WO2004042295A1

WO2004042295A1 - A procedure and system for producing a cryogenic product and application of the product

Info

Publication number: WO2004042295A1
Application number: PCT/NO2003/000369
Authority: WO
Inventors: Åse SPANGELO; Aage Grimsland; Stig Are Karlsen; Arve Ryen; Ingunn Sviggum; Frank Normann Andersen
Original assignee: Yara International Asa
Priority date: 2002-11-04
Filing date: 2003-11-04
Publication date: 2004-05-21
Also published as: AU2003278620A1

Abstract

The present invention concerns a procedure and system for producing a cryogenic product, more precisely supercooled ice, and application of this product. In accordance with the present invention, the cryogenic product is produced based on ice in various forms/pieces. The ice, which is made from fresh water and/or salt water, possibly with other additives, is mixed with a cryogenic agent such as carbon dioxide in solid form or liquid form and/or liquid nitrogen and/or liquid air to form a mixture. The carbon dioxide is subsequently permitted to sublimate almost completely and/or the nitrogen and/or the liquid air is permitted to boil before the product is finished and the carbon dioxide gas and/or nitrogen gas is removed from the product. The system comprises a mixer (2 or 102) with an inlet (3 or 107) for the supply of a cryogenic agent and a supply pipe (5 or 103) for the supply of ice, and the mixer comprises means (2 or 102) for mixing the products stated and an outlet (6 or 105) for the removal of the finished product. An extraction system (4 or 104) is provided to remove carbon dioxide gas and/or nitrogen gas. The temperature in the cryogenic product can be maintained, the temperature increase can be reduced, or the temperature in the product can be further lowered by storage in a freezing room. The cryogenic product is particularly well suited for the processing/treatment/transport/storage of products, for example foods, especially fish and other seafood products.

Description

A Procedure and System for Producing a Cryogenic Product and Application of the Product

The present invention concerns a procedure and system for producing a cryogenic product, more precisely supercooled ice, and application of this product.

Ice is used today in various operations for temperature control in, among other things, treatment/transport/storage of foods such as fish. Ice produced by ice producers has a temperature of around 0°C or lower, usually -0.1 °C, on delivery to the customer, and then gradually melts to form water in operations above freezing point. Ice can be made from various mixture ratios of water/salt water, possibly with other additives. One problem with this product that is offered on the market is that when, for example, fish is stored for a few days at the temperature course that this product follows, bacterial decomposition may occur. Temperature is one of the factors that determines the shelf life of foods.

GB 2,146,943 concerns production of composite pellets consisting of dry ice particles coated with water. The water forms an ice film that envelops the dry ice particles and delays their sublimation. The dry ice particles will have a temperature of down to around -80°C. One disadvantage of this product is that it will have a relatively low temperature for a period of time until the surrounding layer of ice is broken down. Subsequently, the dry ice will sublimate relatively fast with the associated rise in temperature. The product's usefulness in connection with storage of easily perishable goods seems therefore to be low.

With the present invention, the above problem can be reduced or avoided. With the present invention, it is now possible to create a product that can be adapted, in terms of temperature, to the products to be processed/treated/stored/transported so that an optimal temperature course is maintained during the operation. Moreover, the product will be harmless to use as the product residues are water, possibly salt water.

The above advantages and other advantages can be achieved with the invention as it is defined in the attached claims.

The present invention will be described in further detail in the following by means of examples and figures, where:

Fig. 1 shows a diagram of a system in accordance with the present invention for batch production of the product.

Fig. 2 shows a diagram of a system in accordance with the present invention designed for continuous production of the product.

Fig. 3 shows the product being used on a fishing boat.

Fig. 4 shows a temperature course in caught fish, treated traditionally and treated with the product in accordance with the present invention.

Figure 1 shows a diagram of an apparatus in accordance with the present invention, designed for production of the product in batches, in which ice and a cryogenic agent such as LCO₂ (liquid carbon dioxide) or LIN (liquid nitrogen) or liquid air are supplied to a mixer 2 (mixing methods other than that shown in the drawing can be used) via a supply pipe 5 and an LCO₂, LLN or a LAIR tank 1 respectively. The mixer may comprise one or more agitators (not shown). The store 1 for liquid carbon dioxide may comprise a standard LCO₂ tank with an outlet in the base for removal of liquid carbon dioxide. This is fed via a pipe with a shutoff valve to one or more nozzles 3, possibly snow horns, for injection of liquid carbon dioxide into the mixer. When liquid carbon dioxide flows out of the nozzles 3, the liquid (LCO₂) will be depressurised and carbon dioxide snow and carbon dioxide gas will be formed. The surplus carbon dioxide gas can be removed from the mixer 2 via an extraction system 4 comprising an RPM-controUed fan located in the upper part of the mixer. Part of the surplus gas may be fed into the supply pipe 5 for ice via a duct 10 to precool the ice that is fed in via the supply pipe. Equivalent equipment to that described above can be used for injection of LIN or liquid air into the mixer and for removal of nitrogen gas. LCO₂, LIN and liquid air may all be supplied to the mixer from separate stores (not shown).

In connection with the mixer 2, devices are shown for measuring the temperature 8 and for measuring the carbon dioxide (or possibly nitrogen) concentration 9. One meter of each type is shown in the figure mounted both at the base of the tank and at its upper part for measuring gas concentration and temperature. The devices stated may be connected to a control unit (not shown) that may be preprogrammable. The purpose of the devices stated will be explained in a description of a process course for the creation of the cryogenic product.

The mixer 2 has an outlet 6 for removal of the product when it is ready. The mixer may be designed to be inclinable so that the outlet will constitute the mixer's lowest point during emptying. The mixer may be fitted with a discharge device (not shown) to remove the product from the mixer. The product may thus be fed into a container 7 that may be insulated. The container 7 may also have a system for maintenance of cold by part of the carbon dioxide gas being fed via pipes 11 to the container.

Surplus gas that cannot immediately be used to advantage can be fed back to the tank 1 via a pipe 12 and a system for liquefaction by means of condensation compression (not shown in detail).

Alternatively, dry ice snow or dry ice pellets may be fed into the mixer to avoid the ice clumping. The dry ice may be added via the same opening as the ice. The system shown in the figure for the supply/expansion of liquid carbon dioxide or liquid nitrogen or liquid air in the base of the mixer may then be superfluous. The treatment can take place until the dry ice has almost completely sublimated and the gas has been removed.

Process description for batch production:

Ice and carbon dioxide in liquid or solid form and/or nitrogen and/or liquid air are added/supplied to the mixer in such a way that clumping is avoided, h one specific embodiment, this can be done by a given quantity of liquid carbon dioxide being injected at the base of the mixer 2. The liquid carbon dioxide will be depressurised and be converted into dry ice. The mixer's agitators will ensure an even distribution of dry ice in the mixer. The agitators may be driven by an infinitely adjustable motor (not shown). A quantity of ice is subsequently supplied via the supply pipe 5, after which the ice and dry ice are agitated to form a mixture. The ice may be made from fresh water, salt water or a mixture of the two or with other additives and may have various forms and sizes (0.5 cm and greater). During this operation, cold will be applied to the ice while the dry ice sublimates and becomes carbon dioxide gas. Devices for measuring temperature and carbon dioxide gas concentration monitor the process and send signals to the preprogrammable control unit.

If the temperature in the mixer 2 has become too high after a given period of time, additional LCO₂ (or LIN or liquid air) may be supplied. If the temperature has become too low, additional ice may be supplied. When, after a certain period, a sufficiently low carbon dioxide gas concentration is measured in the mixer, this indicates that the sublimation is decreasing. At a sufficiently low level of sublimation, the batch is emptied into the container 7. The same applies if a sufficiently high oxygen gas concentration is measured.

When sensors are used for the temperature, the carbon dioxide gas and/or oxygen gas concentration and the time elapsed, the values measured may be coordinated to form the basis of the response of the control unit. Alternatively, it is possible to operate with threshold values for individual sensors so that the control unit responds to one given value in connection with values measured at the base of the mixer while a different value may produce a response for measurements in the upper part of the mixer.

The control unit can adjust the supply of LCO₂, alternatively LL or alternatively liquid oxygen and ice and control the speed of the mixer and the extraction fan.

Continuous production

Figure 2 shows a diagram of a system in accordance with the present invention, designed for continuous production of a cryogenic product. As in the previous example, the system comprises a store or a tank 101 for the supply of liquid carbon dioxide (LCO₂), liquid nitrogen (LLN) or liquid air to an inlet 107 in a mixer via a pipe with a shutoff valve. The mixer may comprise a mixing screw 102 that is designed to rotate in an oblong, cylindrical housing that encloses the mixing screw. The mixing screw may be driven by an infinitely adjustable electric motor. LCO₂ and/or LLN and/or liquid air is supplied in a manner equivalent to that shown in the previous example by means of nozzles/snow horns placed in an area upstream of the mixing screw (not shown), h addition to the nozzles stated, one or more nozzles may also be placed downstream of the mixing screw. A supply pipe 103 for ice is mounted downstream of the former nozzles. Further downstream of the supply pipe stated, an extraction system 104 is mounted, where cryogenic gas (CO₂ and/or N₂ and/or liquid air) is extracted and fed into the supply pipe 103 to precool the ice. The length of the mixer is adapted to the other operating conditions so that, at its outlet 105, almost all solid CO₂ is removed when this agent is used. The cryogenic product leaves the outlet 105 and is put into an insulated container 106. As in the previous example, devices may be mounted in the housing of the mixing screw to measure temperature and gas concentration (also the temperature of the extracted gas). These devices may be connected to a control unit (not shown) to monitor and check the process. The control unit may also be connected to means for adjusting the supply of cryogenic agent (LCO₂ and/or LLN and/or liquid air) and ice, and control the speed of the motor that drives the mixing screw (not shown). Moreover, the extraction system 104 may comprise an infinitely adjustable fan that is controlled by the control unit so that a large or small quantity of cryogenic gas may be removed from the mixing screw.

Alternatively, dry ice snow or dry ice pellets may be fed in at the upstream end of the mixing screw. The dry ice may be added via the same opening as the ice. The system stated in the example for the supply/expansion of liquid carbon dioxide and/or liquid nitrogen and/or liquid air in the base of the mixer will then be superfluous.

hi the previous examples, the initial temperature of the ice may be 0°C or lower. Solid carbon dioxide will have a temperature of approximately -79°C. Liquid air has a temperature of -194°C. Liquid nitrogen has a temperature of -196°C. With different mixing ratios of the quantities of cryogenic agent and ice in the mixture, it is possible, in accordance with the present invention, to produce ice with a temperature that, in theory, will lie between -0°C and -79°C or -194°C or - 196°C respectively.

Supercooled ice at a temperature of between -10°C and -180°C in accordance with the present invention will have very favourable areas of application. The raw materials in the mixture may generally consist of 70-95% by weight of ice and 30-5% dry ice or liquid nitrogen or liquid air. A mixing ratio of 85% by weight of ice and 15% by weight of carbon dioxide snow or pellets produces a temperature in the finished product (supercooled ice) of approximately -55°C.

Supercooled ice can have a number of areas of application such as cooling in bleeding containers and cooling in containers after cleaning, processing, transport and storage of fish in the ratio 1 part supercooled ice to 1 to 2 parts fish (by weight). The product is particularly well suited for treating roundfish that are delivered to the market as fresh fish (not frozen).

Among other things, the fish will have a firmer consistency, reduced bacterial growth and better odour and taste (on account of reduced TMA). In other words, the storage time can be increased considerably in relation to competing solutions in a comparison of quality levels. Figure 3 shows an application of the product on board a fishing boat, on which putting out and hauling in fishing tackle are indicated by 201, 202. Caught fish are cut/have their throats cut at 203 and are placed in the bleeding container 204, which may contain a cryogenic product produced in accordance with the present invention and mixed with seawater or freshwater. Subsequently, the fish can be cleaned/washed at the station 205, then cooled at the station 206 and then placed in the station 209 for further cooling. Trawl crates 207 for storing fish and containers for cooling media (SICE) 208 are shown in the hold of the boat.

Maintenance of temperature

The temperature of SICE can be further lowered by storage in a freezing room/freezing cabinet, or the temperature can be maintained or the increase in temperature can be reduced. The temperature in the freezing room/freezing cabinet can be in the interval -10 to -50°C.

The procedure for the above can be described in the following stages:

1. Letting out the autoline with hooks

At the start of fishing, the autoline with hooks is let out in the sea. The hooks are fixed to a continuous line that is lined up in slides on board on deck. The number of slides varies from boat to boat.

2. Hauling in the autoline

After a while with the autoline in the sea, the hooks are hauled up again, back onto the slides in the boat.

3. Cutting/Throat-cutting When the hooks are taken up out of the sea, one person usually removes the fish from the line and cuts their throats before throwing/placing the fish in a container for bleeding 204.

4. Bleeding container with supercooled ice (SICE)

The bleeding container contains fish in water that is cooled with SICE. The fish have only had their throats cut at this stage and have not been cleaned.

The temperature in the bleeding container will vary with the quantity of SICE used. The temperature in the SICE water should be low enough to ensure that the fish are cooled to a core temperature of 0°C or lower as soon as possible.

The theoretical value for the freezing point is -2°C in salt water (34 per thousand). Experience shows that the practical value is -1.5°C at the lowest temperature achieved.

The fish will remain in the bleeding container (depending on the volume of work on the boat) for 30 minutes or more, provided that the core temperature of the fish has reached the desired value.

5. Cleaning/washing

After the fish have been bled and cooled in the bleeding container(s), they are cleaned and washed of blood residue/gut residue before being placed in a cooling container with SICE.

6. Cooling

Experience shows that, as for 204, the temperature in the cooling containers 206, 209 will be a minimum of -1.5°C.

The time for which the fish remain in the cooling container will vary, but is estimated at 30 minutes or more. 7. Storage crates

After the fish have been hauled on board the boat, had their throats cut, been cleaned and cooled, they are placed in storage crates. For optimal temperature control (core temperature -1.5-0°C), SICE should be placed in the storage crates.

The SICE is first placed on the bottom of the storage crates and on the heads and tails after the fish have been placed in the crates. This may vary.

The quantity of SICE in each crate will vary, depending on the quantity of fish in each crate.

In the same way as for the SICE water in the bleeding container, the lowest temperature achieved in practice will be -1.5°C.

8. SICE

Depending on the estimated catch volume, x numbers of containers of SICE are taken on board and placed in the boat's hold or another suitable location.

The temperature of the SICE will be approximately -60°C, depending on the mixing ratio between the quantities of ice and dry ice used.

Figure 4 shows a temperature course in caught fish, treated traditionally and treated with the product in accordance with the present invention.

Fish are mostly treated traditionally today. That means that the fish are cut, left to bleed, cleaned and left dry until they are brought ashore. They are then packed in crates with ice. h this case, it took 3 hours from the time at which the fish were caught until they were placed in crates with ice. The quantity of fish was approximately 10 kg and the quantity of ice 10 kg. SICE treatment means the treatment shown in the figure in which SICE is added to salt water containers both for bleeding and after cleaning. The fish were packed in crates with SICE when they were brought ashore. The quantity of fish was approximately 10 kg and the quantity of SICE 10 kg.

The top curve shows the ambient temperature. This was approximately 19°C when the fish were brought ashore. The fish were packed immediately. It took approximately 45 minutes from when the fish were brought ashore until they were put in the cold store. The temperature in the cold store fluctuated between 0.6 and 9°C (defrosting the cold store). The cold store door was closed throughout this period of 12.5 hours. The crates with fish were then opened and the quality of the fish was assessed.

SICE C2 represents fish that have had SICE treatment on the boat and SICE added to the crate. The curve shows the temperature development in the core of the fish. On account of the SICE treatment on the boat, the start temperature is -0.5°C. During storage in the cold store, the temperature falls further to -1°C on account of the SICE added to the fish crate.

SICE C4 represents different fish that have had SICE treatment on the boat and SICE added to the crate. The curve shows the temperature development in the core of the fish. On account of the SICE treatment on the boat, the start temperature is -0.6°C. During storage in the cold store, the temperature falls further to -1°C on account of the SICE added to the fish crate.

STD Cl represents fish that have had standard treatment on the boat and ice added to the crate. The curve shows the temperature development in the core of the fish. On account of the lack of cooling on the boat, the start temperature is 17°C. During storage in the cold store, the temperature falls to 0°C in 1.5 hours on account of the ice added to the fish crate. The lowest temperature measured was -0.2°C. STD C7 represents fish in a different crate that have had standard treatment on the boat and ice added to the crate. The curve shows the temperature development in the core of the fish. On account of the lack of cooling on the boat, the start temperature is 16°C. During storage in the cold store, the temperature falls to 0°C in 5 hours on account of the ice added to the fish crate. The lowest temperature measured was -0.1 °C. It takes longer to cool these fish because they were considerably larger than the fish in STD Cl.

The quality assessment after 12.5 hours in the cold store showed a very clear difference in quality between the fish in these four crates. The fish handled with SICE had a very much higher quality than the fish handled with ice.

The product proposed (SICE) will cover a number of advantageous applications:

- Faster cooling of the product treated.

- Lower product temperature. - Less clumping of supercooled ice than standard ice.

- The product is drier with supercooled ice.

- More cold per weight unit.

- The residual product is water.

- Lower freight costs on account of lower gross weight. - Red gills are obtained when used with fish, for example.

- Less slimy skin, when used with fish, for example.

- Pale fish eyes are avoided when used with fish, for example.

- More reliable temperature control produces better quality and thus a higher price.

- The low temperature of the product extends the period of inactivity of bacteria and, with fish, for example, postpones rigor mortis.

Claims

1. A procedure for producing a cryogenic product based on ice in various forms/pieces, characterised in that ice is made from fresh water and/or salt water, possibly with additives, and is mixed with a cryogenic agent such as carbon dioxide in solid form or liquid form (LCO₂) and/or nitrogen in liquid form (LLN) and/or liquid air to form a mixture with the desired temperature, after which the cryogenic agent is permitted to be converted almost completely into a gaseous phase before the product is finished and the gaseous phase stated is removed from the product.

2. A procedure in accordance with claim 1, characterised in that a predetermined quantity of ice is mixed with a predetermined quantity of a cryogenic agent such as carbon dioxide in solid form, LCO₂ or LLN or liquid air or a mixture of these agents.

3. A procedure in accordance with claim 1, characterised in that ice is mixed with carbon dioxide in solid form, LCO₂ or LLN or liquid air or a mixture of these agents in a continuous process.

4. A procedure in accordance with claims 1-3, characterised in that ice is precooled by means of carbon dioxide gas and/or nitrogen gas and/or cold air that is formed in the process.

5. A procedure in accordance with claims 1-3, characterised in that carbon dioxide gas and/or nitrogen gas and/or cold air that is formed in the process is used to maintain the temperature of the product produced during subsequent storage of the product.

6. A procedure in accordance with claims 1-3, characterised in that the carbon dioxide in solid form either consists of pellets or similar made in advance or is made continuously by the depressurisation of liquid carbon dioxide.

7. A procedure in accordance with claims 1-3, characterised in that liquid nitrogen or liquid air is supplied continuously via one or more nozzles (3).

8. A system for producing a cryogenic product, characterised in that it comprises a mixer (2, 102) with an inlet (3, 107) for the supply of a cryogenic agent such as carbon dioxide and/or nitrogen and/or liquid air and a supply pipe (5, 103) for the supply of ice and that the mixer comprises means for mixing the products stated and an outlet (6, 105) for the removal of the finished product.

9. A system in accordance with claim 8, characterised in that it also comprises means (4, 104) for the removal of cryogenic gas such as carbon dioxide gas or nitrogen gas.

10. A system in accordance with claim 9, characterised in that it also comprises a control unit that receives signals from devices that measure temperature, time and cryogenic gas concentration and that the control unit can adjust the supply of cryogenic agent and ice, the quantity of cryogenic gas that is removed and the speed of the mixer.

11. Application of a cryogenic product produced in accordance with claims 1-7, characterised in that it is used for the processing/treatment/transport/storage of products such as foods, including fish.

12. Application in accordance with claim 11, characterised in that the temperature in the cryogenic product is between -10 °C and -180°C.