EP0959307B1 - Sorption plate heat exchanger - Google Patents

Abstract

An air conditioning system has plate type heat exchangers to exchange heat between the incoming air flow and the expelled air flow to conserve energy. The incoming air is dehumidified using hydroscopic liquid sprayed over the plate heat exchangers. Liquid which drains off the heat exchangers is collected and recycled, ie. the water is removed by heating. The liquid is cooled and recycled to the heat exchangers.

Description

The invention relates to a method for drying or drying and Cooling of at least one plate heat exchanger in a room conducted moist air, with a liquid, hygroscopic sorbent.

The common term air is used here for the sake of simplicity atmospheric outside air, process air and other air to be dried or closed drying and cooling gases are used. Under a room there is a closed one Volume understood, which is a room of a building Vessel or a defined body content means in general.

For the air conditioning of living, working and storage rooms as well as temperature-sensitive ones Objects are heating and / or depending on the sensitivity level Cooling systems used, which, however, not only for heating, but also cause a relatively high energy consumption for cooling. in the Framework of increasingly sharp ecological conditions, paired with long-term rising energy costs, the recycling principle also has this Territory moved in. The escaping exhaust air depends on the season used for pre-cooling or preheating the outside air. To achieve a the highest possible efficiency, the two air flows become more strict Separation with the largest possible exchange areas. The plate heat exchangers often used for this work in known way according to the counter or the cross-flow principle.

The constantly increasing requirements for a comfortable living quality can but can no longer be met by heating and cooling only, Air conditioning also includes controlling air humidity. In particular in the hot season, the air conditioning requirements include one Reduced air humidity, which increases relatively when cooling. at Dehumidification of the outside air does not only become solid, hygroscopic materials used, but also liquid sorbents. Saturated solutions of hygroscopic salts dissolved in water reduce the moisture content of passing air by absorbing or condensing water becomes. As with any condensation process, heat is generated, which however, because of the greater absorbency at lower temperatures is undesirable.

Sorbents known per se are saturated solutions of salts of Alkali and alkaline earth metals, for example lithium chloride and / or calcium chloride. In addition to the absorbency, other options also play a part in the selection Factors play a role, such as environmental compatibility, toxic Influences and last but not least the price.

For understanding the driving force in an absorption process in which Practice usually referred to briefly as the sorption process, is the knowledge of Vapor pressure above the liquid level of great importance. A good Sorbent has a lower vapor pressure than water in air. at a larger difference, the sorption capacity is higher.

Sorption systems for dehumidifying air are well known, in which the mass and heat transfer during absorption via suitable Exchange areas of packs are made. The saline solution is made using a suitable Spray devices distributed over the exchange surfaces and flows in counterflow in the direction of gravity. For example, a pack consists of: Packings such as Raschig rings, Pall rings, Intalox saddles or Berl saddles.

By absorbing humidity, the hygroscopic salt solution diluted until it can absorb significantly less or no more water.

Inexpensive and ecologically harmless salt solutions are based on the one-way principle used and disposed of. This applies, for example, to an aqueous one Calcium chloride solution too. In contrast to that in this sorption technology Often used lithium chloride, calcium chloride is non-toxic and even fully food-safe. In addition, calcium chloride is much less corrosive than the health-damaging lithium chloride. With lithium chloride you can a lower dew point than achieved with calcium chloride. Against, and this is Also important for economic processes, calcium chloride is essential cheaper than lithium chloride. Finally, calcium chloride can be used in winter maintenance Road freezing can be used in large quantities.

Another advantage of liquid hygroscopic sorbents is in the fact that a perfect supply of outside air into a room The supply air is kept germ-free, which is particularly the case in inhabited areas or other rooms with a special purpose is important.

With a rotating sorption dehumidifier, the sorption wheel known per se, the condensation heat generated during dehumidification, which greatly reduces the water absorption of the sorbent, not sufficient be dissipated. Added to this is the so-called drag heat through regeneration.

The increasing density of regulations in all areas also contributes the regulations on dehumidification of outside air do not stop. For example in Germany (except coastal areas) according to DIN 4710 (11.82) for a dehumidification of the outside air to 8 g / kg with 2900 dehumidification program hours be calculated to the above maximum outside air condition to reach. This means that mostly in the summer months must be dehumidified, according to statistics, for 71 days. The average Stress during these 71 days is only about 24% of the maximum Dehumidification.

From US, A 5351497 is a method for drying and cooling air an absorption device known, which with a liquid dehumidifier is working. The absorption device is in counter or cross flow of coolant and liquid dehumidifier with certain flow rates traversed. This is aimed at the upward Sprayed outlet side of the process gases and flows with dots in Fig. 1 indicated beddings, against the upward flowing process gases, down. The beds are arranged in layers in parallel, the spaces between them are flowed through by sprayed cooling water and cooling air. Although it can be assumed that the outlet openings for the liquid Dehumidifiers are placed above the bedding layers Droplets of escaping dried process air are entrained, which is ecological and is economically disadvantageous.

The inventor has set himself the task of a method and a device to create the kind of dehumidification Enable air in a simple, economical way without the usual warming-up.

With regard to the method, the object is achieved according to the invention in that that the air on the inlet side of a plate heat exchanger with the liquid, hygroscopic sorbent in the flow direction continuously or sprayed periodically and the heat of condensation while maintaining a practically isothermal dehumidification of the air either directly or via medium is led into the room for cooling. Special and further training embodiments the method are the subject of dependent claims.

The plate heat exchanger used to carry out the method according to the invention is usually a cross-flow, but can also be a Counterflow exchanger to be known design. Must have material the requirements regarding thermal conductivity and corrosion resistance be fulfilled.

• Das aufgesprühte Wasser darf nicht abtropfen.
• Die luftbestrichenen Flächenelemente müssen jedoch bis zum nächsten Besprühen feucht bleiben.

The condensation heat generated during the sorption process can be fulfilled particularly advantageously while maintaining a practically isothermal dehumidification of the air if a fine spray jet of treated water is sprayed into the cooling air flow channels at the inlet side of a cross-flow heat exchanger. Two conditions must be met at the same time:

• The sprayed water must not drip off.
• However, the air-coated surface elements must remain moist until the next spraying.

These conditions are met by a program-controlled wandering and cooling water spraying nozzle bar or a correspondingly controlled Nozzle array designed in a matrix. The cleaning of the cooling air flow channels takes place by flushing out at the end of a working period.

This preferred cooling method has the great advantage that there is no cooling water drips off, further diluting the sorbent and the regeneration at most difficult and more expensive. For details regarding a plate heat exchanger with the wetting submissions mentioned on the WO, A1 96/22497.

The preferably saturated sorbent solution is continuous or in relatively short intervals of a few seconds to a few Minutes, expediently 10 seconds to 3 minutes, into the sorption flow channels sprayed. Due to the condensation of air humidity the sorbent is diluted, more solution flows out of the channels than is sprayed.

Cheap, ecologically safe sorbents, such as one aqueous calcium chloride solution, are fed directly into the sewage system or led to a meaningful third use.

As a rule, that which drips from the sorption flow channels is diluted Sorbent collected to desorb the absorbed Water is heated and / or the cavity above is partially evacuated. The The process is programmed so that the one recorded during the sorption process Amount of water is expelled again. The concentrated in the saturated area Saline solution is cooled into the input side for reuse Spray nozzles of the plate heat exchanger passed and again returned to the cycle.

Regeneration is essential for hygrocospic salt solutions, which reused for their environmental impact or their high price have to or want to be. By evaporation or other expulsion of Water is the aqueous salt solution, also called brine, again in its saturated returned to original condition and reused.

According to the known state of the art, to obtain a certain Air condition with a refrigeration system to be cooled to the point that or immediately above the dew point line a point below the desired one Air condition is reached. By heating the air with a normal, hot water operated heating register then becomes the desired air condition reached. This method is energy-intensive and complicated.

In contrast, after a further development of the invention, for example for the air conditioning of inhabited rooms, the air at one Temperature of 30 to 35 ° C, especially at about 32 ° C, almost isothermal dehumidified. With isothermal dehumidification, the temperature fluctuations lie in a range of ± 2 ° C, preferably ± 1 ° C. With an isothermal Dehumidification in the temperature range of about 32 ° C, at about 40% relative The sorbent takes on moisture, which corresponds to about 12.7 g water / kg air about half the humidity. At a final temperature of also about 32 ° C the relative humidity is still 26.6%, which is about 8g Corresponds to water / kg air. In the case of sorption without cooling, the Heat the supply air adiabatically instead of isothermally to over 42 ° C. There on both Side of the plate heat exchanger energetically with a change of state (Condensation and evaporation), it is possible to start the dehumidification process Allow to run isothermally.

The dehumidified air, which is still too warm in relation to the room temperature, can now cooled by evaporative cooling in a second plate heat exchanger be, preferably by the special evaporative cooling described above. So the temperature can be around 5 to 15, preferably around about 10 ° C, and the desired room temperature can be reached.

After this cooling, the optimal air humidity is not yet available can be at a pre-calculated temperature above the desired one Cooled to room temperature and then cooled further while maintaining the same temperature Enthalpy can be rewetted in a second heat exchanger. The cooling with humidification, however, becomes clear before it is reached the dew point line is completed. The cooling with constant enthalpy humidification is, for example, 2 to 10 ° C., in particular approximately 5 ° C. The approximation to the dew point line is expedient at most about 2 ° C.

With regard to the device for performing the method, the task solved according to the invention in that a sorption system for Drying or for drying and cooling air at least one corrosion-resistant Plate heat exchanger with one of the sorption flow channels on the inlet side arranged spray nozzle bar or a spray nozzle matrix for the processed sorbent and one on the inlet side of the cooling air flow channels arranged spray nozzle bars for the cooling water, one Drip pan for the dripping, diluted sorbent and a treatment circuit for the sorbent with a desorption device, a cooling device and a pump. Special and continuing education Embodiments of the device are the subject of dependent claims.

The plate heat exchanger is preferably constructed from plastic films. Plate heat exchangers with alternating ones are particularly suitable crossing sorption and cooling air flow channels. In contrast to metallic The plastic plates may be used as materials for the plate heat exchanger be thin due to their low thermal conductivity, for example from tear-resistant plastic films with a thickness in the range of 0.1 up to 1 mm, in particular 0.5 to 0.7 mm. With a correspondingly greater thickness these can also be provided with covered metallic reinforcements, for example foils or crossing threads.

Allow the inventive method and the associated device using simple means to dehumidify large air volumes easily and inexpensively and to cool where necessary or desired. Reaching the dew point line is avoided in all process steps. Thanks to the brine that either disposed of or regenerated is also a perfect sanitation the supply air guaranteed.

• Fig. 1 eine Sorptionsanlage mit einem Plattenwärmeaustauscher,
• Fig. 1a ein Detail des Wärmeaustauschers gemäss Fig. 1,
• Fig. 2 eine Sorptionsanlage mit zwei Plattenwärmeaustauschern,
• Fig. 3 eine Variante von Fig. 2,
• Fig. 4 ein Mollier-h-x Diagramm für feuchte Luft, und
• Fig. 5 eine Variante von Fig. 4.

The invention is explained in more detail with reference to exemplary embodiments shown in the drawing, which are also the subject of dependent claims. They show schematically:

• 1 is a sorption plant with a plate heat exchanger,
• 1a shows a detail of the heat exchanger according to FIG. 1,
• 2 shows a sorption system with two plate heat exchangers,
• 3 shows a variant of FIG. 2,
• Fig. 4 is a Mollier-hx diagram for humid air, and
• 5 shows a variant of FIG. 4.

A sorption system 10 shown in FIG. 1 with the possibility of cooling comprises as the centerpiece for sorption-based air conditioning, a plate heat exchanger 12. This is designed as a cross-flow heat exchanger and constructed in modular form from plastic films. This type of heat exchanger is well known per se, for example from EP, B1 0449783 and WO, A1 96/22497. Because of the low susceptibility to corrosion Plastic foils preferred despite the lower conductivity compared to metal foils.

The moist outside air 14 flows through, as indicated in FIGS. 1 and 1a parallel sorption flow channels 16 and are dried Supply air 18 is directed into a room 20, for example an occupied room. Due to the alternating arrangement between the sorption flow channels 16 Cooling air flow channels 22 also flow moist outside air 14 through the cross-flow heat exchanger 12 and occurs as heated cooling air 24 back into the atmosphere. Analogously, the cooling air flow channels 22 entering outside air 14 may also be exhaust air that heated In this case, cooling air 24 is the exhaust air.

The plastic films 28 forming the plate heat exchanger 12 are in accordance with Fig. 1a arranged such that the flow channels 16, 22 each sealed alternately in a flow direction for the outside air 14 are.

Arranged on the input side of the sorption flow channels 16 is a wall-mounted spray nozzle bar 26 (WO, A1 96/22497) or a spray nozzle matrix 30 which sprays a liquid, hygroscopic sorbent 32 into all sorption flow channels 16. In the present case, the sorbent 32 is an aqueous, saturated CaCl ₂ solution. During the flow through the sorption flow channels, the sprayed sorbent 32 absorbs moisture from the outside air 14 and dries it, whereby heat of condensation is released. In the course of the flow through the sorption flow channels, the atomized sorbent precipitates on the plastic films 28 and can - if still sufficiently concentrated - absorb residual moisture. The surface of the plastic films 28 of the plate heat exchanger 12 can be made enlarged, for example by roughening or velor coating. The sorption process is intensified by the enlarged surface with a layer of sorbent. In the case of a walled spray nozzle bar 26, the moisture absorption takes place predominantly through deposited sorbent 32. Dried supply air 18, which for example still contains half of the original moisture, emerges from the plate heat exchanger 12. Diluted sorbent 34 also drips from the plate heat exchanger 12.

The advantages essential to the invention, a higher specific dehumidification performance and a practically isothermal dehumidification process can only be achieved if the heat of condensation is optimally dissipated.

According to the example in FIG. 1, the cooling air flow channels are therefore on the inlet side 22 (Fig. 1a) also a spray nozzle matrix or preferably one Wandering spray nozzle bar 38 arranged, it will be again in this regard expressly referred to WO, A1 96/22497. The incoming outside air 14 so much cooling water 36 is added that nothing drips on the outlet side, however, the plastic films 28 always remain moist.

• Im Winter zum Befeuchten der Aussenluft 14, indem durch den wandernde Spritzdüsenbalken 26 oder die Spritzdüsenmatrix 30 statt Sorptionsmittel 32 reines Kühlwasser 36 eingedüst wird.
• Zusätzlich zum Befeuchten kann die Aussenluft 14 durch Einleiten von Abluft in die Kühlluft-Strömungskanäle 22 vorgewärmt werden.
• Durch Einleiten von Kühlluft oder Warmluft in die Kühlluft-Strömungskanäle 22 kann eine reine Wärmeregulierung ohne Änderung des absoluten Feuchtigkeitsgehaltes der einströmenden Aussenluft erfolgen.

The plate heat exchanger 12 with the spray devices can be used in a variety of ways as required:

• In the winter to humidify the outside air 14, by means of the moving spray nozzle bar 26 or the spray nozzle matrix 30, instead of sorbent 32 pure cooling water 36 is injected.
• In addition to humidification, the outside air 14 can be preheated by introducing exhaust air into the cooling air flow channels 22.
• By introducing cooling air or warm air into the cooling air flow channels 22, pure heat regulation can take place without changing the absolute moisture content of the incoming outside air.

In the area below the outlet openings for the supply air 18 there is a trough 40 arranged for the draining dilute sorbent 34. The supply air 18 flows through a droplet separator 42 known per se, which prevents that droplets of sorbent 34 remain in the supply air 18. To the Expulsion of the water condensed in the sorbent 34 is a treatment circuit 52 formed, which a brine / brine heat exchanger 44, a desorption device 46, a cooling device 48 and a pump 50 comprises the now again enriched sorbent 32 in the area of the plate heat exchanger 12 and thus brings back the processing circuit 52 closes.

The desorption device 46 is in the present case as an evaporator 54 a drain 55 and a heater 56 are formed. The heating takes place with Steam, however, could also be electrical energy or on others per se known way. The preheated one in the middle dilute sorbent 34 is heated and by evaporating water concentrated until the value determined by the process computer is reached.

The concentrated sorbent pre-cooled in the brine / brine heat exchanger 44 32 is in the cooling device 48, a ventilated air cooler, on a brought optimal operating temperature.

A collecting trough is located below the outlet openings for the heated cooling air 24 58 with a drain 59 for cleaning water of the cooling air flow channels 22 arranged. These channels are washed out at the end of work (WO, A1 96/22497) cleaned.

2 is a sorption system with two plate heat exchangers 12, 12 ' shown, the preparation of the dilute sorbent 34 according to Fig. 1 takes place and is therefore not shown.

The first plate heat exchanger 12 corresponds essentially to that of Fig. 1. However, flows out through the cooling air flow channels 22 (Fig. 1a) exhaust air 60 exiting space 20, which is sprayed with cooling water 36 and exits into the atmosphere as exhaust air 62. The sprayed, with condensed Moisture of the outside air 14 diluted sorbent 34 is from a deflection profile 64 deflected into the area above the tub 40.

The dried outside air 14 is through a second plate heat exchanger 12 'guided and metered if necessary by spraying with cooling water 36 moistened. The supply air 18 entering the space 20 is therefore temperature-related air-conditioned and water content.

Cooling water is generated at regular time intervals via the spray nozzle bar 38 ' 36 sprayed, in compliance with the above-mentioned conditions of constantly keeping the plastic films 28 (Fig. 1a), but without dripping.

Here, too, are different depending on the external conditions (season, weather conditions, etc.) Operating modes possible. The plate heat exchanger 12 can be switched off and with the heat exchanger 12 'by in the description of Fig. 1 mentioned modes of operation are cooled and / or heated without the absolute moisture content is changed. The plate heat exchanger can also be used 12 'switched off and with the plate heat exchanger 12 dried or dried and cooled.

Another variant of a sorption system with two plate heat exchangers 12, 12 'is shown in Fig. 3. The outside air 14 becomes as above shown continuously before entering a first plate heat exchanger 12 or periodically sprayed with liquid, hygroscopic sorbent 32, the outside air 14 is dehumidified. The dehumidified outside air is passed through a droplet separator 42 passed to a second plate heat exchanger 12 'and there cooled.

The exhaust air 60 from the room 20 is divided into two partial flows. A first partial flow is after the periodic spraying with cooling water 36 by the led first plate heat exchanger 12 and enters as exhaust air 62 in the Atmosphere out, analogous to a second partial flow 62 ', which for cooling is guided through the second plate heat exchanger 12 '.

In the present case, outside air of 32 ° C with 12.5 g water / kg air is isothermal passed through the first heat exchanger 12. Through the sorption process the absolute air humidity isothermally reduced to 8g water / kg air, which As mentioned, the temperature remains at 32 ° C. In the second plate heat exchanger 12 'the partially dried air is cooled to 22 ° C, the absolute humidity stays unchanged.

4, a so-called Mollier-h-x diagram for moist air, is one Air conditioning with a sorption system 10 e.g. 2 or 3 shown. Humid outside air has a temperature of 32 ° C and an absolute. Humidity of 12.8 g water / kg air. The moist outside air of a relative Humidity of 40% is achieved by sorption in a plate heat exchanger 12 practically isothermal by means of a sprayed-in sorbent dehumidified. The temperature rises slightly to 34 ° C, so it remains practical isothermal and in this first step it becomes 6 g water / kg air dried. The relative humidity has dropped from 40% to below about 17%. With stronger cooling, this first step could easily be done are kept more precisely isothermal.

In a second step, the outside air is no longer dehumidified, only still chilled. This causes the temperature to drop at the same absolute humidity to 22 ° C. The relative humidity is now around 35%.

In a third step, the dehumidified and cooled air gets through passed another plate heat exchanger and humidified and cooled there. The temperature drops to about 17 ° C, the absolute humidity will increased to 8 g water / kg air. The relative humidity is now just above 60%. This last step takes place with unchanged enthalpy, the curve runs parallel between two enthalpy curves 66 in the Mollier-h-x diagram. Dew point line 68 with 100% relative humidity is not reached.

Using a further Mollier-h-x diagram, a simplified, usually preferred variant shown in two instead of three steps. Moist outside air has a temperature of 32 ° C and a absolute humidity of 12.8 g water / kg air, which is a relative humidity corresponds to 40%. According to an isothermal sorption process 1 the absolute humidity is reduced to 8 g water / kg air, the relative humidity has dropped to about 26%. In the second step the air is directly reduced to the final temperature of 20 ° C without dehumidification, the relative humidity rises to about 52%.

Claims (10)

1. Process for drying or drying and cooling of damp air (14) passed into a room (20) by way of at least one plate heat exchanger (12), with a liquid hygroscopic absorption medium (32), characterised in that the air (14) on the inlet side of a plate heat exchanger (12) is sprayed continuously or periodically in the flow direction with the liquid hygroscopic absorption medium (32) and the condensation heat is passed directly or by way of cooling means (12') into the room (20) while maintaining a practically isothermic dehumidification of the air.
2. Process according to claim 1, characterised in that in a crossflow plate heat exchanger (12, 12') on the input side at equal time intervals a fine spray jet of prepared water (36) is sprayed into the cooling air flow channels (22), where no sprayed water drips and the air-swept surface elements (28) remain damp until the next spraying.
3. Process according to claim 1 or 2, characterised in that the diluted absorption medium (24) dripping from the absorption flow channels (16) is caught, heated to desorb the absorbed water and passed under cooling to the plate heat exchanger (12) for re-use.
4. Process according to any of claims 1 to 3, characterised in that the air is dehumidified isothermically at a temperature of 30 to 35°C, in particular around 32°C, and by evaporative cooling the temperature is lowered by 5 to 15°C, in particular by around 10°C.
5. Process according to claim 4, characterised in that the drying and cooling is performed by isothermic dehumidification in a first plate heat exchanger (12) and subsequent cooling in a second plate heat exchanger (12').
6. Process according to any of claims 1 to 5, characterised in that the dehumidified or dehumidified and cooled air is rehumidified under further cooling with constant enthalpy, where the cooling and humidification are clearly completed before the dew point line (68) is reached.
7. Process according to any of claims 1 to 6, characterised in that the dried supply air (18) is passed by way of a droplet precipitator (42) into the room (20).
8. Device for performance of the process according to any of claims 1 to 7, characterised in that an absorption plant (10) for drying or drying and cooling air comprises at least one corrosion-resistant plate heat exchanger (12, 12') with a spray nozzle bar (26) or a spray nozzle matrix (30) for the saturated absorption medium (32) arranged on the inlet side of the absorption flow channels (16), a spray nozzle bar (38) for the coolant water (36) arranged on the inlet side of the coolant air flow channels (22), a catchment tray (40) for the dripping diluted absorption medium (34) and a preparation circuit (52) for the absorption medium (34) with a desorption device (46), a cooling device (48) and a pump (50).
9. Device according to claim 8, characterised in that the plate heat exchanger (12, 12') is constructed of plastic film (28), preferably with alternating crossing absorption and coolant air flow channels (16, 22).
10. Device according to claim 8 or 9, characterised in that the desorption device (46) is formed as an evaporator (54) and/or evacuator and the cooling device (48) is formed as a ventilated air cooler, where between the desorption and cooling devices is preferably arranged a brine/brine counterflow heat exchanger (44).

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