat from the condensation of the moisture at the outside of the tubes <NUM> is discharged by the phase change of a refrigerant liquid <NUM> to a refrigerant vapour <NUM>. The pressure at which this phase change takes place is typically significantly higher than the subatmospherical pressure at which the moisture was evaporated from the desiccant in the dryer <NUM> and condenser <NUM>.

The refrigerant vapour is transported to a refrigerant compressor <NUM> and is pressurized by this compressor <NUM> to a sufficiently high pressure, such that a second phase change of the refrigerant, from vapour to liquid, can take place inside the tubes <NUM> of the dryer <NUM> at a sufficiently high temperature level to achieve adequate drying of the liquid desiccant at the outer surface of the tubes <NUM>.

Optionally, the tubes <NUM> inside the dryer <NUM> can be positioned in an upright position and mounted between two horizontal sheets, one at a lower end and one at an upper end of the tubes. In that configuration, the liquid desiccant can flow downwards in a thin film along the outer surface of these tubes <NUM>, permitting high heat transfer between the tube wall and the falling film of desiccant liquid. The falling film can be established by means of a horizontal plate <NUM> mounted underneath the desiccant inlet connection <NUM> and close to the upper end of the vertical tubes <NUM>. The plate <NUM> can be provided with holes centered around each tube, with a hole diameter slightly larger than the outer diameter of the tubes <NUM>, establishing a small gap around each of the tubes <NUM> for the passage of the desiccant, initiating development of the falling film. The dried desiccant can be collected on top of the lower tube sheet <NUM>, from where it is discharged via an desiccant outlet <NUM> to the desiccant pump <NUM> and returned to the conditioner <NUM>.

Optionally, the condensed refrigerant liquid <NUM> might be collected in the space in the shell of the desiccant dryer <NUM> underneath the lower tube sheet <NUM>, just above the refrigerant outlet <NUM>.

The to be dried desiccant <NUM> from the conditioner in this example is preheated in a heat exchanger <NUM> in counterflow with the dried desiccant <NUM> from the dryer <NUM>.

Optionally, an additional heater <NUM> might be incorporated in the desiccant supply line to the desiccant dryer <NUM>, for example for initial start-up of the evaporation process or for other control purposes, indirectly heating the desiccant by heat from a hot water or steam circuit <NUM>, <NUM>.

Optionally, a condenser <NUM> can be incorporated in the refrigerant circuit, to discharge excess heat from this circuit, for cases in which the available condensation heat from the refrigerant phase change from <NUM> to <NUM> would exceed heat demand of the desiccant dryer <NUM>.

The desiccant dryer <NUM> has pipes <NUM> and a shell 40A that have to be fabricated from a material that is resistant to the corrosive properties of generally applied desiccants. The pipes have to be able to withstand high pressures from the refrigerant. Applicable construction materials for the dryer that meet these demands, such as titanium, are known to be rare and expensive. Therefore, a further possible embodiment of the invention is proposed, with essentially the same working principle as that of the embodiment of <FIG>, but alleviating the mentioned disadvantage. This alternative embodiment is shown in <FIG>.

<FIG> shows an example of a diagram of an air dehumidification system with integrated dryer <NUM> and condenser <NUM> in a common enclosure. The embodiment according to <FIG> contains several items with similar names and functions as in the embodiment of <FIG>. These similar items are indicated by the same reference numerals. The explanation of the working principle of the embodiment according to <FIG> is limited to the differences with <FIG> for conciseness. In the embodiment of <FIG>, the dryer <NUM> and condenser <NUM> are unified into a common enclosure 40B, for example being a cylindrically formed shell with closed ends. <FIG> shows in this example a cross-sectional view of this shell 40B of a plane directed perpendicularly to the length axis of the shell.

The to be dried desiccant is supplied to the dryer at <NUM> and subsequently distributed for example by means of sprayers <NUM> over a corrosion resistant packed column <NUM> on the surface of which the drying process takes place. The packed column is encapsulated at the sides and bottom by a corrosion resistant holder 40C, for example fabricated from a kind of relatively cheap plastic material. At the top side of this holder, hence at the vapour outlet, a corrosion resistant demister <NUM> is provided to avoid any possible carry over of desiccant. All items in contact with the desiccant <NUM>, <NUM>, <NUM> and <NUM> and even the supply and discharge connections <NUM> and <NUM> can preferably be fabricated from a corrosion resistant plastic material, because the strength of most commonly applied plastics is sufficient for the application according to this embodiment.

The water vapour from the demister <NUM> flows freely, at a low velocity, e.g. a velocity of less than <NUM>/s, with negligible pressure losses and via various flow paths <NUM> to the vapour condenser <NUM> which is situated in the upper part of the shell 40B of the dryer/condenser. This vapour condenser <NUM> comprises a bundle of multiple internally cooled tubes <NUM>. Preferably the refrigerant flowing through the tubes <NUM> evaporates inside the tubes <NUM>. The external surfaces of these tubes are, during the condensation process, only exposed to clean water vapour. The tubes <NUM> therefore have to withstand the internal pressure of the refrigerant <NUM>, but do not have to be fabricated from highly corrosion resistant materials. Commonly applied materials for refrigeration tube bundles such as steel, copper or stainless steel are therefore applicable for this item <NUM> in this embodiment.

The refrigerant vapour is transported from the tubes <NUM> to the refrigerant compressor <NUM> and is pressurized by this compressor <NUM> to a sufficiently high pressure, such that a second phase change of the refrigerant, from vapour to liquid, can take place inside a heat exchanger <NUM>. The heat exchanger <NUM> pre-heats the wet desiccant before distribution over the packed column to promote moisture evaporation in the dryer <NUM>. Thus, heat removed from the evaporated moisture during condensation in the condenser is absorbed by the heat transfer medium, and said heat is used in evaporation of the absorbed moisture from the liquid desiccant. After condensation of the refrigerant in the heat exchanger <NUM> the condensed refrigerant <NUM> is collected in a receiver vessel <NUM>, ready to be fed to the tubes <NUM> again. The internal space of the condenser <NUM> is preferably only accessible for the water vapour <NUM> from the upper side, to guarantee a downwardly directed flow direction of the vapour inside the condenser <NUM>. The flow of vapour in the condenser can then be in counter current with the here mainly upwardly directed flow direction of the evaporating refrigerant inside the tubes <NUM>. The vapour access from above can be accomplished by closed encapsulations at the sides <NUM> and bottom <NUM> of the condenser <NUM>. The formed condensate is in this example collected on an inclined bottom plate <NUM> underneath the tube bundle <NUM> and is discharged via a condensate outlet pipe <NUM>. A condensate pump <NUM> can pressurise the condensate from the subatmospherical pressure to atmospherical pressure. The liquid condensate is discharged via condensate drain <NUM>.

Non-condensable gases can be discharged to the atmosphere via a perforated pipe <NUM> located near the center of the tube bundle <NUM>. A vacuum pump <NUM> can connect the pipe <NUM> to a discharge pipe <NUM>.

The dried desiccant is discharged from the drying system <NUM> via an outlet connection <NUM> and is supplied to a circulation pump <NUM>. A part of the desiccant <NUM> is returned to the conditioner. In this example, another part passes a heater/cooler <NUM>. This heater/cooler <NUM> indirectly provides extra heat to the desiccant circuit if the supply temperature of the to be dried desiccant to the dryer <NUM> is too low and cools the to be dried desiccant if this temperature is too high. This temperature stabilisation process can be carried out by changing the temperature of a secondary circuit <NUM>, <NUM> accordingly. The thermal capacity of this lieater/cooler <NUM> is evidently preferably minimal and only to be used for start-up of a cold system or for small temperature corrections during operation. The main heat source of the system, for evaporation and dissolution of the moisture is in this example namely provided by the condenser <NUM>, by the condensation of refrigerant <NUM>.

An objective of the system according to the present invention is to provide an energy efficient solution for the removal of absorbed moisture from a desiccant. This can be achieved by reclaiming the latent heat released from the moisture condensation inside the condenser, and by the transfer of this latent heat to an evaporating refrigerant liquid. The enthalpy of this refrigerant can further be increased by mechanical energy transfer from the compressor to the refrigerant, to a level which is high enough to provide the latent heat for moisture evaporation and dissolution enthalpy necessary to evaporate and separate the moisture from the desiccant inside the dryer. In other words: the energy for the evaporation process of moisture from the desiccant and for the dissolution of this moisture are supplied from a secondary circuit which receives energy by the condensation of the evaporated moisture and from a mechanical compressor. This method of re-use of energy makes the process highly energy efficient.

Another objective of the invention is to accomplish this goal by means of generally available, standard components against relatively low cost. This is achieved by selecting a refrigerant with optimal physical properties, aiming at a compressor with relatively small pressure ratio and small suction volume flow rate. This can for example be achieved using refrigerant R1234ze, with a pressure ratio of typically <NUM> to <NUM> and a specific volume of the suction vapour in the range of <NUM> to <NUM><NUM> suction volume of the compressor per kg removed water from the desiccant. These requirements for the compressor are more easily attainable with commonly available equipment than the requirements for known mechanical water vapour compression systems.

The typically large evaporation area of the packed column, the placement of a demister above, upwards velocities of the vapour well below <NUM>/s and the typically low prevailing pressures inside the enclosure, e.g. less than <NUM> mbar, provide that unwanted carry over of expensive desiccant, from the to be dried moisture towards the condensate drain is not expected to occur.

Furthermore, the thermal performance is independent of external climate conditions, for example because the desiccant drying process according to the present invention does not require any fresh air from outside for the discharge of moisture. The system according to the present invention is therefore suitable for indoor installation and does in that case additionally not require any frost protection measures.

The vertical configuration of <FIG> as well as the alternative embodiment of <FIG> with integrated dryer and condenser in a common enclosure require minimal, e.g. less than <NUM><NUM>, floor space, which is another advantage of the present invention.

<FIG> shows an example of an air dehumidification method <NUM>. Thereto, in a first step <NUM> moisture is absorbed from air into a liquid desiccant. The absorbed moisture is evaporated from the liquid desiccant to evaporated moisture in step <NUM>. The evaporated moisture is condensed in step <NUM>, wherein heat released during condensation of the evaporated moisture is absorbed in step <NUM> by a heat transfer medium, and wherein said heat is used in the evaporation of the absorbed moisture from the liquid desiccant. The step <NUM> can be performed after step <NUM>, or in parallel with step <NUM>. Heat for evaporating the moisture from the desiccant in step <NUM> can be provided by condensation of the heat transfer medium. Heat released during condensation of the evaporated moisture can be used for evaporation of the heat transfer medium in step <NUM>. In this example, the heat transfer medium is compressed In step <NUM> after condensing in step <NUM> the evaporated moisture. The condensed moisture is discharged in step <NUM> from the liquid desiccant in liquid form. Discharging step <NUM> can be performed before steps <NUM> and/or <NUM>, after steps <NUM> and/or <NUM>, or in parallel with steps <NUM> and/or <NUM>.

Claim 1:
An air dehumidification system, comprising:
- a conditioner (<NUM>) for absorbing moisture from air into a liquid desiccant (<NUM>);
- a desiccant dryer (<NUM>) for evaporating the absorbed moisture from the liquid desiccant (<NUM>) to evaporated moisture;
- a condenser (<NUM>) for condensing the evaporated moisture; characterized in that the system furthermore comprises:
- a heat transfer medium flow circuit arranged such that heat removed from the evaporated moisture during condensation in the condenser (<NUM>) is absorbed by the heat transfer medium, and such that said heat is used in evaporation of the absorbed moisture from the liquid desiccant, the heat transfer medium comprising a refrigerant;
wherein the condenser (<NUM>) comprises at least one cooling tube (<NUM>) forming part of the heat transfer medium flow circuit and having a first surface for condensation of the evaporated moisture thereon,
wherein the heat transfer medium flow circuit comprises a compressor (<NUM>) downstream of the at least one cooling tube (<NUM>).