Jet ejector plasma (JEP) fluid treatment apparatus and method

Abstract

A jet ejector plasma reactor apparatus (100) has a venturi (130) having a nozzle section (162), a diffuser section (172), and a throat therebetween, the venturi having a venturi flow direction (F) along a flow axis (RA) from the nozzle to the diffuser. A suction chamber is provided surrounding the venturi such that the venturi lowers the chamber pressure. At least one non-thermal plasma generator (136) is provided comprising a gas inlet and a plasma outlet, the plasma outlet directed towards, and in fluid communication with, the chamber and therefore the venturi.

Description

Jet ejector plasma (JEP) fluid treatment apparatus and methodTechnical Field

[0001] The present application is concerned a jet ejector plasma fluid treatment apparatus and method of jet ejection of plasma. More specifically the present invention is concerned with an apparatus and method for treatment of a fluid with a non-thermal plasma. The present invention is also concerned with a non-thermal plasma generator and method of generation of a non-thermal plasma.Background Art

[0002] Non-thermal plasmas (also known as cold plasmas) are plasmas generated by partial ionisation of gases. Non-thermal plasmas may be generated in several ways. For example, plasma jet, dielectric barrier discharge and corona discharge. In all cases, an electric discharge between a high voltage electrode and ground potential, through a gas, produces a cocktail of reactive species including radicals and molecular species.

[0003] One application of non-thermal plasma is in the treatment of water and wastewater in an advanced oxidation process. The reactive species act to oxidise and thereby break down various compounds in water, enhancing its safety for human consumption and environmental protection. This includes pesticides, dyes, chemicals such as endocrine disrupting chemicals, pharmaceuticals and natural organic matter. Non-thermal plasma processes produce highly reactive radicals (e.g. *OH and *H) and molecular species (e.g. H2O2, O3, H2, O2) in water and a variety of other reactive species in gas phase. From the perspective of water treatment, three reactive species including hydroxyl radicals, ozone, and hydrogen peroxide are of particular importance given their powerful oxidative properties as singular or combined oxidants. These oxidants can oxidise a variety of organic and inorganic compounds such as phenols, nitro- and chloro-substituted phenols, polycyclic aromatic hydrocarbons, pesticides, polychlorinated biphenyls (PCBs), dyes, arsenic, manganese, iron, and many other persistent pollutants. Out of the three species, hydroxyl radicals are the most powerful oxidant and are unselective with very short lifetime (few nanoseconds) while ozone and hydrogen peroxide are selective oxidants but have relatively longer lifetimes. Hydroxyl radicals can be formed through various mechanisms inboth gas and liquid phases. In gas phase, the highly energetic electrons produced by the discharge produce hydroxyl radicals via collision reactions with water molecules. These hydroxyl radicals can then recombine to form hydrogen peroxide. Non-thermal plasma also forms ozone, which when combined with hydrogen peroxide dissociates in water to form even more hydroxyl radicals.

[0004] Having a high redox potential of 2.8V, hydroxyl radicals (*OH) are the most potent oxidants in water, capable to break down almost all contaminants unselectively. In fact, *OH are the basis of advanced oxidation processes (AOPs) in water treatment. Amongst other technologies, non-thermal plasma stands out as an important AOP since it can produce hydroxyl radicals in sufficient quantity to accomplish water treatment.

[0005] Non-thermal plasma generated by electrical discharges initiate the formation of various short-lived radical reactive species (*OH, H* O* and *NO) and relatively long-lived molecular oxidants including H2O2 and O3. Hydrogen peroxide is one of the principle reactive species involved in the degradation of organic compounds in water.

[0006] Ozone is the strongest oxidant amongst the long-lived reactive species generated in plasma. Ozone is generated from oxygen because of the effect ofthe electrical discharge and molecular collisions. The powerful oxidation characteristic of ozone can be enhanced even further in the presence of the other reactive species, particularly hydrogen peroxide. A combination of ozone with hydrogen peroxide forms the Peroxone process, which provides additional OH radicals available for the oxidation of contaminants in water. Plasma also produces UV light which is when combined with ozone produces even more hydroxyl radicals.

[0007] In short, non-thermal plasma treatment is simple, effective and does not produce chemical byproducts. That said, prior art plasma reactors are inefficient because of a significant loss of the produced reactive species during contact between the plasma and water to be treated. This increases the energy cost of the technology, forming a barrier to its uptake by industry.

[0008] Another application is in the creation of plasma activated water (PAW). There is increasing demand for PAW by several sectors. It may be used for disinfection, the reactive species oxidising harmful compounds and microbes. It can also be used in seed germination processes. The current plasma systems used to produce PAW are inefficient due to their inability to harness all reactive species, and difficult to scale up.

[0009] As well as water applications, the non-thermal plasmas are used in a wide range of other industries including, but not limited to, nanotechnology, synthetic chemistry, disinfection, food industry, etc.

[0010] US 2023 / 0242420 A1 discloses a system and method for water treatment with venturi plasma discharge. Wastewater is fed through a venturi which lowers the static pressure in accordance with Bernoulli's principle. Non-thermal plasma is generated by a plasma jet having an outlet at the venturi throat. Pressurised gas is fed through a HV electrode. A ground electrode is placed in various locations- for example opposite the outlet (on the opposite side of the throat) and at the venturi inlet or outlet. Air bubbles of non-thermal plasma are entrained in the water flow. In all cases, the ground electrode is integrated within the venturi.

[0011] The system of US'420 is therefore designed with a single application in mind. It will be noted that satisfactory operation only occurs within a specific range of liquid or liquidgas mixture conductivities due to the fact that the plasma circuit passes through the liquid. This is a drawback. Any change in the conductivity of the treated liquid will require reconfiguration of the apparatus of US'420.Summary of Invention

[0012] According to a first aspect of the present invention there is provided a jet ejector plasma reactor apparatus comprising:a venturi having a nozzle section, a diffuser section, and a throat therebetween, the venturi having a venturi flow direction along a flow axis from the nozzle to the diffuser;a chamber at least partially surrounding the venturi, the chamber having an internal volume in fluid communication with the venturi downstream of the nozzle section to thereby reduce pressure in the internal volume;at least one non-thermal plasma generator comprising a gas inlet and a plasma outlet, the plasma outlet in fluid communication with the internal volume of the chamber.

[0013] Advantageously, the pressure drop in the chamber caused by the fluid communication with the venturi proximate the throat causes the plasma to be sucked intocontact with the working fluid for better mixing and therefore treatment with the reactive species.

[0014] Preferably the chamber completely surrounds the venturi in a plane normal to the flow axis.

[0015] Preferably the plasma outlet is directed towards the venturi between the nozzle section and the diffuser section.

[0016] Preferably the chamber defines at least one plasma generator port in a chamber wall bounding the internal volume, the plasma generator port receiving the plasma generator.

[0017] Preferably the chamber wall defines a plurality of plasma generator ports.

[0018] Preferably the enclosed chamber comprises a plurality of ports to receive a respective plurality of non-thermal plasma generators, each non-thermal plasma generator being removeable and replaceable with a port plug.

[0019] The non-thermal plasma generator may be configured to direct a flow of non-thermal plasma along a generator axis having a component parallel to the flow axis. The component may be in the same direction as the venturi flow- this is particularly advantageous for a liquid (e.g. water) as the working fluid.

[0020] Preferably the generator axis is at an angle of less than 90 degrees to the flow axis. More preferably the generator axis is at an angle of less than 45 degrees to the flow axis. It may be less than 10 degrees.

[0021] Preferably there is provided an enclosed (suction) chamber, wherein the venturi defines an opening in fluid communication with the enclosed chamber downstream of the nozzle section to thereby reduce pressure in the enclosed chamber. The use of a suction chamber better entrains the plasma into the flow, and assists with avoiding back flow into the upstream parts of the system. The suction chamber is preferably of a diameter and height customisable to accommodate multiple plasma generators. It can take the form of a cylinder, a rectangular, or any other shape. The plasma generators can be placed on an upstream horizontal area of the chamber or along an external surface of the chamber. The external surface may be vertical in use (i.e. aligned with the flow axis).

[0022] Preferably the venturi opening is at the throat.

[0023] Preferably the plasma generator outlet is directed towards the venturi opening to thereby direct plasma to a fluid flowing through the venturi.

[0024] Preferably the venturi opening is a gap in the venturi separating the venturi into an upstream section and a downstream section.

[0025] Preferably the enclosed chamber comprises a first part and a second part, the first and second parts being joined together to form the enclosed chamber, wherein the upstream section is mounted to the first part, and the downstream section is mounted to the second part.

[0026] Preferably the venturi comprises a further nozzle section downstream of the venturi opening.

[0027] Preferably the enclosed chamber comprises a plurality of ports to receive a respective plurality of non-thermal plasma generators, each non-thermal plasma generator being removeable and replaceable with a port plug.

[0028] Preferably there is provided a plurality of non-thermal plasma generators, each having a plasma outlet, the plasma outlets directed towards, and in fluid communication with, the venturi.

[0029] Preferably each of the plurality of non-thermal plasma generators is level with respect to the flow axis. Alternatively, they can be distributed along the external surface of the chamber at different heights.

[0030] Preferably the non-thermal plasma generators are circumferentially spaced around the flow axis.

[0031] Preferably each of the plurality of non-thermal plasma generators, particularly if they are at the same height, each have a generator axis at respective angle to the flow axis, the angle can be the same for each non-thermal plasma generator.

[0032] Alternatively, each of the plurality of non-thermal plasma generators, particularly if they are placed at different heights, each have a generator axis at respective angle to the flow axis, the angle being different for at least two of the plurality of non-thermal plasma generators.

[0033] The at least one non-thermal plasma generator may be of any type, including but not limited to at least one of:a plasma jeta dielectric barrier discharge type;a corona discharge type;a (i) one of a pin or wire to (ii) one of a plate or liquid type;a microwave type; and,a radio frequency type plasma generator.

[0034] Preferably the at least one non-thermal plasma generator comprises a first electrode and a second electrode surrounding the first electrode defining a flow path surrounding the first electrode, for generation of plasma.

[0035] Preferably the flow path surrounding the first electrode is annular.

[0036] Preferably the first electrode is a high voltage electrode, and the second electrode is a ground electrode.

[0037] Preferably the first electrode comprises a plurality of external protrusions extending into the annular flow path.

[0038] Preferably the first electrode comprises an external thread. It may be a standard or a non-standard thread.

[0039] Preferably the thread is a standard thread, more preferably at least one of and ISO metric threads, unified thread standard thread, American national standard pipe thread, and British standard pipe thread.

[0040] Preferably the external thread of the first electrode has a first portion extending into the annular flow path, and a second portion engaged with a female thread for mounting in the non-thermal plasma generator.

[0041] Preferably there is provided a mixer downstream of the venturi.

[0042] Preferably there is provided a treated fluid circuit arranged to pass a treated fluid through the venturi multiple times.

[0043] Preferably there is a gas separator for separating liquid and gas in the treated fluid.

[0044] Preferably the treated fluid is water. Alternatively, the fluid may be a solvent or a gas.

[0045] According to a second aspect there is provided a method of generating a plasma treated fluid comprising the steps of:providing a venturi having a nozzle section, a diffuser section, and a throat therebetween;providing a chamber at least partially surrounding the venturi, the chamber having an internal volume in fluid communication with the venturi downstream of the nozzle section;passing a fluid to be treated through the venturi in a venturi flow direction along a flow axis from the nozzle to the diffuser to thereby reduce pressure in the internal volume;directing a flow of non-thermal plasma into the chamber to contact with the fluid to be treated in the venturi.

[0046] Preferably the method of generating a plasma treated fluid according to the second aspect, uses an apparatus according to the first aspect.

[0047] According to a third aspect there is provided a non-thermal plasma generator comprising:a first electrode; and,a second electrode surrounding the first electrode to define a gap surrounding the first electrode for passage of a gas for plasma generation;wherein the first electrode defines an external thread extending into the gap.

[0048] Advantageously, the thread provides an active length (the helix) for plasma generation significantly higher than if e.g. a simple wire was used. For example, in the case of an M6 thread, the helix length, which provides the active length for plasma generation, is many times greaterthan the length ofthe rod itself, resulting in a smaller reactor footprint.

[0049] Such an apparatus can be used e.g. for the generation of ozone (O3).

[0050] The thread may be standard or non-standard. Preferably the thread is a standard thread, more preferably at least one of an ISO metric thread, unified thread standard thread, American national standard pipe thread, and British standard pipe thread.

[0051] Preferably the gap is annular.

[0052] Preferably there is provided a dielectric barrier in the gap, forming a dielectric barrier discharge generator.

[0053] Preferably the external thread of the first electrode has a first portion extending into the gap, and a second portion engaged with a female thread for mounting in the nonthermal plasma generator.

[0054] Preferably there is provided a mount defining the female thread, wherein a high voltage connection point is provided on a first side of the mount, and a flow inlet in fluid communication with the annular channel is provided on a second side of the mount.

[0055] According to a fourth aspect there is provided a method of generating a nonthermal plasma comprising the steps of:providing a generator according to the third aspect;generating a non-thermal plasma with the generator.

[0056] According to a fifth aspect of the present invention there is provided a jet ejector plasma reactor apparatus comprising:a venturi having a nozzle section, a diffuser section, and a throat therebetween, the venturi having a venturi flow direction along a flow axis from the nozzle to the diffuser;at least one non-thermal plasma generator comprising a gas inlet and a plasma outlet, the plasma outlet directed towards, and in fluid communication with, the venturi;wherein the non-thermal plasma generator is configured to direct a flow of non-thermal plasma along a generator axis having a component parallel to the flow axis.

[0057] Advantageously the plasma flow direction is at least partially in the direction of the main (treated) flow. This enables better mixing between the fluids, particularly in the low pressure throat area of the venturi.

[0058] Preferably the generator axis is at an angle of less than 90 degrees to the flow axis. More preferably the generator axis is at an angle of less than 45 degrees to the flow axis. It may be less than 10 degrees.Brief Description of Drawings

[0059] An embodiment of the present invention will now be described with reference to the following figure in which:FIGURE 1 is a perspective view of a first apparatus according to the present invention; FIGURE 2 is a perspective view of the apparatus of Figure 1 with various panels, cables and pipes removed;FIGURE 3 is a perspective view of a reactor of the apparatus of Figure 1 ;FIGURE 4 is a section view through line IV in Figure 3;FIGURE 5 is a detail view of the region V in Figure 4;FIGURE 6 is a detail view of part of Figure 5;FIGURE 7 is a side view of a plasma generator used in the apparatus of Figure 1 ;FIGURE 8 is a section view along line VIII in Figure 7;FIGURE 9 is a section view along line IX in Figure 7;FIGURE 10 is a section view along line X in Figure 7;FIGURE 11 is a section view along line XI in Figure 7;FIGURE 12 is a section view along line XII in Figure 7;FIGURE 13 is a section view along line XIII in Figure 12;FIGURE 14 is a side view of a second reactor assembly in accordance with the present invention; and,FIGURE 15 is a plan view of the reactor of Figure 14.Description of the first embodiment

[0060] Referring to Figures 1 to 11, there is shown an apparatus 100 according to the present invention.Configuration

[0061] Figure 1 shows the apparatus 100 with various cover panels 102 installed to provide a sealed unit. On the exterior unit there is provided an interactive control panel 104, an emergency stop button 106, a set of gas flow controls 108 and a set of liquid flow controls 110. Referring to Figure 2, the panels 102 are mounted on a frame 112 containing the various features as described below.

[0062] Referring to Figure 2, the apparatus 100 comprises a plurality of water tanks. The tanks will be described here in as "water tanks" but it will be understood that they are suitable for holding other liquids to be treated as required. The plurality of tanks includes an untreated water tank 114, a treated water tank 116 and a reactor water tank 118. The apparatus further comprises a high voltage power supply 120, a reactor assembly 122, a separator 124, and a gas purifier 240. It will be understood that the apparatus 100 comprises various pumps, valves, controllers and so on to facilitate the function described herein, although the detailed selection and configuration of such components is within the understanding of the skilled person and as such will not be described in detail here.

[0063] The high voltage power supply 120 is configured to generate a voltage in the order of tens of kV for the generation of plasma as will be described below. In this embodiment it is a pulse type supply with pulse width in the nanosecond range, although other HV supplies are envisaged.Reactor assembly

[0064] The reactor assembly 122 is described in more detail with reference to Figures 3 to 6.

[0065] The reactor assembly 122 comprises an inlet conduit 126, a suction chamber 128, a venturi 130, an outlet conduit 132, a static mixer 134 and a plurality of four plasma jetgenerators 136. The reactor assembly has a primary axis RA about which is generally rotationally symmetric.

[0066] The inlet conduit 126 is connected to a liquid supply and is configured to pass liquid in a flow direction F, along a flow axis RA, through the venturi 130 and to the outlet conduit 132. The inlet conduit 126 and outlet conduit 132 connect to the venturi 130 within the suction chamber 128.

[0067] The suction chamber 128 is a two-part cylindrical structure having a first part 138 and a second part 140 held together by a connecting and sealing collar 142. The first part 138 defines a first end wall 144 and a first outer wall 146. The second part 140 defines a second end wall 148 and a second outer wall 150. The end walls 144, 148 bound the ends of the chamber 128, and the outer walls 146, 150 the periphery. Aside from the fluid inlets and outlets described herein, the chamber 128 is gas-tightto enable the pressure within to be controlled.

[0068] The suction chamber 128 has a first valve 152 and a second valve 154 positioned in the outer wall.

[0069] The venturi 130 is positioned within the suction chamber 128. It is connected to the inlet conduit 126 and the outlet conduit 132. The venturi comprises a first (inlet) section 156, connected to the inlet conduit 126, in the first part 138 and a second (outlet) section 158, connected to the outlet conduit 132, in the second part 140. The first section 156 and second section 158 are separate and separated by a gap G open to the inside of the chamber 128. The first section 156 depends from the first end wall 144, and the second section 158 depends from the second end wall 148. In this way, separation of the parts 138, 140 also separates the venturi into two either side of the gap G.

[0070] The inlet section 156 comprises a constant area region 160 which is in communication with a nozzle section 162 leading to a further, smaller, constant area region 163 leading to an outlet orifice 164. It will be noted that the region 160 is of smaller cross section area than the inlet conduit and is jointed thereto via an annular step or shoulder at the chamber end wall 144. This may be replaced by a smoother transition to reduce losses. The nozzle section 162 is converging in cross sectional area towards the orifice 164. The outlet 164 is open- i.e. in fluid communication with the surroundings (in this case the suction chamber 128). The outlet 164 acts as the throat of the venturi.

[0071] The outlet section 158 has an inlet opening 166 facing, but spaced apart from, the outlet 164 of the inlet section 156 (forming the gap G). The inlet opening 166 is in communication with a tapered (narrowing) area region 168, which is in communication with a constant area section 170. The constant area section 170 leads into an outwardly tapered area diffuser section 172, leading to the outlet conduit 132.

[0072] The static mixer 134 comprises an elongate, constant cross-section conduit 172 containing elements 174 which tubulate the flow therein to provide mixing as the fluid passes therethrough. It will be noted that the static mixer can be of any type. In this specific example a helical static mixer is employed, but it is envisaged that a mixer may be omitted from the reactor assembly design or, where it is included, any type of mixer can be used, static or otherwise.Plasma generators

[0073] The plasma generators 136 are substantially identical and described with reference to Figures 7 to 13.

[0074] The generators 136 produce non-thermal plasma. Each generator 136 is a self-contained subassembly comprising a housing assembly 176 and an electrode assembly 178. The ejector has a generator axis in the form of a main ejector axis EA.

[0075] The housing assembly 176 comprises a first part 180, second part 182, third part 184 and fourth part 186. Each part 180, 182, 184, 186 is generally cylindrical in shape and aligned along the axis EA.

[0076] The first part 180 (also shown in section in Figure 9) comprises a base 188 with four fastener openings 190 and a central cylindrical projection 192. An electrode opening 194 is defined through the centre of the first part 180.

[0077] The second part 182 is generally cylindrical having four fastener openings 196 and an electrode opening 198 is defined through the centre.

[0078] The third part 184 (also shown in section in Figure 10) is also generally cylindrical, having four stepped fastener openings 200 each with a narrow portion 202, a wide portion 204 and a shoulder 206 therebetween. The third part further defines a stepped electrode opening 208 having a narrow portion 210, a wide portion 212 and a shoulder 214 therebetween. A radial gas inlet port 216 is provided in communication with the wideportion 212 of the electrode opening 208, proximate the shoulder 214. A connector 218 is engaged with the inlet port 216.

[0079] The fourth part 186 (also shown in section in Figure 11 ) is also generally cylindrical. It comprises four fastener openings 220 and an electrode opening 198 defined through the centre. A high voltage (HV) connection port in the form of a radially extending closed slot 222 is provided extending most of the way through the fourth part 186.

[0080] The electrode assembly 178 comprises a mount 224 and an electrode subassembly 179 comprising a ground electrode 226, a dielectric layer 228, a high voltage (HV) electrode 230 and an end cap 232. The mount 224 has an electrode receiving central opening 234 defining a female thread. The ground electrode 226 is a tubular member constructed from a conductive material such as copper. On the inner surface of the ground electrode 226 there is provided the dielectric layer 228. The HV electrode 230 is constructed from a conductive steel (or other conductive materials such as copper) rod having an external male thread 236. In this embodiment, the HV electrode 230 is a standard IVI6 threaded rod constructed from stainless steel. Such components can be sourced off-the-shelf and are inexpensive as well as effective, as explained below. The end cap 232 is constructed from an insulator material.

[0081] The HV electrode 230 is mounted in the third part 184 of the housing, in which a female thread in the opening 208 engages the male thread 236. The inner dielectric layer 228 is mounted in the mount 224, which is inserted into the wide portion 212 of the third part 184 of the housing. The HV electrode extends through the centre of the ground electrode226 and innerdielectric layer 228 leaving an annular gap 238 therebetween, such that the inner surface of the inner dielectric layer 228 faces the thread 236 across the gap 238. Therefore the electrode subassembly 179 has a first end 227 where the HV electrode extends from the ground electrode 226 and inner dielectric layer 228, and a second, outlet, end 229 where the HV electrode, ground electrode 226 and inner dielectric layer 228 terminate together.

[0082] The housing parts 180, 182, 184, 186 are stacked, with the first end 227 extending into the slot 222, and the second end 229 terminating in the end cap 232. At the second end 229 the annular gap 238 is open, for the ejection of the formed plasma.

[0083] The inner dielectric layer 228 terminates in the third part 184 of the housing to allow (as shown in Figure 10) the inlet port 216 to be in fluid communication with the gap 238. The ground electrode 226 terminates at the first part 180.

[0084] Referring back to Figures 3 to 6, four plasma generators 136 are provided, each oriented with their respective axes EA at an ejection angle JAto the reactor axis RA (Figure 5). In the present embodiment, all four generators 136 have the same ejection angle JA to the reactor axis RA, with each ejector axis EA meeting at a focal point FP in the gap G. In this embodiment J A is 15 degrees, although it should be noted that this may vary. It should also be noted that with 0<JA<90 degrees, there is a directional component of the ejector axis EA parallel to the reactor axis RA, i.e. in the direction of the fluid to be treated, which aids mixing. Figure 5 shows the directional components EA1 and EA2 of EA, noting that because JA<45 degrees, EA1 > EA2.

[0085] The angle JA is selected to ensure ejection of the plasma into the convergent inlet section of the venturi opening 166. Referring to Figure 6, it can be seen that the axes EA each intersect the opening 166.

[0086] Each plasma generator 136 is mounted such that the housing assembly 176 is positioned outside of the suction chamber 128 with the electrode assembly extending into the suction chamber 128. Referring to Figure 6, each second end 229 of each electrode subassembly 179 is positioned adjacent the downstream nozzle section 162 of the venturi's inlet section 156 and is generally directed towards the inlet opening 166 of the venturi's outlet section 158. In other words, the second end 229 of each electrode subassembly 179 is directed towards the gap G between the sections 156, 158.

[0087] It will be noted that each plasma generator 136 is a self-contained unit containing both electrodes upstream of the outlet into the venturi. The plasma is generated outside the venturi and ejected into the venturi flow at the plasma generator outlet. This means that the number of plasma generators can be varied depending on need.Separator

[0088] The separator 124 is not shown in detail, but its construction and use will in general be familiar to the person skilled in the art. The separator is configured to separate liquid droplets suspended in a gas, for reasons outlined below.Gas purifier

[0089] The gas purifier 240 is not shown in detail, but its construction and use will in general be familiar to the person skilled in the art. The gas purifier utilises a catalyst, typically an ozone destruction catalyst composed of activated carbon, copper oxide, and manganese oxide, to capture ortransform any residual reactive gases in the gas stream into the plasma generators. For example, it converts ozone into oxygen, resulting in purified air. Other catalysts or technology for purifying the gas stream could also be used.Use

[0090] In use, liquid to be treated is stored in the tank 114. It is pumped to the inlet conduit 126 of the reactor assembly where it passes in the direction F. The liquid (for example eater) is passed through a flow meter via which flow rate is controlled. The liquid is accelerated through the nozzle section 162 of the venturi to the constant area region 163 leading to the orifice 164. The region 163 guides the flow to the throat of the venturi at section 170. The liquid traverses the gap G to the inlet opening 166, passing through the section 170 to the diffuser section 172 where it slows (per the well understood operation of venturis).

[0091] In normal use, the valves 152, 154 are closed, but during startup and shutdown phases, the valves 152, 154 can be used to equalise the chamber pressure.

[0092] The gap G is immediately downstream of a throat formed at the orifice 164. Acceleration of liquid flow causes a drop in static pressure. Because the venturi is open at the gap G, this reduces the pressure in the suction chamber 128 in general.

[0093] Pressurised gas (in this embodiment air, although other gases such as oxygen may be used) is provided to each plasma generator 136 at each respective connector 218. The gas flows into the annular gap 238 in the direction of the free, second end 229. A high potential difference (in the order of kV) is applied between the HV electrode 230 and the ground electrode 226. This results in discharge across the gap 238.

[0094] The sharp outside surface of the thread crests provides a thin surface that favours the discharge to take place, enabling plasma ignition at lower voltages while providing a strong and durable electrode. This type of electrode provides a discharge length for plasma generation approximately 20 times higher than the length of the rod itself, assuming an M6 thread is used. It is also easy to maintain and replace. This construction makes for an effective dielectric plasma discharge (DBD) with a small footprint. Plasma isejected at the second end 229. The plasma generated by the present invention contains both short lived radicals (e.g. *OH, *O) and long-lived molecular oxidants (e.g. O3, H2O2).

[0095] The reduced pressure at the gap G, and suction chamber 128, draws plasma generated by each plasma generator 136 into the liquid flow. As it traverses the gap G, plasma reactive species are rapidly entrained into the liquid and mixes therewith as it enters the opening 166. This creates a very fine gas-liquid emulsion containing very small gas bubbles mixture of liquid and gas.

[0096] The treated water passes through the diffuser section 172. The decrease in velocity results in pressure increase to a value that lies between the motive and suction pressures at the exit of the ejector. Thus, at the exit of the jet, the low pressure of sucked plasma will be compressed whilst the motive water stream will have its pressure reduced to compensate for the energy dissipated on the suction side of the device. The rapid mixing of the plasma stream with the water flow permits to achieve high mass transfer and rapid uptake of the reactive species into the liquid phase.

[0097] The use of a suction chamber minimises the risk of water being sucked back to the plasma electrodes when pressure changes (e.g. pressure of the motive fluid changes during switch off of the water pump, or as a result of drop in pump efficiency during operation).

[0098] The flow then passes into the outlet conduit 132 and into the static mixer 134. The static mixer 134 further distributes the plasma containing gas into the liquid before it enters the reactor water tank 118.

[0099] In the tank 118, the plasma reactive species have already passed from the gas to the liquid and reacted with water contaminants. The reactor water tank 118 contains residual gases (e.g. O2, N2, O3) in which liquid droplets are suspended. These gases are passed to the separator 124 where any remaining liquid droplets are separated and returned to the tank 118.

[0100] Optionally, the valve 152 allows the introduction of supplementary gases, such as hydrogen peroxide or ozone, to further increase system performance.

[0101] It will be noted that in the specific example described above, it is oriented with the plasma outlets above the opening in the venturi in use, and the chamber extending belowthe opening in the venturi. This allows any liquid that escapes the venturi to be collected in the chamber lower section under gravity without contacting the plasma generators.

[0102] It will be noted that the valve 154 can be used to drain off liquid such as water that has accumulated in the chamber. The valve 152 is used to re-establish atmospheric pressure in the chamber when the system is shut down.Description of the second embodiment

[0103] Referring to Figures 14 to 15, there is shown a second reactor assembly 1122 according to the present invention.

[0104] The second reactor assembly 1122 comprises an inlet conduit 1126, a suction chamber 1128, a venturi (not shown), an outlet conduit 1132, a static mixer 1134 and a plurality of eight plasma jet generators 136 (as described above). The reactor assembly has a primary axis RA.

[0105] The inlet conduit 1126 is connected to a liquid supply and is configured to pass liquid in a flow direction F, along a flow axis RA, through the venturi and to the outlet conduit 1132. The inlet conduit 1126 and outlet conduit 1132 connecttothe venturi within the suction chamber 1128 in the same way as the first embodiment. The configuration and operation of the reactor 1122 is almost identical to that of the reactor 122.

[0106] The suction chamber 1128 is a two-part cylindrical structure having a first part 1138 and a second part 1140 held together by a connecting and sealing collar 1142. The first part 1138 defines a first (circular) end wall 1144 and a (cylindrical) outer wall 1146. The end wall 1146 bounds the upstream end of the chamber 1128, and the outer wall 1146 the upstream periphery. Aside from the fluid inlets and outlets described herein, the chamber 1128 is gas-tight to enable the pressure within to be controlled.

[0107] The first part 1138 has a plurality of generator ports 1139, four of which are defined in the end wall 1144 and four of which are defined in the outer wall 1146. Plasma generators 136 are shown engaged with each port 1139 in this embodiment, but it will be noted that the ports may optionally not be used, and the ports plugged. It will also be noted that ports may provide differing generator injection angles- for example the ports defined in the endwall 1146 may be at a shallower angle with respect to RA than the ports defined in the sidewall 1144.Variations

[0108] Although the above embodiment describes an annular DBD ejector, other types of plasma generator could be used, such as pin or wire to ground.

[0109] A stainless steel M6 HV electrode is described above. Other forms of electrode could be used, for example a copper material, or M4 thread.

[0110] Although four electrodes are described in the above embodiment, the invention is not so limited. Due to the inclination angle and the position along the body of chamber 128 of the plasma generators to the treated fluid flow, many such electrodes can be installed.

[0111] The present invention also facilitates a flexible system- the various ports provided through which the plasma generators enter the suction chamber (and access the venturi) can be plugged when not in use to vary the number of plasma generators used. This allows the number and type of generators to be varied depending on the application.

[0112] Although a single pass reactor is described above, it is within the scope of the present invention for multiple passes to take place- i.e. liquid that has already been exposed to plasma reactive species could be re-treated through the reactor one or more further times.

[0113] The present invention can be used for the treatment of water using reactive species, generation of plasma activated water (PAW) and in a wide range of other industries including, but not limited to, nanotechnology, synthetic chemistry, disinfection, the food industry, and gas cleaning.

[0114] The chamber can be a right circular cylinder (as described) or any other enclosed shape as long as it holds the plasma generators and the venturi system within.

Claims

Claims1. A jet ejector plasma reactor apparatus comprising:a venturi having a nozzle section, a diffuser section, and a throat therebetween, the venturi having a venturi flow direction along a flow axis from the nozzle to the diffuser; a chamber at least partially surrounding the venturi, the chamber having an internal volume in fluid communication with the venturi downstream of the nozzle section to thereby reduce pressure in the internal volume;at least one non-thermal plasma generator comprising a gas inlet and a plasma outlet, the plasma outlet in fluid communication with the internal volume of the chamber.

2. A jet ejector plasma reactor apparatus according to claim 1, wherein the chamber completely surrounds the venturi in a plane normal to the flow axis.

3. A jet ejector plasma reactor apparatus according to claim 1 or 2, wherein the plasma outlet is directed towards the venturi between the nozzle section and the diffuser section.

4. A jet ejector plasma reactor apparatus according to any of claims 1 to 3, wherein the chamber defines at least one plasma generator port in a chamber wall bounding the internal volume, the plasma generator port receiving the plasma generator.

5. A jet ejector plasma reactor apparatus according to claim 4, wherein the chamber wall defines a plurality of plasma generator ports.

6. A jet ejector plasma reactor apparatus according to claim 5, wherein the enclosed chamber comprises a plurality of ports to receive a respective plurality of non-thermal plasma generators, each non-thermal plasma generator being removeable and replaceable with a port plug.

7. A jet ejector plasma reactor apparatus according to any preceding claim, wherein the non-thermal plasma generator is configured to direct a flow of non-thermal plasma along a generator axis having a component parallel to the flow axis.

8. A jet ejector plasma reactor apparatus according to claim 7, wherein the generator axis is at an angle of less than 90 degrees to the flow axis.

9. A jet ejector plasma reactor apparatus according to claim 8, wherein the generator axis is at an angle of less than 45 degrees to the flow axis.

10. Ajet ejector plasma reactor apparatus according to any of claims 7 to 9, wherein the component parallel to the flow axis is in the same direction as the venturi flow.

11. A jet ejector plasma reactor apparatus according to any preceding claim, wherein internal volume in fluid communication with the venturi at the throat.

12. Ajet ejector plasma reactor apparatus according to claim 11 , wherein the generator plasma outlet is directed towards a venturi opening at the throat to thereby direct plasma to a fluid flowing through the venturi.

13. A jet ejector plasma reactor apparatus according to claim 12, wherein the venturi opening is a gap in the venturi separating the venturi into an upstream section and a downstream section.

14. Ajet ejector plasma reactor apparatus according to claim 13, wherein the chamber comprises a first part and a second part, the first and second parts being joined together to form the chamber, wherein the nozzle section is mounted to the first part, and the diffuser section is mounted to the second part.

15. Ajet ejector plasma reactor apparatus according to any of claims 12 to 14, wherein the venturi comprises a further nozzle section downstream of the venturi opening.

16. A jet ejector plasma reactor apparatus according to any preceding claim, comprising a plurality of non-thermal plasma generators, each having a plasma outlet, the plasma outlets directed towards, and in fluid communication with, the venturi.

17. A jet ejector plasma reactor apparatus according to claim 15 or 16, wherein non-thermal plasma generators are circumferentially spaced around the flow axis.

18. Ajet ejector plasma reactor apparatus according to any preceding claim, wherein the at least one non-thermal plasma generator is at least one of:a dielectric barrier discharge type;a corona discharge type;a (i) one of a pin or wire to (ii) one of a plate or liquid type;a microwave type; and,a radio frequency type plasma generator.

19. A jet ejector plasma reactor apparatus according to claim 18, wherein the at least one non-thermal plasma generator comprises a first electrode and a second electrode surrounding the first electrode defining a flow path surrounding the first electrode, for generation of plasma.

20. A jet ejector plasma reactor apparatus according to claim 19, wherein the flow path surrounding the first electrode is annular.21 . A jet ejector plasma reactor apparatus according to claim 19 or 20, wherein the first electrode is a high voltage electrode, and the second electrode is a ground electrode.

22. A jet ejector plasma reactor apparatus according to any of claims 19 to 20, wherein the first electrode comprises a plurality of external protrusions extending into the annular flow path.

23. A jet ejector plasma reactor apparatus according to claim 22, wherein the first electrode comprises an external thread.

24. A jet ejector plasma reactor apparatus according to claim 23, wherein the thread is a standard thread, preferably at least one of an ISO metric thread, unified thread standard thread, American national standard pipe thread, and British standard pipe thread.

25. A jet ejector plasma reactor apparatus according to any of claims 22 to 24, wherein the external thread of the first electrode has a first portion extending into the annular flow path, and a second portion engaged with a female thread for mounting in the non-thermal plasma generator.

26. A jet ejector plasma reactor apparatus according to any preceding claim, comprising a mixer downstream of the venturi.

27. A jet ejector plasma reactor apparatus according to any preceding claim, comprising a treated fluid circuit arranged to pass a treated fluid through the venturi multiple times.

28. A jet ejector plasma reactor apparatus according to any preceding claim, comprising a gas separator for separating liquid and gas in the treated fluid.

29. A jet ejector plasma reactor apparatus according to any preceding claim, wherein the treated fluid is water.

30. A method of generating a plasma treated fluid comprising the steps of:providing a venturi having a nozzle section, a diffuser section, and a throat therebetween;providing a chamber at least partially surrounding the venturi, the chamber having an internal volume in fluid communication with the venturi downstream of the nozzle section;passing a fluid to be treated through the venturi in a venturi flow direction along a flow axis from the nozzle to the diffuser to thereby reduce pressure in the internal volume;directing a flow of non-thermal plasma into the chamber to contact the fluid to be treated in the venturi.

31. A method of generating a plasma treated fluid according to claim 30, using an apparatus according to any of claims 1 to 29.

32. A non-thermal plasma generator comprising:a first electrode; and,a second electrode surrounding the first electrode to define a gap surrounding the first electrode for passage of a gas for plasma generation;wherein the first electrode defines an external thread extending into the gap.

33. A non-thermal plasma generator according to claim 21, wherein the thread is a standard thread.

34. A non-thermal plasma generator according to claim 33, wherein the thread is at least one of and ISO metric threads, unified thread standard thread, American national standard pipe thread, and British standard pipe thread.

35. A non-thermal plasma generator according to any of claims 32 to 34, wherein the gap is annular.

36. A non-thermal plasma generator according to any of claims 32 to 35, comprising a dielectric barrier in the gap, forming a dielectric barrier discharge generator.

37. A non-thermal plasma generator according to any of claims 32 to 36, wherein the external thread of the first electrode has a first portion extending into the gap, and a second portion engaged with a female thread for mounting in the non-thermal plasma generator.

38. A non-thermal plasma generator according to claim 37, comprising a mount defining the female thread, wherein a high voltage connection point is provided on a first side of the mount, and a flow inlet in fluid communication with the annular channel is provided on a second side of the mount.

39. A method of generating a non-thermal plasma comprising the steps of:providing a generator according to any of claims 32 to 38;generating a non-thermal plasma with the generator.

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