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Railway refrigerated transportation - an important field for the preservation of perishable food (Part 2)

2. Tibetan containers

refrigerated containers can achieve door-to-door transportation, which can reduce the loading and unloading operation time, reduce the loading and unloading of goods between different means of transportation, and thus avoid the temperature rise and the possibility of contamination of goods during the loading and unloading process. Because of these advantages, refrigerated containers are widely used in the transportation of perishable food abroad. According to statistics, the global reefer container inventory reached 629000 TEU in mid-1996, accounting for 6% of the total container inventory. The growth rate of refrigerated containers is quite fast. The number of refrigerated containers in 1997 increased by nearly 1.6 times compared with 1990. The world's refrigerated containers are mainly international standard containers of 20 feet and 40 feet.

foreign refrigerated containers are usually transported in groups or trains with centralized power supply during railway transportation. For example, the Canadian railway uses a 40 foot power box to centrally supply power to refrigerated containers, the flat car carrying the power box is hung in the middle of the train, and the containers are loaded in double layers. There is a power socket at the end of the generator box, and each generator box can supply power for 12 ~ 14 40 foot refrigerated containers. The automatic control of the generator box does not follow people. A direct train from Montreal on the east coast to Vancouver on the west coast can be opened without refueling

during the whole transportation, only the technical operation is carried out in Winnipeg to check the technical status of the box, and there is no technical operation in other stops, just to change the driver

at present, although there are several refrigerated container manufacturing plants in China, such as Yantai "iceship" and Yangzhou "Tongli", which are producing refrigerated containers, only from 1995 to 1996, the domestic production capacity of newly increased refrigerated containers reached an annual output of nearly 20000 containers, and Wuchang rolling stock factory also developed 20 foot refrigerated containers. However, due to the limitations of the current railway objective conditions, the power supply problem during the transportation of refrigerated containers cannot be completely solved for the time being, Therefore, while the domestic railway competes with its peers in these traditional packaging fields to consolidate the market, the refrigerator has not yet formed a batch transportation capacity.

(II) transportation of perishable food

for a long time, China's railway refrigerated transportation has been playing a major role in the transportation of perishable food throughout the country, and has made significant contributions to ensuring supply, regulating surplus and shortage, and meeting the growing demand for perishable food in people's lives. Although the road transportation volume has increased in recent years, the railway transportation of perishable food still plays a vital role. In 2001, the transportation volume of fresh and perishable goods was 7.328 million tons. In the transportation of perishable food, 25.8% are completed by cold cars, 12.8% by machine cold cars, and another part is completed by open box cars (mainly fruits and vegetables, but also a small amount of meat and fish); The refrigerated transportation rate is about 40%, an increase of 20 percentage points from less than 20% in the early 1990s. Nevertheless, there is still a large gap with the 100% refrigerated transportation rate of foreign developed countries.

"express" is very important for the preservation of perishable food. Therefore, China's railways opened three express trains to provide fresh and live goods for Hong Kong in the 1960s, which played a positive role in ensuring the food supply of Hong Kong residents and promoting the prosperity and stability of Hong Kong. In order to further improve the work of transporting vegetables from the South and fruits from the south to the north, Liuzhou Railway Bureau has operated a green channel fruit and vegetable express train from Zhanjiang to Zhengzhou since December 1998, and the loading destinations include more than 50 cities in the three north directions. As of May 31, 2000, 397 trains, totaling 14327 vehicles, have been operated in the two transportation seasons for nearly a year. In addition, a total of 622000 tons of fruits and vegetables have been sent. The income of western Guangdong and Hainan alone is more than 900million yuan, of which the railway directly contributes more than 17million yuan to the society, which has played a huge role in promoting the economic development of these two regions and achieved good economic and social benefits. The emergence of parcel express has opened up a faster way for the transportation of perishable food, which is deeply welcomed by shippers. Urumqi Railway Bureau shipped 30000 tons of fruits and melons in 1998, accounting for 21% of the total export volume of fruits and melons of the Bureau. Guangzhou Railway Group Corporation also accounted for 10% of the fresh and perishable goods in the luggage special train in 1999

the emergence of various express transportation forms has provided favorable conditions for reducing the quality loss of perishable food in the transportation process and improving transportation services, as well as for perishable food distributors to seize the time to compete for the market. In order to further ensure the transportation quality of perishable food, relevant railway research institutes and colleges and universities in China have carried out a series of experimental studies on the transportation conditions of perishable food for many years, including the controlled atmosphere storage and transportation tests of some delicate fruits such as litchi, which provides technical support for improving transportation regulations and transportation technology

III. new requirements of the green channel for railway refrigerated transportation

the implementation of the "three green projects" green channel puts forward higher requirements for railway refrigerated transportation, which is to further strengthen the transportation quality system, ensure that perishable food is fresher and safer in transportation, and ensure the transportation quality for residents to eat green and safe food. For this reason, the following aspects should be done well

(I) change the composition of refrigerated transportation tools to further improve the technical performance of refrigerated trucks

the change of the composition of refrigerated transportation tools here refers to the formation of batch transportation capacity of new transportation tools such as single section machine cooled cars, special luggage cars and refrigerated containers as soon as possible. To improve the technical performance of refrigerated trucks, we should further improve their heat insulation performance, refrigeration capacity and temperature control level, so as to ensure strict temperature standards and further develop to humidity control

according to the famous "t, t, t" theory, which realizes one of the "cold chain" conditions, time - temperature - is closely related to the allowable quality (or daily storage resistance) of food (tolerance). For each perishable food, there is a definite relationship between the quality decline of food and the time experienced at a certain temperature. For example, the quality loss of frozen beef stored at -15 ℃ for 120 days is almost twice that stored at -20 ℃ for 150 days. Therefore, it is of great significance to ensure the transportation quality that the temperature of perishable food is always within the appropriate temperature range during transportation. The main factors that affect the temperature and temperature control level in the engine cooled vehicle include the heat insulation performance of the vehicle body, the cooling capacity of the unit, and the accuracy and reliability of the temperature control equipment

from the perspective of domestic B23 machine cooled vehicle at present, although its technical performance is greatly improved compared with the old machine cooled vehicle, its body structure is still a hybrid structure, including polystyrene board filled and polyurethane foam with sandwich structure. Therefore, it is necessary to further optimize the design that the rebound force of the product is absorbed by the workpiece, and improve the car body structure and production process, so as to further improve the heat insulation performance of the car body. At the same time, we should also study and master the aging law of the heat insulation performance of the car body under the application conditions, and study and improve the air distribution mode of its ventilation system, temperature uniformity and other issues.

in terms of refrigeration units, although the technical performance of the newly developed lft56 unit is greatly improved compared with the old unit, its unit volume and unit weight cooling capacity are 3008w/m.3 and 9.5W/kg respectively, which is still a certain gap from the international advanced level of 4000W/m.3 and 12W/kg. To narrow this gap, we should start from the overall structural design of the unit and heat exchanger.

in order to further improve the accuracy and reliability of temperature control equipment, computer control technology should be developed and applied; In addition to the traditional automatic temperature control function, the microcomputer control should also realize the functions of temperature clamping the standard tensile sample of the corresponding force value on the experimental machine, the display, recording and data storage of operating parameters, as well as the self inspection, self diagnosis and display of faults.

temperature also affects the transportation quality of food. Excessive temperature is easy to accumulate condensate on the surface of packaging or food, which is conducive to the breeding of microorganisms; Too low humidity will increase the dry consumption of food. The existing refrigerated truck can only control the temperature, and has no humidity control function. In order to further improve the freshness of the transported food, we should actively develop the humidity control system of the refrigerator truck.

judging from the current structure of China's railway refrigerated transport vehicles, they are mainly group machine cooled vehicles and ice cooled vehicles. As mentioned earlier, the cold car is a kind of car that should be eliminated, and production has been stopped at present. However, the ice cold car is the only single car in the batch operation of China's railway at present. The transportation of perishable food has the requirements of small batch and multi variety transportation. Therefore, it is urgent for the railway to replace it as soon as possible with refrigerated transportation tools with more advanced technical performance suitable for the transportation of small batch goods. Single section machine cooled trucks and refrigerated containers are ideal alternative tools. We should solve and implement the construction and operation management mode of supporting facilities for single section refrigerated trucks and refrigerated containers as soon as possible, so that they can play a role in railway refrigerated transportation as soon as possible. 

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