Method and system for treating a product using a gas

Abstract

A gas is transported to a treatment chamber (106) of a fluidized bed reactor (108). The gas is used for treating a product (P), such as a granular product (P), in the treatment chamber (106). An ionic composition controller (130) controls the ionic composition of the gas so as to compensate for an electric charge build-up in the treatment chamber (106). The ionic composition controller (130) can neutralize ions or add ions to the gas. The ionic composition controller (130) may control the ionic composition based on measurements of the electric charge in the treatment chamber (106).

Description

[0001] METHOD AND SYSTEM FOR TREATING A PRODUCT USING A GAS

[0002] The present invention relates to a method and system for treating a product using a gas and, in particular, for treating a product in a gas using a fluidised bed reactor.

[0003] BACKGROUND

[0004] Fluidised bed reactors are a known type of reactor device used to treat a product. A solid, granular, product is held within a treatment chamber of the reactor. A fluid is introduced into the treatment chamber via a gas distributor. At a sufficiently high fluid velocity, the granular particles are suspended in the gas flow.

[0005] Recent developments involve using fluidised bed reactors in plasma-based systems. These can involve using a plasma-activated gas as input to the fluidised bed reactor. The plasma-activated gas can be used to decontaminate the product in the treatment chamber. The product may be, for example, a granular food product such as herbs, spices, seeds or food powders. Dry granular products such as baby formula, powdered milk, and spices are especially vulnerable to contamination due to their high surface area and exposure during production.

[0006] Nonthermal (cold) plasma technology has the potential to revolutionise the decontamination and functionalisation process for granular, powdered, and ground products, offering a non-thermal, dry, and residue-free alternative to conventional methods. This approach relies on plasma-activated gas, a highly reactive mixture of short-lived and long-lived chemical species, which may include ions, free radicals, and ultraviolet photons. Plasma-activated gas has demonstrated effectiveness as a decontamination agent, capable of neutralising a wide range of pathogens, including bacteria, spores, and fungi, without the need for heat or harmful chemicals.

[0007] One of the standout advantages of nonthermal plasma is its adaptability to treat various product types and geometries. The gaseous nature of a plasma-activated gas allows it to penetrate deep into granular or powdered materials, reaching areas that conventional methods like UV light or steam treatments often miss. This ensures uniform decontamination even in complex structures or densely packed configurations.Additionally, nonthermal plasma operates at or near ambient temperatures, preserving the sensory, nutritional, and functional qualities of sensitive materials, such as spices, seeds, or baby formula. This makes it particularly advantageous for products where maintaining flavour, aroma, or texture is critical. The absence of residual chemicals also addresses safety and regulatory concerns, enhancing consumer acceptance.

[0008] However, the tendency for fine powder particles to agglomerate in a fluidised bed reactor limits the effectiveness of existing systems for treating products using a fluidised bed reactor. Agglomeration reduces fluidisation efficiency and leads to operational challenges such as clumping, uneven treatment, and reactor fouling. Particle agglomeration limits the adoption of developing technologies such as nonthermal plasma for use with fluidised bed reactors.

[0009] There is a need to limit or mitigate the effect of particle agglomeration in a treatment chamber of a fluidised bed reactor.

[0010] SUMMARY

[0011] According to the present invention, there is provided a method and system for treating a product as set out in the accompanying independent claims. Other aspects of the invention will be apparent from the dependent claims and the description which follows.

[0012] According to a first aspect of the disclosure, there is provided a method of treating a product using a gas. The method comprises transporting a gas to a treatment chamber of a fluidised bed reactor for treating a product in the treatment chamber. The method comprises controlling an ionic composition of the gas so as to compensate for an electric charge build-up in the treatment chamber.

[0013] Controlling the ionic composition of the gas refers to controlling the composition of positively and / or negatively charged ions in the gas. The controlling is performed such that the gas, when it reaches the treatment chamber, has an ionic composition that compensates for electric charge build-up in the treatment chamber. This can mean that the ionic composition is selected to neutralize an electric charge in the treatment chamber. The controlling may occur outside of the treatment chamber.Products such as non-conductive powders are susceptible to electrostatic charging due to the triboelectric effect. This can occur when such insulating powders are transported, handled, or subjected to mechanical agitation. During these processes, particles collide with each other and with the surfaces of the handling or transport system, accumulating electrostatic charge. In a fluidised bed reactor, this charging can significantly increase particle adhesion and cohesion, impairing fluidisation efficiency and leading to operational challenges such as clumping, uneven treatment, and reactor fouling. Significantly, by controlling the ionic composition of the gas delivered to the fluidised bed reactor, the present method is able to compensate for a build-up of electric charge in the treatment chamber due to the above described triboelectric effect. In this way, the charge in the treatment chamber can be neutralised to prevent particle agglomeration.

[0014] Controlling the ionic composition of the gas may comprise controlling a charge density such as by increasing or decreasing a number density of positively or negatively charged ions in the gas. For example, controlling the ionic composition may comprise increasing or decreasing the (relative) concentration of positively charged ions. For example, controlling the ionic composition may comprise increasing or decreasing the (relative) concentration of negatively charged ions.

[0015] Controlling the ionic composition may comprise controlling the relative composition of positively and negatively charged ions in the gas.

[0016] The ionic composition may be modified based on the electric charge within the treatment chamber. This may mean that the charge density I relative composition of positively and negatively charged ions is controlled based on whether the electric charge within the treatment chamber is positive or negative. This may mean that the charge density I relative composition of positively and negatively charged ions is controlled based on the polarity and magnitude of the electric charge within the treatment chamber.

[0017] The method may comprise measuring the electric charge within the treatment chamber. The ionic composition may be modified based on the measured electric charge within the treatment chamber.

[0018] The electric charge may be measured by an electric charge sensor such as a capacitive sensor, piezoelectric sensor, or Faraday cup. Other forms of electric chargesensor are possible. By modifying the composition of charged ions based on the measured electric charge, real-time closed loop control is possible.

[0019] Controlling the ionic composition of the gas may comprise neutralizing charged ions in the gas. This may comprise selectively neutralizing positively or negatively charged ions in the gas based on, for example, the electric charge within the treatment chamber.

[0020] Controlling the ionic composition may comprise controlling an ion selector to selectively neutralize charged ions in the gas. The ion selector may be located outside of the treatment chamber. The ion selector may be controlled to selectively neutralize positively or negatively charged ions in the gas.

[0021] The ion selector may comprise an electrode. By setting a potential on the electrode it is possible to control whether positively or negatively charged ions are attracted to the electrode. Charged ions that are attracted to the electrode may collide with the electrode and be neutralized.

[0022] Controlling the ion selector may comprise controlling the bias of the electrode such that the electrode selectively attracts or repels ions in the gas. The bias of the electrode may be set to have a negative polarity so as to attract positively charged ions in the gas. The bias of the electrode may be set to have a positive polarity so as to attract negatively charged ions in the gas.

[0023] The electrode may be a grid electrode. The grid electrode has spaces through which plasma species may pass through. The spaces are bounded by wires of the grid electrode. Depending on the bias of the electrode either positively or negatively charged ions may be attracted to the wires and may collide with the wires so as to neutralize their charge.

[0024] The ion selector may comprise an electrode that is selectively controlled to have either a positive or negative bias. The ion selector may comprise a plurality of electrodes. A first of the electrodes may be selectively controlled to have a positive bias. A second of the electrodes may be selectively controlled to have a negative bias. The first electrode may therefore be controllable to neutralize negatively charged ions and the second electrode may be controllable to neutralize positively charged ions.Controlling the ionic composition may comprise introducing ions into the gas. By introducing ions into the gas the relative concentration of positively and negatively charged ions in the gas may be modified. By introducing ions into the gas, the charge density of positively charged ions and / or negatively charged ions may be modified. Controlling the ionic composition may comprise introducing positively charged ions into the gas. Controlling the ionic composition may comprise introducing negatively charged ions into the gas.

[0025] Introducing ions may comprise controlling an ion generator to generate ions. The ion generator may comprise a plasma source. The ion generator may comprise a corona discharge ionization source.

[0026] The ion generator may be selectively controlled to generate either positively charged ions or negatively charged ions. This selective control may be achieved by varying the input voltage supplied to the ion generator. A first ion generator may be provided for generating positively charged ions. A second ion generator may be provided for generating negatively charged ions.

[0027] The gas may be a plasma-activated gas. Plasma-activated gas refers to a gas with plasma species. The plasma-activated gas may be supplied by a plasma source and transported from the plasma source to the treatment chamber. The plasma source may be a plasma generator. The plasma-activated gas may be a nonthermal (cold) plasma.

[0028] Controlling the ionic composition of the gas may comprise controlling the operation of the plasma source to control the ionic composition of the plasma-activated gas. This controlling may be performed to promote / suppress the generation of ions and in particular may comprise promoting the generation of one of positively and negatively charged ions while supressing the generation of the other of the positively and negatively charged ions.

[0029] The gas may be a plasma-activated gas. The plasma-activated gas may be supplied by a plasma source and transported from the plasma source to the treatment chamber. Controlling the ionic composition of the gas may comprise controlling an ion selector to selectively neutralize charged ions in the plasma-activated gas. The ion selector may be arranged between the plasma source and the treatment chamber.The gas may be a plasma-activated gas. The plasma-activated gas may be supplied by a plasma source and transported from the plasma source to the treatment chamber. Controlling the ionic composition of the gas may comprise controlling an ion generator to generate ions for introduction to the plasma-activated gas.

[0030] The plasma source may comprise a dielectric barrier discharge (DBD) or surface dielectric barrier discharge (SDBD) source. Other types of plasma source may be used such as microwave plasma generators, radio frequency plasma generators, pulsed plasma generators, and DC plasma generators. The ion generator may comprise a corona discharge ionization source.

[0031] Advantageously, DBD / SDBD sources are suited for non-thermal generation of neutral reactive species which are useful for treating products in the treatment chamber. Meanwhile, corona discharge ionization sources are suited for the generation of positively I negatively charged ion species and can be controlled (by controlling the polarity of the input voltage) to generate either positively or negatively charged ion species. In this way, an optimum composition of neutral reactive species for treatment and positively I negatively charged ion species for compensating electric charge buildup can be provided through the combination of a DBD / SDBD source and a corona discharge ionization source.

[0032] According to a second aspect of the disclosure, there is provided a system for treating a product. The system comprises a fluidised bed reactor comprising a treatment chamber. The fluidised bed reactor is arranged to receive a gas for treating a product in the treatment chamber. The system further comprises an ionic composition controller arranged to control an ionic composition of the gas so as to compensate for an electric charge build-up in the treatment chamber.

[0033] The ionic composition controller may be arranged to control the ionic composition based on the electric charge within the treatment chamber.

[0034] The system may comprise an electric charge sensor arranged to measure the electric charge within the treatment chamber. The ionic composition controller may be arranged to control the ionic composition based on the measured electric charge. The ionic composition controller may comprise an ion selector arranged to selectively neutralize ions in the gas.The ion selector may be located outside of the treatment chamber.

[0035] The ion selector may comprise an electrode, and wherein the ionic composition controller may be arranged to control the bias of the electrode such that the electrode selectively attracts or repels ions in the gas.

[0036] The electrode may be a grid electrode.

[0037] The ionic composition controller may comprise an ion generator arranged to generate ions for introduction into the gas.

[0038] The ion generator may comprise a corona discharge ionization source.

[0039] The gas may be a plasma-activated gas, and wherein the system further comprises a plasma source for supplying the plasma-activated gas.

[0040] The plasma source may comprise a plasma generator arranged to generate plasma-activated gas.

[0041] The plasma generator may comprise a dielectric discharge barrier source or surface dielectric barrier discharge source.

[0042] BRIEF DESCRIPTION OF DRAWINGS

[0043] Figure 1 shows a schematic diagram of an example system according to aspects of the present disclosure.

[0044] Figure 2 shows a schematic diagram of a fluidised bed reactor used in an example system according to aspects of the present disclosure.

[0045] Figure 3A shows a schematic diagram of an example gas distributor used in an example system according to aspects of the present disclosure.

[0046] Figure 3B shows a schematic diagram of an example gas distributor used in an example system according to aspects of the present disclosure.

[0047] Figure 4 shows a schematic diagram of an example system according to aspects of the present disclosure.

[0048] Figure 5 shows a schematic diagram of an example plasma generator and ion selector arrangement used in an example system according to aspects of the present disclosure.Figure 6 shows an example plasma generator used in an example system according to aspects of the present disclosure.

[0049] Figure 7 shows a schematic diagram of an example system according to aspects of the present disclosure.

[0050] Figure 8 shows a flow diagram for an example method according to aspects of the present disclosure.

[0051] DETAILED DESCRIPTION

[0052] The following description with reference to the accompanying drawings is provided to assist in a comprehensive understanding of various embodiments of the disclosure as defined by the claims and their equivalents. It includes various specific details to assist in that understanding but these are to be regarded as merely exemplary. Accordingly, those of ordinary skill in the art will recognize that various changes and modifications of the various embodiments described herein can be made without departing from the scope and spirit of the disclosure. In addition, descriptions of well-known functions and constructions may be omitted for clarity and conciseness.

[0053] The terms and words used in the following description and claims are not limited to the bibliographical meanings but are merely used by the inventor to enable a clear and consistent understanding of the disclosure. Accordingly, it should be apparent to those skilled in the art that the following description of various embodiments of the disclosure is provided for illustration purpose only and not for the purpose of limiting the disclosure as defined by the appended claims and their equivalents.

[0054] It is to be understood that the singular forms “a,” “an,” and “the” include plural referents unless the context clearly dictates otherwise.

[0055] Referring to Figure 1, there is shown an example system 100 for treating products using a gas. In this example, the gas is a plasma-activated gas that is generated by a plasma source 102 and is transported via a conduit 104 to a treatment chamber 106. The treatment chamber 106 houses a product P to be treated by the plasma-activated gas. The product is typically a granular product such as a powder. The product P can be a food product, and in particular, a food powder. The plasma-activated gas interacts with the product P and may decontaminate or otherwise treat the product. Example granular food products include herbs, spices, seeds, powdered milk and baby formula.Treating the product P with the gas may involve decontaminating or functionalising the product P, surface modification, or deposition. This is particularly the case when the gas is a plasma-activated gas as shown in this example. The gas is not required, in all implementations, to be a plasma-activated gas and could be a gas used to otherwise treat the product P in the treatment chamber 106. The gas could be used, for example, to dry the product P which may use but is not required to use a plasma-activated gas. An example gas used for drying the product P is carbon dioxide. Another example gas used for drying the product P is nitrogen which may, in particular, be used when drying is required in the absence of oxygen.

[0056] The plasma source 102 and treatment chamber 106 are spatially separated. The plasma source 102 is located externally to the treatment chamber 106. Separating the plasma generation and treatment zones enhances safety particularly when the product P is a powder as fine powders are explosive and plasma is a potential ignition source. Moreover, separating the plasma generation and treatment zones helps to prevent potential thermal damage to sensitive products and allows for modular system configurations. Example modular system configurations enable more or fewer plasma sources I ion generators to be provided to supply plasma-activated gas to the fluidised bed reactor 108. Including multiple plasma sources I ion generation modules can increase the concentration of neutral species I ions generated which is beneficial for treating larger quantities of powders.

[0057] The spatial separation between the treatment chamber 1061 fluidised bed 108 and the plasma source 102 is ideally sufficient to allow for an ion selector (as described below) to be positioned between the treatment chamber 106 I fluidised bed 108 and the plasma source 102. The spatial separation can be at least 1 mm, at least 5 mm, at least 1 cm, at least 5 cm, at least 10 cm, at least 50 cm, or at least 1 metre.

[0058] The plasma source 102 may comprise any suitable plasma generator. The source 102 may, for example, be a Dielectric Barrier Discharge (DBD) or Surface Dielectric Barrier Discharge (SDBD) plasma generator. Ideally, the plasma generator is able to efficiently generate plasma comprising high concentrations of neutral plasma species. In some examples, the source 102 comprises a corona discharge ionization source. While generally used to generate ions as described in greater detail below, a corona discharge ionization source can produce neutral plasma species. One or more coronadischarge ionization sources may provide sufficient neutral plasma species for implementations without requiring a DBD or SDBD. Particularly advantageous implementations of the present disclosure use the combination of a DBD / SDBD source and a corona discharge ionization source as described in greater detail below.

[0059] A plasma source 102 such as a SDBD source can generate a large quantity of neutral plasma species. For example, over 70 different types of neutral plasma species may be generated if humid air is used as the plasma generating gas. Only a small number of neutral plasma species will propagate more than a few mm from the electrode of the plasma source 102. Consequently, the plasma-activated gas reaching the fluidised bed reactor 108 will typically comprise a limited number of neutral plasma species and namely O3, NO, N2O, NO2, H2O2, HNO3, N2O5. The specific composition depends on plasma generation conditions and could be dominated by one neutral species such as O3 or NO2. Concentrations of neutral species can range from a few PPM to 1000’s PPM.

[0060] The treatment chamber 106 is part of a fluidised bed reactor 108. The reactor 108 comprises an inlet 110 arranged at the base of the reactor 108. Plasma-activated gas flows into to the reactor 108 via the inlet 110. The plasma-activated gas flows from the inlet 110 into a gas cavity 112 of the reactor 108, through a gas distributor 114 and into the treatment chamber 106. While the reactor 108 shown in the drawings is substantially rectangular, it may have a different shape such as a conical shape which widens outwards towards the top. With a conical arrangement, product blown upwards can slide back down into the treatment zone. Other suitable shapes of fluidised bed reactors 108 are possible.

[0061] Figure 2 shows the construction of the reactor 108 in more detail. The gas cavity 112 is a volume within the reactor 108 that helps to create a uniform flow of plasma-activated gas through the gas distributor 114. The gas distributor 114 is permeable to the plasma-activated gas but impermeable to the products P (e.g., food powders) in the treatment chamber 106. In this way, plasma-activated gas may flow into the treatment chamber 106 via the gas distributor 114 but the products in the treatment chamber 106 are prevented from entering the gas cavity 112.

[0062] The gas cavity 112 and gas distributor 114 help achieve a uniform distribution of plasma-activated gas within the treatment chamber 106. This helps ensure high-efficacy mixing and subsequent treatment of granular and powdered products in the treatment chamber 106. By creating a dynamic environment in which particles are suspended in an upward gas flow, the reactor 108 helps maximise the exposure of each particle of the product P to the reactive plasma species, thereby promoting uniform treatment. This approach is particularly advantageous for irregularly shaped or densely packed materials, as it mitigates shadowing and inconsistent exposure issues observed in more static systems.

[0063] Figures 3A and 3B show examples of gas distributors 114. Figure 3A shows a gas distributor 114 in the form of a perforated / porous plate. Figure 3B shows a gas distributor 114 in the form of a sintered plate. Both examples have gas channels 128 that permit the flow of plasma-activated gas into the treatment chamber 106, but prevent or restrict products P within the treatment chamber 106 from leaving the treatment chamber 106 via the gas distributor 114. The plates could be formed from stainless steel or other non-oxidising material. The plates may be formed from a conductive material (such as stainless steel mentioned above) or a non-conductive material such as a ceramic. The material used is typically desired to be food safe, such as stainless steel grade 316. The gas distributor 114 can be designed in various ways and is not limited to these examples. For example, the gas distributor 114 may comprise filter paper, fabric, or other suitable materials.

[0064] The size of the gas channels 128 may depend on the diameter of the granular products to be treated in the treatment chamber 106. The gas channels 128 are desired to have a size smaller than the diameter of the granular products. For example, fine ground pepper has an average diameter of around 1.5 pm and in this application, the gas channels 128 should have a nominal size of less than 1.5 pm such as a nominal size of 1 pm or less. Finer powders would require the gas channels to have an even smaller nominal size. In general, the nominal size is typically less than 50 pm.

[0065] Returning to Figure 1, the reactor 108 further comprises an outlet 116 arranged at the top of the reactor 108 that allows gas to output from the reactor 108. In this example, a closed loop system is provided and the output gas flows back to the inlet 110 of the reactor 108 via conduit 122 and conduit 104. Between conduit 122 and 104 is a chamber 118. The chamber 118 has an inlet 120 that is connected to the outlet 116 of the reactor 108 via conduit 122. The output gas flows to the chamber 118 and servesas the working gas (plasma generating gas) used by the plasma source 102 to create plasma-activated gas. The plasma chamber 118 has an outlet 124 which is connected to the conduit 104. Returning the output gas back to the reactor 108 via the chamber 118 has the advantage of enabling plasma species in the output gas to be recirculated back to the reactor 108. This enables a high concentration of plasma species to be supplied to the reactor 108. A system with an external gas (e.g., air) supply is also possible and could be used in conjunction with or separately to the closed loop system described herein.

[0066] The system 100 further comprises a pump 126 that controls the flow of gas within the system.

[0067] Electrostatic charge may accumulate in the treatment chamber 106 when the product P is in the form of insulating powders or other granular materials, and particularly fine insulating granules such as those used in food and pharmaceutical applications. Electrostatic charging may occur when insulating granules are transported, handled or subjected to mechanical agitation. During these processes, particles collide with each other and with the surfaces of the handling or transport system, accumulating electrostatic charge. This charging can significantly increase particle adhesion and cohesion, impairing fluidisation efficiency and leading to operational challenges such as clumping, uneven treatment, and reactor fouling. While the problem of charge buildup is worse for non-conductive powders, it can also be problematic for conducting powders and other granular materials.

[0068] The electrostatic charging of granules depends heavily on the construction materials of the reactor 108. Metallic reactors tend to generate negatively charged granules. Insulating reactors typically produce positively charged granules. This variability in charge behaviour complicates the uniform operation of fluidised beds and introduces inconsistencies in powder treatment and processing. The introduction of the plasma activated gas into the treatment chamber 106 can also further contribute to the charge buildup within the treatment chamber 106.

[0069] The present invention is, in particular, directed towards techniques for mitigating the issue of electrostatic charging within the treatment chamber 106. The system 100 comprises ionic composition controller 130 arranged to control the ionic composition of the plasma-activated gas. The modification occurs outside of the treatment chamber106 such that the ionic composition is modified before the plasma-activated gas reaches the treatment chamber. The ionic composition controller 130 is used to change the composition of ions within the plasma-activated gas so as to mitigate the issue of electrostatic charging within the treatment chamber 106. Changing the ionic composition can be understood as changing the charge density of the plasma-activated gas. The ionic composition controller 130 may, in particular, control the relative concentrations of positively and / or negatively charged ions.

[0070] In an example, if negatively charged powders are present in the treatment chamber 106, the ionic composition controller 130 can increase the concentration of positively charged ions relative to negatively charged ions in the plasma-activated gas.

[0071] In an example, if positively charged powders are present in the treatment chamber 106, the ionic composition controller 130 can increase the concentration of negatively charged ions relative to positively charged ions in the plasma-activated gas.

[0072] The ionic composition controller 130 may change the ionic composition of the gas by selectively neutralizing ions in the plasma-activated gas (Figure 1) or by selectively introducing ions into the plasma activated gas (Figure 4) or by a combination of both neutralizing and introducing ions (Figure 5). Additionally, or separately, the ionic composition controller 130 may change the composition of ions by changing one or more operational parameters, such as the plasma power, of the plasma source 102 to promote / suppress the generation of charged ions.

[0073] In the example of Figure 1, the ionic composition controller 130 comprises an ion selector 132. The ion selector 132 is positioned to interact with the plasma-activated gas and is controlled to selectively neutralize ions in the gas.

[0074] In the example of Figure 1, the ion selector 132 comprises an electrode 132. The electrode 132 is arranged in the flow path between the plasma source 102 and the treatment chamber 106. The electrode 132 is, in this example, arranged in the chamber 118. The electrode 132 is connected to a voltage source 134. The voltage source 134 sets the bias on the electrode 132.

[0075] If the voltage source 134 sets a positive bias on the electrode 132, then negatively charged ions in the plasma-activated gas will be attracted to the electrode 132, will collide with the electrode 132, and will be neutralized. Positively charged ions will berepelled by the electrode 132 and neutral plasma species will be unaffected by the electrode 132. The ionic composition controller 130 therefore increases the relative concentration of positively charged ions in the plasma-activated gas. This can be used to neutralize a buildup of a negative electrostatic charge within the treatment chamber 106.

[0076] If the voltage source 134 sets a negative bias on the electrode 132, then positively charged ions in the plasma-activated gas will be attracted to the electrode 132, will collide with the electrode 132, and will be neutralized. Negatively charged ions will be repelled by the electrode 132 and neutral plasma species will be unaffected by the electrode 132. The ionic composition controller 130 therefore increases the relative concentration of negatively charged ions in the plasma-activated gas. This can be used to neutralize a buildup of a positive electrostatic charge within the treatment chamber 106.

[0077] The system 100 comprises a controller 136. The controller 136 controls the voltage source 134 to set the bias on the electrode 132. The controller 136 may control whether the voltage source 134 applies a bias to the electrode 132. The voltage source 134 may be a variable voltage source. The controller 136 may control whether the voltage source 134 sets a positive or negative bias on the electrode 132. The controller 136 may control the magnitude of the bias applied to the electrode 132.

[0078] The ion selector 132 may comprise more than one electrode 132.

[0079] The electrode 132 may be in the form of a grid. Species are able to flow through gaps in the grid. By setting a bias on the grid, charged species are either attracted to or repelled by the wires of the grid while neutral species are unaffected and able to flow through the grid. The magnitude of the bias can be controlled to control the extent with which ions are neutralized.

[0080] In the example of Figure 1, the ion selector 132 is arranged in the chamber 118 proximate to the plasma source 102. The ion selector 132 may be located elsewhere in the path between the plasma source 102 and the treatment chamber 106 such as in the conduit 104.

[0081] The ion selector 132 in this example comprises a grid electrode 132 that is arranged orthogonal to the direction of travel of the gas from the plasma source 102. Otherarrangements of ion selector 132 are possible. The ion selector 132 may comprise, for example, an electrostatic lens or other arrangements where setting a polarity of an electrode enables ions within the gas to be either attracted to or repelled from the electrode.

[0082] The system 100 comprises an electric charge sensor 138 arranged to measure the electric charge within the treatment chamber 106. The electric charge sensor 138 is communicatively coupled to the controller 136 such as over a wired or wireless connection. The controller 136 receives electric charge measurements from the electric charge sensor 138 and can control the ionic composition controller 130 to modify the ionic composition of the plasma-activated gas based on the electric charge measurement. If the electric charge measurement indicates a build-up of a negative charge in the treatment chamber 106, the ionic composition controller 130 can be controlled to increase the concentration of positively charged ions relative to negatively charged ions in the plasma-activated gas. If the electric charge measurement indicates a build-up of a positive charge in the treatment chamber 106, the ionic composition controller 130 can be controlled to increase the concentration of negatively charged ions relative to positively charged ions in the plasma-activated gas. The electric charge sensor 138 may comprise one or more of a capacitive sensor, piezoelectric sensor, Faraday cup or other form of charge sensor.

[0083] The combination of electric charge sensor 138 and controller 136 enables real-time monitoring and control of the electric charge within the treatment chamber 106. The controller 136 can implement a closed-loop feedback system that adjusts the charge composition of the plasma-activated gas being delivered to the treatment chamber 106 to maintain a balanced charge environment within the treatment chamber 106. This adaptive control helps ensure consistent reactor performance and prevents charge-related disruptions during operation.

[0084] The controller 136 may control the operation of the plasma source 102 to promote generation of a particular type of neutral species. This can involve controlling parameters of the plasma source 102 such as the temperature, input power, and frequency. In this way, the plasma source 102 can generate different mixtures of plasma species based on the intended treatment application.Figure 4 shows another example system 100’ for treating products using a plasma-activated gas. The system 100’ shares similar features with the system 100 of Figure 1 and like reference numerals are used to indicate like components. A detailed discussion of the components described above in relation to the system 100 of Figure 1 is omitted.

[0085] The ionic composition controller 130 in system 100’ additionally comprises an ion generator 140 that is arranged to generate ions for introduction into the plasma-activated gas that flows from plasma source 102 to the treatment chamber 106 via the conduit 104. The ion generator 140 generates positively or negatively charged ions to increase a desired concentration of positively or negatively charged ions in the plasma-activated gas. The ion generator 140 may comprise a corona discharge ionization source.

[0086] The ion generator 140 is fluidly connected to the conduit 122 such that it may receive input gas from the same source as the plasma chamber 118. The ion generator 140 is fluidly connected to the conduit 104 such that the generated ions are carried by the gas to the plasma-activated gas flowing through conduit 104.

[0087] The ion generator 140 is controlled, by controller 136, to generate either positively charged or negatively charged ions. The ion generator 140 is controlled based on measurements of the electric charge within the treatment chamber 106 by the electric charge sensor 138.

[0088] Beneficially, the system 100’ comprises effectively two plasma generators. The plasma source 102 and the ion generator 140. The plasma source 102 may be a DBD or SDBD discharge source and the ion generator 140 may be a corona discharge ionization source. (S)DBD sources are effective in production of neutral species which are desired for the treatment (e.g., decontamination) of the product in the treatment chamber 106. The corona discharge ionization sources are more effective at producing charged species than (S)DBD sources and thus are ideal for controlling the charge composition of the plasma-activated gas.

[0089] The ionic composition controller 130 can include both the ion generator 140 and the ion selector 132 described above in relation to Figure 1. This provides two mechanisms for controlling the charge composition of the plasma-activated gas. It will be appreciated that only the ion generator 140 or the ion selector 132 may be provided.In the system 100’ the pump 126, voltage source 134 and controller 136 are provided within a common housing. This is not required in all examples. In addition, a high voltage power source 142 for powering the plasma source 102 and ion generator 140 is included in the common housing. The high voltage power source 142 is connected to the plasma source 102 and ion generator 140 by power lines 144, 146. Other implementations of the high voltage power source 142 are possible. For example, each of the plasma source 102 and ion generator 140 may have a dedicated power source.

[0090] While charged plasma species neutralize electrostatic charges, the neutral reactive species in the plasma are unaffected by the biased plates and are therefore able to simultaneously decontaminate and functionalize the powder particles. This dual-action approach addresses two critical challenges: maintaining fluidization efficiency and achieving high-efficacy microbial decontamination or powder functionalization.

[0091] In the example of Figure 4, the plasma source 102 and ion generator 140 are spatially separated. This is not required in all examples. The plasma source 102 and ion generator 140 may be provided together.

[0092] Figure 5 shows an example of this. In this example, the plasma source 102 comprises a Surface Dielectric Barrier Discharge (SDBD) source 148. The plasma source 102 also comprises a corona discharge ionization source 150 that functions as the ion generator 140. The corona discharge ionization source 150 is arranged together with the SDBD source 148 such as in the chamber 118. The corona discharge source 150 is powered by a voltage supply 151 which may be a DC supply (e.g., positive or negative or able to switch between positive and negative voltages), a pulsed supply, or a sine wave.

[0093] The SDBD source 148 predominantly generates neutral plasma species. The corona discharge ionization source 150 predominantly generates charged species. The polarity of the species is dictated by the polarity of the input voltage supplied to the corona discharge ionization source 150.

[0094] The corona discharge ionization source 150 or combination of corona discharge ionization sources 150 can selectively produce negative ions or positive ions. Corona discharges are inherently weak and so they do not produce many neutral species. Beneficially, when combined with the plasma source 102 (e.g., DBD or SDBD source),this allows for the controlled production of the desired concentrations of neutral and charged plasma species.

[0095] When the electric charge sensor 138 indicates that there is minimal charge build-up in the treatment chamber 106, the controller 136 can disable operation of the corona discharge ionization source 150 and activate the plasma source 102 to generate the desired neutral plasma species for treatment of the product. However, if there is charge-build up, the corona discharge ionization source 150 can be activated to generate positively or negatively charged ions to compensate for the charge build-up. The further inclusion of the ion selector 132 provides improved control of the concentration of charged species that reach the treatment chamber 106. A minimum voltage is required to produce a corona discharge, after breakdown occurs a number of positively or negatively charged ions will be produced. Increasing the voltage allows more ions to be produced, but decreasing the voltage would cause the plasma to extinguish. In general, there is a minimum concentration of ions that are created and this cannot be reduced by reducing the voltage. Introducing the ion selector 132 allows precise control of how much charge is let through to the treatment chamber 106. The corona produces an abundance of ions and by simply controlling the ion selector 132 (e.g., varying voltage on the electrode 132) the system 100, 100’ can prevent charge passing through depending on the output measured by the electric charge sensor 138. Figure 5 shows neutral plasma species being generated by the SBD source 148 and positive charged ions generated by the corona discharge ionization source 150. Ion selector 132 in the form of a grid electrode 132 is arranged downstream of the plasma source 102, 148, 150. Selectively setting a negative bias on the grid electrode 132 can remove positively charged ions to provide a desired charge density for the plasma-activated gas flowing to the treatment chamber. This desired charge density is selected to neutralise an electrostatic charge in the treatment chamber 106.

[0096] Figure 6 shows the SDBD source 148 in isolation. The SDBD source 148 comprises a plurality of electrode pairs, with each electrode pair comprising a ground electrode 152 and high voltage electrode 154. The electrodes 152, 154 are coupled to power source 142. Copper is a suitable material for the electrodes, but other known suitable conductive materials may be used. For example, stainless steel or other chemically resistant materials could be used. A dielectric barrier 156 is located between theelectrodes 152, 154. The electrode 152 and electrode 154 could use different materials such as copper for the high voltage electrode 154 and stainless steel for electrode 152.

[0097] The electrodes 152, 154 are configured to apply a voltage across the dielectric barrier to generate a plasma in a discharge area 158 on a surface of the dielectric barrier 156. Figure 7 shows a simplified schematic diagram of an example system 100, 100’ for treating products using a plasma-activated gas.

[0098] The system 100, 100’ comprises sensors for monitoring properties of the system 100, 100’.

[0099] The system 100, 100’ comprises a pressure I mass flow sensors 160 arranged at the input 120 and output 124 of the plasma chamber 118. Feedback from the pressure I mass flow sensors 160 are transmitted to the controller 136 to enable regulation of air to maintain the desired flow rate and pressure. If the measurement data indicates a leak in the system 100, 100’ the controller 136 can trigger an error alert or initiate a shutdown to prevent further issues. The pressure I mass flow sensors 160 could be differential, piezoelectric, MEMS or other forms of pressure I mass flow sensors 160. The system 100, 100’ comprises a temperature sensor 162 arranged to measure the temperature of the plasma-activated gas entering the reactor 108. Control of the temperature of the plasma-activated gas is desirable to prevent material damage or clumping caused by excessive heat. Heating of the plasma-activated gas may result from heating in the plasma source 102 or from other sources. Feedback from the temperature sensor 162 is transmitted to the controller 136. If the temperature rises beyond safe levels, the controller 136 can activate one or more cooling mechanisms 168 such as fans, liquid cooling of the conduit 104, or radiators to restore the plasma-activated gas to a safer working temperature. The temperature sensor 162 could be a thermocouple, RTD, IR sensor or other.

[0100] The system 100, 100’ comprises a gas composition sensor 164 arranged at the inlet 110 and outlet 116 of the reactor 108 to monitor the gas composition entering and exiting the reactor 108. Monitoring the gas composition and making changes to the performance of the system 100, 100’ based on the monitored gas composition helps ensure uniform plasma gas coverage and effective decontamination of granularmaterial. A low concentration of plasma species in the output gas may indicate absorption by the product or moisture. This could suggest partial decontamination or that only a portion of the product is being effectively treated. Output gas concentration can be optimised through feedback to controller 136, enabling real-time adjustments to plasma power and / or gas flow rate as needed. Measurements of gas composition could be via UV / laser-based / FTIR spectroscopy or other gas detection to measure one or more of the plasma species.

[0101] The system 100 / 100’ further comprises a powder / gas filter 166 arranged at the outlet 116 of the reactor 108. The powder I gas filter 166 prevents product from the treatment chamber 106 flowing out of the reactor 108 via the outlet 116.

[0102] In an example implementation, the system 100 / 100’ is used to treat a granular product such as herbs, spices, or other granular food / material. The granular product is transported to the treatment chamber 106 of the reactor 108 and plasma-activated gases are used for decontamination. This process could be configured as either a batch system or a continuous flow system with the product entering and exiting the treatment chamber through conduits (not shown).

[0103] The above examples involve a plasma source 102 that provides a plasma-activated gas for treating product in the treatment chamber 106. This is not required in all examples. Treating product in the treatment chamber 106 does not necessarily require a plasma-activated gas such as, for example, when the treatment involves drying the product rather than decontamination or functionalization.

[0104] In these examples, controlling the composition of charged ions in the gas is still beneficial to prevent agglomeration in the treatment chamber 106. In other words, the advantageous effects associated with controlling the composition of charged ions are achieved in applications where gas (plasma-activated or otherwise) is delivered to a fluidized bed reactor.

[0105] For example, a gas may be supplied to the treatment chamber 106 for drying product in the treatment chamber 106. The gas may be carbon dioxide for example. The ionic composition controller 130 may selectively control the composition of ions in the gas to compensate for electric charge build-up in the treatment chamber 106. In some implementations, the ionic composition controller 130 may comprise the ion generator 140 to selectively generate positively or negatively charged ions. In someimplementations, the ionic composition controller 130 may further comprise the ion selector 132 to enable the charge density of the positively / negatively charged ions to be controlled.

[0106] In summary, there is provided a method and system for treating a product using a gas. A gas is transported to a treatment chamber (106) of a fluidised bed reactor (108). The gas is used for treating a product (P), such as a granular product (P), in the treatment chamber (106). An ionic composition controller (130) controls the ionic composition of the gas so as to compensate for an electric charge build-up in the treatment chamber (106). The ionic composition controller (130) can neutralize ions or add ions to the gas. The ionic composition controller (130) may control the ionic composition based on measurements of the electric charge in the treatment chamber (106).

[0107] Various combinations of optional features have been described herein, and it will be appreciated that described features may be combined in any suitable combination. In particular, the features of any one example embodiment may be combined with features of any other embodiment, as appropriate, except where such combinations are mutually exclusive. Throughout this specification, the term “comprising” or “comprises” means including the component(s) specified but not to the exclusion of the presence of others.

[0108] All of the features disclosed in this specification (including any accompanying claims, abstract and drawings), and / or all of the steps of any method or process so disclosed, may be combined in any combination, except combinations where at least some of such features and / or steps are mutually exclusive.

[0109] Each feature disclosed in this specification (including any accompanying claims, abstract and drawings) may be replaced by alternative features serving the same, equivalent, or similar purpose, unless expressly stated otherwise. Thus, unless expressly stated otherwise, each feature disclosed is one example only of a generic series of equivalent or similar features.

[0110] The invention is not restricted to the details of the foregoing embodiment(s). The invention extends to any novel one, or any novel combination, of the features disclosed in this specification (including any accompanying claims, abstract and drawings), or to any novel one, or any novel combination, of the steps of any method or process so disclosed.

Claims

22P10008WOCLAIMS1. A method of treating a product using a gas, the method comprising:generating, using a plasma source, a plasma-activated gas comprising neutral plasma species;transporting the plasma-activated gas to a treatment chamber of a fluidised bed reactor for treating a product in the treatment chamber;measuring the electric charge within the treatment chamber; and controlling, upstream of the treatment chamber, an ionic composition of the plasma-activated gas generated using the plasma source based on the measured charge within the treatment chamber so as to compensate for an electric charge build-up in the treatment chamber.

2. A method as claimed in claim 1 , wherein controlling the ionic composition of the plasma-activated gas comprises controlling a charge density of the plasma- activated gas.

3. A method as claimed in claim 1 or 2, wherein controlling the ionic composition comprises neutralizing ions in the gas.

4. A method as claimed in claim 3, wherein controlling the ionic composition comprises controlling an ion selector to selectively neutralize ions in the gas.

5. A method as claimed in claim 4, wherein the ion selector is located outside of the treatment chamber.

6. A method as claimed in claim 5, wherein the ion selector is arranged between the plasma source and the treatment chamber.

7. A method as claimed in any of claims 4 to 6, wherein the ion selector comprises an electrode, and wherein controlling the ion selector comprises controlling the bias of the electrode such that the electrode selectively attracts or repels ions in the gas.

8. A method as claimed in claim 7, wherein the ion selector comprises a plurality of electrodes, and controlling the ion selector comprises controlling the bias of a first of the electrodes to have a positive bias, and controlling the bias of a second of the electrodes to have a negative bias.

9. A method as claimed in any preceding claim, wherein controlling the ionic composition comprises introducing ions into the gas.

10. A method as claimed in claim 9, wherein introducing ions comprises controlling an ion generator to generate ions.

11. A method as claimed in claim 10, wherein the ion generator comprises a corona discharge ionization source.

12. A method as claimed in claim 10 or 11, wherein controlling the ion generator comprises selectively controlling the ion generator to generate either positively charged or negatively charged ions.

13. A method as claimed in any preceding claim, wherein controlling the ionic composition comprises controlling the operation of the plasma source to control the ionic composition of the plasma-activated gas.

14. A method as claimed in any preceding claim, wherein the plasma generator comprises a dielectric discharge barrier source or surface dielectric barrier discharge source.

15. A system for treating a product, the system comprising:a plasma source configured to generate a plasma-activated gas comprising neutral plasma species;a fluidised bed reactor comprising a treatment chamber, the fluidised bed reactor arranged to receive the plasma-activated gas for treating a product in the treatment chamber;an electric charge sensor arranged to measure the electric charge within the treatment chamber; andan ionic composition controller arranged to control, upstream of the treatment chamber, an ionic composition of the plasma-activated gas generated by the plasma source based on the measured charge within the treatment chamber so as to compensate for an electric charge build-up in the treatment chamber.

16. A system as claimed in claim 15, wherein the ionic composition controller comprises an ion selector arranged to selectively neutralize ions in the gas.

17. A system as claimed in claim 16, wherein the ion selector is located outside of the treatment chamber.

18. A system as claimed in claim 17, wherein the ion selector is arranged between the plasma source and the treatment chamber.

19. A system as claimed in any of claims 16 to 18, wherein the ion selector comprises an electrode, and wherein the ionic composition controller is arranged to control the bias of the electrode such that the electrode selectively attracts or repels ions in the gas.

20. A system as claimed in any of claims 15 to 19, wherein the ionic composition controller comprises an ion generator arranged to generate ions.

21. A system as claimed in claim 20, wherein the ion generator comprises a corona discharge ionization source.

22. A system as claimed in any of claims 15 to 21, wherein the plasma source comprises a dielectric discharge barrier source or surface dielectric barrier discharge source.

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