Refrigerated, Land, Air and Sea Transport

Vehicles used for refrigerated transport must be built in accordance with national and international standards to ensure the integrity and preservation of the products.

According to data from the Food and Agriculture Organization of the United Nations (FAO), it is estimated that the world production of perishable food is more than 450 million tons, 10% are objects of long-distance world trade; and the rest is consumed in the country or lost (about 30% of fruits and vegetables).

These global assessments mask large differences between continents and countries. In the most industrialized nations, processing and consumption are better organized and the part exported can be increased, as reported in the Guide to Refrigerated Transport published by the International Cold Institute in 2006.

The same document specifies that "international trade in perishable goods comprises seven major groups. Certain products (fish, meat...) are usually transported dead. Others, specifically fruits and vegetables, plants, bulbs and cut flowers, remain alive, absorb oxygen and give off carbon dioxide. They emit heat and water vapor. This imposes particular limits on the refrigeration techniques used in their conservation and transport."

We also find "non-food products such as chemical, pharmaceutical, photographic and medical products, which must also be transported at a controlled temperature."

"The transport and marketing of all these products requires the implementation of adapted techniques to protect them, as continuously as possible, against temperature variations from the outside, as well as for live products against the consequences of breathing. The set of these techniques and the means put into practice is known as the cold chain."

In this sense, it should be taken into account that the proper handling of products during transport is crucial for the safety of products. All the time and efforts spent on reducing microbial contamination during production, harvesting, washing and packaging will have been futile if the transport conditions are not adequate. Loading, unloading and transport operations can result in direct contamination by contact with other products, whether food or not. It is necessary to evaluate hygienic conditions wherever they are transported or handled.

Fresh fruit and vegetable products are usually transported in isothermal boxes with or without internal cooling, so it is important to remember that transport companies also mobilize other types of products.

In the best case, refrigerated boxes or containers should be used only to transport the same type of food, and should be thoroughly cleaned and disinfected between loads. Another aspect of great importance is to prevent food of agricultural origin from being transported in boxes that have been used to mobilize meat, fish, seafood, eggs or chemicals, unless it has been washed and disinfected correctly.

These aspects are detailed in the Manual of Storage and Transport of Fresh Fruits and Vegetables in Matters of Safety. But it is also important to take into account the following consideration: before starting the loading process, refrigerated trucks or boxes must be inspected to ensure that they are clean, that they do not present odors and that no dirt or waste is seen in them.

Workers participating in the loading and unloading process must at all times adopt the Good Hygiene and Cleaning Practices described in the company's policies. In Mexico, refrigerated transportation for the domestic market is incipient, since a large number of fresh products are handled by public transport without adequate refrigeration conditions. Only export products (fresh or frozen) or products of high commercial value (with added value) have adequate refrigeration logistics.

That is why all people involved in the transport not only of fruits and vegetables must actively participate, ensuring that at all stages of the transport chain, the cleaning and hygiene requirements related to trucks and other forms of transport are met.

The thermal load depends on the capacity of the vehicle, amount of product transported, cooling medium (air, ice, etc.), product temperatures (refrigeration or freezing), the variation of the ambient temperature during the transfer, etc.

COLD TRANSPORT

The refrigerated transport of food can be carried out in three ways: by land, sea, air or rail. Using thermally insulated vehicles or containers and equipped with refrigeration equipment capable of maintaining a sufficiently low temperature.

These transport vehicles must be built in accordance with national and international standards. Generally, the standards specify the maximum heat transmission economically allowed, through the insulated bodywork. Meanwhile, land refrigerated transport is classified according to the cooling method, distance to travel, construction materials, among the most important factors (see Figure 1).

Vehicles can have different cold production systems:

Mechanical systems

Provided with a mechanical compression system for optimal regulation and control of temperature and therefore cold needs inside the boxes or containers.

Non-mechanical systems

» With ice. When used in refrigerated trailers it is also known as high temperature transport. Ice provides satisfactory cooling for products that must maintain a temperature scale of 2°C to 4°C (see Figure 2).

» Dry ice (Solid carbon dioxide) This system is used in trucks to produce temperatures close to -18°C. A great advantage of dry ice is that, as a refrigerant, it sublimates. As the temperature of the dry ice is approximately -79°C, after sublimation additional cooling results. By sublimating the dry ice, the resulting carbon dioxide gas expels the air from the vehicle. If the cargo is a vegetable product, the deterioration due to oxidation is reduced by the removal of air, in other cases, such as in the transport of fresh meats, this gas provides bacteriostatic properties on the product. This system is free of mechanical failures, plus it is convenient because it is clean.

» Eutectic plates are containers containing a eutectic solution. Generally the eutectic solution is high-concentration brines or glycol solutions. The size of the plates is determined by the amount of eutectic solution needed to provide the appropriate heat absorption capacity for the estimated duration of service. To facilitate repeated freezing operations, a coolant coil is constructed inside the plate, where a chiller or coolant brine is circulated from a mechanical system during the period of temporary shutdowns.

The simplicity of the construction and the limited need for maintenance make this a reliable system.

Storage plates are designed to be mounted on the ceiling or wall. Sometimes a fan is installed in the body to obtain a uniform temperature (see Figure 3).

Eutectic plates provide cold only for a limited time, usually one day of service. This requires it to be refreezed to provide service the next day. The plates can be connected to quick couplers with a remote system as shown in Figure 4.

» Liquid Nitrogen System Liquid nitrogen has a very low boiling temperature (–196°C) at atmospheric pressure; consequently, the mobile vessel containing it must be specially constructed with extraordinary insulation and pressure relief valves. One or more containers can be used in each vehicle, the amount of this refrigerant depends on the size of the compartment, thickness of insulation on the walls, floor and ceiling, the storage temperature and the number of door openings. This system allows to cool multiple compartments. Loads whose temperature requirements are different can be transported in the same vehicle.

The advantages of the liquid nitrogen spray system are as follows:

1. Rapid recovery of desired temperature in the compartment.

2. It provides an inert atmosphere that not only reduces the rate of respiration of fruits and vegetables but also protects against decomposition by excluding oxygen.

3. Simplicity of the equipment, minimum of moving parts and easy maintenance.

» Combination of low temperature evaporator and nitrogen system These combinations are suitable to preserve product quality and reduce annual refrigeration costs for delivery service (see Figure 5).

The low temperature evaporator is responsible for compensating for heat inputs to the body, reducing the temperature of the returned product during the loading operation on the platform, providing cold at night, weekends or the hours when the truck is stationary. While the liquid nitrogen system is responsible for compensating for heat leaks to the body mainly by opening doors.

» Combination of nitrogen-eutectic plates-evaporator Combinations of systems such as liquid nitrogen, eutectic plate and evaporator at low temperature, constitute a desirable method and a lower annual cost than liquid nitrogen. This type of combination also provides continuous cooling of the product and the additional protection of two independent cooling systems.

According to a report by the SCT, until 2005 it was known that the states that concentrated the largest part of the registrations of the refrigerated fleet in the country were Sinaloa, Distrito Federal, Nuevo León and Baja California. On a second level is Sonora, Jalisco, Michoacán and Chihuahua.

»Combination of eutectic plates-nitrogen. It is a system of eutectic plates and liquid nitrogen. The plates compensate for heat inputs at 16°C, provide protection for the product. While nitrogen compensates for the temperature by opening doors above 16°C (see Figure 6).

» For the choice of vehicle should be considered mainly:

• Duration of transport

• Distance to travel

• Frequency of door opening

• Investment costs in vehicles

• Maintenance

» Factors to consider. To remove the heat that penetrates, and prevent it from affecting the load, a forced cold air circulation is necessary. Air should be directed between the load and the vertical walls and floor of the vehicle. Air circulation should ensure a uniform temperature. In addition, modern vehicles must be manufactured with sandwich panels, and thus avoid with extreme care the penetration of moisture and avoid mechanical damage.

It is necessary and recommended as a preventive measure, to check at regular intervals the physical condition of the structures. Inside the body, any surface that may come into contact with food shall be made of materials that do not affect its smell and taste. All interior walls will be smooth, resistant to corrosion and cleaning agents, waterproof, fungal-proof, easy to clean and disinfect. The exterior dimensions of vehicles are limited by traffic regulations. The maximum interior volume is obviously sought, for which it is necessary to adopt walls as thin as possible.

Materials for making refrigerated boxes

The most important component of the vehicles is the isothermal box composed basically of the following materials:

1. A rigid support (wood or metal) that provides mechanical strength to the case.

2. The insulating material (expanded polystyrene or expanded polyurethane) that provides thermal protection and ensures temperature maintenance during the transfer of products.

3. From an isothermal and hermetic door.

4. Of the internal devices for an adequate circulation of the air in quantity and speed to keep the interior temperature constant.

RAIL TRANSPORT

The capacity of refrigerated wagons can reach up to 60 to 70 tons (for long distances). As in vehicle transport, insulating coating, cooling system and loading and unloading should be considered in rail transport.

Therefore, the cooling systems of wagons are similar to those of trucks and must have the following characteristics:

•For low temperatures, wagons cooled with dry ice, is the most widespread transport.

•Wagons cooled with liquid nitrogen are quite common in America and are beginning to be introduced in Europe.

The main disadvantage of this cooling system is its high cost of nitrogen.

•The eutectic plate system allows the wagon temperature of -18 to -20°C to be maintained for two days.

If it is very long transports, a small amount of carbonic snow can be coupled.

•Cooling wagons with refrigeration machines is the most frequent method than previous systems.

•The equipment is located at one end of the wagon, the equipment can be of adjustable power; in addition, to enter into function automatically.

» Characteristics of the insulator. The requirements of the coating broadly coincide with those of trucks. The outer lining of refrigerated wagons is usually made of welded steel sheet, which constitutes an impermeable barrier of vapors and gases.

The insulation of the floor, walls and ceiling is with polystyrene or polyurethane foam. And to reduce the thermal action of the sun's rays, the outer face of the wagons is painted white and the roof should have special protection from the sun.

SHIPPING

The perishability of fresh produce, coupled with the property they have of being heated in confined spaces, gives rise to rapid deterioration and decomposition, which explains why unrefrigerated ships are rarely used for transport over long distances and in these cases, the levels of deterioration are very high.

Improvements in the design of unrefrigerated ships are unlikely to be made in order to make the transport of fresh produce less risky.

In most cases, maritime transport is carried out with refrigerated ships, which are widely used in the export of fresh products. Maritime transport, because of the duration of the trips, is a form of cold storage, so all the necessary precautions for this type of storage are valid in these circumstances.

» Refrigerated Boats. Fully equipped for cooling, they have efficient systems for air circulation and air exchange rate control. Loading is facilitated by the existence of side hatches or by the use of special continuous conveyor belts that transport the individual packages from the loading dock to the central hatches of the ship and then to the cargo holds (they are used in the same way for unloading).

Refrigerated ships are generally of large capacity (greater than 4,000 tons) and regularly transport fresh produce, mainly fresh or frozen fruit and vegetables, around the world. The factors that limit their use are the duration of trips that can be longer than the storage life of most products and the considerable handling that is required to load and unload. Palletizing products has greatly reduced handling, but bulk handling of individual packaging is still widely used.

» Refrigerated containers. They are a specialized form of shipping that is rapidly gaining international popularity. Each container may have its own independent cooling system, which is connected to the ship's electricity network, or it may have at one end special air ducts, which are aligned in relation to the ship's ducts so that cooling is provided entirely by the ship's own system ("Con-Air" system).

Refrigerated containers have standard dimensions, all are 8×8 feet wide, but can be 10, 20, 30, or 40 feet long. The most commonly used dimensions are 40 feet and then 20 feet. The container can be purchased or leased; its cost can be very high and can vary in quality and performance.

Its main advantages are:

• They allow the shared use of the ship for containers refrigerated by many producers of different products, as long as they have access to the use of containers and that they are exporting by the same route.

•Independently set and monitor the temperature.

• Able to quickly pre-cool the product under tropical environmental conditions.

Its disadvantages are:

•The purchase or lease is very expensive.

•They are large and heavy and require special equipment for handling.

•It is necessary to hire more containers thanthose used due to the time it takes to return and due to decomposition.

•Not all countries have facilities to handle containers, which limits the ports of embarkation and disembarkation, although some ships are loaded and unloaded with their equipment.

In modern transport vessels, refrigeration with refrigeration machines is used exclusively, due to the duration and distance of transport. The ships have in their structure with traditional constructions of cold rooms, but currently they begin to be replaced by "containers" ships with the corresponding cargo spaces. Depending on the type of load, the temperature handled ranges from 12°C to –30°C. The size of these vessels can be from 100 to 600 thousand ft³.

AIR TRANSPORT

Air transport is very expensive and is only justified for high-value export products, such as exotic tropical fruits and vegetables for markets in Europe, North America and other countries that do not produce them in certain seasons of the year. These markets are very sophisticated and demand products of the highest quality, which must be carefully packaged in standardized and correctly labeled containers.

All air exports require careful market research, planning, organization and administration. To be successful, a pre-cooling facility, refrigerated trucks and possibly refrigerated facilities at the airport need to be incorporated into the infrastructure. Due to the weight of the facilities and insulation, it is impossible to build refrigerated aircraft. Insulation difficulties are accentuated by the pressure difference between the prevailing conditions on the ground and during flight at altitudes of 9,000 to 12,000 m. In addition, the possibility of using dry ice and nitrogen systems is reduced, due to the danger of the decrease of oxygen in the atmosphere of the aircraft. The only admissible solution is the transport of the products in containers.

Authors:

See original.