Process for reducing energy consumption in the storage of fruits and vegetables in cold rooms

Abstract

A method for reducing energy consumption in the storage of fruit and vegetables in cold rooms, where the cold used for storage is provided by a given source, for example using mechanical cold, characterized in that, in replacement of all or part of said source, liquid nitrogen is injected into the cold room where the products are stored, to bring about a very rapid drop in the temperature of the stored products, a drop being, depending on the products considered, within a chosen range of decrease speed, the injection of nitrogen also making it possible to replace the air present in the cold room around the products with gaseous nitrogen resulting from the vaporization of the injected cryogen.

Description

Title of the invention: Method for reducing energy consumption in the storage of fruit and vegetables in cold rooms

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

[0002] All fruits and vegetables breathe, and are therefore subject to releasing heat during storage in cold rooms or in any other environment.

[0003] The technique of placing packaging in a "controlled atmosphere" (known as MAP in this industry) is based on controlling this respiration, to enable long-term preservation of the products.

[0004] In the case of cold room 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 formed around the products is generally based on an injection of nitrogen: 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 is of 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, it is then desired to propose a new method for storing plants in a cold room, allowing: • To reduce by a very significant factor, up to 10, the time required for the core temperature of stored products to drop. • Quickly achieve and maintain a controlled atmosphere around the products by injecting liquid nitrogen. (Liquid nitrogen also provides the necessary frigories to maintain the low temperature of the cold room). • Depending on the products targeted, 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 humidity in the cold room using a gas washing 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 remembered 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, ambient air is replaced with a specific combination of gases, usually nitrogen, carbon dioxide, and oxygen, to maintain optimal storage conditions.

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

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

[0011] In a modified atmosphere, the ambient air is changed in the packaging to slow down product deterioration. This may include adding preservative gases, reducing oxygen, or controlling humidity.

[0012] This method is more common and less expensive than controlled atmosphere. 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 the atmosphere to be modified.

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

[0015] Let us consider in the following the example of the conservation of endive roots.

[0016] For the production and forcing of endives, electricity represents 90% of energy consumption (530 kWh / t of endives produced). It is particularly used for the production of cold and ventilation. Endives are produced all year round, and for this, good preservation of the roots and appropriate forcing management is necessary.

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

[0018] For forcing endive roots, the temperature requirements depend on the physiological stage of the plants at uprooting and the varieties. As the season progresses, with the increase in the shelf life of the roots, it is necessary to lower the temperature by about one degree per month to respect the forcing period and obtain a chicory that meets marketing requirements. The main sources of heat are due to the respiration of the roots and the heating of the nutrient solution. This is why it is rare to have to heat the ambient air; on the contrary, we seek to cool it. This prevents the end of the chicory from opening and its growth too quickly. This cooling can be ensured at certain times by fresh air taken from outside. However, this source of cold is not sufficient for forcing taking place from March to October.Gas is used for heating premises and forcing rooms (6% of energy requirements).

[0019] As a result, endive growers are highly dependent on electricity to produce high-quality endives that meet consumer requirements. Producers' efforts continue to implement systems and processes that reduce their dependence on the electricity and gas grid in order to reduce energy bills (heat recovery systems, methanization, and building compliance). This requires heavy investments that not all producers can afford.

[0020] Controlled atmosphere storage is an interesting way to reduce the electricity consumption of cold rooms. Using less energy is a logical response to curb rising refrigeration costs.

[0021] The invention then relates to a method for reducing energy consumption in the storage of fruit and vegetables in a cold room, where the cold used for storage is provided by a given source, for example using mechanical cold, characterized in that, in replacement of all or part of said source, liquid nitrogen is injected into the cold room where the products are stored, to bring about a very rapid drop in the temperature of the stored products, a drop being, depending on the products considered, within a chosen decrease speed range, the injection of nitrogen also making it possible to replace the air present in the cold room around the products with 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” must be understood to mean that the intervention of the cryogen according to the invention will allow to lower the temperature to the desired temperature range in one day or even less than one day, typically a few hours, when commonly, in a conventional cold room, it is necessary to wait several days, up to 10 days, to lower this temperature to the desired proportions.

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

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

[0026] The use of a cryogenic liquid such as liquid nitrogen allows for the instant release of high refrigerating power. The change of state of this cryogenic liquid also allows for the rapid supply of a large volume of inert gas (1 liter of liquid nitrogen releases 680 liters of gaseous nitrogen). Products stored in this way in a cold room are quickly put into a state of respiratory slowdown. The addition of a CO2 and ethylene capture process allows for the reduction of air renewal rates.

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

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

Claims

Claims

1. A method for reducing energy consumption in the storage of fruit and vegetables in a cold room, where the cold used for storage is provided by a given source, characterized in that, in replacement of all or part of said source, liquid nitrogen is injected into the cold room where the products are stored, to bring about a reduction in the temperature of the stored products, a reduction being, depending on the products considered, within a chosen decrease speed range, the injection of nitrogen also making it possible to replace the air present in the cold room around the products with gaseous nitrogen resulting from the vaporization of the injected cryogen.

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

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

4. Method according to one of the preceding claims, characterized in that the cold used for storage is provided by a source consisting of mechanical cold.