Patent Application
20120070334
The present invention relates to a system for detecting and reducing ethylene in a storage room or a reefer container, the system comprising:
Furthermore the invention relates to a method for detecting and reducing ethylene in a storage room.
Ethylene concentrations more than 1 ppmv (part per million volume) may have an adverse influence on the freshness and stock life time of perishable produce like fruit, vegetables as well as flowers and living plants. The produce may emit ethylene when it matures, which may influence other produce in the vicinity leading to decay and reduced stock life. Therefore there is a demand for systems which effectively and economically profitably can control, reduce and/or remove ethylene in produce stocks and transport containers equipped with cooling machines and similar devices in order to control the internal atmosphere.
Known methods of ethylene removal are ventilation, scrubbing in potassium permanganate scrubbers, or chemical reaction with ozone. Adequate ventilation may be unacceptable, because it influences the other control parameters of the controlled atmosphere and will increase energy consumption in cooled and temperature-controlled environments. Scrubbing with potassium permanganate is taking up space and needs service and renewal of the used potassium permanganate.
Japanese Patent Application JP 2002065152 relates to a system for removing ethylene, wherein the gas to be treated is transferred through an ozone generator, a photocatalyst unit and an ozone decomposition catalyst. Part of the generated ozone reacts with ethylene which is oxidized resulting in products such as formic acid, acetic acid and formaldehyde. The remaining unreacted ozone is removed from the gas phase using an ozone decomposition catalyst. The latter is, however, poisoned by the ethylene reaction products, which therefore need to be removed by the photocatalyst unit. Thus, there is a need for two separate, potentially expensive and maintenance-intensive catalytic units for treating ozone in excess of what is needed to remove ethylene. In addition, the production and subsequent removal of excess ozone constitutes an undesirable waste of resources. In order to make the ozone removal more efficient, the skilled person is pointed towards improvements of the photocatalyst, which increase the lifetime and functionality of the ozone decomposition catalyst.
It is a first object of the present invention to provide an ethylene removal system that is energy-efficient and cost-effective.
It is another object of the present invention to provide an ethylene removal system that is simple and easily maintained.
It is a further object of the present invention to provide a system that can control the atmosphere for produce storage and transport, with respect to ethylene concentration control, that to a wholly or partly overcome the above disadvantages and drawbacks of the prior art.
These objects are obtained by providing a system for detecting and reducing ethylene in a storage room or a reefer container, the system comprising:
In this way it is achieved that the ozone generated by the ozone generator is used for determining the level of ethylene by means of detecting the light emitted from the reaction between ozone and ethylene in the sensing reaction chamber. The ozone generated by the ozone generator is furthermore used for reducing the concentration of ethylene in the air in the container. This facilitates that the system can be so compact and robust, that it can be used in reefer containers/cooling containers for ship and land transport.
The system of the present invention thus provides a closed loop controlled process, which efficiently optimizes and controls the ethylene removal from the treated gas. The system of the present invention also obviates the necessity of installing several successive catalytic units for removing ethylene reaction products and ozone. In principle, the system of the present invention may be operated such that none or very little excess ozone is produced.
The method for ethylene C2H4 detection appears to be very useful in this special case, where ozone (O3) generation is implemented for ethylene removal. This sensing method uses the known phenomena, that when ozone and ethylene reacts with this chemical reaction,
C2H4+O3->CH2OOOCH2->CH2O+OCH2O
OCH2O->CO+H2O(60%)
OCH2O->CO2+H2(40%),
fluorescence or chemiluminescence is emitted. The fluorescence may be detected with a light-sensitive photo multiplier tube or avalanche photo diode or similar. This ozone dependent sensing method, combined with the ozone produced by a dedicated ozone generator, also needed and used to produce ozone for ethylene removal, gives synergy in an optimal solution to both ethylene removal and sensing as well.
The mineralization of ethylene and the secondary breakdown product formaldehyde may be further facilitated by implementing a photocatalytic reactor of the prior art. The photocatalytic reactor or reaction chamber may comprise an UV light source which may be used to degrade ozone to O2 at a wavelength of 254 nm.
The use of bandgap semiconductors such as TiO2, ZnO, ZrO2, CdS, etc. and their various modified forms as photocatalysts is well known in the prior art. For example TiO2 in the anastase crystalline form in particular are readily exited upon exposure to near UV radiation (wavelengths below approximately 400 nm) producing electron/hole (e−/h+) pairs on the semiconductor surface. The recombination of e−/h+ pairs has the resulting effect of reducing the process quantum efficiency. The recombination can occur either between the energy bands or on the semiconductor surface. TiO2 has a bandgap energy of 3.1 eV.
It has long been recognized that certain materials such as noble metals (e.g. Pt, Pd, Au and Ag) and some metal oxides (e.g. RuO2, WO3, and SiO2) facilitate electron transfer and prolong the length of time electrons and holes remain segregated. The electrons and holes act as strong reducing and oxidizing agents that cause breakdown of the target compounds (ethylene, formaldehyde and ozone etc.) via formation of active radicals on the photocatalyst surface. The photocatalytic process is dependent on water i.e. from the humidity in the air.
This atmosphere in the storage room may also be controlled with respect to one or more parameters like temperature, humidity, CO2 and O2. It was found that changes in humidity may interfere with and/or alter the chemiluminescent signal from the ozone-ethylene reaction. Hence, according to one embodiment of the present invention, the system further comprises a humidity sensoring device for determining the humidity in the storage room. Signals produced from the humidity sensoring device are directed to the signal processing unit which is adapted to correct the feedback signal for potential changes in relative humidity. Advantageously, the humidity sensoring device comprises a humidity sensor element producing a relative humidity signal, heating means and timer means for activating and deactivating the heating means. With this type of humidity sensoring device it is possible to obtain an accurate relative humidity reading even at high relative humidities, since potential moisture or water accumulated in the humidity sensor element is dried up by the heating action of the heating means. The timer will cause the heating means to be turned off after a predetermined time.
In a further embodiment the ozone generator may be turned off when the concentration of ethylene reaches a threshold value. Likewise, in a further embodiment according to the invention the production of ozone from the ozone generator may be reduced when the concentration of ethylene reaches a threshold value.
In another embodiment according to the invention the ozone generator is turned on again after a definable period of time after having been turned off.
In a further embodiment the airstream means may be turned off when the concentration of ethylene reaches a threshold value. In one embodiment the threshold value is 1 ppmv. A threshold value of below 1 ppmv ensures that the degeneration of the produce is kept to a minimum. According to another embodiment the threshold value is 0.1 ppmv. This ensures an atmosphere in the storage container that is particularly conducive to maintaining freshness and stability of the produce.
In yet a further embodiment according to the invention airstream through the system may be reduced when the concentration ethylene reaches a threshold value. In an embodiment according to the invention the airstream is increased after a definable period of time after having been turned off or reduced.
The reduction or complete shutdown of the ozone generator and/or of the airstream means ensures a particularly cost-efficient and energy-reduced system with a so-far unknown degree of flexibility. Hence, the system of the present invention may be employed for a wide range of produce.
According to the invention the system may further comprise a venturi for supplying ozone from the ozone generator into the airstream to the ethylene/ozone reactor chamber.
In a further embodiment the ethylene/ozone reactor chamber may comprise a labyrinth for stimulating reactions with ozone and ethylene.
According to the invention the labyrinth may comprise a number of channels being open in the one end and closed in the other end so as to achieve that the airstream is directed through a wall of a channel in order for the airstream to pass through the labyrinth.
According to a further embodiment of the invention the ethylene/ozone reaction chamber may comprise an inner surface made of synthetic fibres, plastic, metal, porous ceramic or sintered material.
According to yet a further embodiment of the invention the ethylene/ozone reaction chamber material synthetic fibres, plastic, metal, porous ceramic or sintered material may be coated with a catalytic material. In this way the ozone/ethylene reaction is enhanced.
According to a further embodiment of the invention the system may further comprise a photocatalytic reaction chamber comprising an inner surface coated with the photocatalytic material TiO2 and a UV light source for activating the catalytic reaction. In the photocatalytic reaction chamber, ethylene reaction products such as formaldehyde or ethylene itself may be degraded. Furthermore, the UV light may be used to degrade excess ozone directly, for example at a wavelength of 254 nm.
The use of bandgap semiconductors such as TiO2, ZnO, ZrO2, CdS, etc. and their various modified forms as photocatalysts is well known in the prior art. For example TiO2 in the anastase crystalline form in particular are readily exited upon exposure to near UV radiation (wavelengths below approximately 400 nm) producing electron/hole (e−/h+) pairs on the semiconductor surface. The recombination of e−/h+ pairs has the resulting effect of reducing the process quantum efficiency. The recombination can occur either between the energy bands or on the semiconductor surface. TiO2 has a bandgap energy of 3.1 eV.
According to a further embodiment of the invention, the system may further comprise an ozone scrubber reaction chamber, in which ozone is regenerated to oxygen by catalytic influence of MnO2 and said ozone scrubber reaction chamber is positioned after the ethylene/ozone reaction chamber and the photocatalytic reaction chamber.
According to a preferred embodiment of the present invention, the system further comprises an electronic data logging device connected to the processing means for recording detection signals over time. The data logging device preferably comprises data storage means and one or more interfaces for telecommunication for reading out the stored data. The measurement/feedback system of the present invention offers the opportunity to produce time series of ethylene concentrations as derived from the detection signals. This is particularly advantageous for monitoring system status and efficiency, and for documenting the conditions under which a given produce has been kept for a given time.
The invention further relates to a method for detecting and reducing the level of ethylene in a storage room, comprising the steps of:
According to another embodiment of the invention the method may further comprise the step of:
According to yet another embodiment of the invention the method may further comprise the step of:
According to another embodiment of the present invention, the method further comprises the step of:
According to the invention, the system might comprise a timer in order to start up the system after the ozone generator has been turned off.
According to an embodiment of the invention the UV light source (32) may be turned off when the concentration of ethylene reaches a threshold value.
According to another embodiment of the invention the method may further comprise the step of:
According to another embodiment of the present invention, the method further comprises the step of recording the detection signals over time. This is preferably done by using an electronic data logging device connected to the processing means of the system.
In a further embodiment according to the invention, the photocatalytic reaction chamber and the ozone scrubber reaction chamber may be integrated into one unit.
According to the invention, the control system for ethylene removal is characterized by the use of ozone, to react with and thereby breaking down and remove the ethylene and using the fluorescence occurring from this chemical process to detect the ethylene concentration. As the ethylene concentration changes, the intensity of the fluorescence is changing accordingly. The emitted light from the fluorescence is detected by a photomultiplier or similar very light-sensitive semiconductor sensor like an avalanche photo diode. The raw detected signal from the sensor is connected to an electronic signal processing circuit and the resulting output controls the ozone generator and the resulting ozone supply, in order to reduce the ethylene concentration to a desired level. An optical filter may be placed between the sensor and the fluorescence in the mixing chamber. This filter passes the light, in order to remove light with other wavelengths than the wavelength emitted from the ethylene/ozone reaction fluorescence signals and blocks light from other chemical reactions with ozone than ethylene, i.e. O3+NO=>2 NO2+fluorescence. The filtering effect depends on process specific radiation of light of characteristic wavelengths for each type of chemical reaction.
According to the invention, an electrical air pump or a fan may blow or suck the air from the storage room through the ozone generator and through the sensing reaction chamber, where the chemical reaction starts and fluorescence is detected.
According to the invention, a changeable and disposable air-filter made of porous material like paper or fabric, commonly implemented for particle filtration of air, may be placed inline the airstream before the, the reaction chambers and the ozone generator. The purpose of the air filter is to avoid contamination of the internal surfaces in the various system modules exposed to the internal air in the storage and transport container environment.
According to the invention, an ethylene/ozone reaction chamber with a mixing labyrinth may optionally be inserted in the air flow after ozone is added, in order to improve the reaction efficiency, before the air flow is returned to the storage room or container. This reactor may be made of porous ceramic or sintered material with many parallel air channels as known from catalytic converters and exhaust filters for diesel particles. In a special construction, every channel is closed in one end and open in the other end and arranged in a pattern which is forcing the gas flow through the porous wall from the channels open on the input side into the adjacent channels with output on the output side in the other end. Coating of the porous material with catalytic material may also accelerate the chemical reaction. The catalytic coated surface of the reactor intensify the fluorescence on its surface visible from the photo detector and increase the signal to noise ratio of this.
According to the invention an ozone scrubber reaction chamber for ozone to oxygen regeneration may be inserted in the air flow path after the ethylene/ozone reaction chamber, in order to remove excess residual ozone from the airstream before it returns to the produce storage room through a return pipe. This third reaction chamber may be constructed by the same method as the above mentioned ethylene reactor.
According to the invention a venturi device may improve oxygen and ethylene gas mixing and provide an appropriate air flow through the ozone generator, caused by the pressure drop in the venturi. The ozone enriched airstream from the ozone generator flows through a tube and a nozzle and is discharged inside the venturi, where it is mixed with the ethylene-containing main airstream from the storage room. Mixing of the two gas streams facilitates the chemical reaction between ethylene and ozone and fluorescence occurs.
According to the invention a photocatalytic reaction chamber with photocatalytic reacting surface like TiO2 and an ultra violet light source to activate the photocatalytic effect of the TiO2 may be applied in the main airstream of the system in order to decompose and remove ethylene. Furthermore, formaldehyde and other organic gasses are removed. Another function of the ultraviolet light source may be to degrade ozone directly, for example at a wavelength of 254 nm.
The term “storage room” is to be understood in the broadest sense as equipment or structures where produce is stored and/or transported such as containers, reefer containers or similar.
Excess ozone is to be understood as ozone produced by the ozone generator that is in excess from what is needed to carry out the detection of ethylene in the means for light detection.
The invention and its many advantages will be described in more detail below, with reference to the accompanying schematic drawings, which for the purpose of illustration show some non-limiting embodiments and in which
All the figures are highly schematic and not necessary to scale, and they show only parts which are necessary in order to elucidate the invention, other parts being omitted or merely suggested.
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Although the invention above has been described in connection with preferred embodiments of the invention, it will be evident for a person skilled in the art that several modifications are conceivable without departing from the invention as defined by the following claims.
| Number | Date | Country | Kind |
|---|---|---|---|
| 09161510.4 | May 2009 | EP | regional |
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/EP10/57422 | 5/28/2010 | WO | 00 | 11/28/2011 |
