Description:
FORM 2

The Patents Act, 1970
(39 of 1970)
&
The Patents Rules, 2003

COMPLETE SPECIFICATION
(See sec 10 and rule 13)

SYSTEM AND METHOD FOR TREATMENT OF MATERIALS BY EXPOSURE TO REACTIVE CHEMICAL SPECIES

INGENIUM NATURAE PRIVATE LIMITED
A-601, SAPPHIRE LIFESTYLE, BHARUCH (E), BARUCH-392001,
GUJARAT STATE, INDIA

The following specification particularly describes the invention and the manner in which it is to be performed.

TECHNICAL FIELD OF INVENTION
The present invention relates to a system and method for treatment of materials by exposure to reactive chemical species generated by electric discharges in a gas or gas mixture in a partially closed volume at a specified pressure, humidity and temperature. The invention further relates to an apparatus for atmospheric pressure plasma processing and controlling the atmospheric pressure plasma discharges for stable continuous operation, without arcing, while achieving a desired plasma reactive species chemistry.
BACKGROUND AND PRIOR ART OF THE INVENTION
A plasma is an ionized state of a gas or gas mixture comprised of ions, electrons, radicals, and several reactive forms of gaseous chemical species. As an example, plasma obtained in a gas mixture containing nitrogen, oxygen and/or water (or water vapours) results in one or more forms of reactive oxygen and reactive nitrogen species, including, but not limited to ozone, singlet oxygen, various forms of peroxides (H2O2), hydroxides and several forms of nitrogen oxides (NO2, NO3, N2O4, N2O5), as demonstrated by Misra (2018), Park et al. (2018), Moiseev et al. (2014) using optical absorption spectroscopy. Further, using optical emission spectroscopy it has been demonstrated that plasma in air results in several forms of nitrogen ions, OH, and singlet oxygen, besides some weak UV emission (Misra, 2018). These reactive chemical species in plasma have potential applications in several domains including food, agriculture, medical, polymer, catalysis, semiconductor, material processing, combustion, water treatment, and textile industry. Specifically, the food industry is interested in use of plasma discharges for microbiological decontamination of foods; reduction or elimination of aflatoxins from grains and nuts; reduction of pesticides from fresh produce surface; and modification of surface hydrophobicity or hydrophilicity of material surface.
Cold plasma is typically achieved in air under ambient conditions by applying strong electric fields across two parallel electrically conductive plates separated by a dielectric material - a configuration referred to as a dielectric barrier discharge. In an alternate configuration the electric field is applied between a sharp pin and a plate – a configuration referred to as a corona discharge. In yet another configuration the electric field is applied across a thin metallic wire and a concentric metallic tube with or without a dielectric barrier in between, and a gas is forced through this thin gap; this configuration is referred to as a plasma jet.
When a strong electric field is applied across two electrically conductive electrodes to ionize a gas, occurrence of uncontrolled electric arcs is typically an undesirable effect. Arcing could result in damage to the product being exposed to the plasma discharge or treated with plasma, in addition to damaging the power source itself. Frequent arcing results in current surges that could decrease the life of the equipment, increase the power consumption, result in undesired plasma chemical kinetics or undesired concentration of a particular reactive chemical species, besides making an operator surprised or afraid of the unpredictable, sudden high pitch noise. Arcing in a plasma discharge limits the ability of industry to employ strong plasma discharges for treatment of particulate materials, powders, flours, grains, and nuts as it could result in fire hazards and explosion. Therefore, an arc-free cold plasma capable of operating at atmospheric pressures with power delivery at industrial or high frequencies would be of great commercial advantage for the food grains, seeds and food/pharma/chemical powder processing industry.
Reference is taken from US 2022/0007690A1 which speaks of a product and a gas introduced into a container, and the container being hermetically sealed. The container contains a plasma reactor inside it that ionizes the gas inside for a defined time or until a concentration of a gas is achieved, then the seal is opened and the product is discharged.
Reference is taken from WO 2009/040130A1, in which a gas mixture (air + one inert gas) and product are sealed inside a package and a portion of the headspace gas is exposed to a strong electric field for forming a plasma. The package containing product and gas is placed between two electrodes for plasma generation.
US 2017/0112157A1 employs a specific gas mixture in which a high voltage cold plasma is generated using a dielectric barrier discharge, which in turn results in a reactive gas with ozone and one another undisclosed species. This reactive gas mixture is then stored in a container and transported through a closed volume by at least 50 mm and opened up to bring in contact with a product. The process results in lowering of mycotoxins that are already present in the product.
WO 2020/197837A1 employs UV and IR light emitted from a microwave plasma source for detection of plasma chemistry.
US 2018/0148209 A1 describes a cuboidal shaped object wrapped inside a polymeric packaging being conveyed on a metallic conveyor and brought in contact with flexible electrodes which electrically discharge onto the package surface causing surface sterilization.
Reference is taken from US9745660B2, which describes a system and method for controlling arcing in RF plasma chambers (frequency range between 3 kHz to 300 GHz) involving comparison of the rate of change of the amplitude of voltage, amplitude of current, and determination of the phase angle between voltage and current signals at the chamber input against a reference rate of change. On detecting a predetermined number of repetitive change conditions, the RF power is decreased. Herein the method attempts to control the arcing after the arcing events have onset (and several arcs have stuck within the predetermined number of events), by sensing at the RF input junction of the chamber. This method would require a high frequency of sampling for timely detection.
US9170295B2 describes an apparatus and method for detecting the voltage and current ration of the input RF supply to a RF plasma chamber, and using this ratio as a means to identify an arcing event when it occurs. When arcing is detected, the controller reduces or blocks the power to the chamber. Herein the method attempts to control the arcing after the arcing event has occurred.
US8502689B2 claims a system and method for detection of arcs in a plasma chamber by directly sensing a bias voltage from the RF powered electrode and filtering it to obtain an output signal which is compared against a pre-set voltage value indicative of an arc, and generating an alarm signal.
US8587321B2 claims a system and method for detection of arcs in a plasma chamber by non-invasively sensing the RF current prior to the powered electrode in the form of a voltage signal, filtering it and comparing against a pre-set voltage value indicative of an arc, and generating an alarm signal.
US8890537B2 describes an arc detection system using a radio frequency signal probe (for voltage or current or power) at the input of a plasma chamber. The signal from the probe is analysed for frequency components that have a frequency greater than or equal to a fundamental frequency of the RF signal, and an arc detection is confirmed based on the frequency components.
KR100935406B1 describes an arc detection method employing real-time, high-frequency measurement and analysis of RF voltage and current input to a plasma load, and detection and classification of the arc on the basis of perturbations in these signals.
It is evident that these disclosures have focused on detection of arcing after the arcing has been onset but not to prevent arcing from occurring. The system disclosed herein prevents arcing from occurring by operating in a constant voltage regime until a threshold current limit is achieved, and momentarily decreasing the voltage when this threshold is reached. The threshold is so selected by the controller based on mathematical models or as set by the user that an arcing event never onsets. For safety reasons, when a user overrides the threshold decided by the control unit and a higher threshold value is set for any reason known to the user, a second current threshold value higher than first current threshold value that was pre-fed into the system or pre-set by the controller gets priority. Up on reaching this second threshold value, the system is shut down by the controller and a warning signal is generated for correction. A current value beyond this second threshold is indicative of entry into an operation regime where arcing is onset and the system never enters into that regime.
OBJECT OF THE INVENTION
The main objective of the invention is to provide a system for treatment of materials by exposure to reactive chemical species in a partially closed volume.
Another object is to provide a system for treatment of materials by exposure to reactive chemical species generated by electrical discharges in a gas or gas mixture, in a partially closed volume.
Another object is to provide a system for plasma treatment of materials with specific reactive species concentration.
Yet another object is to provide an arcing free plasma treatment for materials.
Yet another objective is to provide a method of treating materials by exposing them to reactive chemical species generated by electric discharge over the gas or gas mixture in a partially closed volume.
Another object is to provide a control system to regulate the plasma discharge in the treatment apparatus in which the supply voltage is reduced whenever the plasma current exceeds a certain threshold value, such that no arcing is experienced in the plasma reactors.
Yet another object is to provide a system to monitor and regulate the type and concentration of reactive species in the plasma chamber available for treating the materials in the partially closed volume.
Yet another object is to provide high power factor plasma reactors for a system for treatment of materials in the partially closed volume.
Yet another object of the proposed invention is to provide a system for plasma discharge treatment of materials at a specified operating pressure, temperature and humidity.
SUMMARY OF THE INVENTION
The present invention relates to a system for treatment of materials by exposure to reactive chemical species generated from electrical discharges in the presence of one or more gases inside a partially closed volume, at a specified operating pressure, humidity and temperature; comprising of: a partially closed volume of a treatment apparatus, one or more plasma reactor chambers on the periphery of the partially closed volume, a power transformation unit, one or more sensors, a spectroscopy set, and a control unit; in which
- the partially closed volume of treatment apparatus consists of a means for feeding a material into the partially closed volume; a means for conveying the material from one end to the other end of the partially closed volume; a means, for introducing a gas or gas mixture into the partially closed volume, with temperature controllers; one or more cold plasma reactor chambers consisting of multi-convex to plane configuration of plasma modules, feeding plasma to the enclosed conveyor from the periphery of the treatment apparatus; a means for creating an electrical discharge in a fraction of the gas or gas mixture in the partially closed volume to result in ionization and formation of plasma in the plasma modules; a means for venting the unused gas or gas mixture out of the partially closed volume; a means for collecting the product exposed to the plasma after at least one criterion is met;
-the power transformation unit is configured to supply the required high voltage to the plasma reactor;
-one or more sensors for sensing the voltage, mains current, plasma current, temperature and humidity in real time;
-an optical spectroscopy set consisting of one or more optical sensors with a motorized assembly, configured to sense the attenuation of optical signal by the reactive species, by dynamically varying the path length between a light source and optical sensor between 0.5cm to 10cm, and measure the variation in concentration of reactive species in real time; and
-a control unit for controlling the voltage, mains current, plasma net charge, temperature, humidity, and the concentration of reactive chemical species inside the partially closed volume to provide an arcing free treatment to the materials.
In an embodiment, the system is configured to operate at a pressure in the range of 680 mm Hg to 795 mm Hg; a temperature in the range of -25 degree Celsius to +78 degree Celsius, and a relative humidity in the range of 20% to 85%.
In another embodiment, the system is used for decontamination by inactivation and/or elimination and/or partial chemical transformation and/or complete chemical transformation of micro-organisms, including at least one among bacteria, bacterial spores, fungi, fungal spores, yeasts, moulds, insects and/or their metabolites.
In yet another embodiment, the system is used for chemical transformation or elimination of chemical residues, including agrochemical residues, pesticides, fungicides, insecticides, and plant growth hormones.
In another embodiment, the treatment apparatus comprises of a hopper at an elevation above the ground level to introduce the material to be decontaminated from a distant point to the hopper.
In yet another embodiment, the treatment apparatus comprises of at least one mesh conveyor to convey the material, that allows only the movement of reactive chemical species of plasma through the conveyor, but not the materials being treated.
In yet another embodiment, the treatment apparatus comprises of a screw conveyor to convey powdered or particulate materials such as food grains, grits, polymer granules or a combination thereof.
In another embodiment the distance between the plasma reactor chamber and one or more conveyors is less than 80 millimetres.
In yet another embodiment the gas or gas mixture contains at least two among oxygen, nitrogen, carbon-di-oxide, and water as liquid or as vapour.
In yet another embodiment, the gas or gas mixture is introduced by means of a pressure difference between the inside of the partially closed volume and the ambient.
In another embodiment, the gas or gas mixture is ionized using the plasma modules.
In another embodiment, the gas mixture is propelled over the conveyor by means configured to create fluid convection such as a fan or blower.
In yet another embodiment, the plasma reactor comprises of multiple electrodes and another independent electrode separated by a distance from the said electrodes, such that the multiple electrodes are at an electric potential different from that of the independent electrode.
In yet another embodiment, the surface area of each electrode of the multiple electrodes is less than the surface area of the independent electrode.
In another embodiment each electrode of the multiple electrodes has the shape of a disc with a curvature at its circumference, with the radius of curvature less than or equal to the radius of the disc.
In yet another embodiment, application of an electric potential difference, in the range of -100kV to +100kV, across the multiple electrodes and the independent electrode results in a non-uniform electric field within the minimum volume occupied by the electrode pair.
In another embodiment, the volume between the multiple electrodes and the independent electrode is optionally and partially occupied with a dielectric other than the gas or gas mixture.
In yet another embodiment, the distance between the multiple electrodes and the independent electrode ranges between 0.1 centimetres to 25 centimetres.
In yet another embodiment, the control unit consists of a microprocessor with a digital signal processor or a special purpose computing device; and it
-receives data from human machine interface;
-receives a current signal from the current and/or charge sensor component configured to measure current drawn from the mains supply and a plasma current signal from a current and/or charge sensor component configured to measure current at input of the plasma reactor;
-receives a current signal from the current and/or charge sensor component configured to measure current drawn from the mains supply and a plasma current signal from a current and/or charge sensor component configured to measure current at the output of the plasma reactor;
-receives a signal from temperature-humidity sensor; compares it with reference data from HMI and data obtained from optical sensor components and sends control signal to component or components configured to create a fluid convection across the plasma reactors;
-controls plasma chemistry by controlling component or components configured to create a fluid convection across the plasma reactors in tandem with components configured to heat the gas or gas mixture;
-controls the high voltage power supply to provide a constant user-defined voltage to power the plasma reactor until a first current threshold is sensed;
-temporarily decreases the power supply output voltage on sensing the first current threshold ;
-temporarily decreases the power supply voltage, on sensing an excess current of magnitude between first and second current thresholds;
-switches off the power supply output voltage and generates a warning signal upon sensing the second current threshold; wherein the second current threshold is of higher magnitude than the first current threshold.
The proposed invention also relates to a method for treatment of materials by exposure to reactive chemical species inside a partially closed volume having steps:
-receiving a predetermined high voltage output from a power transformation unit;
-application of a predetermined high voltage to the electrodes of one or more plasma reactors to obtain a strong non-uniform electric field;
-introducing a gas or gas mixture using a component configured to create a fluid convection; introduction of the material into the partially closed volume;
-conveying the material using a material conveying component at a controllable speed; sensing the current, voltage, temperature, humidity, and optical data and forwarding it to a control unit;
-regulating the plasma reactor to control the concentration of reactive chemical species generated by the plasma reactor, wherein the reactive species include at least one among ozone (O3), singlet oxygen (O), peroxide (HO2) and at least one among nitrogen dixode (NO2), dinitrogen tetraoxide (N2O4), dinitrogen pentaoxide (N2O5);
-regulating the plasma reactor to control the total charge in the plasma reactor and operating without any event of electrical arcing; wherein the said regulation means
sensing the voltage across the plasma reactor, and the current through the plasma reactor;
providing a constant user defined voltage till the sensed current through the plasma reactor is below a first current threshold;
momentarily decreasing the voltage applied across the plasma reactor on sensing at least the first current threshold but not a second current threshold, which is higher than the first current threshold;
providing no voltage across the plasma reactor on sensing the second current threshold, wherein it is known that arcing occurs only upon exceeding the second current threshold;
- performing the treatment of the material introduced into the partially closed volume with the desired reactive chemical species; wherein the concentration of the chemical species, is evaluated by means of optical sensors in real-time;
- the plasma chemistry control is initiated by controlling the gas convection across the plasma reactor and gas temperature;
- regulating the material treatment efficacy by adjusting the residence time of the product inside the partially closed volume; and
- directing the unused plasma reactive species through a carbon filter for destruction.
In yet another embodiment, the residence time of the material, inside the enclosed conveyor, ranges between 30 seconds and 60 minutes.
BRIEF DESCRIPTION OF THE DRAWINGS
The foregoing summary and the detailed description of the exemplary embodiments herein will be better understood from the following detailed description with reference to the drawings, in which:
Fig. 1(a) illustrates an exploded view of an independent cold plasma generating unit for production of reactive gaseous chemical species.
Fig. 1(b) is a front and side view of an independent cold plasma generating unit shown in Fig 1(a).
Fig. 2 illustrates an exploded view of a plasma reactor with donut and/or toroidal shaped high voltage electrodes and an optional dielectric barrier.
Fig. 3 illustrates the assembly view of the system (100) for continuous plasma treatment of materials moving on a conveyor inside a partially closed volume /treatment apparatus (1).
Fig. 4(a) is a partial front and side view of the apparatus shown in Fig. 3.
Fig. 4(b) is an assembly view of an apparatus for continuous plasma treatment of particulate or granular products conveyed and blended via a screw conveyor.
Fig. 5 is a block diagram of an embodiment of a system for control of a plasma equipment and a plasma process.
Fig. 6 and Fig. 7 are flow charts of an embodiment of a method for controlling a plasma equipment and a plasma process involving reactive plasma gas chemistry.
Fig. 8(a) and Fig. 8(b) shows the time evolution of the concentration of reactive species under different temperature, relative humidity, voltage, discharge gap and fan speed conditions.
It should be noted that the invention is not limited to the precise arrangements and instrumentalities shown in these figures.
DETAILED DESCRIPTION OF THE INVENTION
The proposed invention, relating to the treatment of materials by reactive chemical species inside a partially closed volume is further described more fully hereinafter with reference to the accompanying drawings, in which some, but not all, embodiments of the invention are shown. Indeed, this invention may be embodied in many different forms and should not be construed as limited to the embodiments set forth herein; rather, these embodiments are provided so that this disclosure will satisfy applicable legal requirements.
Fig. 1(a) and Fig. 1(b) describe a single cold plasma generating unit operating at atmospheric pressure (hereafter referred to as a cold plasma module) comprising of a stainless steel or plastic enclosure (1) with provisions for entry and exit of high voltage and grounding wires through cable glands (6). The high voltage and ground wires entering from the glands (6) are connected to two electrodes of a cold plasma reactor, which could be in the form of a multi-convex to plane configuration or optionally, a dielectric barrier discharge. The cold plasma reactor (2) is fixed to the enclosure (1) via threaded bolts (7) from underneath the enclosure. The enclosure also has provision on one side for fixing impellers to push air or fans (3). Optionally, a gas stream could be fed through a gas-feeding element connected to an external blower. The fan directs the air through a heating element integrated with a thermostat (4), whose temperature is regulated manually or via a computer-controlled unit. The enclosure also accommodates temperature-humidity sensors (9) for measurement of gas temperature and humidity in the discharge chamber. A motorized ultraviolet-visible gas absorption spectroscopy set-up (8) placed after the plasma discharge electrodes allows to sample the ionized gas in the immediate vicinity to send a signal to the control unit or a computer to decide appropriate control action. A fibre optic cable carrying the electromagnetic signal from a well-defined ultraviolet-visible-infrared source (14) enters into the module via an entrance (14a), and the signal after absorption by the reactive gas species exits via another fibre optic cable through an exit (14b) to reach the spectrometer (8). The distance between the two optic fibres wherein the reactive species are located, is referred to as the “path length”. A lower than optimal path length would result in very less reactive species in the path of the beam of the light, thereby resulting in less signal attenuation and difficulty in estimating the concentration. A higher than optimal path length could result in complete attenuation of the signal, thereby leaving insufficient signal intensity for the spectrometer. To overcome this difficulty the path length between the optic fibres is dynamically varied via a motorized assembly between 0.5 cm and 10 cm to measure the concentration of the reactive species as they evolve within the partially enclosed space.
The multipoint-plane configuration of a plasma is well-established in the literature for electrohydrodynamic drying and corona discharge applications. However, in the state of the art, the point geometry of the stainless-steel electrodes (2.4) is sharp with a steep cone angle of the tip. For the present application the radius of the tip is convex outwards with a preferred arc radius between10 mm and 2 mm, but not in the shape of a cone or radius close to infinity (that is to say a pin surface parallel to ground electrode). For the purpose of demonstrating the present invention, the individual convex discharge electrodes are fixed on the holes drilled on a perforated stainless-steel plate (2.3), which in turn is held at an elevation via two plastic supporting elements (2.1), a plastic sheet (2.2) and stainless-steel bolts (2.6). The bolts could optionally be made of Teflon, or Teflon-coated stainless steel. The plastic supporting element has protruding slots at accurately defined distances from a tangent to the tip of the convex electrodes (2.4). The stainless-steel ground electrode (2.5) slides into these slots, thereby allowing to vary the electric field strength.
A dielectric barrier discharge for ionizing a gas or gas mixture is typically constructed by placing two parallel plates that are aligned or concentrically placed, with one or more dielectric in between. Dielectric barrier discharges commonly known to people familiar with the art include two symmetric plates stacked parallel to each other with one or more dielectric barriers in between. However, it is known to people skilled in the art that such geometric configurations or their variations require very high voltages to achieve gas ionization of practical significance, result in a poor power factor, besides resulting in frequent arcing and degradation of a polymer dielectric layer over time. At the same time, a pointed pin-plane configuration operates within a narrow range of electric parameters (voltage, inter-electrode gap, and therefore, electric field strength). In Fig. 2 is described a plasma discharge configuration, wherein the high voltage electrode is comprised of several small donut-shaped electrodes (2.4). These electrodes are fixed on the holes drilled on a perforated stainless-steel plate (2.3), which in turn is held at an elevation via two plastic supporting elements (2.1), a plastic sheet (2.2) and stainless-steel bolts (2.6). The bolts could optionally be made of Teflon, or Teflon-coated stainless steel. Each plastic supporting element has protruding slots at accurately defined distances from the surface of the donut electrodes (2.4) facing the ground electrode. The stainless-steel ground electrode (2.5) slides into these slots, thereby allowing to vary the electric field strength. An optional dielectric barrier sheet may be introduced for achieving stability of the discharges, placed above the ground electrode and in contact with the ground electrode. The dimensions of this barrier, if used, may be same as the dimension of the ground electrode or higher (length as well as width or radius or other characteristic dimensions), but not smaller. The outer diameter of each donut shaped electrode is more than 5 mm but less than 500 mm. Preferably, the diameter is between 12 mm and 106 mm; and more preferably it is less than 60 mm. The distance between the centre of one donut electrode to other is more than the diameter of a donut electrode, but less than 80 mm; preferably less than 50 mm and more than 5 mm. A person skilled in the art would recognize that the shape of each electrode could not only be donut-shaped, but also toroidal or hemispherical.
The configuration of employing multiple small donut shaped electrodes instead of one single donut or cylindrical electrode allows to obtain uniformity in the plasma discharge, requires less power vis-à-vis conventionally known dielectric barrier discharge configurations, improves the power factor, and results in production of higher concentrations of reactive gaseous species with comparable voltages and discharge gaps. People skilled in the art would appreciate that this effect results from the development of a non-uniform electric field as opposed to the uniform electric field conventionally employed in parallel plate discharge configurations.
Fig. 3 illustrates an embodiment of assembly view of the system (100) for continuous plasma treatment of materials moving on a conveyor inside the treatment apparatus (1). The system is powered through a power transformation circuitry (11.3) and controlled by the control unit (12). Fig. 4(a) is a partial front and side view of the apparatus shown in Fig. 3. The equipment/treatment apparatus (1) is made of stainless steel and comprises of a hopper (10.1) that allows to feed the product on to a perforated or wire mesh conveyor belt, moved using a chain sprocket mechanism (10.11) which is driven by a motor (10.9) and an optional gear drive, whose speed can be controlled. The measure of the open area in the wire mesh or the perforated conveyor can be adapted depending on the product. For example, a wire mesh conveyor of approximately 3 to 5 mm diameter holes is suitable for treatment of tomatoes, capsicum, and cucumbers; a diameter of 0.5 to 0.8 mm is suitable for wheat, brown rice, corn or spices like black or white pepper; and a diameter of 1 to 2 mm is suitable for peanut and almond. The speed of the drive motor ultimately translates into residence time of the product inside the plasma discharge zone. The chain drive is protected from accidental access by a user using the chain guard (10.10).
The product moves in the direction shown in figure (10.2) and exits via the exit plate (10.5), whose inclination can be adjusted depending on the product being treated using the mounting slot (10.4). The cold plasma modules (1a and 1b) are mounted on either side of the conveyor belt such that module (1a) is at the same elevation of the conveyor belt or slightly higher, while module (1b) is located below the conveyor belt. The product conveyor may be fitted with minor obstacles in the path of the product movement, above the belt but not necessarily in contact with belt. These approaches ensure that the product is completely exposed to the reactive gas species of plasma, including from underneath the conveyor belt. The plasma modules are fed with gas or air meant for ionization using independent fans (3) or a gas feeder (10.6) connected to a blower. The impeller speed of each fan can be controlled manually or autonomously by a control unit (12). The impeller speed in one plasma module may be relatively higher or lower as compared to in another plasma module when several of them are mounted on a conveyor. It is preferred that a differential pressure is always maintained between the gas underneath the conveyor and above it. Such differential treatment across the length of the conveyor allows to create unique plasma treatment processes with greater efficacy in various applications. A person skilled in the art would appreciate that the gas mentioned here could not only be air but any mixture of gas (preferably containing nitrogen and oxygen) or a single gas (preferably nitrogen or preferably oxygen). The high voltage wires are introduced through the entrances (10.8) via cable glands (6). Viewing windows (10.7) are also included to visualize the glow of the cold plasma discharge. A fraction of the reactive gas composition generated as a result of the plasma discharge that is not consumed for the purpose of product treatment exits from a duct connected to the equipment (10.3) and could be passed through an activated carbon filter for destruction. The elevation between the hopper and the exit duct allows for natural gas convection in the direction of the exit duct. However, an extractor fan could also be used for removing the unused reactive gaseous species from the closed enclosure. The entire equipment is preferably mounted on caster wheels for ease of mobility. Further, the equipment may be placed inside a shipping container or a trailer and powered by a mobile generator or battery or solar panel for processing of agricultural commodities and food or feed materials in transit from one location to another. The mobile facility may or may not have air-conditioning facility.
Fig. 4(b) illustrates an example of a screw conveyor based atmospheric pressure plasma treatment apparatus suitable for powdered materials, particulates, food grains, grits, and their combination. Examples of such products with no limitation as such, include wheat, corn, rice, peanuts, whole pulses, spices, flours, polymer granules, fodder, feed, animal feed pellets, starch etc. The equipment is made of stainless steel and comprises of a hopper (10.1) that allows to feed the untreated material into the body of the apparatus (10.14) containing a screw conveyor/auger (10.12) mounted on a shaft. The shaft is rotated via a motor (10.9) that is optionally linked via a gearbox to adjust the rotational speed, and mounted on an optional supporting column (10.15). The rotation of the shaft via the drive motor (10.9) results in displacement of the untreated material fed from the hopper (10.1) towards the exit passage or unloading section (10.5) of the apparatus. The top of the conveyor is mounted with at least one plasma discharge module (1a) that draws a gas or gas mixture and impinges the ionized gas containing reactive chemical species onto the material being conveyed. This results in the desired physical-chemical-microbiological changes in the product, including but not limited to inactivation of spoilage and pathogenic micro-organisms, modification of hydrophobicity and/or hydrophilicity, changes in rheological properties, foaming properties, emulsifying properties etc.
Fig. 5. is a block diagram of the system (100) to control a plasma discharge module. A variety of accessories are provided herein that are operatively interactive with the plasma system disclosed herein. The system is powered from the alternating current of the line power supply (11.1) that is transformed through appropriate means (11.3) to obtain a high voltage output. It will be known to people well-versed with the state of the art that the power transformation circuitry (11.3) typically involves AC-DC-AC converters or AC-AC converters or other related approaches. The output from this power transformation step may provide a high voltage output necessary to initiate and sustain a plasma discharge. However, a subsequent step involving steeping-up of the voltage to achieve a sufficiently higher voltage may be necessary. This optional step is achieved by means of a step-up transformer (11.4). Depending on the operating frequency of the power transformation circuitry (11.3), an iron-core, powdered iron-core, nano-crystalline core, or ferrite core transformer can be employed as the step-up transformer (11.4). The power transformation circuitry (11.3) is controlled by means of a control unit (12) containing an electronic circuitry, preferably with a microprocessor and/or a digital signal processor, but more preferably a single bard computer. The high voltage output from the power transformation unit (11.3) or the optional step-up transformer (11.4) is fed to a plasma reactor (2)- for example, the reactor described in Fig. 2. The plasma reactor (2) is a component of the plasma discharge module along with the fan/blower (3) and mounted on to a product conveyor (10) carrying the material to be treated. The gas or gas mixture propelled by the blower or fan (3) towards the plasma reactor (2) can be heated or cooled as required by means of a gas heating element (4). The temperature and humidity inside the plasma discharge module is monitored using a temperature-humidity sensor (9). The reactive chemical species formed inside the plasma discharge are monitored in real-time using an optical absorption spectroscopy set-up, wherein electromagnetic radiation from a defined source (14) is brought into the region of ionized gas using an optic fibre (F1); a part of the electromagnetic radiation is absorbed by the ionized gas to result in a modified electromagnetic radiation spectrum; the modified electromagnetic radiation is carried via another optic fibre (F2) held at a distance from the previous optic fibre (F1), into a spectrometer (8) that detects the changes in the electromagnetic radiation spectrum caused by the ionized gas. Based on these changes, the concentrations of several reactive chemical species in the ionized gas are calculated via mathematical routines run by the control circuitry (12). The reactive chemical species formed inside the plasma discharge are also monitored in real-time using an optical emission spectroscopy set-up, wherein the electromagnetic radiation emitted by the plasma discharge in the ultraviolet-visible-infrared region is brought to a spectrometer (8) using a fibre optic cable. Based on the frequency of at least one emission signal of the plasma discharge, the concentration of at least one reactive species is estimated by the control unit (12). Based on the ratio of frequencies of at least two emission signals of the plasma discharge, a control decision is made by the control unit (12). While only one spectrometer and one electromagnetic radiation source is described for simplicity, there could be one electromagnetic emission source, but multiple spectrometers. Alternatively, there could be multiple electromagnetic emission sources, and an equal number of spectrometers. Alternatively, there could be no light source but multiple spectrometers. The control unit (12) receives user inputs from a human-machine interface (HMI) (13) that is either touch-based or includes buttons and a display (such as an LCD or TFT display or CRT monitor). The control unit (12) also generates alpha-numerical and/or graphical outputs of the plasma process to be displayed on the HMI (13).
A current sensor (11.2) is placed just after the input AC supply to monitor the current drawn from the mains/line supply. This current signal is read by the control unit (12). A current sensor or time-varying charge sensor (11.5) is placed in the line returning from the plasma reactor (2) to monitor the current drawn by the reactor and/or the total charge in the plasma reactor (2). This plasma current signal or total charge in the plasma reactor is read by the control unit (12). Based on the signal received from sensors (11.2) and (11.5), a decision is made by the control unit (12), and a signal is sent by the control unit (11.2) to perturb or tweak the power transformation via the power transformation circuitry (11.3). Based on the signal received from sensors (11.2) and (11.5), the data received from the HMI (13), and the values of some parameters used for power transformation in the power transformation circuitry (11.3), a decision is made by the control unit (12), and a signal is sent by the control unit (11.2) to the motor drive of the product conveyor (10). The control unit (12) receives a signal from the gas temperature-humidity sensor (9), analyses the signal, compares against data received from the HMI (13), and data received from the spectrometer (8) following an analysis, then sends a signal to the gas heater (4). The control unit (12) receives a signal from the gas temperature-humidity sensor (9), analyses the signal, compares against data received from the HMI (13) and against the data from analysis of the optical absorption spectroscopy (14 and 8) and/or optical emission spectroscopy (8), then sends a signal to the fan/blower (3).
In several embodiments, the system is comprised of a control unit which serves to integrate and coordinate the function of one or more components of the system through sensing, receiving user input, data processing, decision making, interactive message outputs through the display/HMI and self-learning of the optimal process parameters. The controller comprises one or more special-purpose computing devices that are hard-wired or programmed to perform the necessary data processing and control functions. Examples of programmable computing devices used in the system include, application-specific integrated circuits (ASICs) or field programmable gate arrays (FPGAs) or microcontrollers with digital signal processors (DSPs). Such special-purpose computing devices may also comprise of an integration of hard-wired logic, ASICs, or FPGAs with custom programming. The special purpose computing device can be a desktop computer system, portable computer system, a single board computer, networking device, mobile phone, or any other device that performs similar functions.
Fig. 6. illustrates additional non-limiting examples of embodiments configured to help maintain desired voltage and current levels to avoid any form of dangerous arcing in the electrical plasma discharge, besides allowing to receive desired inputs from a user. In some embodiments, the system is coupled via a bus to a display and/or an alphanumeric keypad to display information to the user or acquire operational inputs from the user. The display may be a cathode ray tube (CRT) or LCD or TFT or a touchscreen HMI (13). Another type of user input device is cursor control, such as a mouse, a trackball, or cursor direction keys for communicating direction information and command selections to the processor and for controlling cursor movement on display. In some embodiments, the same direction information and command selections as cursor control may be implemented via receiving touches on a touchscreen without a cursor. Examples of user inputs that are provided through the alphanumeric keypad or touchscreen HMI (13) include -
(13.1) the desired voltage to be applied to the plasma system (Vset);
(3.1) the required process time (tP) that is equivalent of the residence time of the product being disinfected in the system, specifically on the conveyor;
(13.3) the maximum time rate of change of charge beyond which the system is tripped or shutdown (Itrip);
(13.4) the maximum time rate of change of charge beyond which the system initiates a voltage control (Itrigger);
(13.5) the voltage-drop factor (Dset) by which the magnitude of the voltage supplied to the plasma reactor (Vplasma) is modulated when the instantaneous time rate of change of charge exceeds the maximum time rate of change of charge to trigger the system to initiate a voltage control method (Itrigger);
(13.6) the optional input from the user for the system to decide whether or not the gas flow rate across the plasma discharge is to be varied;
(13.7) the optional input from the user for the system to decide whether or not sensing of the plasma chemistry and control of the reactive species chemical composition is required.
(13.8) the optional input required upon selection of the optional input (13.7) for the system to decide whether or not the application requires a higher value of reactive nitrogen species (RNS) in comparison to the reactive oxygen species (ROS) in the ionized gas resulting from electrical plasma discharge.
The system will optionally, and preferably always, sense the concentration of several reactive species resulting from the plasma discharge, irrespective of the inputs provided through input (13.7) and input (13.8).
Other optional inputs from the user may include the upper and/or lower range of at least two reactive species in the plasma discharge, among ozone (O3), singlet oxygen (O), peroxide (HO2), dinitrogen penta-oxide (N2O5), nitrogen di-oxide (NO2), nitrogen tri-oxide (NO3), dinitrogen tetra-oxide (N2O4), hydroxyl radical (OH), and several form of ionized nitrogen species. Furthermore, the optional inputs could also include concentration ratios of at least two reactive species.
In several embodiments sensors may be used for monitoring the voltage on the primary side of a step-up transformer (11.4) and/or on the secondary side of the set-up transformer (11.4) (indicated by Vplasma in Fig. 6). In several embodiments sensors may also be used for monitoring the time rate of change of charge (equivalent of current; Iplasma) on the secondary side of the set-up transformer (11.4). In one embodiment, the time rate of change of charge (Iplasma) is measured on the high side of the power fed to the plasma reactor(s) (2). In another embodiment, the time rate of change of charge (Iplasma) is measured on the low side of the power fed to the plasma reactor(s) (2), i.e., return power line from the plasma reactor(s) (2). It shall be appreciated that the sensors mentioned above can be used in any component of the system individually, or can be used to monitor the system as a whole, for example, providing a plurality of types of data to the controller (12), which integrates the data and adjusts the system as needed. It may also be appreciated that the time rate of change of charge (Iplasma) may also be measured within the plasma reactor (2).
As mentioned briefly above, in several embodiments, one or more sensors are used to monitor various aspects of the components and/or performance of the plasma reactor (or reactors) for various applications. For example, sensors (11.2) may be used to monitor and/or regulate the time rate of change of the charge (or electric current) (I-line) flowing from the mains line into the power supply. When this current exceeds a threshold value (Imax), including the value, an error message may be propagated in the form of an audio-visual signal; subsequently, the system may be shutdown momentarily or until restarted again by the user. In one embodiment, the threshold value (Imax) is decided by the user. In another embodiment, the threshold value (Imax) is alternatively and autonomously decided by the controller (12) based on logical reasoning and mathematical calculations. As a further example, if the current is under the threshold value (Imax), the system will (i) begin operation by initiating a voltage control loop by means of an analog or digital circuitry involving a “soft-start”. This voltage control would initiate the power supply with an output voltage magnitude of Vmin (such that Vmin << Vset), and subsequently initiate a current control loop;
(ii) initiate the fan or blower with a duty cycle (Df) less than Df-set (including the boundary value), where Df-set is programmed into the controller (12), and gradually increase the duty cycle to Df-set within a time span of 1 second to 90 second, in particular from 5 second to 60 second.
(iii) initiate the conveyor with the speed of driving motor (10.9) set to a pre-calibrated value allowing for a residence time (RTset) of the product on the conveyor, wherein RTset is at least equal to or greater than the process time (tP) input by the user (13.2). When the conveyor is initiated, the product fed from the hopper (10.1) travels towards the exit (10.5). In several embodiment, the values of RTset and tP range between 30 seconds to 60 minutes, in particular between 30 seconds to 28 minutes, and more preferably between 1 minute to 20 minutes.
In the said example, upon initiation of the current control loop, the system controller (12) compares the time rate of change of the charge in the plasma reactor (Iplasma) against the tripping current (Itrip), and
(i) if the time rate of change of the charge in the plasma reactor (Iplasma) is greater than or equal to the tripping current (Itrip), turns off the power being drawn by the system from the line and/or shuts down the system, using for example, a solid-state relay, and display an audio-visual warning for the user to take action.
(ii) if the time rate of change of the charge in the plasma reactor (Iplasma) is less than the tripping current (Itrip), the system controller (12) compares the time rate of change of the charge in the plasma reactor (Iplasma) against the maximum time rate of change of charge to trigger the system to initiate the voltage control method (Itrigger), and
(iii) if the time rate of change of the charge in the plasma reactor (Iplasma) is less than the trigger current (Itrigger), the system controller (12) increases the output voltage from the transformer (Vplasma), by a magnitude of dV, while continuing to compare the Iplasma against the Itrip and Itrigger, until it reaches the value of voltage (Vset) desired by the user. The time rate of the increase in voltage (dV) is pre-programmed into the controller (12), and this time preferably ranges between 800 nanoseconds and 10 seconds, in particular about 1 microsecond to 2 second, and any values in between.
(iv) if the time rate of change of the charge in the plasma reactor (Iplasma) is greater than or equal to the trigger current (Itrigger), OR the voltage across the plasma reactor (Vplasma) exceeds the voltage desired by the user (Vset), the system controller (12) decreases the instantaneous voltage output from the secondary of the transformer (Vplasma(t)) being fed to the plasma reactor (2) by a voltage-drop factor of Dset within a time span of dt1 seconds; subsequently, the controller increases the instantaneous voltage output from the secondary of the transformer (Vplasma(t)) being fed to the plasma reactor (2) by a factor of Dset within a time span of dt2 seconds. In several embodiments, the value of voltage-drop factor (Dset) ranges from 0.1% to 100%, in particular about 0.5% to 90%, and any values in between. In several embodiments, the values of time spans dt1 and dt2 ranges from 800 nanoseconds and 10 seconds, in particular about 1 microsecond to 2 second, and any values in between.
(v) if the time rate of change of the charge in the plasma reactor (Iplasma) is greater than or equal to the trigger current (Itrigger) and the user has input an optional desire to allow control of the gas flow (or fan), the system controller (12) increases the duty cycle (Df) of the fan or blower from Df-set to maximum allowed (Df-max) within a time span of dt1 and dt2, whose values are per description provided earlier. Subsequently, the system controller decreases the speed of the fan from Df-max to Df-set in a time span of dt1. In several embodiments, the relative value of Df ranges between 0 to 100%, the value of Df-max is 100%, and the relative value of Df-set ranges between 1% and 99%, more preferably, the value of Df-set ranges between 10% and 50%. The absolute value of Df-max ranges between 0.004 seconds to 0.00004 seconds. In one embodiment, the change in duty cycle of the fan or blower is achieved by the system controller (12) by means of a triac (silicon-controlled rectifier) or power MOSFET or IGBT or a rheostat.
(iv) if the time rate of change of the charge in the plasma reactor (Iplasma) is greater than or equal to the trigger current (Itrigger) and the user has input an optional desire to allow control of the gas flow (or fan) and the user has input an optional desire to control the plasma chemistry (13.7), the system controller (12) initiates the plasma chemistry control loop.
Fig. 7. illustrates additional non-limiting examples of embodiments configured to help maintain desired reactive plasma gas chemistry to achieve the targeted application involving the simultaneous action of reactive oxygen species and reactive nitrogen species in various combinations. When the plasma chemistry control loop is activated by the system controller (12),
(i) if the user has opted for a reactive species chemistry such that the total concentration of the reactive oxygen species (ROS) is less than the total concentration of the reactive nitrogen species (RNS), the system controller (12) turns on the gas heater (4) if it were not already, until the gas temperature, Tg signal (9.1) sensed by the temperature sensor (9) is less than a model temperature (Tm), autonomously decided by the data processing unit (12.2) of the system controller (12). When the model temperature, Tm for the gas is achieved, the controller turns off the heater (4). Simultaneously, the system controller (12) checks if the duty cycle of the blower/fan (Df) is less than or equal to the default duty cycle set by controller (Df-set), in which case it increments the duty cycle by a modulation duty cycle (Dfm1) in a time span of dt1, wherein the modulation duty cycle, Dfm1 is decided by the data processing unit of the controller until the instantaneous ROS to RNS ratio (ROS(t)/RNS(t)) is equivalent to the desired ROS to RNS ratio; when the desired ROS to RNS ratio is achieved the system controller (12) decrements the duty cycle of the blower/fan (Df) to Df-set in a timespan of dt1. This process continues until the desired residence time (RTset) is achieved.
(ii) if the user has opted for a reactive species chemistry such that the total concentration of the reactive oxygen species (ROS) is greater than the total concentration of the reactive nitrogen species (RNS), the system controller (12) turns off the gas heater (4), and simultaneously checks if the duty cycle of the blower/fan (Df) is less than or equal to the default duty cycle set by controller (Df-set), in which case it checks if the desired ROS to RNS ratio is achieved. When the instantaneous ROS to RNS ratio (ROS(t)/RNS(t)) is equivalent to the desired ROS to RNS ratio, the controller (12) increments the duty cycle by Dfm2 in a time span dt1, and the process continues until the desired residence time (RTset) is achieved. The modulation duty cycle, Dfm2 is decided by the data processing unit of the controller.
While not described here, a person with average skill in the art would appreciate that the temperature and humidity of a gas are inter-related when there is vapour present in the gas or gas mixture, such as with humid air. The system may optionally employ humidification controller through misting mechanisms or any other means besides control of the temperature for varying the humidity of the operating gas. The relative humidity in such cases can varied between 15% to 95%, and particularly between 20% to 86%. In one embodiment the system comprises of one or more pre-defined set of user parameters that enable the user of the system to select and initiate a disinfection cycle that is optimal for the product intended to be disinfected from the contaminating agent. The system is further capable of storing the control parameters in its memory, and taking user inputs with respect to the quantitative levels of disinfection achieved. The system is further able to suggest improvements to the pre-defined set of user parameters by self-learning from the quantitative data fed by the user in regards to the disinfection efficacy achieved. This self-learning is preferably based on a machine-learning algorithm; more preferably, the self-learning by the system is based on any of the neural network architectures.
As exemplary embodiments, Figure 8(a) and 8(b) are provided to show the time evolution of the concentration of reactive species under temperature, relative humidity, voltage, discharge gap and fan speed for air convection of [48ºC, 76%, 37 kV RMS, 45 mm, 3000 rpm] and [25ºC, 62%, 35 kV RMS, 50 mm, 1200 rpm], respectively. Herein completely different profiles for reactive species concentrations have been realized using a multi-donut to plane type of plasma reactor by means of coordinated control of the process parameters by the control unit. As one example, the profile shown in Figure 8(a) may be more suitable for dissipation of mycotoxins or pesticide residues on food grains and seeds, while that shown in Figure 8(b) could be more suitable for inactivation of micro-organisms on fruits and vegetables.
Although the operations of exemplary embodiments of the disclosed system and method may be described in a particular, sequential order for convenient presentation, it should be understood that the disclosed embodiments can encompass an order of operations other than the particular, sequential order disclosed. For example, operations described sequentially may in some cases be rearranged or performed concurrently. Further, descriptions and disclosures provided in association with one particular embodiment are not limited to that embodiment, and may be applied to any embodiment disclosed herein. Moreover, for the sake of simplicity, the figures may not show the various ways in which the disclosed system, method, and apparatus can be used in combination with other systems, methods, and apparatuses.
In order to evaluate the performance of the system, several tests have been conducted and successful applications have been demonstrated. The performance of the system for various applications are described here under –
(i) Inactivation of micro-organisms on food products and shelf-life extension –
Fruit and vegetable samples were procured from the local vegetable market in Mumbai. The initial aerobic plate count and yeast and mould count were determined by standard microbiological spread plating technique using tryptic soy agar with yeast extract, and Dicholoran Rose Bengal Chloramphenicol (DRBC) agar medium, respectively. The microbial colonies were enumerated and reported as log10 CFU/g for the untreated and post-treated exemplary products, and samples of the products were also stored in a refrigerator (Godrej, India) at 4 to 5 degree Celsius. The samples treated with the mesh conveyor plasma system were always found to exhibit longer life in terms of spoilage as compared to untreated controls. The self-explanatory results are summarized in Table 1. Similarly, wheat and wheat flour samples that were known to be naturally contaminated, were treated with plasma on a screw-conveyor system, and the results are summarized in Table 2, wherein a decrease in the load of yeast and mould was observed.
Table 1 : Results of plasma treatment on food products
Total Plate Count Yeast and Mold
Food Product Residence Time [min] Field Strength [kV/cm] ROS/RNS ratio (±8%) Initial Load [lof10 cfu/g] Final Load [log10 cfu/g] Initial Load [log10 cfu/g] Final Load [log10 cfu/g] Shelf- life extension [days in refrigeration] Quality at end of life
Cucumber 6 6 0.8 6.63 3.96 4.3 1.5 2 Higher firmness than control
Tomato 10 8.75 2.05 5.7 3.24 6.1 3.35 3 No significant change detected
Carrot 7.3 7.5 3.42 5.14 2.3 4.9 2.05 4 No significant change detected
Pears 3 6.66 1.3 4.56 2.46 5.72 4.13 1.5 No significant change detected
Chicken
breast 8.5 5.15 2.82 4.8 2.2 - - 1 No off-odours vis-à-vis control

Table 2: Results of plasma treatment on grains
Yeast and Mold
Food Product Residence Time [min] Field Strength [kV/cm] approx. ROS/RNS (±8%) Initial Load [lof10 cfu/g] Final Load [log10 cfu/g]
Wheat 30 6 1.5 - 2.1 5.04 1.82
Wheat flour 30 6 0.3 - 0.6 6.2 3.4

(ii) Dissipation of pesticide residues from products
Fruit and vegetable samples were procured from the local vegetable market in Mumbai. They were divided into control and treatment groups and the treatment group was exposed to cold plasma reactive species on a mesh type conveyor system. Subsequently, both the groups were stored under refrigerated conditions for overnight (18 hours). The samples were ground, macerated, and chemically extracted using QuEChERS method, followed by analysis for prominent pesticide residues using gas chromatography mass-spectrometry. The results of the pesticide analysis were above the limit of detection (0.001 mg/kg) of the method employed. Table 3 demonstrates that plasma treatment using the disclosed system resulted in a significant reduction in the pesticide residue levels.
Table 3 : Results of plasma treatment for reduction of pesticide residue levels.
Food Product Pesticide Residence Time [min] Field Strength [kV/cm] approx. ROS/RNS (±8%) Control [mg/kg] Cold Plasma Exposure [ppb] Reduction [%] Quality
Grapes cypermethrin 15 5 1.8 0.009±0.002 0.005±0.002 44.44 No change
Grapes chlorpyrifos 15 5 1.8 0.014±0.005 0.007±0.003 64.29 No change
Green chilly Dimethoate 18 5.83 3.1 0.094±0.002 0.053±0.010 43.62 No change
Brinjal Permethrin 12 7 2.5 0.082±0.011 0.031±0.01 62.20 No change
Brinjal Deltamethrin 12 7 2.5 0.051±0.009 0.043±0.013 15.69 No change

(iii) Dissipation of mycotoxins from grains and flour
Samples of grains and flours, naturally contaminated or artificially contaminated were subjected to plasma reactive species exposure using the screw conveyor plasma system. The mycotoxins, namely, deoxynivalenol (DON) and zearalenone were quantified using ultraperformance liquid chromatography (UPLC) separation with formic acid and methanol mobile phases, coupled with a electrospray ionization mass spectrometer. The results (Table 4) indicated a considerable decrease in the levels of mycotoxins following plasma treatment via the screw conveyor plasma system.
Table 4: Results of plasma treatment on level of mycotoxins
Food Product Pesticide Residence Time [min] Field Strength [kV/cm] approx. ROS/RNS (±8%) Before treatment [ug/kg] Post-Plasma Exposure [ug/kg] Reduction [%] Quality
Wheat Deoxynivalenol 15 5 1.8 - 2.3 1110 155.4 86.00 Insignificant change
Maize grains Deoxynivalenol 15 5 1.8 - 2.3 680 394.4 42.00 Insignificant change
Wheat flour Deoxynivalenol 18 5.83 3.1 994 367.78 63.00 Insignificant change
Oat Zearalenone 12 5 0.8 - 1.8 28 3.2 88.5 Insignificant change

The description and drawing only illustrate embodiments of the present invention and should not be construed in limiting the scope of the invention.
ADVANTAGES
1. The proposed invention provides a system and method for plasma treatment of materials inside a partially closed volume with no event of arcing.
2. The plasma discharge is performed at high power factor without the need of external power factor correction modules.
3. The type of reactive chemical species to treat the material can be selected and the concentration of the species can be regulated.
4. The accurate evaluation of concentration of species inside the plasma reactor is done through a combination of emission and absorption spectrometry.
5. The system and method of treatment of exposing the material to reactive chemical species ensures complete coverage.
6. The proposed invention has application in food preservation, medical decontamination,
7. The control unit of the system, carries out data processing, and has self-learning ability by storing and processing data from previous disinfection cycles.
, Claims:We Claim :
1. A system (100) for treatment of materials by exposure to reactive chemical species generated from electrical discharges in the presence of one or more gases inside a partially closed volume, at a specified operating pressure, humidity and temperature; comprising of: a partially closed volume of a treatment apparatus (1), one or more plasma reactor chambers (2) on the periphery of the partially closed volume, a power transformation unit (11.3), one or more sensors (9, 11.2,11.5, 11.6), a spectroscopy set (8,14), and a control unit (12); wherein,
- the partially closed volume of treatment apparatus (1) consists of
i. a means for feeding (10.1) a material into the partially closed volume;
ii. a means for conveying (10) the material from one end to the other end of the partially closed volume;
iii. a means, for introducing a gas (10.6, 3.2) or gas mixture into the partially closed volume, with temperature controllers (4);
iv. one or more cold plasma reactor chambers (2) consisting of multi-convex to plane configuration of plasma modules, feeding plasma to the enclosed conveyor from the periphery of the treatment apparatus (1);
v. a means for creating controlled electrical discharges (2.4, 2.5) in a fraction of the gas or gas mixture in the partially closed volume to result in ionization and formation of plasma in the plasma modules;
vi. a means for venting (10.3) the unused gas or gas mixture out of the partially closed volume;
vii. a means for collecting (10.5) the product exposed to the plasma after at least one criterion is met;
- the power transformation unit (11.3) is configured to supply the required high voltage to the plasma reactor (2);
- one or more sensors (9, 11.2, 11.5,11.6) for sensing the voltage, mains current, plasma current, temperature and humidity in real time;
- an optical spectroscopy set (8,14) consisting of one or more optical sensors with a motorized assembly, configured to sense the attenuation of optical signal by the reactive species, by dynamically varying the path length between a light source (14) and optical sensor (8) between 0.5cm to 10cm, and measure the variation in concentration of reactive species in real time; and
- a control unit (12) for controlling the voltage, mains current, plasma net charge, temperature, humidity, and the concentration of reactive chemical species inside the partially closed volume to provide an arcing free treatment to the materials.
2. The system (100) for treatment of materials by exposure to reactive chemical species, as claimed in Claim 1, wherein system is configured to operate at a pressure in the range of 680 mm Hg to 795 mm Hg; a temperature in the range of -25 degree Celsius to +78 degree Celsius, and a relative humidity in the range of 20% to 85%.
3. The system (100) for treatment of materials by exposure to reactive chemical species, as claimed in Claim 1, wherein the system is used for decontamination by inactivation and/or elimination and/or partial chemical transformation and/or complete chemical transformation of micro-organisms, including at least one among bacteria, bacterial spores, fungi, fungal spores, yeasts, moulds, insects and/or their metabolites.
4. The system (100) for treatment of materials by exposure to reactive chemical species, as claimed in Claim 1, wherein the system is used for chemical transformation or elimination of chemical residues, including agrochemical residues, pesticides, fungicides, insecticides, and plant growth hormones.
5. The system (100) for treatment of materials by exposure to reactive chemical species, as claimed in Claim 1, wherein the treatment apparatus (1) comprises of a hopper (10.1) at an elevation above the ground level to introduce the material to be treated from a distant point to the hopper (10.1).
6. The system (100) for treating materials by exposure to reactive chemical species, as claimed in Claim 1, wherein the treatment apparatus (1) comprises of at least one mesh conveyor (10) to convey the material, that allows only the movement of reactive chemical species of plasma through the conveyor, but not the materials being treated.
7. The system (100) for treating materials by exposure to chemical species, as claimed in Claim 1, wherein the treatment apparatus (1) comprises of a screw conveyor (10.12) to convey the powdered or particulate materials such as food grains, grits, fodder, polymer granules or a combination thereof.
8. The system (100) for treating materials by exposure to reactive chemical species, as claimed in claim 1, wherein the distance between the plasma reactor chamber (2) and one or more conveyors (10, 10.12) is less than 80 millimetres.
9. The system (100) for treatment of materials by exposure to reactive chemical species, as claimed in Claim 1, wherein
a. the gas or gas mixture contains at least two among oxygen, nitrogen, carbon-di-oxide, and water as liquid or as vapour.
b. the gas or gas mixture is introduced by means of a pressure difference between the inside of the partially closed volume (1) and the ambient.
c. the gas or gas mixture is ionized using the plasma modules.
d. the gas mixture is propelled over the conveyor (10, 10.12) by means of a fan (3) or blower.
10. The system (100) for treating materials by exposure to reactive chemical species, as claimed in Claim 1, wherein the plasma reactor (2) comprises of multiple electrodes (2.4) and another independent electrode (2.5) separated by a distance from the said electrodes, such that
a. the multiple electrodes (2.4) are at an electric potential different from that of the independent electrode (2.5) ;
b. the surface area of each electrode (2.4) of the multiple electrodes is less than the surface area of the independent electrode (2.5);
c. each electrode (2.4) of the multiple electrodes has the shape of a disc with a curvature at its circumference, with the radius of curvature less than or equal to the radius of the disc;
d. application of an electric potential difference, in the range of -100kV to +100kV, across the multiple electrodes (2.4) and the independent electrode (2.5) results in a non-uniform electric field within the minimum volume occupied by the electrode pair;
e. the volume between the multiple electrodes (2.4) and the independent electrode (2.5) is optionally and partially occupied with a dielectric other than the gas or gas mixture;
f. the distance between the multiple electrodes and the independent electrode (2.5) ranges between 0.1 centimetres to 25 centimetres.
11. The system (100) for treatment of materials by exposure to reactive chemical species, as claimed in Claim 1, wherein the control unit (12);
a) consists of a microcontroller or microprocessor with a digital signal processor or a special purpose computing device;
b) receives data from human machine interface (13);
c) receives a current signal from the current (11.2) and/or charge sensor (11.5) component configured to measure current drawn from the mains supply and a plasma current signal from a current and/or charge sensor component configured to measure current at the input of the plasma reactor ;
d) receives a current signal from the current (11.2) and/or charge sensor (11.5) component configured to measure current drawn from the mains supply and a plasma current signal from a current and/or charge sensor component configured to measure current at the output of the plasma reactor;
e) receives a signal from temperature-humidity sensor (9); compares it with reference data from HMI (13) and data obtained from optical sensor components and sends control signal to component or components configured to create a fluid convection across the plasma reactors (2);
f) controls plasma chemistry by controlling component or components (3, 10.6, 3.2) configured to create a fluid convection across the plasma reactors (2) in tandem with components configured to heat (4) the gas or gas mixture;
g) controls the high voltage power supply to provide a constant user-defined voltage to power the plasma reactor (2) until a first current threshold is sensed;
-temporarily decreases the power supply output voltage on sensing the first current threshold;
-temporarily decreases the power supply voltage, on sensing an excess current of magnitude between first and second current thresholds;
-switches off the power supply output voltage and generates a warning signal upon sensing the second current threshold;
wherein the second current threshold is of higher magnitude than the first current threshold.
12. A method of treatment of materials by exposure to reactive chemical species inside a partially closed volume, the said method comprising steps of
- receiving a predetermined high voltage output from a power transformation unit (11.3);
- application of a predetermined high voltage to the electrodes (2.4) of one or more plasma reactors (2) to obtain a strong non-uniform electric field;
- introducing a gas or gas mixture using a component (3, 10.6) configured to create a fluid convection;
- introduction of the material into the partially closed volume (1);
- conveying the material using a material conveying component (10, 10.12) at a controllable speed;
- sensing the current, voltage, temperature, humidity, and optical data and forwarding it to a control unit (12);
- regulating the plasma reactor (2) to control the concentration of reactive chemical species generated by the plasma reactor, wherein the reactive species include at least one among ozone (O3), singlet oxygen (O), peroxide (HO2) and at least one among nitrogen dixode (NO2), dinitrogen tetraoxide (N2O4), dinitrogen pentaoxide (N2O5);
- regulating the plasma reactor (2) to control the total charge in the plasma reactor and operating without any event of electrical arcing; wherein the said regulation consists of :-
sensing the voltage across the plasma reactor, and the current through the plasma reactor;
providing a constant user defined voltage till the sensed current through the plasma reactor is below a first current threshold;
momentarily decreasing the voltage applied across the plasma reactor on sensing at least the first current threshold but not a second current threshold, which is higher than the first current threshold;
providing no voltage across the plasma reactor on sensing the second current threshold, wherein it is known that arcing occurs only upon exceeding the second current threshold.
- performing the treatment of the material introduced into the partially closed volume (1) with the desired reactive chemical species; wherein
the concentration of the chemical species, is evaluated by means of optical sensors in real-time;
the plasma chemistry control is initiated by controlling the gas convection across the plasma reactor and gas temperature;
regulating the material treatment efficacy by adjusting the residence time of the product inside the partially closed volume;
- directing the unused plasma reactive species through a carbon filter (10.3) for destruction.
13. The method of treatment of materials by exposure to reactive chemical species inside a partially closed volume (1), as claimed in claim 12, wherein the residence time ranges between 30 seconds and 60 minutes.
Dated this 31st day of July, 2022.

Anjali Menon (IN/PA-2696)
IPRGENIE LLP
(Agent for APPLICANT)