NO830235L - WORKING MEDIUM FOR ABSORPTION HEAT PUMPS. - Google Patents

Abstract

1. A working medium for use in absorption heat pumps and comprising the refrigerant difluorochloromethane (R-22) and an adsorbent, in which the adsorbent is triezthylene glykol dimethyl ether.

Description

The invention relates to a working medium which contains difluorochloromethane and can be used in a heat pump of the absorption type to produce cold or heat.

The use of heat pumps for cooling and heating purposes has been known for a long time. While initially electrically driven compression machines for the production of cold were in the foreground, in recent times heating heat pumps are finding interest as they are able to save energy. In principle, both compression and sorption heat pumps can thereby be used. However, compared to electrically driven compression heat pumps, sorption heat pumps have some advantages, mainly quietness,

less wear and tear, as there are hardly any mechanically driven parts, less need for maintenance, less installation costs, above all, however, less primary energy consumption. In the case of an electrically driven compression heat pump, e.g. to take into account that until power generation has been lost approx. 2/3

of the primary energy.

Substance pairs for sorption heat pumps, consisting of a solvent and a volatile soluble substance, are already known. Such substance pairs were primarily developed for use in large-scale refrigeration machines (water/ammonia) lithium bromide/water).

For private households, the use of ammonia is admittedly limited for toxicological and safety reasons. Combinations with lithium bromide require a lot of work with regard to tightness, as the plants work in a high vacuum.

Moreover, the crystallization limit is at low temperatures

of the heat source to take into account.

For use in smaller systems, particularly in private households, systems have been proposed that contain a fluorochlorohydrocarbon as a volatile phase, as this group of substances is not flammable and relatively low-toxic and low-corrosive.

Work substance pair for sorption heat pumps in which the solvent is a phosphoric acid amide with alkyl or phenyl groups and the volatile phase is a fluorochloroalkane is the subject of DE-OS 29 44 189. As the most favorable system of a fluoro-chlorohydrocarbon with a solvent is considered in the literature the combination of FKW 22 (difluorochloromethane) with tetraethylene glycol dimethyl ether (B. Eisemann, Absorption refrigeration, ASHRAE Journal, Dec. 1959, pages 45-50, S. Mastrangelo, Chlor-fluorohydrocarbons in tetraethylene glyco dimethyl ether, ASHRAE Journal, Oet. 1959 , pages 64-67, K. Stephan, D. Seher, Arbeitsgemische fur Sorptions-Warmepumpen, Klima-Kalte-Heizung 1/1980 pages 874, 875).

Figure 1 of the drawing shows a strong simplification of an absorption heat pump circuit process. The heat flow into and out of the system is denoted by Q and is indicated by the direction of the arrow.

The mode of operation is as follows:'

In the evaporator 6, the refrigerant (e.g. F KW 22) is evaporated by heat absorption at a low temperature (e.g. 0°C). The refrigerant vapor enters via line 7 into the absorber 8 and dissolves there in the solvent. Thereby, heat is released as e.g. can be discharged to a water circuit to be heated.

The refrigerant-enriched solvent (rich solution) is pumped via lines 10 and 11 with a pump 12 into the expeller 1. The expeller 1 is heated (e.g. at 130°C) whereby coolant is desorbed from the solution and comes via line 2 into the liquefier 3. In the liquefier 3, the refrigerant vapor is liquefied at a higher temperature, e.g. 50°C. The heat of evaporation thereby released can e.g. is delivered to a water circuit to be heated. Ideally, the heat pump is operated in such a way that the liquefier's and the absorber's heat release takes place at the same temperature (e.g. 50°C).

From the liquefier 3, the liquid refrigerant enters the evaporator 6 via line 4 and expansion valve 5.

The one in expeller 1 during desorption of refrigerant on refrigerant-depleted solution (poor solution) comes over line 9

and throttle valve 13 back into the absorber 8 and can again dissolve refrigerant vapor from the evaporator 6 there.

The heat pump circuit process takes place between two pressure levels.

The pressure on the low pressure side (after expansion valve, evaporator, absorber to dissolution pump) results from the saturation vapor pressure of the refrigerant at the evaporation temperature. E.g. FKW 22 has a saturation vapor pressure of 5 bar at 0°C. The pressure of the high-pressure side (from the dissolution pump exit, expeller, liquefier to expansion valve) results from the saturation vapor pressure of the refrigerant at the liquefaction temperature. E.g. At 50OC, FKW 22 has a saturation vapor pressure of 19 bar.

It is at hand that per kilo of solvent, the more heat can be transported in the plant, the greater the difference between the solubility of the refrigerant in the absorber and expeller. The solubility difference in kilograms of refrigerant per kilogram of solvent is referred to as degassing width. If you multiply the degassing width by the vaporization heat of the refrigerant (FKW 22 has a vaporization heat of 154 KJ per kilogram at 50°C), you get it per kilogram of solvent transported amount of heat.

For the FKW 22/tetraethylene glycol dimethyl ether system mentioned in the literature, according to our own experiments, the degassing width amounts to 0.19 kilograms of FKW 22 per kilos of solvent. The measurement was made under the following conditions: Evaporator/absorber part: 5 bar steam pressure of FKW 22 and 50°C solution temperature. Extruder/condenser part: 19 bar steam pressure of FKW 22 and 130°C solution temperature_.__

The transportable amount of heat therefore amounts to 29.3 KJ/kilogram of solvent.

The invention is based on the task of providing

a pair of working materials which per unit weight of the solvent transports a considerably higher amount of heat, but also fulfills the other requirements for such a system. For example, the system in the work area must have a low viscosity and not be corrosive. It must be possible to remove heat from the surroundings at -20°C. The volatile compound must be able to be expelled by the solvent at temperatures from 90°C to 180°C.

It was now found that the substance pair difluorochloromethane (FKW 22)/ triethylene glycol dimethyl ether (TEG) meets these requirements. This system's degassing width is around 50% greater than with the FKW 22/tetraethylene glycol dimethyl ether system. The amount of heat which

can be transported per kilos of solvent therefore in the present case amount to approx. 46.2 KJ/kilogram of solvent. It is further advantageous that the solvent TEG at 20°C has a viscosity of only 3.0 mPa-s, while tetraethylene glycol dimethyl ether has a viscosity of 5.1 mPa-s. The sorption heat pumps filled with material pairs according to the invention can be operated both as a cooling machine and also as a heating heat pump.

The use of substance pairs according to the invention is possible in certain temperature ranges. The temperature ranges for different plant parts are listed below.

1. Evaporator:

The evaporation can take place in the range from -20°C to +40°C, preferably in the range -10°C to +20°C, especially in the range -5°C to +10°C.

2. Co-condensation:

The condensation can take place in the range from 20°C to 80°C, preferably between 35 and 65°C.

3. Absorbs:

The absorption can take place at temperatures between 20 and 80°C, preferably between 35 and 65°C.

4. Expels:

The expulsion of FKW 2 2 from the solution can take place between

90 and 180°C, preferably between 110 and 150°C.

The position of the center point of plant part 1 (expander), 3 (flow finisher), 6 (evaporator) and 8 (absorber) with respect to the suitable coordinate system in the figure simultaneously illustrates preferred working conditions for a heat pump with working medium according to the invention.

Under the already mentioned conditions in the evaporator/absorber part and expeller/condenser part, FKW 22 in TEG and comparatively in tetraethylene glycol dimethyl ether have the following solubilities:

It is surprising that the system according to the invention containing TEG has an advantage over the analogous system based on tetraethylene glycol-dimethyl-tex- It is known that both ethers are good solvents for FKW 21. however, the same literature review states that no conclusions can be drawn from the solubility properties of a certain halogen derivative of methane with regard to the solubility properties of another halogen derivative of methane. The lower the temperature in the absorber, the higher the achieved charging of TEG with FKW 22. The higher the temperature in the expeller, the smaller the residual charging. The TEG/FKW 22 mixing ratio therefore depends on the working conditions. In most cases, the weight portion of FKW 22 is 10 - 75%, preferably 20 - 40%.

Claims (3)

1. Working medium for use in sorption heat pumps and consisting of the refrigerant difluorochloromethane (FKW 22) and an absorbent, characterized in that the absorbent is triethylene glycol dimethyl ether. 2. Use of substance pairs according to claim 1 in a sorption heat pump which is operated as a cooling machine or as a heating heat pump. 3. Process for heat transport using an absorption heat pump containing an evaporator, an absorber, an expeller and a liquefier, in which liquid difluorochloromethane is evaporated in the evaporator at temperatures from -20 to +40°C during heat absorption and the formed vapor is fed into the absorber and dissolved there at 20 to 80°C in an organic solvent, the heat occurring during the dissolution process is at least partially removed from the absorber, the formed difluorochloromethane/solvent mixture is pumped into the expeller, heated there to 90 to 180°C so that difluorochloromethane at least is partially driven out of the solution, the driven out gaseous difluoro-chloromethane is fed into the liquefier, liquefied there as in the absorber at temperatures from 20 to 80°C, however at a temperature that is above the temperature in the evaporator, the resulting heat of evaporation is given off, the liquid difluorochloromethane is returned to the evaporator, the depleted solution formed on difluorochloromethane in the expeller during the expulsion of difluorochloromethane is returned to the absorber, characterized by the fact that triethylene glycol dimethyl ether is used as an organic solvent.