Methods and systems of operating a plasma generating vessel at least 4 barg

Abstract

A method of operating a plasma generating vessel, wherein the plasma generating vessel comprises: an internal volume configured to receive fluid from a fluid supply system; a first electrode at least partially within the internal volume and configured for receiving electrical energy from an electrical supply system; and a second electrode arranged capacitively with the first electrode, wherein the vessel is configured to use the first electrode to apply electrical energy to fluid within the internal volume and to capacitively couple the first and second electrodes to generate one or more bubbles of plasma within the fluid in the internal volume; wherein the method comprises operating the plasma generating vessel with a vessel pressure of at least 4 Barg.

Description

[0001] Methods and Systems

[0002] Technical Field

[0003] The present disclosure relates to the field of plasma generating vessels and methods of operating a plasma generating vessel.

[0004] Background

[0005] The Applicant has described features of their plasma generating vessel technology in GB2604853, GB2631978, GB2631979 and GB2631980. The present application relates to refinements of this plasma generating technology based on subsequent experiments performed using that plasma generating technology.

[0006] Summary

[0007] The present inventors have identified that operation of the plasma generating vessel technology mentioned above and described in their earlier applications may be improved when operating with one or more parameters having values in certain ranges. Embodiments of the present disclosure relate to systems and methods which utilise the plasma generating vessel with these identified parameter values. As outlined in more detail below, embodiments of the present disclosure may utilise one or more of the following parameters with values in selected ranges: (i) pressure, (ii) mass flow rate, (iii) electrical conductivity, (iv) pH, and / or (v) salinity. For each one of these parameters, vessel operation may be improved when using a value for that parameter in the ranges mentioned below and as claimed.

[0008] Embodiments of the present disclosure comprise methods and systems in which the parameter(s) in question are within selected value ranges. For this, methods may comprise operating the plasma generating vessel and / or other components of the apparatus such as a fluid supply system so that one or more of the parameter values in question are within their selected range(s). Systems may comprise one or more components configured to operate with said one or more parameter values in their selected range(s). Embodiments may also comprise one or more feedback loops in which parameter value(s) are monitored and controlled accordingly so that they remain within their selected ranges.

[0009] Aspects of the disclosure are set out in the independent claims and optional features are set out in the dependent claims. Aspects of the disclosure may be provided in conjunction with each other, and features of one aspect may be applied to other aspects.

[0010] In an aspect, there is provided a method of operating a plasma generating vessel, wherein the plasma generating vessel comprises: an internal volume configured to receive fluid from a fluid supply system; a first electrode at least partially within the internal volume and configured for receiving electrical energy from an electrical supply system; and a second electrode arrangedcapacitively with the first electrode, wherein the vessel is configured to use the first electrode to apply electrical energy to fluid within the internal volume and to capacitively couple the first and second electrodes to generate one or more bubbles of plasma within the fluid in the internal volume. The method comprises operating the plasma generating vessel with a vessel pressure of at least 4 Barg.

[0011] Embodiments may facilitate stable formation of bubbles in the fluid located around and / or near to the first electrode within the internal volume of the vessel. The present inventors have identified that, at vessel pressures of at least 4 Barg, a two-phase mixture of gas bubbles and liquid may occur in the volume around the first electrode in a stable manner. For instance, at lower vessel pressures it has been identified that any bubble formation may not occur in a stable and reliable manner, and so e.g. by retaining the vessel pressure at at least 4 Barg, bubble formation may occur with improved reliability and utility. In turn, the presence of such bubbles in this region may further facilitate the generation of bubbles of plasma within the fluid, as well as subsequent conditions to access desired exothermic chemical processes for increasing the thermal energy output and / or efficiency for the vessel.

[0012] The method may comprise operating the plasma generating vessel with a vessel pressure between 4 Barg and 200 Barg. Preferably, the method may comprise operating the plasma generating vessel with a vessel pressure between 4 Barg and 20 Barg. Further preferably, the vessel may be operated at a vessel pressure of between 4 Barg and 15 Barg. For example, the vessel may be operated with a vessel pressure of at least 4 Barg, and within a threshold range of 4 Barg (e.g. not significantly greater than 4 Barg), such as between 4 and 14 Barg, e.g. between 4 and 12 Barg, e.g. between 4 and 10 Barg, e.g. between 4 and 8 Barg, e.g. between 4 and 6 Barg, e.g. between 4 and 5 Barg. The method may comprise controlling operation of said electrical supply system to control the application of a voltage to the first electrode, thereby to apply electrical the energy to the fluid in the internal volume and capacitively couple the first and second electrodes to generate the bubbles of plasma within the fluid in the internal volume. The method may comprise controlling operation of said fluid supply system to control the supply of fluid to the internal volume in which bubbles of plasma are to be generated. The vessel may comprise: (i) a fluid inlet for receiving a fluid in which bubbles of plasma are to be generated, and (ii) a fluid outlet for outputting heated fluid from the vessel. The method may comprise controlling at least one of an inlet fluid pressure and an outlet fluid pressure. The method may comprise controlling at least one of the inlet fluid pressure and the outlet fluid pressure thereby to operate the plasma generating vessel with a vessel pressure of at least 4 Barg, e.g. to operate the plasma generating vessel with a vessel pressure of between 4 and 200 Barg, such as between 4 and 20 Barg. The method may comprise using a pressure regulating apparatus coupled to the outlet of the plasma generating vessel to control the outlet fluid pressure, e.g. to control the outlet fluid pressure thereby to operate the plasma generating vessel with a vessel pressure of at least 4 Barg (e.g. of between 4 and 200 Barg, such as between 4 and 20 Barg). The pressure regulating apparatusmay be set to a selected pressure regulation value of at least 4 Barg thereby to operate the plasma generating vessel with a vessel pressure of at least 4 Barg (e.g. to a vessel pressure of between 4 and 200 Barg, such as between 4 and 20 Barg). The pressure regulating apparatus may comprise a pressure regulator configured to regulate the vessel pressure. The pressure regulator may be located downstream of the fluid outlet. The pressure regulator may be configured to regulate its upstream fluid pressure thereby to regulate the vessel pressure. The pressure regulator may comprise a back pressure regulator and / or a steam engine (e.g. with a pressure regulator and governor). The method may comprise using a pump coupled to the inlet of the plasma generating vessel to control the inlet fluid pressure. The method may comprise using the pump to control the inlet fluid pressure thereby to operate the plasma generating vessel with a vessel pressure of at least 4 Barg (e.g. between 4 and 200 Barg, such as between 4 and 20 Barg). The method may comprise obtaining an indication of vessel pressure and controlling operation based on the obtained indication thereby to operate the plasma generating vessel with a vessel pressure of at least 4 Barg (e.g. between 4 and 200 Barg, such as between 4 and 20 Barg). For example, the method may comprise increasing at least one of: the amount of electrical energy applied to the first electrode, the selected pressure value for the pressure regulating apparatus and / or operation of a pump of the fluid supply system, to increase pressure (and vice-versa). The method may comprise supplying the plasma generating vessel with fluid at a mass flow rate of at least 2 grams per second, such as at least 3 grams per second, preferably with a mass flow rate of between 2 (e.g. 3) and 20 grams per second, more preferably with a mass flow rate of between 4 and 15 grams per second. The method may comprise supply the plasma generating vessel with fluid having an electrical conductivity of no more than 5500 micro-Siemens per centimetre, preferably with an electrical conductivity of between 1.3 and 5500 micro-Siemens per centimetre, more preferably with an electrical conductivity of between 50 and 5500 micro-Siemens per centimetre. The method may comprise supplying the plasma generating vessel with fluid having a pH of between 5.8 and 7.6, preferably with a pH of between 6.3 and 7.1. The method may comprise supplying the plasma generating vessel with fluid having a salinity of between 50 parts per million and 100 parts per thousand.

[0013] In an aspect, there is provided a plasma generating vessel comprising: an internal volume arranged to receive fluid from a fluid supply system; a first electrode at least partially within the internal volume and arranged for receiving electrical energy from an electrical supply system; and a second electrode arranged capacitively with the first electrode. The plasma generating vessel is configured to use the first electrode to apply electrical energy to fluid within the internal volume and to capacitively couple the first and second electrodes to generate one or more bubbles of plasma within the fluid in the internal volume, the plasma generating vessel is configured to operate with a vessel pressure of at least 4 Barg.

[0014] The plasma generating vessel may be configured to operate with a vessel pressure of between 4 and 200 Barg, such as between 4 and 20 Barg. The vessel may comprise a pressure regulatingapparatus coupled to a fluid outlet from the plasma generating vessel, wherein the pressure regulating apparatus is configured to regulate the vessel pressure to be at least 4 Barg (e.g. to between 4 and 200 Barg, such as between 4 and 20 Barg). The pressure regulating apparatus may be set to a selected pressure regulation value of at least 4 Barg (e.g. to between 4 and 200 Barg, such as between 4 and 20 Barg). The vessel may comprise a pump could to a fluid inlet to the plasma generating vessel. The pump may be configured to pump fluid to the plasma generating vessel to regulate the vessel pressure to be at least 4 Barg (e.g. to between 4 and 200 Barg, such as between 4 and 20 Barg). The vessel may comprise one or more further electrodes (e.g. a ‘third electrode’). The third electrode may be at least partially within the internal volume and spaced apart from the first and second electrodes. The first electrode may be arranged to provide a conductive path for current to be applied to fluid in the internal volume. The second electrode may be arranged to provide a conductive path for carrying current away from the internal volume. The third electrode may be arranged away from a conductive path from the first electrode to the second electrode. The vessel may comprise a plurality of third electrodes, e.g. the third electrode may be provided by a plurality (e.g. a family) of electrodes. The vessel may comprise a resistive element provided in the internal volume between the first electrode and the second electrode to increase the electrical resistance of the conductive path therebetween. The vessel may comprise a controller configured to obtain an indication of vessel pressure and to control operation based on the obtained indication to operate the plasma generating vessel with a vessel pressure of at least 4 Barg (e.g. to between 4 and 200 Barg, such as between 4 and 20 Barg). The controller is configured to increase the amount of electrical energy applied to the first electrode and / or the amount or fluid supplied to the vessel in the event that the obtained indication of vessel pressure is below a lower threshold value. The plasma generating vessel may be configured to be supplied fluid (e.g. the fluid supply system may be configured to supply fluid to the plasma generating vessel) with a mass flow rate of at least 2 grams per second, such as at least 3 grams per second, preferably with a mass flow rate of between 2 (e.g. 3) and 20 grams per second, more preferably with a mass flow rate of between 4 and 15 grams per second. The plasma generating vessel may be configured to receive fluid (e.g. the fluid supply system may be configured to supply fluid to the plasma generating vessel) having an electrical conductivity of no more than 5500 micro-Siemens per centimetre, preferably with an electrical conductivity of between 1.3 and 5500 micro-Siemens per centimetre, more preferably with an electrical conductivity of between 50 and 5500 micro-Siemens per centimetre.. The plasma generating vessel may be configured to receive fluid (e.g. the fluid supply system may be configured to supply fluid to the plasma generating vessel) with fluid having a pH of between 5.8 and 7.6, more preferably with a pH of between 6.3 and 7.1. The plasma generating vessel may be configured to receive fluid (e.g. the fluid supply system may be configured to supply fluid to the plasma generating vessel) having a salinity of between 50 parts per million and 100 parts per thousand.In an aspect, there is provided a method of operating a plasma generating vessel, wherein the plasma generating vessel comprises: an internal volume configured to receive fluid from a fluid supply system; a first electrode at least partially within the internal volume and configured for receiving electrical energy from an electrical supply system; and a second electrode arranged capacitively with the first electrode, wherein the vessel is configured to use the first electrode to apply electrical energy to fluid within the internal volume and to capacitively couple the first and second electrodes to generate one or more bubbles of plasma within the fluid in the internal volume. The method comprises supplying the plasma generating vessel with fluid at a mass flow rate of at least 2 grams per second, such as at least 3 grams per second.

[0015] Embodiments may facilitate operation of the plasma generating vessel with a greater amount and / or greater efficiency for the thermal energy output by the vessel. For example, by supplying the plasma generating vessel with at least 2 (e.g. at least 3) grams per second of fluid, the thermal energy output for the vessel, and the coefficient of performance for that vessel, may be substantially elevated as compared to operating at lower flow rates.

[0016] The method may comprise supplying the plasma generating vessel with fluid at a mass flow rate of between 2 (e.g. 3) and 20 grams per second, such as with fluid at a mass flow rate of between 2 and 14 grams per second, e.g. between 4 and 13 grams per second. For example, the vessel may be supplied with fluid at a mass flow rate of at least 4 grams per second. Preferably, the vessel may be supplied with fluid at a mass flow rate of between 4 and 20 grams per second, more preferably at a mass flow rate of between 5 and 15 grams per second, even preferably at a mass flow rate of between 7 and 13 grams per second. The method may comprise controlling operation of said electrical supply system to control the application of a voltage to the first electrode, thereby to apply electrical the energy to the fluid in the internal volume and capacitively couple the first and second electrodes to generate the bubbles of plasma within the fluid in the internal volume. The method may comprise controlling operation of said fluid supply system to control the supply of fluid to the internal volume in which bubbles of plasma are to be generated. The method may comprise controlling operation of the fluid supply system to control the supply of fluid to the internal volume of the plasma generating vessel to be at a mass flow rate of at least 2 grams per second, such as at least 3 grams per second (e.g. of between 2 (e.g. 3) and 20 grams per second, such as between 4 and 15 grams per second). The fluid supply system may be coupled to a fluid inlet to the internal volume of the plasma generating vessel, and the method may comprise controlling operation of the fluid supply system to supply fluid through the fluid inlet at a mass flow rate of at least 2, e.g. at least 3, grams per second (e.g. of between 2 (e.g. 3) and 20 grams per second, such as between 4 and 15 grams per second). The method may comprise controlling operation of the fluid supply system to supply fluid to the internal volume of the plasma generating vessel to provide a vessel pressure of at least 4 Barg, such as to provide a vessel pressure of between 4 and 200 Barg. The method may comprise obtaining an indication of mass flow rate of fluid supplied to the vessel and controlling operation based on the obtained indicationthereby to supply the vessel with fluid at a mass flow rate of at least 2, e.g. at least 3, grams per second (e.g. of between 2 (e.g. 3) and 20 grams per second, such as between 4 and 15 grams per second). Controlling operation based on said obtained indication comprises controlling operation of the fluid supply system, e.g. controlling operation of one or more pumps thereof, thereby to supply the vessel with fluid at a mass flow rate of at least 2 (e.g. at least 3) grams per second (e.g. of between 2 (e.g. 3) and 20 grams per second, such as between 4 and 15 grams per second). The method may comprise operating the plasma generating vessel with a vessel pressure of at least 4 Barg, preferably with a vessel pressure of between 4 and 200 Barg, and more preferably with a vessel pressure of between 4 and 20 Barg. The method may comprise supplying the plasma generating vessel with fluid having an electrical conductivity of no more than 5500 micro-Siemens per centimetre, preferably with an electrical conductivity of between 1.3 and 5500 micro-Siemens per centimetre, more preferably with an electrical conductivity of between 50 and 5500 micro-Siemens per centimetre.. The method may comprise supplying the plasma generating vessel with fluid having a pH of between 5.8 and 7.6, preferably with a pH of between 6.3 and 7.1. The method may comprise supplying the plasma generating vessel with fluid having a salinity of between 50 parts per million and 100 parts per thousand.

[0017] In an aspect, there is provided a plasma generating vessel comprising: an internal volume arranged to receive fluid from a fluid supply system; a first electrode at least partially within the internal volume and arranged for receiving electrical energy from an electrical supply system; and a second electrode arranged capacitively with the first electrode. The plasma generating vessel is configured to use the first electrode to apply electrical energy to fluid within the internal volume and to capacitively couple the first and second electrodes to generate one or more bubbles of plasma within the fluid in the internal volume. The plasma generating vessel is configured to receive fluid at a mass flow rate of at least 2 grams per second, such as at least 3 grams per second.

[0018] The plasma generating vessel may be configured to receive fluid at a mass flow rate of between 2 (e.g. 3) and 20 grams per second. The vessel may comprise one or more further electrodes (e.g. a ‘third electrode’), wherein the third electrode may be at least partially within the internal volume and spaced apart from the first and second electrodes. The first electrode may be arranged to provide a conductive path for current to be applied to fluid in the internal volume. The second electrode may be arranged to provide a conductive path for carrying current away from the internal volume. The third electrode may be arranged away from a conductive path from the first electrode to the second electrode. The vessel may comprise a plurality of third electrodes, e.g. the third electrode may be provided by a plurality (e.g. a family) of electrodes. The vessel may comprise a resistive element provided in the internal volume between the first electrode and the second electrode to increase the electrical resistance of the conductive path therebetween. In an aspect, there is provided an apparatus comprising: the plasma generating vessel disclosed herein; and a fluid supply system configured to supply fluid to the internal volume of the plasmagenerating vessel at a mass flow rate of at least 2 (e.g. at least 3) grams per second (e.g. of between 2 (e.g. 3) and 20 grams per second, such as between 4 and 15 grams per second). The apparatus may comprise a controller configured to obtain an indication of a mass flow rate of fluid being supplied to the vessel and to control operation of the fluid supply system based on the obtained indication. Controlling operation based on the obtained indication comprises controlling operation of the fluid supply system, e.g. one or more pumps thereof, to increase the mass flow rate of fluid supplied to the plasma generating vessel in the event that the obtained indication of mass flow rate is below a lower threshold value. For example, the lower threshold value may be 2 grams per second (e.g. 3 grams per second) or a value selected to cause the fluid supply to be at a mass flow rate of at least 2 (e.g. at least 3) grams per second. The fluid supply system may be configured to supply fluid to the internal volume to provide a vessel pressure of at least 4 Barg. The plasma generating vessel may be configured to operate with a vessel pressure of at least 4 Barg, preferably with a vessel pressure of between 4 and 200 Barg, and more preferably with a vessel pressure of between 4 and 20 Barg. The plasma generating vessel may be configured to receive fluid (e.g. the fluid supply system may be configured to supply fluid to the plasma generating vessel) having an electrical conductivity of no more than 5500 micro-Siemens per centimetre, preferably with an electrical conductivity of between 1.3 and 5500 micro-Siemens per centimetre, more preferably with an electrical conductivity of between 50 and 5500 micro-Siemens per centimetre.. The plasma generating vessel may be configured to receive fluid (e.g. the fluid supply system may be configured to supply fluid to the plasma generating vessel) with fluid having a pH of between 5.8 and 7.6, preferably with a pH of between 6.3 and 7.1. The plasma generating vessel may be configured to receive fluid (e.g. the fluid supply system may be configured to supply fluid to the plasma generating vessel) having a salinity of between 50 parts per million and 100 parts per thousand.

[0019] In an aspect, there is provided a method of operating a plasma generating vessel, wherein the plasma generating vessel comprises: an internal volume configured to receive fluid from a fluid supply system; a first electrode at least partially within the internal volume and configured for receiving electrical energy from an electrical supply system; and a second electrode arranged capacitively with the first electrode, wherein the vessel is configured to use the first electrode to apply electrical energy to fluid within the internal volume and to capacitively couple the first and second electrodes to generate one or more bubbles of plasma within the fluid in the internal volume. The method comprises supplying the plasma generating vessel with fluid having an electrical conductivity of no more than 5500 micro-Siemens per centimetre.

[0020] Embodiments may facilitate an increased amount and / or efficiency of thermal generation for operation of the vessel. In particular, the present inventors have identified that such conditions may facilitate application of electrical energy to the first electrode thereby to initiate exothermic chemical processes within the fluid in the vessel. For example, at higher electrical conductivities,apparatuses may less reliably be able to generate electrical stresses for initiating such processes without running an elevated risk of electrical arcing occurring within the vessel. The method may comprise supplying the plasma generating vessel with fluid having an electrical conductivity of between 1.3 and 5500 micro-Siemens per centimetre, more preferably with an electrical conductivity of between 0.3 and 0.5 milli-Siemens per centimetre. Preferably, the electrical conductivity may be between 50 and 5500 micro-Siemens per centimetre. The method may comprise controlling operation of said electrical supply system to control the application of a voltage to the first electrode, thereby to apply electrical the energy to the fluid in the internal volume and capacitively couple the first and second electrodes to generate the bubbles of plasma within the fluid in the internal volume. The method may comprise controlling operation of said fluid supply system to control the supply of fluid to the internal volume in which bubbles of plasma are to be generated. The method may comprise controlling operation of the fluid supply system to control the supply of fluid to the internal volume of the plasma generating vessel to have an electrical conductivity of no more than 5500 micro-Siemens per centimetre. The method may comprise controlling operation of the fluid supply system to control the supply of fluid to the internal volume of the plasma generating vessel to have an electrical conductivity of at least 1.3 micro-Siemens per centimetre, e.g. of at least 50. The method may comprise controlling operation of the fluid supply system to adjust the electrical conductivity of fluid to be supplied to the plasma generating vessel. For example, one or more reference substances may be supplied to the vessel, where those substances have a known electrical conductivity and / or one or more substances may be added to the fluid supply to adjust (e.g. decrease or increase) the electrical conductivity accordingly. Adjusting the electrical conductivity of fluid may comprise adding one or more substances to the fluid to alter the electrical conductivity of said fluid. The method may comprise adding one or more minerals, optionally soluble minerals, to increase the electrical conductivity of said fluid. The method may comprise diluting the fluid with additional liquid to decrease the electrical conductivity of said fluid. The additional liquid may be provided from a separate storage region for said liquid and / or said additional liquid may comprise liquid which has already passed through the vessel. The method may comprise obtaining an indication of the electrical conductivity of fluid to be supplied to the plasma generating vessel and controlling operation of the fluid supply system based on said obtained indication thereby to provide fluid to the plasma generating vessel having an electrical conductivity of no more than 5500 micro-Siemens per centimetre (e.g. of between 1.3 and 5500 micro-Siemens per centimetre, e.g. between 50 and 5500). Controlling operation of the fluid supply system may comprise operating the fluid supply system to alter the electrical conductivity of said fluid in the event that the obtained indication of electrical conductivity is outside a selected range, e.g. to increase if the obtain indication is too low and vice-versa. The method may comprise operating the plasma generating vessel with a vessel pressure of at least 4 Barg, preferably with a vessel pressure of between 4 and 200 Barg, and more preferably with a vessel pressure of between 4 and 20 Barg. The method may comprise supplying fluid to theplasma generating vessel with a mass flow rate of at least 2 (e.g. at least 3) grams per second, preferably with a mass flow rate of between 2 (e.g. 3) and 20 grams per second, more preferably with a mass flow rate of between 4 and 15 grams per second. The method may comprise supplying the plasma generating vessel with fluid having a pH of between 5.8 and 7.6, preferably with a pH of between 6.3 and 7.1. The method may comprise supplying the plasma generating vessel with fluid having a salinity of between 50 parts per million and 100 parts per thousand. In an aspect, there is provided a plasma generating vessel comprising: an internal volume arranged to receive fluid from a fluid supply system; a first electrode at least partially within the internal volume and arranged for receiving electrical energy from an electrical supply system; and a second electrode arranged capacitively with the first electrode. The plasma generating vessel is configured to use the first electrode to apply electrical energy to fluid within the internal volume and to capacitively couple the first and second electrodes to generate one or more bubbles of plasma within the fluid in the internal volume. The plasma generating vessel is configured to receive fluid having an electrical conductivity of no more than 5500 micro-Siemens per centimetre. The plasma generating vessel may be configured to receive fluid having an electrical conductivity of between 1.3 and 5500 micro-Siemens per centimetre. The plasma generating vessel may comprise one or more further electrodes (e.g. a ‘third electrode’). The third electrode may be at least partially within the internal volume and spaced apart from the first and second electrodes. The first electrode may be arranged to provide a conductive path for current to be applied to fluid in the internal volume. The second electrode may be arranged to provide a conductive path for carrying current away from the internal volume. The third electrode may be arranged away from a conductive path from the first electrode to the second electrode. The vessel may comprise a plurality of third electrodes, e.g. the third electrode may be provided by a plurality (e.g. a family) of electrodes. The vessel may comprise a resistive element provided in the internal volume between the first electrode and the second electrode to increase the electrical resistance of the conductive path therebetween. In an aspect, there is provided an apparatus comprising: the plasma generating vessel disclosed herein; and a fluid supply system configured to supply fluid to the internal volume of the plasma generating vessel having an electrical conductivity of no more than 5500 micro-Siemens per centimetre (e.g. of between 1.3 and 5500 micro-Siemens per centimetre). The fluid supply system may be configured to adjust an electrical conductivity of the fluid to be supplied to the plasma generating vessel. The apparatus may comprise a controller configured to obtain an indication of an electrical conductivity of the fluid to be supplied to the plasma generating vessel and to control operation of the fluid supply system so as to supply fluid to the plasma generating vessel having an electrical conductivity of having an electrical conductivity of no more than 5500 micro-Siemens per centimetre (e.g. between 1.3 and 5500 micro-Siemens per centimetre). The plasma generating vessel may be configured to operate with a vessel pressure of at least 4 Barg, preferably with a vessel pressure of between 4 and 200 Barg, and more preferably with a vessel pressure of between 4 and 20 Barg. The plasma generatingvessel may be configured to be supplied fluid (e.g. the fluid supply system may be configured to supply fluid to the plasma generating vessel) with a mass flow rate of at least 2 (e.g. at least 3) grams per second, preferably with a mass flow rate of between 2 (e.g. 3) and 20 grams per second, more preferably with a mass flow rate of between 4 and 15 grams per second. The plasma generating vessel may be configured to receive fluid (e.g. the fluid supply system may be configured to supply fluid to the plasma generating vessel) with fluid having a pH of between 5.8 and 7.6, preferably with a pH of between 6.3 and 7.1. The plasma generating vessel may be configured to receive fluid (e.g. the fluid supply system may be configured to supply fluid to the plasma generating vessel) having a salinity of between 50 parts per million and 100 parts per thousand.

[0021] In an aspect, there is provided a method of operating a plasma generating vessel, wherein the plasma generating vessel comprises: an internal volume configured to receive fluid from a fluid supply system; a first electrode at least partially within the internal volume and configured for receiving electrical energy from an electrical supply system; and a second electrode arranged capacitively with the first electrode, wherein the vessel is configured to use the first electrode to apply electrical energy to fluid within the internal volume and to capacitively couple the first and second electrodes to generate one or more bubbles of plasma within the fluid in the internal volume. The method comprises supplying the plasma generating vessel with fluid having a pH of between 5.8 and 7.6.

[0022] Embodiments may enable the vessel to provide a greater amount and / or greater efficiency of the thermal energy output. For instance, at pH values outside this range, the desired exothermic chemical processes may occur in lower quantities and / or they may be harder to initiate and / or sustain.

[0023] The method may comprise supplying the plasma generating vessel with fluid having a pH of between 6.3 and 7.1. The method may comprise controlling operation of said electrical supply system to control the application of a voltage to the first electrode, thereby to apply electrical the energy to the fluid in the internal volume and capacitively couple the first and second electrodes to generate the bubbles of plasma within the fluid in the internal volume. The method may comprise controlling operation of said fluid supply system to control the supply of fluid to the internal volume in which bubbles of plasma are to be generated. The method may comprise controlling operation of the fluid supply system to control the supply of fluid to the internal volume of the plasma generating vessel to have a pH of between 5.8 and 7.6, e.g. to have a pH of between 6.3 and 7.1. The method may comprise controlling operation of the fluid supply system to adjust the pH of fluid to be supplied to the plasma generating vessel. The fluid supply system may be configured to supply a reference fluid, e.g. with a known pH in the selected range, or the fluid supply system may be configured to adjust the pH of a supplied liquid to be in the selected range. Adjusting the pH of fluid may comprise adding one or more substances to the fluid to alter the pHof said fluid. The method may comprise adding one or more minerals, optionally soluble minerals, to increase the pH of said fluid. The method may comprise diluting the fluid with additional liquid or adding an acidic substance to decrease the pH of said fluid. Adding an acidic substance may comprise bubbling carbon dioxide through the fluid to decrease the pH of said fluid. The method may comprise obtaining an indication of the pH of fluid to be supplied to the plasma generating vessel and controlling operation of the fluid supply system based on said obtained indication thereby to provide fluid to the plasma generating vessel having a pH of between 5.8 and 7.6, e.g. between 6.3 and 7.1. Controlling operation of the fluid supply system may comprise operating the fluid supply system to alter the pH of said fluid in the event that the obtained indication of pH is outside a selected range, e.g. thereby to retain the pH of the fluid between 5.8 and 7.6 (or between 6.3 and 7.1). The method may comprise operating the plasma generating vessel with a vessel pressure of at least 4 Barg, preferably with a vessel pressure of between 4 and 200 Barg, and more preferably with a vessel pressure of between 4 and 20 Barg. The method may comprise supplying the plasma generating vessel with fluid at a mass flow rate of at least 2, e.g. at least 3, grams per second, preferably with a mass flow rate of between 2 (e.g. 3) and 20 grams per second, more preferably with a mass flow rate of between 4 and 15 grams per second. The method may comprise supplying the plasma generating vessel with fluid having an electrical conductivity of no more than 5500 micro-Siemens per centimetre, preferably with an electrical conductivity of between 1.3 and 5500 micro-Siemens per centimetre, more preferably with an electrical conductivity of between 50 and 5500 micro-Siemens per centimetre. The method may comprise supplying the plasma generating vessel with fluid having a salinity of between 50 parts per million and 100 parts per thousand.

[0024] In an aspect, there is provided a plasma generating vessel comprising: an internal volume arranged to receive fluid from a fluid supply system; a first electrode at least partially within the internal volume and arranged for receiving electrical energy from an electrical supply system; and a second electrode arranged capacitively with the first electrode. The plasma generating vessel is configured to use the first electrode to apply electrical energy to fluid within the internal volume and to capacitively couple the first and second electrodes to generate one or more bubbles of plasma within the fluid in the internal volume. The plasma generating vessel is configured to receive fluid having a pH of between 5.8 and 7.6.

[0025] The apparatus may comprise one or more further electrodes (e.g. ‘a third electrode’). The third electrode may be at least partially within the internal volume and spaced apart from the first and second electrodes. The first electrode may be arranged to provide a conductive path for current to be applied to fluid in the internal volume. The second electrode may be arranged to provide a conductive path for carrying current away from the internal volume. The third electrode may be arranged away from a conductive path from the first electrode to the second electrode. The vessel may comprise a resistive element provided in the internal volume between the first electrode and the second electrode to increase the electrical resistance of the conductive path therebetween.The vessel may comprise a plurality of third electrodes, e.g. the third electrode may be provided by a plurality (e.g. a family) of electrodes. In an aspect, there is provided an apparatus comprising: the plasma generating vessel disclosed herein; and a fluid supply system configured to supply fluid to the internal volume of the plasma generating vessel having a pH of between 5.8 and 7.6, e.g. with a pH of between 6.3 and 7.1. The fluid supply system may be configured to adjust a pH of the fluid to be supplied to the plasma generating vessel. The apparatus may comprise a controller configured to obtain an indication of a pH of the fluid to be supplied to the plasma generating vessel and to control operation of the fluid supply system so as to supply fluid to the plasma generating vessel having a pH of between 5.8 and 7.6, e.g. between 6.3 and 7.1. The fluid supply system may be configured to add one or more substances to the fluid to adjust the pH thereof. The fluid supply system may be configured to add one or more minerals to the fluid to raise the pH thereof and / or to add one or more acidic substances to the fluid to lower the pH thereof, e.g. wherein adding one or more acidic substances comprises bubbling carbon dioxide through the fluid. The plasma generating vessel may be configured to operate with a vessel pressure of at least 4 Barg, preferably with a vessel pressure of between 4 and 200 Barg, and more preferably with a vessel pressure of between 4 and 20 Barg. The plasma generating vessel may be configured to be supplied fluid (e.g. the fluid supply system may be configured to supply fluid to the plasma generating vessel) with a mass flow rate of at least 2 (e.g. at least 3) grams per second, preferably with a mass flow rate of between 2 (e.g. 3) and 20 grams per second, more preferably with a mass flow rate of between 4 and 15 grams per second. The plasma generating vessel may be configured to receive fluid (e.g. the fluid supply system may be configured to supply fluid to the plasma generating vessel) having an electrical conductivity of no more than 5500 micro-Siemens per centimetre, preferably with an electrical conductivity of between 1.3 and 5500 micro-Siemens per centimetre, more preferably with an electrical conductivity of between 50 and 5500 micro-Siemens per centimetre. The plasma generating vessel may be configured to receive fluid (e.g. the fluid supply system may be configured to supply fluid to the plasma generating vessel) having a salinity of between 50 parts per million and 100 parts per thousand.

[0026] In an aspect, there is provided a method of operating a plasma generating vessel, wherein the plasma generating vessel comprises: an internal volume configured to receive fluid from a fluid supply system; a first electrode at least partially within the internal volume and configured for receiving electrical energy from an electrical supply system; and a second electrode arranged capacitively with the first electrode, wherein the vessel is configured to use the first electrode to apply electrical energy to fluid within the internal volume and to capacitively couple the first and second electrodes to generate one or more bubbles of plasma within the fluid in the internal volume. The method comprises supplying the plasma generating vessel with fluid having a salinity of between 50 parts per million and 100 parts per thousand.Embodiments may enable the vessel to provide a greater amount and / or greater efficiency of the thermal energy output. For instance, at salinity values outside this range, the desired exothermic chemical processes may occur in lower quantities and / or they may be harder to initiate and / or sustain.

[0027] The method comprises controlling operation of said electrical supply system to control the application of a voltage to the first electrode, thereby to apply electrical the energy to the fluid in the internal volume and capacitively couple the first and second electrodes to generate the bubbles of plasma within the fluid in the internal volume. The method may comprise controlling operation of said fluid supply system to control the supply of fluid to the internal volume in which bubbles of plasma are to be generated. The method may comprise controlling operation of the fluid supply system to control the supply of fluid to the internal volume of the plasma generating vessel to have a salinity of between 50 parts per million and 100 parts per thousand. The method may comprise controlling operation of the fluid supply system to adjust the salinity of fluid to be supplied to the plasma generating vessel. / Adjusting the salinity of the fluid may comprise adding one or more substances to the fluid to alter the salinity of said fluid. The method may comprise adding salt to increase the salinity of said fluid. Adding salt may comprise adding a saline solution to said fluid to be supplied to the plasma generating vessel. The method may comprise diluting the fluid with additional liquid to decrease the salinity of said fluid. The fluid may be diluted at least partially with fluid which has already passed through the plasma generating vessel. The method may comprise obtaining an indication of the salinity of fluid to be supplied to the plasma generating vessel and controlling operation of the fluid supply system based on said obtained indication thereby to provide fluid to the plasma generating vessel having a salinity of between 50 parts per million and 100 parts per thousand. Controlling operation of the fluid supply system may comprise operating the fluid supply system to alter the salinity of said fluid in the event that the obtained indication of salinity is outside a selected range. The method may comprise operating the plasma generating vessel with a vessel pressure of at least 4 Barg, preferably with a vessel pressure of between 4 and 200 Barg, and more preferably with a vessel pressure of between 4 and 20 Barg. The method may comprise supplying the plasma generating vessel with fluid at a mass flow rate of at least 2 (e.g. at least 3) grams per second, preferably with a mass flow rate of between 2 (e.g.

[0028] 3) and 20 grams per second, more preferably with a mass flow rate of between 4 and 15 grams per second. The method may comprise supplying the plasma generating vessel with fluid having an electrical conductivity of no more than 5500 micro-Siemens per centimetre, preferably with an electrical conductivity of between 1.3 and 5500 micro-Siemens per centimetre, more preferably with an electrical conductivity of between 50 and 5500 micro-Siemens per centimetre. The method may comprise supplying the plasma generating vessel with fluid having a pH of between 5.8 and 7.6, more preferably with a pH of between 6.3 and 7.1.

[0029] In an aspect, there is provided a plasma generating vessel comprising: an internal volume arranged to receive fluid from a fluid supply system; a first electrode at least partially within theinternal volume and arranged for receiving electrical energy from an electrical supply system; and a second electrode arranged capacitively with the first electrode. The plasma generating vessel is configured to use the first electrode to apply electrical energy to fluid within the internal volume and to capacitively couple the first and second electrodes to generate one or more bubbles of plasma within the fluid in the internal volume. The plasma generating vessel is configured to receive fluid having a salinity of between 50 parts per million and 100 parts per thousand.

[0030] The vessel may comprise one or more further electrodes (e.g. a ‘third electrode’). The third electrode may be at least partially within the internal volume and spaced apart from the first and second electrodes. The first electrode may be arranged to provide a conductive path for current to be applied to fluid in the internal volume. The second electrode may be arranged to provide a conductive path for carrying current away from the internal volume. The third electrode may be arranged away from a conductive path from the first electrode to the second electrode. The vessel may comprise a plurality of third electrodes, e.g. the third electrode may be provided by a plurality (e.g. a family) of electrodes. The vessel may comprise a resistive element provided in the internal volume between the first electrode and the second electrode to increase the electrical resistance of the conductive path therebetween. In an aspect, there is provided an apparatus comprising: the plasma generating vessel disclosed herein; and a fluid supply system configured to supply fluid to the internal volume of the plasma generating vessel having a salinity of between 50 parts per million and 100 parts per thousand. The fluid supply system may be configured to adjust a salinity of the fluid to be supplied to the plasma generating vessel. The apparatus may comprise a controller configured to obtain an indication of a salinity of the fluid to be supplied to the plasma generating vessel and to control operation of the fluid supply system so as to supply fluid to the plasma generating vessel having a salinity of between 50 parts per million and 100 parts per thousand. The fluid supply system may be configured to add one or more substances to the fluid to adjust the salinity thereof. The fluid supply system may be configured to add salt to the fluid to raise the salinity thereof and / or to add one or more diluting liquids to the fluid to lower the salinity thereof, optionally wherein adding one or more diluting liquids comprises adding a liquid which has already passed through the plasma generating vessel. The plasma generating vessel may be configured to operate with a vessel pressure of at least 4 Barg, preferably with a vessel pressure of between 4 and 200 Barg, and more preferably with a vessel pressure of between 4 and 20 Barg. The plasma generating vessel may be configured to be supplied fluid (e.g. the fluid supply system may be configured to supply fluid to the plasma generating vessel) with a mass flow rate of at least 2 (e.g. at least 3) grams per second, preferably with a mass flow rate of between 2 (e.g. 3) and 20 grams per second, more preferably with a mass flow rate of between 4 and 15 grams per second. The plasma generating vessel may be configured to receive fluid (e.g. the fluid supply system may be configured to supply fluid to the plasma generating vessel) having an electrical conductivity of no more than 5500 micro-Siemens per centimetre, preferably with an electrical conductivity of between 1.3 and 5500 micro-Siemens per centimetre, morepreferably with an electrical conductivity of between 50 and 5500 micro-Siemens per centimetre. The plasma generating vessel may be configured to receive fluid (e.g. the fluid supply system may be configured to supply fluid to the plasma generating vessel) with fluid having a pH of between 5.8 and 7.6, more preferably with a pH of between 6.3 and 7.1.

[0031] Embodiments of the present disclosure may comprise one or more computer program products comprising computer program instructions configured to program a controller to control operation of a plasma generating vessel to implement any of the methods disclosed herein.

[0032] Figures

[0033] Some examples of the present disclosure will now be described, by way of example only, with reference to the figures, in which:

[0034] Fig. 1 is a schematic diagram of an example apparatus which includes a plasma generating vessel.

[0035] Fig. 2a is a graph showing Gross (DC) Coefficient of Performance data for different Vessel Pressures (in Barg).

[0036] Fig. 2b is a graph showing data for DC power (in kV) and thermal output (in kW) for different Vessel Pressures (in Barg).

[0037] Fig. 2c is a graph showing Gross (DC) Coefficient of Performance data for different Vessel Pressures (in Barg).

[0038] Fig. 3a is a graph showing Gross (DC) Coefficient of Performance data for different Mass Flow Rates (in grams per second).

[0039] Fig. 3b is a graph showing data for DC Current (in Amps) for different Mass Flow Rates (in grams per second).

[0040] Fig. 3c is a graph showing Gross (DC) Coefficient of Performance data for different Mass Flow Rates (in grams per second).

[0041] Fig. 4a is a graph showing the relationship between Electric Stress (in Volts per metre) and Current (in Log Amps) for different regions of plasma operation.

[0042] Fig. 4b is a sequence of images showing bubble formation (or lack thereof) for different voltages (350V, 650V, 1000V, 1500V and 2000V) for tap water and deionised water.

[0043] Specific Description

[0044] Embodiments of the present disclosure relate to systems and methods which utilise a plasma generating vessel. The vessel comprises a plurality of electrodes and is arranged to receive a liquid. The vessel is configured to apply electrical energy to the received liquid to generate one or bubbles of plasma therein. In turn, one or more exothermic physical and chemical processes occur which give rise to emission of thermal energy within the liquid in the vessel. The present inventors have identified that the operation of the vessel, and the processes occurring within the liquid in the vessel, may be enhanced by operating with one or more parameters in selected valueranges. The parameter(s) may include each, all, or any combination of: pressure, mass flow, electrical conductivity, pH and / or salinity. For each of these parameters, operating in specified value ranges for this parameter may be associated with elevated performance for the vessel. Embodiments may also provide adaptive systems for monitoring and controlling one or more parameter values to be within their selected value ranges.

[0045] An example apparatus with a plasma generating vessel will first be described with reference to Fig. 1. After this, relevant parameters and their associated values will be described with reference to the graphs of Figs 2a to 4b.

[0046] Plasma generating vessel

[0047] Fig. 1 shows a schematic diagram of an apparatus 100. The apparatus 100 includes an energy vessel 1. The apparatus 100 includes an electrical supply system 60 and a fluid supply system 70 (both for controlling the relevant supply to the vessel 1). The vessel 1 may optionally be connected downstream to further componentry. In Fig. 1, a work extraction system 80 is shown (for using the heated fluid output from the vessel 1).

[0048] The vessel 1 includes a fluid inlet 54 and a fluid outlet 58. The vessel 1 has a housing 50. The housing 50 defines an internal volume 56 of the vessel 1. The vessel 1 also includes a plurality of electrodes. As shown, this includes a first electrode 10, a second electrode 20 and a third electrode 30. The vessel 1 may also include a resistive element 40. A mount 32 for the third electrode 30 is shown in Fig. 1. The vessel 1 may also include an earth connector 22. The earth connector 22 is coupled to the second electrode 20 and an electrical earth 24.

[0049] The electrical supply system 60 is coupled to the first electrode 10. The fluid supply system 70 is coupled to the fluid inlet 54 of the vessel 1. The (optional) work extraction system 80 is coupled to the fluid outlet 58 of the vessel 1.

[0050] The electrical supply system 60 is configured to supply electrical energy to the first electrode 10. The fluid supply system 70 is configured to supply fluid to the internal volume 56 of the vessel 1. The work extraction system 80 is configured to extract useable work from heated fluid received from the fluid outlet 58 of the vessel 1.

[0051] The housing 50 of the vessel 1 encapsulates the internal volume 56. The fluid inlet 54 provides a flow path for fluid into the internal volume 56 of the vessel 1. The fluid outlet 58 provides a flow path for fluid out from the internal volume 56 of the vessel 1. Fluid may flow along any suitable path between the fluid inlet 54 and the fluid outlet 58. For example, it may flow along a very indirect (e.g. tortuous) path. The internal volume 56 of the vessel 1 may otherwise be sealed bythe housing 50.

[0052] The first electrode 10 is at least partially disposed within the internal volume 56 of the vessel 1. The second electrode 20 may also be disposed at least partially within the internal volume 56 of the vessel 1. The first and second electrode 20 are arranged concentrically. The first electrode 10 extends within a central region of the internal volume 56 of the vessel 1. The second electrode 20 is arranged radially outward from the first electrode 10. The second electrode 20 may be cylindrical, as may the first electrode 10. The first and second electrode 20 are arranged co-axially in the example shown in Fig. 1. The second electrode 20 is located adjacent to an internal surface of the housing 50 (however in some examples, the second electrode 20 may be integrated with the housing 50, e.g. to form a part thereof, and / or a portion of the housing 50 may provide the second electrode 20, e.g. if said portion of the housing 50 is electrically conductive).

[0053] A first end of the first electrode 10 is located outside the internal volume 56 of the housing 50. A second end of the first electrode 10, distal to the first end, is located within the internal volume 56 of the housing 50. The second electrode 20 may extend along some, or all, of the length of the internal volume 56 of the housing 50. At least one end of the second electrode 20 may extend out of the internal volume 56 of the vessel 1. Although not shown in Fig. 1 the first and / or second electrode 20 may each be coupled to a power supply. For example, each electrode may have one end which extends outside the internal volume 56 (e.g. into the housing 50), and this end may be coupled to the power supply. In some examples, the housing 50 may provide a ground (e.g. via the earth connector 22 to the electrical ground), and the first electrode 10 may be connected to a positive terminal of the power supply. In Fig. 1, the second electrode 20 is shown as being a separate component to the housing 50, but this need not be the case, as the second electrode 20 may be provided by the housing 50 (e.g. the housing 50 may be made of an electrically conductive material which may function to provide the second electrode 20).

[0054] The third electrode 30 is also provided in the internal volume 56 of the vessel 1. As shown in Fig.

[0055] 1, the third electrode 30 may be located entirely within the internal volume 56. For example, a mount 32 is shown for attaching the third electrode 30 to the housing 50. The third electrode 30 may extend from a first end (e.g. where it is held by the mount 32) to a second end located proximal to the second end of the first electrode 10 within the internal volume 56. The first and third electrodes 10, 30 may be parallel (e.g. they may be co-axial). The second and third electrodes 20, 30 may be parallel (e.g. coaxial). The first electrode 10 may extend from outside a first end of the housing 50 into the internal volume 56 towards an opposite end of the housing 50. The third electrode 30 may extend towards the first electrode 10 within the housing 50. The first and third electrodes 10, 30 may extend into the internal volume 56 so that there is no spatial overlap between these electrodes 10, 30 (e.g. their respective second ends do not touch / overlap).The second electrode 20 may extend along the length of the internal volume 56 from at or outside the first end to at or outside the opposite end. The distance between the second end of the first electrode 10 and the second end of the third electrode 30 may be less than the smallest distance between the first electrode 10 and the second electrode 20. The third electrode 30 may be located away from an expected current path between the first and second electrode 20. The third electrode 30 may be arranged to electrically float within the internal volume 56. While the third electrode 30 and first electrode 10 are shown as being coaxial, parallel and central within the vessel 1, this need not be the case. One or both electrodes 10, 30 may be laterally offset from the centre of the vessel. For example, the third electrode 30 may be laterally offset from the first electrode, e.g. the third electrode 30 may not be central (e.g. but the first electrode 10 may still be central). Additionally, or alternatively, the first electrode 10 may not be central.

[0056] A resistive element 40 may also be included in the internal volume 56. The resistive element 40 may be cylindrical. The resistive element 40 may be arranged to increase the electrical resistance of the conductive path between the first electrode 10 and the second electrode 20. The resistive element 40 may be provided by a single (e.g. contiguous) piece of material or it may be provided by multiple pieces of material. For example, different portions of the resistive element 40 could be provided by different components, wherein each potion may contribute to providing an electrical resistance for the resistive element 40 as a whole. Different portions of the resistive element 40 could be electrically connected and provided by different materials / components. For example, the resistive element 40 could include circuitry, such as a sensor (e.g. a photovoltaic sensor). The different portions of the resistive element 40 need not be physically and / or electrically connected. The resistive element 40 may increase the electrical resistance between the first and second electrodes 10, 20. The resistive element 40 may extend around a majority of the internal volume 56 (e.g. along a length and width of the internal volume 56 to impede the majority of possible conductive paths between the first and second electrodes 10,20). The resistive element 40 may be located between the first / third and second electrodes 10, 20. For example, the resistive element 40 may be located radially outward from the first / third electrodes 10, 30, but not as far radially outward than the second electrode 20. The resistive element 40 may extend along some or all of the length of the internal volume 56.

[0057] The housing 50 may be cylindrical. That is, a cross-sectional shape (i.e. when viewed in plan) of the housing 50 may be circular. Alternatively, the housing 50 may be polygon shaped. The housing 50 may be provided by a shape which is tessellatable (i.e. which is capable of being tessellated with other copies of that same shape). For example, multiple vessels 1 may be provided together, e.g. to increase output as compared to that provided by a single vessel. In which case, the vessels 1 may be stacked together. The vessels 1 may be designed to facilitate more space efficient stacking. For example, the vessels 1 may be arranged so that, when stackedtogether, they tessellate with each other (or at least substantially tessellate to provide more space efficient stacking). As will be appreciated, any suitable tessellatable shape may be used for this purpose. For example, the shape may be any suitable polygon, such as a hexagon or an octagon. The shape may be imparted by an outer surface of the housing 50, e.g. with everything thereinside being circular (including the inner surface of the housing 50), or the shape may be impaired by the inner surface of the housing 50.

[0058] The fluid inlet 54 is arranged at an opposite end of the housing 50 to the fluid outlet 58. The first and second electrode 20 extend along an axis extending from the fluid inlet 54 to the fluid outlet 58 (e.g. a longitudinal axis of the vessel 1). The fluid outlet 58 may be arranged higher than (e.g. above, such as directly above or above and laterally offset from) the fluid inlet 54. For example, the fluid outlet 58 may extend vertically out of the internal volume 56 of the vessel or it may extend with a lateral component, such as diagonally or horizontally from an upper portion of the vessel 1. The housing 50 is configured to encapsulate the internal volume 56. The housing 50 is arranged to define the internal volume 56 to provide a region in which liquid may be heated. An internal surface of the housing 50 (e.g. which faces / defines the internal volume 56) may be configured to generate heat in response to incident photons (for example, the housing 50 may be conductive). The internal surface may comprise the region of the housing 50 which lies adjacent to the internal volume 56. This may comprise part of the housing 50 and / or it may comprise an additional component, such as a layer / film provided there to absorb incident photons, and in response, to generate heat. For example, the internal surface may be configured to absorb electromagnetic energy, such as in the form of visible light. The internal surface is configured to heat up as it receives incident photons. The internal surface is configured to provide heating of fluid within the internal volume 56, e.g. as it heats up from incident photons.

[0059] The housing 50 may be made of a metal, such as steel, or other materials may be used, such as a ceramic. For example, a glass with e.g. boron or lead, or Quartz may be used. The housing 50 may be formed of multiple different materials. The different materials may be selected based on their photon absorption and / or transmissive characteristics (e.g. based on application needs). For example, materials may be selected which absorb photons in different wavelength range(s) for which photons are expected within the internal volume 56, e.g. for visible, infrared, ultraviolet. The housing 50 may comprise a plurality of layers, e.g. with an outer housing layer, and an inner layer, such as a sleeve, inside the outer layer. The different layers may be made of different materials. The housing 50 is configured to retain fluid in the internal volume 56 under pressure.

[0060] The fluid inlet 54, the internal volume 56, and the fluid outlet 58 are arranged to define a flow path for fluid to flow through the internal volume 56 of the housing 50 (e.g. from the fluid supply system 70 through the vessel 1 and to the work extraction system 80). The internal volume 56 is arrangedto receive liquid to be heated through the fluid inlet 54. The vessel 1 is arranged to heat this liquid in the internal volume 56 to provide a heated fluid. The fluid outlet 58 is arranged to provide a flow path for this heated fluid away from the internal volume 56.

[0061] The first and second electrodes 10, 20 are configured to provide a current flow path through the internal volume 56 of the vessel 1. One of the electrodes 10, 20 may provide an anode, and the other may provide a cathode. The first electrode 10 may be configured to supply electrons to the internal volume 56. That is, the first electrode 10 may be configured to deliver electrons, from the first electrode 10, and into any fluid surrounding the first electrode 10 in the internal volume 56. In this sense, the first electrode 10 may act as a cathode. The second electrode 20 may be configured to act as an anode, e.g. for carrying away any electrons.

[0062] The first electrode 10 may be configured to bring electrical energy into the internal volume 56 of the vessel 1 (e.g. by having a voltage applied to it from the electrical supply system 60). The second electrode 20 may be configured to carry away electrical energy from the internal volume 56 of the vessel 1. The first and second electrode 20 are spaced apart from each other. The first electrode 10 is arranged to receive a voltage so that a potential difference exists between the first and second electrodes 10, 20. Either polarity arrangement may be employed for the first and second electrodes 10, 20. The first and second electrodes 10, 20 are arranged capacitively. The fluid may provide an electrical resistance between the two electrodes 10, 20 (e.g. so that they are arranged capacitively across this fluid). As will be appreciated, the fluid may not have an infinite resistance, and so some electrical conduction may occur through the fluid between the first electrode 10 to the second electrode 20. In this sense, the electrodes 10, 20 and the fluid in the vessel 1 may act as a leaky capacitor. For instance, the first and second electrodes 10, 20 with fluid in the vessel 1 may effectively provide a circuit having a capacitance and a resistance. This resistance provided by this fluid may be sufficiently large that only a relatively small current will flow across the fluid, even in response to high voltages being applied. The first and second electrodes 10, 20 are configured to provide a voltage stress to fluid and / or plasma within the internal volume 56.

[0063] The third electrode 30 may be active or passive. When active, a voltage is applied to the third electrode 30. When passive, the third electrode 30 may be conductive for receiving current within the internal volume 56, but without receiving power from the power supply 30. The third electrode 30 is shown passive in Fig. 1. The third electrode 30 may be configured to provide a balancing electrode (e.g. it may be arranged to balance electric field / current generated within the internal volume 56). The third electrode 30 may comprise a tip of electrically conductive material (i.e. which is arranged within the internal volume 56 of the vessel 1). The tip need not be electrically connected to a component outside of the vessel 1. For example, where the third electrode 30 ispassive, the provision of an electrical conductor within the housing 50 may provide passive balancing. For example, such a tip could be capable of charging and discharging by itself.

[0064] For example, the first electrode 10 may be active, the second electrode 20 may be passive and third electrode 30 could be active or passive. A distal tip of the first electrode 10 (i.e. the exposed tip within the vessel 1 would be electrically connected to a voltage source (e.g. external to the vessel 1). The second electrode 20 may be electrically grounded (e.g. so that current may flow from the second electrode 20 to ground). The third electrode 30, when passive, may provide an exposed portion of electrically conductive material within the internal volume 56 of the vessel 1. That passive exposed portion of electrically conductive material may be arranged to be charged and / or discharged within the vessel 1 (e.g. due to internal electrical conditions of the vessel 1). The third electrode 30, when active, may be connected to a voltage source. An exposed portion of the third electrode 30 within the vessel 1 may then be connected to the voltage source.

[0065] The resistive element 40 may be arranged on a current flow path between the first electrode 10 and the second electrode 20, e.g. so that current would need to flow through the resistive element 40 to get from the first electrode 10 to the second electrode 20. The resistive element 40 may extend along one or both of the ends of the internal volume 56 (e.g. to reduce the likelihood of a conductive path from between the first and second electrodes 10, 20 not via the resistive element 40 being possible). The resistive element 40 may be configured to be of relatively high resistance (e.g. as compared to the resistance of the electrodes and / or fluid within the internal volume 56). In other words, the resistive element 40 may increase the electrical resistance for current flow from one electrode to the other (e.g. across the fluid).

[0066] Operation of the plasma generating vessel

[0067] In operation, a fluid is supplied from the fluid supply system 70 through the fluid inlet 54 and into the internal volume 56 of the vessel 1. In this example, the fluid will be water, but other liguids may be used. For example, the fluid may be any agueous solution, such as tap water, sea water, ionised water etc. The fluid may comprise one or more minerals therein, e.g. in either solution or suspension within the liguid. The minerals(s) may comprise one or more transition metals. The fluid may be any non-Newtonian liguid. The liguid may be a non-electrically insulating liguid. The liguid may be at least partially electrically resistive (but not fully resistive). The vessel 1 will fill up with fluid (e.g. water). Any gas previously in the vessel 1 may be forced out through the fluid outlet 58 of the vessel 1. The vessel 1 may then be substantially filled with water. It will be appreciated that the fluid supplied to the vessel 1, while predominantly liguid (e.g. water) may contain trapped gasses and / or solid substances (e.g. which are otherwise trapped within the fluid.

[0068] A voltage is applied to the first electrode 10. This will cause some current flow into the water. Dueto the electrical resistance of water, this current flow and resistance will cause some heating of the water (e.g. I2R heating). This process of resistive heating continues as a voltage is applied to the first electrode 10. As the temperature of the water within the internal volume 56 rises, microbubbles of gas will start to form within the water in the internal volume 56. These may be steam bubbles forming or bubbles of air being released which were trapped in the water supplied to the internal volume 56 of the vessel 1. As a result, some pockets of gas will develop within the liquid in the internal volume 56 of the vessel 1. With continued application of the voltage to the first electrode 10, bubbles of plasma will be generated within the internal volume 56 of the housing 50. These bubbles will release energy into the surrounding fluid and the internal surface of the housing 50. In turn this provides heating of the fluid within the internal volume 56.

[0069] By applying the voltage to the first electrode 10, this may charge up the capacitor provided by the first and second electrode 20. As the fluid within the internal volume 56 heats up, its permittivity may change, and this may change a capacitance of the vessel 1 (e.g. between the first and second electrodes 10, 20). For example, when water is used, its permittivity will decrease as it heats up (and then also when it becomes steam). In particular, where microbubbles of gas (e.g. steam) begin to form within the liquid in the internal volume 56, these will provide localised regions of lower permittivity. This process may effectively provide a permittivity collapse in localised regions. For example, where water is used, this difference in permittivity between bubbles forming in the water and the surrounding water may be a factor of approximately 40 (e.g. the capacitance per unit volume in those bubbles may be 1 / 40th of that of the surrounding water). During this process, the volumetric energy density for fluid and / or plasma within the internal volume 56 will remain constant. Due to the permittivity collapse within the bubbles of gas, capacitance will decrease in this region. As the volumetric energy density remains constant and the capacitance decreases, the voltage per meter will rise accordingly (e.g. to conserve energy as per E=1 / 2 CV2). For examples where water is used, the voltage per meter will rise by a factor of approximately 40.

[0070] With electrical energy still being applied to the first electrode 10, these microbubbles of gas (at lower density than surrounding liquid) will try to rapidly expand into their surroundings. However, the surrounding liquid will resist this expansion, e.g. due to the non-Newtonian nature of the liquid in these conditions. This will cause the microbubbles to rapidly increase in temperature and pressure. In turn, their capacitance will further decrease (e.g. causing an increased dV / dr), thereby further increasing the voltage stress across the bubble. With sufficient voltage stress across the bubble, ionization may occur leading to the formation of plasma within the bubble. Thus, one or more plasma bubbles may form in the liquid in the internal volume 56. The plasma may be at an even lower density than the gas, and so with a voltage still applied to the first electrode 10, the plasma bubble will further try to rapidly expand. In particular, this process ofplasma bubble generation will occur rapidly, and so each bubble of plasma will drive for rapid expansion. In turn, this will bring about non-Newtonian fluid responses in the liquid in the internal volume 56 of the vessel 1. For instance, where water is used, the water does not immediately yield before the pressure wave brought about by the bubble of plasma trying to expand. The bubble of plasma is therefore held in a relatively fixed volume (e.g. it may only expand relatively slowly). While the volume of the plasma remains relatively constant, the temperature and pressure within this bubble rise rapidly in response to the voltage stress brought about by the voltage applied to the first electrode 10.

[0071] As mentioned above, the breakdown of gas may occur such that a low impedance bridge forms (e.g. the gas resistivity drops), but not as far as a full breakdown in which electrical arcing occurs. In addition to this, thermionicemission may occur within the vessel 1. Electron spraying may occur with electrons moving between different electrodes of the vessel 1. In particular, electrons may pass from the first electrode 10 to the second electrode 20 and / or from the first electrode 10 to the third electrode 30. In turn, this may also cause electrons to pass from the third electrode 30 to the second electrode 20. In other words, the third electrode 30 may act to draw in electrons (i.e. from the first electrode 10) before then sending them out (i.e. to the second electrode 20). This may act to stretch out the plasma generating region, which in turn may increase the stability thereof. The electrons may accelerate through the gas bubbles which have formed.

[0072] The electrodes may be designed to provide a preferential flow for the electron movement. For example, the material of each electrode (and in particular its valence) may be selected to impart this preferential flow of electrons. For example, tungsten may be used for the first electrode as it has a high valence and high melting point. The electrodes may be arranged to provide a preferential flow from the first electrode 10 to the third electrode 30 (as compared to a flow from the first electrode 10 to the second electrode 20). This may act to stretch out the plasma generating region, which in turn may provide greater stability and / or a greater amount of work output.

[0073] Energy may be absorbed by atoms (and molecules) within the bubble. The energy levels (e.g. states) of these particles may therefore rise. Within the plasma, atoms may have their electrons move to higher electron energy levels, and / or spin states for these particles may change. For example, Hydrogen atom spin states may change from their lower energy para-state to their higher energy ortho-state. Molecules may also move to higher rotational and / or vibrational energy levels, and / or further splitting up of these molecules may occur. As a result, the atoms within each bubble will be at disproportionately high energy levels (e.g. as compared to conventional fluids / the fluid within the internal volume 56). Photon emission from the plasma may occur to accommodate for the high energy within the plasma. Electrons may move to lower energy electron states, and / orchanges to lower energy vibrational / rotational / spin states may occur for atoms / molecules. It is this returning to lower energy configurations which gives rise to the emission of photons (e.g. to accommodate for the drop in energy levels as per the Bohr model). This emission of photons may occur on a relatively large scale. Where water is used, a large proportion of this photon emission may occur in the visible light spectrum.

[0074] The photons emitted from each plasma bubble will then be absorbed by either fluid in the internal volume 56 or the housing 50 of the vessel 1. In response to receiving such incident photons, the fluid and / or housing 50 will heat up as it absorbs said photons. The inner surface of the housing 50 in particular may absorb a large number of these photons and thus increase in temperature. As the inner surface of the housing 50 heats up, it will in turn provide conductive heating of the fluid within the internal volume 56. This may give rise to convection currents occurring and thus increased turbulence for fluid within the internal volume 56 of the vessel 1. As a result of this process, the fluid within the internal volume 56 will heat up. The majority of the liquid provided to the internal volume 56 of the vessel 1 may then evaporate to provide a gas (e.g. steam). It is to be appreciated in the context of the present disclosure that some of the fluid which exits the vessel 1 may have somewhat unconventional, or at least lower energy configurations, as compared to the liquid that was provided to the vessel 1. This is as a consequence of the plasma generation and subsequent energy release which occurred within the vessel 1.

[0075] Additionally, the conditions within the vessel 1 may give rise to a number of different mechanisms for releasing heat, as compared to purely resistive heating (i.e. I2R). For instance, thermionic emissions from the first electrode 10 may cause heating, as may photoelectric emissions from substances in the internal volume 56. One particular source of heat release may arise due to thermionically emitted electrodes being rapidly accelerated across plasma bubbles and inducing very high-speed collisions within the fluid in the internal volume 56.

[0076] In other words, this process may act to initiate separation processes in which molecules are broken into multiple parts (e.g. towards constituent parts). In turn, this may render certain atoms or molecules available for chemical processes within the fluid in the vessel that would otherwise not be available. For example, component constituents within previously stable molecules may be separated from other components of that molecule, thereby leaving much more reactive substances available within the fluid in the vessel. As an example, the quantity of free radicals produced may increase, and these free radicals may be used in exothermic chemical processes occurring in and around the plasma. For instance, there may be a highly reactive mix of free radicals such as OH, H2O2 and O, which will readily oxidise dissolved salts and gases in the water, with these processes resulting in an exothermic cascade of further chemical processes that result in a net release of heat. As such, heavily exothermic chemical processes may beoccurring within the vessel 1 which further generate heat therein. For example, the conditions within the vessel 1 may cause one or more Fenton processes to occur, one or more single-atom catalyst (‘SAC’) processes to occur, oxidation of minerals and / or hydration of protons to occur.

[0077] As a result of these exothermic processes, in some operating conditions, the vessel 1 may be capable of providing more heating of fluid than the corresponding amount of electrical energy being supplied to the vessel 1. That is, some substances within the fluid supplied may effectively be consumed as part of the chemical processes occurring within the vessel, with the associated exothermic energy release from these processes bridging the difference in energy between the electrical energy applied to the vessel and thermal energy being output from the vessel.

[0078] In view of these processes occurring within the vessel 1, the vessel 1 may be operated with a coefficient of performance (‘COP’) for generating thermal energy (i.e. with COP = thermal energy output / electrical energy input) that is superior to the COP associated with a purely resistive heating apparatus (i.e. where all heating is as per l2R).

[0079] In this sense, the vessel 1 may operate as a heat pump. That is, the vessel 1 is receiving a liquid, such as water (e.g. cold water) and turning this into steam. Although not shown, the vessel 1 may also include one or more filters. The filters may be for filtering solid contaminants, such as Manganese, Iron compounds or other material deposits which may accumulate within the vessel 1. For example, this may comprise a gravity filter or another suitable type of filter arranged to prevent excess build up of such material deposits within the vessel 1. This heated fluid then passes through the fluid outlet 58. Typically, the heated fluid is in the form of steam, which is generated within the internal volume 56, and which rises up and out through the fluid outlet 58. This heated fluid output from the vessel 1 may then be used in the work extraction system 80 to extract useable work from that heated fluid.

[0080] Vessel pressure

[0081] The present inventors have identified that the thermal energy output and the operating efficiency for the vessel 1 may be elevated when operating the vessel 1 in a selected pressure range.

[0082] As mentioned above, as electrical energy is applied to the fluid in the internal volume 56 of the vessel 1 using the first electrode 10, bubbles may begin to form in the liquid in the vessel 1. As will be appreciated, the formation of these bubbles will vary in dependence upon the pressure within the vessel 1. At higher vessel pressures, bubbles may be harder to form, and they will tend to be smaller bubbles (i.e. due to the elevated surrounding pressure which will act to try to compress those bubbles). Conversely, at lower vessel pressures, the bubbles which form may be greater in size.The present inventors have identified that the vessel 1 may be operated at elevated levels (e.g. in terms of efficiency and / or total output) when the bubble size is at a desired level.

[0083] Without wishing to be bound by theory, it is considered that the properties of the bubbles will influence the intensity of the voltage stress across the fluid within the vessel 1. The bubbles within the liquid may act to provide a lens effect on the electrical field, e.g. causing localised concentration of electrons. It has been found that the presence of bubbles may increase the electrical stress from a value of 0.25 MV / m to a much greater value of 7 MV / m. As such, it is considered that this formation of bubbles within the liquid may contribute to the conditions mentioned above for accessing certain exothermic chemical processes, and this effect may be accentuated by the vessel pressure being at a value which facilitates stable and widespread formation of bubbles within the liquid within the vessel 1.

[0084] In particular, the present inventors have identified that desirable bubble formation may occur for vessel pressure values at and above 4 Barg.

[0085] The present inventors have identified that, for vessel pressures below 4 Barg, the operating conditions of the vessel are less preferable to those at or above 4 Barg. For instance, without wishing to be bound by theory, it is considered that the two-phase mixture of gas and liquid may become increasingly unstable at pressures below 4 Barg, and this may lead to unsatisfactory (or sub-optimal) bubble formation, and similarly any effect of electrical field intensification and lensing may be less substantial with larger bubbles.

[0086] The present inventors have identified that, at vessel pressures above 4 Barg, desirable operating characteristics for the vessel may occur. Again, without wishing to be bound by theory, improved bubble generation may occur with the pressure at or above 4 Barg, thereby further facilitating the vessel 1 to access the above-mentioned exothermic chemical processes which contribute to elevated thermal energy output from the vessel 1.

[0087] Without wishing to be bound by theory, the exothermic chemical processes may remain accessible at increasingly elevated vessel pressures, with the vessel potentially requiring larger electrical energy inputs to be used when operating at higher pressures. Similarly, as will be appreciated by one of skill in the art in the context of the present disclosure, operating at increasingly elevated vessel pressures may place further constraints on the design choice for components of the system downstream of the vessel 1 (e.g. which carry the pressurised gas away from the vessel 1) and this may also limit the volume of the plasma region within the internal volume 56 of the vessel 1.In view of these potential practical constraints associated with operating the vessel 1 at increasingly elevated pressures, the present inventors have identified that it may be preferable to operate the vessel 1 at pressures of up to 200 Barg, e.g. within a vessel pressure range of 4 Barg to 200 Barg. Further preferably, the vessel may be operated with a pressure of between 4 and 20 Barg.

[0088] Where a liquid, such as water, is supplied to the vessel, that liquid may be heated into its gaseous form within the vessel (e.g. with water boiling to become steam). As will be appreciated in the context of the present disclosure, the point at which the liquid being supplied to the vessel (e.g. water) will boil into its gaseous form will be dependent upon the vessel pressure. For example, for water, the boiling point will be 156.6 degrees Celsius at 4.65 Barg and 217.1 degrees Celsius at 20.9 Barg. As such, the choice of vessel pressure may influence operating temperatures for the heated fluid (e.g. steam) output from the vessel. For example, in applications where higher temperature heated fluid (e.g. steam) is desired, the vessel may be operated at a correspondingly higher vessel pressure, e.g. thereby to further facilitate the provision of heated fluid at that temperature. As will be apparent from the data shown in Figs. 2a to 2c, the vessel pressure may be selected to be at a lower value (above 4 Barg), where possible, e.g. to obtain higher COP values.

[0089] Vessel pressure examples

[0090] Example data for operating a vessel 1 at different vessel pressures is shown in Figs. 2a, 2b and 2c. These three figures, and the data shown therein, will now be described in turn.

[0091] Fig. 2a shows a graph of Gross DC Coefficient of Performance (‘COP’) against Vessel Pressure.

[0092] COP is measured as the ratio of thermal energy output from the vessel to the electrical energy applied to the first electrode of the vessel. As will be appreciated in the context of the present disclosure, the electrical supply system itself may indicate the electrical energy it is using (i.e. in view of the applied voltage and associated current it applies to the first electrode of the vessel). The thermal energy output from the vessel may be determined by measuring the change in enthalpy of fluid between the inlet and outlet to the vessel. Data was processed by time averaging results captured from an Arduino.

[0093] In particular, The Gross Coefficient of Performance (COP), as shown in the y-axis of Fig. 2a, was calculated by dividing the enthalpy rise in the water by the DC electrical power supplied to the HV generator, as per:rn n • (hout h-in)

[0094] COP = m - - -

[0095]

[0096] ?DC

[0097] Where COP is the Gross Coefficient COP, m is the mass flow rate of fluid (e.g. as measured by the fluid supply system), houtis the vessel outlet specific enthalpy, hinis the vessel inlet specific enthalpy, and PDCis the DC power supplied to a high voltage generator of the electrical supply system.

[0098] The enthalpies were calculated from the pressure and temperature conditions measured at the inlet and outlet of the cell using REFPROP (the NIST Reference Fluid Thermodynamic and Transport Properties Database (REFPROP): Version 10. All sensors were calibrated by a qualified third party, and individual instrument channels were calibrated using a Druck DPI880 calibrator from sensor output to the data logger to account for any electrically induced errors in the signal conditioning chain. Errors in the enthalpy calculations (from the measured cell outlet pressure and temperature) and DC power measurement accuracy were <0.5%. The accuracy of the flow measurement varied between the highest and lowest flow measurement due to the accuracy of the weighing scales. The total error was calculated at <5% at highest flow rate and <10% at the lowest flow rate varying linearly between the highest and lowest flow rates. Error bars presented in the figure show the (conservative) maximum error of 10%.

[0099] The vessel pressure shown is the pressure in Barg (i.e. gauge pressure) for the vessel. The vessel pressure relates to the pressure within the internal volume of the vessel. The vessel pressure was measured using a pressure sensor downstream of the outlet. For example, a pressure regulator, such as a back pressure regulator, may be used downstream of the vessel (i.e. coupled to the outlet of the vessel), and this back pressure regulator may be set to a selected pressure value so as to fix the vessel pressure to the selected value.

[0100] A high voltage current was supplied using a Technix 12 kW high voltage (HV) generator, and an Arduino mega microcontroller and recorded on a PC at an interval of 1.5 seconds but oversampled by a factor of 75. Five minutes stabilization time was allowed at each test condition and data time averaged over a two-minute period after stabilization. Tap water was supplied to the vessel, with a pH of between 6 and 8 (mainly between 6.6 and 6.8) during the process, the water was supplied with a flow rate of 8 grams per second, the water had a conductivity of 0.4 mS / cm, a total hardness of 100 parts per million, and a dissolved CO2 content of 10 parts per million. The first and third electrodes were separated with a gap of between 10 and 15 mm, and the first and second electrodes were separated by a gap of 45 mm.

[0101] As shown in Fig. 2a, the highest value for COP was achieved at a vessel pressures of close to 4Barg. For instance, at 4.00 Barg, a COP of 4.17 was achieved, and at 4.16 Barg, a COP of 4.28 was achieved. At higher vessel pressure values, e.g. at above 5 Barg, high COP values are still obtained (between 3 and 4.5). These COP values generally decrease with increased vessel pressure (with the decrease being gradual for increased vessel pressure). Although not shown in the figure, it is considered that the general decline in COP values with increased vessel pressure would continue to much greater vessel pressures than the highest value shown in Fig. 2a (at 14.56 Barg). Below 4 Barg, the vessel operation was increasingly unreliable (e.g. due to instability of suitable bubble formation within the fluid in the internal volume of the vessel), with vessel operation at below these pressures hard to maintain.

[0102] As such, the vessel 1 may preferably be operated at a vessel pressure of above 4 Barg.

[0103] As shown in Fig. 2a, at vessel pressure values between 4 and 10 Barg, the COP values are at their highest. For instance, at 9.95 Barg, the COP is above 3.5 (at 3.64), and this increases with decreasing pressure. As already mentioned at around 4 Barg, i.e. just above 4 Barg, the COP value peaks. For example, in view of this, the vessel 1 may preferably be operated with a vessel pressure of between 4 and 20 Barg, even more preferably between 4 and 10 Barg.

[0104] Fig. 2b shows a graph of DC power (kV) against vessel pressure (Barg) and thermal output (kW). These parameters are the same as those introduced above in relation to Fig. 2a.

[0105] As shown in Fig. 2b, there are two different variables: an ‘upper curve’ (with crosses and circles) which shows thermal output versus vessel pressure, and a ‘lower curve’ (with squares and triangles) which shows DC power in versus vessel pressure.

[0106] As can be seen from the upper curve, the total thermal energy output from the vessel remains somewhat constant at different vessel pressure (albeit with a gradual rise in thermal output from the lowest pressure to the highest pressure). At higher vessel pressures (e.g. above 8 Barg), there is no particular increase in thermal energy output for operating at higher vessel pressures. Between a pressure of 4 Barg and 8 Barg, the thermal energy output increases (albeit relatively gradually) with increased pressure.

[0107] As can be seen from the lower curve, the DC power input increases with increased vessel pressure. This increase is relatively linear for increased vessel pressure. As a result, at higher vessel pressures, the required electrical energy input is greater. In turn, this is why the higher vessel pressures shown in Fig. 2b are associated with lower COP values (despite them potentially achieving greater total thermal energy output values).In view of this data shown in Fig. 2b, it can be seen that operating with lower vessel pressure values may simplify the equipment used to achieve the required DC power in values. For example, it may be preferable to operate at pressure values of between 4 and 10 Barg, e.g. in order to reduce the DC power in burden on the equipment used (and also to achieve the higher COP values shown in Fig. 2a).

[0108] As mentioned above, the choice of vessel pressure may be influenced by the temperature requirements for the output fluid, and so vessel pressure may be chosen to be towards the lower end of the range (and above 4 Barg) for pressures at which the desired temperature of heated fluid output from the vessel may be achieved.

[0109] Fig. 2c shows another a graph of Gross DC Coefficient of Performance (‘COP’) against Vessel Pressure, and Table A below lists the numerical values shown in Fig. 2c.

[0110] Pressure COP

[0111] 4.00 4.17

[0112] 4.16 4.28

[0113] 4.27 4.43

[0114] 5.31 3.88

[0115] 7.08 3.76

[0116] 8.57 3.84

[0117] 9.95 3.64

[0118] 11.18 3.46

[0119] 11.76 3.28

[0120] 12.69 3.14

[0121] 13.31 3.10

[0122] 14.56 3.01

[0123] 15.8 2.87

[0124] 17.8 2.9

[0125] 19.8 2.91

[0126]

[0127] Table A - numerica values for Fig. 2c

[0128] For Fig. 2c, the operating conditions for the vessel were the same as those described above in relation to Fig. 2a. Again, the vessel was supplied with fluid at a mass flow rate of 8 grams per second.

[0129] As shown in Fig. 2c and Table A, the highest COP values were achieved at the vessel pressures closer to 4 Barg. In particular, between vessel pressures of 4.00 and 4.27, the highest COP valueswere obtained. At vessel pressures above this range, the COP value gradually decreased with increased pressure. As shown, the tail of the curve plateaus with not much change in COP at vessel pressures greater than 15. Again, therefore, the vessel may preferably be operated at vessel pressures at or above 4 Barg. An upper limit for the vessel pressure may be selected based on desired temperature ranges for the heated fluid and / or in view of practical constraints the elevated pressure may place on equipment downstream of the vessel output.

[0130] Mass flow rate

[0131] The present inventors have identified that the thermal energy output and the operating efficiency for the vessel 1 may be elevated when supplying the vessel 1 with fluid within a selected range for mass flow rate of fluid provided to the vessel 1.

[0132] As mentioned above, it is considered that the formation of plasma bubbles within the fluid in the internal volume of the vessel facilitates access to exothermic chemical processes which may significantly increase the thermal output from the vessel. Without wishing to be bound by theory, it is considered that the mass flow rate of fluid into the vessel will influence the interaction between fluid flowing into the vessel and the plasma within the vessel. For instance, it is considered that mass transfer into and out of the high temperature zone within the vessel will be influenced by the mass flow rate of the fluid supplied to the vessel, as well as the amount of substances which are available to be utilised in the above-mentioned exothermic chemical processes occurring in the vessel.

[0133] In particular, the present inventors have identified that desirable thermal performance of the vessel may occur for mass flow rates at and above 2 grams per second, such as at and above 3 grams per second.

[0134] The present inventors have identified that, for mass flow rates below 2 grams per second, and in particular below 3 grams per second, the operating conditions of the vessel are less preferable to those at or above 2 grams per second (e.g. at or above 3 grams per second). For instance, without wishing to be bound by theory, it is considered that, at the lower flow rates, less mixing of incoming fluid with the plasma region occurs, and in turn this may constrain the amount of thermal energy which is output from the vessel at those flow rates. For example, it is considered that lower values of flow rate limit the amount of thermal energy capable of being output from the vessel, as well as reducing the amount of substance(s) delivered to the plasma region which could be used in the above-mentioned exothermic chemical processes.

[0135] At increasingly elevated mass flow rates, the amount of thermal energy output from the vessel may remain high and / or may continue to increase. Without wishing to be bound by theory, it isconsidered that the relevant mixing of incoming fluid with the plasma zone may continue to occur at elevated flow rates, thereby continuing to facilitate access to the exothermic chemical processes. As will be appreciated by one of skill in the art in the context of the present disclosure, operating at increasingly elevated flow rates may place constraints on other aspects of the apparatus, such as any pumps required to provide those flow rates, as well as the amount of electrical energy to be applied and / or the properties of the outlet and components downstream of the outlet (which would need to receive increasingly larger flow rates and thus velocities of heated fluid), and elevated mass flow rates may also influence the vessel pressure (and e.g. lead to the above-mentioned potential drawbacks associated with operating at higher vessel pressures).

[0136] In view of these potential practical constraints associated with operating the vessel 1 at increasingly elevated flow rates, the present inventors have identified that it may be preferable to operate the vessel 1 at flow rates of up to 20 grams per second, e.g. with a mass flow rate in a range of 2 (e.g. 3) grams per second to 20 grams per second.

[0137] The flow rate of fluid supplied to the vessel 1 may be influenced by the operating vessel pressure. For example, higher vessel pressures may limit the maximum flow rates achievable. In other words, for a given vessel pressure, a maximum flow rate may be identified above which the vessel operation (e.g. in terms of amount and / or efficiency of thermal energy generation) begins to decrease. As mentioned above, a desired operating temperature for the heated fluid output from the vessel 1 may influence the choice of vessel pressure, and in turn this choice of vessel pressure. As mentioned above and as will be described in more detail below in relation to Figs 3a to 3c, to increase the output from the vessel, higher flow rates may be used. It follows that, lower vessel pressures may be selected (heated fluid output temperature constraints permitted) in order to facilitate use of greater mass flow rates. As shown above for Figs. 2a to 2c, such use of lower vessel pressures (e.g. between 4 and 10 Barg) may provide an increased COP for a given flow rate, and as will now be described for Figs. 3a to 3c, by using a lower vessel pressure (and thus permitting greater maximum flow rates) the COP may be increased by operating at greater mass flow rates.

[0138] Mass flow rate examples

[0139] Example data for supplying a vessel 1 with fluid at different flow rates is shown in Figs. 3a, 3b and 3c. These three figures, and the data shown therein, will now be described in turn.

[0140] Fig. 3a shows a graph of Gross DC COP against Mass Flow Rate in grams per second. The COP is the same as that described above in relation to the vessel pressure example.

[0141] The mass flow rate is shown in grams per second. Here, mass flow rate refers to the mass of fluidsupplied to the vessel, i.e. from a fluid supply system. The mass flow rate may be a parameter value which can be preset for a pump apparatus, e.g. so that the fluid is pumped by that apparatus at the selected mass flow rate. Additionally, or alternatively, mass flow rate may be measured by monitoring a weight difference associated with the fluid to be supplied (i.e. which confirms how much mass of fluid is being ‘lost’, e.g. provided to the vessel, per second) and / or one or more flow meters could be incorporated to identify this mass flow rate. In the example data shown in Figs. 3a to 3c (and also as relevant to Figs. 2a to 2c above), the mass flow rate was controlled by selecting a mass flow rate value for the fluid pump responsible for driving fluid flow into the vessel. In other words, the mass flow rate may comprise a mass flow rate of fluid being driven by a pump (or one or more pumps) of the fluid supply system towards the fluid inlet of the vessel.

[0142] In the example of Figs. 3a to 3c, the properties of the vessel and the fluid (water) being supplied to that vessel are the same as those shown above in relation to the vessel pressure example, except that in this case the mass flow rate was the variable, and the vessel pressure was held constant at 10 Barg ± 0.5 Barg.

[0143] As shown in Fig. 3a, the water flow rate was varied between 2.1 grams per second and 10.9 grams per second. Results from five separate test runs are shown together.

[0144] As shown, the value for COP generally increases with increased mass flow rate. At mass flow rates of above 3 grams per second, the COP achieved was greater than 3. Below 3 grams per second, the COP decreases relatively steeply with decreasing mass flow rate. At flow rates greater than 3 grams per second, high COP values are still obtained (between 3 and 4), with these COP values gradually increasing for higher mass flow rates. For instance, at a flow rate of 3 grams per second, a COP of 3.07 was achieved, at a flow rate of 4.0 grams per second, a COP of 3.51 was achieved, with a peak COP value of 3.67 being achieved at 9.9 grams per second. At flow rates above 3 grams per second (e.g. above 4 grams per second), the increase in COP with increased flow rate was relatively gradual, with the higher flow rate values not exhibiting a substantially improved COP as compared to those at the lower end of the range (e.g. closer to 3 or 4 grams per second). As shown, reasonable COP values were obtained between 2 and 3 grams per second (albeit with these COP values being below those associated with flow rates at or greater than 3 grams per second).

[0145] As such, the vessel 1 may preferably be operated at a mass flow rate of above 2 grams per second, such as at a mass flow rate of above 3 grams per second. More preferably, the vessel 1 may be operated at a mass flow rate of 4 or more grams per second, as high COP values are obtained throughout this range of values (e.g. with an improvement compared to lower flow rates). Yet more preferably, the vessel 1 may be operated at a mass flow rate of 8 or more grams persecond, as the highest COP values obtained are generally all in this region and the obtained COP values are consistently high.

[0146] Fig. 3b shows a graph of DC current (Amps) against mass flow (grams per second). Mass flow is the same parameter as that introduced above in relation to Fig. 3a, and DC current refers to the current as supplied to the first electrode from the electrical supply system. For instance, this current may be a parameter value which is output by that electrical supply system, or a separate amp meter may be used to measure current. In the example of Fig. 3b, the DC current was a parameter value that was output and recorded by the electrical power system itself (e.g. which kept a log of the current it was delivering) when applying electrical energy to the first electrode of the vessel. As with Fig. 3a, for the data shown in Fig. 3b, five runs were performed to obtain this data, and the individual data points correspond to the relevant points shown in Fig. 3a. The DC power (the same parameter as mentioned above in relation to vessel pressure) did not exceed 9 kW.

[0147] As shown in Fig. 3b, the relationship between mass flow rate and current indicates the current rising steadily with increasing flow rate. As can be seen, the highest DC current value occurs at the highest flow rate (10.9 grams per second). The DC current value decreases relatively linearly with decreased mass flow rate.

[0148] As shown in Fig. 3b, the DC current value does not exceed 3.5 Amps. The present inventors have identified that Amp values in this region (at or around 3.5 Amps) can be sensibly managed by the apparatus, and as such do not place significant constraints (electrical or otherwise) on the apparatus design. As such, the present inventors have identified that operating at higher mass flow rates may provide advantageous effects in the form of elevated thermal energy output and / or higher COP, without unduly limiting the ability of the system to cope with the corresponding elevated Amp levels.

[0149] In view of this, it can be seen that operating with higher flow rates may enable greater values to be achieved for thermal energy output and COP. For example, it may be preferable to operate at mass flow rates of at least 2 (e.g. at least 3) grams per second (and preferably between 2 (e.g.

[0150] 3) and 20 grams per second), e.g. in order to achieve higher COP values (as shown in Fig. 3a) with the higher associated DC current values (as shown in Fig. 3b) being manageable at this level.

[0151] Fig. 3c shows another a graph of Gross DC Coefficient of Performance (‘COP’) against Mass Flow Rate, and Table B below lists the numerical values shown in Fig. 3c.Mass Flow Rate COP

[0152] 2.1 2.69

[0153] 2.6 2.65

[0154] 2.7 2.62

[0155] 3.0 3.07

[0156] 3.9 3.30

[0157] 4.0 3.51

[0158] 4.1 3.25

[0159] 4.2 3.22

[0160] 4.8 3.17

[0161] 5.1 3.50

[0162] 5.8 3.54

[0163] 5.9 3.56

[0164] 5.9 3.38

[0165] 7.3 3.43

[0166] 7.8 3.19

[0167] 7.9 3.06

[0168] 8.0 3.66

[0169] 8.2 3.52

[0170] 8.5 3.55

[0171] 9.0 3.58

[0172] 9.9 3.67

[0173] 10.0 3.55

[0174] 10.9 3.65

[0175] 11.0 3.73

[0176] 12.0 3.65

[0177] 13.0 3.85

[0178]

[0179] Table B - numerical values for Fig. 3c

[0180] For Fig. 3c, the operating conditions for the vessel were the same as those described above in relation to Fig. 3a. Again, the vessel was operated at a vessel pressure of 10 Barg ± 0.5 Barg.

[0181] As is clear from this data, at mass flow rates below 3 grams per second, the performance of the vessel (i.e. the COP) is significantly less than that at mass flow rates above 3 grams per second.For instance, a mass flow rate of 3 grams per second is the lowest value at which a COP of greater than 3 (3.07) is achieved. A mass flow rate of 4 grams per second is the lowest value at which a COP of greater 3.5 (3.51) is achieved. At mass flow rates of 8 and above, the COP values are consistently high (with an average of 3.64). Nevertheless, reasonable COP values were still obtained at mass flow rates of between 2 and 3 grams per second, e.g. such that embodiments of the present disclosure may utilise fluid supply at a mass flow rate of at least 2 grams per second, e.g. and even more preferably of at least 3 grams per second.

[0182] As mentioned above, the vessel pressure may influence available values for mass flow rate of fluid supplied to the vessel. In the example of Figs. 3a to 3c, the vessel pressure was 10 Barg ± 0.5 Barg. Use of a lower vessel pressure may facilitate greater mass flow rates to be provided. As such, while the highest value mass flow rate was at 13.0 grams per second, higher mass flow rates may be employed, especially if operating at lower vessel pressures (e.g. at pressures below 10 Barg).

[0183] Electrical conductivity

[0184] The present inventors have identified that the thermal energy output and the operating efficiency for the vessel 1 may be elevated when supplying the vessel 1 with a fluid having an electrical conductivity in a selected range.

[0185] As mentioned above, as electrical energy is applied to the fluid in the internal volume 56 of the vessel 1 using the first electrode 10, bubbles may begin to form in the liquid in the vessel 1. Without wishing to be bound by theory, it is considered that this application of electrical energy to the vessel acts akin to a leaky capacitor (i.e. a capacitor coupled in parallel with a resistor). That is, as a voltage is applied to the first electrode 10, this will act to charge up a capacitor provided between that first electrode 10 and the second electrode 20, with the fluid (and the resistive element 40) between the two electrodes 10, 20 acting as an electrical insulator between two conductive plates of the capacitor. As will be appreciated by one of skill in the art in the context of this disclosure, the electrical conductivity (or electrical resistivity - the two being analogous) of the intervening fluid in the internal volume 56 of the vessel 1 may influence the flow of electrical energy in this leaky capacitor arrangement, i.e. the proportion of current flow to either charge up the capacitor or flow across the resistor.

[0186] Without wishing to be bound by theory, it is considered that, as the electrical conductivity of the fluid increases (i.e. as the fluid is less electrically resistive), more current will flow through the fluid, with less charge building up across the capacitor. In turn, it is considered that this will give rise to a greater proportion of resistive heating (i.e. as per l2R) occurring for the fluid in the internal volume, but with a lower electrical stress being applied across the path from the first electrode 10to the second electrode 20. Additionally, and as mentioned above, it is considered that access to the desired exothermic chemical processes may be facilitated by high levels of electrical stress within the internal volume 56 of the vessel. For instance, it is considered that the gas bubbles (and associated elevated electrical stress levels thereacross) within the fluid in the internal volume may contribute to initiating a sequence of exothermic chemical processes which contribute to the significant thermal energy output from the vessel 1.

[0187] The present inventors have identified that the vessel 1 may be operated at elevated levels (e.g. in terms of efficiency and / or total output) when the electrical conductivity of the fluid in the internal volume 56 of the vessel 1 is at a desired level.

[0188] In particular, and again without wishing to be bound by theory, it is considered that higher levels of electrical conductivity may inhibit the ability of the vessel to generate the desired electrical stress levels between the first and second electrodes 10, 20. Also, by operating with higher electrical conductivity fluids, the risk of an electrical arc occurring within the vessel becomes greater, and this is an undesirable outcome. As such, the present inventors have identified that where the electrical conductivity of the fluid gets too high, the ability of the vessel 1 to reliably create the required electrical stress to initiate the exothermic chemical processes without electrical arcing will be reduced. In other words, at overly elevated levels of electrical conductivity, the vessel may get too close to electrical arcing to achieve the desired voltage stresses across the fluid. In which case, the primary source of heating of fluid within the vessel will arrive from other means, such as resistive heating, rather than through heat release from the desired exothermic chemical processes.

[0189] In particular, the present inventors have identified that desirable electrical conditions within the vessel 1 may be achieved when supplying the vessel 1 with a fluid having an electrical conductivity of or below 5500 micro-Siemens per centimetre (pS / cm).

[0190] The present inventors have identified that, for electrical conductivities above 5500 pS / cm, the operating conditions of the vessel are less preferable to those at below 5500 pS / cm. For instance, without wishing to be bound by theory, it is considered that at electrical conductivities above 5500 pS / cm, the ability of the apparatus to reliably generate a voltage stress large enough to initiate the desired exothermic chemical processes is reduced, especially in view of the elevated risk of electrical arcing occurring associated with those higher electrical conductivity values. Conversely, the present inventors have identified that, for electrical conductivities below 5500 pS / cm, the vessel may reliably generate a voltage stress to access the desired exothermic chemical process without a significantly elevated risk of electrical arcing occurring.Without wishing to be bound by theory, generating the relevant voltage stress and accessing the exothermic chemical processes may remain accessible for lower electrical conductivity values (i.e. for increasingly electrically resistive fluids). For fluids with lower electrical conductivities, the vessel may require larger electrical energy inputs to be used. For instance, as the resistive heating drops (i.e. due to the current being lower), fewer bubbles may be formed within the fluid without a correspondingly greater Voltage being applied. As will be appreciated by one of skill in the art in the context of the present disclosure, operating at increasingly elevated electrical energy levels (e.g. Voltages) may then place further constraints on the design choice for components of the system such as those required to generate and deliver the higher voltage electrical signals to the first electrode 10.

[0191] In view of these potential practical constraints associated with operating the vessel 1 at increasingly elevated electrical energy inputs, the present inventors have identified that it may be preferable to supply the vessel 1 with a fluid having an electrical conductivity at above 1.3 pS / cm, e.g. within an electrical conductivity range of 1.3 pS / cm to 5500 pS / cm. More preferably, the vessel 1 may be supplied with fluid having an electrical conductivity of between 50 and 5500 pS / cm.

[0192] Electrical conductivity examples

[0193] Reference will now be made to Figs. 4a and 4b to demonstrate the influence of electrical conductivity on operation of the vessel 1.

[0194] Fig. 4a is a graph showing the relationship between electrical stress (in Volts per metre) and current (in Log Amps) for different use cases for plasma generation. The selected region of operation for the current technology is indicated in Fig. 4a. As can be seen, this region is towards the higher end in terms of electrical current. Fig. 4a also shows two different breakdown voltages (VB): one for pure (deionised) water at greater than 3 kV and one for tap (mineralised) water at around 1.5 kV.

[0195] As will be appreciated in the context of the present disclosure, when generating a plasma within a fluid, the conductivity of that fluid will govern the relationship between voltage and current. At higher electrical conductivities, the voltage required to generate the desired current will be lower, and at lower electrical conductivities, a higher voltage will be required. The present inventors have identified that operation of the vessel will be improved when operating in the region indicated in Fig. 4a, but without encroaching towards the thermal arcing region. For this, it has been identified that use of a fluid with a conductivity of no more than 5500 pS / cm may facilitate avoiding the overly conductive region (i.e. and converging upon an electrical arc). Similarly, it has been identified that using a fluid with a conductivity of more than 1.3 pS / cm facilitates the desiredplasma-induced chemical processes to be accessed with reasonable voltages being used.

[0196] Fig. 4b shows optical images of the formation of bubbles around the first electrode in response to the application of selected voltages thereto. For the first row, tap water was used as the fluid provided to the vessel, and for the second row, deionised water was used. The tap water had an electrical conductivity of 400 pS / cm and the deionised water had an electrical conductivity of below 1.3 pS / cm, both measured using a conductivity probe. For both liquids, images are shown to demonstrate the bubble formation occurring at 350 V, 650 V, 1000 V, 1500 V and 2000 V. As can be seen, for the tap water, significant bubble formation is occurring, whereas for the deionised water, minimal bubble formation is occurring even at the higher voltages.

[0197] In other words, the present inventors have identified that satisfactory bubble formation (and subsequent plasma-induced chemical processes) may readily occur without requiring unduly high voltages and without overly risking the possibility of electrical arcs when using fluid having an electrical conductivity of between 1.3 pS / cm and 5500 pS / cm, such as between 50 pS / cm and 5500 pS / cm.

[0198] pH

[0199] The present inventors have identified that the thermal energy output and the operating efficiency for the vessel 1 may be elevated when supplying the vessel 1 with fluid having a pH in a selected range.

[0200] As mentioned above, the thermal energy output (and also COP) for the vessel 1 will be increased where the relevant exothermic chemical processes are occurring within the vessel 1. Where the vessel 1 is operated without these exothermic chemical processes occurring, or where they are occurring in relatively small quantities, the thermal energy output from the vessel will be closer in value to the amount of electrical energy being applied to the vessel, i.e. as the majority of the heat generation (or all of the heat generation where no chemical processes are happening) will be due to resistive heating (i.e. I2R heating) for current flowing from the first electrode 10 into the fluid in the vessel 1.

[0201] Without wishing to be bound by theory, it is considered that the minerals within the fluid supplied to the vessel may be utilised (e.g. consumed) as part of the above-mentioned exothermic chemical processes. For this, it is considered that fluids which are more acidic, i.e. which have a lower pH value, will have a lower mineral content. The present inventors have identified that, if the pH is too low (and thus the amount of minerals available to be consumed in these exothermic chemical processes is too low), then this will inhibit the ability of the vessel 1 to operate at elevated levels for thermal energy output and / or COP.Without wishing to be bound by theory, it is also considered that the presence of carbon dioxide molecules (i.e. free CO2) within the fluid may contribute to initiating the desired chemical processes. For instance, it is considered that having more available CO2 molecules will facilitate the initiation of these chemical processes, as these molecules may be separated into their component parts, with further acceleration of these substances, as driven by the electric field differentials across the plasma bubbles, causing a cascade of further chemical processes due to the interaction with these incoming atoms and / or molecules. For this, it is considered that if the pH is too high, i.e. too alkaline, then this may indicate that the amount of CO2 available may be lower than desired. The present inventors have identified that, if the pH is too high (and thus the amount of CO2 available to initiate these exothermic chemical processes is too low), then this will inhibit the ability of the vessel to operate at elevated levels for thermal energy output and / or COP.

[0202] In particular, the present inventors have identified that the thermal energy output and / or COP for operating the vessel 1 may be at elevated levels if the vessel 1 is supplied with a fluid having a pH value of between 5.8 and 7.6, and more preferably with a pH of between 6.3 and 7.1.

[0203] The present inventors have identified that, for pH values below 5.8 and above 7.6, the operating conditions of the vessel are less preferable to those inside this pH range, and that within the range of 6.3 to 7.1 the operating conditions are even more preferable. For instance, at lower pH values (i.e. below this range), the total amount of exothermic processes occurring may be relatively low (or zero), e.g. due to a lack of mineral content. For instance, at higher pH values (i.e. above this range), the lack of CO2 may render it harder for the exothermic chemical processes to initiate. Also, once the exothermic chemical processes are occurring, having an excess amount of minerals present (e.g. at higher pH values) may cause more damage to the vessel 1 and other components of the apparatus, thereby reducing a mean time between failure for the apparatus, e.g. due to corrosion of relevant materials.

[0204] The present inventors have identified that, when supplying the vessel 1 with a fluid having a pH value within the range of 5.8 to 7.6 (and more preferably with a pH of between 6.3 and 7.1), improved operating characteristics may occur, as compared to the use of a fluid with a pH value outside of this range. For instance, the vessel 1 may operate at elevated COP levels, as well as outputting a greater quantity of thermal energy, while still facilitating an easy start up for operation of the vessel 1 and without a significant decrease in the mean time between failure associated with operating the vessel 1.

[0205] The present inventors have identified that the thermal energy output and the operating efficiencyfor the vessel 1 may be elevated when supplying the vessel 1 with fluid having a salinity in a selected range.

[0206] As mentioned above in relation to pH, it is considered that the mineral content of the fluid supplied to the vessel 1 may influence the ability of the vessel 1 to utilise the desired exothermic chemical processes. As mentioned above, it is considered that, at lower levels of mineral content (which correspond to lower pH values), less exothermic chemical processes may take place (and thus lower thermal energy output and COP values may be achieved). Likewise, at higher levels of mineral content (which correspond to higher pH values), the mean time between failure for the system may be reduced, and also this may indicate a shortage of CO2 molecules in the fluid.

[0207] The present inventors have identified that the salinity of the fluid supplied to the vessel may also influence the ability of the apparatus to utilise these exothermic chemical reactions to achieve higher thermal energy outputs and / or COP values. Without wishing to be bound by theory, it is considered that utilising a fluid with too low a salinity may cause a corresponding restriction on the available mineral content to be used in the exothermic chemical processes, and utilising a fluid with too high a salinity may cause a corresponding decrease on the mean time between failure for the vessel 1.

[0208] Additionally, and again without wishing to be bound by theory, it is considered that the salinity level of the fluid supplied to the vessel 1 also plays a similar role to the electrical conductivity (as mentioned above). That is, at higher levels of salinity, the fluid will become increasingly electrically conductive, whereas at lower levels of salinity, the fluid will be come increasingly electrically resistive. As such, the same constraints mentioned above in relation to electrical conductivity may also apply to fluid salinity. That is, for high levels of salinity, the increased electrical conductivity of the fluid within the vessel may make it harder for plasma generation to initiate within the vessel (due to the decreased electrical resistance between the plates of the leaky capacitor), and the risk of electrical arcing may be greater. At low levels of salinity, the increased electrical resistivity of the fluid may place some practical constraints on the electrical supply apparatus, e.g. in order to generate voltages high enough to initiate the plasma generation within the fluid.

[0209] In particular, the present inventors have identified that the thermal energy output and / or COP for operating the vessel 1 may be at elevated levels if the vessel 1 is supplied with a fluid having a salinity value of between 50 parts per million (‘ppm’) and 100 parts per thousand (‘ppt’).

[0210] The present inventors have identified that, for salinity values below 50 ppm and above 100 ppt, the operating conditions of the vessel are less preferable to those inside this salinity range. For instance, at lower salinity values (i.e. below this range), the total amount of exothermic processesoccurring may be relatively low (or zero), e.g. due to a lack of mineral content. In this case, the primary mineral in question being sodium chloride. For instance, at higher salinity values (i.e. above this range), once the exothermic chemical processes are occurring, there may be an excess amount of minerals present which may cause more damage to the vessel 1 and other components of the apparatus, thereby reducing a mean time between failure for the apparatus, e.g. due to corrosion of relevant materials.

[0211] Similarly, the present inventors have identified that at salinity values below 50 ppm, the electrical conductivity of the fluid may be lower, thereby placing undue constraints on the voltages required to initiate the plasma generation. Likewise, at salinity values above 100 ppt, the present inventors have identified that the electrical conductivity of the fluid may be greater rendering it harder to generate the required voltage stresses without an elevated risk of electrical arcing occurring within the vessel.

[0212] The present inventors have identified that, when supplying the vessel 1 with a fluid having a salinity value within the range of 50 ppm to 100 ppt, improved operating characteristics may occur, as compared to the use of a fluid with a salinity value outside of this range. For instance, the vessel 1 may operate at elevated COP levels, as well as outputting a greater quantity of thermal energy, while still facilitating an easy start up for operation of the vessel 1 and without a significant decrease in the mean time between failure associated with operating the vessel 1.

[0213] Control of the apparatus

[0214] As described above, the present inventors have identified preferred values to be used for vessel pressure, mass flow rate, electrical conductivity, pH and / or salinity.

[0215] In some embodiments, components of the apparatus and the fluids to be supplied to the apparatus may selected accordingly so as to utilise these preferred parameter values. For example, one or more selected fluids may be supplied to the vessel 1 which are known to have desired values for electrical conductivity, pH and / or salinity. Likewise, for example, the vessel 1, the fluid supply system 70 and components downstream of the fluid outlet 58 may be designed to utilise mass flow rates and / or pressures at values within the preferred range(s).

[0216] Additionally, or alternatively, embodiments of the present disclosure may include apparatuses and methods for controlling operation of the apparatus so as to utilise these preferred parameter values. In other words, one or more feedback loops may be utilised to control one or more of these parameter values, e.g. so that the parameter value remains within the preferred range of values.Controller and sensors

[0217] For this, the apparatus 1 may include a controller and one or more sensors. The sensor(s) may be configured to obtain an indication of one or more properties of the apparatus and / or the fluid to be supplied to the apparatus. For example, the sensor(s) may be configured to sense a property of the fluid to be supplied to the vessel. As another example, the sensor(s) may be configured to sense a property of the flow of fluid through the vessel. The controller may be configured to obtain an indication of such a parameter value, e.g. to receive data from the sensor about the sensed parameter. The controller may be configured to control operation of one or more components of the apparatus based on the obtained indication of parameter value. For example, the controller may be configured to control the supply of fluid to the vessel (e.g. to control operation of the fluid supply system), to control operation of the electrical energy applied to the first electrode 10 (e.g. to control operation of the electrical supply system) and / or to control operation of any components downstream of the vessel 1.

[0218] Example feedback loops to be used by embodiments of the present disclosure will now be described in relation to each individual parameter value. It will be appreciated in the context of the present disclosure that each individual feedback loop may be used and / or multiple feedback loops may be used together.

[0219] Pressure

[0220] The apparatus 1 may include a pressure regulating system coupled to the fluid outlet 58. The pressure regulating system may comprise one or more pressure release valves, one or more back pressure regulators and / or a steam engine (e.g. with pressure regulator and / or governor) or other such system. The pressure regulating system may be configured to permit an upstream pressure (i.e. a vessel pressure) to be up to a selected value before that system permits the flow of heated fluid therethrough. For example, the pressure regulating system may be set to have a selected pressure of at least 4 Barg, e.g. at a value between 4 and 200 Barg. As such, as the upstream pressure of the pressure regulating system, i.e. the vessel pressure, reaches the selected pressure value, the pressure regulating system may permit the flow of fluid therethrough to maintain the pressure at or close to this selected pressure value. In so doing, the selected pressure value may be selected to avoid the vessel pressure exceeding an upper limit, e.g. 200 Barg.

[0221] The controller may be configured to vary a selected pressure value for this pressure regulating system. Additionally, or alternatively, the controller may be configured to control operation of one or more other components of the apparatus to adjust vessel pressure. For instance, the controller may be configured to adjust the amount of electrical energy applied and / or the flow rate of fluid to be delivered to adjust the vessel pressure. For example, by increasing the amount of electricalenergy applied and / or flow rate of fluid, the vessel pressure may be increased (and vice-versa). The controller may be configured to select these operational parameter values so as to provide the vessel pressure within the selected range of values. For instance, the controller may be configured to determine, based on the obtained indication of vessel pressure, whether any further adjustments of the operating conditions of the apparatus are needed in order to achieve the desired vessel pressure. If such adjustments are needed, then the controller may control operation accordingly so as to move the vessel pressure towards the preferred zone. If not, then the controller may permit continued operation of the vessel without adjusting these parameters to adjust vessel pressure.

[0222] Mass flow rate

[0223] The controller may be configured to control operation of the fluid supply system to adjust the mass flow rate values. For instance, the fluid supply system may comprise one or more pumps for pumping fluid towards and into the vessel. The controller may be configured to control the pumping operation by these pumps to achieve the preferred mass flow rates. For this, the controller may increase pumping to increase flow rate and vice-versa. The controller may be configured to obtain an indication of the mass flow rate being delivered to (or about to be delivered to) the vessel 1. The controller may be configured to determine, based on this mass flow rate, whether or not adjustment of the pump operation is needed. For example, if the obtained indication of mass flow rate is too low, e.g. below 2 (e.g. 3) grams per second, the controller may control the fluid supply system to increase pumping. If the obtained indication is too high, e.g. above 20 grams per second, the controller may control the fluid supply system to decrease pumping. The apparatus may comprise one or more sensors configured to sense a flow rate (e.g. flow meters) which are configured to determine a value for flow rate of liquid being supplied to the vessel, e.g. the fluid supply system may be configured to indicate and control its flow rate.

[0224] In other words, based on the obtained indication of flow rate, the controller may be configured to control operation of the fluid supply system so that the mass flow rate to be delivered to the vessel is within the selected range of preferred values for this parameter.

[0225] Electrical conductivity, pH and salinity

[0226] As will be appreciated in the context of the present disclosure, electrical conductivity, pH and salinity all relate to properties of the fluid itself which is being supplied to the vessel. In some examples, a selected fluid may be used which is known to have the desired properties. This may be used as a standalone fluid, or it may be mixed with one or more other fluids.

[0227] The controller may be configured to obtain an indication of a parameter value for fluid which is to be delivered to the vessel. For example, the fluid supply system may itself have a fluid input (e.g.a constant supply of fluid or a fluid reservoir from which fluid is drawn to be delivered to the vessel). The apparatus may comprise one or more sensors configured to sense the relevant parameter(s) for this fluid which is to be delivered to the vessel (e.g. conductivity, pH and / or salinity). The controller may be configured to obtain an indication of such sensed parameter(s) and to determine whether they are within the selected parameter range. The controller may be configured to permit continued operation where the selected parameter(s) are within their range.

[0228] In the event that the controller determines that the parameter value is either outside the selected range, or getting close to being outside that range, it may determine that the fluid to be supplied to the vessel needs to have one or more such properties adjusted. For example, it may be determined that the conductivity, pH and / or salinity need to be adjusted. For this, the fluid supply system may comprise one or more additional substance stores. The additional substance stores may contain a substance which can be added to the fluid to be supplied to adjust the parameter value accordingly. For example, the fluid supply system may contain a store of one substance which will increase the relevant parameter value and another substance which will decrease the relevant parameter value. The controller may be configured to select which substance is added, and how much is to be added, based on the obtained sensor value.

[0229] For example, for electrical conductivity, minerals may be added to increase the electrical conductivity. The minerals may be in soluble form. These may be added to the existing fluid before being delivered to the vessel. These minerals may be selected to increase the electrical conductivity of the fluid. To decrease the electrical conductivity, the fluid may be diluted, e.g. with a purer version of that fluid. For example, a low mineral content liquid, such as water, may be used. Additionally, or alternatively, fluid which has already passed through the vessel 1 (e.g. which may have subsequently been condensed from a gas such as steam back into a liquid such as water) may be added to the fluid to be supplied to the vessel, e.g. to dilute that fluid. The controller may select which approach is taken, and how much of that approach is to be taken, based on the obtained indication of conductivity.

[0230] For example, for pH, a similar approach may be taken to that above for electrical conductivity. To increase pH, a more alkaline substance may be added. For instance, minerals may be added. To decrease pH, a more acidic substance may be added. For instance, CO2 may be bubbled through the fluid until the fluid is more acidic. Again, the controller may controller which approach is taken, and the extent to which this approach is taken based on the obtained indication of pH for the fluid to be provided to the vessel 1.

[0231] For example, for salinity, a similar approach may be taken. To increase salinity, more salts may be added, and to decrease salinity, the fluid may be diluted with a lower salinity fluid. For instance,varying degrees of saline (e.g. sea water) may be added to increase the salinity, and a purer water or fluid which has already passed through the vessel 1 may be added to decrease salinity. Again, the controller may controller which approach is taken, and the extent to which this approach is taken based on the obtained indication of salinity for the fluid to be provided to the vessel 1.

[0232] It will be appreciated that the particular choice of substance to be added should not be considered limiting. As will be appreciated in the context of the present disclosure, there are a wide number of different substances that could be added to the fluid to adjust one or more of its properties. Some substances may have a larger effect on one, or a few, of these parameters while having less of an effect on one or more other parameters, and some substances may have a similar effect on a number of the parameters. For example, one substance may be added if pH is to be increased, but not conductivity, whereas another substance may be added if both pH and conductivity are to be increased. For example, calcium nitrate may cause a relatively low change to pH while providing a more significant change to conductivity. Alternatively or additionally, other substances such as iron nitrate, sulphuric sulphates and / or nitrates or any other suitable substances may be selected in order to provide the desired adjustment of one or properties of the fluid supplied.

[0233] Alternatives and variants

[0234] In the examples described herein, the fluid itself that is supplied to the vessel from a fluid supply system may have one or more parameters with values in selected ranges, i.e. electrical conductivity, pH and / or salinity. As will be appreciated in the context of the present disclosure, fluid supply systems of the present disclosure may utilise a source of fluid and one or more pumps (or other driving means) in order to supply fluid to the vessel at a chosen flow rate. It will be appreciated that the interaction of such pump(s) with the fluid may have some (minor) influence on one or more of these properties, e.g. the use of a pump may introduce some air into the liquid, thereby potentially adjusting the pH of that liquid. The parameter value of that fluid (e.g. electrical conductivity, pH and / or salinity), as referred to herein, may be measured upstream of such pump(s). For example, the parameter value may be as measured for the source of fluid before that fluid is delivered to the vessel using the pump(s). Of course, it will be appreciated that other locations for measuring the parameter values for fluid to be delivered to the vessel may be used.

[0235] As described herein, each of five different parameter values may be selected to provide improved operation for the plasma generating vessel. It will be appreciated that these parameter values may be selected independently of other parameter values, or any suitable combination of the different parameters may have values selected together. For example, all of the ranges of parameter properties disclosed herein may be provided together in combination, or any particularcombination of value ranges for the different permutations of parameter properties may be utilised.

[0236] As described herein, it will be appreciated that there may be some relationship between these different parameters, and the selection of different parameter values may take account of this fact.

[0237] For instance, parameter values for vessel pressure and mass flow rate may be selected together. For example, the vessel 1 may be operated at a vessel pressure of between 4 and 200 Barg and a flow rate of between 2 (e.g. 3) and 20 grams per second. Preferably, the vessel 1 may be operated at a vessel pressure of between 4 and 20 Barg and a flow rate of between 4 and 20 grams per second (e.g. higher flow rate, lower pressure) or the vessel 1 may be operated at a vessel pressure of between 4 and 200 Barg and a flow rate of between 2 (e.g. 3) and 15 grams per second (e.g. higher pressure, lower flow rate). More preferably, the vessel 1 may be operated at a vessel pressure of between 4 and 10 Barg and a flow rate of between 8 and 20 grams per second.

[0238] For instance, parameter values for 2 or all 3 of: electrical conductivity, pH and salinity may be selected together. For example, the vessel may be supplied with a fluid having an electrical conductivity of no more than 5500 pS / cm and a pH of between 5.8 and 7.6. Preferably, the vessel may be supplied with a fluid having an electrical conductivity of between 1.3 and 5500 pS / cm and a pH of between 5.8 and 7.6 (e.g. between 6.3 and 7.1). More preferably, the vessel may be supplied with a fluid having an electrical conductivity of between 50 and 5500 pS / cm and a pH of between 6.3 and 7.1. The electrical conductivity may be no more than 5500 pS / cm (preferably between 1.3 and 5500, and more preferably between 50 and 5500) with a salinity of between 50 parts per million and 100 parts per thousand. The pH may be between 5.8 and 7.6 (preferably between 6.3 and 7.1) with a salinity of between 50 parts per million and 100 parts per thousand. For instance, the electrical conductivity may be no more than 5500 pS / cm (preferably between 1.3 and 5500, and more preferably between 50 and 5500) with a salinity of between 50 parts per million and 100 parts per thousand, and a pH of between 5.8 and 7.6 (preferably between 6.3 and 7.1). Of course, such parameters for the fluid may be provided in combination with the above-mentioned flow rates (e.g. between 2 (e.g. 3) and 20, preferably between 4 and 20, even more preferably between 8 and 20 grams per second) and / or vessel pressures (e.g. at least 4 Barg, preferably between 4 and 200 Barg, more preferably between 4 and 10 Barg).

[0239] It will be appreciated from the discussion above that the examples shown in the figures are merely exemplary, and include features which may be generalised, removed or replaced as described herein and as set out in the claims. With reference to the drawings in general, it will beappreciated that schematic functional block diagrams are used to indicate functionality of systems and apparatus described herein. In addition, the processing functionality may also be provided by devices which are supported by an electronic device. It will be appreciated however that the functionality need not be divided in this way, and should not be taken to imply any particular structure of hardware other than that described and claimed below. The function of one or more of the elements shown in the drawings may be further subdivided, and / or distributed throughout apparatus of the disclosure. In some examples the function of one or more elements shown in the drawings may be integrated into a single functional unit. As will be appreciated by the skilled reader in the context of the present disclosure, each of the examples described herein may be implemented in a variety of different ways. Any feature of any aspects of the disclosure may be combined with any of the other aspects of the disclosure. For example, method aspects may be combined with apparatus aspects, and features described with reference to the operation of particular elements of apparatus may be provided in methods which do not use those particular types of apparatus. In addition, each of the features of each of the examples is intended to be separable from the features which it is described in combination with, unless it is expressly stated that some other feature is essential to its operation. Each of these separable features may of course be combined with any of the other features of the examples in which it is described, or with any of the other features or combination of features of any of the other examples described herein. Furthermore, equivalents and modifications not described above may also be employed without departing from the invention. Certain features of the methods described herein may be implemented in hardware, and one or more functions of the apparatus may be implemented in method steps. It will also be appreciated in the context of the present disclosure that the methods described herein need not be performed in the order in which they are described, nor necessarily in the order in which they are depicted in the drawings. Accordingly, aspects of the disclosure which are described with reference to products or apparatus are also intended to be implemented as methods and vice versa. The methods described herein may be implemented in computer programs, or in hardware or in any combination thereof. Computer programs include software, middleware, firmware, and any combination thereof. Such programs may be provided as signals or network messages and may be recorded on computer readable media such as tangible computer readable media which may store the computer programs in non-transitory form. Hardware includes computers, handheld devices, programmable processors, general purpose processors, application specific integrated circuits (ASICs), field programmable gate arrays (FPGAs), and arrays of logic gates. Other examples and variations of the disclosure will be apparent to the skilled addressee in the context of the present disclosure.

Claims

49Claims1. A method of operating a plasma generating vessel, wherein the plasma generating vessel comprises:an internal volume configured to receive fluid from a fluid supply system;a first electrode at least partially within the internal volume and configured for receiving electrical energy from an electrical supply system; anda second electrode arranged capacitively with the first electrode, wherein the vessel is configured to use the first electrode to apply electrical energy to fluid within the internal volume and to capacitively couple the first and second electrodes to generate one or more bubbles of plasma within the fluid in the internal volume;wherein the method comprises operating the plasma generating vessel with a vessel pressure of at least 4 Barg.

2. The method of claim 1 , wherein the method comprises operating the plasma generating vessel with a vessel pressure between 4 Barg and 200 Barg.

3. The method of any preceding claim, wherein the method comprises operating the plasma generating vessel with a vessel pressure between 4 Barg and 20 Barg.

4. The method of any preceding claim, wherein the method comprises controlling operation of said electrical supply system to control the application of a voltage to the first electrode, thereby to apply electrical the energy to the fluid in the internal volume and capacitively couple the first and second electrodes to generate the bubbles of plasma within the fluid in the internal volume.

5. The method of any preceding claim, wherein the method comprises controlling operation of said fluid supply system to control the supply of fluid to the internal volume in which bubbles of plasma are to be generated.

6. The method of any preceding claim, wherein the vessel comprises: (i) a fluid inlet for receiving a fluid in which bubbles of plasma are to be generated, and (ii) a fluid outlet for outputting heated fluid from the vessel; andwherein the method comprises controlling at least one of an inlet fluid pressure and an outlet fluid pressure.

7. The method of claim 6, further comprising controlling at least one of the inlet fluid pressure and the outlet fluid pressure thereby to operate the plasma generating vessel with a vessel pressure of at least 4 Barg, optionally thereby to operate the plasma generating vessel with a50vessel pressure of between 4 and 200 Barg, such as between 4 and 20 Barg.

8. The method of claim 6 or 7, further comprising using a pressure regulating apparatus coupled to the outlet of the plasma generating vessel to control the outlet fluid pressure.

9. The method of claim 8, further comprising using the pressure regulating apparatus to control the outlet fluid pressure thereby to operate the plasma generating vessel with a vessel pressure of at least 4 Barg.

10. The method of claim 8 or 9, wherein the pressure regulating apparatus is set to a selected pressure regulation value of at least 4 Barg thereby to operate the plasma generating vessel with a vessel pressure of at least 4 Barg.

11. The method of any of claims 8 to 10, wherein the pressure regulating apparatus comprises a pressure regulator configured to regulate the vessel pressure, optionally wherein the pressure regulator is located downstream of the fluid outlet and is configured to regulate its upstream pressure thereby to regulate the vessel pressure.

12. The method of any of claims 6 to 11 , further comprising using a pump coupled to the inlet of the plasma generating vessel to control the inlet fluid pressure.

13. The method of claim 12, further comprising using the pump to control the inlet fluid pressure thereby to operate the plasma generating vessel with a vessel pressure of at least 4 Barg.

14. The method of any preceding claim, further comprising obtaining an indication of vessel pressure and controlling operation based on the obtained indication thereby to operate the plasma generating vessel with a vessel pressure of at least 4 Barg.

15. A plasma generating vessel comprising:an internal volume arranged to receive fluid from a fluid supply system;a first electrode at least partially within the internal volume and arranged for receiving electrical energy from an electrical supply system; anda second electrode arranged capacitively with the first electrode;wherein the plasma generating vessel is configured to use the first electrode to apply electrical energy to fluid within the internal volume and to capacitively couple the first and second electrodes to generate one or more bubbles of plasma within the fluid in the internal volume; and wherein the plasma generating vessel is configured to operate with a vessel pressure of51at least 4 Barg.

16. The plasma generating vessel of claim 15, wherein the plasma generating vessel is configured to operate with a vessel pressure of between 4 and 200 Barg.

17. The plasma generating vessel of claim 15 or 16, further comprising a pressure regulating apparatus coupled to a fluid outlet from the plasma generating vessel, wherein the pressure regulating apparatus is configured to regulate the vessel pressure to be at least 4 Barg.

18. The plasma generating vessel of claim 16, wherein the pressure regulating apparatus is set to a selected pressure regulation value of at least 4 Barg.

19. The plasma generating vessel of any of claims 15 to 18, further comprising a pump could to a fluid inlet to the plasma generating vessel, wherein the pump is configured to pump fluid to the plasma generating vessel to regulate the vessel pressure to be at least 4 Barg.

20. The plasma generating vessel of any of claims 15 to 19, further comprising a third electrode, wherein the third electrode is at least partially within the internal volume and spaced apart from the first and second electrodes.

21. The plasma generating vessel of claim 20, wherein the first electrode is arranged to provide a conductive path for current to be applied to fluid in the internal volume, the second electrode is arranged to provide a conductive path for carrying current away from the internal volume, and the third electrode is arranged away from a conductive path from the first electrode to the second electrode.

22. The plasma generating vessel of any of claims 15 to 21, further comprising a resistive element provided in the internal volume between the first electrode and the second electrode to increase the electrical resistance of the conductive path therebetween.

23. The plasma generating vessel of any of claims 15 to 22, further comprising a controller configured to obtain an indication of vessel pressure and to control operation based on the obtained indication to operate the plasma generating vessel with a vessel pressure of at least 4 Barg.

24. The plasma generating vessel of claim 23, wherein the controller is configured to increase the amount of electrical energy applied to the first electrode and / or the amount or fluid supplied to the vessel in the event that the obtained indication of vessel pressure is below a lower threshold52value.

25. A computer program product comprising computer program instructions configured to program a controller to control operation of a plasma generating vessel to implement the method of any of claims 1 to 14.

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