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Reefer cargo stuffing- Pre-cooling, treatment & handling of a reefer container

Pre-treatment of reefer products prior stuffing

The condition of reefer products before they are stuffed plays an important role in their condition upon arrival. That is why it is essential that all products are treated correctly prior to stuffing. Even though the temperature, ventilation and humidity are all optimal during the entire voyage, products will only arrive in perfect condition if the pre-treatment has been performed correctly. Successful shipping begins at the product sourcing area.

Pre-cooling of cargo

The proper pre-cooling of products will have a positive effect on both shelf life and out turn, compared to products that have not been pre-cooled. Reefer containers are built primarily to maintain the temperature of the products, therefore, products should always be pre-cooled to the required carriage temperature prior to being loaded into the container.

No pre-cooling of reefer container itself

Pre-cooling of the reefer container itself should never take place. Once the doors of a pre-cooled container are opened, hot ambient air will meet internal cold air, resulting in a large amount of condensation on the interior surfaces.

As a result, condensed water may drip from the roof of the container and cause stains and weaken the structure of the boxes. Therefore, condensed water must be removed through the evaporator located inside the reefer machinery. Heat that enters the container during stuffing, combined with heat that is constantly generated by the “respiring” cargo, must also be removed through the evaporator.

As soon as water and heat pass the evaporator, ice is formed and the machinery enters a short defrost mode. Consequently, there will be less capacity available for cooling the cargo. In a tropical climate with excessively hot and humid air, any pre-cooling of the container is likely to cause problems and damage the products.

Pre-cooling of the reefer container is only allowed when the container is connected to the cold store and the temperatures are identical. The connection is achieved by the use of a “Cold Tunnel” – a tight duct between the cold store and the container, which prevents ambient air from entering.

Air delivery container with chilled or frozen cargo
Fig 1 :Correct way of stuffing chilled cargo

Things to do during stuffing

The stuffing and placement of cargo will directly affect the flow of air. Figure above illustrates the correct way to stuff a bottom-air delivery reefer with chilled or frozen cargo. In the case of chilled cargo, covering the entire floor with cargo forces the cool air to flow through both the cartons as well as the product, throughout the entire load. When frozen cargo is stuffed in this manner, the cold air flows around the cargo – blanketing the cartons and removing any heat that enters the reefer container through the walls.

Improperly stuffed chilled or frozen cargoReefer stuffing incorrect way
Fig 2 :Improperly stuffed chilled or frozen cargo

Things not to do during stuffing

Air always takes the path of least resistance. Here are a few examples that illustrate reefer cargo which has been stuffed improperly. In the first three examples, air tends to “short circuit” or flow past the cartons/products rather than through them. The last two examples illustrate restricted airflow scenarios.

Never run a reefer with doors open

When the ambient temperature is warmer than the cargo, operating the reefer with the rear doors open will not cool down the cargo . Rather, the introduction of hot ambient air will heat up the cargo. When hot humid air enters the reefer, moisture condenses on the cold cooling coil and turns to ice.

Cooled air escapes through the rear door, and the cycle continues. Once stuffing is complete and the doors are closed, the reefer could run for hours with a partially iced-up cooling coil. This would reduce its cooling effect and put the cargo in danger until the unit completes a defrost cycle. Further, the genset should be stopped during stuffing, due to the risk of exhaust gas reaching the fresh cargo. Fig. 1 The correct way to stuff a bottom-air delivery container with chilled or frozen cargo

To avoid cargo damage :

• do not leave any areas open or uncovered on the floor, the front bulkhead or the side walls (if pallets are placed at the front bulkhead, be sure to place cardboard under empty pallets)
• do not run unit with rear doors open
• do not stuff cargo beyond the end of the T-floor
• do not plug channels at the end of the T-floor
• do not stuff cargo above the red load line
• do not put reefer set point at a temperature below what is required for the cargo (this will not expedite the cooling process)

Optimal stuffing of reefer cargoReefer container configuration

Fig 3 : Optimal stuffing of reefer cargo, Fig: Reefer container inside

Optimal stuffing – Top View

Covering the floor in a proper manner will improve the flow of air and hence, refrigeration. In order to force air up and through the cargo, the entire floor should be covered. Cover the floor from the front bulkhead to the end of the T-floor. Where the cargo does not cover the floor, some type of filler should be used, such as dunnage or cardboard. Do not stuff past the end of the T-floor with cargo or filler (fig. 3).

Reefer stuffing for blocking or bracing cargo
Fig 4 : Reefer stuffing for blocking or bracing cargo

Blocking and bracing

For blocking and bracing cargo, wood is still the preferred material. Use wood as necessary (fig. 4), but do not nail wood or dunnage to the container. Cover floor with a filler between pallets to help force air through the cargo (as seen in the Top 4 view, fig. 4). Cover the ends of the last two pallets in order to force air up and through the cartons. Do not block off airflow past the end of the T-floor.

Other useful articles :

  1. Methods of refrigeration

  2. Refrigeration is essentially the removal of heat through the process of evaporation. We choose to refrigerate commodities such as fruits and vegetables because we want to prolong their “practical shelf life” – the time from harvest until the product loses its commercial value.
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  3. Reefer cargo stuffing

  4. it is essential that all products are treated correctly prior to stuffing. Even though the temperature, ventilation and humidity are all optimal during the entire voyage, products will only arrive in perfect condition if the pre-treatment has been performed correctly. Successful shipping begins at the product sourcing area.
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  5. Growing demand for container refrigeration

  6. On deck refrigerated containers are generally serviced by clip-on air cooled electric motor drive cooling units. The units are plugged into the ships electrical system by way of suitable deck sockets.
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  7. Frozen products packaging requirement

  8. Proper packaging procedures will help protect frozen cargo during transport. Frozen products do not require air holes in the top and bottom of the cartons. Air flowing around the load is sufficient to remove heat that has penetrated the container. The cartons should be stacked directly on top of each other to take advantage of their strength in the corners.
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  9. Packaging & stowage guideline for reefer cargo

  10. Packaging plays an important role when it comes to protecting the cargo. The packaging material must be able to support a stacking height of up to 2.4 metres (7’10’’). The material should be able to withstand humidity without collapsing, and should allow the passage of an adequate vertical airflow through the cartons in order to maintain the desired temperature..
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  11. Choice of packaging for various commodities

  12. Goods should be well stowed within the package, evenly distributed and properly secured. Items completely filling the case or carton contribute to the strength of the whole package. Items which do not completely fill the package must be cushioned against shock or vibration.
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  13. How to keep cargo fresh ?

  14. Proper ventilation of fresh, chilled products is necessary to remove the heat, carbon dioxide and other gases produced by the cargo. Heat is removed by continuously circulating the internal air, whereas carbon dioxide and other gases are removed by replacing the internal air supply with cooled fresh air..
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  15. Loading precautions for refrigerated cargoes

  16. Refrigerated cargoes include meat carcases, carton (packed) meat, fruit, cheese, butter, fish and offal. Ships are specifically designed for their carriage, with separate spaces in holds and ’tween decks, each fitted with suitable insulation and individual control of ventilation. Ordinary general cargoes may be carried in the spaces at other times, the temperature being regulated accordingly for the type of cargo being carried.
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  17. Role classification societies maintaining seaworthiness of vessels

  18. classification societies publish rules and regulations which are principally concerned with the strength of the ship, the provision of adequate equipment, and the reliability of the machinery .
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  19. Periodic survey requirement by classification societies

  20. To maintain the assigned class all steel ships are required to be surveyed and examined by the Society’s surveyors at regular periods. The major hull items to be examined at these surveys only are discussed here..
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