GAS IRRADIATION TREATMENT

Abstract: Apparatus for treatment of gas for admission to a controlled atmosphere container, comprises a compressor, and a radiation source for irradiating gas flowing towards the container. The radiation source is arranged so that gas to be irradiated with radiation from the radiation source is exposed to heat generated by the compressor to cause the temperature of the gas and, as a result, its susceptibility to a reaction initiated by the radiation from the radiation source to increase.

Description: GAS IRRADIATION TREATMENT This invention relates to apparatus for treatment of gas for admission to a controlled atmosphere container and to a method of treating a gas. The method is applicable to degrading one or more components of a mixture of gases. It can be desirable to treat a gas for admission to a controlled atmosphere container, for example to optimise the atmosphere for goods to be stored in the container. For example, the storage life of perishable goods within a transportation container can be affected by the amounts of gases such as oxygen, carbon dioxide and certain hydrocarbon gases in the container. It is known to use adsorbent materials to separate components such as oxygen, carbon dioxide and nitrogen. Adsorbent materia such as a molecular sieve material adsorbs one of the components of the mixture preferentially relative to another of the components . Apparatus which comprises two adsorbent chambers allows the adsorbent in one of the chambers to be used for separation while the adsorbent in the other of the chambers is regenerated by passage through it of a purge stream of gas supplied from the outlet of the chamber that is in use for separation. It has been found that hydrocarbon materials present in gas mixtures can be made to degrade when subjected to irradiation. The present invention provides a technique for enhancing a radiation initiated reaction of a gas that is to be admitted to a controlled atmosphere container by heating it prior to the irradiation using heat from a compressor. Accordingly, in one aspect, the invention provides apparatus for treatment of gas for admission to a controlled atmosphere container, which comprises: (a) a compressor, and (b) a radiation source for irradiating gas flowing towards the container, arranged so that gas to be irradiated with radiation from the radiation source is exposed to heat generated by the compressor to cause the temperature of the gas and, as a result, its susceptibility to a reaction initiated by the radiation from the radiation source to increase. The invention has the advantage that it enables the reaction of a gas (especially a degradation reaction) to be optimised. Heat that used to optimise the reaction is available without increasing the energy costs. Furthermore, the gas can be heated without having to incorporate additional heating components, allowing the apparatus to be constructed simply and at lower costs. It also allows reliability problems to be minimised. The compressor from which the heat is derived can be the one that is used to circulate the gas in the container. The heat which is used to heat the gas to be irradiated can be waste heat from the compressor. This can be used for example by passing gas to be irradiated over the compressor before admission to the apparatus . It might also be heated by incorporation in a heat exchange unit of a heat sink on the compressor and the conduit for the gas to be irradiated. It is particularly preferred that the heat is supplied from gas that has been heated as a result of compression due to the compressor. For example, the conduit for gas from the compressor and the conduit for gas to be irradiated can be arranged in heat exchange relationship. This might be achieved by appropriate wrapping of one of the conduits around the other. The conduit for gas from the compressor can be arranged around the chamber in which the irradiation takes place. The apparatus can be used to treat gas that is to be admitted to a container in which the gas is refrigerated. The heating of the gas by means of a compressor in the apparatus can assist in the balancing energy transfers in the apparatus. For example, when the gas to be irradiated is heated by heat exchange with a gas heated by the action of a compressor, that compressed gas will be cooled in part before supply to the refrigerated container, minimising temperature gain in the container when the new gas is admitted. When the apparatus is used to treat gas for admission to a refrigerated container, it can include a refrigeration unit for gas in the container. The compressor which generates the heat for the gas can then be incorporated into the refrigeration unit . Surprisingly, the technique of the present invention which involves heating a gas for admixture to a controlled atmosphere container can provide advantages even when the gas is admitted to a refrigerated container in view of the enhancement that is available in the reaction rate notwithstanding the increase in temperature in the gas that is delivered to the container. The increase in the temperature of the gas can be reduced by using the heated gas as the heat source for gas that is to be irradiated, so that the gas to be irradiated is heated as a result of heat exchange with compressed fluid from the compressor. The heat exchange relationship can be arranged by providing the compressor with cooling fins and heating the gas to be irradiated by passage over the cooling fins. The reaction of the gas will often be a degradation reaction. The radiation source will then be selected appropriately to ensure that it initiates the reaction. The invention is applicable to degradation of certain hydrocarbon gases, for example olefins, especially ethylene. The reaction products include carbon dioxide and water. Ultraviolet radiation can be appropriate to initiate degradation of such gas materials. Radiation with a wavelength of about 184 nm has been found to be appropriate for degradation of ethylene. The intensity of the radiation will be selected according to the quantity of the gas that is to be treated. It has been found for some applications in which ethylene is to be degraded that the intensity of ultraviolet radiation (wavelength 184 nm) is related to the quantity of ethylene by the formula: Intensi ty ( W) = 284 x ( scrub ra te) where the "scrub rate" is the amount of ethylene to be treated in μl.h "1 . In another aspect, the invention provides a method of treating a gas for admission to a controlled atmosphere container, which comprises : (a) heating the gas, (b) subjecting the gas to radiation to initiate a reaction, (c) admitting the gas under pressure from a compressor to the container, the gas being heated by exposure to heat from the compressor. The method of the invention can include the step of passing the gas through a refrigeration unit, especially when the controlled atmosphere container to which the treated gas is admitted is a refrigerated container. Preferably, the temperature to which the gas is heated prior to the irradiation step is at least about 25°C, more preferably at least about 30°C. The temperature will generally be less than about 50°C, preferably less than about 40°C. The invention can be used with apparatus for selectively adsorbing components of a gas mixture. The apparatus might then by used to increase or to decrease as required the amount of a component of the gas mixture in the controlled environment container. Suitable twin bed adsorption apparatus is disclosed in the specification of a copending patent application filed with the present application claiming priority from UK patent application no. 9723033.8, entitled SELECTIVE ADSORPTION OF COMPONENTS OF A GAS MIXTURE and bearing agents' reference P11261WO. Subject matter incorporated in that document is incorporated in the specification of the present application by this reference. Preferably, the apparatus includes means for reducing the amount of ozone in the gas mixture following the irradiation. This can be important when the gas is to be supplied to a controlled environment container. When the apparatus includes twin bed adsorption apparatus as discussed above, passage of the gas over the adsorbent can lead to degradation of the ozone . The treatment technique provided by the present invention can be used to control the atmosphere in a container which might be used for transportation or storage or both of vulnerable materials. An example of an application might be for transportation and/or storage of perishable foodstuffs. The container might be transported by land (for example by road or by rail) , sea or air. The invention is applicable to containers with a capacity of at least about 1000 litres, for example at least about 10 4 litres, especially at least about 3 x 10" litres. The present invention will now be described, by way of example only, with reference to the accompanying drawings in which: Figure 1 is a schematic representation of apparatus for controlling the composition of a gas mixture which includes apparatus according to the present invention, and Figure 2 is an enlarged view of the conduits for the gas to be irradiated and gas from the compressor in a heat exchanger in the apparatus shown in Figure 1. Referring to the drawings, Figure 1 shows apparatus which is intended for conditioning the gases in a controlled environment container such as might be used for transportation or storage of perishable goods, especially foodstuffs. The apparatus comprises a compressor 2 for circulating gas in the container. Air is admitted to the compressor suction through an inlet 4 which will generally incorporate a filter for particulate contaminants. The air is then passed through a compressor outlet 5 to pressure swing adsorption apparatus 6 through a drain 8 which can collect condensed liquids entrained in the air, especially water. The adsorption apparatus 6 comprises first and second chambers 10, 12 which both contain a quantity of an activated alumina desiccant towards their lower inlet ends and a quantity of a molecular sieve material towards their upper outlet ends. The adsorption apparatus 6 can be used adsorb selectively components of a gas mixture. The provision of first and second chambers can be operated alternately, adsorbent in the chamber not in use being regenerated by passage through it of a purge gas. Details of the construction and operation of appropriate apparatus are disclosed in the copending application referred to above . Associated with the inlet 4 to the compressor is an ultraviolet scrubbing unit 14 by means of which air flowing through the inlet conduit is exposed to radiation which initiates a reaction involving the degradation of polyethylene in the air. The radiation has a wavelength of 184 nm. The compressor inlet 4 and the compressor outlet conduit 5 are incorporated into a heat exchanger 15 so that air admitted to the compressor inlet is heated prior to irradiation in the scrubbing unit 14. The air is heated to a temperature in the range 25 to 40°C. The apparatus of the invention can be incorporated into a controlled environment container such as a container for transporting perishable foodstuffs for example by road, rail, sea or air. The adsorbent material in the chambers 10, 12 can enable the amount of one or more components of the mixture in the container to be increased or decreased as required. Figure 2 shows in more detail the heat exchange arrangement between the compressor inlet 4 conduit and the compressor outlet conduit 5. Air is admitted to the inlet 4 through a filter 20. It flows through a heat exchanger 22, a chamber 24 in which it is exposed to ultraviolet radiation and then to the compressor 2. Air from the compressor passes through the outlet conduit 5 which takes the air through the heat exchanger 22 in which the outlet conduit 5 is arranged helically around the inlet conduit 4. The air in the conduit is heated as a result of the compression. By passing through the heat exchanger 22, the air in the compressor inlet is heated, increasing the susceptibility of ethylene in the air to being degraded by an ultraviolet radiation initiated reaction, and cooling the air in the compressor outlet conduit 5. This cooling of the air in the outlet conduit has advantage when the controlled environment container to which the air is supplied is refrigerated.

Claims: CLAIMS : 1. Apparatus for treatment of gas for admission to a controlled atmosphere container, which comprises: (a) a compressor, and (b) a radiation source for irradiating gas flowing towards the container, arranged so that gas to be irradiated with radiation from the radiation source is exposed to heat generated by the compressor to cause the temperature of the gas and, as a result, its susceptibility to a reaction initiated by the radiation from the radiation source to increase. 2. Apparatus as claimed in claim 1, in which the compressor is used to circulate gas in the container. 3. Apparatus as claimed in claim 1 or claim 2, in which the gas is irradiated prior to admission to the compressor. 4. Apparatus as claimed in claim 3, which includes a conduit in which the gas is irradiated while flowing towards the compressor. 5. Apparatus as claimed in any one of claims 1 to 4 , in which the gas to be irradiated is heated as a result of heat exchange with compressed fluid from the compressor. 6. Apparatus as claimed in any one of claims 1 to 5, in which the compressor has cooling fins and the gas to be irradiated is heated by passage over the cooling fins. 7. Apparatus as claimed in any one of claims 1 to 6 , in which the radiation source emits ultraviolet radiation with a wavelength selected to initiate the degradation of hydrocarbon gases . 8. Apparatus as claimed in any one of claims 1 to 7, which includes a refrigeration unit for gas in the container. 9. Apparatus as claimed in claim 8, in which the compressor is incorporated into the refrigeration unit. 10. A method of treating a gas for admission to a controlled atmosphere container, which comprises: (a) heating the gas, (b) subjecting the gas to radiation to initiate a reaction, (c) admitting the gas under pressure from a compressor to the container, the gas being heated by exposure to heat from the compressor. 11. A method as claimed in claim 10, which includes the step of passing the gas through a refrigeration unit. 12. A method as claimed in claim 10 or claim 11, in which the gas is heated to a temperature of at least about 25°C.

Inventors: BANKS ROBERT, BANKS, ROBERT
Applicants: BANKS ROBERT, DOMNICK HUNTER LTD, BANKS, ROBERT, DOMNICK HUNTER LIMITED
Application year: 1998
Main classification: A23L3
IPC codes: A23L3, B01D53