WO2006102940A1

WO2006102940A1 - Refrigeration installation that operates according to sorption principles and method for operating said installation

Info

Publication number: WO2006102940A1
Application number: PCT/EP2005/051441
Authority: WO
Inventors: Jürgen Ullrich; Andreas Karsdorf; Heinz-Dieter Bürger; Kira Bürger; Günter Heinrich
Original assignee: MIWE-ÖKOKÄLTE GmbH
Priority date: 2005-03-30
Filing date: 2005-03-30
Publication date: 2006-10-05

Abstract

The invention relates to a refrigeration installation that operates according to absorption principles, comprising an absorption circuit. In said circuit, a pump (1) circulates an aqueous absorption fluid between an absorber (6), in which water vapour is absorbed and a generator (3), in which water is expelled again in the form of water vapour. The installation also comprises a collector (11), in which the water vapour is re-condensed. According to the invention, an aqueous solution, which is contained in an evaporator (14), is used as the coolant, said evaporator being connected to the vapour chamber of the absorber (6) via a water vapour line (7) and being supplied with condensate from the collector (11). The generator (3) interacts with a mechanical vapour compression pump (9) and comprises a condensation coil (10) that is immersed in the absorption fluid. The inlet of the condensation coil is connected to the pressure outlet of the vapour compression pump (9) and the outlet of said coil is connected to the collector (11).

Description

description

COOLING SYSTEM ACCORDING TO THE SORPTION PRINCIPLE AND METHOD FOR THE OPERATION

Technical environment

The invention relates to a cooling system according to the absorption principle with an absorption circuit in which a pump circulates an aqueous absorption fluid between an absorber, in which it absorbs water vapor, and an expeller, in which water is expelled as steam again, and with a Collector in which the steam is brought back to condensation.

Such systems, for example with a LiBr SoIe, are known from the document DE 44

15 199 Al known. If temperatures below 0 ⁰ C are to be achieved, then used to date refrigerant, for example, the toxic ammonia, which cause problems in operation and disposal. In addition, one would need for the condensation of the low-boiling component of the fluid in the evaporator downstream collector a low-cost heat sink sufficiently low temperature, which is not always and everywhere available. Disclosure of the invention

The object of the invention is therefore to provide a cooling system, with a

Cooling fluid temperature is well below 0 ° C achievable and yet allows to use an aqueous solution that causes no problems in the disposal. In addition, a high coefficient of performance (COP coefficient of power) and a low cost of equipment and external energy value should be placed.

This object is achieved by the cooling system according to the enclosed main claim. With regard to features of preferred embodiments of the invention and the preferred means for operating the system, reference is made to the dependent claims.

The cooling system according to the invention according to the preamble of claim 1 is characterized in that an aqueous solution is used as the cooling fluid, which is located in an evaporator, which communicates via a steam line with a vapor space of the absorber and from the collector with condensate is fed, and that the expeller interacts with a mechanical vapor compression pump and has a immersed in the absorption fluid condensation coil, which is the input side connected to a pressure outlet of the vapor compression pump and the output side with the collector.

This system allows cooling to low temperatures, which previously seemed unreachable with an aqueous solution as cooling fluid. In practice, a gas space of the expeller can be connected to a vacuum pump. Further, the evaporator may be provided with an agitator which prevents in operation the formation of compact ice and thus allows the use of an aqueous solution to achieve a low temperature.

[008] In addition, in a practical embodiment, a pump may be located in a cooling fluid passage between the evaporator and the header to supply cooling fluid to the header. The collector can also be provided with a stirrer.

[009] In one embodiment variant, the cooling system may have a further absorption circuit as a deep-freezing stage. In the further absorption cycle, a pump circulates an aqueous absorption fluid between an absorber and an expeller. This absorber extracts steam from another evaporator whose cooling fluid circulates in a consumer circuit. In this variant, the vapor space of the expeller of the further absorption circuit may be connected to the vapor space of the absorber of the first absorption circuit. The further evaporator may likewise be provided with an agitator in order to avoid the formation of ice.

The invention also relates to a method for operating the previously described

Cooling system. This method is characterized in that the cooling fluid is admixed with at least one substance from the group comprising alkaline earth and alkali halides, formates, acetates, perchlorates and sulfates.

[011] The cooling fluid may be added, besides water, a substance from the group comprising polyol, polyethylene oxide and polyether. Furthermore, at least one substance from the group comprising ethylene glycol, butylene glycol, polyethers and alcohols can be added to the cooling fluid.

In practice, the absorption fluid may differ from the cooling fluid only by its lower water content.

[013] Also concerned is a method for operating the cooling system with a further absorption cycle, in which a substance lowering the freezing point is added to the aqueous absorption fluid of the further absorption cycle. Short description of drawings

[014] The invention will be explained in more detail below with reference to exemplary embodiments and the accompanying drawings.

FIG. 1 schematically shows the construction of a first cooling system according to FIG

Invention.

[016] FIG. 2 shows a two-stage cooling system, which is based on the system according to FIG

FIG. 1 has a further absorption circuit and a deep-freeze circuit.

[017] The system according to FIG. 1 contains an absorption circuit in which a

Pump 1, an absorption fluid from a sump 2 in an expeller. 3 promoted. The expeller is heated by a heat source 4, which is, for example, a solar collector and allows the low-boiling component of the absorption fluid, namely water, to evaporate. This reduces the water content of the fluid. The hot fluid is then supplied via a cooler 5 to a spray absorber 6, into which a steam line 7 opens, so that water enriched in water collects at the bottom of the spray absorber. The outlet of the spray absorber 6 is connected via a siphon 8 to the sump 2, whereby the circle for the absorption fluid closes. The siphon 8 has the task of separating the gas space of the collecting container 2 from that of the spray absorber under all operating conditions, which of course can also be achieved without a siphon, if the collecting container is positioned so that its gas space is equal to the gas space of the spray absorber.

The expeller 3 is provided with a vapor compression pump 9, which the in

Gas space of the expeller sucks up forming water vapor and compressed in a lying in the lower part of the expeller cooling coil 10 feeds. As a result of the compression and the cooling effect of the coil, the water vapor condenses and then flows into a collector 11, which is cooled by a schematically indicated heat sink 12. The vapor compression pump is preferably a positive displacement type positive displacement pump, that is with an additional inlet for the compressed and cooled vapor into the pumping chamber shortly before it opens to the outlet. This relieves the pump and increases the pumping capacity.

Although the collector 11 receives water from the expeller, but is additionally charged via a pump 13 with the actual cooling fluid consisting of water and an admixture of alkaline earth or alkali halides, formates, acetates, - perchlorates or sulfates consists, for example, potassium formate KCOOH. The absorption fluid in the expeller may also contain one of these admixtures, but this may not necessarily be the same substance. In a preferred embodiment, the fluids in the expeller 3 and in the collector 11 differ only by the concentration of the aqueous solution, which is lower in the cooling fluid in the collector 11. The supply of condensate to the collector 11 leads there due to the heat of solution to a temperature increase, so that the cooling with the help of the sink 12 at a given temperature is more effective. An agitator in the collector 11, which is indicated in the figure, improves the mixing effect and evened out the heat development.

[020] The cooling fluid comes from an evaporator 14, which is also an agitator

May have 15 and offers the vapor to the spray absorber 6 via the above-mentioned steam line 7. This results in a cycle for evaporating from the evaporator 14 water on the Sprühabsorber 6 (absorption of water vapor), the sump 2, the expeller 3 (desorption) and the collector 11 back to Evaporator 14. The capacity of the pump 13 is adjusted so that the collector 11 never completely emptied. Via a valve 17 in a connecting line 18 between the collector 11 and the evaporator 14, the fluid level and thus the temperature in the collector 11 can be lowered, for example when the sink 12 does not provide the desired temperature alone.

The concentration of the absorber fluid in the expeller 3 is measured with a probe 16 am

Input of the spray absorber 6 measured and readjusted by controlling the pump 1 to a desired value: As long as the pump 1 is turned off, the concentration increases in the expeller.

Finally, a vacuum pump 19 is still present, the permanent gases at startup from the various gas chambers, namely the expeller 3, the absorber 6, the collectors 2 and 11 and the evaporator 14 sucks.

In order to prevent ice from forming in the cooling fluid, the freezing point depressant is added to the cooling fluid selected from ethylene glycol, butylene glycol, polyethers or alcohols.

[024] It is also possible deliberately to produce ice-sludge by

Crystallization allows, up to an ice content of about 30%. Then the agitator 15 is turned on. Beyond a 30% level of ice, which is crowded at the surface due to its lower density relative to water, the evaporation rate in the evaporator decreases significantly and the temperature thus increases. Ice-sludge is favorable for isothermal cooling because the temperature remains constant as long as the enthalpy of fusion still works. Furthermore, it is possible to add polyol, polyethylene oxide or polyether to the cooling fluid for a more homogeneous distribution of ice crystals and for improved circulation capability of the cooling fluid.

[025] The use cycle of the cooling fluid consists of a circulation pump 20 and the

Heat exchanger 21 with the (not shown) refrigerated goods. To this still more coolers are connected in parallel, namely the already mentioned cooler 5 at the inlet to the spray absorber and a cooler 22 in the return line 18 from the collector 11 to the evaporator 14th

Is used as the absorption fluid, an aqueous solution of lithium chloride LiCl at a concentration of 40%, then the temperature of this fluid behind the condenser 5 at a vapor pressure of 1 mbar 20 ⁰ C, at a vapor pressure of 0.6 mbar 10 ° C and at a vapor pressure of 0.3 mbar still 0 ⁰ C without salt crystallization of the brine occurs.

If a KCOOH solution is used in the evaporator 14, the following temperatures result with corresponding vapor pressures at different concentrations of potassium formate KCOOH:

For a concentration of 28% (vapor pressure p = l, 0 mbar) results at -20 ⁰ C. no ice crystallization yet.

For a concentration of 55% (vapor pressure p = 0.6 mbar) results at -20 ° C still no crystallization.

[030] For a concentration of 46% (vapor pressure p = 0.3 mbar) no crystallization is obtained at -32 ⁰ C.

For a concentration of 30% (vapor pressure p = 0.3 mbar) begins at -23 ⁰ C the

Crystallization.

For a concentration of 39% (vapor pressure p = 0.2 mbar) begins at -35 ° C the

Crystallization.

In the range of 0 to 28% KCOOH concentration, the crystallization temperature at which an ice suspension is formed between 0 ⁰ C and -30 ⁰ C can be adjusted. The vapor pressure depression compared to water or ice is not high in this area.

The device according to the invention requires apart from the drive of the pump, and agitators only inexpensive heat energy, especially for the expeller. In addition to a high coefficient of performance, the device according to the invention is also characterized by a small amount of equipment, compared, for example, with a device for shaving off ice from a water-sprayed cooling wall.

The system according to FIG. 2 does not fundamentally differ from the system described above with reference to FIG. 1, which is manifested by the same reference symbols for similar elements. Here only an additional freezing stage was added, so that the temperature in the evaporator 14 can be above 0 ⁰ C. This additional stage uses an aqueous potassium formate solution as the absorption fluid, which acts as an antifreeze. The solution absorbs steam in a further spray absorber 23. The latter supplies the so-enriched solution via a circulation pump 32 to an expeller 24, which is heated by a heat source 25 and whose vapor space communicates via the line 7 with the vapor space of the spray absorber 6. The loop for the potassium formate solution closes via a cooler 26, from which cooled, depleted cryogenic fluid reaches the spray heads of the spray absorber 23. The loss of water in the evaporator 27 can be compensated via a valve 31 from the evaporator 14 and by returning cooling fluid from the evaporator 27 by means of a pump 33 into the collector 11.

The vacuum pump 19 for the removal of permanent gases at the start of operation additionally performs the same task in the gas chambers of the further spray absorber 23, the further expeller 24 and the further evaporator 27 in this system.

The task of the spray absorber 23 is the removal of water vapor from an evaporator 27 provided with a stirrer 28, the aqueous KCOOH solution of which is conveyed by a pump 29 to a consumer heat exchanger 30. [038] In addition to the two circuits with the absorption fluid and the cooling fluid according to FIG. 1, there is therefore still a second stage with an absorption and a cooling fluid circuit. The absorption fluid is again an aqueous solution of KCOOH, and also the cooling fluid in the evaporator 14 is KCOOH as before, but in a preferred mode, the flow temperature of the consumer heat exchanger 21 of the first stage only at -10 ° C without the use of the enthalpy of fusion of an ice suspension , If there is no need for cooling in this temperature range, the consumer heat exchanger 21 can be omitted. At a KCOOH concentration of 63% and a temperature of -1O ⁰ C in the evaporator 14, this fluid has a vapor pressure of 1, 0 mbar. At this temperature, the cooler 26 can be fed at the inlet to the absorber 23 from the absorber fluid in the evaporator 14.

The cryogenic fluid is at the outlet of the evaporator 27, a temperature of -32

Reach ° C. An aqueous KCOOH solution with a concentration of 34% can, at this temperature, form a fluid / ice suspension which makes use of the melting enthalpy of ice for the consumer heat exchanger. The heat capacity of this fluid without ice is 41.8 kJ / kg at a temperature difference of 10 degrees. Such a suspension has a heat capacity of about 100 kJ / kg in isothermal cooling. If one tolerates a warming of 10 degrees, then one achieves a heat capacity of even 140 kJ / kg.

In order to reach a temperature of -34 ° C in the evaporator 27, would have in the

Absorber 23 injected KCOOH solution have a concentration of 77%. However, crystallized at -10 ⁰ C formate. Here you can either keep the formate crystals in suspension with an ultrasonic device or direct a partial flow of frozen fluid from the pump 29 to the radiator 26 to bring the temperature of the sprayed into the spray absorber 23 solution to -2O ⁰ C. It then works with a formate concentration of 71%, which at -20 ⁰ C has a vapor pressure of 0.3 mbar. The fluid / ice suspension with 34% concentration has a vapor pressure of 0.33 mbar under these conditions.

In the cooling system according to FIG. 2, a significantly higher coefficient of performance results at the same final temperature than in the cooling system according to FIG. 1. It would also be possible to extend this cascade principle to more than two stages.

The invention is not limited to the illustrated embodiments in all details, but includes within the scope of the main claim numerous variants, some of which have been indicated above.

Claims

claims

Cooling system according to the absorption principle with an absorption circuit in which a pump (1) an aqueous absorption fluid between an absorber (6), in which it absorbs water vapor, and an expeller (3), is expelled in the water as steam again, circulated, and with a collector (11), in which the vapor is brought back to the condensation, characterized in that an aqueous solution is used as the cooling fluid, which is located in an evaporator (14) via a steam line (7) a vapor space of the absorber (6) is in communication and is fed from the collector (11) with condensate, and that the expeller (3) with a mechanical vapor compression pump (9) cooperates and has a immersed in the absorption fluid condensation coil (10) On the input side with a pressure outlet of the vapor compression pump (9) and the output side with the collector (11) is connected.

[002] Cooling system according to claim 1, characterized in that a gas space of the

Exporter (3) with a vacuum pump (19) is connectable.

Cooling system according to one of the preceding claims, characterized in that the evaporator (14) is provided with an agitator (15) which prevents the formation of compact ice during operation.

Cooling system according to one of the preceding claims, characterized in that a pump (13) is located in a cooling fluid line between the evaporator (14) and the collector (11) to supply the latter cooling fluid.

Cooling system according to claim 4, characterized in that the collector (11) is provided with a stirrer.

Cooling system according to one of the preceding claims, characterized in that a further absorption circuit is present, in which a pump (32) circulates an aqueous absorption fluid between an absorber (23) and an expeller (24), and in that this absorber (23 ) Withdrawing steam from another evaporator (27) whose cooling fluid circulates in a consumer circuit (29, 30).

Cooling system according to claim 6, characterized in that the vapor space of the expeller (24) of the further absorption circuit is connected to the vapor space of the absorber (6) of the first absorption circuit.

Cooling system according to one of claims 6 and 7, characterized in that the further evaporator (27) is provided with a stirrer (28).

Method for operating the cooling system according to one of the preceding claims, characterized in that the cooling fluid at least one substance from the Group which comprises alkaline earth and alkali halides, formates, - acetates, -Perchlorate and sulfates.

A method of operating the refrigerating plant according to any one of claims 1 to 8, characterized in that the cooling fluid contains, besides water, a substance from the group comprising polyol, polyethylene oxide and polyether.

[011] Method according to claim 9 or 10, characterized in that the

Cooling fluid is added to at least one substance from the group comprising ethylene glycol, butylene glycol, polyethers and alcohols.

Method according to one of claims 9 to 11, characterized in that the absorption fluid differs from the cooling fluid only by its lower water content.

Method for operating the cooling system according to one of Claims 6 to 8, characterized in that a substance which lowers the freezing point is added to the aqueous absorption fluid of the further absorption cycle.