0 The Prior Art

A number of systems for keeping goods cooled or frozen are known, from the conventional cooling with ice, cooling with mechanical cooling system, cooling by means of the cold generated when dry ice (C0 ₂ ice) evaporates, and s cooling by means of vaporized liquified gases e.g. C0 ₂ or Ν ₂ at low temperature.

The means for maintaining the goods cooled or frozen vary considerably from small portable cooling means, like cooling bags, to large industrial cooling plants. 0 When using liquid carbon dioxide as freezing agent it is known from Norwegian Patent No. 16961 to introduce the li¬ quid carbon dioxide in controlled manner into a tight, closed freezing container in which the goods to be cooled or frozen are present, and the liquid carbon dioxide will provide the 5 necessary cold owing to its expansion to gas in the freezing container. Therefrom the carbon dioxide gas is passed into a hollow room which surrounds the freezing container, and the carbon dioxide gas expands further in the hollow room and flushes the outside of the freezing container and cools the o freezing container further. This freezing apparatus is intended for use in households, hotels, restaurants, hospitals or on ships etc. By means of the known apparatus the wall sur¬ rounding the hollow room which surrounds the freezing container per se is heat-insulated whereas the walls surroun- 5 ding the freezing container per se is not heat-insulated. From European patent application No 175044 it is known when using C0 ₂ .dry ice to perform cooling of various goods. The dry ice is kept in a separate container in an in¬ sulated box which is placed in the freezing room per se for

the goods. An air supply is passed about the dry ice container, and the dry ice evaporates by heat exchange with the air. The evaporated carbon dioxide is in controlled manner introduced into the cooling room through a thermostat control- led throttle valve for providing so called basic cooling in the cooling room, and in order to obtain supplemental cooling part of the evaporated C0 ₂ may be introduced into the air supply through another throttle valve and a nozzle, for heat exchange with the dry ice. Due to the current set up in the air supply by the blowing of evaporated carbon dioxide into the heat exchange air supply, the evaporation of dry ice in the dry ice container increases, and the cooling effect increases correspondingly.

Thus, the inventions according to the two publications mentioned above utilize a so called primary cooling effect (basic cooling) and a secondary cooling effect (supplemental cooling) for one and the same cooling or freezing container for goods of various kinds which are sen¬ sitive to heat or which may readily putrefy. According to this prior art, the same freezing agent is used, i.e. liquid respectively dry C0 ₂ , which upon evaporation provides the com¬ bined cooling or freezing effect. This means that a particularly exactly controlled supply of evaporated C0 ₂ , from liquid C0 ₂ or from C0 ₂ dry ice, to the cooling or freezing room for the stored goods must be made due to the integrated utilization of evaporated C0 ₂ for obtaining both the primary freezing or cooling effect and the secondary or supplemental freezing or cooling effect.

Objects of the Invention

It is an object of the invention to provide a process and means for freezing of goods whereby the disadvantage men¬ tioned above connected with the integrated provision of the primary freezing effect and the supplemental freezing effect when using one and the same freezing agent for obtaining the two effects is avoided. More particularly, it is an object of the present invention to provide a means which is particularly suited for use for storing and transportation of frozen comes¬ tibles and for storing and transportation of various kinds of

special products, e.g. within medicine and biotechnology. It is a particular object of the invention to provide a means which will be especially preferred for transportation purposes and in particular where surface container transport (by ships, trailers, trains) must compete with air transport, i.e. where the market sets high quality demands and the product costs are relatively high.

Summary of the Invention Thus, the invention relates to a process of freezing goods in an inert gas atmosphere, wherein for the freezing of the goods an inner container is used in which the inert s freezing gas atmosphere is maintained, and an outer container surrounds the inner container while forming an intermediate room between the inner container and the outer container, the intermediate room being kept cooled, and the process is characterized therein that the intermediate room is cooled by o the use of a mechanical cooling system.

The present invention also relates to a means for freezing of goods in an inert freezing gas atmosphere, comprising an inner container for freezing of the goods, a means for controlled supply of inert freezing gas to the inner 5 container, and an outer container which surrounds the inner container so that an intermediate room which is cooled is formed between the inner container and the outer container, and wherein the wall about the outer container is heat insulated, and the means is characterized therein that the 0 means for controlled supply of the inert freezing gas is arranged in the inner container, that the wall about the inner container is heat-insulated, that the inner container is without communication with the intermediate room, and that in the intermediate room there is a means for mechanical cooling 5 thereof.

According to a preferred embodiment of the means ac¬ cording to the invention a shield is arranged in the inner container between the means for controlled supply of the freezing gas and the goods to be frozen, in order to protect

the means for supply of the freezing gas and contribute to the distribution of evaporated inert freezing gas to the goods in the inner container.

According to a further preferred embodiment of the means of the invention a container for inert freezing gas is arranged in the inner container and communicates with the means for controlled supply of the inert freezing gas.

According to yet another preferred embodiment of the means of the invention an evaporator battery is arranged in the intermediate room as the cooling part of the mechanical cooling system which cools the intermediate room.

Brief Description of the Drawing The invention will now be further described with s reference to the attached drawing which shows a vertical sec¬ tion through an embodiment of the means according to the in¬ vention.

Detailed Description of the Invention an Drawing 0 with Best Embodiment

The means according to the invention is in principle based upon four main components as shown in the drawing, viz. a) a storage/freight container 1 for goods to be frozen, b) an outer room or intermediate room 4 which is kept cooled 5 by means of a mechanical cooling system 9, c) a container 6 with inert medium for freezing of the goods, d) control organ 7, 8 for supply of the inert freezing medium to the storage/freight container 1.

Moreover, in the drawing it has been shown that the o wall 2 about the inner room in the inner container 1

(storage/freight container) is thermally insulated and that the wall 5 about the intermediate room or the outer room 4 also is thermally insulated. A door opening 3 from the inner room 1 has small ventilation slots respectively control valve 5 or valves for letting out small amounts of inert gas which is generated in order to maintain the freezing temperature in the inner room, and a shield 10 is placed in the inner room in order to protect a container 6 with the inert freezing medium and the control organ 7, 8 and in order to contribute to the

distribution of inert gas to the goods in the inner room 1. An evaporator battery 9 which constitutes the cooling part of a mechanical cooling system which cools the outer room or the intermediate room 4 is placed in the outer room or the inter- s mediate room.

The wall 2 about the inner room 1 has been built with thermal insulation having an insulation effect which is related to how low the temperature is to be in the inner room 1 compared with the temperature in the outer room 4. When in- o sulating the wall 2 regard must also be taken to the intended uses of the means according to the invention, viz. whether it is a transport unit or a stationary storage unit for the goods to be frozen. The wall 5 about the outer room 4 is in its turn thermally insulated in accordance with the use of the means as s transport unit or stationary storage unit and in accordance with the temperature conditions on both sides of the wall 5 (exterior air temperature and air temperature in the outer room 4).

The materials of the walls 2, 5 will depend upon the foreseen use of the means according to the invention. For transport purposes as container sandwich walls made of plas¬ tics or steel are most usual. For larger freezing stores there are several alternatives for the wall materials and also for the insulation. It is in any case important to ensure that there is a good water vapor barrier on the warm side of the walls (on the outside) in order to prevent uptake of moisture in the insulation. For insulating the walls 2 and 5 conven¬ tional insulating materials for cooling and freezing purposes may be used. The selection will in all cases be based on a consideration of economy and design technology. Moreover, the shield 10 may be made of the same material as the inner wall 2.

In order to keep the inner and outer room separated from each other in order to obtain an outer room 4 of desired volume large enough to distribute cooling air about the inner room 1 the outer room 4 and the inner room 1 must be mutually braced. This bracing is dependent upon the building method for the means and upon the use of the means. For example, use of the means as transport unit requires stronger bracing than use

of the means as stationary storage unit.

For the inner room 1 it is recommended that the tem¬ perature of the inert atmosphere, C0 ₂ or N ₂ , be maintained in the range from -30 °C till -70 ^β C, and for the outer room 4

5 with mechanical cooling system it is recommended that the temperature be maintained in the range from -18 °C to -30"C. The inert freezing medium in the container 6 may consist of C0 ₂ in liquid form or as dry ice, or of N ₂ in liquid form. For the control organ 7/8 for the supply of C0 ₂ or N ₂ it has been shown o in the drawing that it comprises a thermostat 8 for temperature control. The control may also be thermal control of dry ice melting (e.g. dry ice blocks in insulated boxes). In the drawing the control organ 7/8 has been shown as a thermostat 8 controlled valve 7 but also other forms of s control may be resorted to. Because the outer mechanical cooling system 9 ensures a certain freezing temperature it may for some uses be sufficient to let out a small but constant amount of freezing agent through a valve 7 of quite simple design in order to maintain the desired temperature in the o inner container 1. Moreover, for some uses the most suitable supply of cooling agent may be by the use of dry ice blocks in thermally insulated packings with adapted insulation value in relation to the coldness yield desired, e.g. dry ice blocks in foamed polyurethane boxes of suitable thickness. 5 The means according to the invention is based on a combination of three principles for freeze preservation, viz. a) traditional mechanical freezing system, b) inert atmosphere maintained in a thermally insulated room, and 0 c) extra low freezing temperature by utilizing latent heat of dry ice or liquid C0 ₂ (or liquid N ₂ ). A such combination of said three principles for freeze preservation means that extraordinary low temperature and inert gas effect are utilized in a thermally insulated inner room which in its turn 5 is cooled in an outer room.

It is important that the supply of inert freezing agent is controlled in order to avoid that the consumption of the inert freezing agent, C0 ₂ or N ₂ , becomes (unrealistically) high, and with the means according to the invention this

control may take place independent upon the secondary cooling effect which is to be maintained in the surrounding outer room. Thereby a more flexible and more readily controllable freezing system is obtained than when using the means described above in accordance with the prior art.

The combination according to the invention of freezing with inert medium and freezing with mechanical cooling system together with the inner insulated room makes independent control of temperature and gas concentration/gas consumption possible. Thereby energy consumption and costs may be optimally adapted to the goods and to the actual storage time. The means according to the invention also substantially increases the safety against accidental thawing of the goods compared with previously known systems for freezing with inert medium.

By means of the means according to the invention a practically absolute preservation is obtained without it being necessary to go all the way down to the extremely low freezing temperatures which are necessary in order to obtain comparable preservation conditions (-70 °C and lower) when using known freezing means in which inert gas is used as freezing agent. Accordingly, the costs of preservative freezing using the means according to the invention are favourable compared with alternative systems of corresponding preservation effect. When using the means according to the invention extra good preservation of fish is obtained which is readily subjected to freeze denaturation, drying out and rancidity. Examples of such products are schri ps and products of salmon, and fat fish, like herrings and mackerels. The means may also be of interest for freeze preservation of several product types and offers great advantages. Examples of such product types are shellfish in general, eel and special products of e.g. sea urchins, hard roe in general and fish products for pharmaceutical use (e.g. shark products which are subjected to rapid freeze denaturation and rancidity).

Even though the means shown in the drawing for the supply of freezing agent to the inner room is intended for supply of liquid C0 ₂ or liquid Ν ₂ which when coming into the inner room evaporates with formation of the inert freeze

atmosphere, the means may also be adapted for supply of dry ice (C0 ₂ -ice). This may be done in the form of blocks of dry ice which are supplied in boxes having correctly adapted ther¬ mal insulation. When using the means according to the invention chemical advantages are obtained in the form of a combination of reduced chemical reaction rate, reduced protease and lipase activity and absence of oxygen, which together provide for a substantial retardation (and partly complete stop) of the deterioration of the goods.

Further, when using the means according to the inven¬ tion the water vapor pressure above the frozen goods, and thereby the water activity, becomes extremely low. This reduces the drying out potential of the goods when stored, and the drying out during storage may thereby become quite minimal.

Fresh and living fish has enjoyed substantial market progress on important markets at the cost of frozen fish. This is due to frequently occurring quality failure in the freezing chains. In Japan and at other places efforts to develop improved freezing technology are made, primarily by making use of extremely low freezing temperatures, so called super freezing. The use of the means according to the present inven¬ tion is based on a system which might be termed "Inert Freezing" and is a good alternative within said development because extreme keeping quality can be obtained at more moderate temperatures by the use of the present means.

It should also be mentioned that the means according to the invention is well suited for surface freeze transport for quality competition with air freight of e.g. fresh fish. Thereby inter alia significant environmental advantages will be obtained. For example, a ship transport from Norway to Japan may require 150 kg oil per ton payload. The freight rate may be as low as 500 NOK per ton payload for transport by ship against 20000 NOK per ton payload for air freight.

The means according to the invention may open for a qualitatively safe freight by boat and thereby inter alia enable better utilization of incidental catches in the fisheries because more exotic types of fishes and products may

then arrive at the demanding markets in Europe, USA or in Asia in qualitatively good condition and thereby become more readily saleable on said markets.