Golddeer Security Equipment Co., Ltd. , http://www.sybluelight.com
1 The principle of composite modified atmosphere packaging The composite modified atmosphere packaging is also called gas replacement packaging, which is called MAP packaging (Modified Atmosphere Packing). The principle is to replace the air in the packaging container with a composite gas (2-4 kinds of gases mixed according to the characteristics of the packaged food), and change the gas environment around the food in the packaging container, thereby inhibiting the growth and reproduction of bacteria (microorganisms). Slow down the metabolic rate of packaged foods and extend the shelf life or shelf life of foods [1, 2].
Modified atmosphere gas is generally composed of carbon dioxide (CO2), nitrogen (N2), oxygen (O2) and a small amount of special gases. High concentration of CO2 gas can inhibit the growth and reproduction of most microorganisms causing food spoilage, prolong the stagnation period (or incubation period) of its reproductive growth and delay its logarithmic growth period, which is the main antibacterial component in fresh-keeping gas; O2 can inhibit large Most anaerobic bacteria grow and multiply, high oxygen can maintain the color of fresh meat and hypoxia can keep the fresh fruit and vegetables in the fresh state while inhibiting the breathing speed of fresh fruits and vegetables; N2 is an inert gas, can not chemically interact with food, as a filling gas Preventing the CO2 from escaping and causing the package to fall off. Nitrogen-filled packaging can reduce the oxidation of fat, aroma and color in food [3]. The combination of CO2, O2, N2 and special gases to form a fresh-keeping gas for food and vegetable preservation is the development trend of today's fresh-keeping packaging.
2 basic configuration of the composite gas distribution system in order to mix different proportions of carbon dioxide (CO2), nitrogen (N2 of), oxygen (O2) fed into the packaging container, generally CO2, N2, O2 gas mixing chamber fed by a certain percentage ( After the gas storage chamber is mixed, it is injected into the packaging container, thereby changing the gas environment around the food in the packaging container according to the characteristics of the packaged food to achieve the purpose of keeping fresh. Gas mixing and distribution can be performed in the following two ways.
(1) Controlled air pressure composite gas mixing and distribution system control air pressure compound gas mixing and distribution system is mainly composed of gas source, gas mixing chamber, vacuum air-packing machine and pipeline, pressure reducing valve, pressure gauge and switch, etc. Show. Generally, the gas source used in small batch production is compressed gas in steel cylinders. Carbon dioxide is used in food grade and nitrogen is used in dehydrated refined nitrogen. When the cylinder is filled, the pressure can reach 15MPa, generally 10~12MPa.
After the various compressed gases are depressurized by the pressure reducing valve, they enter the gas mixing chamber to carry out the optimal proportion mixing of various products, and then are introduced into the air-packing machine for inflation packaging.
The gas distribution principle of the mixer, assuming that the gas after decompression is an ideal gas, there is a state equation:
PV = nRT
Where: P—gas pressure, Pa;
V—gas volume, m3;
N—moles of gas, mol; Figure 2 modified atmosphere packaging system Fig.2 The Modified Atmosphere Packing system
R—gas state parameter, 8.31 J/mol·°K; 1-air source 2-pressure reducing valve 3-switch 4-gas mixing chamber 5-packaging machine T-temperature, °K.
It can be seen from the above formula that at a certain temperature, when the gas volume V is constant, the gas mole number n is only related to its partial pressure P. By controlling the partial pressure of each gas entering the fixed volume gas mixing chamber, the gas can be mixed in the desired ratio. For example, a mixture of 70% CO 2 + 30% N 2 is used, and the total pressure of the desired mixture is assumed to be P. The mixed volume of indoor air is first removed. After feeding 0.7P of CO2 and 0.3P of N2, the desired ratio of the mixture can be obtained [4].
(2) Equal pressure composite gas mixing and distribution system
1- CO2 gas cylinder 2- O2 gas cylinder 3- N2 gas cylinder 4, 5, 6-inflating solenoid valve 7-control device 8-gas mixing chamber 9-deflation shut-off valve
The basic structure of the equal pressure composite gas mixing and distribution system is shown in Figure 3.
1, 2, 3 are CO2, O2, N2 gas cylinders respectively, 4, 5, 6 are solenoid valves for inflating the mixing chamber 8, 7 is a control device, and 9 is a shut-off valve for inflating the packaging container. The gas mixing and distribution system requires equal pressure between each gas source, and the effective cross-sectional area of ​​the gas-filled solenoid valves 4, 5, 6 of the three gases and their pipelines is in a 1:1:1 ratio, each The control ends of the solenoid valves are respectively connected to the control device, and the control device includes a time control circuit corresponding to each of the solenoid valves. Assuming that the mixing ratio of the three gases CO2, O2, and N2 is 7:2:1, the control circuit for setting the gas conduction time is set to 7:2:1 by the control device, so that when the gas mixing and distributing device operates, three types The gas flows into the mixing chamber 8 from the respective solenoid valves and pipes according to the set amount, and is mixed in proportion in the mixing chamber to become a fresh gas suitable for packaging food, and then filled into the packaging container through the shut-off valve 9, and the package is sealed. .
In the above basic structural composition, the pressures of each of the gas sources are equal, the effective cross-sectional area of ​​each of the gas-filled pipeline channels is equal, and the flow rate of the gas passing through the channels is equal within a unit time. Therefore, as long as the opening time of each gas-filled solenoid valve is adjusted, the purpose of adjusting the gas distribution ratio of the mixed gas can be achieved. During the working process, the opening and closing of each pneumatic solenoid valve is controlled by the control device, so that the opening time of each channel is consistent, and the closing time is determined according to the gas mixing ratio relationship.
This gas mixing and distribution system has the following characteristics:
(1) Using the ordinary solenoid valve and pipeline structure, the ratio of the mixed gas can be adjusted by controlling the opening time of each pneumatic solenoid valve, and the precision can reach the requirement of the proportion of food fresh-keeping gas.
(2) The system technical scheme is reasonable in concept and simple in structure.
(3) The gas mixing ratio of the system can be set and adjusted by the control device, and the automatic control and operation can be conveniently realized, and the function extension is better.
(4) The pressure requirements between various gas sources are equal. It is difficult to meet the requirements of commercial gas cylinders in operation. Therefore, it is necessary to have a gas source voltage regulator, which is difficult to achieve continuous air-filled packaging.
3 new composite gas mixing and distribution systems through the study of the composite modified atmosphere packaging machine gas mixing system, design and test a new composite gas mixing and distribution systems developed, FIG. 4 shows this new hybrid composite gas distribution system consisting of the basic structure . The key to the research is to eliminate the bulky gas mixing chamber in the system, and use the pneumatic proportional valve to open and supply the gas proportionally. The working principle is as follows: the CO2 gas with a certain pressure passes through the channel 1 as a double pneumatic The opening force of the proportional valve CO2 end valve, push the proportional valve to open, turn on the CO2 gas; turn on the CO2 gas as the opening power, open the O2 gas proportional valve through the passage 4, and open the N2 gas proportional valve through the passage 5. The three gases enter the solenoid valve at equal pressures respectively, and the CO2 gas enters the solenoid valve through the passages 2, 3, and 6; the O2 gas enters the solenoid valve through the passages 7, 8; the N2 gas enters the solenoid valve through the passages 9, 10, and then After mixing the three gases, they enter the packaging container for sealing and packaging.
The advantages of this new composite gas mixing and distribution system:
(1) The bulky gas mixing chamber is eliminated in the system, which further simplifies the structure and saves space.
(2) The pneumatic proportional valve is adopted, and a gas source with the same pressure is obtained with reference to a gas source pressure, and the gas of the set proportion mixing can be continuously supplied.
(3) The pressures of various air sources are the same, the size of the pipeline and the solenoid valve are the same, and the ratio of the mixed gas can be adjusted by setting and adjusting the valve opening degree by the control device, and the precision thereof is further improved.
(4) When the pressure of any of the air sources does not meet the requirements, the machine can be alerted and stopped by the control device. Replace the new gas cylinder and continue working after the system is turned on.
(5) It adopts computer automatic control and man-machine interface, which is convenient to adjust the gas combination of different proportions to meet the requirements of various packaged articles, and can realize multi-purpose of one machine.
(6) It can be designed and manufactured into an independent new compound gas mixing and distribution system, and it can be used with any type of air-packing machine.
FIG 4 continuously fed composite gas mixing and distribution system
Fig.4 The continuous compound gas mixing and supply system
1- CO2 gas cylinder 2- O2 gas cylinder 3- N2 gas cylinder 4-double pneumatic proportional valve
5- simplex pneumatic proportional valve 6,7,8-9-4 solenoid valve means for controlling the gas mixing new composite key technology of new hybrid composite gas distribution system of one of the techniques is the use of the key distribution system of the proportional valve in the system, The structure diagram is as shown in Fig. 5. The gas of the set pressure is introduced into the pneumatic proportional valve starting chamber, and the gas to be supplied is supplied to the pneumatic proportional valve supply chamber. When the pressures of the two gases are equal, the The delivery valve will open the delivery gas. Therefore, a gas with a set pressure can be selected as the starting gas source in the system. When the pressure of the other gas that is introduced into the pneumatic proportional valve reaches the pressure balance with the starting source, the pressure supply of each gas is achieved.
The key technology of the new composite gas mixed distribution system is the proportional control precision of the composite fresh-keeping gas. Due to the different performance characteristics of foods and vegetables, they are quite sensitive to the proportional characteristics of fresh-keeping gas. With the new composite gas mixing and distribution system, the proportional error of the supplied mixed gas can be less than 2%.
The new composite gas mixing and distribution system adopts computer automatic control and man-machine interface, and is used with the composite air-conditioning fresh-keeping packaging machine. It can adjust the gas combination of different proportions to meet the requirements of the packaged articles, and prolong the shelf life of the packaged products. It can truly guarantee the original juice, original taste and original appearance of food and vegetables. It is especially suitable for the production of agricultural and sideline products, agricultural and sideline products distribution centers, food processing enterprises, supermarket fresh agricultural and sideline products processing rooms, etc. The new composite gas mixed distribution system and composite gas fresh-keeping packaging machine is a development direction of food and vegetable fresh-keeping technology in the future.
Modern air-conditioning fresh-keeping packaging machine integrates microcomputer technology, vacuum technology, pneumatic technology, magneto-optical induction technology, program control technology and compound gas mixing technology. It has high technical content and process performance requirements, and foreign countries began in the late 1980s. Research and application, due to its obvious effect on food preservation, it has been rapidly developed. China's modified atmosphere packaging began in the 1990s, and the research and development and application of modified atmosphere preservation equipment is still in its infancy. The key technology of advanced multi-functional modified atmosphere preservation technology and equipment is to research and design a suitable compound gas mixed distribution system.