WO2002089569A1

WO2002089569A1 - Method and apparatus for killing entomology

Info

Publication number: WO2002089569A1
Application number: PCT/NL2002/000284
Authority: WO
Inventors: Hubertus Van Houten; Henk Arnold Jenner; Wijnand Reijer Rutgers
Original assignee: N.V. Kema; Iv-Consult B.V.
Priority date: 2001-04-26
Filing date: 2002-04-26
Publication date: 2002-11-14
Also published as: EP1381273A1; NL1017942C2

Abstract

Method and apparatus (10) for killing entomology in dry matter, comprising a treatment chamber (16), through which the dry matter can be fed, and meand (12, 14, 22) for generating a corona discharge or a glow discharge in the treatment chamber (16). The means for generating a corona discharge or a glow discharge comprise electrode means (12, 14) that are placed in the treatment chamber (16) and a high voltage power supply (22) that is connected to the electrode means (12, 14) and is equipped to supply high voltage pulses to the electrode means (12, 14).

Description

Method and apparatus for killing entomology

The present invention relates to a method and apparatus for killing entomology in dry matter. Dry matter, such as foodstuffs that are transported in bulk (rice, cereals, flour- spices, granules., grains, seeds, humus), frequently contain entomology, that is to say insects, insect larvae and insect eggs which feed on the dry matter. To kill this entomology, at present use is made of treatment of the dry matter with chemical agents, such as methyl bromide. However, the use of these chemical agents has many disadvantages, Not only are these toxic substances, which are undesirable from the environmental standpoint, but a (minimal) proportion of the chemical substance also often remains behind in. the treated dry matter.

The aim of the present invention is to provide an alternative for killing entomology in dry matter. According to the present invention a method of the type defined in the preamble is provided, in which the method comprises the steps of generating a corona discharge or a glow discharge in a treatment chamber and passing the dry matter through the treatment chamber. The dry matter is, for example, a dry foodstuff in bulk form, such as rice, cereals, flour, spices, granules or grains. Glow discharge is a discharge generated by high voltage under a vacuum in a homogeneous field. Corona discharge is a discharge generated by high voltage in a highly mhomogeneous field under atmospheric pressure.

As a result of the corona or glow discharge free radicals and ions are formed, which kill the entomology (insects, insect larvae, insect eggs) immediately without adversely affecting the organoleptic properties of the dry matter. For example, as a result of ionisation of the oxygen present (in the mixture of dry matter and air), ozone, which is highly reactive, is formed. In addition, ions are formed which after acceleration, in the boundary layer of the glow discharge bombard the entomology. An ancillary effect is that a reduction in any microorganisms present, such as bacteria and moulds, also occurs.

Preferably, the corona or glow discharge is generated in the treatment chamber by supplying (AC) high voltage pulses to electrode means. The electrode means can, for example, be formed by a flat earth plate and a number of thin wires or small flat plates or ceramic pipes parallel to the flat plate. By an advantageous arrangement of the electrodes it is possible to ensure that all dry matter is subjected to the effect of the free radicals and ions formed as a result of the corona or glow discharge. The high voltage pulses have a peak voltage of 2 kV or more, for example more than 20 kV, and the peak voltage is, for example, 40 kV in order to generate the corona discharge and 1 kV or more, for example 2 kV, in order to generate the glow discharge. This ensures, depending on the dry matter to be treated, reliable plasma formation and thus the formation of free radicals and ions, Preferably, the high voltage pulses for the corona discharge have a pulse width of approximately 1 μsec and the high voltage pulses for the glow discharge have a pulse width of more than approximately 100 μsec. This ensures an adequate energy supply to guarantee the production of corona or glow discharge and to prevent arcing and an energy supply for maintaining the discharge. In a second aspect the present invention relates to an apparatus for killing entomology in dry matter, comprising a treatment chamber through which the dry matter can be fed and means for generating a corona in the treatment chamber. As in the case of the above mentioned method, free radicals, which kill the entomology, are produced by the corona in the treatment chamber.

In one embodiment the means for generating a corona or glow discharge comprise electrode means that are placed in the treatment chamber and a high voltage power supply that is connected to the electrode means and is equipped to supply alternating voltage or high voltage pulses to the electrode means. The electrode means have to generate a homogeneous corona or glow discharge and comprise, for example, a first fiat earthed plate and a second flat plate that is arranged opposite the first flat plate and comprises a plurality of electrodes in the form of protrusions, Preferably, the first and second flat plates are parallel to one another and the protrusions on the second flat plate are oriented towards the first fiat plate; As an alternative, the second flat plate is made of insulating material and provided with a series of ceramic tubes in which electrodes are located. Preferably, the apparatus further comprises a control device for controlling the high voltage power supply. Thus, the peak voltage of, or the current during, the high voltage pulses, the pulse width and the repeat frequency can be set depending on the substance to be treated. In a further embodiment the apparatus further comprises a discharge detector that is connected to the control device. The discharge detector can be of the optical type, which detects the optical effects of corona or glow discharge, or of the current type, which detects the current pulses of the high voltage power supply to the electrode- means. A manometer can also be present for measuring the gas pressure. By this means a feedback loop that ensures reliable generation of the corona or glow discharge can be implemented in the control device. In addition, the controller can reduce the voltage in the event of electric arcing or if sparks arise.

In yet a further embodiment the apparatus has a sensor that is positioned in the treatment chamber upstream of the electrode means and is connected to the control device to provide information on at least one property of the dry matter and the control device is further equipped to control the high voltage power supply in accordance with the information. The sensor can, for example, measure the degree of humidity of the dry matter to be treated, after which the control device adapts the characteristics of the high voltage pulses accordingly.

In a farther embodiment of the present invention the apparatus furthermore has separating means for separating the dry matter that has been passed through depending on a signal from the discbarge detector. By this means it can be reliably ensured that only treated product that has actually been exposed to free radicals and ions is obtained. The present invention will be explained in more detail on the basis of a few illustrative embodiments, with reference to the appended figures, in which

Fig. 1 shows,, diagrammatically, one embodiment of the apparatus according to the present invention;

Fig. 2 shows, in cross-section, an electrode of the apparatus shown in Fig. 1; and Figs 3a and 3b show, in section, two variants of the electrode arrangement in the apparatus in Fig. 1,

Many types of imported dry matter that are carried in bulk, for example by ship, such as imported rice, contain living organisms such as insects, insect larvae and insect eggs, which are generally referred to as entomology. The dry matter can be a dry foodstuff, such as rice, cereals, flour, spices, granules or grains. In the majority of cases large insects (> 5 mm) can be removed by means of sieving. However, other smaller insects are not separated off by the sieving method. Examples of the smaller insects are the mealworm beetle (Tenebrio molitor) and rice weevil (Sitophilus oryzae). Frequently insect larvae and eggs are also too small or have been laid in the dry matter itself, as a result of which these can also not be removed by sieving.

In current processing methods chemical agents such as methyl bromide are frequently used to kill the entomology. The disadvantage is that the chemical agents are often themselves toxic and that residues of the chemical agents can remain behind in the product.

Fig. 1 shows, diagrammatically, an apparatus 10 according to the present invention. The dry matter is fed via a feed device IS to a treatment chamber 16. The treatment chamber 16 is, for example, of rectangular cross-section and is delimited by walls 17, 1 . The treatment chamber 16 can have been provided with input and output locks to make it possible to obtain a reduced pressure in the treatment chamber. Following treatment the treated dry matter is discharged via a discharge device 20 for further processing (such as packing or storage).

Two or more electrodes 12, 14 are placed in the treatment chamber 16. In the embodiment shown the electrodes 12, 14 are two plate-shaped electrodes that have been placed in the walls 17, 19 of the treatment chamber 16. The two electrodes 12, 14 are connected to a high voltage power supply 22, which is controlled by a control device 23. The control device 23 and high voltage power supply 22 are equipped such that short high voltage pulses are supplied to the electrodes 12, 14. As an alternative, alternating voltages with a frequency of 50 or 60 Hz are used.

In a variant the distance between the walls 17, 19 (and thus between the two electrodes 12, 14) can also be varied. The irihomogeneous electrical field between the electrodes 12, 14 is dependent on the conductivity of the substance between the electrodes 12, 14 (the dielectric). The conductivity is dependent on which substance is fed between the electrodes 12, 14. The distance between the electrodes 12, 14 can be adjusted manually or by a servomotor under the control of the control means 23.

Preferably, the high voltage pulses have a peak voltage of more than 2 kV, more than 5 kV or even more than 20 kV. For highly effective corona generation the peak voltage is even 40 kV. The pulse duration of the high voltage pulses is approximately 1 μsec for the corona discharge and more than 100 μsec for the glow discharge. However, it is possible with the aid of the control device 23 to influence the pulse duration, peak voltage and repeat frequency of the high voltage pulses, for example depending on which type of dry matter is being fed through the treatment chamber 16. It is thus also possible to use a pulse duration of 100 μsec with a frequency of 1 kHz. The treatment chamber 16 has a shape such that all dry matter is fed past the electrodes 12, 14, and can have a cylindrical or rectangular cross-section.

The high voltage pulses give rise to a corona in the region around the electrodes 12, 14 in the treatment chamber 16 under atmospheric pressure and in the case of a vacuum in the treatment chamber 16 give rise to a glow discharge. The corona or glow discharge gives rise to the formation of UV photons, free radicals and ions by ionisation in the treatment chamber 16 (or more accurately in the mixture of dry matter and air, as a result of which transport of the dry matter becomes possible). Thus, for example, the oxygen O₂) in the treatment chamber 16 is converted into ozone (O₃), or OH^* is formed from water vapour. This oxygen can be between the particles of dry matter, within the dry matter itself or in the entomology present in the dry matter. The ozone (and any other free radicals, photons and ions) kills the entomology present in the dry matter. A secondary effect that arises is that the free radicals also produce a reduction in the number of microorganisms (bacteria and moulds) in the dry matter. The killed entomology is separated from the dry matter with the aid of methods known per se.

The apparatus 10 further comprises a sensor 24 that is connected to the control device 23. The sensor measures one or more properties of the dry matter that is being fed through the treatment chamber 16, such as the humidity, and possible further parameters that are of importance, such as the atmospheric humidity of the environment. The control device 23 is then able to influence the control of the high voltage power supply 22 on the basis of the data received. Thus, for example, when rice is unloaded in rainy weather the humidity of the dry matter ill be higher than is the case in dry weather. As a consequence the conductivity of the dry matter increases, as a result of which the control device 23 has to control the high voltage power supply 22 in a different way.

The apparatus 10 can also be equipped with a discharge detector 26 that is connected to the control device 23, Depending on the detection of the presence of a corona, glow discharge, sparks or arcing, a feedback to the control device 23 can be implemented. The discharge detector 26 can be an optical detector 26, which, for example, comprises a fibre optic sensor and a light detector (not shown) that are able to detect light that is generated by the discharges. As an alternative a current sensor 27, which measures the short current pulses (less than 100 μs) of the corona discharges, can be incorporated in the connection between the high voltage power supply 22 and the electrodes 12, 14. The detectors 26, 27 can also be used to detect arcing. Arcing must always be prevented, because a severe voltage drop then occurs between the^" electrodes and a corona or homogeneous glow discharge is not produced, as a result of which some of the product remains untreated.

The electrodes 12, 14 can have many different shapes. For generating glow discharge the electrodes must generate a homogeneous field. This can be achieved in an embodiment in which an electrode 12 is constructed as a flat plate and a further electrode 14 is constructed as a plate with a multiplicity of sub-electrodes, for example with a large number of wire electrodes surrounded by insulating pipes. A highly inhomogeneous field is needed for the generation of a corona discharge. This can be implemented, for example, by constructing an electrode 12 as a flat plate and constructing a further electrode 14 as a plate with a plurality of pointed protrusions which extend towards the electrode 12 (fakir bed), h an alternative embodiment one of the electrodes 12, 14 can be constructed as a plate (flat or cylindrical) and a further electrode 12, 14 can be constructed as a multiplicity of wires which run parallel to the plate.

As shown in Fig. 1, the electrodes 12, 14 are made of a conducting material, such as copper. However, it is possible to make use of the electrode 12 shown in Fig. 2, which consists of a glass or plastic body 28 with a conducting layer 29 of a metal foil or coating thereon. It is also possible for the electrodes 12, 14, or one of the electrodes 12, 14, to have an insulating layer 30 precisely on that part that is located in the treatment chamber 16 (see Fig. 3b below). As a result, the risk of arcing, for example because of reasonably conductive dry matter, is reduced.

Two alternative configurations of the electrodes 12, 14 are shown in Figs 3a and 3b. In this arrangement the two electrodes are arranged coaxially with respect to one another. One of the electrodes, electrode 12 here, in this case forms the outside wall 17 of the treatment chamber 16. The inner electrode 14 can also be a cylinder (Fig. 3a) or solid rod-shaped electrode or wire (Fig. 3b). In order to obtain a highly inhomogeneous electrical field between the electrodes 12, 14, the outer electrode 14 m the configuration shown in Fig. 3b can be provided with an insulating layer 30 on the side facing the other electrode 12. The insulating layer 30 can, for example, be made of glass or ceramic. In this case the wall 17 of the treatment chamber 16 (or outer electrode 12) must be electrically insulated from the feed and discharge device 18, 0.

Experiments have been carried out using a test set-up, in which the distance between the electrodes 12, 14 was 9 mm, the high voltage on the electrodes 12, 14 was 30 kV/cm and the pulse repeat frequency was 1 kHz. Rice was poured through the treatment chamber 16 at a throughput rate of approximately 1 kg hour, In a further experiment an electrode spacing of 30-50 mm, a pressure of 25-50 bar, a high voltage of 2-3 kV and a pulse repeat frequency of I kHz were used. In addition a test was carried out using alternating voltage of 50 Hz and 60 Hz;. Various batches of rice containing entomology were treated, which batches consisted of rice containing mealworm beetles, Stalliaan round grain containing rice weevils and basmati rice containing rice weevils. The experiments showed that the treatment chamber has to remain completely filled in order to achieve a permanent lethal effect on the entomology. After batches were simply passed through, approximately 5% of the entomology was found to be visibly alive, and 5% was found to be still alive after a recovery period of 3 minutes. With a completely filled treatment chamber 16, however, 100% of the entomology was found to be killed. Even after a period of 72 hours in an incubating oven at a temperature of 35^ repeated (microscopic) checks (every 24 hours) showed no visible development of organisms in one of the treated batches.

The further experiments demonstrated that the degree of killing is dependent on the current density of the product, the gas pressure in the treatment chamber 16 and the type of voltage used (AC voltages, DC voltages or voltages in pulse form),

To make the apparatus suitable for the treatment of large batches of dry matter with a high throughput rate (30 tonnes/hour), various parallel treatment chambers 16 containing electrodes 12, 14 can be provided, or electrodes of other dimensions can be used. In order to achieve a correct and effective action the treatment chamber 16 of the apparatus 10 must remain filled with dry matter. In order to prevent blockage problems due to settlement of the dry matter, the apparatus 10 can also contain a vibratory element (not shown).

In one embodiment of the present apparatus 10, the apparatus 10 is furthermore provided with an outflow drum 31 in the discharge device 20. The outflow drum 31 can be driven (for example depending on the level of the dry matter in the feed device 18) in order to ensure a uniform throughput.

The outflow drum 31 can also be used for a further purpose. Depending on the detection of a corona or glow discharge by the control means 23, the outflow drum 31 is driven in a specific direction. In this way product that has been correctly treated can, for example, be discharged via collection means 32 and product that has not been correctly treated can be discharged via further collection means 33. The product in the further collection means 33 can then be treated again,

Claims

1. Method for killing entomology in dry matter, comprising the following steps: generation of a corona discharge or a glow discharge in a treatment chamber (I6)r passing the dry matter through the treatment chamber (16).

2. Method according to Claim I, wherein the dry matter comprises dry foodstuffs.

3. Method according to Claim 1 or 2, wherein the corona discharge or the glow discharge is generated in the treatment chamber (16) by supplying high voltage pulses to electrode means (12, 14).

4. Method according to Claim 3, wherein the high voltage pulses have a peak voltage of more than 2 kV, for example more than 20 kV and, for example, equal to 40 kV.

5. Method according to Claim 3 or 4, wherein the high voltage pulses have a pulse width of approximately 1 μsec For the generation of the corona discharge or of more than approximately 100 μsec for the generation of the glow discharge.

6. Apparatus (10) for killing entomology in dry matter, comprising a treatment chamber (16) through which the dry matter can be fed; means (12, 14, 22) for generating a corona discharge or a glow discharge in the treatment chamber (16).

7. Apparatus according to Claim 6, wherein the means for generating a corona discharge or a glow discharge comprise electrode means (12, 14) that are placed in the treatment chamber (16) and a high voltage power supply (22) that is connected to the electrode means (12, 14) and is equipped to supply high voltage pulses to the electrode means (12, 14).

8. Apparatus according to Claim 6 or 7, wherein the apparatus further comprises a control device (23) for controlling the high voltage power supply (22), wherein the alternating voltage has a peak voltage of more than 2 kV, for example more than 20 kV, and, for example, equal to 40 kV.

9. Apparatus according to Claim 6, 7 or 8, wherein the high voltage pulses have a pulse width of approximately 1 μsec for generating the corona discharge or of more than approximately 100 μsec for generating the glow discharge.

10. Apparatus according to Claim 8 or 9, wherein the apparatus further comprises a discharge detector (26; 27) that is connected to the control device (23).

11. Apparatus according to Claim 8, 9 or 10, wherein the apparatus further comprises a sensor (24) that is placed in the treatment chamber (16) upstream of the electrode means (12, 14) and is connected to the control device (23) to provide information on at least one property of the dry matter and the control device (23) is furthermore equipped to control the high voltage power supply (22) in accordance with the information.

12. Apparatus according to Claim 10 or 11, wherein the apparatus further comprises separating means (31) for separating the dry matter that has been passed through depending on a signal from the discharge detector (26; 27),