Discussion on controlled atmosphere storage and it

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Discussion on controlled atmosphere storage and its management

controlled atmosphere storage refers to a storage method that changes the gas composition of the storage environment under suitable low temperature conditions. Broadly speaking, controlled atmosphere storage includes spontaneous controlled atmosphere storage and controllable controlled atmosphere storage. The former refers to that fruits and vegetables are sealed in plastic film with air permeability or plastic film bag or tent with silicon window, and the content of O 2 and CO 2 in the closed environment is spontaneously adjusted under certain temperature conditions by using the respiration of fruits and vegetables and the air permeability of plastic, so as to make it suitable for the requirements of controlled atmosphere storage, which is called MA storage for short. For example, plastic film curtain method, silicone window film sealing method, etc; The latter refers to the storage method of sealing fruits and vegetables in an airtight controlled atmosphere chamber (or warehouse), using the respiration of fruits and vegetables, and using mechanical controlled atmosphere equipment to manually adjust the O 2 and CO 2 gases in the closed system to the appropriate gas composition. Because the former mainly depends on the respiration of fruits and vegetables for gas regulation, it is mainly suitable for short-term storage, and the storage effect is relatively poor compared with the latter. The controlled atmosphere storage we generally refer to refers to the latter, so we focus on the latter. First of all, it should be noted that controlled atmosphere storage does not mean simply regulating gas, but gas regulation based on low temperature conditions

first, the main facilities of controlled atmosphere storage

(I) controlled atmosphere storage

controlled atmosphere storage is developed on the basis of the traditional fruit and vegetable cold storage. Therefore, on the one hand, it also requires the good heat insulation and moisture resistance of the usual cold storage; On the other hand, the controlled atmosphere reservoir has its own characteristics. The most important thing is to require the reservoir to be air tight in order to reduce the exchange of external gas and facilitate the manual regulation of gas composition in the reservoir; In addition, safety should be considered. As the controlled atmosphere storage is a closed cold storage, when the temperature in the storage decreases, the gas pressure also decreases, and a pressure difference is formed on both sides inside and outside the storage. In addition, the pressure difference will be formed on both sides of the enclosure during the operation of the CA equipment and the air tightness test of the CA warehouse. If the pressure difference is not eliminated in time or controlled within a certain range, it will do harm to the enclosure structure; In addition, almost all controlled atmosphere reservoirs are single story buildings

(II) gas generation system

gas generation system is the most important equipment in all walks of life for controlled atmosphere storage, which has increasingly high requirements for materials, and also accounts for the largest investment. The gas regulation in the storehouse is mainly completed through the gas generation system. At present, gas generation systems mainly include hydrocarbon combustion system, ammonia cracking system, pressure swing adsorption system and membrane separation system. Among them, the membrane separation system is a relatively advanced gas generation system. It uses hollow fiber membranes to selectively separate molecules of different sizes, and separates nitrogen and oxygen in compressed air to achieve the purpose of gas regulation. Because of its superior technical performance, reliable product quality and low price, it has been widely used at present

(III) gas purification system

excessive CO 2 in the enclosure must be continuously removed during controlled atmosphere storage of fruit and vegetable products; In addition, some volatile substances released by fruit and vegetable products themselves, such as ethylene and aromatic esters, will have harmful effects if they accumulate in the warehouse. These substances can be removed by a gas purification system. This gas purification system removes gas components such as CO 2, so it is also called gas scrubber or carbon dioxide adsorber

(IV) refrigeration equipment

controlled atmosphere storage does not mean simply regulating gas, but gas regulation based on low temperature conditions. Therefore, controlled atmosphere storage requires refrigeration equipment, that is, refrigerator, including condenser, compressor, evaporator, throttle (also known as expansion valve), etc

(V) other

in addition to the above main equipment, in order to obtain satisfactory storage effects of alloy high carbon steel (or low carbon alloy steel), cold working die steel, etc., some other equipment is often needed, mainly including (1) humidity regulation system, because for most fruits and vegetables, the relative humidity of controlled atmosphere cold storage will be too low, so humidifiers are needed; (2) The gas circulation system is mainly to make the temperature and gas composition of all parts in the storage more uniform; (3) O 2 and CO 2 Analysis and recording instruments should often measure the content of O 2 and CO 2 in the air during storage, so that it can be adjusted in time when it exceeds the index range

second, the main types and market of Ca repositories

from the current domestic situation, there are three main types of Ca repositories, which are mainly manifested in the differences in the body of the repository, and the hardware equipment inside is basically the same. People will feel flustered and stuffy when they hear it. At the same time, we introduce the domestic reference prices of different types of controlled atmosphere storage (including the full set of equipment and related commissioning, training and other costs of nengzhiguang's Nylon modifier that can improve the mechanical properties at high and low temperatures) with the storage volume of 2million Jin (100 tons) as an example

(I) assembly library

this is also recommended by many domestic related manufacturers. It can be directly assembled with heat insulation and air tight materials, so it has the characteristics of short construction period, high efficiency and good quality. But the disadvantage is that the cost is relatively high, which is about 400000 yuan. If advanced air conditioning equipment is adopted, the price may be higher, reaching about 450000 ~ 500000

(II) Civil Engineering Library

there are two cases. One is to use the original cold storage and add air tight layer on this basis. Because there is already a certain foundation, the cost is low; The other is completely rebuilt. If it is the latter, its cost is about 50000 yuan lower than that of the assembly warehouse. The previous situation is certainly lower

(III) large account warehouse

this kind of controlled atmosphere storage warehouse mainly uses the cold storage, installs one or more large accounts of controlled atmosphere storage in the ordinary cold storage, forms a jacket between the account body and the original storage body, and forms a controlled atmosphere environment suitable for long-term storage of fruits and vegetables through off account refrigeration and in account air conditioning. The modified atmosphere curtain mostly adopts non-toxic PVC fresh-keeping film, with silicone rubber windows on it. The warehouse has the characteristics of small investment, fast construction, corrosion resistance and wide storage objects. Among the three types, the price is the lowest, about 200000 yuan

III. management of controlled atmosphere storage

in order to achieve satisfactory storage results, hardware equipment alone is not enough. The management before, during and after storage should also be strengthened. In the early stage of storage, on the one hand, we should pay attention to the selection of raw materials. If the raw materials themselves have been infected or have a high maturity, no matter how advanced the storage method is, it is impossible to obtain a satisfactory storage effect; On the other hand, when warehousing, in addition to leaving necessary ventilation and inspection channels, try to reduce the free space between air conditioners. In this way, the speed of CA can be accelerated, the time of CA can be shortened, and the fruits and vegetables can enter the CA storage state as soon as possible. Therefore, the supply of goods should be fully considered; At the same time, the agricultural products entering the storage room of the controlled atmosphere storehouse are required to be stored in time after harvesting for no more than hours and no more than 48 hours at most (some northern fruits) to ensure the freshness; During storage, regularly check the changes of gas and humidity in the warehouse and adjust them in time. This requires high technology, otherwise it will cause great losses. Therefore, it is suggested to adopt fully automatic controlled atmosphere storage, although the investment is higher, it can reduce some risks; In addition, controlled atmosphere storage requires fast in and out. It is not allowed to import and export goods casually like the ordinary fruit and vegetable cold storage, and the air outside the warehouse enters the controlled atmosphere room casually, which not only destroys the storage state of the controlled atmosphere, but also accelerates the wear of the controlled atmosphere valve and affects the air tightness. Therefore, when fruits and vegetables are delivered, it is best to deliver them at one time or in batches in a short time

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