Plasma reactor

Abstract

A plasma reactor for decomposing a hydrocarbon fluid is described that can achieve long-term uninterrupted operation. The plasma reactor includes a reactor chamber and a plasma torch attached to a wall of the reactor chamber, extending into the reactor chamber, and having a free end. The plasma torch includes an inner tubular electrode and an outer tubular electrode at least partially surrounding the inner tubular electrode. A feed lance for dispensing hydrocarbon fluid is disposed within the inner tubular electrode and is movable relative to the tubular electrode. The plasma reactor further comprises a plasma gas outlet disposed between the inner tubular electrode and the outer tubular electrode for distributing a plasma gas, and further comprises an oxidizing fluid outlet for distributing an oxidizing fluid wherein the oxidizing fluid preferably comprises CO2 or H2O, and the oxidation fluid outlet is arranged in the inner tubular electrode.

Description

Field of the Invention

[0001] The present invention relates to a plasma reactor and a method of operating a plasma reactor. Background Art

[0002] Plasma reactors of the prior art for decomposing hydrocarbon fluids are known, wherein these plasma reactors include a reactor chamber and a plasma torch that projects into the reactor chamber and is capable of generating a high temperature exceeding 1000 °C. The hydrocarbon fluid is introduced into the plasma reactor and decomposed into an aerosol of carbon and hydrogen, i.e., an H2 / C carbon aerosol, at the high temperature.

[0003] For example, WO 93 / 12634 describes such a plasma reactor that includes a reactor chamber and a plasma torch attached to the wall of the reactor chamber, projecting into the reactor chamber, and having a free end. The plasma torch includes an inner tube electrode, an outer tube electrode, and a feed lance for dispensing the hydrocarbon fluid, which is disposed within the inner tube electrode. In such a known plasma reactor, there is a problem that carbon deposits grow (scale) at the hydrocarbon fluid inlet, which may clog the inlet. This may lead to electrode damage and method failure. Therefore, various attempts have been made to prevent carbon deposits. However, carbon deposits cannot be avoided, and only a relatively short operating time of the plasma reactor can be achieved. Another problem is that the liquid-cooled feed lance is prone to leakage, which may cause damage to the electrodes and the reactor. Summary of the Invention

[0004] It is an object of the present invention to overcome the above disadvantages, in particular to provide a plasma reactor that can achieve long-term uninterrupted operation. This task is solved by the plasma reactor of claim 1 and the method of operating a plasma reactor of claim 8.

[0005] The above object and other problems are solved by a plasma reactor for decomposing hydrocarbon fluids, which reactor comprises a reactor chamber and a plasma torch, wherein the plasma torch is attached to the wall of the reactor chamber, projects into the reactor chamber and has a free end. The plasma torch comprises an inner tube electrode and an outer tube electrode, the outer tube electrode at least partially surrounding the inner tube electrode. A feed lance for dispensing the hydrocarbon fluid is disposed within the inner tube electrode and is movable relative to the tubular electrode during operation of the plasma reactor by a sliding mechanism. Accordingly, the sliding mechanism is configured to axially move the feed lance during operation when plasma is generated in the plasma reactor. The plasma reactor further comprises a plasma gas outlet for dispensing plasma gas, the plasma gas outlet being disposed between the inner tube electrode and the outer tube electrode, and further comprises an oxidizing fluid outlet for dispensing an oxidizing fluid, wherein the oxidizing fluid preferably comprises CO2 or H2O, and the oxidizing fluid outlet is disposed within the inner tube electrode. The hydrocarbon fluid is preferably a gas and has the composition C n H m , where n and m are integers and n ≥ 1 and m ≥ 2. A plasma gas source is connected to the plasma gas outlet, an oxidizing fluid source is connected to the oxidizing fluid outlet, and a hydrocarbon fluid source is connected to the feed lance. In this arrangement, the dispensed hydrocarbon fluid flows along the inner tube electrode towards the free end of the plasma torch, where plasma is generated during operation. In the absence of oxygen, the hydrocarbon fluid decomposes into a mixture of H2 and C particles, also known as H2 / C carbon aerosol. Some of the C particles may form carbon deposits on the electrodes. On the other hand, graphite or carbon electrodes may corrode or wear under the influence of the plasma or arc between the electrodes during operation.

[0006] On the one hand, moving the feed lance relative to the tubular electrode allows the electrodes to be protected by depositing carbon at various positions on the electrodes, wherein the flow of the hydrocarbon fluid through the feed lance can be controlled to promote carbon deposition.

[0007] On the other hand, if there are too many carbon deposits on the electrodes or the feed lance, the carbon deposits can be reduced by controlling the position of the oxidizing fluid outlet and the flow of the oxidizing fluid therethrough, enabling the oxidizing fluid to reduce or consume the carbon deposits. This keeps the feed channels of the feed lance clear for the hydrocarbon fluid.

[0008] Third, the feed lance can be moved to a cooler region, i.e., the plasma region away from the free end of the electrode, for example at the start and end of operation, or when the electrode becomes short due to wear. Then the worn electrode can be restored to its full length afterwards and the operation time can be extended.

[0009] The inner electrode and the outer tubular electrode each have a hollow internal space, preferably with a circular cross-section. However, the electrodes can have any other cross-section. When the inner electrode is located within the internal space of the outer electrode, a gap is formed between the inner electrode and the outer electrode through which the plasma gas can pass. The electrodes are made of a conductive heat-resistant material capable of withstanding the temperature in the plasma arc environment during operation. The heat-resistant material of the electrodes can be, for example, a metal, a conductive ceramic material, carbon, or graphite, and these materials can also be fiber-reinforced.

[0010] In a first embodiment of the plasma reactor, the oxidation fluid outlet is part of the feed lance. For example, the feed lance has a first outlet for the oxidation fluid and a second outlet for the hydrocarbon fluid. In another embodiment of the plasma reactor, the oxidation fluid outlet is formed by the annular space between the inner tubular electrode and the feed lance, where the oxidation fluid passes between the inner surface of the inner electrode and the outer periphery of the feed lance. The distribution of the oxidation fluid can be switched between two cases for building the electrode with carbon or reducing carbon deposits. This means that the source of the oxidation fluid can be connected to the first outlet for the oxidation fluid or to the annular space between the inner tubular electrode and the feed lance. In both cases, the oxidation fluid is distributed inside the inner tubular electrode, and the above-mentioned positive effects, namely selectively building the electrode with carbon and reducing carbon deposits, can be achieved.

[0011] When the oxidation fluid outlet is part of the feed lance, the plasma torch preferably includes a feed lance formed by an inner tube and an outer tube that at least partially surrounds the inner tube. In this case, the oxidation fluid outlet is formed by the inner tube or by the space between the inner tube and the outer tube. When the oxidation fluid outlet is formed by the inner tube, the oxidation fluid does not directly contact the inner electrode. Advantageously, the inner tube and the outer tube of the feed lance can be relatively moved in their longitudinal directions, so that the nozzle can be positioned at different positions relative to the electrode and relative to the free end of the plasma torch. This allows for better adjustment of the positions of carbon accumulation and degradation. In this case, the sliding mechanism is configured to axially move the inner tube / outer tube of the feed lance during the operation of generating plasma in the plasma reactor.

[0012] If the inner electrode is made of carbon or graphite, the oxidation fluid may affect the inner electrode. In this case, it is advantageous if the oxidation fluid outlet is part of the feed lance and is formed by the inner tube of the feed lance, while the outlet for distributing the hydrocarbon fluid is formed by the space between the inner tube and the outer tube. Thus, the hydrocarbon fluid is inserted like a protective curtain between the electrode and the centrally distributed oxidation fluid.

[0013] In any of the above embodiments, a thermal insulation layer can be selectively provided outside the feed lance or inside the inner electrode to protect these components from the heat of the plasma or the heat from the inner electrode during operation.

[0014] In all of the above embodiments, the feed lance is selectively connected to the inner electrode via at least one conductive element such that the feed lance and the inner electrode have the same potential. By having the same potential, electrical flashover from the electrode to the feed lance is avoided or at least the probability of flashover is reduced. Alternatively, an insulating layer having both electrical insulation and heat insulation properties may be provided on the inner electrode or the feed lance.

[0015] Advantageously, a structure is provided in the feed lance to rotate the injected hydrocarbon fluid stream. Alternatively, a structure is provided in the oxidizing fluid outlet to generate rotation of the oxidizing fluid, particularly CO2 and / or H2O.

[0016] Preferably, the plasma reactor further includes an annular magnet disposed outside the reactor wall at the level of the free end of the electrode. The magnet can generate movement of the arc at the electrode and turbulence of the material in the reactor chamber through the Lorentz force. To enhance this positive technical effect, preferably, a portion of the reactor wall adjacent to the magnet is made of austenitic metal, particularly austenitic steel, stainless steel, or a metal mixture having an austenitic portion. In an embodiment where the inner electrode has a positive potential, the outer electrode has a negative potential, and the free end of the electrode is located on the upper edge of the annular magnet, another technical advantage is achieved because the operation of the arc can be better stabilized. However, in a similar embodiment where the free end of the electrode is disposed on the lower edge of the annular magnet, the inner electrode has a negative potential, and the outer electrode has a positive potential, the operation of the arc can be stabilized in the same manner.

[0017] In an advantageous embodiment, the reactor chamber includes an outlet opposite the plasma torch, and a heat exchanger is directly disposed at the outlet of the reactor chamber. Preferably, the outlet of the reactor chamber is directly merged with the inlet of the heat exchanger. When the plasma reactor is configured to produce a synthesis gas stream containing CO and H2, the heat exchanger is preferably adapted to cool the synthesis gas stream to 800 - 1000 °C, particularly to achieve a temperature range from 1400 - 1200 °C to 200 - 400 °C. This serves as a quenching effect to achieve the fixation of the synthesis gas and avoid reverse reactions. Optionally, the heat exchanger is designed to achieve the cooling of the synthesis gas stream within 1 - 3 seconds, preferably within 2 seconds.

[0018] The above object and other problems are solved by a method of operating a plasma reactor, which, according to one of the above embodiments, includes the following steps:

[0019] Measuring the mass flow rate of the oxidizing fluid or the hydrocarbon fluid stream before distribution within the inner tubular electrode;

[0020] Controlling the distribution of the oxidizing fluid from the oxidizing fluid outlet based on the change in the mass flow rate;

[0021] In operation, carbon may deposit on the inner side of the inner electrode or at the outlet of the feed lance. If the feed pressure is kept constant, the mass flow rate of the oxidizing fluid or the hydrocarbon fluid may vary based on the amount of deposited carbon. The decrease in the mass flow rate will be related to the accumulation of carbon deposits, as the flow cross-section inside the inner tubular electrode is reduced by the carbon deposits.

[0022] Similarly, when carbon deposits accumulate, the inlet pressure of the oxidizing fluid or the hydrocarbon fluid may change while the mass flow rate remains constant. Therefore, the method may include the following steps to achieve the same effect:

[0023] Measure the pressure or pressure history of the oxidizing fluid or the hydrocarbon fluid before distribution inside the inner tubular electrode;

[0024] Control the distribution of the oxidizing fluid from the oxidizing fluid outlet based on the pressure change;

[0025] Or

[0026] Measure the mass flow rate or mass flow rate history of the oxidizing fluid or the hydrocarbon fluid before distribution inside the inner tubular electrode;

[0027] Control the distribution of the oxidizing fluid from the oxidizing fluid outlet based on the mass flow rate change.

[0028] In this method, the distribution of the oxidizing fluid is thus controlled based on the change in the mass flow rate or the pressure at the time of distribution, that is, more oxidizing fluid is provided when the carbon deposits are large; less or no oxidizing fluid is provided when the carbon deposits are small. The oxidizing fluid decomposes the carbon deposits. Therefore, by implementing this method, the above positive effects can be achieved. In addition, when there are very high temperatures, radiation, and other extreme conditions in the reactor chamber during operation, measuring the mass flow rate provides feedback on the state of the electrode, the oxidizing fluid outlet, and the feed lance, as well as feedback on the accumulation or degradation of carbon deposits, which was not possible to obtain before.

[0029] In the first embodiment of this method, the step of distributing the oxidizing fluid is carried out through the outlets in the feed lance, such as through the first outlet for the oxidizing fluid and the second outlet for the hydrocarbon fluid. In the second embodiment of this method, the step of distributing the oxidizing fluid is carried out through the annular space between the inner tubular electrode and the feed lance, where the oxidizing fluid passes between the inner surface of the inner electrode and the outer periphery of the feed lance. In the third embodiment of this method, the hydrocarbon fluid and the oxidizing fluid are distributed through a single or common pipe of the feed lance, (a) alternately in time (first the hydrocarbon fluid, then the oxidizing fluid through the same pipe, and vice versa), or (b) mixed together. In all cases, the oxidizing fluid can remove the carbon deposits, thus keeping the hydrocarbon fluid feed channel unobstructed.

[0030] Additionally, the method may include the step of variably mixing a hydrocarbon fluid, CO2, and / or H2O based on the measured wear amount of at least one tubular electrode. Further, the hydrocarbon fluid, CO2, and / or H2O may be variably mixed based on the measured amount of solid deposits (i.e., solid carbon deposits) on at least one tubular electrode. For example, the amount of wear or solid deposits may be measured optically, e.g., by laser, camera, or other known optical methods.

[0031] Preferably, the feed lance is axially displaced relative to the inner tubular electrode based on the mass flow rate or pressure change of the feed. Similarly, the oxidation fluid outlet may be axially moved relative to the inner tubular electrode.

[0032] In one embodiment, the step of dispensing the oxidation fluid is carried out through an outlet that is part of the feed lance, and the feed lance includes an inner tube and an outer tube that at least partially surrounds the inner tube. In this case, the first version of the method provides the steps of passing the oxidation fluid through the inner tube and passing the hydrocarbon fluid through the space between the inner tube and the outer tube. The oxidation fluid then keeps the inner tube unobstructed, and the hydrocarbon fluid passes near the inner electrode. In the second version of the method, this embodiment of the feed lance provides the step of passing the oxidation fluid through the space between the inner tube and the outer tube. The oxidation fluid then passes near the inner electrode and can rapidly reduce the carbon deposits on the electrode.

[0033] In any of the above embodiments of the method, when no hydrocarbon fluid is introduced, a cooling gas having a temperature lower than that of the inner tubular electrode may be introduced through the feed lance. As an example, the temperature of the cooling gas may be lower than 700 °C, preferably lower than 550 °C, since the temperature of the inner tubular electrode is higher. The cooling gas replaces the cooling effect of the hydrocarbon fluid and prevents cracking or other damage to the electrode and the feed lance caused by temperature changes.

[0034] Furthermore, in all of the above method embodiments, the pressure inside the reactor chamber may be adjusted to be within the range of 10 to 30 bar. Similarly, in all of the above method embodiments, the temperature at the inlet of the heat exchanger may be adjusted to 1100 - 1300 °C, preferably adjusted to 1200 °C. These measures improve the output of the plasma reactor. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] The present invention and its further details and advantages are explained below with reference to the exemplary preferred embodiments shown in the figures.

[0036] Figure 1 Shown is a plasma reactor for decomposing a hydrocarbon fluid, the plasma reactor including a reactor chamber and a plasma torch;

[0037] Figure 2 ForFigure 1 Magnified detail A of the plasma torch;

[0038] Figure 3 is Figure 1 Magnified detail A of the plasma torch in operation; and

[0039] Figure 4 is Figure 1 the separating electrode of the plasma torch. Detailed description of the specific implementation

[0040] In this description, the terms "upper", "lower", "right", and "left" and similar indications refer to the directions or arrangements shown in the figures and are only used to describe the embodiments. These terms may represent preferred arrangements, but should not be understood in a limiting sense. Among other things, Figure 1 the plasma reactor shown can be installed in different orientations, such as tilted or horizontal. In addition, the terms "substantially", "about", "approximately" and similar expressions mean that a deviation of + / - 10%, preferably + / - 5% from the stated value is allowed. In the context of this description, the term hydrocarbon fluid refers to a fluid (gas, aerosol, liquid) containing hydrocarbons, such as natural gas, methane, liquefied petroleum gas, biogas, or liquid atomized hydrocarbons or mixtures thereof.

[0041] The plasma reactor 1 according to the present disclosure includes a reactor chamber 2 surrounded by a reactor wall 3, which reactor wall 3 includes a lower part 3a and a lid 3b. The reactor chamber 2 can also be separated at a position different from Figure 1 that shown. The reactor chamber 2 is substantially cylindrical and has a central axis 4. The plasma torch 7 is attached to the reactor wall 3 (here attached to the lid 3b), which includes an elongated electrode (shown in more detail in Figure 2 and 3 ). The plasma torch 7 can be attached to the reactor wall 3 by means of an electrode holder or a plasma torch holder (not shown). In Figure 1In the example, the lid 3b serves as an electrode support, but additional electrode supports can be provided on the lid 3b. The plasma torch 7 includes a base 9 attached to the reactor wall 3 (to the lid 3b or the electrode support). The plasma torch 7 includes a torch portion 11 at the other end opposite to the base 9, and the torch portion 11 has a free end 12 of the electrode that extends into the reactor chamber 2. The plasma 13 is formed between and outside the electrodes by a plasma gas and an electric arc. An annular magnet 14 is provided on the outer side of the reactor wall 3 at the height of the free end 12 of the electrode and affects the electric arc by magnetic force. The magnet 14 can generate the movement of the electric arc on the electrode and the vortex of the material in the reactor chamber 2 through the Lorentz force. To enhance this positive effect, a part of the reactor wall 2 can be made of an austenitic metal, in particular austenitic steel, stainless steel, or a metal mixture with an austenitic content. In a first further improvement, the free end of the electrode is located at the upper edge of the annular magnet, the inner electrode has a positive potential, and the outer electrode has a negative potential. In a second further improvement, the free end of the electrode is located at the lower edge of the annular magnet, the inner electrode has a negative potential, and the outer electrode has a positive potential. Through the combination of these two electrode potentials and the magnet position, the force fields of the magnet and the electric arc are added together to better stabilize the operation of the electric arc.

[0042] At the other end of the reactor chamber 2, opposite to the plasma torch 7, the plasma reactor 1 includes an outlet 15 through which the substances generated by the decomposition of the injected hydrocarbon fluid can escape. The outlet 15 is provided at the opposite end of the reactor chamber 2 in the flow direction and can be larger or smaller than that shown in the figure. However, for the sake of easy distinction, Figure 1 the outlet 15 shown in the figure is smaller than the reactor chamber. Optionally, a secondary outlet 16 can be provided at the lower end of the reactor chamber 2. The heat exchanger 17 is directly provided at the outlet 15 of the reactor chamber 2. Preferably, the outlet 15 is directly merged into the inlet of the heat exchanger 17. Since the plasma reactor 1 is configured to generate a synthesis gas stream containing CO and H2, the heat exchanger 17 is designed to cool the synthesis gas stream by 800 to 1000 °C, especially by 1400 - 1200 °C, so that the synthesis gas at the outlet of the heat exchanger 17 is within the temperature range of 200 - 400 °C. This arrangement serves as quenching (the stage and step of cooling), thereby fixing the synthesis gas and avoiding reverse reactions. For example, the heat exchanger 17 is a tubular heat exchanger with multiple interconnected stages. Here, the heat exchanger 17 is designed to achieve the cooling of the synthesis gas stream within 1 - 3 seconds, preferably within 2 seconds.

[0043] The reactor chamber 2 may also have an enlarged flow cross-section that increases (measured perpendicular to the longitudinal extension of the second reaction chamber) between the upper end (at the cover 3b) and the outlet 15. Advantageously, the reactor chamber 2 does not include a substantial reduction in the flow cross-section between the upper end and the outlet 15. In particular, the reactor chamber 2 may expand conically to provide a continuous and uniform increase in the flow cross-section. However, a stepped increase or, for example, several different conical expansions may also be provided. However, such an enlarged flow cross-section may remain the same within a relatively small range compared to the length (less than about 10%).

[0044] Figure 2 An enlarged detail A of the torch part 11 at the free end of the plasma torch 7 is shown. The plasma torch 7 includes an inner electrode 18 and an outer electrode 20 surrounding the inner electrode 18 (see Figure 3 ). The electrodes 18 and 20 each have a hollow interior, which has a circular cross-section in the example shown. When the inner electrode 18 is disposed within the inner space of the outer electrode 20, a gap 24 is formed between the electrodes 18 and 20 ( Figure 3 ). That is, the electrodes 18 and 20 are arranged as if they were tubes assembled together. The electrodes 18 and 20 are made of a conductive heat-resistant material (metal, conductive ceramic material, carbon, or graphite) capable of withstanding the temperature of the plasma arc during operation. For the following description, it is assumed that the electrodes 18 and 20 are made of carbon or graphite.

[0045] The gap 24 between the inner electrode 18 and the outer electrode 20 is connected to a plasma gas source (not shown), thereby forming a plasma gas outlet for distributing the plasma gas to the reactor chamber 2. A valve is provided between the plasma gas source and the gap 24, and the distribution of the plasma gas can be controlled by the valve.

[0046] The plasma torch 7 also has a feed lance 22 for distributing a hydrocarbon fluid to the reactor chamber 2. The feed lance 22 is disposed inside the inner electrode 18, i.e., in its hollow inner space 19, and is movable relative to the tubular electrode. Optionally, an electrically insulating and thermally insulating layer (not shown) may be provided outside the feed lance 22 or inside the inner electrode. The feed lance 22 may include structures such as guide vanes or inclined nozzles for rotating the introduced hydrocarbon fluid. Alternatively, a guiding structure with a similar effect is provided in the oxidation fluid outlet to generate rotation of the oxidation fluid, particularly CO2 and / or H2O. The feed lance 22 is connected to a hydrocarbon fluid source (not shown).

[0047] The plasma torch 7 also has an oxidation fluid outlet for distributing an oxidation fluid. The oxidation fluid outlet is located inside the inner electrode and is connected to an oxidation fluid source. The oxidation fluid is suitable for oxidizing carbon and preferably includes CO2 or H2O.

[0048] In a first embodiment of the plasma torch 7, the oxidizing fluid outlet is formed by an annular gap 23 between the inner electrode 18 and the feed lance 22. Herein, the oxidizing fluid is simply directed between the inner side of the inner electrode and the outer periphery of the feed lance. This embodiment has the advantage that carbon deposits on the inner surface of the inner electrode 18 can be rapidly dissolved (i.e., oxidized). However, preferably, the annular gap 23 is connected to a source of plasma gas that does not oxidize or otherwise degrade the inner surface of the inner electrode 18.

[0049] In Figure 2 and 3 In a second embodiment of the plasma torch 7 as shown, the oxidizing fluid outlet is part of the feed lance 22 and has a first outlet 25 for the oxidizing fluid and a second outlet 26 for the hydrocarbon fluid. The feed lance 22 is formed by (among other things) an inner tube 28 having an internal space 29 and an outer tube 30 surrounding the inner tube 28. Thus, an intermediate space 31 is formed between the inner tube 28 and the outer tube 30. This second embodiment of the plasma torch 7 again provides a variety of operating modes (A), (B), and (C), which can also be applied in chronological order.

[0050] First operating mode (A)

[0051] In Figure 2 and 3 In the arrangement shown, the oxidizing fluid passes through the internal space 29 of the inner tube 28 such that the internal space 29 forms the outlet for the oxidizing fluid. The hydrocarbon fluid passes through the intermediate space 31 between the inner tube 28 and the outer tube 30 such that the intermediate space 31 forms the outlet for the hydrocarbon fluid. In operation, the hydrocarbon fluid flows between the inner electrode 18 and the centrally distributed oxidizing fluid such that the oxidizing fluid does not directly contact the inner electrode 18. When operating with an electrode made of carbon or graphite, this operating mode (A) has the effect that the oxidizing fluid does not overly degrade the inner electrode 18.

[0052] Second operating mode (B)

[0053] In Figure 2 and 3In the arrangement shown, the hydrocarbon fluid passes through the internal space 29 of the inner tube 28 such that the internal space 29 forms the outlet 26 for the hydrocarbon fluid. The oxidizing fluid passes through the intermediate space 31 between the inner tube 28 and the outer tube 30 such that the intermediate space 31 forms the outlet for the oxidizing fluid. In operation, the oxidizing fluid flows between the inner electrode 18 and the centrally distributed hydrocarbon fluid such that the hydrocarbon fluid does not come into direct contact with the inner electrode 18. This mode of operation (B) has the effect that carbon deposits on the inner side of the inner electrode 18 can be rapidly dissolved (i.e., oxidized). Compared with mode of operation (A), there is also an effect that the carbon particles of the H2 / C aerosol cannot be deposited on the inner electrode 18 so easily.

[0054] The feed lance 22 is movable in the direction of the central axis 4 relative to the tubular electrodes 18, 20. In particular, the feed lance 22 is movable relative to the inner electrode 18. In addition, the inner tube 28 and the outer tube 30 of the feed lance 22 are movable relative to each other. For example, Figure 3 the inner tube 28 in Figure 2 protrudes from the outer tube 30, while

[0055] A third mode of operation (C)

[0056] The hydrocarbon fluid and the oxidizing fluid can be distributed through a single or common pipe of the feed lance, (a) alternately in time (first the hydrocarbon fluid and then the oxidizing fluid pass through the same pipe and vice versa), or (b) mixed together, although this is not shown in the figure.

[0057] Optionally, at least one of the tubular electrodes 18, 20 includes tubular segments 34 separated in the longitudinal axis direction of the electrodes 18, 20. The tubular segments 34 are shell-shaped and together form the electrodes 18, 20. When the cylindrical tubular electrodes 18, 20 are cut twice in their longitudinal axis direction, two shell-shaped tubular segments 34 are formed, each of which extends 180° and they are separated by two longitudinal grooves. In Figure 4 is shown a cylindrical tubular electrode 18, 20 which is cut three times in its longitudinal axis direction (see the longitudinal grooves 35), thereby producing three shell-shaped tubular segments 34, each of which extends 120°, and which form the tubular electrode 18 or 20 in the assembled state. The shell-shaped tubular segments 34 are in close contact with each other such that the longitudinal grooves 35 are very small to allow as little or no gas (i.e., plasma gas) to escape between the tubular segments 34. For example, the shell-shaped tube segments 34 can abut against each other smoothly, can include tongue-and-groove interfaces, or can include labyrinth seals.

[0058] Alternatively, at least one of the tubular electrodes 18, 20 comprises annular tubular members (not shown in the figures) arranged in a row. The annular tubular members can be connected to each other, for example, by gluing, screwing or plugging. When three annular tubular members are arranged in a row, the entire tubular electrode is formed by connecting the first, second and third annular tubular members together by screwing or plugging. In this case, the first tubular member is located at the free end 12 of the plasma torch 7, the second tubular member is located in the middle, and the third tubular member is located at the end of the plasma torch 7, where this end is attached to the reactor chamber 2 (for example, attached to the cover 3b or the electrode holder).

[0059] The shell-shaped tube section 34 or the annular tubular member helps to compensate for the difference in thermal expansion. By adding an annular tubular member, the electrode length can also be maintained within a certain range when the electrodes 18, 20 are worn in the arc region. In addition, the components of the electrodes 18, 20 can be replaced, which is useful for electrodes made of carbon or graphite. The shell-shaped tube section 34 or the annular tubular member can be fixed by mounting elements, for example by pins, especially pins made of carbon or graphite.

[0060] In operation, the above-described plasma reactor 1 generally operates according to the following method for decomposing hydrocarbon fluids.

[0061] The plasma gas is distributed between the inner tubular electrode 18 and the outer tubular electrode 20, and a part of the plasma gas that meets the arc between the electrodes is excited to form the plasma 13. The plasma 13 is formed near the torch part 11, and the average temperature of the plasma gas exceeds 2500 °C after passing through the arc, but locally it may reach a higher temperature of up to 4900 °C. In particular, if the plasma torch 7 uses carbon or graphite electrodes, as assumed here, a part of the electrodes 18, 20 may be eroded due to the high temperature and the electric spark of the arc.

[0062] The hydrocarbon fluid (preferably natural gas or methane) is distributed inside the inner tubular electrode 18. At the high temperature of the reactor chamber 2, since there is no oxygen in the reactor chamber 2, the hydrocarbon fluid decomposes into hydrogen (H2 gas) and carbon (C particles). The carbon and hydrogen escape from the inner space 19 of the inner electrode 18 in the form of an H2 / C aerosol and flow towards the outlet 15 in the direction of the central axis 4. Part of the H2 / C aerosol can be removed through the optional outlet 16.

[0063] Part of the carbon produced may deposit on the surrounding components and may form solid carbon deposits. In particular, the internal space 19 of the inner electrode 18 and the feed channels of the feed lance 22 may be covered with carbon deposits and may even be completely blocked. This changes the operating characteristics. As the carbon deposits grow, the remaining flow cross-sections of the internal space 19 and the feed channels of the feed lance 22 (i.e., the internal space 29 and the intermediate space 31) become smaller. As a result, the inflow of the oxidizing fluid and / or the hydrocarbon fluid is throttled and the mass flow rate decreases. If a significant decrease in the mass flow rate is measured, this indicates a large amount of carbon accumulation. If the change in the mass flow rate is small, this indicates no or little carbon accumulation.

[0064] To maintain a constant mass flow rate, the feed pressure of the oxidizing fluid and / or the hydrocarbon fluid can be increased first to keep the mass flow rate the same.

[0065] If increasing the feed pressure is not advisable or insufficient to counteract the throttling effect, the oxidizing fluid (CO2 or H2O) is distributed inside the inner tubular electrode 18. Alternatively, or in addition, the feed lance can be axially moved relative to the inner tubular electrode in response to the change in the mass flow rate. The oxidizing fluid may oxidize carbon to form carbon monoxide (C + CO2 -> CO) or syngas (C + H2O -> CO + H2) at the high operating temperature of the reactor chamber 2. In addition, the feed lance is cooled by the hydrocarbon fluid and the oxidizing fluid.

[0066] In Figure 2 and 3 the feed lance includes an inner tube 18 and an outer tube 20, which allows the above operating modes (A), (B), and (C).

[0067] Operating mode (A) The oxidizing fluid passes through the internal space 29 of the inner tube 28, and the hydrocarbon fluid passes through the intermediate space 31 between the inner tube 28 and the outer tube 30.

[0068] Operating mode (B) The hydrocarbon fluid passes through the internal space 29 of the inner tube 28, and the oxidizing fluid passes through the intermediate space 31 between the inner tube 28 and the outer tube 30.

[0069] Operating mode (C) The hydrocarbon fluid and the oxidizing fluid can be distributed through a single or common pipe of the feed lance, (a) alternately in time (first the hydrocarbon fluid and then the oxidizing fluid through the same pipe and vice versa), or (b) mixed together, although this is not shown in the figure. When doing so, the pipe orifice can be moved to the position where carbon deposits need to be removed or added.

[0070] The process of distributing (i.e., controlling the mass flow rate and the feed pressure) the oxidizing fluid is controlled according to the operating conditions of the plasma reactor 1.

[0071] - When there is a large amount of carbon deposit, a large amount of oxidation fluid is dispensed.

[0072] - When there is little or no carbon accumulation, little or no oxidation fluid is dispensed. Thus, the oxidation fluid does not have to be dispensed continuously, but can be dispensed intermittently.

[0073] - If the graphite or carbon electrode shows severe erosion, it may be necessary to deposit carbon on the electrode, and in this case little or no oxidation fluid is also output. In addition, the first operating mode (A) is advantageous in this case because the hydrocarbon fluid passes through the intermediate space 31 between the inner tube 28 and the outer tube 30, i.e., close to the inner electrode 18.

[0074] - If a severe reduction in mass flow is detected at one of the outlets 25 or 26 of the feed lance 22, the oxidation fluid can be dispensed specifically through the affected outlet 25 or 26.

[0075] In addition, the variable mixing of the hydrocarbon fluid, CO2, and / or H2O can be based on the measured wear of at least one tubular electrode or on the amount of solid deposit (i.e., solid carbon deposit) measured on one of the tubular electrodes. For example, the wear or the amount of solid deposit can be measured optically, e.g., by laser, camera, or other known optical methods.

[0076] In all embodiments of the method described above, the plasma gas can be discharged through the annular gap 23 between the inner tubular electrode 18 and the feed lance 22 to blow away the C particles on the inner electrode 18.

[0077] In all embodiments of the method described above, when no hydrocarbon fluid is dispensed, a cooling gas having a temperature lower than that of the inner electrode 18 can be conveyed through the feed lance 22. In addition, in all embodiments of the method described above, the feed lance can be axially moved relative to the inner tubular electrode. In either case, when the cooling effect of the hydrocarbon fluid is eliminated, the feed lance 22 can be protected from thermal damage. During start-up and shutdown of the operation, it may be beneficial to introduce the cooling gas.

[0078] In addition, the flow characteristics and turbulence of the fluid dispensed through the feed lance 22 can be affected by a combination adjustment of (i) the axial position of the feed lance 22, (ii) the amount or pressure of the dispensed fluid, and (iii) the amount or pressure of the plasma gas dispensed through the annular gap 23.

[0079] In all embodiments, any suitable gas or gas mixture can be selected as the plasma gas, which is supplied externally to the plasma reactor or generated in the plasma reactor 1. By way of example, an inert gas is suitable as the plasma gas, such as argon or nitrogen. On the other hand, H2, CO or synthesis gas are suitable gases since these gases are generated anyway during hydrocarbon decomposition.

[0080] In all embodiments, the plasma reactor 1 can have further inlets for CO2 or H2O (not shown in the figures), which are arranged between the plasma torch 7 and the outlet 15 in the direction of the central axis 4, i.e., in the flow direction of the H2 / C aerosol. These further inlets for CO2 or H2O are far enough away from the plasma torch 7 in the direction of the central axis 4 such that the temperature exceeds 1200 °C and preferably far enough away such that more than 90% of the supplied hydrocarbon fluid decomposes into the H2 / C aerosol. In this case, the amount of CO2 or H2O supplied to the reactor chamber 2 through the further inlets for CO2 or H2O is preferably greater than the amount of oxidizing fluid supplied through the feed lance 22. However, for simple embodiments, it is also possible to supply the entire amount of oxidizing fluid (CO2 and / or H2O) required for the process in the plasma reactor 1 through the feed lance 22.

[0081] Furthermore, in all embodiments of the method described above, the pressure in the reactor chamber can be adjusted to a range of 10 to 30 bar. Similarly, in all of the above-described embodiments of the method, the temperature at the inlet of the heat exchanger can be adjusted to 1100 - 1300 °C, preferably 1200 °C.

[0082] The concepts described here have been described in connection with a plasma reactor for decomposing hydrocarbon fluids, but can also be applied to other plasma reactors and plasma torches whose operation is affected by deposits on the electrodes or the outlet.

[0083] The invention has been described with reference to preferred embodiments, in which the individual features of the described embodiments can be freely combined and / or interchanged, provided they are compatible. Similarly, the individual features of the described embodiments can be omitted, provided they are not absolutely necessary. For a person skilled in the art, numerous variations and embodiments are possible and obvious within the scope of the wording of the claims.

Claims

1. A plasma reactor (1) for decomposing hydrocarbon fluids, comprising: A reactor chamber (2) and a plasma torch (7) attached to the wall of the reactor chamber (2), protruding into the reactor chamber (2) and having a free end (12); The plasma torch (7) includes an inner tubular electrode (18) and an outer tubular electrode (20), and the outer tubular electrode (20) at least partially surrounds the inner tubular electrode (18), A feed spray gun (22) for distributing the hydrocarbon fluid, which is arranged inside the inner tubular electrode (18) and is movable relative to the tubular electrodes (18, 20) through a sliding mechanism; A plasma gas outlet for distributing plasma gas between the inner tubular electrode (18) and the outer tubular electrode (20); An oxidation fluid outlet for distributing the oxidation fluid, Wherein the oxidation fluid preferably includes CO2 or H2O, Wherein the oxidation fluid outlet is arranged inside the inner tubular electrode (18).

2. The plasma reactor (1) according to claim 1, wherein the oxidation fluid outlet is a part of the feed spray gun (22), or the oxidation fluid outlet is formed by a gap (23) between the inner tubular electrode (18) and the feed spray gun (22).

3. The plasma reactor (1) according to claim 2, wherein a structure is arranged in the feed spray gun (22) or in the oxidation fluid outlet, and its shape is used to generate turbulence of the distributed hydrocarbon fluid, CO2 and / or H2O.

4. The plasma reactor (1) according to any one of the preceding claims, wherein the feed spray gun includes an inner tube and an outer tube, the outer tube at least partially surrounds the inner tube, and the oxidation fluid outlet is formed by the inner tube or by the space between the inner tube and the outer tube of the feed spray gun.

5. The plasma reactor (1) according to any one of the preceding claims, wherein the feed spray gun is connected to the inner electrode through at least one conductive element; Or an insulating layer is arranged on the inner electrode or on the feed spray gun, and the insulating layer is both electrically insulating and thermally insulating.

6. The plasma reactor (1) according to any one of the preceding claims, including an annular magnet (14), arranged outside the reactor wall (3, 3a, 3b) and at the level of the free end (12) of the electrodes (18, 20); wherein preferably a part of the reactor wall near the magnet is made of austenitic metal, especially austenitic steel, stainless steel or a metal mixture having an austenitic part.

7. The plasma reactor (1) according to any one of the preceding claims, wherein the reactor chamber (2) includes an outlet (15) opposite to the plasma torch (7), and a heat exchanger (17) is directly arranged at the outlet (15) of the reactor chamber (2).

8. The plasma reactor (1) according to claim 7, configured to generate a synthesis gas stream comprising CO and H2, wherein the heat exchanger (17) is adapted to cool the synthesis gas stream to 800 to 1000 °C; and wherein preferably the heat exchanger (17) is configured to effect the cooling of the synthesis gas stream in 1 - 3 seconds, particularly preferably in 2 seconds.

9. A method of operating a plasma reactor (1) according to any one of the preceding claims, the method comprising the steps of: measuring the mass flow rate of the oxidizing fluid or the hydrocarbon fluid prior to dispensing within the inner tubular electrode (18); controlling the dispensing of the oxidizing fluid from the oxidizing fluid outlet based on a change in the mass flow rate; or wherein the method comprises the steps of: measuring the pressure of the oxidizing fluid or the hydrocarbon fluid prior to dispensing within the inner tubular electrode (18); controlling the dispensing of the oxidizing fluid from the oxidizing fluid outlet based on a change in the pressure.

10. The method according to claim 9, comprising the steps of: variably mixing a hydrocarbon fluid, CO2 and / or H2O, wherein the variable mixing of the hydrocarbon fluid, CO2 and / or H2O is based on the wear of at least one of the tubular electrodes (18, 20), or wherein the variable mixing of the hydrocarbon fluid, CO2 and / or H2O is based on the amount of solid deposition on at least one of the tubular electrodes (18, 20).

11. The method according to claim 9 or 10, wherein the feed lance (22) is axially displaced relative to the inner tubular electrode (18) based on a change in the mass flow rate or a change in the pressure.

12. The method according to any one of steps 9 to 11, wherein the dispensing of the oxidizing fluid is effected through an outlet that is part of the feed lance, and the feed lance comprises an inner tube and an outer tube that at least partially surrounds the inner tube; wherein the method provides the steps of passing the oxidizing fluid through the inner tube and passing the hydrocarbon fluid through the space between the inner tube and the outer tube; or wherein the method provides the step of passing the oxidizing fluid through the space between the inner tube and the outer tube of the feed lance.

13. The method according to any one of steps 9 to 11, wherein the dispensing of the oxidizing fluid is effected through an outlet in the feed lance, the feed lance comprising a first outlet for the oxidizing fluid and a second outlet for the hydrocarbon fluid; or wherein the step of dispensing the oxidizing fluid is effected through an annular space between the inner tubular electrode and the feed lance, wherein the oxidizing fluid passes between the inner surface of the inner electrode and the outer periphery of the feed lance; or wherein the hydrocarbon fluid and the oxidizing fluid are dispensed through a single or common tube of the feed lance, (a) alternately through the same tube in time, or (b) mixed together.

Images