Method and device for exciting plasma in situ in high-temperature and high-pressure medium

Abstract

The invention discloses a method and a device for in-situ excitation of plasma in a high-temperature and high-pressure medium, at least one electrode is provided, the surface of the electrode is provided with a micro-nano structure with a tip enhancement effect, and the micro-nano structure is used for improving a local field enhancement factor on the surface of the electrode; placing the electrode in a reaction container filled with an aqueous solution; voltage is applied to the electrode through the power supply, the micro-nano structure generates a local high electric field at the tip of the micro-nano structure under the voltage, electron tunneling emission is caused, liquid phase discharge is triggered, and discharge plasma is generated. Through the electrode with the micro-nano structure on the surface, a local field enhancement factor is improved, so that the electrode can trigger liquid phase discharge under a relatively low potential. Resonance driving or three-phase alternating current input is adopted, and the self-adaptive tuning technology that the dielectric constant of an aqueous solution changes along with temperature and pressure is combined, so that efficient excitation of plasmas in a container is achieved. The method does not need an external heating device, is low in energy consumption and quick in response, and is particularly suitable for efficient heat management in a space limited or linear pipeline heat transfer scene.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of hydrothermal liquefaction, and mainly relates to a method and device for exciting plasma in situ in a high-temperature and high-pressure medium. BACKGROUND

[0002] In the prior art, heating of an aqueous solution is usually mainly dependent on a heat conduction mode. Due to inherent limitations of conduction heating, when the temperature of the aqueous solution in a reaction kettle is relatively high (for example, higher than 300 DEG C), the energy utilization efficiency of the heat conduction method will be significantly reduced, and in general cases, the heating efficiency is difficult to exceed 70%. Taking a fuel boiler as an example, only about 48% of the heat released by fuel combustion is effectively converted into kinetic energy of water molecules through conduction, and the remaining part is lost in the form of heat radiation; at the same time, local high-temperature heating also easily accelerates the aging of the boiler equipment, and there is a risk of causing safety accidents.

[0003] In the electric heating technology, it is known that by adjusting the resonance conditions of the electrode, the surface of the electrode can continue to be pressurized after reaching the charge threshold, and when the electric field intensity exceeds 2 x 10 6 V / m, the excess charge on the surface of the electrode will escape under the action of the electric field, interact with water molecules, and generate discharge plasma. The active particles generated by the discharge diffuse into the aqueous solution through mass transfer, and then increase the average kinetic energy of the water molecules, so that the system crosses the subcritical to supercritical state in turn.

[0004] However, the existing plasma-assisted heating mode usually adopts discharge between two electrodes to realize mass transfer, and is mainly powered at a fixed frequency, which is difficult to adapt to the characteristics that the dielectric constant of the aqueous solution changes with temperature and pressure. For example, the dielectric constant of the aqueous solution at normal temperature and pressure is about 78.3, and at the supercritical state, it will decrease to less than 10, which will cause significant changes in the discharge characteristics and coupling efficiency. Therefore, if the output frequency of the power supply is not dynamically adjusted according to the dielectric constant, the discharge stability and heating efficiency will be affected. In addition, the existing industrial power supply is usually three-phase alternating current, and when it is converted into the required power supply for discharge by using a traditional conversion circuit, the energy consumption and operating cost are inevitably increased. SUMMARY

[0005] In order to solve the problem that the existing technology needs extremely high electric field intensity and breakdown voltage to generate plasma in a liquid phase, the present application provides a method for exciting plasma in situ in a high-temperature and high-pressure medium, comprising:

[0006] providing at least one electrode, the surface of the electrode being provided with a micro-nano structure with a tip enhancement effect, the micro-nano structure being used to increase the local field enhancement factor of the surface of the electrode;

[0007] placing the electrode in a reaction container containing an aqueous solution;

[0008] A voltage is applied to the electrode by a power supply, and the micro-nano structure generates a local high electric field at its tip under the voltage, resulting in electron tunneling emission and initiating liquid-phase discharge to generate discharge plasma.

[0009] Further, the electrode comprises at least one of a tungsten electrode, a tungsten-titanium electrode, a titanium-based oxide electrode of ruthenium and iridium, an iridium electrode, an iridium-tungsten electrode, an iridium-rhenium electrode, or a tungsten-iridium-rhenium electrode, and the electrode spacing is greater than 2 mm. The electrode is selected from electrodes made of conductive, oxidation-resistant, and high-temperature-resistant materials.

[0010] Further, the micro-nano structure comprises at least one of a nanocone array, a concave-convex array, or a slit-like structure.

[0011] Further, the electrode comprises an electrode substrate, a transition layer formed on the electrode substrate, and a functional film layer formed on the transition layer, and the surface of the functional film layer is provided with a micro-nano structure.

[0012] Further, the micro-nano structure is formed on the surface of the functional film layer by at least one of the following methods, including thermal decomposition, sol-gel method, or high-temperature oxidation.

[0013] Further, the material of the transition layer comprises at least one of CrN, TiN, WC, TaC, Cr2N, TiO2, or SnO2.

[0014] Further, the material of the functional film layer comprises a mixture composed of ruthenium oxide and iridium oxide.

[0015] Further, when the micro-nano structure is a nanocone array, the structural parameters of the nanocones in the nanocone array satisfy:

[0016] The structure height is between 100 nm and 150,000 nm;

[0017] The tip radius is between 5 nm and 500 nm.

[0018] Further, the electrode is at least two titanium-tungsten alloy rods with a diameter of 50 mm and a length of 1000 mm, and the surface of the titanium-tungsten alloy rod is prepared with about 1.16×10 13 nanocones, the nanocone height is 25 μm, and the diameter is 125 nm.

[0019] Further, the composition of the solution comprises water, ions, and an organic solution, and the conductivity is greater than 50 μS / cm.

[0020] Further, the output frequency of the power supply is adaptively tuned according to the change of the dielectric constant of the aqueous solution with temperature and pressure. The resonant driving or three-phase alternating current input is adopted, and the adaptive tuning technology of the dielectric constant of the aqueous solution with temperature and pressure is combined to realize efficient excitation of the plasma inside the container.

[0021] In another aspect, the present application also provides a device for in-situ plasma excitation in high-temperature and high-pressure medium, comprising:

[0022] a reaction container;

[0023] at least one electrode arranged in the aqueous solution in the reaction container, the surface of the electrode being provided with micro-nano structures, the micro-nano structures comprising at least one of a nanocone array, a concave-convex array or a slit-shaped structure, for improving the local field enhancement factor of the electrode surface;

[0024] a power supply for applying a voltage to the electrode, forming a local high electric field on the surface of the electrode by the micro-nano structures, causing electron tunneling emission and initiating liquid-phase discharge to generate plasma; and heating the solution by the plasma to make the solution reach a subcritical or supercritical state.

[0025] Further, the device comprises a control unit configured to:

[0026] when the output end of the power supply is a high-voltage end and a ground electrode end, obtaining a first relationship curve of the output frequency changing with temperature;

[0027] when the output end of the power supply is a three-phase power, obtaining a second relationship curve of the output frequency changing with temperature and output voltage;

[0028] dynamically adjusting the output frequency and output voltage of the power supply based on the first relationship curve or the second relationship curve.

[0029] Further, the reaction container comprises at least one of an elongated cylindrical container, a high-depth container or a special-shaped container.

[0030] The technical effect of the present application is to provide a method and device for in-situ plasma excitation in high-temperature and high-pressure medium, by using an electrode with micro-nano structures such as a nanocone array on the surface to improve the local field enhancement factor, so that the electrode can trigger liquid-phase discharge at a lower potential. The resonant driving or three-phase alternating current input is adopted, and combined with the self-adaptive tuning technology of the dielectric constant of the aqueous solution changing with temperature and pressure, to realize efficient excitation of plasma inside the container. This method does not require external heating devices, has low energy consumption and fast response, and is particularly suitable for space-limited or linear pipeline heat transfer fields

[0031] The accompanying drawings, which are incorporated herein and form a part of the specification, illustrate the embodiments and, together with the description, further serve to explain the principles of the application. It will be readily appreciated that other embodiments and many of the intended advantages of the embodiments will be better understood from the following detailed description when considered in connection with the accompanying drawings. The elements in the figures are not necessarily to scale as some components have been exaggerated to facilitate understanding of the embodiments. Like reference numerals in the various drawings indicate like elements.

[0032] Figure 1A flow chart of a method of in-situ plasma excitation in high temperature and high pressure medium according to an embodiment of the present application is shown;

[0033] Figure 2 A curve of the effect of loss rate and local field enhancement factor of RuO2 / IrO2 nanotaper on breakdown potential according to an embodiment of the present application is shown;

[0034] Figure 3 A curve of the change of breakdown potential and local field enhancement factor with temperature of 300 μS / cm aqueous solution according to an embodiment of the present application is shown;

[0035] Figure 4 A curve of the change of breakdown potential and output power with time according to an embodiment of the present application is shown;

[0036] Figure 5 A structure diagram of a device of in-situ plasma excitation in high temperature and high pressure medium according to an embodiment of the present application is shown;

[0037] Figure 6 A schematic diagram of inserting three 2mm-diameter elongated titanium-tungsten electrodes along the pipeline direction in an elongated pipeline for hot water transmission according to an embodiment of the present application is shown;

[0038] Figure 7 A schematic diagram of a nanotaper structure according to an embodiment of the present application is shown;

[0039] Figure 8 A schematic diagram of adding a sub / supercritical reactor heating device in an elongated pipeline for hot water transmission according to an embodiment of the present application is shown. DETAILED DESCRIPTION

[0040] The present application will be further described below in conjunction with the drawings and embodiments. It can be understood that the specific embodiments described herein are only used to explain the related application, and not to limit the application. In addition, it should be noted that only the parts related to the application are shown in the drawings for ease of description.

[0041] It should be noted that the embodiments in the present application and the features in the embodiments can be combined with each other without conflict. The present application will be described in detail below with reference to the drawings and embodiments.

[0042] According to an embodiment of the present application, a method of in-situ plasma excitation in high temperature and high pressure medium is provided, Figure 1 A flow chart of a method of in-situ plasma excitation in high temperature and high pressure medium according to an embodiment of the present application is shown, referring to Figure 1 , comprising:

[0043] S1, providing at least one electrode, a surface of the electrode is provided with a micro-nano structure with a tip enhancement effect, the micro-nano structure is used to improve the local field enhancement factor of the electrode surface;

[0044] Specifically, the electrode includes at least one of platinum, Hastelloy C-276, C-22, Inconel 625, 718, tantalum, carbon-based electrode, glassy carbon electrode, graphite electrode, tungsten electrode, tungsten-titanium electrode, titanium-based ruthenium and iridium oxide electrode, iridium electrode, iridium-tungsten electrode, iridium-rhenium electrode or tungsten-iridium-rhenium electrode, and the electrode spacing is greater than 2 mm. The electrode includes at least one of tungsten electrode, tungsten-titanium electrode, titanium-based ruthenium and iridium oxide electrode, iridium electrode, iridium-tungsten electrode, iridium-rhenium electrode or tungsten-iridium-rhenium electrode, and the electrode spacing is greater than 2 mm. The electrode is selected from electrodes made of electrically conductive, oxidation-resistant and high-temperature-resistant materials.

[0045] Specifically, the micro-nano structure includes at least one of a nano-cone array, a concave-convex array or a slot-like structure, which can significantly improve the local field enhancement factor (β) of the electrode surface, thereby effectively enhancing the local electric field strength. This structure can greatly reduce the inhibitory effect of the exponential term in the Fowler-Nordheim tunneling formula on the current density, achieve lower initial discharge voltage and higher electron emission current density, and significantly improve discharge efficiency and plasma excitation capability.

[0046] The influence mechanism of the micro-nano structure on the local field enhancement factor β can be expressed as:

[0047] Where h represents the structure height of the micro-nano structure (such as a nano-cone), r represents the tip radius of the micro-nano structure (the smaller the sharper), d represents the spacing between the micro-nano structure units, and θ is the cone angle or edge sharpness of the micro-nano structure;

[0048] Specifically, it includes:

[0049] 1) The sharpness of the micro-nano structure, i.e. the curvature radius r, is inversely proportional to the local field enhancement factor β:

[0050] 2) The structure arrangement density of the micro-nano structure, i.e. the smaller the spacing d between the micro-nano structure units, i.e. the closer the cones / cylinders, the stronger the electric field shielding effect, resulting in a decrease in the local field enhancement factor β. A reasonable spacing (usually d≈2h) can maintain a high local field enhancement factor β and avoid mutual interference;

[0051] 3) Array shape: nano-cone > nano-column > micro-groove > smooth surface, wherein the slot and blade structure have a directional enhancement effect.

[0052] Specifically, the electrode comprises an electrode substrate, a transition layer formed on the electrode substrate, and a functional film layer formed on the transition layer, and the surface of the functional film layer is provided with a micro-nano structure, the micro-nano structure is formed on the surface of the functional film layer by at least one of the following methods, including thermal decomposition method, sol-gel method or high-temperature oxidation.

[0053] Specifically, the material of the transition layer comprises at least one of CrN, TiN, WC, TaC, Cr2N, TiO2 or SnO2.

[0054] Specifically, the material of the functional film layer comprises a mixture composed of ruthenium oxide and iridium oxide.

[0055] When the electrode is a tungsten electrode or a tungsten-titanium electrode, the transition layer comprises at least one of titanium oxide and tin oxide, and the functional film layer comprises a mixture composed of ruthenium oxide and iridium oxide.

[0056] A transition layer (chromium nitride (CrN), titanium nitride (TiN), tungsten carbide (WC), tantalum carbide (TaC), Cr2N, TiO2 or SnO2) with a thickness of 1-5 um is prepared on the surface of a tungsten electrode or a tungsten-titanium electrode, and then a RuO2 / IrO2 thin film is prepared; finally, a micro-nano structure (such as a nano-taper array) is constructed, which can be prepared by the following two methods:

[0057] Method one: double-layer structure + anodic oxidation + oxide deposition

[0058] Steps: 1) mechanical polishing of the surface of the tungsten / titanium electrode; 2) if it is a titanium base, anodic oxidation (TiO2 nanopore / taper) is performed; 3) seed treatment is performed on the surface (such as SnO2 deposition); 4) RuO2 / IrO2 thin film is deposited by thermal decomposition method or sol-gel method; 5) taper grain structure (nano-taper array) is formed by high-temperature sintering.

[0059] Method two: laser / plasma induction + oxide growth

[0060] Steps: 1) laser (LIPSS) etches nano-taper skeleton on the surface of W / Ti; 2) Ru / Ir precursor is deposited by vapor deposition (CVD), magnetron sputtering or spray pyrolysis method; 3) high-temperature oxidation → RuO2 / IrO2 taper particle / cluster array is formed; 4) repeated deposition-oxidation cycle can be performed to enhance the structural integrity.

[0061] S2, place the electrode in a reaction container containing an aqueous solution;

[0062] Specifically, the composition of the solution comprises water, ions and organic solution, and the conductivity is greater than 50 μS / cm.

[0063] Further, when the micro-nano structure is a nanocone array, the key structural parameters of the nanocones in the nanocone array and the corresponding effects are shown in Table 1.

[0064] Table 1. Nanocone parameters

[0065]

[0066]

[0067] At this time, the local field enhancement factor β of 30, 100, and 300 under different temperature and pressure breakdown potentials are shown in Table 2:

[0068] Table 2. Gas film thickness and breakdown potential under different temperature and pressure

[0069]

[0070] By comparing Table 1 and Table 2, it can be found that the construction of the conical structure (nanocone and microcone) is conducive to the aggregation of charges and thus conducive to the formation of the gas film, while the breakdown potential is also greatly reduced. Among them, the breakdown voltage of the microcone structure is usually 3000-5000V, which is suitable for medium voltage systems; the breakdown voltage of the nanocone structure can be reduced to 100-300V, which is suitable for plasma excitation; in a supercritical water reactor, the nanocone structure is used to realize low-pressure triggering breakdown and low-power discharge.

[0071] S3, the power supply applies voltage to the electrode, and the micro-nano structure generates a local high electric field at the tip thereof under the voltage, resulting in electron tunneling emission and initiating liquid-phase discharge to generate discharge plasma.

[0072] Specifically, step S3 also uses two-phase output terminals of the power supply, or directly uses three-phase alternating current input, and cooperates with the optimized design of the resonant circuit parameters, so that the electrode system forms a resonant discharge inside the reaction container (such as a reaction kettle or a high-pressure boiler), realizes in-situ plasma excitation, and avoids energy loss and response delay caused by poor power coupling and frequency mismatch in the traditional external heating mode or fixed frequency discharge. It should be noted that, according to the two-phase output terminals of the power supply or the three-phase alternating current input, the change of the resonant frequency f b will be divided into the following two cases:

[0073] When the output terminals of the power supply are high-voltage and ground electrode terminals, i.e., two-phase output terminals, the resonant frequency f b between the capacitance C where L is the self-inductance of the device, and C is the intrinsic capacitance of the device. As the temperature and pressure in the reaction container increase, the self-inductance L of the device is basically unchanged, while the intrinsic capacitance C of the device satisfies C∝ε r , and as the temperature and pressure increase, the dielectric constant ε rAs the capacitance decreases, the amount of electrode charge decreases. As an example, the intrinsic capacitance C of the device satisfies C∝ε. r Such as parallel plate capacitors Where C represents the intrinsic capacitance of the device, ε r ε0 represents the relative permittivity of the medium, and ε0 represents the vacuum permittivity, ε0 = 8.854 × 102 -12 F / m, S represents the effective area of ​​the electrode, and d represents the electrode spacing. It can be deduced that when the power supply output is a two-phase output, the resonant frequency only changes with the temperature and pressure inside the reaction vessel.

[0074] When the power supply output is a three-phase AC input, the resonant frequency is... capacitors in w is the angular frequency, and the angular frequency w satisfies the relationship w = 2πf. g Choose C ab =C bc =C ca C ab C is the capacitance between phase a and phase b. bc C is the capacitance between phase b and phase c. ca Let C be the capacitance between phase C and phase A. Substituting this into the above formula, we can obtain... Substituting the above resonant frequency f g From the formula, we can obtain: Therefore, the resonant frequency f g With line voltage U N Capacitor C ab and inductor L b Inversely proportional, once the device is determined, the inductance L b The changes in temperature, pressure, and current are not significant, f g With external voltage and capacitance C ab The resonant frequency f changes, therefore, when three-phase AC is input. g It is inversely proportional to voltage and directly proportional to temperature and pressure.

[0075] Therefore, this invention utilizes either the two-phase output of a power supply or a three-phase AC input, and incorporates optimized resonant circuit parameters. The specific method includes:

[0076] When the power supply output terminal is the high voltage terminal and the ground terminal, obtain the first relationship curve of the output frequency changing with temperature.

[0077] When the power output is three-phase, obtain the second relationship curve of the output frequency as a function of temperature and output voltage.

[0078] The power supply's output frequency and voltage are dynamically adjusted based on either the first or second relationship curve to maintain the electrode surface charge below the discharge threshold and at its peak. At this point, the output frequency is close to the resonant frequency under the current temperature and pressure. This allows the electrode to increase its output voltage under resonant conditions, breaking down the gas film to generate plasma and subsequently heating the aqueous solution to subcritical / supercritical levels.

[0079] It should be noted that this invention increases the surface charge of the electrode to a threshold through resonance, thereby further increasing the surface potential. This leads to a continued enhancement of the surface electric field, which lowers the Coulomb barrier on the metal surface, causing tunneling. At this point, surface electrons overcome the metal's work function and are emitted from the metal into the aqueous solution. This process conforms to the Fowler-Nordheim field emission theory. Further increasing the surface potential of the electrode accelerates the collisions between electrons and water molecules. When the kinetic energy of the electrons exceeds the ionization energy of the water molecules (approximately 12.6 eV), the electrons ionize the water molecules, releasing new free electrons and positive ions. These newly generated electrons are again accelerated by the electric field, continuing to collide with and ionize surrounding water molecules, forming an exponentially growing ionization chain reaction, thus generating a discharge plasma. The active particles within the plasma rapidly diffuse in the solution, undergoing inelastic collisions with surrounding water molecules, increasing the average kinetic energy of the water molecules and leading them into a subcritical / supercritical state.

[0080] The above analysis shows that an avalanche effect can only occur when the electrode surface charge reaches a threshold and the emitted electron kinetic energy exceeds 12.6 eV. Electrons meeting both conditions can accelerate in an electric field at an energy ΔE. e It is divided into two parts: 1) Threshold charges of the same nature on the electrode surface drive the electric field to accelerate energy E. σ (r); 2) Electron energy E accelerated by electrode surface potential V (r); From this, the total energy of the electrons can be obtained as: E tot (r)=E σ (r)+E V (r), the total energy ΔE gained by electrons during acceleration. e for:

[0081] Where, σ th The threshold charge density is represented by ε0, and the dielectric constant is represented by ε0. The electrode is near the electrode (<500 nm) and is charge-driven. Primarily, electrons are accelerated by potential when leaving the electrode (>500nm), i.e., E V (r) = eV0, and Where ΔE = 12.6 eV, d is the thickness of the gas layer on the electrode surface, and λ is the mean free path, it can be found that the electrode potential needs to be higher than 9500V to break down water molecules and generate discharge plasma. Considering the work function and losses of the metal, the potential on the electrode surface should be greater than 9850V to break down the gas layer on the electrode surface. However, with the increase of temperature and pressure, according to the energy exchange process model between the electrode surface charge and water molecules in the solution, it can be seen that the electron density emitted by the discharge is the key factor determining the formation of the gas film and the thickness d of the gas layer. The thickness of the gas layer can be expressed by the function d = f(σ,V0,T,P,κ,J,β,C). p ,L v ) represents, where σ represents electrical conductivity, V0 represents electrode potential, T and P represent temperature and pressure respectively, κ represents thermal conductivity, J represents current density, β represents local field enhancement factor, and C p , represents the specific heat of water, L v This represents the latent heat of vaporization of water. The emission per unit area per second on the tungsten electrode surface is calculated using Na. e =10 17 m 2 Table 3 shows the air film thickness at / s.

[0082] Table 3. Gas film thickness on the surface of the tungsten electrode under different temperatures and pressures.

[0083]

[0084] As shown in Table 3, the thickness of the gas film layer on the electrode surface first increases, and then thins as the pressure increases, decreasing from 10 μm, 300 μm, 500 μm at room temperature to 100 μm. Based on the gas layer thickness, the corresponding breakdown potential can be calculated, as shown in Table 3. Upon entering the supercritical state, the water clusters decompose into unimolecular molecules, exhibiting gas behavior. At this point, the mean free path can be expressed as... Where D is the diffusion coefficient. The average velocity (which can be expressed as a function of temperature and pressure) is approximately 1 nm. The breakdown voltage is then calculated to be approximately 4800 V. The above calculations show that the breakdown voltage varies under different temperatures and pressures, and a higher voltage is required.

[0085] Therefore, this invention introduces a high-β local field enhancement structure on the electrode surface, and in conjunction with the focusing behavior of ions at the electrode interface, effectively enhances the local electric field strength, enabling the surface micro-regions to preferentially reach the water ionization threshold, thereby achieving stable discharge under an applied voltage significantly lower than the conventional breakdown potential. This method also enhances electron emission, increases free radical yield, and optimizes the energy efficiency of the discharge process.

[0086] E local E represents the local electric field strength on the electrode surface. avgrepresents the average field strength on the electrode surface, and β represents the local field enhancement factor, which is dimensionless. As can be seen from the above formula, the local field strength can be effectively increased by using the local field enhancement factor β when the electrode surface potential V is constant. When E local greater than 10 7 ~ 10 8 V / m, the electrons will be accelerated to have an energy greater than 12.6 eV, so as to generate a discharge plasma. The factors affecting the local field enhancement factor β can be divided into three categories: 1) geometric enhancement: the sharp structure (such as nanotaper, protrusion, crack) on the electrode surface changes the electrode surface distribution (charge is concentrated at the tip), thereby increasing E local 2) charge focusing enhancement: ions are focused near the electrode to form a high-density space charge layer; and 3) thermal field linkage: the electron work function decreases at high temperature (Schottky effect).

[0087] Specifically, the plasma discharge heating process is also an electron bombardment water cluster process, and the emission electron density determines the mass transfer and energy coupling. The emission electron current density J can be described by the Fowler-Nordheim tunneling model, which is represented as:

[0088]

[0089] wherein J represents the current density, E represents the local surface electric field, represents the work function, and A and B are Fowler-Nordheim tunneling model constants. In the experiment, according to the output power 550 KW of the power supply, in combination with the local field enhancement factor β, the breakdown voltage, the temperature and the mean free path parameters, the relationship between the current density and the number and diameter of nanotapers can be obtained as follows:

[0090]

[0091] wherein N represents the number of nanotapers, j cone represents the current density of each nanotaper, S represents the bottom area of each nanotaper, β represents the local field enhancement factor, represents the potential, and when two titanium / tungsten alloy rods with a diameter of 50 mm and a length of 1000 mm are selected as the discharge electrodes, about 1.16 x 10 13 nanotapers with a height of 25000 nm and a diameter of 125 nm are prepared on the surface thereof according to the above relationship.

[0092] It should be noted that the nanotaper structure has certain energy loss mechanisms when discharging in a liquid (such as water or supercritical water) environment. These losses mainly include the coupling behaviors of heat, material, electron, plasma and interface physical processes.

[0093] Table 4. Degradation rate of tungsten-titanium electrode with RuO2 / IrO2 cone coating in liquid / supercritical water

[0094]

[0095] Figure 2 Figure 1 shows the effect of RuO2 / IrO2 nano-cone degradation rate and local field enhancement factor β on breakdown potential according to one embodiment of the present application; from Table 4 and Figure 2 it can be seen that as the nano-cone degrades, the surface degradation rate in liquid / supercritical water gradually increases (from less than 1 nm / min in normal water, 5-10 nm / min in subcritical water and 20-50 nm / min in supercritical water), the local field enhancement factor β gradually decreases, and the breakdown voltage also increases over time, from a few hundred volts to a few thousand volts.

[0096] Figure 2 (a) is a plot of RuO2 / IrO2 nano-cone degradation rate curves under different operating conditions, referring to Figure 2 (a), experiments show that the cone loss is greatly affected by temperature and pressure during discharge, the discharge loss rate under supercritical state at 374°C and 22.1 MPa is about 20 nm / min, at 350°C and 17 MPa is about 10 nm / min, at 320°C and 11.4 MPa is about 5 nm / min, and at 280°C and 6.5 MPa is about 1 nm / min;

[0097] Figure 2 (b) is a plot of the corresponding curves of local field enhancement factor β and breakdown potential, referring to Figure 2 (b), as the cone degrades, the local field enhancement factor β decreases significantly, resulting in an increase in the breakdown potential,

[0098] On the other hand, the increase in temperature and pressure in the reaction vessel will also increase the mean free path of molecules, thereby reducing the breakdown potential. When the mean free path continues to increase in the supercritical state, the breakdown potential further decreases. At this time, the local field enhancement factor β in the above expression of J should be a function of β(T), where T is the temperature, and the temperature and pressure of the reaction vessel satisfy the real van der Waals equation; in addition, the breakdown potential is a function of the mean free path (λ) The above formula becomes:

[0099]

[0100] where ε i represents the ionization energy, d represents the gas layer thickness, e represents the electronic charge, and λ represents the mean free path. Using plasma heating of a 300 μS / cm aqueous solution, the breakdown potential and the local field enhancement factor β as a function of the temperature of the aqueous solution are shown inFigure 3 As shown, from Figure 3 It can be seen that when the local field enhancement factor β is 200, the lowest breakdown voltage is 800V. However, when the aqueous solution is at 374℃ and 22.1MPa, the local field enhancement factor β is 40, and the corresponding breakdown potential increases to 7300V. However, at 390℃ and 30MPa, as the free path of water molecules increases, although the local field enhancement factor β decreases to 30, the corresponding breakdown potential decreases to 6100V.

[0101] The breakdown potential versus time curve under the influence of the local field enhancement factor β and the mean free path λ is shown below. Figure 4 As shown in (a), the corresponding output power versus time curve is as follows: Figure 4 (b) shows the case (with 1.16 × 10¹³ nanocones, each 25000 nm high and 125 nm in diameter). Through Figure 4 It can be seen that 589 kg of water can be heated to 447°C and 92.8 MPa in just 144 minutes. The required energy consumption is 869 kWh of electricity, and the efficiency is...

[0102] Based on the above analysis, this invention effectively enhances the local electric field intensity on the electrode surface by increasing the field enhancement factor β, combined with geometric structure optimization and a charge focusing mechanism. Utilizing the dual output terminals of the power supply, or directly employing three-phase alternating current, and by matching appropriate resonance parameters, in-situ plasma excitation is achieved within the reactor or boiler. This process induces charge accumulation on the electrode surface exceeding the discharge threshold, thereby triggering liquid-phase discharge to form plasma.

[0103] This invention requires no external heating device and can rapidly increase the temperature and pressure of the reaction medium under high temperature and high pressure conditions, achieving rapid entry into the supercritical state. Compared with traditional heating or fixed-frequency discharge methods, this invention has significant advantages such as low energy consumption, fast response, and high coupling efficiency, making it suitable for plasma heating and efficient energy transfer applications in high-temperature and high-pressure reaction environments.

[0104] Once the surface electric field intensity E reaches a critical value, the tunneling emission effect becomes significant, electrons escape rapidly, locally ionizing the surrounding medium and initiating the initial micro-discharge channel. As the applied voltage further increases, the discharge can gradually develop into a macroscopic spark or plasma discharge.

[0105] on the other hand, Figure 5 A structural diagram of an apparatus for in-situ plasma excitation in a high-temperature, high-pressure medium, according to an embodiment of the present invention, is shown, as follows. Figure 5 As shown, the present invention also provides an apparatus for in-situ plasma excitation in a high-temperature and high-pressure medium, comprising:

[0106] Reaction vessel 501;

[0107] At least one electrode 502 is disposed in an aqueous solution within a reaction vessel 501. The surface of the electrode 502 is provided with a micro-nano structure, which includes at least one of a nanocone array, a concave-convex array, or a slit structure, for improving the local field enhancement factor of the surface of the electrode 502.

[0108] Power supply 503 is used to apply voltage to electrode 502, and to form a local high electric field on the surface of electrode 502 using micro-nano structures, so that electrons tunnel out and trigger liquid phase discharge to generate plasma; the plasma heats the solution, so that the solution reaches a subcritical or supercritical state.

[0109] Specifically, the device includes a control unit 504, which is configured to:

[0110] When the output terminal of the power supply 503 is the high voltage terminal and the ground terminal, the first relationship curve of the output frequency changing with temperature is obtained.

[0111] When the output terminal of the power supply 503 is three-phase, a second relationship curve of the output frequency as a function of temperature and output voltage is obtained.

[0112] The output frequency and output voltage of the power supply are dynamically adjusted based on the first or second relationship curve.

[0113] Specifically, the reaction vessel 501 includes at least one of a long and thin cylindrical vessel, a deep vessel, or an irregularly shaped vessel. For space-constrained applications (such as long and thin cylindrical, deep, or irregularly shaped vessel structures), the present invention can arrange a micro discharge electrode 502 in a narrow gap region to trigger local plasma discharge and achieve high-speed heating of a small volume of liquid.

[0114] For details, please refer to Figure 6 Three slender titanium-tungsten electrodes 502, each 2 mm in diameter, were inserted along the pipe's direction in a long, narrow pipe for transmitting hot water. Each electrode 502 was coated with a 5-micron RuO2 / IrO2 film, and the film layer had... Figure 7 The nanocone shown has a diameter of 125 nm and a height of 25,000 nm (density of 10). 14 / m 3 The temperature and pressure inside the pipeline are kept constant through intermittent discharge. The standard for the wall thickness of the high-pressure reactor body is GB150, the standard for the high-temperature and high-pressure through-wall electrode 502 is JB / T10548, and the standard for the nanocone is ISO25178 series (three-dimensional surface structure). The standard for the thickness, life and corrosion resistance of functional films such as IrO2 and RuO2 is GB / T12172 and GB / T 30725-2014 "Noble Metal Oxide Coated Titanium Electrode 502".

[0115] refer to Figure 8In the elongated water heating pipeline, a subcritical / supercritical reactor heating device is added, and the elongated pipeline is heated and pressurized by the pressure and temperature in the reactor. The diffusion coefficient alpha represents the diffusion coefficient, T represents the temperature, t represents the time, v represents the velocity, lambda represents, and rho represents p The pressure c represents the pressure, and gamma represents the adiabatic index. The pressure c represents the pressure, and gamma represents the adiabatic index. s The local sound speed c represents the local sound speed, specifically 1000-1500 m / s, gamma represents the adiabatic index, and x represents the diffusion distance.

[0116] Therefore, the application is suitable for long-distance heat transfer systems (such as water heating pipelines), and can realize continuous heating of water solution in the pipeline to a subcritical or supercritical state by arranging linear electrodes 502 or multi-section distributed discharge devices. Relying on the high-temperature discharge characteristics of plasma and the high thermal conductivity, high density and low viscosity characteristics of critical state water, the water flow rate and heat transfer efficiency are significantly improved, thereby improving the heat transfer capacity and energy utilization efficiency of the entire system, and the application is particularly suitable for efficient heat management and plasma control applications under complex conditions such as energy recovery, pipeline heating and flow reaction.

[0117] The above describes the specific embodiments of the application, but the protection scope of the application is not limited thereto, and any person skilled in the art can easily think of changes or replacements within the technical range disclosed by the application, which should be covered within the protection scope of the application. Therefore, the protection scope of the application should be subject to the protection scope of the claims.

[0118] In the description of the application, it should be understood that the terms "upper", "lower", "inner", "outer" and the like indicate the orientation or positional relationship based on the orientation or positional relationship shown in the drawings, and are only for the convenience of describing the application and simplifying the description, and do not indicate or imply that the devices or elements referred to must have a particular orientation, be constructed and operated in a particular orientation, therefore cannot be understood as a limitation on the application. The word 'includes' does not exclude the existence of elements or steps not listed in the claims. The word 'one' or 'a' in front of an element does not exclude the existence of multiple such elements. The simple fact that certain measures are recorded in mutually different dependent claims does not mean that the combination of these measures cannot be used for improvement. Any reference signs in the claims should not be interpreted as limiting the scope.

Claims

1. A method for in-situ plasma excitation in a high-temperature, high-pressure medium, characterized in that, include: At least one electrode is provided, and the surface of the electrode is provided with a micro / nano structure having a tip enhancement effect, the micro / nano structure being used to improve the local field enhancement factor of the electrode surface; The electrode is placed in a reaction vessel containing an aqueous solution; When a voltage is applied to the electrode by a power source, the micro / nano structure generates a local high electric field at its tip under the voltage, which causes electron tunneling emission and triggers liquid phase discharge, generating discharge plasma.

2. The method according to claim 1, characterized in that, The electrodes include at least one of platinum, Hastelloy, Kronenium, tantalum, carbon-based, glassy carbon, graphite, tungsten, tungsten-titanium, titanium-based ruthenium and iridium oxide electrodes, iridium, iridium-tungsten, iridium-rhenium, or tungsten-iridium-rhenium electrodes, and the electrode spacing is greater than 2 mm.

3. The method according to claim 1, characterized in that, The micro / nanostructure includes at least one of a nanocone array, a concave-convex array, or a slit-like structure.

4. The method according to claim 1, characterized in that, The electrode includes an electrode substrate, a transition layer formed on the electrode substrate, and a functional film layer formed on the transition layer, wherein the surface of the functional film layer is provided with micro-nano structures.

5. The method according to claim 4, characterized in that, The micro / nano structure is formed on the surface of the functional film layer by at least one of the following methods: thermal decomposition, sol-gel method, or high-temperature oxidation.

6. The method according to claim 4, characterized in that, The material of the transition layer includes at least one of CrN, TiN, WC, TaC, Cr2N, TiO2, or SnO2.

7. The method according to claim 4, characterized in that, The material of the functional membrane layer includes a mixture of ruthenium oxide and iridium oxide.

8. The method according to claim 1, characterized in that, When the micro / nano structure is a nanocone array, the structural parameters of the nanocones in the nanocone array satisfy: The structural height is between 100nm and 150,000nm; The tip radius is between 5nm and 500nm.

9. The method according to claim 1, characterized in that, The electrodes are at least two titanium-tungsten alloy rods, each 50 mm in diameter and 1000 mm in length, with a surface texture of approximately 1.16 × 10⁻⁶ mm. 13 A nanocone, the nanocone having a height of 25 μm and a diameter of 125 nm.

10. The method according to claim 1, characterized in that, The solution comprises water, ions, and organic solvent, and has a conductivity greater than 50 μS / cm.

11. The method according to claim 1, characterized in that, Applying voltage to the electrodes via a power source includes: When the output terminal of the power supply is a high voltage terminal and a ground terminal, obtain the first relationship curve of the output frequency changing with temperature. When the output of the power supply is three-phase, a second relationship curve of the output frequency as a function of temperature and output voltage is obtained. Based on the first or second relationship curve, the output frequency and output voltage of the power supply are dynamically adjusted so that the charge on the electrode surface is maintained below the discharge threshold and at its peak value.

12. A device for in-situ plasma excitation in a high-temperature, high-pressure medium, characterized in that, include: Reaction vessel; At least one electrode is disposed in an aqueous solution in the reaction vessel, and the surface of the electrode is provided with a micro-nano structure, the micro-nano structure including at least one of a nanocone array, a concave-convex array, or a slit structure, for improving the local field enhancement factor of the electrode surface; A power source is used to apply voltage to the electrode, and the micro-nano structure is used to form a local high electric field on the surface of the electrode, which causes electron tunneling emission and triggers liquid phase discharge to generate plasma. The solution is heated by the plasma to reach a subcritical or supercritical state.

13. The apparatus according to claim 12, characterized in that, The device includes a control unit, which is configured to: When the power output terminal is a high voltage terminal and a ground terminal, obtain the first relationship curve of the output frequency changing with temperature. When the power supply output terminal is three-phase, a second relationship curve of the output frequency as a function of temperature and output voltage is obtained. The output frequency and output voltage of the power supply are dynamically adjusted based on the first or second relationship curve.

14. The apparatus according to claim 12, characterized in that, The reaction vessel includes at least one of a long, narrow cylindrical vessel, a deep vessel, or an irregularly shaped vessel.

Images