Method for disinfesting dry products under gas in an autoclave

Abstract

Method for disinfesting dry products, in particular cereals, legumes, pulses or herbaceous plants or spices, according to which method: the product is loaded into a unit of the autoclave type, said autoclave being at atmospheric pressure P1; a treatment gas is injected into the unit of the autoclave type, thereby pressurizing the unit of the autoclave type with said gas to a treatment pressure PT, said treatment pressure being maintained for a treatment period; an operation of depressurization of the unit of the autoclave type to atmospheric pressure is performed; characterized in that said operation comprises a phase of transition from an intermediate pressure to atmospheric pressure, said intermediate pressure being in the range from 4 to 5 bar, in a decay time of from 1 to 3 minutes, preferably of about 2 minutes.

Description

Technical Field

[0001] This invention relates to the field of pest control for dried products (dried goods). The invention particularly relates to grains, dried fruits, cereals, legumes (leguminous plants), or herbs and spices, whose pest infestations are well-known and therefore must be treated before they are marketed. Background Technology

[0002] Although methyl bromide has been used as a pesticide in this industry for a long time, its dangers are now widely recognized, and its use is now prohibited (except in a few cases with justifiable reasons).

[0003] Therefore, other more environmentally friendly pest control technologies have emerged, among which the methods listed below can be mentioned.

[0004] It is generally known that insects are resistant, but certain conditions are essential for their survival. Besides food (found in the dried product being treated), insects need oxygen, but only at very low levels, as a concentration generally slightly above 2% is sufficient for them, provided there are no toxic gases in the rest of the atmosphere. Similarly, most species tolerate temperatures between 10°C and 40°C, and humidity typically between 30% and 95%.

[0005] These different conditions necessary for insect survival thus create the possibility of generally inhibiting their proliferation in different foods.

[0006] Heat treatment can be mentioned: generally, in the absence of any other adverse conditions, an increase in temperature can kill insects. However, it may cause changes in the texture, taste, or other aspects of the product being treated, especially since the exposure time required at an acceptable temperature for the product is relatively long, while the temperature applied is too high when the treatment time should be much shorter.

[0007] CO2-based gas treatment has also been proposed. The literature on this topic is abundant. Some of these gas treatments are carried out at atmospheric pressure. High concentrations (70-80%) of carbon dioxide can be used for treatment without negative consequences for the product. However, the long duration required for this treatment limits its use to products with significant longevity. Specifically, depending on temperature, the operation typically takes 7 to 12 days to complete. Furthermore, humidity greater than 65% or the presence of dust can significantly extend this time (between 30% and 50%). Therefore, in practice, this system is only considered for pest control in grain silos, where storage times are considerable in any case (typically exceeding one year).

[0008] Other treatments also combine CO2 and vacuum: using very high concentrations (>95%) of carbon dioxide in a closed space under near-vacuum (<0.3 bar absolute pressure) can significantly reduce treatment time, but they are still relatively long, typically tens of hours.

[0009] Finally, the literature mentions other treatments combining CO2 and high pressure (20 to 25 bar or even 30 bar) for pest control of products that most frequently have high added value and / or whose shelf life does not support long-term treatment. The fact that a cycle lasts only a few hours between loading, unloading, and processing is highly advantageous.

[0010] The existing technology of autoclaves can be illustrated by reference DE-44 10 116, which describes a mechanism in which the chamber is emptied, followed by the introduction of process gas under processing pressure, and the steps of emptying and pressurizing with process gas are repeated only when the residual oxygen content in the chamber (as measured periodically) is no longer satisfactory.

[0011] Nevertheless, grain pest control using autoclaves under gas (typically CO2 or nitrogen) must adhere to the contact time to achieve the desired mortality rate at all stages of insect development, especially the much more resistant latent forms (eggs and larvae). This has a direct impact on the productivity and investment costs (OpEx and CapEx) associated with the method.

[0012] It is generally accepted that, to meet productivity requirements, it is known to combine two autoclaves installed in parallel to recover a portion of the gas remaining in the second autoclave through pressure equalization. After this equalization, the remaining gas is preferably removed by purging and venting. This represents approximately 4 to 5 bar of direct emission into the atmosphere.

[0013] Furthermore, it is known that global warming will create more problems related to insect populations, and regulations on the use of chemicals (not approved for use in the organic sector) will become increasingly stringent, leading to a greater volume and diversity of products to be treated, which will necessitate adjustments to these methods. Summary of the Invention

[0014] As will be seen in more detail below, the present invention proposes to optimize the processing time in an autoclave under a gas (preferably CO2 or nitrogen or a mixture thereof, particularly preferred for cost reasons, although other gases may be considered), and this is achieved by controlling the decompression time (reducing from a measured pressure that is typically close to and preferably 5 bar to atmospheric pressure) to achieve optimal efficiency even with shorter cycle times, regardless of the stage of the insect pest: egg, larva, or adult.

[0015] The efficiency of the method presented herein is particularly advantageous when reducing pressure from a selected pressure (preferably about 5 bar, as described above) to atmospheric pressure, compared to, for example, reducing pressure from 10 bar to 5 bar.

[0016] Specifically, the advantages of the present invention are that, under the conditions proposed, it is possible to utilize a pressure of approximately 5 bar without releasing it into the atmosphere, and it is understood that reducing pressure from 10 bar to 0 bar has no greater effect on pests than reducing pressure from approximately 5 bar to 0 bar.

[0017] What is particularly commendable about this invention is its understanding of the importance of decompression and its research into a solution that makes such decompression technically feasible while reducing gas consumption.

[0018] As will be seen later in this application, according to one embodiment of the invention, in this controlled decompression from a selected pressure, preferably about 5 bar, to atmospheric pressure, two autoclaves are used, and an exchange is performed between an autoclave without gas and another autoclave that has just been used (and therefore at the processing pressure, for example, about 20 bar). More specifically, gas transfer occurs between the autoclave that has just been used (referred to as autoclave No. 1) and the autoclave without gas (referred to as autoclave No. 2).

[0019] According to the present invention, it is not necessary to recirculate all the gas from the autoclave, because the lower the pressure, the more expensive the operation in terms of gas extraction and compression. Therefore, it is conceivable that rapid decompression from an intermediate pressure of 4 to 5 bar is advantageous: - Optimize gas consumption; - Optimize the power required for compression; - The effectiveness of the treatment of the product; - Reduces the risk of explosion caused by suspended grain dust or other dust particles; - Reduce wear that may occur on mounting components due to high-speed gas abrasion. Attached Figure Description

[0020] Figure 1 An example of a pressure curve according to an embodiment of the invention is shown, showing pressure change in bar versus elapsed time in minutes. Detailed Implementation

[0021] This invention relates to a method for controlling insects in dried products, particularly grains, beans, legumes, herbs, or spices, according to said method: - Load the product into a high-pressure vessel type unit called No. 1 high-pressure vessel, which is under atmospheric pressure P1; - Inject processing gas into autoclave No. 1 to pressurize autoclave No. 1 to the processing pressure PT using the gas, and maintain the processing pressure for the processing period; - Perform the operation of reducing the pressure of autoclave No. 1 to atmospheric pressure; The operation of depressurizing the No. 1 autoclave is characterized by comprising: i) an exchange phase between the No. 1 autoclave, which has just been used and is at processing pressure PT, and a gas-free autoclave-type unit referred to as the No. 2 autoclave; and ii) a phase of transitioning from intermediate pressure to atmospheric pressure within a decay time of 1 to 3 minutes, preferably about 2 minutes, wherein the intermediate pressure is in the range of 4 to 5 bar.

[0022] Attached Figures Figure 1 The diagram illustrates an example of a pressure curve (pressure change in bar vs. elapsed time in minutes) implemented according to the invention, which is achieved by means of two autoclaves arranged in parallel and both in fluid communication with the source of the processing gas.

[0023] The curve clearly shows the stages of increasing the pressure to approximately 10 bar, maintaining the treatment at around 20 bar, allowing the pressure in autoclave 1 to drop from 20 bar to 10 bar, which is achieved by equalization with autoclave 2; then comes the stage of depressurization of autoclave 1, where the treatment is carried out, from 5 bar to atmospheric pressure (the stage indicated by the large arrow), which is achieved within minutes.

[0024] In other words, and generally speaking, according to one example of implementing the invention: - The initial increase to 10 bar corresponds to the equilibrium between autoclave 1 and autoclave 2: autoclave 1 is empty of gas, and autoclave 2 is full. After the previous product processing is completed in autoclave 2, the pressure in the full autoclave 2 is approximately 20 bar; - After equalization between the two autoclaves, the units of both autoclave types are thus returned to 10 bar; - Then, in order to change the pressure of the No. 1 autoclave, which must handle the load, from 10 bar to 15 bar, a gas (e.g., CO2) storage tank at least at 18 bar is used to provide a "free" pressure source; To change the pressure of the same pressure vessel No. 1 from 15 bar to 20 bar, a compressor (booster) is used, for example, to draw gas from pressure vessel No. 2, which is at 10 bar. Therefore, pressure vessel No. 1, which is handling the load, must be increased to 20 bar, while pressure vessel No. 2 is reduced from 10 bar to 5 bar.

[0025] According to one embodiment of the invention, there are therefore two autoclaves, No. 1 and No. 2, arranged in parallel, and both are in fluid communication with the processing gas source, and the following measures are implemented: - Load the product to be processed into autoclave No. 1, which is under atmospheric pressure P1; - Processing gas is injected into autoclave 1, thereby pressurizing autoclave 1 to pressure P2, which is lower than PT. The injection to reach P2 is achieved by equalizing autoclave 1 and autoclave 2. Since the previous product processing has been carried out in autoclave 2, autoclave 2 is full and at a pressure equal to or close to PT. After this equalization operation, both autoclaves return to pressure P2. - Change the pressure of autoclave No. 1 from P2 to PT by implementing one or another of the following methods: - i) Inject additional gas from the storage tank to change the pressure of autoclave No. 1 from P2 to PT; or - j) By injecting additional gas from the storage tank, the pressure of the No. 1 autoclave is changed from P2 to P3, which is lower than the pressure PT; then, in order to change the pressure of the No. 1 autoclave, which must handle the load, from P3 to PT, a compression device (compressor, booster) that draws gas from the No. 2 autoclave at pressure P2 is used, thus bringing the pressure in the No. 2 autoclave back to the intermediate pressure in the range of about 4 to 5 bar. - Maintain the processing pressure PT in the No. 1 autoclave during the processing period; - At the end of the processing period, the operation of reducing the pressure of autoclave No. 1 to atmospheric pressure is performed.

Claims

1. A method for controlling insects in dried products, especially grains, beans, legumes, herbs, or spices, according to the method described above: - The product is loaded into a high-pressure vessel type unit called High Pressure Vessel No. 1, which is at atmospheric pressure P1; - Inject processing gas into autoclave No. 1 to pressurize autoclave No. 1 to the processing pressure PT using the gas, and maintain the processing pressure for the processing period; - Perform the operation of reducing the pressure of autoclave No. 1 to atmospheric pressure; - The operation of depressurizing the No. 1 autoclave is characterized by comprising: i) an exchange phase between the No. 1 autoclave, which has just been used and is at processing pressure PT, and a gas-free autoclave-type unit referred to as the No. 2 autoclave, and ii) a phase of transitioning from intermediate pressure to atmospheric pressure with a decay time of 1 minute to 3 minutes, preferably about 2 minutes, the intermediate pressure being in the range of 4 to 5 bar.

2. The method according to claim 1, characterized in that... Both high-pressure reactors, No. 1 and No. 2, are connected in parallel and are in fluid communication with the gas storage tank, and the following measures are implemented: - Load the product to be processed into autoclave No.

1. Autoclave No. 1 is under atmospheric pressure P1. - Processing gas is injected into autoclave 1, thereby pressurizing autoclave 1 to pressure P2, which is lower than PT. The injection to reach P2 is achieved by equalizing autoclave 1 and autoclave 2. Since the previous product processing has been carried out in autoclave 2, autoclave 2 is full and at a pressure equal to or close to PT. After this equalization operation, both autoclaves return to pressure P2. - Change the pressure of autoclave No. 1 from P2 to PT by implementing one or another of the following methods: - i) Inject additional gas from the storage tank to change the pressure of autoclave No. 1 from P2 to PT; or - j) By injecting additional gas from the storage tank, the No. 1 autoclave is changed from pressure P2 to pressure P3, which is lower than pressure PT. Then, in order to change the No. 1 autoclave, which must handle the load, from P3 to PT, a compression device such as a compressor or booster is used to draw gas from the No. 2 autoclave, which is at pressure P2, so that the pressure in the No. 2 autoclave is returned to the intermediate pressure in the range of about 4 to 5 bar. - Maintain the processing pressure PT in the No. 1 autoclave during the processing period; - At the end of the processing period, the operation of depressurizing the No. 1 autoclave to atmospheric pressure is performed, the depressurization including a phase of transitioning from an intermediate pressure in the range of 4 to 5 bar to atmospheric pressure with a decay time of 1 to 3 minutes.

Images