A METHOD AND A SYSTEM FOR PRODUCTION OF LOOSE ICE AT LARGE CAPACITY

Abstract: Loose ice is produced at large capacity by injecting water into a vacuum chamber (2), in which ice or snow is generated by flash evaporation of the water. The loose ice is sluiced out of the vacuum chamber (2) and the large volume or flow of low pressure vapour is extracted by means of a simple single stage centrifugal compressor (16) which supplies the slightly compressed vapour to an external, positively refrigerated condenser (22) operating at a condensation temperature just slightly above 0<o>C, whereby the condensation pressure of the vapor is low enough to condition or enable the use of a compressor (16) of maximum simplicity, while on the other hand the condensation temperature is just sufficient to avoid icing problems in the condenser (22). The required auxiliary refrigeration system (24, 26, 28) may be a simple standard system of high efficiency because of the relatively high evaporator temperature, and also the vapour compressor (16) may be a simple unit, because it is handling the vapour only at the lower end of the pressure and density range thereof. The condenser (26) of the auxiliary refrigeration system will be usable as an efficient heater means for an external heating system.

Description: A method and a system for production of loose ice at large capacity. The present invention relates to the production of loose ice at large capacity. In conventional small scale ice production the ice is formed by contact freezing and then broken off the freezer surface, but in large scale production such a method is far too expensive. A more suitable method or production principle is dis¬ closed in the German Patent Specification No. 917.491, in which it is proposed that water is sprayed into a vacuum chamber holding such a low pressure that the water tends to evaporate almost instantaneously, where¬ by the associated temperature drop by evaporation causes the remaining water to freeze. The ice may be sluiced out continually from the vacuum chamber without giving rise to loss of vacuum, and the major problem, of course, will be to remove the considerable amounts of vapour and maintain the high vacuum anyway. This will require a large capacity compressor operable to handle the vapour 3 at a rate of e.g. 50.000-1.000.000 per hour from a vacuum of only some 2-3 mm Hg, and such a solution is unrealistic. In * the said German Patent Specification is suggested the improvement that the vapour as let out from the high capacity compressor is fed to a condenser, in which the vapour is condensed by active cooling by means of cooling water at ambient temperature, 20-24 C. It will be suffi¬ cient, then, that the compressor is able to cause a va¬ pour pressure rise from 2-3 mm Hg to about 25 mm Hg as corresponding to a condensation temperature of said 20-24 C. However, even a pressure rise of this restricted magnitude requires a very expensive and complicated multi¬ stage compressor, and it is believed that the entire system would still be unrealistic. The invention relates to a method of the type as here discussed and as defined in the introductory clause of claim 1 , and it is the purpose of the invention to provide a further improved method, whereby a large scale ice production is realistically possible. According to the invention the vapour as exhausted from the vapour compressor is supplied to a condenser which is cooled by active refrigeration so as to operate at a condensation temperature at or only slightly above the freezing temperature of the water, whereby the vapour is compressed by means of a centrifugal compressor through a single or at most a few compressor stages. It will be readily understood that the use of a positively refrige¬ rated condenser will involve a complication as compared with a condenser as cooled by cooling water at ambient temperature, but it is far more important that the com¬ pression of the vapour will be correspondingly effectable through a single or a few compressor stages only. The invention is based on the recognition that a possible reduction of the necessary number of compression stages will be particularly important if or when the re¬ maining stage or stages refer to the low pressure end of the pressure range in question. In the low end of the pressure range the density of the vapour is very low, and the first and only stage or the first few stages of the vapour compressor, therefore, may be designed in a relatively simple manner for handling the required large flow of vapour, while higher compressor stages tend to be increasingly more complicated and expensive. In practice the use of a refrigeration system for the active cooling of the vapour condenser will be a con¬ siderably simpler measure than the provision of a multi¬ stage high capacity compressor, because the required compressor of a single or a few stages shall handle the vapour solely in the lowermost end of the pressure and density range thereof, whereby the compressor may be re- latively simple and inexpensive. The required refrigerat¬ ing system may also be a simple system, e.g. of an already existing standard type, because in operation the cooling requirements will not go below the freezing temperature of the water. With the system according to the invention it is possible to produce large amounts of loose ice, without the ice being difficult to loosen from any freezer surface, but an associated condition will be that no corresponding icing problem occurs elsewhere in the system; for this reason it is important that the said refrigerated condenser should operate at or just above, but not below 0°C. The invention relates to both a method and a system and is defined more precisely in the appended claims. In the following the invention is described in more ' detail with reference to the drawing which shows schematic¬ ally a system according to the invention. The system shown comprises a heat insulated vacuum chamber 2 having a bottom outlet sluice 4. A small vacuum pump 6 is provided for compensating for the loss of vacuum which is unavoidably caused by the sluicing out of the material, and the pump 6 is usable even for building up the required vacuum prior to the operational start of the system. Midways in the chamber 2 is provided a water inlet nozzle 8 to which water is supplied from a water supply source 12 through an inlet pipe 10 and through a deaerator 40. To the right in the drawing is shown an auxiliary refrigeration system generally designated A and used for cooling the vacuum chamber 2 through a cooler unit 3 and optionally for cooling the inlet water to the nozzle 8 in 'a cooler unit 14. Topwise of the vacuum chamber 2 is mounted a water vapour compressor 16 which is operable at high capacity to suck up the vapour from the chamber 2 and discharge the vapour flow into a heat insulated conduit 18 leading to a condenser 20, the cooling element 22 of which is constituted by an evaporator unit of a refrigeration system as shown in the left hand side of the drawing. This system comprises a refrigeration compressor 24, a condenser 26 and an evaporator as constituting said cooling element 22 and designed as an evaporator condenser in connection with an associated liquid separator 28 for the refrigerant. In the drawing is shown an evaporator unit with self circulation of the refrigerant, but of course other types of evaporators may be used. The suction side of the refrigeration compressor is connected with the top of the separator 28. The system is adapted to work at an evaporator temperature of ca. 0 C, while the auxiliary refrigeration system A as shown to the right is adapted to produce lower temperatures. The condenser 20 has a bottom Outlet 34 for the condensed water vapour, and this water is passed through a pressure pump 36 and a pipe 38 back to the water supply pipe 10 or through a pipe 39 for some other purpose. Prior to the operational start of the plant a vacuum of ca. 2 T 5 mm Hg is built up in the heat insulated system 2,18,20 by means of the vacuum pump 6 or by other means. Thereafter the compressor 16 is started, and the water supply to the diffusor nozzle 8 is opened upon both the main and the auxiliary refrigeration systems having been started. The water sprayed out from the nozzle 8 will be subjected to a sudden pressure drop to said ca. 2 5 mm Hg, whereby the water will boil up and get cooled by the associated vivid evaporation so as to assume a temperature of ca. -7 C, whereby the remaining free water in the water fog or drops will rapidly freeze into ice, i.e. it will form snow or ice particles. Of the injected amount of water ca. 6/7 will freeze to snow or ice, while 1/7 will be separated as vapour. The freezing will take place almost momentarily, such that no non-frozen water, possibly in supercooled condition will reach the walls G■-? of the vacuum chamber before the ice formation has taken place, i.e. there will not be built up any rigid ice layer on these walls. The produced mass of snow or ice particles is let out through the bottom sluice 4 to a suitable receptacle 34, and the generated water vapour is continually sucked out by means of the compressor 16. The compressor 16 is designed so as to effect a pressure rise of the vapour from said ca. 2.5 mm Hg to ca. 6 mm Hg. in the conduit 18, corresponding to a temperature rise from ca. -7 C to ca. +5°C. As mentioned, the condenser 20 is operated at an interior evaporator temperature of ca. 0 C, and by exterior condensation of the vapour at ca. 5 C corresponding to a pressure of ca. 6 mm Hg the condensate will be prevented from freezing. The condensed water will constitute a real destillate and may, upon delivery from the pressure pump 36, be collected for sale as distilled water, though with the limitation that the water has not been heated to pasteurization temperature and cannot, therefore, be designated as sterile. However, it will be perfectly usable for many technical fields of application, though produced at such high amounts that it may be difficult to find use for all of it. The water, therefore, should possibly be regarded as clean waste water, or it may, as shown, be returned to the water supply 10 to the nozzle 8, whereby it will be advantageous that the temperature of the return water will normally be lower than that of the water as supplied from the source 12. It should be remarked, however, that for the operational economy of the system it is in fact not too important whether the supply water is particularly cold, because the production of cold by the evaporation of the water in the vacuum chamber is much larger than the amount of heat which is represented by a slightly decreased temperature of or in the inlet water itself. The system illustrated on the drawing is adapted to produce loose ice at a capacity of ca. 15 tons per hour. - A preferred purpose of such production is to provide for a continuous flow of loose ice to be dumped into deep 5 mining localities for cooling the air to a reduced and more convenient working temperature than otherwise existing in deep mines. It will be appreciated that the technical main problem as solved by the invention is the problem of creating a 10 considerable temperature change of an inlet medium with the use of a minimized amount of external energy in connection with large scale production. It is clear in advance that the consumption of external energy cannot be minimized beyond or even reduced to what is theoretic- 15 ally or ideally necessary for effecting the desired temperature change, but it will be appreciated both that the system according to the invention is operable to effect the ice production in an economical manner and that the economy will be still much better if it is possible 20 to make use of the counterresult of the freezing process, viz. the heat development as occuring in the condenser 26 of the refrigeration system which serves the purpose of condensing the vapour as subtracted from the vacuum chamber 2 through a simple one stage or few stage compres- 25 sor 16. A large production of ice is inevitably associated with a correspondingly large heat production of the condenser 26. While under circumstances the ice production may be regarded as economical even if the heat generation of the 30 condenser 26 is accepted as waste heat, it will invertedly be possible to appreciate the heat generation of the condenser 26 as useful and economical even if the associated production of ice is considered as a waste phenomena. Thus, the system may be used as an efficient high capacity heat 35 pump serving to extract heat energy from a relatively cold starting medium, e.g. river or sea water at a temperature as low as some 1-3 C. With the invention is obtained an effective utilis¬ ation of the vaporization heat/freezing heat of the water, such that even with a small resulting temperature differ- ence between the inlet water from the source 12 and the outlet water from the condenser 20 it has been possible to create both large amounts of ice and large amounts of heat, the latter as derived from the condenser 26. The main condition for this operation is the formation of the vapour as an intermediate operative heat carrier from the vacuum evaporation chamber 2 to the condenser 20, and the main problem is to effect the transfer of the vapour in a sufficiently economical manner:. As already mentioned, it is the main aspect of the invention that this transfer of the vapour is effected by means of a simple single stage or few stages centrifugal compressor combined with the use of a condenser 20 which is actively refrigerated to a temperature level which is low enough to correspond to the pressure of the vapour as compressed from the vacuum chamber through said one or few stages only, yet high enough to prevent the formation of ice on the condenser It should be mentioned that a single stage vapour compressor capable of extracting a large vapour flow from a vacuum chamber is known from the USA Patent Specification No. 3,202,343, which discloses a system for producing sweet water from sea water by letting the sea water into a vacuum chamber and collecting and condensing the vapour produced hereby. In that system, however, the condensation of the vapour is effected with the outside of the vacuum chamber itself constituting the condenser, and the result of the process is a separation of sweet water from the sea water rather than a pronounced and usable production of cold and/or heat. The effect added by the operation of the vapour compressor is to be regarded as a compensation for thermal and other losses in the system, while in connection with the invention the compressor is an active ' ■ unit in a regular heat pump system of the relevant particular type. Nevertheless, the compressor 16 as used with the invention is a highly important unit, and it is deemed appropriate to refer to the said USA Patent Specification No. 3,202,343 in order to show more detailed a type of a simple compressor which is well suited for use in a system according to the invention together with another simple main part, viz. the refrigeration system 24,26,28 as operating at a relatively high evaporator temperature, which, as well known, conditions a simple and highly efficient refrigeration system. When the main purpose of the system is to produce ice it is to be preferred that the product of the vacuum chamber 2 is dry ice, while for optimizing the heat production of the condenser 26 when heat pumping is the main purpose it will be advisable to accept wet ice to be produced; when wet ice is accepted the vacuum need not be as high as for dry ice production, and even a slight increase of the vacuum chamber pressure from e.g. 2.5 mm Hg to 3-4 mm Hg will result in a better effect factor of the heat pump system. Correspondingly and naturally enough wet ice will be cheaper to produce than dry ice because of its generally higher temperature, and the economy of the production system, of course, should be related to the desired character or temperature of the ice product.

Claims: CLAIMS : 1. A method of producing loose ice at large capacity by injecting water into a vacuum chamber in which the pressure is low enough to cause the water to freeze by flash evaporation, the vapour as hereby generated being exhausted from the vacuum chamber by means of a vapour compressor, which brings the vapour to an external condenser at a pressure and temperature level by which the vapour is effectively condensable by said condenser so as to leave the system as condensed water, while the ice as produced in the vacuum chamber is sluiced out therefrom, characterized in that the vapour as exhausted from the vacuum chamber (2) is only slightly compressed through a single stage or at most a few stages of a centrifugal vapour compressor (16), and that the vapour thus compressed is condensed in said external condenser (20) by a condensation temperature at or only slightly above the freezing temperature of the water as correspond¬ ing to the only slightly increased pressure of the com¬ pressed vapour. 2. A method according to claim 1, whereby the external condenser (20) is cooled by means of a conventional refrigeration system (24,26,28) , the condenser (26) of which operates at such increased temperature as to be coolable by a cooling medium at ambient temperature. 3. A system for producing loose ice according to the method claimed in claim 1 , comprising a vacuum chamber and means for injecting water into the chamber for ice generation by flash evaporation, means for sluicing out the generated ice from said chamber and external compressor means for extracting the generated vapour from the chamber and supplying the compressed vapour to a condenser having an outlet for the water as condensed therein, characterized in that the said compressor means is a single few stages centrifugal compressor (16) operable to raise the vapour pressure to a value corresponding to a con¬ densation temperature between 0 C and 10 C, preferably be- - tween °C and 4 C, and that the condenser (20) is positive- ly refrigerated in being constituted by the evaporator (22) of a preferably conventional refrigeration system (24,26, 28) operable to provide for said condensation temperature at or only slightly above 0 C. 4. A system according to claim 3, in which the condenser (26) of the said refrigeration system (24,26,28) is con¬ nected with an external heating system for utilizing the heat as developed by this condenser (26) complementary to the cooling of the said evaporator condenser (20,22) for condensing the vapour as received from the vapour co - pressor (16).

Inventors: VILLADSEN VAGN HOVGAARD
Applicants: SABROE & CO AS THOMAS THS, VILLADSEN VAGN HOVGAARD, THOMAS THS SABROE & CO AB
Application year: 1982
Main classification: F25C1
IPC codes: F25B7, F25C1