The present invention concerns a method for cooling containers, wherein cold is generated in a primary circuit containing a cooling medium and is supplied via a heat exchanger to a cold carrier in a secondary circuit, where the secondary circuit's cold carrier flows into a container through pipes with releasable couplings, transferring cold to the container through a heat exchanger.

The invention also concerns a cooling system for implementation of the method, comprising a primary circuit with a cooling medium for generating cold, a secondary circuit with a cold carrier and releasable couplings for connecting a container to a heat exchanger for transferring cold from the cold carrier to the container, and a heat exchanger for supplying cold from the primary circuit to the secondary circuit.

There are previously known cooling systems for cooling containers in connection with transport of food such as fish and the like, where the cold is generated by a primary circuit and transferred to a secondary circuit. An appropriate cold carrier in the secondary circuit, normally brine, transfers the cold into transportable containers, thus cooling their contents. The containers are exposed to cooling in the cooling circuit for as long as possible, whereupon they are disconnected from the circuit for further transport, e.g. by trailer or rail, on the final stage of the journey to the recipient.

Another known method is the use of transport containers with a store of a cold carrier, e.g. ice or dry ice, where the ice or the dry ice is placed in the container together with the goods which require to be cooled, and give off their cold during that part of the transport when the container is not connected to the cooling circuit.

Thus, in the known cooling systems there is a limit to how long a transport container can be located outside the cooling system before the contents are warmed to an unacceptable temperature. Alternatively, the cooling medium

in the form of ice or dry ice requires to be placed in the container manually or by other means at the same time as the goods are placed therein, which entails extra work and increased costs.

The object of the present invention is to provide a method for cooling containers and a cooling system where the containers can be kept cold in a simple manner without the supply of cold from the cooling system.

This object is achieved with a method and a cooling system of the type mentioned in the introduction, characterized by the features which are indicated in the claims.

In this patent application the terms "emit cold", "supply cold" a d "transfer cold" are used instead of the more correct "supply heat", "emit heat" and "transfer heat". This terminology has been chosen in order to make the description easier to understand.

The invention therefore consists of a cooling system consisting of a primary circuit and a secondary circuit connected to a heat exchanger, where the cold is generated in the primary circuit in the known manner. The cold is transferred from the primary circuit to the secondary circuit via the heat exchanger, where the cold is passed to a container by means of a cold carrier. The secondary circuit has one or more cold stores for storage of cold and emission of cold in the event of an interruption in the cold supply. This interruption may be due to operational problems or a failure of the energy supply to the cooling system, or it may be an interruption in the cold supply resulting from the disconnection of the container from the cooling system.

In a preferred embodiment one of the cold stores is located inside the container, with the result that the container is self-sufficient in cold emission during transport.

The cold carrier may preferably be pressurized carbon dioxide. This is a cold carrier which affords moderate dimensions, small volume and no corrosion in the pipe system. The cold store or cold stores may consist of dry ice, which can be generated directly from the carbon dioxide by reducing its pressure.

The dry ice can be stored in a separate compartment in the container for subsequent emission of cold when the dry ice turns into carbon dioxide in a gaseous state, which can be done by the emission of the carbon dioxide directly into the container's atmosphere.

The cold store may also consist of an enclosed quantity of pressurized carbon dioxide. When the pressure of the carbon dioxide is reduced, dry ice is produced, which can then emit its cold into the container in the same manner as that described above.

When a cold store is employed in the secondary circuit some carbon dioxide will have to be consumed, thus making it necessary to replenish with new carbon dioxide. Since it is natural to employ the cooling system in connection with transport means with internal combustion engines, such as ships, this carbon dioxide is preferably supplied by means of a C0 ₂ generator which generates CO ₂ from the internal combustion engine's exhaust gases.

The invention will now be explained in more detail by means of an embodiment, with reference to the drawing, where the figure is a schematic flow chart for the cooling system according to the invention.

A cooling system 1 consists of a primary circuit 2 and a secondary circuit 3. The primary circuit 2 is of a known type and contains a cooling unit 4 for generating cold. The cold is transferred to the secondary circuit 3 through a heat exchanger 5. In the secondary circuit 3 a cold carrier flows through a pipe system 6 in the direction indicated by the arrow P. In this embodiment the cold carrier is pressurized carbon dioxide, C0 ₂ . A circulation pump 7 passes the carbon dioxide through the heat exchanger 5 for cold absorption from the primary circuit, and on through a cold store 8 where cold can be emitted for storage, for subsequent emission back to the secondary circuit. The cold carrier flows on through a releasable coupling 13 into a container 9 with goods (not shown). The container 9 is insulated with insulation 10, thus reducing as far as possible the heat supply from the environment. In the container 9 the cold carrier can either flow into a cold store 11 , which will be described in more detail later, or it can flow into a heat exchanger 12 for emission of cold to the container 9 by means of a fan 16. From the heat

exchanger 12 the cold carrier can flow out of the container through a new releasable coupling 13 and on to the circulation pump 7.

The two cold stores 8 and 1 1 are only illustrated schematically in the figure, and may be designed in many ways. Nor does the figure show valves, instruments and other components which are necessary for a complete cooling system, since these other components are of a known type, and are of no consequence for the invention.

The cold stores 8 and 1 1 may consist of dry ice, and are supplied with cold by the controlled release of the secondary circuit's carbon dioxide, the carbon dioxide thereby forming dry ice as the pressure is reduced. Cold is emitted from the cold stores when the dry ice evaporates, forming carbon dioxide in gaseous form during emission of cold. In the cold store 8 this cold is used to cool the liquid carbon dioxide which is located in the pipe system. In the cold store 11 the cold can be emitted in several ways: the cold can be transferred from the carbon dioxide in gaseous form to the carbon dioxide in the pipe system, the carbon dioxide in gaseous form can emit its cold to surfaces in the container, or the carbon dioxide in gaseous form can be led via an outlet 15 into that part of the container which contains the goods, thus cooling them directly. This latter method is advantageous for the container's atmosphere, since the carbon dioxide will reduce the growth of micro-organisms and contribute to the preservation of the foodstuffs.

The cold stores 8 and 1 1 can also consist of enclosed quantities of pressurized carbon dioxide. A store of this kind can be achieved by means of a pressure vessel, or by using pipes and manifolds which already exist in the container, perhaps increasing their dimensions. This latter alternative is considered to be advantageous, since it provides a simple and reasonably priced version of the cold store. Cold is emitted by pressure reduction under the controlled release of a portion of the carbon dioxide, thus forming dry ice. The cold can then be transferred as described above.

When the cold stores 8 and 11 are used, carbon dioxide will be consumed in the secondary circuit. Hence, in order to maintain the operation the supply of carbon dioxide has to be replenished. In the embodiment in the figure this is

done by means of a C0 ₂ generator 14. The C0 ₂ generator may preferably be based on membrane technology, being supplied with exhaust gases from an internal combustion engine. The exhaust gases are passed through the membranes, and due to the properties of the membranes, C0 ₂ is separated from the other exhaust gases. The C0 ₂ generator further contains a compressor which pressurizes the carbon dioxide before it is supplied to the secondary circuit.

In the above the invention has been explained with reference to a specific embodiment described by means of a schematic flow chart. The process can be advantageously controlled by a microprocessor (not shown) which receives information from instruments and a control console, controlling the process by means of controlled valves. Thus it is obvious that a number of different possibilities exist for instrumentation, control and localisation of valves in the process. Similarly it is obvious that the pipe system can be designed in other ways, the pump 7 , e.g., and the supply of carbon dioxide from the C0 ₂ generator 14 being placed in other locations, there can be connections for more containers 9, more cold stores 8 can be provided in the secondary circuit, and bypass lines can be provided around the different components.

The cold emission from the dry ice stores can be self-regulating, the cold in the secondary circuit normally being kept at a level where the evaporation of carbon dioxide from the dry ice is zero or minimal. Should the temperature rise in the container the evaporation will increase by itself, and the carbon dioxide in gaseous form will cool the interior of the container. In this manner a reasonably priced and reliable regulation is obtained of the cold emission from the cold stores.