TWO SELECTIVE MODULES FOR A CONTROLLED ATMOSPHERE CONTAINER

Abstract

The invention relates to a reefer container (1) having a controlled atmosphere system (3) comprising:a first selective unit (4) comprising an absorber or a membrane (9) being selective for carbon dioxide over oxygen and nitrogen;a second selective unit (11) comprising an absorber or a membrane (14) being selective for oxygen over nitrogen; anda vacuum pump (6) for extracting and removing separated gasses from a permeate side (8, 13) of the first and second selective units (4, 11) to outside the container(1), where the system (3) is further comprising a pump (15) for providing an overpressure in the container(1). The pump (15) can be connected to the container (1) through a feed side (12) of the second selective unit (11). The invention further relates to a method of controlling reefer container (1) having a controlled atmosphere system (3).

Claims

1. A reefer container having a controlled atmosphere system comprising: a first selective unit comprising an absorber or a membrane being selective for carbon dioxide over oxygen and nitrogen; a second selective unit comprising an absorber or a membrane being selective for oxygen over nitrogen; and a vacuum pump for extracting and removing separated gasses from a permeate side of the first and second selective units to outside the container, characterized in that the system is further comprising a pump for providing an overpressure in the container.

2. The reefer container according to claim 1, characterized in that the pump is connected to the container through a feed side of the second selective unit.

3. The reefer container according to claim 1, characterized in that the pump is a positive displacement pump.

4. The reefer container according to claim 1, characterized in that flow of enriched nitrogen pressed into container by the pump is larger than flow out of container from the permeate side of the first selective unit.

5. The reefer container according to claim 1, characterized in that flow of enriched nitrogen pressed into container by the pump is 10% larger than flow out of container from the permeate side the first selective unit.

6. The reefer container according to claim 1, characterized in that flow of enriched nitrogen pressed into container by the pump is 25% larger than flow out of container from the permeate side the first selective unit.

7. The reefer container according to claim 1, characterized in that flow of enriched nitrogen pressed into container by the pump is 50 litre per hour (L/h) larger, preferable 100 L/h larger, more preferable 200 L/h larger than flow out of container from the permeate side the first selective unit.

8. The reefer container according to claim 1, characterized in that flow of enriched nitrogen pressed into container by the pump is more than 200 L/h larger than flow out of container from the permeate side of the first selective unit.

9. The reefer container according to claim 1, characterized in that the vacuum pump for removing permeate from the selective units is driven by a shaft also driving the pump forcing ambient atmosphere through the feed side of the second membrane unit.

10. The reefer container according to claim 1, characterized in that the first selective unit is placed in a cargo space of the container.

11. A method of controlling the atmosphere within a reefer container having a controlled atmosphere system, which comprises: a first selective unit comprising an absorber or a membrane being selective for carbon dioxide over oxygen and nitrogen; a second selective unit comprising an absorber or a membrane being selective for oxygen over nitrogen; and a vacuum pump extracting and removing separated gasses from a permeate side of the first and second selective units to outside the container, the method comprising: providing an overpressure in the container through the second selective unit by use of a pump.

12. The method according to claim 11 comprising connecting the pump to the container through a feed side of the second selective unit.

13. The method according to claim 11 comprising adjusting a flow of enriched nitrogen passed into the container by the pump to be larger than the flow out of the container from the permeate side of the first selective unit.

Description

[0045] The above and other features and advantages of the present invention will become readily apparent to those skilled in the art by the following detailed description of exemplary embodiments thereof with reference to the attached drawings, in which:

[0046] FIG. 1 shows a reefer container for shipping perishable products such as fruit and vegetables comprising equipment for establishing and maintaining a controlled atmosphere within the container using two selective units; and

[0047] FIG. 2 shows an embodiment of FIG. 1, where one selective unit is placed within the cargo space of the container.

[0048] Various embodiments are described hereinafter with reference to the figures. Like reference numerals refer to like elements throughout. Like elements will, thus not be described in detail with respect to the description of each figure.

[0049] It should also be noted that the figures are only intended to facilitate the description of the embodiments.

[0050] They are not intended as an exhaustive description of the claimed invention or as a limitation on the scope of the claimed invention. In addition, an illustrated embodiment needs not have all the aspects or advantages shown.

[0051] An aspect or an advantage described in conjunction with a particular embodiment is not necessarily limited to that embodiment and can be practiced in any other embodiments even if not so illustrated, or if not so explicitly described.

[0052] Throughout, the same reference numerals are used for identical or corresponding parts.

[0053] In FIG. 1 is shown a reefer container 1 with a space 2 for shipping perishable products such as fruit and vegetables. The container 1 is provided with equipment 3 for establishing and maintaining a controlled atmosphere within the container 1. The controlled atmosphere is meant to establish an atmosphere within the container 1 having a content of oxygen in a range of 1-10%, preferably 2-5% and a content of carbon dioxide in a range of 0-10%, preferably 2-6%.

[0054] In the following, the embodiments described are using membranes in the first and second selective units 4, 11 even though an absorber can be used as a selective element.

[0055] When using an absorber (not shown) for removing carbon dioxide from a gas stream by adsorption on to a solid adsorbent two methods are commonly used. The methods are temperature swing adsorption (TSA) and pressure swing adsorption (PSA). In both techniques, a bed of adsorbent is exposed to a flow of gas from inside the container and forced by a pressure difference above and below the evaporator fans for a period to adsorb carbon dioxide from the gas stream. Then, the flow of gas is shut off from the adsorbent bed and the adsorbent is exposed to a flow of heated ambient air forced by fans, which heated ambient air strips the adsorbed gas (and water) from the adsorbent and regenerates it for further use. In TSA, the heat needed to desorb the carbon dioxide (and the water) from the adsorbent in the regeneration phase is supplied by heated regenerating gas. In PSA, the pressure of the gas stream is lower than that of the feed gas and the change in pressure is used to remove the carbon dioxide (and water) from the adsorbent with the heat required for desorption being supplied by the heat of adsorption retained within the bed.

[0056] Generally, the pressure of the regenerating gas is lower than that of the feed gas in TSA also. However, in a TSA process, the adsorption phase is carried on for a prolonged period and the heat of adsorption of the carbon dioxide and water on the adsorbent liberated during most of the adsorption phase is displaced out of the bed by the flow of gas. It is necessary that the adsorbent bed has a substantial capacity for adsorbing carbon dioxide (and water).

[0057] An example of adsorbent used for the bed can be activated charcoal.

[0058] An alternative can be to use a gas selective membrane.

[0059] A gas selective membrane 9, 14 operates with a pressure difference between a primary 7, 12 and a secondary side 8, 13, here being a feed side 7, 12 and a permeate side 8, 13 as a driving force is gas partial pressure.

[0060] An up-concentration requires therefore a pressure difference from the feed side 7, 12 to the permeate side 8, 13 of the membrane 9, 14.

[0061] As an example following values can illustrate a composition of gasses within a container with a controlled atmosphere system:

[0062] When the primary membrane selectively removes carbon dioxide (a permeate concentration of 30-50% when setpoint=5% carbon dioxide) and oxygen (a permeate concentration of approx. 5% when setpoint=3% oxygen and 5% carbon dioxide) from the container atmosphere, this volume will be replaced by ambient air containing 21% oxygen.

[0063] By having a secondary membrane 14 for nitrogen enrichment operated with the same vacuum pump 6 as the first membrane 9 the replacement atmosphere can contain 2-5% oxygen instead of 21% thereby making the overall oxygen mass balance more tolerant to low commodity respiration and to air leakages through the container wall or container doors. Further by providing a positive flow of nitrogen enriched atmosphere to the container, the leakages will be outgoing of the container instead of ingoing.

[0064] A reefer container 1 according to the invention has a controlled atmosphere system 3 comprising: [0065] a first selective unit 4 comprising an absorber or a membrane 9 being selective for carbon dioxide over oxygen and nitrogen; [0066] a second selective unit 11 comprising an absorber or a membrane 14 being selective for oxygen over nitrogen; and [0067] a vacuum pump 6 for extracting and removing separated gasses from a permeate side 8, 13 of the first and second selective units 4, 11 to outside the container 1,
where the system 3 further comprises a pump 15 for providing an overpressure in the container 1.

[0068] In an embodiment, the pump 15 is connected to the container 1 through a feed side 12 of the second selective unit 11.

[0069] In an embodiment, the pump 15 is a positive displacement pump.

[0070] In an embodiment, flow of enriched nitrogen pressed into container 1 by the pump 15 is larger than flow out of container from the permeate side 8 of the first selective unit 4.

[0071] In an embodiment, flow of enriched nitrogen pressed into container 1 by the pump 15 is 10% larger than flow out of container from the permeate side 8 of the first selective unit 4.

[0072] In an embodiment, flow of enriched nitrogen pressed into container 1 by the pump 15 is 25% larger than flow out of container from the permeate side 8 of the first selective unit 4.

[0073] In an embodiment, flow of enriched nitrogen pressed into container 1 by the pump 15 is 50 litre per hour (L/h) larger, preferable 100 L/h larger, more preferable 200 L/h larger than flow out of container from the permeate side 8 of the first selective unit 4.

[0074] In an embodiment the flow of enriched nitrogen pressed into container 1 by the pump 15 is more than 200 L/h larger than flow out of container 1 from the permeate side 8 of the first selective unit 4.

[0075] In an embodiment, the vacuum pump 6 for removing permeate from the selective units 4, 11 is driven by a shaft also driving the pump 15 forcing ambient atmosphere through the feed side 12 of the second membrane unit 11.

[0076] In an embodiment, the first selective unit 4 is placed in a cargo space 2 of the container 1.

[0077] A method according to the invention controls the atmosphere within a reefer container 1 having a controlled atmosphere system 3 comprising: [0078] a first selective unit 4 comprising an absorber or a membrane 9 being selective for carbon dioxide over oxygen and nitrogen; [0079] a second unit 11 comprising an absorber or a membrane 14 being selective for oxygen over nitrogen; and [0080] a vacuum pump 6 extracting and removing separated gasses from a permeate side 8, 13 of the first and second selective units 4, 11 to outside the container 1;
where an overpressure is provided in the container through the second selective unit by a pump.

[0081] When ripening produce begins to increase production of carbon dioxide, the controlled atmosphere system 3 by means of a first selective unit 4 comprising an absorber or a membrane 9 being selective for carbon dioxide over oxygen, can adjust the carbon dioxide content within the load space 2 of the container 1.

[0082] A second selective unit 11 comprising an absorber or a membrane 14 being selective for oxygen over nitrogen can adjust the nitrogen content within the load space 2 of the container 1.

[0083] The first and second selective units 4, 11 are via pipes 5, 54 connected to a vacuum pump 6.

[0084] Carbon dioxide will be removed through the first selective unit 4 via the pipe 5 and the vacuum pump 6 and led to ambient atmosphere.

[0085] The first selective unit 4 is divided in a feed side 7 and a permeate side 8 by a first membrane 9.

[0086] The feed side 7 being the side from where gas to be controlled passes over the first membrane 9 and the permeate side is the opposite side of the first membrane 9, from where permeate or extracted gas, here carbon dioxide, is directed to the ambient atmosphere by the vacuum pump 6.

[0087] The feed side 7 of the first selective unit 4 is in fluid connection with the cargo space 2 of the container 1 via pipes 51, 52, 53 and can further be provided with a ventilator or pump 10, forcing a flow of gas from the cargo space 2 of the container 1 through feed side 7 of the first selective unit 4 and back into the cargo space 2 of the container 1.

[0088] A second selective unit 11 is divided in a feed side 12 and a permeate side 13 by a second membrane 14. The permeate side 13 of the second selective unit 11 is in fluid connection with the vacuum pump 6 via a pipe 54. Removing oxygen from ambient air forced into the cargo space 2 of the container 1 by a pump 15 results in a rise of nitrogen content within the cargo space 2 of the container 1.

[0089] Nitrogen enriched ambient air is forced into the cargo space 2 of the container 1 via a pipe 55 or other fluid connection from the feed side 12 of the second selective unit 11.

[0090] In an embodiment the pump 15 is placed in fluid connection with the pipe 55 downstream the selective unit 11 and upstream the container 1.

[0091] In an embodiment valves 56, 57 and/or sensors 58, 59 are placed in or on the pipes 5, 54 between the permeate sides 9, 14 of the selective units 4, 11 and the vacuum pump 6.

[0092] Valves 56, 57 and/or sensors 58, 59 communicates with a controller (not shown) controlling the controlled atmosphere system 3.