Systems and methods for producing hydrogen

Abstract

The hydrogen production system includes a hydrogen pyrolysis reactor having a hydrocarbon input, an electrical input, and at least one hydrogen output. The hydrogen production system also includes a hydrogen fueled generator. Means are provided for routing a portion of the hydrogen from one of the at least one hydrogen output to the hydrogen fueled generator. Additionally, the hydrogen fueled generator produces an electrical output, which is routed to the electrical input of the hydrocarbon pyrolysis reactor. Related methods of operating the hydrogen production system are also described.

Description

[Technical field]

[0001] The present invention relates to a hydrogen production system. [Background technology]

[0002] Power and heating of buildings and other facilities have been provided mainly by hydrocarbons in the form of oil and gas, but with the use of hydrocarbons in such applications steadily declining, alternatives to this approach are now being sought. Increasingly, electricity supplies come from renewable sources, but this is not always the most efficient approach, and for control and cost management, local generation is often preferred. Hydrogen is becoming an increasingly attractive fuel, as it releases energy very efficiently and does not produce harmful waste. Hydrogen boilers for use in buildings are now coming into production. Electricity can also be produced from hydrogen, for example, using solid oxide fuel cells.

[0003] Processes to obtain hydrogen from hydrocarbons have been developed, but currently these are usually carried out in large reactors and are not suitable for use in most built environments. It would be desirable to be able to provide hydrogen to the environment in a way that does not rely on off-site hydrogen generation and hydrogen distribution. It would be particularly desirable to make hydrogen production systems as versatile as possible for use in the built environment and in other situations where its use has not previously been considered. Summary of the Invention

[0004] In a first aspect, the present invention provides a hydrogen production system including a hydrocarbon pyrolysis reactor having a hydrocarbon input, an electrical input, and at least one hydrogen output, a hydrogen fuelled generator, and means for supplying a portion of hydrogen from one of the at least one hydrogen output to the hydrogen fuelled generator, the hydrogen fuelled generator adapted to produce an electrical output, and means for supplying the electrical output of the hydrogen fuelled generator to the electrical input of the hydrocarbon pyrolysis reactor.

[0005] Using this approach, the hydrogen production system can be substantially self-sustaining during use, only requiring electrical energy at start-up. This approach can also be used to generate excess electricity for other uses by passing more hydrogen through the hydrogen-fueled generator. Both features can be particularly useful in certain environments, such as to run hydrogen-based heating systems, or to provide a hydrogen production system for use in locations where hydrocarbon gases are present but a steady supply of electricity is not available (e.g., oil fields where flare gas is available). In some embodiments, the hydrogen-fueled generator can be a fuel cell, such as a solid oxide fuel cell. In other embodiments, the hydrogen-fueled generator can include a hydrogen-fueled motor, or a hydrogen-fueled gas turbine.

[0006] In some embodiments, the hydrocarbon pyrolysis reactor can have a first high purity hydrogen output and a second lower purity hydrogen output. Such outputs can be provided by a hydrogen purification stage to provide the first hydrogen output and the second hydrogen output. Such a hydrogen purification stage can include a pressure swing adsorption stage.

[0007] The hydrogen production system may also include a heat exchanger. Hydrogen output from the hydrogen production system may pass through a hydrogen purification stage before or after passing through the heat exchanger, depending on suitable design choices.

[0008] Using this approach, a portion of the second hydrogen output can be provided as fuel for a hydrogen-fueled generator, and another portion of the second hydrogen output can be provided as purge gas for a hydrogen pyrolysis reactor.

[0009] In one embodiment, the first hydrogen output may be substantially 7N purity and the second hydrogen output may be substantially 1.5N purity. If a hydrogen purification stage is used, it may be configured to provide high purity hydrogen and lower purity hydrogen according to the usage requirements of each hydrogen stream.

[0010] The hydrocarbon pyrolysis reactor can include a plasma torch, which in some embodiments can be followed by a liquid metal system to pyrolyze the hydrocarbons and separate the reaction products.

[0011] The hydrocarbon input may be a methane input.

[0012] In a second aspect, the present invention provides a method of operating a hydrogen production system comprising starting a hydrocarbon pyrolysis reactor with a hydrocarbon input and an electrical input, providing at least one hydrogen output from the hydrogen production system and providing hydrogen from one of the at least one hydrogen output to a hydrogen fueled generator, and generating electrical power in the hydrogen fueled generator and providing electrical power for the electrical input to the hydrogen pyrolysis reactor from the hydrogen fueled generator.

[0013] Providing at least one hydrogen output can include providing a first hydrogen output of high purity and a second hydrogen output of lower purity, which can be provided by a hydrogen purification stage, which can be a pressure swing adsorption stage.

[0014] A portion of the second hydrogen output can be provided as fuel for a hydrogen fueled generator, and another portion of the second hydrogen output can be provided as a purge gas for a hydrogen pyrolysis reactor.

[0015] The hydrocarbon pyrolysis reactor can include a plasma torch, and providing power from the hydrogen fueled generator can include powering the plasma torch.

[0016] The hydrocarbon input may be a methane input. [Brief description of the drawings]

[0017] Embodiments of the invention will now be described, by way of example only, with reference to the accompanying drawings in which: FIG. [Figure 1]1 illustrates a hydrogen production system, according to one embodiment of the present invention. [Diagram 2] 1 illustrates a method of operating a hydrogen production system according to an embodiment of the present invention. [Diagram 3] 1 illustrates a longitudinal cross section of a plasma torch of an exemplary hydrogen production system. [Figure 4] FIG. 4 shows a detail of the plasma torch of FIG. 3 showing a further element, the anode, which exhibits features that prevent carbon buildup. [Diagram 5] 4 shows the flow of reactive gases through the plasma torch of FIG. 3. [Figure 6A] 4 shows a side elevational view of a source gas inlet ring for use with the plasma torch of FIG. 3. [Figure 6B] 4 shows a cross-sectional view of a source gas injection ring used in the plasma torch of FIG. [Figure 7] 1 illustrates a reaction process of a reactor structure suitable for use as a hydrogen production system according to an embodiment of the present invention. [Figure 8] 8 illustrates a liquid metal pyrolysis reactor system powered by the plasma torch system of FIGS. 3-7 and including a housing for the plasma torch system. [Figure 9A] FIG. 9 shows the liquid metal circulation system of the reactor of FIG. 8, driven by the plasma torch. [Figure 9B] FIG. 9 shows the liquid metal circulation system of the reactor of FIG. 8, driven by the plasma torch. [Figure 10] The liquid metal pyrolysis reactor is shown in more detail in FIG. [Figure 11] The feed system to the liquid metal pyrolysis reactor of FIG. 10 is shown with carbon output. [Figure 12] 8 illustrates generally a method for operating a hydrogen production system according to an embodiment of the invention using a modification of the reaction process of FIG. [Figure 13] 13 illustrates an alternative embodiment to the method shown in FIG. 12 for operating a hydrogen production system. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0018] General and specific embodiments of the present invention will be described below with reference to the drawings.

[0019] 1 shows an exemplary hydrogen production system according to an embodiment of the invention. Reactor 1 receives a hydrocarbon 11 as a feed gas and has power input to the reactor, which may be provided by power supply 3. The reactor may be a plasma torch reactor of a design to be described below. The reactor produces hydrogen as an output, which in the illustrated arrangement includes a high purity hydrogen output 13 and a lower purity hydrogen output 12. Other outputs 14 from the reactor process may include carbon, for example if methane is used as a feed gas.

[0020] At least a portion of the hydrogen output is provided as input to a hydrogen fueled generator 2. In the illustrated case, this input is all of the lower purity hydrogen output 12, but in other embodiments, a portion of this hydrogen can be recycled to the reactor 1. This can include a hydrogen fueled motor, a hydrogen fueled gas turbine, or a fuel cell, such as a Solid Oxide Fuel Cell (SOFC). The electrical output 10 from the hydrogen fueled generator can be returned to the reactor 1 and used to power the operation of the reactor 1 itself. Alternatively, most of the hydrogen output can be returned to the hydrogen fueled generator 2 to provide further electrical output for other purposes. In this way, the reactor can operate without consuming significant electrical power during most of its operating cycle during operation.

[0021] This is illustrated as a method in FIG. 2. First, a hydrocarbon pyrolysis reactor is started up (22). This requires input of a hydrocarbon feedstock as well as power to operate the reactor (e.g., energizing the plasma torch in a plasma torch reactor). This requires access to a utility power source or a dedicated local system (e.g., a battery or generator) to provide the required power. During operation, a portion of the hydrogen output is routed from the reactor to a hydrogen-fueled generator (24), which uses hydrogen as a fuel source to generate electricity (26). This power is then routed to provide the electrical energy input (28) to the reactor. This means that during normal operation, the reactor is self-sufficient in power.

[0022] As mentioned above, the reactor 1 is adapted to receive a hydrocarbon input, which in certain embodiments may be primarily methane. A natural gas input contains primarily methane, possibly with small amounts of other short-chain hydrocarbons. The pyrolysis reactor pyrolyzes these as well (as described in the following embodiments). In some embodiments, other gas inputs with a predominantly hydrocarbon content may also be used. Of particular interest is "flare gas", a general term for gaseous hydrocarbons found together with liquid hydrocarbons "(petroleum)". Flare gas is also mostly methane, but typically also contains short-chain carbons, and may contain other compounds such as water vapor, hydrogen sulfide (H2S), and carbon dioxide (CO2), and nitrogen (N2). Depending on the type of reactor, some of these may be included in the input and may be pyrolyzed or otherwise reacted with the separated reaction products downstream. Meanwhile, other inputs are separated from the flare gas in one or more separation stages before entering the reactor. For example, a desulfurization step may be performed before the introduction of the flare gas.

[0023] A particularly preferred embodiment of a hydrogen production system will now be described. This approach uses a plasma torch to separate methane into hydrogen and carbon. The embodiment detailed below also includes a liquid metal system to remove the hydrogen and carbon for separation into hydrogen gas and solid carbon outputs. Other embodiments of the invention do not use a liquid metal system, but employ other approaches for separation. For example, in other embodiments, a purge gas such as nitrogen is used to remove the torch output, which is hydrogen and carbon, and one or more cyclones are used downstream to further separate the carbon.

[0024] The elements and working principle of such a hydrogen production system will be described with reference to Figs. 3 to 11. First, a reactor using this method will be described. The reactor is formed as a pressure vessel with a plasma torch or an electrical input for powering the torch (see Fig. 8 for details) and a gas inlet for introducing gaseous raw materials into the system. The exemplary reactor shown here is a multi-stage type. The plasma torch serves as one reaction stage and, in some cases, the liquid metal serves as a further reaction stage that consumes the heat generated by the plasma torch. The reaction products include a heating gas, which in the main example below is hydrogen. And a heat exchanger can use the heating gas to bring the raw material gas to a temperature suitable for the reaction, essentially serving as a pre-reaction stage. In other embodiments, instead of a liquid metal system, there is a single reaction stage and a gas purge.

[0025] In the multi-stage reactor approach, gaseous inputs, e.g., hydrocarbons such as methane, and possibly added hydrogen for cooling (possibly recycled from the output products), are introduced to a plasma torch. The plasma torch consumes the input of feed gas and provides a first set of output products, such as carbon and hydrogen. These first output products flow as inputs to a liquid metal reactor at high temperature and then undergo pyrolysis into further feed gas. Final output products, such as carbon extracted through the liquid metal and hydrogen output as gas, are provided from the liquid metal reactor after a separation process. These final output products include the first output product from the plasma torch as well as further output products generated from pyrolysis in the liquid metal reactor. Although the pyrolysis reaction is endothermic, there is a surplus of heat that can be used since there is sufficient heat remaining at temperatures significantly higher than those required to store the gaseous end products. This heated gas output is then used by a heat exchanger that controls the temperature of the feed gas at various stages of the reaction process. As noted above and further described below, this multi-stage reactor is merely an exemplary hydrogen production system, and not every embodiment of the present invention requires all of the features described for the multi-stage reactor.

[0026] The plasma torch is shown in detail in Figures 3 to 5. In Figure 3, a longitudinal cross-section of a plasma torch 30 is shown. The plasma torch 30 is generally cylindrical and in the apparatus used in the embodiment of the invention extends into a liquid metal circulation system 40 (described further below) and injects directly into the liquid metal. The plasma torch has a central chamber 300 that houses a cathode 31 and an anode 32. These can be of any conductive material suitable for the conditions in the central chamber 300. Carbon (graphite) can be used, or any suitable metal or alloy can be used either uniformly or with a suitable insert. For example, copper with a hafnium insert can be selected. Here, the cathode 31 is located towards the end of the plasma torch 30 away from the liquid metal reactor 39, and a ceramic cup-shaped end 38 terminates the plasma torch. In another torch design, the electrodes can be reversed. Alternatively, an AC plasma torch can be used where it only makes sense to talk about electrodes, rather than anodes and cathodes. The anode is generally cylindrical, but has a contoured inner surface 34 that includes a nozzle 35 and a diffuser section 36, as will be described in more detail below. Between the cathode 31 and the anode 32, a guard electrode 33 may be disposed. Those skilled in the art will appreciate that the electrode configuration may also be varied and may include no intermediate electrode, one or more intermediate electrodes, to achieve the desired field pattern in the plasma torch chamber. Multiple guard electrodes may be cascaded to aid in spark stabilization, for efficient ignition, or to prevent anode wear. A gas inlet 37 is provided to introduce gaseous feedstock into the reactor. In the apparatus shown in FIG. 3, methane is introduced at gas inlet 37 located at guard electrode 33. As will be described in more detail below, different embodiments of the invention provide different gas input locations for different feedstock gases. Although the following description primarily refers to methane, it will be understood that other hydrocarbons may be used as well. For example, propane can be shipped in liquid form, but is readily vaporized during reaction in a plasma torch reactor, making it another particularly suitable option for processing.

[0027] FIG. 4 illustrates a phenomenon when using the plasma torch 30 shown in FIG. 3 to decompose methane. In this reaction, the action of the plasma torch spark breaks down methane into hydrogen gas and carbon at high temperatures. The plasma torch spark can reach temperatures of up to 6000° C., causing the methane to decompose instantaneously. As a practical problem, this can lead to carbon deposits 41 that clog the torch, severely impacting the efficiency of the process and causing significant downtime for maintenance. It is desirable to prevent such carbon buildup and allow both reaction products to exit the plasma torch 30. One feature to achieve this is to protect the anode with a gas that inhibits buildup. This can be achieved by making the anode 32 porous. The anode gas output 42 pumps gas, in this case hydrogen, through the anode, providing a protective curtain along the inside of the anode to inhibit carbon buildup. The gas is pumped at an angle to the anode with a velocity component toward the plasma torch output to provide this protective curtain. Alternatively, a velocity component can be provided away from the plasma torch output while still providing a protective curtain to the electrode. In addition to providing a protective curtain, the deposited carbon can also be actively eroded by hydrogen, which reacts back with the carbon to form methane, further eroding the deposited carbon. The hydrogen also serves to cool the anode and prevent degradation. In addition to using porous anodes in this manner, the cathodes can also be made porous and cooled in a similar manner.

[0028] Further steps can be taken to prevent carbon build-up: the anode can be shaped so that, with the torch in operation, the location where carbon is likely to accumulate is on the anode in the region of the spark gap. The action of the spark can further erode the carbon build-up.

[0029] Another feature that prevents carbon buildup is shown in FIG. 5, which depicts the gas path through the plasma torch structure. Here, methane enters the plasma torch tangentially through gas inlet 37 in the guard electrode, and this input methane travels toward the cathode in a generally helical path. Gas inlet 37 here is realized by a ceramic ring 51, shown in more detail in FIGS. 6a and 6b. In an alternative arrangement, this ring can be metallic and formed as part of the cathode and / or anode. There are various arrangements that allow and maintain the flow regime described here. The ceramic ring 51 has a gallery 52 for circulating the input gas around the ring, allowing the input gas to flow into many (four in the illustrated design) passages 53 that feed the input gas tangentially into the chamber, thereby establishing a helical path for the output gas adjacent to the chamber wall and forming a vortex within the plasma torch chamber. This can be optimized to achieve the desired flow pattern, taking into account the gas type, flow conditions, pressure, and temperature. The structure of the walls (particularly their roughness and shape) encourages the outer spiral of gas to maintain its momentum and separate from the inner spiral of faster rotating gas. The torch shape also forces the gas into the faster, tighter circulating inner returning spiral. The gas chooses these tighter spirals as it travels back between the cathode and anode, and maintains this state against heating as it breaks down into carbon and hydrogen in the spark gap between the cathode and anode. The formation of the plasma is rapid, typically less than a microsecond. With gases, this can be tuned (by pressure, temperature, and density) to minimize the energy exchange between the spirals, similar to a tornado, if properly tuned. This configuration already gives the output gas (hydrogen in this case) a significant velocity towards the output of the plasma torch. It also prevents carbon condensation and deposition, since it forms in the center of the plasma torch chamber, not on the walls. The plasma contains ions and electrons in near thermal equilibrium and the molecules are largely broken down into atoms.At the temperatures and pressures under which the plasma torch operates, the stable state of carbon condensing from the plasma is gaseous, making carbon deposition unlikely. Plasma torch designs are generally dictated to promote reaction in the center of the chamber and inhibit reaction at the walls, so that reaction products are preferentially discharged from the plasma torch into the liquid metal reactor. The outer spiral cools and insulates the walls, preventing atomic carbon in the inner spiral from condensing on the walls. Hydrogen from the reaction passes through nozzle 35, increasing its velocity and decreasing its pressure due to the Venturi effect. The gas then exits plasma torch 30 at high temperature (and with kinetic energy) through diffuser 36, and the plasma exits the torch at supersonic speed. The cumulative effect of these features is that carbon is generally conveyed toward the plasma torch output without significant buildup of deposits on the walls of the anode. The role of diffuser 36 is to match the pressure of the plasma torch output with the next stage of reaction, as described in more detail below. As noted in the embodiment detailed herein, the next reaction stage is a liquid metal reactor, where the liquid metal can also be used to directly interact with the torch, as described further below.

[0030] This device allows operation at high temperatures (over 6000 °C at the reaction point) and pressures in the torch, resulting in very high throughputs of gaseous feedstock. With a power input of 200 kW to the plasma torch and an operating temperature in the torch chamber of about 6000 °C at the reaction point and a pressure of 50 bar, this design allows the processing of about 72 kg of methane per hour. The voltage between the electrodes is usually 150 V to 600 V, typically about 250 V, and the operating current is 100 A to 500 A, typically about 200 A. The hydrogen used to cool the anode is supplied at low temperature, but the feed gas can be preheated using a heat exchanger by utilizing the heat released in the pyrolysis reaction (see further explanation below).

[0031] With reference to FIG. 7, a description of the overall reaction flow of the multi-stage reactor is provided. As previously mentioned, this is only one exemplary reactor type that can be used in embodiments of the present invention, and in other embodiments, the plasma torch can be the only reactor, followed by gas purge and separation stages. Although this reaction flow is specific to the decomposition and pyrolysis of methane, it is used here more generally to describe the different reaction processes that take place in different parts of the hybrid reactor. For example, other hydrocarbons, such as propane, rather than methane, can be used as the feed hydrocarbon in the plasma torch reactor as well as in the liquid metal reactor.

[0032] Two inputs to the system are shown, electricity 1101 and a hydrocarbon 1102 (methane in this case). Two outputs are shown, hydrogen 1103 and carbon black 1104 (although it should be noted that for other reactions, output gases other than hydrogen may be provided as well or instead, and that some of the hydrogen produced is recycled for use in the reaction process). These outputs are used for various purposes, as further illustrated below with reference to FIG. 12. Both inputs are fed to a plasma torch 1105, which provides hydrogen as an input in addition to power and a hydrocarbon feedstock. In the illustrated apparatus, for example, a low temperature hydrogen input 1111 (shown here in the range of 200° C.-400° C.) for cooling the anode is provided to the plasma torch 1105, along with a high temperature hydrocarbon 1112 (shown here at about 700° C.) for use as a reaction feedstock, maintaining the temperature and pressure of the reaction chamber, and facilitating the flow of material through the plasma torch. When the plasma torch consumes electrical energy to produce a high temperature output, this is partially consumed by the pyrolysis reaction in the second reactor 1122, and the heated output gas therefrom can be used in the heat exchanger 1121 to circulate the hydrocarbon feedstock. This can raise the hydrocarbon feedstock from a low temperature hydrocarbon 1113 of about 200°C to a high temperature hydrocarbon 1112 of about 700°C, which is the plasma torch reaction temperature. The heat exchanger 1121 can also provide hydrogen at a lower temperature to the plasma torch. In this way, this heat exchanger 1121 effectively acts as a first reaction process, absorbing the heat of the final process and using it to bring the gases required for the reaction stage to the correct temperature.

[0033] The plasma torch 1105 itself acts as a second reactor 1122, providing hot hydrogen and (mainly) gasified carbon as output 1114. The plasma torch 1105 operates through its own reaction products in the next reaction stage, which is the liquid metal pyrolysis reactor 1123. The plasma torch 1105 provides the heat for this reaction, heating the metal (here lead) to the reaction temperature and also provides circulation to the lead, allowing the extraction of carbon in the center of the reactor. Hotter hydrocarbons 1115 are provided from the heat exchanger 1121 as feed for the liquid metal pyrolysis reactor 1123. The surplus heat generated in the thermoelectrolytic reaction in the pyrolysis reactor returns the hydrogen output 1116, provided at very high temperatures (about 1200 ° C), to the heat exchanger 1121, where it is partly recycled to the plasma torch 1105, but mainly in the form of a (cooler) hydrogen gas output 1104.

[0034] The liquid metal pyrolysis reactor used in a particular embodiment of the invention is shown in more detail in Figures 8-11. Figure 8 shows the main elements of the reactor assembly. A torch mount 121 leads to a liquid metal racetrack 122 that feeds into a main reactor volume 123. There is also a gas inlet 124 into the main reactor volume 123, which contains a vortex chamber 125. Liquid (molten) metal is fed into the vortex chamber 125 to provide circulation to the liquid metal column, allowing the liquid metal to both initiate the pyrolysis reaction in the input gas and to act as a centrifuge, with the reaction products being separated towards the centre of the rotating column. Carbon can then be extracted from the base of the reactor at carbon outlet 126. Hydrogen rises from the liquid metal and is released from the top of the reactor via hydrogen outlet 127. The reaction is carried out at high temperature and pressure (typically 800°C to 1000°C and 50 bar).

[0035] This function can be beneficially combined with that of a plasma torch, even if the liquid metal system is not itself a reactor. In that case, it can only act as a separator to separate the reaction products from the plasma torch, and is powered by the energy of the plasma torch output. However, this leaves excess heat behind. It has been found that using the liquid metal system as the reactor itself for the endothermic pyrolysis of further hydrocarbons results in a particularly effective reactor system.

[0036] 9A and 9B show the plasma torch mount and the liquid metal racetrack from different angles. Once the liquid metal has cooled and the reaction products have been separated, it leaves the reaction chamber and then passes through the liquid metal racetrack 122 and over the elbow joint 128 to the plasma torch mount 121. There, the plasma torch output is injected into the liquid metal. This heats the liquid metal to a temperature sufficient to initiate a pyrolysis reaction in a hydrocarbon such as methane, allowing the reaction products of the plasma torch reaction to be collected from the system for transport to the liquid metal reactor (methane entering the liquid metal from the plasma torch nozzle can also be pyrolyzed at this point). The heated metal passes along the remainder of the liquid metal racetrack and enters the liquid metal reactor chamber from the bottom. As a result, the parts of the racetrack structure must withstand the high temperatures of the heated liquid metal and also accommodate expansion due to the significant temperature difference between during and outside the reaction process. The joints can be protected by using sleeves made of molybdenum, for example.

[0037] The plasma torch is designed to efficiently inject into the liquid metal racetrack 122, and in particular the plasma torch diffuser is designed to pressure match the exterior of the torch. This has the advantage of supporting linear flow rather than turbulent flow in the liquid metal racetrack. The liquid metal can be forced into a vortex or swirl which acts to stabilize the plasma jet. Reaction products from the plasma torch (hydrogen and carbon in the illustrated embodiment) are carried into the liquid metal for subsequent separation in and discharge from the liquid metal reactor, as described below.

[0038] The liquid metal system may also serve to remove impurities from the output of the plasma torch reactor. For example, ethylene may be produced as a by-product, which can then be decomposed again in the liquid metal system. The liquid metal from the liquid metal system may have other functions. For example, the diffuser of the plasma torch may extend far enough into the liquid metal racetrack that the liquid metal will act to clean the diffuser and prevent carbon from accumulating there. In some embodiments, the diffuser section may be partially porous to accommodate the flow of liquid metal. If necessary, the liquid metal from the racetrack may be pushed up to fill the plasma torches, quickly suppressing the reactions and even stopping their operation. In this way, the liquid metal may be used to fill and thus clean the porous anode (and cathode, if used) structures.

[0039] The liquid metal in the liquid metal system can be a low melting element such as lead, or a low melting mixture based on lead. Lead is a suitable option since it is liquid at the reaction temperature without having a high vapor pressure, and it poses fewer toxicity issues than most other suitable metals. Gallium is a further possible option. Other low melting alloys such as bismuth-tin are also suitable options.

[0040] As mentioned above, the liquid metal system is designed here to act as a separator in this structure, but it can also act as a reactor. Figure 10 shows a diagram of the vortex chamber 125, which forms the reaction chamber of the liquid metal pyrolysis reactor. The heated liquid metal is passed into this chamber from below along with the input gas, circulating in the vortex chamber 125, resulting in separation of the reaction products separated by centrifugal action in the center of the circulating liquid metal column, while carbon and hydrogen are first collected in a hat structure 151 at the top of the reactor. This can be used to collect clean hydrogen. This is the best gas at this point and can be easily released through a float valve. A liquid salt structure can be given to this structure to filter the lead and carbon mixture. This separates the carbon from the lead, and the lighter carbon floats on top of both the lead and the salt, completing the process by gravity. This allows the carbon to be separated by dropping it through a chute in the central area of ​​the chamber. The base plate 152 below the vortex chamber 125 has through holes for gaseous input. The cooling metal exits through perforations in the side of the swirl chamber 125 and passes down through the base plate 152 where it circulates on the liquid metal racetracks shown in FIGS.

[0041] Further details of the swirl chamber 125 are shown in Figure 11, which shows the bottom of the liquid metal reactor vessel below the swirl chamber 125 where the reaction takes place. Hot metal heated by a plasma torch enters from below through metal inlet 161 and reactant gases enter through gas inlet 162. Carbon exits through the bottom of the reactor at carbon outlet 163. Hydrogen is circulated downward through the base plate 152 of the swirl chamber 125 for subsequent circulation and collection above the swirl chamber.

[0042] As discussed above, a heat exchanger system is provided that allows the heat generated in the reaction to be used to provide input gases at the correct temperature for use in the reaction. The hydrogen output from the liquid metal reactor is at high temperature (1200°C) and is used to heat the methane feedstock to feed both the plasma torch and the liquid metal pyrolysis reactor. A portion of this hydrogen output is cooled to a much lower temperature (e.g., 200°C-400°C) and is used to cool the anode and cathode of the plasma torch as discussed above.

[0043] Although the reactor embodiment described herein is adapted for the pyrolysis of methane, this reactor configuration can be used for many reactions. As noted in the description of the feed system, various input gases can be used for different reactions, for example with the gas input locations selected to provide proper circulation of gas throughout the plasma torch. Similarly, various inputs can be provided to the liquid metal reactor, rather than simply methane, to provide various reactions.

[0044] It should be emphasized that the particular reactor configurations described above are merely examples of hydrogen production systems suitable for use with embodiments of the present invention. In particular, multi-reactor or composite reactor configurations are not required, what is needed is an effective method to produce hydrogen and appropriately formed carbon at an appropriate scale. This can be achieved by using a plasma torch in conjunction with a liquid metal system to separate the hydrocarbons into hydrogen and carbon. Alternatively, what is needed is another suitable system to achieve an effective separation.

[0045] Figure 12 shows a modified version of the reaction system of Figure 7 for use in an embodiment of the present invention. The reaction streams are used here to more generally illustrate the decomposition and pyrolysis of methane, but different reaction processes taking place in different parts of the composite reactor. For example, other hydrocarbons, such as propane, rather than methane, can be used as feed hydrocarbons in the plasma torch reactor as well as in the liquid metal reactor.

[0046] Two inputs to the system are shown: electricity 2101 and hydrocarbon 2102 (methane in this case). The electrical input is provided by a power system 2205, which can provide power from one or more sources, as described further below. Two outputs are shown: hydrogen 2103 and carbon black 2104 (although it should be noted that other output gases can be provided as well or instead for other reactions, and that some of the hydrogen produced is recycled for use in the reaction process). These outputs are typically used for a variety of purposes. Hydrogen is primarily used as a fuel, while carbon black has many other uses. Both inputs are provided to a plasma torch 2105, but in addition to the power and the hydrocarbon feedstock, hydrogen is provided as an input. In the illustrated arrangement, a low temperature hydrogen input 2111 (shown here in the range 200°C-400°C) is provided to the plasma torch 2105 to cool the anode. Also provided is hot hydrocarbon 2112 (shown here at about 700° C.) used, for example, as a reaction feedstock, to maintain the temperature and pressure of the reaction chamber and to facilitate the flow of material through the plasma torch. When the plasma torch consumes electrical energy to produce a hot output, this is partially consumed by the pyrolysis reaction in the second reactor 2122, from which the heated output gas can be used in the heat exchanger 2121 to circulate the hydrocarbon feedstock. This can raise the hydrocarbon feedstock from the low temperature hydrocarbon 2113 at about 200° C. to the high temperature hydrocarbon 2112 at about 700° C., which is the plasma torch reaction temperature. The heat exchanger 1121 can also provide hydrogen to the plasma torch at a lower temperature. In this way, this heat exchanger 1121 effectively acts as a first reaction process, absorbing the heat of the final process and using it to bring the gas to the correct temperature required for the reaction stage. As will be further explained below, in this apparatus, the heat exchanger 2121 is involved in multiple hydrogen outputs from the reactors.

[0047] The plasma torch 2105 itself acts as a second reactor 2122, providing hot hydrogen and (mainly) gasified carbon as output 2114. The plasma torch 2105 operates via its reaction products in the next reaction stage, in this case a liquid metal pyrolysis reactor 2123. As mentioned before, instead of a liquid metal reactor, it is possible to simply perform a gas purge after the plasma torch and the separation stage to separate the carbon and hydrogen. The plasma torch 2105 provides the heat for this reaction, heating the metal (here lead) to the reaction temperature and bringing about a rotation of the lead, which allows the carbon to be extracted in the center of the reactor. Hotter hydrocarbons 2115 are provided from the heat exchanger 2121 as feed for the liquid metal pyrolysis reactor 2123.

[0048] Unlike the apparatus of FIG. 7, here there is a further separation stage 2200 so that hydrogen is output from the liquid metal pyrolysis reactor 2123 (or separation stage) as two output streams: a high purity output 2201, and a lower purity output 2202. As will be appreciated by those skilled in the art, the purity of each of these outputs can be determined by the extraction, separation, and purification processes used. A standard method for hydrogen purification in industrial processes is pressure swing adsorption. In the reactor process described above, a hydrogen purity of two "9s" (99% purity) can be fully expected. A further separation stage 2200 can then separate this into a high purity output of 7N (99.99999% purity) and a lower purity output of 1.5N (98.5% purity). This lower purity output can be used to power a fuel cell as well as reactor purge gas, as described below. As previously mentioned, systems other than liquid metal reactors can be used for separation. Note that, for example, a suitable purge gas (such as nitrogen) can be used to remove reaction products from the plasma torch prior to separation and pressure swing adsorption of hydrogen. In the case of flare gas, this may be primarily methane, but significant impurities may be present. In the case of liquid metal systems, these can be effectively separated by the liquid metal, but in other cases, further separation steps can be used (or specific impurities can be removed prior to use as feed gas to the reactor).

[0049] Both of these hydrogen outputs are provided at very high temperatures (approximately 1200° C.) by the exothermic reaction in the pyrolysis reactor and returned to the heat exchanger 2121. Here, the high purity output is provided as the hydrogen output 2103 of the reactor system. The lower purity output is partially consumed within the reactor system to provide the low temperature hydrogen input 2111 to the plasma torch 2105, but is also consumed in the hydrogen fuel cell flow path 2203 to the hydrogen fuel generator 2204. This lower purity hydrogen can be readily used to power this hydrogen fuel generator 2204, which provides electricity to the power supply system 2205. In this way, although initial power (e.g., from a utility, battery system, or generator system) may be required to initially operate the reactor, during steady state operation the electrical input required for the plasma torch 2105 to operate can be provided by the hydrogen fuel generator 2204. As a result, during steady state operation the hydrogen production system is substantially self-sustaining.

[0050] In an alternative embodiment shown in Figure 13, the separation stage 2300 can be located after the heat exchanger 2121 instead of before it. In this case the hydrogen lines can be combined into a single line 2301 to the heat exchanger 2121 and then only separated into lower and higher purity hydrogen by the separation stage 2300. In this approach separation stage 2300 can be associated with cooler gases. The output from the separation stage is then fed to the same outputs as described above for the lower and higher purity hydrogen streams from the heat exchanger.

[0051] The choice of hydrogen fueled generator to be used in this system is not critical, but should be determined according to the available input fuel (hydrogen at an appropriate purity level in the devices discussed here) and the power output required to operate the reactor. One option is a solid oxide fuel cell (SOFC), but fuel cells with other electrolytes can also be used. A solid oxide fuel cell element includes a number of stacked layers (mostly ceramic), and a solid oxide fuel cell typically includes a stack of such fuel cell elements connected in series. The operating temperatures of a solid oxide fuel cell are relatively high, typically 500°C to 1000°C, but this is not difficult to achieve in the vicinity of an exothermic reactor. Alternatively, commercially available hydrogen fueled engines and hydrogen fueled gas turbines can be easily powered from such a hydrogen source.

[0052] A plasma torch reactor of this type would typically require around 200 kW of power to operate. At the typical efficiency of solid oxide fuel cells, this output can be achieved by consuming around 9 kg of 1.5N purity hydrogen per hour. This is expected to be around half the "low purity" flow and is a small contribution to the overall hydrogen output, so is apparently sufficient to allow steady-state operation of the reactor without significant external power supplies.

[0053] As will be appreciated by those skilled in the art, the approach taken herein is not dependent on the use of a particular type of hydrogen production system, so long as hydrogen and carbon are provided as outputs. Those skilled in the art will also appreciate that variations on this approach can be made without departing from the basic concepts described herein, for example, a modified "hydrogen production system" can produce an alternative output gas to hydrogen, provided that it can also be consumed as fuel in a suitable generator.

Claims

1. 1. A hydrogen production system, comprising: a hydrocarbon pyrolysis reactor having a hydrocarbon input, an electrical input, and at least one hydrogen output; a fuel cell and means for supplying a portion of the hydrogen from one of the at least one hydrogen output to the fuel cell, the fuel cell adapted to generate an electrical output; and means for supplying the electrical output of the fuel cell to the electrical input of the hydrocarbon pyrolysis reactor.

2. The hydrogen production system of claim 1 , wherein the hydrogen fueled generator comprises one of an engine, a gas turbine, and a fuel cell.

3. The hydrogen production system of claim 2 , wherein the hydrogen fuel generator comprises a solid oxide fuel cell.

4. 4. The hydrogen production system of claim 1, wherein the hydrocarbon pyrolysis reactor has a first high purity hydrogen output and a second lower purity hydrogen output.

5. The hydrogen production system of claim 4 , wherein the hydrogen pyrolysis reactor includes a hydrogen purification stage to provide the first hydrogen output and the second hydrogen output.

6. The hydrogen production system of claim 5 , wherein the hydrogen purification stage comprises a pressure swing adsorption stage.

7. 7. The hydrogen production system according to claim 5 or 6, further comprising a heat exchanger, and wherein hydrogen output by the hydrogen production system passes through the hydrogen purification stage before passing through the heat exchanger.

8. 7. The hydrogen production system according to claim 5 or 6, further comprising a heat exchanger, wherein hydrogen output by the hydrogen production system passes through the hydrogen purification stage after passing through the heat exchanger.

9. 9. The hydrogen production system according to claim 4, wherein a portion of the second hydrogen output is supplied as fuel to the hydrogen fuel generator.

10. 10. The hydrogen production system according to claim 4, wherein a portion of the second hydrogen output is supplied as a purge gas for the hydrogen pyrolysis reactor.

11. 11. The hydrogen production system of claim 4, wherein the first hydrogen output is substantially at a purity of 7N and the second hydrogen output is substantially at a purity of 1.5N.

12. The hydrogen production system according to claim 1 , wherein the hydrocarbon pyrolysis reactor comprises a plasma torch.

13. The hydrogen production system of claim 12 , wherein the hydrocarbon pyrolysis reactor includes a liquid metal system after the plasma torch for pyrolyzing hydrocarbons and separating reaction products.

14. The hydrogen production system of claim 12 , wherein the hydrocarbon pyrolysis reactor includes a purge gas and separation system after the plasma torch for separating reaction products.

15. 15. The hydrogen production system of claim 1, wherein the hydrocarbon input is a methane input.

16. 16. The hydrogen production system of claim 1 , wherein the hydrocarbon input is adapted to receive flare gas.

17. 1. A method of operating a hydrogen production system, comprising: starting up a hydrocarbon pyrolysis reactor using a hydrocarbon input and an electrical input; providing at least one hydrogen output from the hydrogen production system and providing hydrogen from one of the at least one hydrogen output to a hydrogen fueled generator; generating electrical power with the hydrogen fueled generator; and powering the electrical input to the hydrogen pyrolysis reactor from the hydrogen fuel generator.

18. 20. The method of claim 17, wherein the step of providing at least one hydrogen output comprises providing a first high purity hydrogen output and a second lower purity hydrogen output.

19. 20. The method of claim 18, wherein the first hydrogen output and the second hydrogen output are provided by a hydrogen purification stage.

20. 20. The method of claim 19, wherein the hydropurification stage is a pressure swing adsorption stage.

21. 21. The method of any one of claims 18 to 20, further comprising providing a portion of the second hydrogen output to be supplied as fuel for the hydrogen fueled generator.

22. 22. The method of any one of claims 18 to 21, wherein a portion of the second hydrogen output is provided as a purge gas for the hydrogen pyrolysis reactor.

23. 23. The method of any one of claims 17 to 22, wherein the hydrocarbon pyrolysis reactor includes a plasma torch, and providing electrical power from the hydrogen fueled generator includes powering the plasma torch.

24. 24. The method of any one of claims 17 to 23, wherein the hydrocarbon input is a methane input.

25. 25. The method of any one of claims 17 to 24, wherein the hydrocarbon input is adapted to receive flare gas.

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