Facilities for detailed explanation of the hottest

The detailed facilities of controlled atmosphere storage

II. Controlled atmosphere storage facilities

(I) controlled atmosphere warehouse

the warehouse structure and refrigeration equipment of the controlled atmosphere storage are basically the same as those of the mechanical cold storage. In addition to the thermal insulation, moisture-proof, temperature control and humidification performance of the mechanical cold storage, it also needs to ensure that the gas in the warehouse is well sealed, easy to sample and observe, and can remove harmful gases and automatic control. A complete controlled atmosphere storehouse is composed of storehouse body, gas regulation system, refrigeration system and humidification system

1. the type of controlled atmosphere storage can be divided into inflatable type and circulating type according to the mode of controlled atmosphere storage. The aerated controlled atmosphere storage uses the nitrogen generator to continuously flush the generated N2 into the controlled atmosphere storage, supplemented by other adjustment methods, so that the O2 and CO2 in the storage can reach the predetermined indicators. Circulating controlled atmosphere storage refers to the treatment of the gas in the controlled atmosphere storage through the circulating gas generator, removing the O2 therein, and then re entering the treated gas into the storage. In this way, the speed of reducing O2 and increasing CO2 is faster, and it can be delivered or observed at any time during storage

the building structure of the controlled atmosphere storage can be divided into masonry (Civil Engineering) and fabricated controlled atmosphere storage. The building structure of the masonry controlled atmosphere storage is basically the same as that of the ordinary cold storage, which is built with traditional building insulation materials or transformed from the cold storage, but an air tight layer is added to the enclosure structure of the storage body. The cost of this kind of controlled atmosphere storage is low, but the construction period is long and the construction is difficult. Assembled controlled atmosphere storage is a common form in China. Is it made of sandwich storage plates produced in industry and assembled to form a hexahedron or a pentahedron, or is it left with 10 tons of recyclable steel? " Shan yinmu, chairman of Hangxiao Steel Structure Co., Ltd., often puts forward the structural form of this problem surface. These sandwich storage panels have the corresponding functions of gas barrier, thermal insulation and enclosure, and have a certain strength, which can meet the strength requirements of the whole storage body (small refrigerators, generally less than 50t). However, when the capacity of the warehouse is large or medium, it is necessary to install a steel frame structure that plays a bearing or strengthening role. The assembled controlled atmosphere storehouse of pentahedron does not adopt the structure of heat insulation storehouse plate on the ground, but still adopts the practice of ground heat insulation and gas isolation of civil engineering. At this time, attention should be paid to the heat insulation, gas isolation and air tightness treatment at the connection between the vertical plate of the storehouse and the ground heat insulation layer. The sandwich storage plate is very convenient in installation and construction because the thermal insulation layer and the air tight layer form a whole. In order to ensure the air tightness of the whole warehouse, the connection of the warehouse plate shall be sealed with soft mastic in addition to the rubber cushion

2. Design and construction of the air tight layer in the warehouse. Good air tightness is the primary condition for controlled atmosphere storage. The way to meet the air tightness requirements is to lay the air tight layer on the enclosure structure of the controlled atmosphere warehouse. Commonly used air tight materials include steel plate, aluminum alloy plate, aluminum foil asphalt fiberboard, plywood, glass fiber, reinforced plastic and plastic film, various sealants, plasticine, waterproof tape, etc

airtight materials and construction quality determine the performance of the controlled atmosphere storage. The huge surface area of the air tight layer is often affected by temperature and pressure. If the construction is improper or the bonding is not firm, especially when the pressure of the reservoir changes, the air tight layer may peel off and lose its air tight effect. According to the characteristics of the controlled atmosphere storage, the brick concrete structure of civil engineering is mostly set at the inner side of the enclosure structure to facilitate inspection and maintenance

the practice of the air tight layer of the floor of the air-conditioned storage is to use a layer of plastic film (polystyrenes, etc.) as the air barrier (0.25mm thick) on the reinforced reinforced cement base plate, a layer of prefabricated heat insulation panel (special for the floor) for heat insulation, and a layer of reinforced 10 cm thick reinforced concrete as the ground. In order to prevent the seal from cracking due to the load on the floor, leave a flat groove on the floor at the junction of the floor and the wall, and fill the groove with plastic ester adhesive that will not harden

there are usually two ways to set the door of the controlled atmosphere storage room: ① only one door is set, which is both an insulation door and a sealing door. The door slides on the rail on the top of the door frame and is connected by a pulley. There are two on each side of the door, a total of eight mortars to tie the door to the door frame. After fastening the door, apply non hardening adhesive to the door seam around the door for sealing. ② There are two doors, the first is insulation door, and the second is sealing door. Usually, the structure of the second door is very light. It is riveted on the door frame with screws, and the door seam is coated with mastic ester to strengthen the sealing

in addition, sealing materials shall be added to the parts where various pipes pass through the wall and enter the warehouse, and no air leakage is allowed

during the operation of the controlled atmosphere warehouse, stable gas composition is required, and the management personnel should not often enter the warehouse to inspect the products, equipment and the condition of the warehouse. Therefore, observation windows and sampling (product and gas) holes must be set during the design and construction of controlled atmosphere storage. The observation window can be set on the air control valve, and the sampling hole is mostly set at the appropriate position of the side wall

controlled atmosphere storages should be designed by professional design units with certain qualifications. Large and medium-sized controlled atmosphere storages with more than 1000t include controlled atmosphere rooms, precooling rooms, normal temperature halls, technical corridors, finishing rooms, refrigeration and controlled atmosphere rooms and control rooms, power transformation and distribution rooms, pump rooms, platforms, etc. In addition, there are offices, warehouses, quality inspection rooms, roads, fences and other auxiliary facilities

3. Air tightness inspection of the controlled atmosphere storage. The air tightness inspection shall be carried out after the completion of the controlled atmosphere storage or before reuse. If the inspection results do not meet the specified requirements, the causes shall be found out and repaired to make it sealed. It can be used only after reaching the air tightness standard

code for construction and inspection of refrigerator and air separation equipment installation engineering (GB) stipulates that "after the installation of the storage body, the air tightness test of the storage body should be carried out. The test should meet the following requirements: start the blower, shut down when the pressure in the storage reaches the target 100Pa, and start counting. When the test reaches 10min, the pressure in the storage should be greater than 50 pa", that is, the half pressure reduction time is 10min

the following problems should be paid attention to during the air tightness inspection and leakage repair of the controlled atmosphere warehouse: ① try to keep the warehouse in a static state (including adjacent warehouses); ② Maintain the stability of the temperature inside and outside the warehouse; ③ The measurement unit of micro manometer such as PA shall be used as much as possible to ensure the accuracy of the test; ④ The pressure in the storehouse should not rise too high to ensure the safety of the enclosure structure; ⑤ Special attention should be paid to key parts such as enclosure structure, door and window joints in air tightness detection and leakage repair, and the leakage parts should be marked in time; ⑥ In the process of air tightness inspection and leak repair, keep in touch inside and outside the warehouse to ensure personal safety and smooth work. After finding the leaking part, the sealing material sprayed on site is usually used to make up the leak

(II) gas regulation system of the controlled atmosphere storehouse

the controlled atmosphere storehouse completes the regulation of the gas composition in the storehouse through the gas regulation system to carry out the generation, storage, mixing, distribution, testing and adjustment of the gas composition

1. in order to improve vehicle fuel efficiency and reduce pollution, gas distribution equipment includes gas storage tanks and bottles for gas storage and distribution, pressure reducing valves, flow meters, regulating control valves, instruments and pipelines required for gas distribution. Through the reasonable connection of these equipment, the supply of various gases required during controlled atmosphere storage is guaranteed, and they are transported to the controlled atmosphere storage room at the speed and proportion required by fresh fruits and vegetables

2. gas regulating equipment includes vacuum pump, nitrogen generator, CO2 remover, ethylene remover, etc. The application of advanced gas regulating equipment provides a guarantee for rapidly and efficiently reducing O2 concentration, increasing CO2 concentration, removing ethylene, and maintaining each gas component at an appropriate level that meets the requirements of storage objects

(1) the nitrogen generation and oxygen reduction equipment uses the nitrogen generator to produce 95% - 98% purity N2 to replace (dilute) the gas in the controlled atmosphere storage and reduce the O2 concentration in the storage; It can also be used to remove excess CO2, ethylene or other gases in small controlled atmosphere storages

at present, the nitrogen generator used in the CA warehouse is divided into two types: carbon molecule physical adsorption type and hollow fiber membrane separation type, both of which use air as raw material. The former uses the different adsorption rates of carbon molecular sieves on oxygen and nitrogen molecules in the twin towers, adsorbs oxygen under pressure, parses oxygen under reduced pressure, and constantly switches pressure to produce nitrogen in the twin towers; The latter is a hollow fiber membrane made of polymer materials, which has simple structure, easy operation and fast nitrogen production speed. It is a new and efficient nitrogen production equipment

the common hollow fiber membrane nitrogen generator is composed of supporting air compressor, air storage tank and membrane nitrogen generator

its core component is hollow fiber membrane group. It consists of tens of thousands or even hundreds of thousands, with a diameter of 50 ~ 500 μ M hollow fibers are tied in bundles, and the two ends are impregnated with epoxy resin to form a membrane filter element, which is put into a shell. When compressed air passed through the hollow fiber, the company subscribed for 19.9% equity of lithium America with us $49 million. Due to the fast rate of oxygen and water vapor passing through the membrane, oxygen enriched gas was formed and discharged into the atmosphere, while most nitrogen remained in the membrane due to the slow rate of passing through the membrane, forming a product gas with high purity. Its purity can be adjusted by purity control valve. The higher the purity, the smaller the flow

how large a nitrogen generator is selected for a CA warehouse, first of all, it is necessary to consider meeting the oxygen reduction requirements of the largest CA room in the warehouse, that is, to meet the requirements of Ca parameters within 1 ~ 3D after fruits and vegetables enter the warehouse, and at the same time, it is also necessary to take into account the number of rooms and total capacity of the whole warehouse

at present, the nitrogen generator generally adopts the open replacement (inflation dilution) method to charge nitrogen into the air control room, injecting 95% - 97% purity N2 from the upper air inlet of the air control room, and the replaced gas is discharged into the atmosphere from the exhaust port arranged diagonally with the air inlet. The whole process is a dynamic process of continuous dilution, and the oxygen content in the reservoir decreases in a natural logarithmic order until it falls to the specified index

(2) the respiration of fruits and vegetables in controlled atmosphere storage will increase the CO2 concentration in the warehouse. Too high concentration will lead to poisoning, produce a series of adverse symptoms, and finally rot and deteriorate. At this time, the excess CO2 in the warehouse must be removed by CO2 remover to achieve the best parameters of controlled atmosphere storage

at present, activated carbon is used as adsorbent in CO2 removal machines produced at home and abroad. The reservoir gas containing high CO2 is pumped into the activated carbon tank by fan for adsorption. After several minutes of adsorption saturation, it is desorbed and regenerated by air. In this way, the desorbed CO2 is sent to the atmosphere

(3) there are many methods to remove ethylene in ethylene removal device, such as water washing method, dilution method, adsorption method, chemical method, etc., but at present, there are mainly two methods widely used: potassium permanganate (kmn04) oxidation method and high temperature catalysis method

potassium permanganate oxidation method is also called chemical ethylene removal method. It uses potassium permanganate aqueous solution to soak porous materials (i.e. carriers), such as alumina, molecular sieve, vermiculite, broken bricks, foam concrete, etc., and then puts this carrier into the warehouse, packaging box or closed-circuit circulation system to remove ethylene by using the strong oxidation performance of potassium permanganate. At present, the preservative used in many places in China to remove ethylene is mostly this product. Although this method is simple to remove ethylene, its removal efficiency is low, and the carrier must be changed frequently (including the reabsorption of potassium permanganate), and potassium permanganate has a strong corrosive effect on skin and objects, which is not convenient for the operation of modern controlled atmosphere storage. Generally used in small or simple storage

with the development of controlled atmosphere technology, in recent years, an efficient ethylene removal device based on high-temperature catalytic principle, ethylene remover, has been developed. Ethylene can generate water and CO2 under the action of catalyst at a high temperature of 250 ℃ by closing