EP0107755A1 - Direct evaporation energy accumulator - Google Patents

Abstract

The energy accumulator (1), the working substance of which in normal operation is present partially as ice, contains as liquid working substance (71) an aqueous solution of a substance which lowers the freezing point, e.g. of a salt or of an alkaline solution. From such an aqueous solution, the water crystallises on cooling in the form of small ice platelets and ice grains (78) which with the solution (71) form an ice mush (79). As a result the formation of a compact ice layer, by which the evaporation and thus the ice production would be brought to an end in a short time, at the boundary layer between liquid and vapour is prevented.

Description

The invention relates to an energy store designed as a direct-working evaporator for an absorption heat pump system serving to heat and / or cool a building, in which water circulates as working fluid through evaporators, absorbers, expellers, condensers and expansion elements, and a hygroscopic pump that can be pumped even at high concentrations Absorbent with the help of a pump penetrates the absorber and the expeller, whereby on the one hand the heat of absorption and on the other hand the heat of condensation is used for heating purposes or is dissipated as waste heat in the case of cooling, and furthermore the energy store in which a part of the water at least during part times is stored as ice, is part of a second work cycle with at least one low-temperature heat source or a cold consumer.

An absorption heat pump system with an energy store of the type mentioned above is known from EP Bl 0 010 551. In normal heating operation, the thermal energy required for heating in this system, which then works at a vacuum which corresponds to the pressure at the triple point of the water, is essentially the latent heat hold the water in the reservoir removed, which at least partially merges into ice; in cooling operation, "cold" storage in this system also takes place in that part of the water in the storage is in the form of ice.

In both modes of operation, difficulties have arisen in that a closed, compact layer of ice forms in the energy store at the interface between the vapor and liquid space, which, after a short time, severely affects the evaporation of the water. The absorption process therefore comes to a standstill very quickly, even if only a small part of the water contained in the reservoir has been converted into ice.

The object of the invention is to eliminate this disadvantage of the known energy store. According to the invention, this object is achieved in that an aqueous solution in which at least one solute brings about a lowering of the freezing point by at least 1 K serves as the working medium in the energy store.

Inorganic salts have proven to be suitable as freezing point-lowering substances for the formation of the aqueous solution. For salt, for example, a concentration of at least 17 g / 1 is required.

However, it is also advantageous to use the same substances for lowering the freezing point, which - such as an aqueous mixture of caustic soda and potassium hydroxide (NaOH + KOH) in a ratio of 1: 3 to 3: 1 - serve as absorbents in the heat pump system, whereby however, the concentration of the aqueous solution in the energy store is selected so that the freezing point of this solution is preferably between -1 C and -2 ° C; for example at ei ner absorber liquid, each consisting of 50% sodium hydroxide and potassium hydroxide, serve as an aqueous solution of a dilution of this absorbent, in which at least about 8 g / 1 NaOH and KOH are present. Of course, the concentrations of the two alkaline solutions in the aqueous solution change if a different mixing ratio is selected in the absorber liquid, ie the absorbent, of the heat pump system.

With the same substance or substances in absorption liquid and aqueous solution, it is expedient if a lockable connecting line leads from the absorber into the liquid space of the energy store in order, if necessary, to increase the concentration of the aqueous solution by feeding in concentrated absorber liquid.

Since practically pure water evaporates from the aqueous solution in the energy store or evaporator, the heat pump system continues to work with water as the working medium.

The vapor pressure prevailing at the triple point of the aqueous solution is somewhat reduced, however, because of the lower temperature and because of the lower vapor pressure in a solution. While the pressure at the triple point of pure water is 6.1 mbar, a saline solution with 20 g / 1 salt has a pressure of about 5.6 mbar. Apart from this reduction in vapor pressure, the advantages mentioned in the EPS mentioned are retained without the disadvantages described having to be accepted. It has been shown that when ice is produced from an aqueous solution with a lower freezing point, it is not a compact layer of ice that is formed, but small ice crystals. The ice crystals, whose diameters are smaller than approximately 0.5 mm, have a platelet shape. The bigger ones Crystals grow into spherical grains, the diameter of which is of the order of 1 mm. Due to their lower specific weight compared to the solution, the ice crystals float upwards in the solution, forming a thickened ice pulp that does not cake to a compact mass. The ice pulp is flowable and can therefore be fed directly into the second working medium circuit, which contains a low-temperature heat source or a cold consumer.

If different substances are used in the absorber and in the energy store as absorbents or as constituents of the aqueous solution, then it is expedient to provide means by which a transfer of liquid from the evaporator area of the energy store into the absorber is prevented.

The amount of water evaporating in the evaporator area can be increased if a line provided with a pump leads from the liquid area into the steam area of the energy store and ends in a number of spray nozzles; however, it is also possible to distribute the work equipment supported by this line over trickle bodies. Both measures increase the free surface of the work equipment through which the water must evaporate.

In terms of construction, the energy store can advantageously be designed such that its liquid region filled with aqueous solution is divided into two compartments, with evaporation and ice production taking place in one crystallization compartment, while the ice pulp formed is stored in the other compartment; In addition, the storage compartment can be arranged below the ice-making compartment by a height difference AH. You choose about as height differences of 10 m, the vacuum / vacuum in the crystallization compartment can be at least approximately equalized against the ambient pressure for the storage compartment.

In order not to prevent a backflow of the condensate coming from the heat pump system into the evaporator area when the system is at a standstill and temperatures below 0 C in the energy store, it is advantageous if a self-emptying nozzle is available for feeding the condensate into the energy store. If means are provided by which the aqueous solution located in the crystallization or evaporator compartment is moved, new crystallization nuclei continuously arise from the existing ice crystals due to grain breakage and abrasion. Such means are, for example, propellant jets which are generated by suitable shaping of the nozzle-equipped line between the liquid and the vapor area and which set the aqueous solution in motion in the evaporator compartment. Furthermore, measures can be taken by which the flow in the evaporator or ice-making compartment is guided in such a way that relatively large ice crystals are preferably supplied to the storage compartment.

• Fig. 1 zeigt in schematischer Darstellung eine Absorptions-Wärmepumpenanlage mit einem Eisspeicher nach der Erfindung, wobei bei der vereinfachten Darstellung an sich bekannte Details der Anlage - beispielsweise die Vakuumpumpen - weggelassen worden sind;
• Fig. 2 stellt eine zweite Ausführungsform des Energiespeichers mit seinen Anschlüssen für den Einbau in einer Anlage nach Fig. 1 dar;
• Fig. 3 schliesslich ist ein schematisches Beispiel für einen Energiespeicher, bei dem Verdampfer- und Speicherabteil in getrennten Behältern untergebracht sind.

The invention is explained in more detail below on the basis of exemplary embodiments in conjunction with the drawing.

• 1 shows a schematic representation of an absorption heat pump system with an ice store according to the invention, details of the system known per se - for example the vacuum pumps - having been omitted in the simplified representation;
• FIG. 2 shows a second embodiment of the energy store with its connections for installation in a system according to FIG. 1;
• 3 is a schematic example of an energy store in which the evaporator and storage compartments are accommodated in separate containers.

Starting from the steam chamber 12 of an energy store 1 designed as a direct evaporator (FIG. 1), in the liquid region or storage space 13 of which an aqueous solution 71 containing ice crystals 79 is stored as working medium, a steam line 10 connects the evaporator region 12 to an absorber 2 In the vapor space, the water vapor 11 is absorbed by an absorbent with the development of heat and collected at the bottom of the absorber 2 as an absorber liquid 21 enriched with water. The heat thus developed is dissipated with the aid of a coolant 61 circulating in a coil 63 - in the present case, for example, water serving as the heat carrier of a hot water heater 6.

A saline solution containing 20 g / l of saline, for example, serves as the aqueous solution 71 in the energy store 1, which is surrounded by heat-insulating material 16. In the example shown, a mixture of 50% sodium hydroxide solution and 50% potassium hydroxide solution is used as the absorber liquid or absorbent 21. Since the dissolved substances in the aqueous solution 71 and in the absorber liquid 21 are different, a droplet separator 14 is provided in the steam line 10, which prevents liquid droplets from passing from the aqueous solution 71 into the absorber liquid 21.

If the same dissolved substances are used for an aqueous solution 71 and the absorber liquid 21, a connecting line 27 with a shut-off device 28 can be provided be absorbed liquid 21 through which concentrated aqueous solution 71 can be supplied if an increase in concentration is required therein.

For the transport of the water-enriched absorber liquid 21, a line 20, in which a circulation pump 22 is provided, leads via a heat exchanger 23 from the absorber 2 to an expeller 3. This is heated with the aid of a heat exchanger 53, which is connected via a line 50 to a Heat source 5 is connected, in which, for example, waste heat of a higher temperature is available. Of course, the heat source 5 can also consist of a burner for fossil fuels or solar collectors through which a heat transfer medium 51, e.g. Water is heated, which circulates with the aid of a pump 52 through the heat exchanger 53 and the line 50.

By heating in the expeller 3, water vapor 31 is expelled from the absorbent 21 and passed through a steam line 30 in a condenser 4. The absorber 21 concentrated during the separation passes from the expeller 3 via a line 29 and the heat exchanger 23, where it emits heat in countercurrent to its water-rich solution flowing in line 20, back into the absorber 2. There it trickles out of distribution nozzles 24 emerging, absorbing water via the heat exchanger 63 and giving off heat and collecting at the bottom of the absorber 2, which closes the circuit of the absorption medium.

The liquid level of the condensate in the absorber 2 can be kept at least approximately at a constant level by influencing a throttle element (not shown) in the line 29 by a level controller, for example a float.

A short-circuit line 25 for the absorber 2 is provided between the lines 20 and 29, in which an adjustable throttle element 26 is provided. The short-circuit line 25 serves to set the optimal throughput of the absorber liquid 21 through the absorber 2.

The condenser 4, in which the steam 31 expelled in the expeller 3 is condensed, contains a heat exchanger 64. This is connected downstream of the heat exchanger 63 in the flow direction of the coolant 61 circulating therein, which, for example, as mentioned, is the return water of a hot water heating system 6, and via a line 60 is connected to the heating system 6. The circulation of the coolant 61 is maintained by a circulation pump 62 which is provided in the line 65 leading from the heating system 6 to the heat exchanger 63.

The condensed water vapor collects as condensate 41 at the bottom of the condenser 4; connected to this is a line 40, which leads via a relaxation element 42 to a self-draining condensate connector 15 on the energy store 1, whereby the working medium circuit of the heat pump system is closed. As already mentioned, the self-emptying nozzle 15 is intended to prevent the condensate line 40 from being closed by standing water which solidifies into ice when the system is at a standstill in the cold state.

Vacuum pumps (not shown), which can be provided, for example, on the condenser 4 and the absorber 2, are used to maintain the vacuum of approximately 5 mbar, for example in the event of gas ingress.

In order to increase the evaporation by increasing the phase interface between liquid and vapor phase in the energy store 1 improve, the memory 1 is equipped with an internal circuit; In this circuit, a pump 72 conveys aqueous solution 71 from the liquid area or storage space 13 into the evaporator area or steam space 12 through a line 70, the line 70 ending in spray nozzles 73. The droplets 76 sprayed in the steam chamber 12 through the nozzles 73 partially evaporate and thereby change into a supercooled state. When they re-enter the aqueous evaporator solution 71, the supercooled droplets 76 freeze water from the solution 71 in the form of small crystals 78; these ice crystals 78 float due to their lower specific weight compared to solution 71 and thus form an aqueous ice pulp 79 together with solution 71.

The line 70 of the internal circuit preferably starts from the bottom area of the storage space 13, since only a few ice crystals 78 float around in the solution 71; if necessary, the suction end of line 70 may also be provided with a solid particle-retaining screen, not shown.

The second working medium circuit through the energy store 1 containing at least one low-temperature heat source or a cold consumer has a line 80 which branches off from the line 70 on the suction side of the pump 72 and leads via a separate feed pump 82 to the low-temperature heat source, not shown. A line 85 leads from the latter, which leads back to the energy store 1 and opens into the connector 15, as a result of which the second working medium circuit is closed. For example, cold, aqueous solution can circulate through the circuit 80, 85; this solution 71, the temperature of which is <0 ° C according to the invention and is preferably -1 ° C to -2 ° C, is in the Low-temperature heat source or cold consumer warmed up before it flows back into storage 1.

Instead of only supplying liquid 71, which is cooled in the energy store 13, to the low-temperature heat source or the cold consumer, as shown in FIG. 1, the cold transport can also be carried out by means of the ice slurry, as already mentioned. In this way, the advantage is gained that by utilizing the latent heat of fusion at the same currents per unit of time, greater heat transport is achieved than with sensible heat, and that the temperature of the coolant remains practically constant as long as there is ice in the coolant.

1 - for example with regard to the structural design of the condenser 4 or the absorber 2 and with regard to the control and regulation of the individual system parts and the overall system - correspond to those of the system according to the aforementioned EPS O 010 551.

In the energy store 100 (FIG. 2), the liquid space or region receiving the aqueous solution is divided into two compartments 13a and 13b separated by a partition 17. The upper crystallization compartment 13a, which has a liquid surface to the vapor space 12, serves for evaporation and ice production, while the lower one, which is the actual storage compartment 13b, in which the ice pulp 79 is stored. Both compartments 13a and 13b are connected to one another via a pipe 18 leading into the bottom region of the storage compartment 13b, in which freshly produced ice cream is conveyed into the storage compartment 13b.

Near the partition 17 around the tube 18 around a bowl 19 formed as a flat funnel is arranged which sucks out the pump 72 aqueous solution 71 through line 70. With the wide funnel-like opening of the shell 77 it is achieved that very low flow velocities are present at the upper edge of the funnel in the direction of the line 70. Therefore, no or only a few ice crystals 78 are entrained into the line 70 from the relatively dense ice pulp 79 in the upper region of the storage compartment 13b; Of course, the line 70 can also be provided with a strainer at its suction end.

On the pressure side of the pump 72, the line 70 ends in a curved pipe section equipped with spray nozzles 73 (only one of which is shown), which is closed off by a nozzle 74. From this nozzle 74, the aqueous solution 71 emerges as a relatively sharp jet 75 which rotates the ice / liquid mixture in the ice making compartment 13a. The propulsive jet strikes the surface of the liquid flatly and is directed towards the wall, so that part of the ice crystals 78 floating on top are driven against the wall. In the wall zone 77, in which large speed gradients occur, new crystallization nuclei are continuously formed by grain breakage and abrasion by mutual rubbing of the crystals and rubbing on the wall. The predominant part of the ice crystals 78 moves to the centrally arranged drain line 18. The further the crystals have moved from their place of origin in wall zone 77, the larger they have grown due to ice build-up. Therefore, larger crystals preferably enter the ice store 13b.

If the aqueous solution 71 flowing from the line 85 to the energy store 100, which has been heated in the low-temperature heat source or the cold consumer, is not directly via the line 70 for evaporation and ice brought generation, it is returned via the suction end of the line 70 in the ice storage 13b. It passes through the funnel 19 into the uppermost layers of the ice pulp 79, in which the oldest ice crystals 78 are present, which are the first to be melted by this warm solution 71. In these uppermost layers, the ice crystals 78 are present in a relatively compact form, since they are compressed by their buoyancy and the aqueous solution 71 flowing upward in the storage space 13b, which solution is then drawn off by the funnel 77.

The return of the warm solution 71 into the storage compartment 13b - and not into the crystallization compartment 13a - further ensures that the ice crystals in the ice-making compartment 13a are not melted by the warm solution 71, so that even after an interruption in the ice-making process if it is not takes too long, in the aqueous solution 71 in the ice making compartment 13a ice crystals are present as crystallization nuclei for the renewed ice formation.

In the separation of the crystallization and storage compartments, one can go one step further and arrange both compartments 13a and 13b in separate containers. Such an embodiment of an energy store is outlined in FIG. 3. Of course, the aforementioned containers 13a and 13b, as well as the lines 18 and 70 connecting them - if necessary - can be heat-insulated from the environment, which is not expressly shown. The basic arrangement of the connections of the various circuits to the two-part energy store corresponds to those of FIG. 2.

The crystallization compartment 13a and the storage compartment 13b are expediently at different levels arranged so that there is a height difference HH between them. If this difference in height corresponds to a water column of approximately 10 m, the negative pressure prevailing in the crystallization compartment 13a can be compensated for the storage compartment 13b, so that, for example, the circuit 80, 85 operates at the level of the ambient pressure.

If ice-free aqueous solution 71 is to be fed into the crystallization compartment 13a from the storage compartment 13b, it is also possible in this case - i.e. if the buoyancy of the lighter ice alone is not sufficient for the separation of the solid and liquid phases - it is necessary to attach a sieve to the suction end of the line 70 in the reservoir 13b, as has already been described.

Claims (12)

1. As a direct working evaporator trained energy storage for a heating and / or cooling of a building serving absorption heat pump system, in which circulates as a working medium through evaporator, absorber, expeller, condenser and expansion device, and a hygroscopic absorbent that is pumpable even at high concentrations With the help of a pump, the absorber and the expeller penetrate, whereby on the one hand the heat of absorption and on the other hand the heat of condensation is used for heating purposes, or is dissipated as waste heat in the case of cooling, and furthermore the energy store in which part of the working fluid is stored in solid form is part of a second working fluid circuit with at least one low-temperature heat source, characterized in that an aqueous solution (71) serves as the working fluid in the energy store (1), in which at least one solute causes a freezing point reduction of at least 1 K. 2. Energy store according to claim 1, characterized in that the aqueous solution (71) contains the same substances as the absorbent, but the concentrations are chosen so that the freezing point is preferably between -1 ° C and -2 ° C. 3. Energy store according to claim 2, characterized in that a lockable connecting line (27) from the absorber (2) leads into its liquid space (13). 4. Energy store according to claim 1, characterized in that means (14) are provided through which a transition is prevented from liquid from its evaporator area (12) into the absorber (2). 5. Energy store according to claim 1, characterized in that a line (79) provided with a pump (72) leads from its liquid region (13; 13b) into its vapor region (12). 6. Energy storage device according to one of claims 2 to 5, characterized in that its area filled with aqueous solution (71) is divided into two compartments (13a, 13b), the evaporation and ice production taking place in a crystallization compartment (13a) while in other compartment (13b) the ice mash (79) formed is stored. 7. Energy store according to claim 6, characterized in that the storage compartment (13b) is arranged by a height difference ΔH below the ice-making compartment (13a). 8. Energy store according to claim 7, characterized in that the height difference ΔH is approximately 10 m, so that there is no negative pressure in relation to the ambient pressure in the storage compartment (13b). 9. Energy storage device according to claim 1, characterized in that a self-emptying nozzle (15) is provided for feeding liquid working fluid into the evaporator area (12). 10. Energy store according to claim 6, characterized in that means (74) are provided in the ice-making compartment (13a) through which the aqueous solution is moved. 11. Energy store according to claim 10, characterized in that the flow in the ice-making compartment (13a) is designed such that larger ice crystals are preferably fed to the storage compartment (13b). 12. The energy store as claimed in claim 1, characterized in that an ice pulp (79) formed from aqueous solution (71) and ice crystals (78) is fed into the second working medium circuit (80, 85).

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