Gas reservoir solution

1 air conditioned building
On the basis of the fruit and vegetable cold storage, the atmosphere bank has a lot of similarities with the fruit and vegetable cold storage:
(1) the volume of gas reservoir. In Europe and the United States, gas storage room volume is usually between 50 ~ 200t, such as the volume of British apple gas-regulate storage room is about 100t, in Europe is about 200t, but the single volume of vegetable CA storage is usually between 200 ~ 500t, in the North American single larger capacity, generally in 600t about. According to the current situation in our country, with 30 ~ 100t as a bay, a database unit of at least 2, but generally not more than 10.
(2) the gas reservoir must have good air tightness. This is one of the most important features of the construction of the gas reservoir structure, which is different from the common cold storage of fruits and vegetables. There is no special requirement for the air tightness of the common cold storage, but the air conditioning is very important for the air tightness. This is due to the formation of gas composition requirements in atmosphere storage, and long time to maintain a set of indexes in fruits and vegetables during storage, gas permeability and gas exchange relief base, CA storage must have good air tightness. Therefore, in the gas regulating door installation, airtight layer construction process, must be careful, suspicious parts should be timely check and repair. For the brick structure of the library and the construction of the civil air base, such as large area projection or fall off, often due to maintenance of the structure surface caused by drying, before construction, must pay attention to the maintenance of dry structure.
One of the most important aspects of the quality control of gas reservoir is the air tightness test. Stress testing is widely used at present. The utility model has the advantages of simple test method, simple test instrument and visual results. Pressure test method and the positive pressure method and the negative pressure method, usually using positive pressure method, in order to avoid the use of negative pressure test lead to the loss of the air layer. So far, there is no uniform standard for the air tightness test of the gas reservoir in the world. However, the use of positive pressure test, statistical "half time", is commonly used in foreign air tightness test standards and results of the expression. The so-called half time, refers to the time from the test, the test pressure dropped to half the time required for the initial pressure. Airtight existing standards in the world, the highest requirement is: the test pressure of 294Pa (30mmH2O), half the time pressure is equal to or more than 30min for qualified, otherwise unqualified, some manufacturers using this standard only a few countries such as Italy. Italy FCE company in recent years in our country to install a combination of air conditioning experiments in the air tightness of the scope of the experiment is as follows: the library pressurized to 30mmH2O, the pressure in the 30min library is not less than 4.4mmH2O.
(3) safety of gas reservoir. The safety of the gas reservoir should also be considered in the design of the gas reservoir. This is because the gas reservoir is a closed type cold storage, when the temperature in the reservoir, the gas pressure also changes, often make the inside and outside the reservoir formation pressure difference. According to information, when the temperature outside the library is higher than the temperature of 1 degrees in the library, the outside atmosphere will have a 40Pa pressure on the maintenance of the library board, the greater the temperature difference, the greater the pressure difference. In addition, the air pressure difference between the two sides of the maintenance structure is maintained during the operation of air conditioning equipment, humidification and air tightness test. If the pressure difference is eliminated or controlled in a certain range in time, it will be harmful to the maintenance structure. To this end, it is usually installed in the gas reservoir on the balance bag and safety valve, so that the pressure is limited to the safety of the design range. Air pressure balance bag (referred to as the air bag) of the volume of about 0.5% to 1% of the volume of the warehouse, the use of soft material is not easy to wear and aging materials. Recommended safety pressure value is + 190Pa. Therefore, each warehouse should also install a pressure balance valve (referred to as the balance valve), the pressure difference between the internal and external pressure of the reservoir is greater than 190Pa, the gas exchange will occur inside and outside the library, to prevent the destruction of the body structure. The balance valve is divided into two types: dry type and water seal type. In general, the balance of the bag to adjust the role, only when the balance bag capacity is not enough to adjust the pressure changes in the reservoir, the balance valve to play a role. In addition, in some countries, such as Holland, through regular storage of nitrogen to the storage room, so that the air bag has been in a state of semi expansion, maintaining a constant positive pressure, help to reduce the air leakage into the storage room.
(4) a single storey building should be built in the gas reservoir. According to the actual situation, the general fruit and vegetable cold storage can be built into single or multi story buildings, but almost all of them are built on the single layer. This is because the transport of fruits and vegetables in a library, stacking and storage, ground to carry heavy loads, if the use of multi-storey buildings, on the one hand tight treatment is more complex, on the other hand, the use of CA storage may result in airtight layer damage. The building height of the gas reservoir is about 7m.
Configuration of refrigeration equipment and temperature sensor in 2 gas reservoir
(1) refrigeration system. Refrigeration equipment for gas conditioning storage are mostly used in piston type single-stage compression refrigeration system, with ammonia or Freon 22 as refrigerant, cooling pool can be refrigerant of direct evaporative cooling, indirect cooling can also use middle refrigerant for air conditioning, the latter than the former effect to. Because the refrigerant liquid temperature control more convenient to supply air cooler, only the stroke control three-way valve in the liquid supply pipe to a return, at the same time to achieve different warehouse can meet the requirements of different temperature. In order to reduce the library in the storage of dry goods consumption, gas conditioning storage requirements for the good performance of heat transfer temperature 2 to 3 DEG C, that is to say the difference between CA storage and storage requirements of the evaporation temperature of the temperature is 2 to 3 DEG C, which is much smaller than the common cold. Only by controlling and achieving the small difference between the evaporation temperature and the storage temperature, the evaporator can be reduced to maintain the relative humidity of the evaporator. So, in the atmosphere storage design, under the same conditions, the heat transfer area usually cooler than the heat transfer area of ordinary refrigerators of fruit and vegetable cooler, air conditioning is the so-called "big evaporation area and low temperature difference of heat transfer scheme using air cooler design on the library.
(2) configuration of temperature sensor. In the process of operation, a well designed gas reservoir can achieve a temperature difference of less than 0.5 degrees in the library. Therefore, need to use the electronic temperature control instrument accuracy is higher than 0.2 DEG C to control temperature. The number and placement of temperature sensors are also very important for the control of the temperature of the gas reservoir. The number of the recommended probe for at least 3: put in 50t or the following storage, put 4 in the 100t library, put 5 or 6 in the larger database, which used a probe to monitor the air temperature free circulation in the store, the ceiling type air cooler, the probe should be installed from the cargo to the space between the entrance of air cooler. The rest of the probes were placed in different locations of fruits and vegetables to measure the actual temperature of fruits and vegetables.
3 air conditioning equipment and auxiliary equipment
Air conditioning equipment is generally speaking, mainly including nitrogen equipment, carbon dioxide removal equipment, ethylene removal equipment and humidification equipment, of which nitrogen utilization rate is the highest, so it is more important. According to the working principle of nitrogen making equipment, it can be divided into three types, that is, the type of nitrogen production by adsorption separation, the type of nitrogen produced by membrane separation, and the type of oxygen reducing nitrogen.
(1) nitrogen making machine. At present, there are two main types of nitrogen making machine used in the gas storage plant in our country: the adsorption separation type carbon molecular sieve nitrogen making machine and membrane separation type hollow fiber membrane nitrogen making machine. Carbon molecular sieve nitrogen machine and hollow fiber membrane nitrogen machine, the former has lower price, smaller investment, low energy consumption, replacement of gas adsorption agent advantages than the replacement of membrane module is cheap, with ethylene removal function, and the process is relatively complex, large occupied area, the noise is large, as the running stability of hollow fiber membrane nitrogen machine is a relatively weak carbon molecular sieve nitrogen machine.
(2) carbon dioxide removal machine. The carbon dioxide removal device is divided into two types: intermittent type (commonly known as a single tank machine) and continuous (usually called double tank machine). The high concentration of carbon dioxide in the reservoir is pumped into the adsorption device, after the activated carbon adsorption of carbon dioxide, and then the adsorption of low carbon dioxide concentration gas back to the Treasury, to achieve the purpose of carbon dioxide removal. The amount of carbon dioxide adsorbed on activated carbon is a function of temperature and is proportional to the concentration of carbon dioxide. It is usually used as the main economic and technical index in the 24h with 0 of carbon dioxide concentration as the standard. After a period of work, activated carbon for carbon dioxide adsorption is saturated, then can not absorb carbon dioxide, then another set of the circulatory system will start, the fresh air, the adsorption desorption of CO2, and the air is discharged into the atmosphere, such as adsorption and desorption alternately, can achieve the purpose of removing the excess carbon dioxide the removal of the library.
Carbon dioxide after the regeneration of the air contains a lot of carbon dioxide, must be discharged outdoors. The inlet and outlet pipes of the inlet and outlet gas reservoir must be tilted slightly to the reservoir body, so as to avoid the condensation of water to the removal machine, which results in the failure of the activated carbon. The engine room should avoid volatile substances such as gasoline, liquefied petroleum gas, keep the temperature 1 ~ 40.
(3) ethylene removal machine. There are mainly two methods are widely used for removal of ethylene: Potassium Permanganate high temperature oxidation and catalytic decomposition method. One method is to use the saturated aqueous solution of Potassium Permanganate (usually with a concentration of 5% to 8%) wet porous material (such as perlite, vermiculite, alumina, molecular sieve, broken bricks, foam concrete etc.), then the carrier in library, the packing box or closed loop system, using the strong oxidation of Potassium Permanganate the removal of ethylene oxide. This method is simple, but the removal efficiency is low, generally used for small or simple storage.
In the process of ethylene removal by air oxidation, the core part of the device is a special catalyst and a temperature field electric heating device. The catalyst used is a kind of special active silver containing calcium oxide, barium oxide and strontium oxide. Temperature field and electric heating device can produce a temperature change from the outside temperature gradually increased from 15 to 80 DEG C: C, 150 C, 250 C, so that the gas of ethylene plant import and export temperature less than 15 degrees Celsius, but the temperature of oxidation reaction center up to 250 DEG C, so as to reach the effect of reaction the ideal, not to significantly increase the heat load of warehouse. Closed loop system is generally used in the ethylene removal device. In addition to ethylene and Potassium Permanganate in addition to ethylene oxidation device air oxidation method, the investment cost is much higher, but the high efficiency removal of ethylene. There are information on the ethylene plant by air oxidation method, the kiwi can be reduced to 0.02ppm in the library, while the device also has the removal of other volatile harmful gases and disinfection.
(4) humidifying device. Water mixing humidifying, ultrasonic humidification and centrifugal atomization humidification is the air conditioning storehouse three common humidification mode, used in the temperature of above 0 DEG C, the humidifying effect is very good, but when they use at negative temperature, there are how to make the humidifying water avoid the icing problem, this problem at present in the production process has not been well solved yet.
4 rational use and management of gas reservoir
(1) reasonable and effective use of space. The volume utilization coefficient of the gas reservoir is higher than that of the common cold storage, and some people describe it as a "High Filled Pile". The so-called "high fill heap" refers to the atmosphere of the fruit and vegetable should be loaded with a larger load density, in addition to leaving the necessary ventilation and inspection channels, as far as possible to reduce the free space of the reservoir. Because the atmosphere within the pool of free space is small, means that the stock gas in the library is less, so that one can reduce the air conditioning equipment properly, on the other hand can accelerate the gas transfer speed, shorten the gas transfer time, reduce energy consumption, and make fruits and vegetables as soon as possible into the gas storage condition.
(2) fast forward. Air conditioning storage requirements of fruit and vegetable storage speed, fill, seal and timely transfer of gas, so that fruits and vegetables in the shortest possible time into the state of air conditioning. Peacetime management can not be as easy as ordinary cold storage in and out of the goods, otherwise the library will often change the composition of the gas, thereby weakening or losing the role of air conditioning storage. Fruits and vegetables out of the library, it is best to finish out in a short period of time or in batches.
(3) good air circulation. The gas transfer in the cooling process, the range recommended for British cycling rate in fruit and vegetable storage: early air exchanges per hour for 30 times to 50 times the volume of the empty library, so often choose double speed fan or a plurality of axial flow fan can be independently controlled scheme. In the cooling stage, the larger the amount of air, cooling speed, when the temperature dropped to half or less of the initial value, the number of air exchange can be controlled at 15 ~ 20 times per hour.