A process for reducing energy consumption in the cold storage of fruits and vegetables.

Abstract

A process for reducing energy consumption in the storage of fruits and vegetables in cold rooms, where the cold used for storage is supplied by a given source, for example by mechanical refrigeration, is characterized by the fact that, in replacement of all or part of said source, liquid nitrogen is injected into the cold room where the products are stored, in order to effect a very rapid decrease in the temperature of the stored products, a decrease which, depending on the products considered, is within a chosen range of rate of decrease, the injection of nitrogen also making it possible to replace the air present in the cold room around the products with the gaseous nitrogen resulting from the vaporization of the injected cryogen.

Description

Title of the invention: A method for reducing energy consumption in the storage of fruits and vegetables in cold storage

[0001] The present invention relates to the field of cold storage rooms for the storage of plants, and in particular fruits and vegetables.

[0002] All fruits and vegetables respire, and are therefore subject to releasing heat during storage in a cold room or elsewhere in any other environment.

[0003] The technique of putting packaging under "controlled atmosphere" (known as MAP in this industry) relies on controlling this respiration, to allow long-term preservation of the products.

[0004] In the case of cold storage, a rapid drop in the temperature of the cold rooms also contributes to slowing down the respiration of fruits and vegetables. The controlled atmosphere created around the products is generally based on nitrogen injection: to lower the oxygen content in the atmosphere surrounding the products, but also to maintain a level of CO2 and humidity.

[0005] When the gas mixture recognized as optimal for the variety of plants considered has a composition such that the sum O2 + CO2 is less than 21%, it becomes necessary to periodically absorb the excess carbon dioxide by sending the gas mixture to a capture process.

[0006] According to the present invention, we wish to propose a new cold storage method for plants, allowing: • To reduce by a very significant factor, up to 10, the time required for the core temperature of stored products to drop. • To quickly achieve and maintain a controlled atmosphere around the products by injecting liquid nitrogen. (Liquid nitrogen also provides the cooling necessary to maintain the low temperature of the cold room). • Depending on the products concerned, to be able to control the CO2 content around the products with a capture process. • Depending on the products concerned, to be able to control the humidity in the cold room by a gas scrubbing process. • Depending on the products concerned, in the case of certain fruits and vegetables, to be able to control the Ethylene content in the atmosphere surrounding the products by an appropriate process.

[0007] It should be noted that the concepts of controlled atmosphere and modified atmosphere are two methods of managing the gaseous environment around food products to extend their shelf life. Here are their main differences: - Controlled Atmosphere:

[0008] In a controlled atmosphere, the ambient air is replaced by a specific combination of gases, generally nitrogen, carbon dioxide and oxygen, to maintain optimal storage conditions.

[0009] This method is mainly used for high-end products, such as seafood, meats, cheeses and bakery products.

[0010] It requires special equipment, such as controlled storage chambers. - Altered Atmosphere:

[0011] In a modified atmosphere, the ambient air is modified within the packaging to slow down product deterioration. This may include the addition of preservative gases, the reduction of oxygen, or humidity control.

[0012] This method is more common and less expensive than controlled atmosphere packaging. It is used for products such as vacuum-packed vegetables, dairy products, and snacks.

[0013] The products are generally packaged in special plastic films which allow for modification of the atmosphere.

[0014] In summary, controlled atmosphere packaging involves replacing ambient air with a specific gaseous mixture, while modified atmosphere packaging alters the gaseous environment inside the packaging to extend the shelf life of the products. Both methods aim to reduce microbial growth and food spoilage.

[0015] Let us consider in what follows the example of the preservation of endive roots.

[0016] For the production and forcing of endives, electricity accounts for 90% of energy consumption (530 kWh / t of endives produced). It is used primarily for refrigeration and ventilation. Endives are produced year-round, and for this, proper root preservation and appropriate forcing techniques are necessary.

[0017] The preservation of endive roots represents the largest energy consumption item at 56% (297 kWh / t) (38% for forcing the endives in the forcing room). The use of a refrigeration unit (temperature and humidity) controlled) is the method chosen in this field which allows the production potential of endives to be maintained over a very long period.

[0018] For forcing endive roots, temperature requirements depend on the physiological stage of the plants at harvest and the variety. As the season progresses and the storage life of the roots increases, it is necessary to lower the temperature by about one degree per month to meet the forcing time and obtain a chicory that meets market requirements. The main sources of heat are root respiration and the heating of the nutrient solution. Therefore, it is rarely necessary to heat the ambient air; on the contrary, the aim is to cool it. This prevents the tip of the chicory from opening and its growth from becoming too rapid. This cooling can be achieved at certain times by drawing in fresh air from outside. However, this source of cold is not sufficient for forcing, which takes place from March to October.Gas is used for heating the premises and forcing rooms (6% of energy needs).

[0019] As a result, endive growers are highly dependent on electricity to produce endives of a sanitary quality that meets consumer requirements. Producers are continuing their efforts by implementing systems or processes that reduce their reliance on the electricity and gas grid in order to lower energy bills (heat recovery systems, methanization, building upgrades). This requires significant investments that not all producers can afford.

[0020] Controlled atmosphere storage is a promising approach to reducing the electricity consumption of cold storage rooms. Using less energy is a logical response to curb rising refrigeration costs.

[0021] The invention relates to a method for reducing energy consumption in the storage of fruits and vegetables in cold rooms, where the cold used for storage is supplied by a given source, for example by means of mechanical refrigeration, characterized in that, in replacement in whole or in part of said source, liquid nitrogen is injected into the cold room where the products are stored, in order to effect a very rapid decrease in the temperature of the stored products, a decrease being, depending on the products considered, within a range of chosen rate of decrease, the injection of nitrogen also making it possible to substitute the air present in the cold room around the products with the gaseous nitrogen resulting from the vaporization of the injected cryogen.

[0022] Depending on the nature of the fruits and vegetables stored, a chosen residual oxygen threshold is also maintained in the chamber.

[0023] In any event, the expression "very rapid drop in temperature" should be understood to mean that the intervention of the cryogen according to the invention will allow to lower the temperature into the desired temperature range in one day or even less than one day, typically a few hours, whereas commonly, in a conventional cold room, it is necessary to wait several days, up to even 10 days, to lower this temperature to the desired proportions.

[0024] As will be understood from the foregoing, the objective here is to achieve a state of slowed plant respiration as quickly as possible. The process is not intended to stop respiration, but to slow it down. It is therefore recommended to add to the injection process a system for capturing gases produced by residual respiration and / or maturation (CO2 and / or ethylene).

[0025] It is therefore recommended to add to the injection process a system for capturing CO2 and ethylene, systems which are known to those skilled in the art.

[0026] The use of a cryogenic liquid such as liquid nitrogen allows for the instantaneous release of a high cooling capacity. The change of state of this cryogenic liquid also allows for the rapid release of a large volume of inert gas (1 liter of liquid nitrogen releases 680 liters of nitrogen gas). Products stored in this way in cold storage are quickly brought into a state of respiratory slowing. The addition of a CO2 and ethylene capture process makes it possible to reduce air exchange rates.

[0027] In summary, the present invention implements the following: 1. A rapid drop in temperature (within a few hours). 2. A rapid decrease in oxygen content. 3. Decontamination of the atmosphere by reducing (depending on the product being treated) the presence of CO2 and ethylene. 4. Control of humidity levels.

[0028] Applying the process according to the invention to endive roots, by rapidly lowering the temperature of the roots from +15 to -2 °C, first reaching 1% residual oxygen in the chamber, then maintaining 6% residual oxygen and a temperature of -2°C, the reduction in the energy requirement of the producing site was estimated at approximately 33%.

Claims

Demands

1. A process for reducing energy consumption in the storage of fruits and vegetables in cold storage, where the cold used for storage is supplied by a given source, characterized in that, in replacement in whole or in part of said source, liquid nitrogen is injected into the cold storage room where the products are stored, in order to lower the temperature of the stored products, a decrease being, depending on the products considered, within a chosen rate of decrease, the injection of nitrogen also making it possible to substitute the air present in the cold storage room around the products with the gaseous nitrogen resulting from the vaporization of the injected cryogen.

2. A method according to claim 1, characterized in that a residual oxygen threshold is maintained in the chamber using said gaseous nitrogen, chosen according to the products that are stored.

3. A method according to claim 1 or 2, characterized in that an operation is carried out to capture the gases resulting from the residual respiration and / or maturation of the products, namely CO2 and / or ethylene.

4. A method according to any one of the preceding claims, characterized in that the cold used for storage is supplied by a source consisting of mechanical cold.