Controlled Atmosphere Cold Storage
Cold storage, also known as controlled atmosphere storage is the most advanced method of storage of fresh fruits and vegetables. It is based on refrigerated, increasing gas component adjusted by the storage environment, temperature, humidity, carbon dioxide, oxygen concentration and ethylene concentration and other conditions of control, inhibition of respiration of fruits and vegetables, slow down the metabolic processes, better to keep fruits and vegetables fresh degree and commodity, and to extend the shelf life of fruit and vegetable storage (sales shelf life). Typically atmosphere storage than conventional refrigerated storage period may be extended 0.5-1 times; fruits and vegetables controlled atmosphere storage library after library start with "sleep" state "wake up", which made of fresh fruits and vegetables after the library (Sales shelf life) may be extended 21 to 28 days, 3 to 4 times the normal refrigerator.
1. Controlled Atmosphere Technical Overview
The traditional fruit and vegetable storage and preservation methods are simple storage, ventilation library storage, preservation of radiation, chemical preservation, cold storage. Easy storage, database storage ventilation equipment is simple, low investment, but poor storage, short storage period, serious decay losses. Radiation and chemical preservation on the part of the fruit have some applicability, but the presence of residual radiation and chemical pollution, not all fruits and vegetables can be applied.
Controlled Atmosphere storage can fit under low temperature conditions, the storage environment by changing the gas composition, relative humidity, the maximum extent possible to create the best environment for fruit and vegetable storage, the effect in the following ways: to create a hypoxic atmosphere storage (typically O2 content l % -5%), the appropriate concentration of CO2 can effectively inhibit respiration, reduce the loss of nutrients in fruits and vegetables, while suppressing the breeding of pathogens, control the occurrence of certain physiological diseases; remove the ethylene gas storage environment, to suppress their the role of fruits and vegetables ripening, delay ripening and senescence process after; increasing environmental relative humidity of the gas in order to reduce the transpiration of fruits and vegetables, fruits and vegetables in order to achieve long-term storage and preservation purposes.
After controlled atmosphere storage of fruits and vegetables with the characteristics
(1) well maintained vegetable original shape, color, flavor;
(2) Fruit hardness higher than ordinary refrigeration;
(3) the storage period;
(4) fruit rot rate, natural wear and tear (loss rate) is low;
(5) to extend shelf life. Due to the low 02 and high long-term fruits of action by the C02, after the lifting of the state of fruits and vegetables atmosphere is still a very long time "lag effect" or period of dormancy
(6) adapted to long-distance transport and export. Fruit quality improved significantly, creating the conditions for export and distribution
(7) many fruits and vegetables can reached to supply in the whole season even when it is produced in several month. It makes a good social and economic benefits.
Constituting of the controlled atmosphere cold storage: Cold storage generally composed of airtight storage body, air-conditioning systems, refrigeration systems, humidification systems, pressure balancing system as well as temperature, humidity, O2, CO2, automatic gas detection and control system structure.
Controlled Atmosphere Cold Storage
Controlled Atmosphere Cold Storage in accordance with the technical requirements for the gas only function with cold refrigerator, and has a unique structure in the form of management and use.
tightness is the major difference between a controlled atmosphere cold storage configuration and normal refrigerated room. It requires not only building envelope insulation to reduce the impact of external storage temperature, but also requires a sealed envelope to reduce the gas exchange inside and outside the library, the library maintains a more stable gas composition.
This is associated with hermetic and requirements. Cold storage in cool, back to temperature and atmosphere during library due to temperature and pressure changes cause pressure on both sides of envelopes. As pressure not eliminate or control within a certain range, it will cause damage to the body's library. Necessary to ensure an airtight storage body, but also to ensure their safety is another characteristic atmosphere cold storage.
3. High Height of Controlled Atmosphere Cold Storage.
Modern controlled atmosphere cold storage building is usually with high height. almost all single-floor building, high library space. This unique architectural form is designed based on airtight and safety consideration.
4. Fast loading in and out
This is another major feature of controlled atmosphere cold storage. Except the necessary supervised passenger way. Goods should be piled as high as possible in the library filled containers, when the library small remaining gap, reducing the amount of processing gas atmosphere to accelerate the speed, shorten the atmosphere of the time, so as soon as possible the formation of the state of atmosphere.
5. Filled with high pile of products
This is another major feature of the use of management. In addition to leaving out the necessary checks channel, the cargo should be as high as possible in the library filled with equipment, the library when the remaining small gap, reducing the amount of processing gas atmosphere to accelerate the speed, shorten the atmosphere of the time, so that gas transfer status early formation.
2. Controlled atmosphere cold storage library body
Atmosphere cold storage library body requires not only having good insulation, reducing the influence of external heat on the inside temperature, the more important is required to have good air tightness, reduce or eliminate the outside air pressure of gas components library to ensure library gas component adjusting speed, low volatility, and thus improve the storage quality and reduce the cost of storage. Air conditioned storage body is mainly composed of an airtight layer and the insulation layer. Atmosphere libraries are building can be divided into three types: prefabricated, brick style, jacket. Fabricated cold storage building envelope choice of color coated polyurethane sandwich panels assembled with heat, moisture and air tightness role. The library building fast and nice, but the cost is slightly higher, at home and abroad is a new gas for the most common type. Air conditioned atmosphere using a special door that should have good thermal insulation and air tightness. In addition, long-term storage of process gas for the closed door, the atmosphere is generally not allowed to just open the door in order to avoid gas exchange inside and outside the library, causing fluctuations in the gas composition of the library, for ease of understanding the library storage of fruits and vegetables, the observation window should be set . After cold storage built, to conduct air tightness testing. Tightness should reach 300Pa, half-down time is not less than 20-30min.
3, the air conditioning system
To make the atmosphere gas component to achieve the required cold storage and remained relatively stable, in addition to air tightness library in vitro to have to meet the requirements, but also a corresponding gas conditioning equipment, pipes, valves consisting of system, the air conditioning system. The whole atmosphere system includes deoxygenation system or nitrogen, carbon dioxide removal system, vinyl removal system, temperature, humidity and gas composition control system for automatic detection.
Is the most advanced cold storage down the oxygen equipment, its working principle is to use a pressure below 24KPa fan circulates oxygen, and then using a vacuum pump to resolve activation motor adopts frequency control technology. This technique often been mistaken VSA nitrogen machine. The biggest difference between the machine and the VSA-deoxy Nitrogen is, VSA nitrogen machine still uses compressed air as a power source (although a lower pressure), the hydrocarbon source will still lead to failure VSA nitrogen machine materials, and machine-deoxy the micro air compressor is oil-free, oil contamination of raw materials does not exist, the circulating air volume is more than five times the VSA nitrogen machine, which lower oxygen ratio of membrane nitrogen machine equipment, high PSA nitrogen generator efficiency of 40%, compared with VSA nitrogen 30%, saving more than 40% nitrogen existing foreign company in Italy and Germany a few master-deoxy-machine technology, there were only Tianjin Jie Sheng deoxygenated machine made technological breakthroughs that lower oxygen capacity even slightly higher than the foreign brands, more mature technology, the use of a large number of atmosphere library.
2, nitrogen system
Nitrogen generally experienced a catalytic combustion nitrogen → carbon molecular sieve adsorption nitrogen, hollow fiber membrane separation nitrogen, vacuum and low pressure nitrogen adsorption deoxygenation (ie VSA) development process. Now widely used carbon molecular sieves, hollow fiber membrane nitrogen and VSA nitrogen.
2. Carbon molecular sieve adsorption nitrogen machine Nitrogen carbon molecular sieve pressure swing adsorption principle is the use of nitrogen, due to the different kinetic diameter of oxygen molecules and nitrogen molecules, the diffusion rate of oxygen molecules is hundreds of times faster than nitrogen molecules. The adsorption amount proportional to the pressure, the use of oxygen, nitrogen adsorption amount in a short time the great differences in the characteristics of the program controller specific time program between the two towers to quickly switch, combined with oxygen adsorption pressure, oxygen pressure desorption process, the oxygen separated from the air out. Nitrogen Nitrogen carbon molecular sieve having a high purity (99.9%), equipment is simple, low price and features, but the device more valves, switching frequency, the need switch valves per year 20-40 million times, equipment noise Big. Therefore required to ensure the quality of the valve, otherwise it will affect the reliability of the equipment.
2.2 hollow fiber membrane nitrogen machine Nitrogen is the use of membrane separation of oxygen and nitrogen through the differences in the characteristics of the hollow fiber membrane wall velocity, oxygen separated from the air. The hollow fiber membrane nitrogen atmosphere storage machine is the most widely used devices. It consists of a compressor, tank, air dryer, filters, heaters, hollow fiber membrane tubes, valves. It has the following characteristics: (1) simple equipment, small footprint, easy to install; (2) air compressor can be obtained only starting nitrogen-enriched air; (3) concentrations may be between 95% -99% of the adjustable, flexible can quickly start stop; (4) safe and reliable, no moving parts separator, continuous and stable work; (5) the separation process no phase change, no pressure loss, low energy consumption; (6) easy to miniaturization; (7) small investment.
2. Deoxy-vacuum low-pressure nitrogen adsorption mechanism of nitrogen machine uses the principle of CMS is regenerated activated carbon adsorption to absorb atmospheric O2 library to inject high-purity nitrogen. CMS activated carbon filled by two tanks, pumps, valves, piping and control unit. It has the following characteristics: (1) low pressure (0.8bar) run, compared with the same performance of PSA and membrane nitrogen machine saving about 80%. (2) reducing the oxygen effect more than 30%, Atmosphere library oxygen content can be controlled to below 1%, even up to 0.3% (3) low maintenance costs. Stable and reliable. Activated carbon adsorption apparatus main module life of up to 2 - 3 years. (4) with the library system with a more efficient body o prevent gas for the gas leak. (5) cold storage gas loop. More effective operational cost savings.
3, the carbon dioxide removal system
Mainly used to control gas for the carbon dioxide content. Fruits and vegetables rely entirely on carbon dioxide released during respiration, increased concentration of carbon dioxide library atmosphere, the amount of carbon dioxide to the protective effect of fruits and vegetables, make Preservation good effect. However, the carbon dioxide concentration is too high, it will cause damage to fruits and vegetables, so the removal of (washed) excess carbon dioxide, regulate and control the concentration of carbon dioxide, to improve the quality of fruit and vegetable storage is very important; usually carbon dioxide removal unit generally have four in the form of: (1) lime removal unit; (2) water cleaning device; (3) active carbon cleaning device; (4) a silicone rubber membrane cleaning device. Activated carbon removal device is the use of activated carbon adsorption stronger force for carbon dioxide adsorption, to be saturated adsorption drum into the fresh air, so that the activated carbon desorption, adsorption recovery performance, the device current for the gas carbon dioxide removal commonly used . The concentration of carbon dioxide removal system should be based on the respiration rate of the fruit and vegetable storage, modified atmosphere library free space volume of gas, gas for the storage volume, the library required to achieve carbon dioxide gas component to determine the removal of the ability to work the machine.
4, ethylene removal systems
Ethylene is ripe and ripening of fruits and vegetables in the process of self-generated and released from a gas, is an incentive to breathe, to accelerate ripening plant hormone, for postharvest storage of fruits are ripening effect. In the ethylene-sensitive fruit during storage, ethylene should be removed. Therefore, both the storage of fruits and vegetables to try to suppress ethylene production, but also to eliminate the accumulation of ethylene storage library. Now widely used and relatively effective method for the chemical addition of potassium permanganate and ethylene air oxidation removal method. In addition to the chemical ethylene absorber is filled with ethylene in the cleaning device, commonly ethylene absorbent is saturated potassium permanganate solution is adsorbed on the broken bricks, vermiculite or porous materials such as zeolite molecular sieves, contacting ethylene with potassium permanganate , due to oxidation is cleared. The method is simple, low cost, but low efficiency in addition to ethylene and potassium permanganate is a strong oxidizing agent, it will burn the skin. At present, the air oxidation removal method is to use the principle of ethylene in the catalyst and high temperatures to produce carbon dioxide and water react with oxygen to remove ethylene, and potassium permanganate removal method compared to its high investment costs, but has the distinct advantage to be accepted :
(1) In addition to high ethylene efficiency, the gas can be removed library contained 99% of the amount of ethylene can be stored in the control room the ethylene concentration in l-5μL / L; (2) reduce mildew fruit, while the removal of ethylene, library capable of high temperature gas sterilization; (3) use of a machine to remove ethylene at the same time, but also to get rid of fruit aroma gas is released, reducing the adverse effects of these gases on the role of ripening fruit.
Note: In addition to ethylene-sensitive fruit (mainly subtropical and tropical fruits): kiwi, banana endures, apples, pears and other temperate fruits do not need to ethylene prolapse device.
Currently more advanced than ethylene ozone technology is gradually replacing the high temperature catalytic ethylene unit, the biggest advantage of this technology in addition to ethylene work at low temperatures, does not cause fluctuations in storage temperature, and power consumption of only 500 watts, high temperature catalyzed ethylene unit energy consumption 1/105, the main function control system automatically detects the atmosphere library measurement and control systems: temperature of the atmosphere within the library, humidity, O2, CO2 gas measurement and display real-time checks to determine whether compliance with technical requirements atmosphere, and automatic (manual) adjustment to make it in the best atmosphere parameter status. High degree of automation in modern cold storage in general, automatic detection and control equipment, which consists of (temperature, humidity, O2, CO2) sensors, controllers, computers and sampling pipes, valves and other components, the entire system consists of a whole the central control computer to achieve remote real-time monitoring, both to get the various sub-library of O2, CO2, temperature and humidity data, display running curve, recorded and printed automatically activate or deactivate the various systems, while change at any time according to the condition of material library Control parameters. The central control computer using the Windows interface, the operator can use the convenient and intuitive access to information on all aspects.
6, the refrigeration system
Mechanical refrigeration cooling system is to achieve the necessary machinery, equipment and connection of these machines, equipment, piping, valves, closed loop control system and other elements thereof. Atmosphere cold storage refrigeration systems with ordinary cold storage refrigeration system is basically the same. However, cold storage refrigeration systems with higher reliability, higher degree of automation, and maintain the interior temperature required for a long time in the atmosphere storage of fruits and vegetables. Refrigeration systems generally use ammonia or Freon single stage compression liquid supply direct expansion refrigeration systems.
7, humidification systems
Compared with ordinary fresh fruits and vegetables cold storage, controlled atmosphere storage of fruits and vegetables due to the long period of storage, fruits and vegetables high water evaporation, fruits and vegetables to suppress evaporation of water, reduce water vapor storage environment and storage of fruits and vegetables between the partial pressure required for the gas storage environment has the best relative humidity, which reduce the consumption of fruits and vegetables, dry fruits and vegetables fresh and crisp holding great significance. Usually the best library to maintain relative humidity between 90% -95%.
Common cold storage humidification methods are the following:
(1) Ground water filling humidifying;
(2) water chiller chassis;
(3) a spray wetting;
(4) centrifugal atomization humidification;
(5) ultrasonic atomization humidification.
8, for the gas pressure balancing system
In modified atmosphere cold storage building structure design must also consider the security atmosphere cold storage. Since cold storage is a closed refrigerator, when the inside temperature decreases, its gas pressure decreases, the inner and outer sides of the library to form a pressure difference.
According to the information, when the temperature difference between inside and outside the library l ℃, atmospheric envelope will generate pressure 40Pa, the greater the temperature difference the greater the pressure difference. If the pressure difference in a timely manner to eliminate or control within a certain range, it will make the body damage the library. In order to ensure safety for the gas and air tightness, and provide gas for the operation and management to provide the necessary conditions for convenience, should be set for the gas pressure balance system: safety valve, buffer storage bag. Safety valve is closed in cold storage, the pressure balance inside and outside the library to ensure unique safety features, it is possible to prevent excessive library of positive and negative pressure, so that envelope and airtight layer from damage.
Air conditioned occur during operation pressure imbalance trace buffer storage bag role is to eliminate or alleviate the micro-pressure imbalance. When the library pressure slightly higher than atmospheric pressure, the library portion of the gas bag into the buffer reservoir when the library is slightly lower than the atmospheric pressure, gas storage bag inside the buffer will automatically fill into the room atmosphere. Bag storage library is to small changes in pressure, converted into a change in the gas volume of the reservoir bag, so that the pressure inside and outside the library reduce or close to zero, to eliminate and alleviate the pressure force of retaining structure. Buffer storage bag is made of air tightness and has a tensile strength of the flexible material.
CA Cold storage room case study
Huazhong Agricultural University gardening school accredited us to build a controlled atmosphere cold room, after 1 month`s test, it has passed all parameters requirements for refrigeration performance, humidity control, temperature decreasing control, oxygen content, CO2 content, ethylene content control, air tightness etc..
It is the first time to use above national level and European air tightness parameters.
Contact Person: Alex Zhang