GB2144531A - A method and a system for building up an ice store - Google Patents

Abstract

For building up an ice store overnight for auxiliary supply of cold energy during day operation water is circulated through injection nozzles 12 in a vacuum container 2 such that the water in the container is gradually converted into slush ice by evaporation cooling. The vacuum is maintained by sucking the vapours off through a simple compressor 16 and supplying the vapours to a refrigerated condenser 22 at such a slightly raised temperature as to enable a condensation without ice generation problems. The condensate is collected and returned to the water in the container 2. During day operation the slush ice is caused to exchange heat with an external cold consuming system 6, 30. <IMAGE>

Description

SPECIFICATION A method and a system for building up an ice store The present invention relates to a method of building up and utilizing a socalled ice store for accumulation of cold. In many cooling installations the need for cooling capacity is changing considerably, typically in connection with a process cooling during the daytime and an entirely lacking or drastically reduced cooling during the night.The associated refrigeration system should hereby principally have a capacity as required during the periods of high cooling demands, but it is already known that with the use of an ice store it is possible to use an underdimensioned and thus relatively cheap refrigeration system; this system may be in constant operation, viz. for building up the ice store during the periods with no or low cooling demands, while its capacity during the other periods may be supplemented by cold derived from the ice store, also called an ice bank.

The conventional ice stores are materially made as a water container, in which -is mounted a tube battery, which consists of a large number of closely juxtaposed tubes and constitutes the evaporator of the refrigeration system. When the ice store is to be built up the water in the container is frozen on the outside of the tubes, and the cold energy thus bound may later be drawn off the ice store by letting the water to be cooled pass along the ice on the tubes, whereby the ice is gradually melted.

These freezing-on systems are, for a given capacity, very voluminous. The evaporator tubes should have a rather large diameter for being effective with respect to the build up of a reasonable volume of ice, and this in connection with the rather high total length of the tubing accounts for the fact that the effective ice space inside the container is considerably smaller than the volume of the container. It is also important that the layer of ice on the single, parallel tubes should not be so thick as to freeze together with the ice layers of the neighbouring tubes, as this would jeopardize the free flow of thawing water through the container, and even in optimally iced condition the container will thus hoid a considerable inactive volume of water between the various ice carrying tubes.

As far as the refrigeration system is concerned it is characteristic that the operation of the long and thick evaporator tube requires a large and therewith expensive charge of refrigerant, and for the formation of a reasonably thick ice layer on the tube the evaporator temperature should be considerably below 0 C, e.g. - 5 to - 10"C, this being uneco- nomical from a refrigeration point of view, when the freezing itself can be effected by a temperature close to zero.

It is the purpose of the invention to provide a method, whereby the ice store may be built up and used in a more advantageous manner, even with the use of a relatively simple ice store structure, at least when large cooling capacities are considered.

The invention is based on the recognition that already known methods and systems for other purposes may be modified so as to be particularly well suited for the present purpose.

According to the invention use is made of the principle of cooling water by vivid evaporation in a vacuum container, in which the water is introduced through spraying nozzles or the like, while the produced vapour is sucked away for maintaining a high vacuum in the container. The cooled product as successively collected in the container may then be removed for some useful cooling purpose.

Thus, by way of example, US-A-2,023,444 discloses the use of cooled water for cooling an air conditioning device, and the international PCT-publication WO 82/03679 discloses an ice production system, in which the evaporation cooling is highly effective, such that the injected water is transformed into snow or ice, which is sluiced out of the vacuum container.

The basic idea of the invention is that an ice store may be built up inside the vacuum container, when the water or another freezing liquid is recycled through the injector nozzles so as to get gradually cooled to form brash ice in the container. The ice particles in brash ice have practically the same temperature as the surrounding liquid, but they hold a much larger amount of cold energy, because they have given away the associated heat of freezing. The recycling of the liquid may go on until a large percentage of the liquid has been converted into brash ice.

The input energy as required for gradually cooling and freezing the liquid will be the energy required for removing the vapour from the vacuum container. This can be done more or less economically, but no matter how it is done it will be appreciated that the required effect will be relatively small, when the conversion can be done over a long period, e.g.

overnight.

During a following period of use the brash ice mass may be gradually melted when caused to exchange heat with some cold consuming installation, either by actuation of a built-in heat exchanger inside the vacuum container or by externally circulating the liquid of the container. During such use the recycling of liquid through the injector nozzle may go on, i.e. the usable cooling effect will be the effect derivable from the ice store plus the operational cooling effect of the vacuum container system as otherwise used, during inoperative periods, to gradually build up the ice store: It will be appreciated that an ice store simply consisting of brash ice (slush ice) will show none of the serious drawbacks of the conventional ice stores.

A remaining problem, of course, is to effect the removal of the vapour from the vacuum container in an economical way. However, this problem has already found an advantageous solution, which is usable here and is described in the said international PCT-publication No. WO 82/03679. The solution is that the vapour is drawn off from the vacuum container through a centrifugal vapour compressor of only one or very few compression stages, whereby the vapour,now with a temperature slightly above the freezing point, is supplied to a condenser as constituted by the evaporator of an ordinary refrigeration system.

The vapour is condensed at a temperature near the freezing point in such a manner that no icing problems occur, and the cold condensate may even be reintroduced into the vacuum container.

In connection with the invention the said condenser need not show any particularly large capacity, and due to an associated small size it may advantageously be built into the top portion of the vacuum container, above a container portion as housing the said vapour compressor, such that an ice store unit according to the invention may appear as a compact unit. The associated refrigeration system may be relatively simple and cheap, not only because of its required low capacity for building up the ice store during a long period of time, but also because its evaporator temperature can be as high as close to 0 C.

Accordingly, the invention comprises both a method and a system for building up an ice store, all as more precisely defined in the appended claims.

In the following the invention is described in more detail with reference to the drawing in which: Fig. 1 is a schematical view of a system according to the invention, and Figs. 2 and 3 are simplified schematical views of two modified systems of the invention.

The system shown in Fig. 1 comprises a vacuum container 2 having a bottom outlet 4, from which water in the container can be pumped through an external heat exchanger 6 by means of a pump 8, the water being returned to the container through a nozzle pipe 10, from which the water is sprayed into the container vacuum through nozzles 1 2 overhead the water surface in the container.

By this injection spraying a pronounced evaporation and an associated cooling of the water will occur, and the water is partially frozen before it hits the water mass 14 in the container.

The vapour as produced by the injection spraying has to be removed for maintaining the low pressure in the container 2, and this removal is effected by means of a simple centrifugal compressor 16, which sucks the vapour up through a drop separator 1 8 to an upper chamber 20, in which is provided a refrigerated condenser 22 as constituting the evaporator unit of a conventional refrigeration system F, the condenser of which is designated 24. The pressure in the chamber 20 is only slightly higher than in the container 2, e.g. 7 mm Hg and 4 mm Hg, respectively, but this is sufficient to condition the condensation of the cold vapour to take place without the formation of ice on the condenser 22. The condensate is collected on an inclined tray 25 and is guided through a pipe 26 for direct returning into the container 2.

During "night operation" the system is used for progressively freezing the water 14, the water being recirculated through the exterior heat exchanger 6 without this unit otherwise being operative. The conditions are adjusted such that the water, just prior to the following "day operation" period, has been converted into brash ice as far as possible, i.e.

without any initial total freezing of the water.

In other words, the brash ice as floating on or in the water should be produced, optimally, to such an extent as to reach almost down to the bottom outlet 4 or the pump 8.

In "day operation" the heat exchanger 6 is actuated. This exchanger being additionally included in a circuit comprising a pump 28 and one or more devices 30, which should be cooled with a capacity larger than that of the refrigeration system F. The latter system may continue working for cooling the volume of water 14, but during the day operation the water will get heated through the heat exchanger more than corresponding to the cooling in the vacuum container, i.e. the water will show a steadily decreasing content of ice, the melting heat of which is utilized for the cooling of the exterior circuit of the heat exchanger 6.

In an ideally dimensioned system all the ice in the water 14 will be melted just at the end of the day operation period, without the water temperature having raised substantially above 0 C. Thereafter, when the pump 28 in the external circuit is stopped, a new night phase is started, during which the refrigeration system F operates solely to produce a new filling of brash ice in the volume of water 14.

During the day operation the working conditions in the vacuum cooling system may be slightly changed, because the temperature of the water as injected through the nozzles 1 2 will be higher than during night operation, e.g. 8"C and oec, respectively. By the injection the temperature may be some 5 C corresponding to an absolute pressure of some 6.5 mm Hg in the lower chamber of the vacuum container. The compressor 1 6 shall then com press the vapour from 6.5 to 9.8 mm Hg as corresponding to a temperature of 11"C, whereby a suitable condensation temperature in the condenser 22 will be + 5 C as com pared with - 2"C to 0 C during the night operation, all by way of example.

In Fig. 2 it is shown schematically that during night operation the pump 8 may cause the water to circulate through a switch over valve 32 and a pipe 34 direct to the nozzles 12, corresponding to a bypassing of the heat exchanger 6 of Fig. 1. However, in Fig. 2 this exchanger is avoided, and in day operation the valve 32 is switched so as to make the pump 8 supply the cooling water directly to the external system.

As shown in Fig. 3 the water may be circulated through the nozzles 1 2 through an internal circulation pipe 36, while the heat exchange with the external circuit may be effected through an internal heat exchanger as illustrated by a coil 38 inside the vacuum container. As in Fig. 1 the external system comprises a selectively operable circulation pump 28.

Inasfar as the volume of liquid 14 is housed in a closed circuit and the condensed vapours thereof are reintroduced into the liquid it will be possible to use not only water, but any suitable liquid such as alcohol.

Claims (8)

1. A method of building up an ice store for later delivery of cold to an external circuit, characterized in that water or another freezing liquid is circulated through inlet means in a liquid cooler of the vacuum container type until the liquid therein assumes a brash ice state, the vacuum in the container as necessary for evaporation cooling of the liquid being maintained by drawing off, in a known manner, the vapour from the vacuum container to an actively refrigerated condenser, the freezing liquid being accessible for internal or external heat exchange with at least one other medium.

2. A method according to claim 1, whereby the freezing liquid is circulated through external heat exchanger means for reintroduction into the vacuum container through the injection means such as spray nozzles.

3. A method according to claim 1, whereby the vapour is caused to be condensed at a location above the freezing liquid in the vacuum container and the condensate is returned directly to the freezing liquid in the container.

4. An ice store for operation according to the method claimed in claim 1, characterized in comprising a vacuum cooler container of the type having inlet means for introduction of water or another freezing liquid to be cooled by evaporation and means for sucking away the vapour produced hereby and feeding the vapour to a refrigerated condenser, means for circulating the freezing liquid in the container through said inlet means for building up brash ice in the container, and means for effecting heat exchange between the freezing liquid and an external cold consuming system.

5. An ice store according to claim 4, in which the vapour condenser is located inside the top portion of the vacuum container, above a vapour compressor therein, and in which collector means are provided for collecting the condensate and leading it directly back to the liquid or liquid/brash ice mixture in the container.

6. An ice store according to claim 4, in which the freezing medium is circulated from a liquid outlet on the container, through exterior heat exchange means and back through said injector means.

7. An ice store according to claim 6, in which there is arranged an intermediate heat exchanger between the freezing liquid circuit and the exterior, periodically cold consuming external system.

8. An ice store according to claim 4, in which the heat exchanger means are arranged inside the vacuum container.