Refrigeration – Processes – Deodorizing – antisepticizing or providing special atmosphere
Reexamination Certificate
2000-10-19
2002-10-08
Capossela, Ronald (Department: 3744)
Refrigeration
Processes
Deodorizing, antisepticizing or providing special atmosphere
C062S127000, C062S179000
Reexamination Certificate
active
06460352
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to methods and apparatus for controlling the composition of the atmosphere within a container, in particular refrigerated containers during the storage and/or transportation of produce which is perishable and which may respire, such as fruit, vegetables and flowers. (The word “container” as used herein includes not only individual refrigerated containers such as standard ISO transportable containers but also enclosed stores, parts of warehouses, ships holds and the like).
BACKGROUND OF THE INVENTION
It is known that such perishable and/or respiring produce may be carried in refrigerated containers, and refrigeration units have been developed for use with such containers, which units are reliable and function efficiently for long periods of time.
It is also known that perishable and/or respiring produce is affected by the surrounding atmosphere, and that, by modifying the composition of the atmosphere surrounding the produce, its preservation in storage or during transportation can be enhanced. Specific atmospheric components which are usually considered are hydrocarbons, carbon dioxide, oxygen and water vapour. Hydrocarbons are evolved by some types of fruit and vegetable, and these can promote rapid ripening and are therefore undesirable in storage/transportation atmospheres; the principal hydrocarbon is ethylene (C
2
H
4
), and hereinafter and in the accompanying claims the use of the word “ethylene” should be considered to embrace all hydrocarbons, whether evolved by respiring produce or present in ambient air. Carbon dioxide is also produced by respiring products, and is known to have either an adverse or a favourable effect on the preservation of such products. Oxygen and water vapour are also known to affect the preservation of many perishable products, and generally a lower than atmospheric level of oxygen is useful for preserving perishable products.
A problem in controlling the atmosphere surrounding perishable and/or respiring produce in a refrigerated container is that the atmospheric requirements for optimum preservation vary between different kinds of fruit and vegetable. Also, different fruits and vegetables respire at different rates and evolve differing amounts of carbon dioxide, ethylene and/or water vapour. For example, whilst most fruits and vegetables require a carbon dioxide level of about 5% (for example apples and pears about 1% to 3%, cabbage about 3% to 6%), some need a significantly higher level, such as raspberries and strawberries which generally need 15% to 20% carbon dioxide. Similarly, optimum oxygen levels can vary between 2% to 3% (for examples olives, apricots and broccoli) and 5% to 10% (for example figs, lemons and peppers). High respiring products, such as apples and pears can rapidly reduce oxygen levels in a closed container below the levels required for optimum preservation. Relatively high levels of relative humidity are preferred for the preservation of most perishable products; however excessive levels of relative humidity are undesirable as they can promote rotting—although in practice overly high levels of relative humidity are unlikely to occur in the refrigerated atmosphere within a refrigerated container. On the other hand, unduly low levels of relative humidity are usually harmful as they promote dehydration of the produce, which can adversely affect both weight and quality. Accordingly, there is a need for a system to control the atmosphere within a refrigerated container and which is capable of adapting easily to the differing atmospheric requirements of different products, whilst being efficient, effective and relatively simple and inexpensive to manufacture and operate.
SUMMARY OF THE INVENTION
In accordance with one aspect of the invention, there is provided a method of modifying the composition of the atmosphere within a container during the refrigerated storage and/or transportation of perishable and/or respiring produce therein, comprising the following steps:
a) withdrawing and pressurising a portion of said refrigerated atmosphere;
b) adsorbing water vapour from said pressurised atmosphere by passing it concurrently through a layer of an adsorbent which preferentially adsorbs water vapour from said atmosphere;
c) adsorbing carbon dioxide from the water vapour—depleted atmosphere by passing it concurrently through a layer of an adsorbent which preferentially adsorbs carbon dioxide from the atmosphere;
d) adsorbing ethylene from the water vapour and carbon dioxide-depleted atmosphere by passing it concurrently through a layer of an adsorbent which preferentially adsorbs ethylene from the atmosphere;
e) returning the water vapour, carbon dioxide- and ethylene-depleted atmosphere to the container, and
f) regenerating the adsorbent layers by passing ambient air therethrough in a countercurrent direction and thereafter venting said air to ambient atmosphere, wherein water vapour is adsorbed from said ambient air by passing it through a layer of an adsorbent which preferentially adsorbs water vapour from said air before it passes through said ethylene and said carbon dioxide adsorbent layers.
The method is preferably carried out with the above steps being conducted in the order stated.
Such a method (in which the adsorption/desorption processes are preferably carried out on a pressure-swing basis, although those skilled in the art will appreciate how they could be effected on a temperature-swing basis, both pressure-swing and temperature-swing modes of operation being well documented in the art of separating air or gas mixtures into their component parts) is advantageous because it enables the minimum number of separate adsorption processes and/or the minimum size of adsorption apparatus to be used for effective atmosphere control, which (because most adsorption processes do not effect a total separation of each component from the atmosphere) minimises the loss of atmosphere components which are needed to be returned to the container. The method is therefore very efficient. In addition, because it is possible to minimise the number of adsorption processes, it is possible to provide a system which is sufficiently compact to fit within the confines of a standard container but without occupying too much of the available storage space. In particular, the initial adsorption of water vapour and carbon dioxide (in steps b) and c)) can be effected in a single layer of adsorbent material. Additionally or alternatively, all the adsorption steps can be effected in a single adsorption vessel, containing several layers of adsorbent.
Because the ambient air will nearly always contain significantly more water vapour than the refrigerated atmosphere within the container, it is necessary to dry the air for regenerating the adsorbent layers before it reaches the carbon dioxide adsorbent layer (so as to protect the adsorbent material therein) and, optimally, before it reaches the ethylene adsorbent layer; contamination of these layers with water would be likely to degrade their adsorption characteristics to an unacceptable and even irremediable extent.
As part of the process of regenerating the adsorbent layers, the adsorption vessel may be vented to atmosphere prior to the regeneration step (i.e. between steps e) and f)).
During the removal of carbon dioxide, particularly from the atmosphere withdrawn from a container holding produce with a high respiration rate, a partial vacuum is created within the container. Because in practice it is not feasible to make standard containers completely sealed to the ambient air, this vacuum draws ambient air into the container, significantly raising at least the oxygen level within the container and so adversely affecting the preservation of the produce.
Consequently, the method may further comprise pressurising ambient air and depleting it of water vapour, oxygen, carbon dioxide and ethylene by adsorption thereof, cyclically with steps a) to f), and passing the resulting nitrogen-rich atmosphere into the container.
As can be appreciated, cycling the injection
Deng Shuguang
Garrett Michael Ernest
Heywood Michael John
Lemcoff Norberto
Whiteman Ralph John
Capossela Ronald
Cohen Joshua L.
Pace Salvatore P.
The BOC Group plc
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