GB2603524A

GB2603524A - An apparatus and method for power generation

Info

Publication number: GB2603524A
Application number: GB2101712.4A
Authority: GB
Inventors: Budge Grant; Itan Laurent
Original assignee: L&G TECHIT UK Ltd; L&g Techit Uk Ltd
Current assignee: L&G TECHIT UK Ltd; L&g Techit Uk Ltd
Priority date: 2021-02-08
Filing date: 2021-02-08
Publication date: 2022-08-10
Also published as: GB202101712D0

Abstract

A heating arrangement for an industrial process comprises a combustor that produces a stream of heated gas that passes through a magnetohydrodynamic (MHD) electricity generator 17 whose exhaust output provided to a heating area 20 in which one or more materials are heated with the heated gas from the combustor. Ambient air can be separated into components supplied to the generator. A portion of the heated gas can pass through each of plural generators 17. Heating of material can include melting, evaporation, softening or curing and produce a product such as glass sheet 24. The MHD generator (fig 1) can comprise an electron exciter that generates a fluctuating magnetic or electric field between a plasma generator and a power generating region having a magnetic field at right angles to the plasma jet and one or more electrodes. The electron exciter can comprise one or two coils separate that are supplied with alternating current having different frequencies, amplitudes or phases; or one or more solenoids receiving a DC supply in a phased pattern. Heated exhaust gas from the MHD generator can pass through and rotate a turbine to generate power.

Description

Title: An apparatus and method for power generation

Description of Invention

This application relates to an apparatus and method for power generation, and in particular relates to power generation by a magnetohydrodynamic apparatus.

A magnetohydrodynamic generator (MHD generator) is a type of generator that transforms thermal and kinetic energy directly into electricity.

In MHD generators, a stream of fast, charged particles is directed towards a region in which a magnetic field is applied at right-angles to the flow of particles. A current is generated, which can be extracted by placing electrodes on opposite sides of the flow of particles. A key advantage of MHD generators is that they do not have any moving parts, and so MHD generators can have high efficiency and reliability.

In known applications of an MHD generator of this type, the generator is placed so that a stream of gas output from a combustor of a power station passes through the generator. Typically, a power station involved in these applications burns liquid, solid or gaseous fuel using gaseous oxygen or air near-stoichiometric conditions. An example of a suitable gaseous fuel is natural gas.

Once the output stream from a power station combustor has passed through an MHD generator, it can be used to raise steam in a HRSG (heat recovery steam generator) to drive turbines, such as steam turbines, to generate electricity.

The presence of the MHD generator between the combustor and the HRSG and turbines allows generation of further power from the power station (above and beyond the power generated by the turbines), without any additional Co2 emissions.

It is an object of the present invention to provide improved power generation using MHD generators.

Accordingly, one aspect of the present invention provides A heating arrangement for an industrial process, comprising: a combustor having an output comprising a stream of heated gas; a heating area, in which one or more materials are heated with the heated gas from the combustor; and a magnetohydrodynamic (MHD) generator, arranged between the combustor and the heating area, so that the stream of heated has from the combustor passes through the generator, thus generating electricity, with an exhaust output of the generator being provided to the heating area.

Advantageously, the arrangement further comprises an air separator, to separate components of the ambient air and provide at least one of the 20 components to the generator.

Preferably, a plurality of generators is provided between the combustor and the heating area, arranged such that a portion of the stream of heated gas from the combustor passes through each of the generators.

Conveniently, the heating of the materials in the heating area melts, softens, evaporates or cures at least one of the one or more materials in the heating area.

Advantageously, the arrangement further comprises a working area, either within the heating area or downstream from the heating area, in which at least one of the one or more materials are worked to produce a product having a defined form.

Another aspect of the present invention provides a method of generating electricity, comprising the steps of: directing an output from a combustor, comprising a stream of heated gas, into a magnetohydrodynamic (MHD) generator; generating electricity by the MHD generator; and directing an exhaust output of the MHD generator into a heating area, in which one or more materials are heated with the heated gas from the combustor.

Preferably, the step of heating the one or more materials comprises melting, softening, evaporating or curing at least one of the one or more materials in the heating area.

Conveniently, the method further comprises the step, after the step of heating the one or more materials, of working at least one of the one or more materials into a product having a defined form.

Advantageously, the method further comprises the steps of: providing a plurality of MHD generators; directing a portion of the output from the combustor into each of the MHD generators; and directing an exhaust output from each of the MHD generators into the heating area.

A further aspect of the present invention provides a magnetohydrodynamic (MHD) generator, comprising: a plasma generator; a power generation region, comprising a magnetic field generator to generate a field in the region of the plasma jet substantially at right angles to the direction of travel for plasma jet, and one or more electrodes; and an electron exciter arrangement, positioned between the plasma generator and the power generation region, the electron exciter arrangement configured to generate a fluctuating magnetic or electric

field in the region of the plasma jet.

Preferably, the electron exciter arrangement comprises one or more conductive elements which are supplied with an alternating current.

Conveniently, the conductive elements comprise one or more coils.

Advantageously, in the region of the electron exciter arrangement, the plasma jet passes through a housing which contains the plasma jet, and the one or more coils are provided around an exterior of the housing.

Preferably, at least two separate coils are provided.

Conveniently, the two or more coils are each provided with alternating current supplies having different frequencies and/or amplitudes Advantageously, the supply of current to the two or more coils is phased, such that for at least a part of the phase the first one of the coils is provided with alternating current and a second one of the coils is inactive.

Preferably, the electron exciter arrangement comprises at least one conductive element which is arranged to receive a direct current supply.

Conveniently, the generator comprises two or more separate conductive elements, each configured to receive a direct current supply.

Advantageously, the or each conducting element comprises a solenoid.

Preferably, the current carrying elements are activated in a phased pattern, so that at least one time a first one of the current carrying elements is supplied 30 with a DC current, and the other one of the elements is inactive.

Conveniently, the or each MHD generator is a generator according to any of the above.

Another aspect of the present invention comprises a power generation arrangement, comprising: a combustor having an output comprising a stream of heated gas; a turbine which is driven to rotate by the stream of heated gas; and a magnetohydrodynamic (MHD) generator according to any of the above, arranged between the combustor and the turbine, so that the stream of heated has from the combustor passes through the generator, thus generating electricity, with an exhaust output of the generator being provided to the turbine.

A further aspect of the present invention provides a method of generating power, comprising the steps of: directing an output from a combustor, comprising a stream of heated gas, into a magnetohydrodynamic (MHD) generator according to any of the above; generating electricity by the MHD generator; and directing an exhaust output of the MHD generator into a turbine, driving rotation of the turbine and generating power.

In order that the invention may be more readily understood embodiments therefore will now be described, by way of example, with reference to the accompanying figures, in which: Figure 1 is a schematic view of a generator embodying the present invention; 25 and Figure 2 shows use of an MHD generator in an industrial process.

Referring firstly to figure 1, a schematic view of an MHD generator 17 30 embodying the invention is shown. Figure 1 shows a Hall-type MHD generator, although the invention is not limited to this and any type of MHD generator can be used. The generator 17 comprises an inlet 18, into which a stream of input gas may be provided. The example shown includes a first input stream 1 comprising fuel (which may comprise any combination of hydrogen, methane, syngas (a process and/or industrial gas comprising 5 variable amounts of methane, hydrogen, carbon dioxide and carbon monoxide)), and dependent on process application a second input stream 2 comprising oxygen. While figure 1 shows first and second input streams, it should be understood that a single input stream comprising a mixture of all inputs to the generator 17 may be used. Alternatively, more than two input 10 streams may be provided.

The inlet 18 leads to a gas mixing region 3, which may take the form of a manifold, or any other suitable form of passage or chamber, which is preferably shaped or configured to cause a turbulent flow therethrough.

In preferred embodiments, a seed material injector 12 is provided to introduce a seed material into the gas mixing region 3, so that the seed material mixes with the gases delivered in the input stream(s) 1, 2.

As the skilled reader will understand, the conducting gas in an MHD generator is plasma created by thermal ionisation, in which the temperature of the gas is high enough to separate at least some electrons from the atoms of gas. These free electrons make the plasma electrically conductive.

Creation of a plasma typically requires very high temperatures, but the temperature threshold can be lowered by seeding with a readily ionised compound, such as a metal alkali (for instance, potassium carbonate) or hydrazine.

Thus, introducing a seed material into the incoming flow of gas can greatly increase the efficiency of the generator, and also reduce the required temperature of the incoming gas stream(s).

From the gas mixing region 3, the incoming gases, in the form of a working fluid 5, flow into a plasma generator 15. In the example shown the plasma generator 15 comprises a passage or tube (defined by sidewalls 20), through which the working fluid 5 may flow. The plasma generator 15 preferably contains a cathode 4. In the example shown in figure 1 the cathode 4 is mounted within the plasma generator 15 such that the working fluid 5 flows around the cathode 4 as it passes through the plasma generator 15. In this example the cathode 4 is elongate in form, and generally aligned with the direction of gas flow within the plasma generator 15, having a free end 26 past which the working fluid 5 flows.

At its end furthest from the gas mixing region 3, the plasma generator 15 tapers towards a nozzle 7, which has a cross-sectional area which is significantly less than that of the main part of the plasma generator 15. The configuration of the nozzle 7 should preferably be such that it gives rise, in use, to a plasma discharge with a velocity which is between around Mach 5 and Mach 7. The skilled reader will readily understand how the dimensions of the nozzle 7 and the other components of the plasma generator 15 can be chosen to give rise to this result.

In the region of the nozzle 7, an anode 6 is provided. In preferred embodiments, the anode 6 comprises a ring-shaped structure, having an inner surface which defines at least part of the nozzle 7, although this is not essential.

When active, the potential difference between the cathode 4 and the anode 6 is such that electric arcs will form between the cathode 4 and the anode 6, thus igniting and ionising the gases flowing through the plasma generator 15.

The skilled reader will realise that the arrangement of the cathode and anode shown in figure 1 is not essential, and any suitable arrangement of a cathode and anode may be used in order to create a plasma as the gases flow through the plasma generator 15.

The constriction formed by the nozzle 7 will also accelerate the flow of fluid passing therethrough. In preferred embodiments of the invention, the nozzle 7 comprises a Venturi nozzle.

As the gases flow through the anode 6, combustion will occur, and exhaust gases at high temperature and pressure will be generated on the downstream side of the nozzle 7. In examples of the invention, the gases leaving the nozzle 7 will be at a temperature in the range of 3,000°C to 3,400°C, and a pressure in the range of 5MPa to 20Mpa. These gases comprise a plasma jet 8.

The plasma jet 8 emerges from the nozzle 7 into a diffuser 14, which has side walls 19 which diverge away from each other, so that the overall cross-sectional area through which the plasma jet 8 flows increases as the plasma jet 8 passes through the diffuser 14 away from the nozzle 7. As this occurs the temperature will decrease gradually, and this may allow reduction of the temperature to a level that can be accommodated by downstream equipment. In embodiments of the invention the gases leaving the diffuser 14 may be at a temperature of above 2,000°C, with a pressure in the range of 2Mpa to 10M pa.

In preferred embodiments of the invention, an electron exciter arrangement is arranged in the region of the diffuser 14, to increase the number of free electrons in the plasma jet 8 as it passes through the diffuser 14.

In the example shown in figure 1, the electron exciter arrangement comprises an electrically conductive coil 13, which surrounds the diffuser 14 and comprises several turns around the diffuser 14. In preferred embodiments the coil 13 comprises two separate coils, which may (for example) be wound so that turns of a first coil are alternated with turns of a second coil.

An alternating current is passed through the coil 13. This will give rise to a varying magnetic field within the diffuser 14, which will deflect charged particles flowing through the diffuser 14. The result of this will be to increase the rate of collisions within the plasma jet 8, and thus increase the number of free electrons within the plasma jet 8. An avalanche of electron collisions may be created, which will greatly increase the number of free electrons.

In preferred embodiments, the alternating current that is passed through the coil 13 alternates between a low frequency and a high frequency. The frequencies used, and the phase with which the system switches between the two, will again depend on other parameters of the apparatus. In preferred embodiments, the AC frequency may be between around 1kHz and 10kHz (with the low and high frequencies respectively being at or near the lower and upper ends of this range), and the number of turns of coil may range between around 10 and around 50. The overall result will be to create chaotic movement of the electrons within the plasma jet 8, thus increasing the number of collisions and so the number of free electrons. The exact parameters for the AC frequency and the number of turns of coil will, as the skilled reader will appreciate, be influenced or determined by the details of the apparatus (such as the plasma velocity, the composition of the working fluid, the temperature of the plasma jet leaving the nozzle, the drop in temperature per unit distance travelled of the plasma jet, and the material from which the diffuser is manufactured) and the economic priorities of the operators, to manage system parasitic load/energy losses.

In embodiments where the coil 13 is a twin coil, a first one of the coils may carry a high frequency alternating current, and a second one of the coils may carry a low frequency current. The first and second coils may be switched on alternately, with one being inactive or substantially inactive while the other one is active. In other embodiments the first and second coils may be cycled in such a manner that their times of activity overlap for at least some of the cycle.

As well as increasing the number of free electrons within the plasma jet 8, the magnetic field generated by the conductive coil 13 will have the effect of concentrating the free electrons within the centre of the flow of gases which form the plasma jet 8.

As a result of the action of the electron exciter arrangement, therefore, the plasma jet 8 which leaves the diffuser contains a higher number of free electrons, in a more concentrated stream. This will increase the efficiency and power generation of the generator 17. The result may also be to create a non-thermal or cold plasma, in which the electron temperature is significantly higher than the temperature of the heavier particles in the plasma jet 8.

While the above discussion includes a single coil or twin coils as part of the electron exciter arrangement, the invention is not limited to this. Three or more coils may be used, for instance, each carrying different frequencies of alternating current and being cycled in any suitable manner. In addition any other arrangement (not limited to coils) which can generate a fluctuating magnetic field in the region of the diffuser may be used.

The invention is also not limited to the use of alternating current. For instance, in another embodiment, a pair of solenoids (not shown) is provided, one on each side of the diffuser 14. Each solenoid is arranged to receive a DC current supply. In operation, the solenoids are activated in an alternating pattern, thus creating a fluctuating overall magnetic field within the diffuser 14. Once again this will have the effect of increasing collisions within the plasma jet 8 between electrons and other particles, and also concentrating the free electrons towards the centre of the plasma jet 8.

In other embodiments, more than two solenoids may be provided. For instance, four solenoids may be used, which are preferably at least approximately evenly spaced around the perimeter of the diffuser 14.

Any electron exciter arrangement that produces a fluctuating magnetic field within the diffuser 14 may be used. Preferably, the electron exciter arrangement also generates magnetic field(s) that tend to drive the electrons within the diffuser 14 towards the centre of the cross-section of the diffuser 14, leading to an increased concentration of electrons in the central region of the plasma jet 8. The skilled reader will readily appreciate which other types of arrangement may be used.

The discussion above concentrates on arrangements to produce a fluctuating magnetic field, but arrangements which produce a fluctuating electric field may also be used as (or as part of) an electron exciter arrangement. As the skilled reader will understand, an electric field in the region of the diffuser 14 will also lead to deflection of electrons passing through the diffuser 14 as part of the plasma jet 8. As an example of the equipment that could be used to generate a suitable field, parallel or substantially parallel plates, which are arranged so that positive and negative charges can be applied to the plates in a varying pattern. A single pair of plates could be provided, or one or more sets of parallel plates can be provided in the region of the diffuser 14, and charges can be (for example) applied to the sets of plates in a phased pattern, to give rise to chaotic motion of electrons within the diffuser 14.

The plasma jet 8 leaving the diffuser 14 enters a main body 16 of the generator housing. In preferred embodiments the main body 16 comprises a length of a pipe or tube formed from a robust and heat-resistant material. The main body 16 preferably has a substantially consistent cross-sectional size and shape along its length, but this is not essential. In preferred embodiments all or substantially all, or at least some portions of the main body, are generally circular in cross-section. However, this need not be the case and any suitable shape (such as a generally square or hexagonal cross-section, for instance) may be used.

Magnets 9 are positioned on opposing sides of the main body 16. In preferred 15 embodiments of the invention, the magnets 9 are superconducting magnets.

The magnets 9 preferably comprise one or more opposing pairs of magnets.

The magnets 9 are positioned on opposing sides of the flow path of the gases, and generate a fixed magnetic field perpendicular to the direction of flow of the gas. In the view shown in figure 1, the magnetic field created by the magnets 9 will be arranged substantially at right angles to the plane of the paper, within the main body 16.

Any other suitable arrangement to create a magnetic field within the main body 16, at or substantially at right angles to direction of the plasma jet 8, may be used.

Further, a plurality of electrodes 10 is positioned around the flow path of the 30 gases. Two separate electrodes 10 or arrays of electrodes are preferably provided, on opposing sides of the main body 16, in a direction which is generally perpendicular to the direction of the magnetic field created by the magnets 9. The electrodes 10 are preferably provided within the main body 16.

The flow of hot plasma through the magnetic field will generate an electric 5 current between the arrays of electrodes 10, as will be understood by the skilled reader. This current can be conducted away from the system, for instance via superconductors.

Internally-cooled cabled superconducting (ICCS) magnets or solenoids are the preferred type of magnets 9, in order to reduce parasitic losses. Once charged, ICCS magnets consume very little power and can develop intense magnetic fields of 6T and higher. The only parasitic load imposed by these magnets is to maintain cryogenic refrigeration and to make up the small losses for the non-supercritical connections.

The electrodes 10 need to carry a relatively high electric current density. In addition, the electrodes 10 are exposed to high heat fluxes. Because of the combination of high temperature, chemical attack and electric field, it is preferred that the non-conducting walls of the electrodes 10 be constructed from an extremely heat-resistant substance, such as yttrium oxide or zirconium dioxide, in order to retard oxidation.

In preferred embodiments, the plasma gas is expanded supersonically in the MHD generator in order to overcome the deceleration that results from interaction with the magnetic field. The extraction of electrical energy causes the plasma temperature to drop. In preferred embodiments, the main body 16 of the MHD housing is profiled so that the gases passing therethrough maintain a constant Mach number until the temperature becomes too low to have any useful electric conductivity.

The end 21 of the main body 16 which is furthest from the nozzle 7 is preferably open, and hot gases which have passed the electrodes 10 will exit the generator 17 through this open end 21 as an exhaust flow 11. This exhaust flow may be at a temperature of, for example, 1,650°C to 1,900°C.

As discussed above, this example is Hall type MHD generator. However, various other configurations for the magnets and electrodes are known, including the Faraday generator arrangement and the disc generator arrangement, with the latter being the most efficient of these designs.

In embodiments which use DC components such as solenoids in the electron exciter arrangement (as discussed above), it may be efficient to use a portion of the DC current generated by the MHD generator to drive the DC components of the electron exciter arrangement. Where the economics of the application are marginal, this may be an efficient way of arranging the MHD generator. It is also envisaged hat a portion of the current generated by the MHD generator may be used to drive AC components of an electron exciter arrangement, and the skilled person will realise how this may be arranged.

In preferred embodiments of the invention, a generator 17 of the type discussed above is incorporated into a system in which a combustor produces heat for an industrial process, such as the heating of glass, iron, steel or ceramics, or any other industrial heating application. Any industrial process in which heat is supplied to melt, soften, evaporate, cure or otherwise work on or alter one or more materials, and/or an item of manufacture, may be compatible with the invention.

This effectively means that the generator 17 can be inserted into an industrial heating/furnace arrangement, and makes use of the stream of hot gas which exits the combustor to generate further electricity, with minimal impact upon the normal operation of the industrial arrangement.

A stream of hot gas produced by an industrial combustor, furnace or other heating arrangement, to be passed through an MHD generator in accordance with the invention, may comprise a stream of gas which is produced directly by a combustor or furnace, or steam raised by passing the heated gas through a boiler or evaporator of any kind, such as an HRSG, or any heated gas which is produced directly or indirectly by the combustor or furnace.

In some embodiments, the presence of the MHD generator 17 between the combustor and the material to be heated will reduce the temperature of the stream of gas leaving the combustor by an appreciable amount. In the example discussed above, the gases entering the generator 17 are at around 3,000 -3,400°C, and the exhaust flow 11 is at around 1,650 -1,900°C. Depending on the temperature required for the industrial process in question, it may be necessary to increase the temperature of the combustor, so that gases leaving the generator 17 will still be at a sufficient temperature for the industrial process to be carried out, after the temperature drop has been incurred.

An example of use of a generator 17 of this type in an industrial setting is shown in figure 2. Figure 2 shows an industrial arrangement for heating a material.

An elongate heating chamber 20 is provided, with raw materials being introduced into a first end 21 thereof through a delivery pipe 28, and being conveyed along the heating chamber 20 in a first direction. As this occurs, heated gases from a combustor (not shown) are carried by suitable pipes 29 or the like to be introduced into the heating chamber 20, so that they impinge upon the raw materials. In the example shown, jets 22 of heated gas are introduced into the heating chamber 20 from both sides. The effect of these jets 22 is to heat and melt the raw materials.

The materials pass out of a second end 23 of the heating chamber, and are worked upon to form a finished product, and ultimately cooled to produce a finished product in a defined form (such as coil, rebar, or flat glass), such as sheet glass 24 as shown in figure 2.

A series of MHD generators 17 are positioned so that heated gas from the combustor passes through one of the generators 17 before being introduced into the heating chamber 20 as one of the jets 22 of heated gas. In the example shown, each generator 17 is positioned on an exterior side of the outside wall of the heating chamber 20.

In the example shown, an air separator 25 is provided, to separate parts of the ambient air and provide them to the generators 17 through suitable pipes 27. In the embodiments shown, the air separator 25 provides hydrogen and nitrogen to the generators 17.

While MHD generators have been used to generate electricity from the output of combustors in power stations, for instance by using the heated gases leaving the combustor to raise steam and drive turbines, greater efficiency can be achieved by using MHD generators in industrial processes where hot gases from combustors are used to melt or otherwise change the properties or chemical composition of an industrial item of manufacture, such as glass or steel, prior to traditional thermal waste heat recovery.

For instance, in the following industrial applications, net energy efficiencies can be increased from: * In flat glass production: 35% to 65-70% (using methane or hydrogen) * In steel re-heat furnaces: 35% to 65-70% (using methane or hydrogen) * In integrated iron and steel mill process gas power generation: 35% to 40-45% (using syngas and/or methane) The use of MHD generators in such processes represents a significant advantage, as it allows the generation of electricity which can be used in the industrial processes or elsewhere, and thus improve efficiency, with little or no disturbance of the industrial process to which the generators are applied.

A generator 17 of the type described above may also be used with conventional power generators, for instance by capturing the energy from the hot plasma gas in a heat recovery steam generator (HRSG) and passing the product through a standard steam turbine. In coal fed systems, efficiency may be increased in this way from 35% to 50-60%. In natural gas fed systems, efficiency may be increased in this way from 55% to 70-80%. Any type of power generator, including but not limited to generators using steam turbines and using gas turbines, may be used in this way.

While generators of the type shown in figure 1 may be used to capture energy in an industrial process, as shown in figure 2, it should be understood that conventional MHD generators, of any type, may be used in such processes. What is important is that heated gases pass through an MHD generator, before exiting the generator and being used in an industrial heating process, as described above.

Skilled readers will understand that generators and methods embodying the invention may be used in the clean and efficient generation of electrical power, and will find use in many different applications.

When used in this specification and claims, the terms "comprises" and "comprising" and variations thereof mean that the specified features, steps or integers are included. The terms are not to be interpreted to exclude the 30 presence of other features, steps or components.

The features disclosed in the foregoing description, or the following claims, or the accompanying drawings, expressed in their specific forms or in terms of a means for performing the disclosed function, or a method or process for attaining the disclosed result, as appropriate, may, separately, or in any combination of such features, be utilised for realising the invention in diverse forms thereof.

Although certain example embodiments of the invention have been described, the scope of the appended claims is not intended to be limited solely to these embodiments. The claims are to be construed literally, purposively, and/or to encompass equivalents.

Claims

Claims 1. A heating arrangement for an industrial process, comprising: a combustor having an output comprising a stream of heated gas; a heating area, in which one or more materials are heated with the heated gas from the combustor; and a magnetohydrodynamic (MHD) generator, arranged between the combustor and the heating area, so that the stream of heated has from the combustor passes through the generator, thus generating electricity, with an exhaust output of the generator being provided to the heating area.
2. An arrangement according to claim 1, further comprising an air separator, to separate components of the ambient air and provide at least one 15 of the components to the generator.
3. An arrangement according to claim 1 or 2, wherein a plurality of generators is provided between the combustor and the heating area, arranged such that a portion of the stream of heated gas from the combustor passes 20 through each of the generators.
4. An arrangement according to any preceding claim, wherein the heating of the materials in the heating area melts, softens, evaporates or cures at least one of the one or more materials in the heating area.
5. An arrangement according to any preceding claim, further comprising a working area, either within the heating area or downstream from the heating area, in which at least one of the one or more materials are worked to produce a product having a defined form.
6. A method of generating electricity, comprising the steps of: directing an output from a combustor, comprising a stream of heated gas, into a magnetohydrodynamic (MHD) generator; generating electricity by the MHD generator; and directing an exhaust output of the MHD generator into a heating area, in 5 which one or more materials are heated with the heated gas from the combustor.
7. A method according to claim 6, wherein the step of heating the one or more materials comprises melting, softening, evaporating or curing at least one of the one or more materials in the heating area.
8. A method according to claim 6 or 7, further comprising the step, after the step of heating the one or more materials, of working at least one of the one or more materials into a product having a defined form.
9. A method according to any one of claims 6 to 9, further comprising the steps of: providing a plurality of MHD generators; directing a portion of the output from the combustor into each of the 20 MHD generators; and directing an exhaust output from each of the MHD generators into the heating area.
10. A magnetohydrodynamic (MHD) generator, comprising: a plasma generator; a power generation region, comprising a magnetic field generator to generate a field in the region of the plasma jet substantially at right angles to the direction of travel for plasma jet, and one or more electrodes; and an electron exciter arrangement, positioned between the plasma 30 generator and the power generation region, the electron exciter arrangement configured to generate a fluctuating magnetic or electric field in the region of the plasma jet.
11. A generator according to claim 10, wherein the electron exciter arrangement comprises one or more conductive elements which are supplied with an alternating current.
12. The generator according to claim 11, wherein the conductive elements comprise one or more coils.
13. The generator according to claim 12, wherein in the region of the electron exciter arrangement, the plasma jet passes through a housing which contains the plasma jet, and the one or more coils are provided around an exterior of the housing.
14. A generator according to claim 12 or 13, wherein at least two separate coils are provided.
15. A generator according to claim 14, wherein the two or more coils are each provided with alternating current supplies having different frequencies and/or amplitudes.
16. A generator according to any claim 14 or 15, wherein the supply of current to the two or more coils is phased, such that for at least a part of the phase the first one of the coils is provided with alternating current and a second one of the coils is inactive.
17. A generator according to claim 10, wherein the electron exciter arrangement comprises at least one conductive element which is arranged to receive a direct current supply.
18. A generator according to claim 17, comprising two or more separate conductive elements, each configured to receive a direct current supply.
19. A generator according to claim 17 or 18, wherein the or each 5 conducting element comprises a solenoid.
20. A generator according to claim 18 or 19, wherein the current carrying elements are activated in a phased pattern, so that at least one time a first one of the current carrying elements is supplied with a DC current, and the other one of the elements is inactive.
21. An arrangement according to any one of claims 1 to 5, wherein the or each MHD generator is a generator according to any one of claims 10 to 20.
22. A method according to any one of claims 6 to 9, wherein the or each MHD generator is a generator according to any one of claims 10 to 20.
23. A power generation arrangement, comprising: a combustor having an output comprising a stream of heated gas; a turbine which is driven to rotate by the stream of heated gas; and a magnetohydrodynamic (MHD) generator according to any one of claims 10 to 20, arranged between the combustor and the turbine, so that the stream of heated has from the combustor passes through the generator, thus generating electricity, with an exhaust output of the generator being provided to the turbine.
24. A method of generating power, comprising the steps of: directing an output from a combustor, comprising a stream of heated gas, into a magnetohydrodynamic (MHD) generator according to any one of claims 10 to 20; generating electricity by the MHD generator and directing an exhaust output of the MHD generator into a turbine, driving rotation of the turbine and generating power.