Method of controlling a fuel mix for a combustion system

Abstract

A method of controlling a fuel mix for use in a combustion system, the fuel mix comprising different types of combustible fuels with different carbon content. The method involves controlling the composition of the fuel mix in order to minimise or reduce the carbon content of the fuel mix and / or of emissions produced by combustion of the fuel mix. The method involves minimising the use of high combustion temperature fuels and maximising the use of low temperature combustion fuels. The method involves converting feedstock into high temperature combustion fuels.

Description

[0001] METHOD OF CONTROLLING A FUEL MIX FOR A COMBUSTION SYSTEM

[0002] FIELD OF THE INVENTION

[0003] The present invention relates to the optimization of fuel for combustion systems, in particular to minimize or reduce the quantity of fossil fuel used.

[0004] BACKGROUND TO THE INVENTION

[0005] Many industrial processes, for example processes for manufacturing cement, glass or steel, utilise fossil fuels such as coal, oil or natural gas to enable high temperature combustion (typically combustion at at least 500°C) and satisfy the large energy demands. However, combustion of fossil fuel is undesirable in view of the greenhouse gas (GHG) emissions produced, in particular CO2, which contribute to climate change.

[0006] Other fuel types that produce lower GHG emissions are available, but tend either to have a calorific value that is too low, or to be too scarce, to satisfy the demands of high temperature combustion systems.

[0007] It would be desirable to optimize fuel mix composition to enable high temperature combustion processes, high temperature chemical reaction processes, high temperature combustion processes facilitating high temperature reaction(s) or other high temperature heating processes and systems while minimising or reducing the quantity of fossil fuel used and / or reduce or minimise the amount of fossil carbon exhaust gases produced.

[0008] SUMMARY OF THE INVENTION

[0009] From a first aspect, the invention provides a method, typically a computer-implemented method, of controlling a fuel mix for use in a combustion system for performing at least one combustion process in one or more combustion location, the fuel mix comprising a plurality of different types of combustible fuels including at least one first fuel and at least one second fuel, wherein said at least one first fuel has a higher carbon content than said at least one second fuel, and wherein the method comprises controlling the composition of the fuel mix depending on at least one operating condition of the combustion system, said controlling involving controlling the respective quantity of said at least one first fuel and / or of said at least one second fuel in order to minimise or reduce the carbon content of said fuel mix and / or of emissions produced by combustion of said fuel mix by said combustion system.

[0010] Typically, said at least one operating condition comprises a required energy level and / or a required combustion temperature, and wherein said required energy level may comprise total energy required to be produced by said at least one combustion process and / or total energy consumed by the combustion system. Said at least one operating condition may comprise any one or more of: a required adiabatic flame temperature; a required gas composition, in particular exhaust gas composition; a required moisture content, in particular moisture content of the fuel mix and / or of the exhaust gas composition; a required air-to-fuel ratio; energy rate, for example a total energy rate required to be produced by said at least one combustion process and / or consumed by the combustion system.

[0011] In preferred embodiments, the method includes producing one or more of said at least one second fuel from at least one other type of fuel, preferably using renewable energy, and using the, or each, produced second fuel in the fuel mix. Preferably, said at least one other type of fuel has a lower calorific value and / or a lower combustion temperature than the, or each, produced second fuel, and preferably has a lower combustion temperature than said at least one first fuel. Typically, producing one or more of said at least one second fuel from said at least one other type of fuel involves using one or more fuel production process or fuel conversion process, preferably including any one or more of: biomass reforming, steam reforming, water splitting, electrolysis, thermal H2generation, the Fischer-Tropsch process, anaerobic digestion, pyrolysis, gasification, fermentation, enzymatic generation, thermochemical water-splitting cycle(s) (e.g. the sulphur-iodine cycle, cadmium carbonate cycle, hybrid sulphur cycle, hybrid copper chloride cycle, carbon-sulphur cycle, nickelmanganese ferrite cycle, ISPRA series, vanadium chloride cycle), fermentation steam reforming, autothermal reforming, partial oxidation reforming, aqueous-phase reforming and supercritical water reforming.

[0012] Preferably, the method includes incorporating at least one other type of fuel into said fuel mix, wherein said at least one other type of fuel has a lower combustion temperature than said at least one first fuel and said at least one second fuel. Preferably, said controlling the composition of the fuel mix depending on at least one operating condition of the combustion system involves controlling the respective quantity of said at least one other type of fuel incorporated into the fuel mix to minimise or reduce the individual or combined quantity of said at least one first fuel and of said at least one second fuel in the fuel mix. The method may further include using said at least one other type of fuel to provide relatively low temperature energy during said at least one combustion process, and using said at least one first fuel and said at least one second fuel only for higher temperature energy during said at least one combustion process. Preferably, the method further includes adjusting the respective quantity of said at least one first fuel and of said at least one second fuel in said fuel mix in order to minimise or reduce the carbon content of said fuel mix and / or of emissions produced by combustion of said fuel mix in said at least one combustion process.

[0013] In preferred embodiments the method includes controlling the composition of the fuel mix based on a grade of each fuel, wherein the grade is indicative of the respective fuel’s suitability for combustion at a target combustion temperature, which may be based on one or more thermophysical and / or one or more thermodynamic property of the respective fuel, preferably being based at least on the adiabatic flame temperature of the respective fuel, and wherein, preferably, said controlling involves minimising or reducing the respective quantity of the, or each, fuel that is suitable for or capable of combustion at said target combustion temperature, and preferably increasing, or maximising, the quantity of the, or each, fuel that suitable for or capable of combustion at a respective temperature lower than said target combustion temperature. Preferably, the grade of each fuel depends on the combustion temperature, or adiabatic flame temperature, of the respective fuel, and wherein controlling the composition of the fuel mix based on the respective grade of each fuel involves minimising or reducing the respective quantity of one or more fuel of one or more relatively high grade, and preferably in maximizing or increasing the respective quantity of one or more fuel of one or more relatively low grade, wherein the or each relatively high grade corresponds to one or more respective combustion temperature, or adiabatic flame temperature, that is higher than one or more respective combustion temperature, or adiabatic flame temperature, associated with the or each relatively low grade. Preferably, controlling the composition of the fuel mix based on the respective grade of each fuel involves minimising or reducing the respective quantity of one or more fuel of a highest grade, and preferably in maximizing or increasing the respective quantity of one or more fuel of one or more lower grade, wherein the highest grade corresponds to one or more combustion temperature, or adiabatic flame temperature, that is higher than one or more respective combustion temperature, or adiabatic flame temperature, associated with the or each lower grade.

[0014] In preferred embodiments, the method includes controlling the composition of the fuel mix based on the carbon content, preferably the fossil carbon content, of the respective fuel, which may be based on one or more thermophysical and / or one or more thermodynamic property of the respective fuel, for example any one or more of: fossil carbon content; carbon content; biogenic-to-fossil carbon ratio; carbon dioxide production rate, and wherein, preferably, said controlling involves minimising or reducing the carbon content, preferably the fossil carbon content, of said fuel mix and / or of emissions produced by combustion of said fuel mix in said at least one combustion process. Preferably, controlling the composition of the fuel mix based on carbon content, in particular fossil carbon content, involves adjusting the respective amounts of fuels that are of the same grade, wherein the grade of each fuel is indicative of the respective fuel’s suitability for combustion at a target combustion temperature, which may be based on one or more thermophysical and / or one or more thermodynamic property of the respective fuel. Preferably, the grade of each fuel depends on the combustion temperature, or adiabatic flame temperature, of the respective fuel. Preferably, said adjusting the respective amounts of fuels that are of the same grade is performed in respect of each grade of fuel. Preferably, said controlling the composition of the fuel mix based on the carbon content is performed after controlling the composition of the fuel mix based on a grade of each fuel.

[0015] The method may include identifying said at least one other type of fuel for use in production of said one or more of said second fuel based on a respective grade of each fuel, wherein the respective grade is indicative of the respective fuel’s suitability for conversion to said one or more second fuel and / or of the respective fuel’s suitability for conversion to a fuel type having a higher adiabatic flame temperature than the respective fuel, preferably in order to minimise or reduce the carbon content of said fuel mix and / or of emissions produced by combustion of said fuel mix by said combustion system. The method may include determining, in respect of at least one type of fuel, either to incorporate said at least one type of fuel into the fuel mix or to use said at least one type of fuel to produce another type of fuel, preferably to produce one or more of said at least one second fuel, depending on the suitability of said at least one type of fuel for being converted to a different type of fuel having a higher adiabatic flame temperature than said at least one type of fuel, preferably in order to minimise or reduce the carbon content of said fuel mix and / or of emissions produced by combustion of said fuel mix by said combustion system.

[0016] Optionally, the method includes heating said fuel mix, or at least one fuel for inclusion in said fuel mix, prior to combustion by said combustion system. The method may include combusting at least one fuel available to said combustion system to provide heat for heating said fuel mix, or said at least one fuel for inclusion in said fuel mix, preferably using a combustion heating apparatus such as a furnace or boiler, and preferably in order to minimise or reduce the carbon content of said fuel mix and / or of emissions produced by combustion of said fuel mix by said combustion system.

[0017] In preferred embodiments, said at least one first fuel comprises one or more type of fossil fuel, for example any one or more of: coal, oil, peat, fuel oil, diesel, kerosene and natural gas. Preferably, said controlling the respective quantity of said at least one first fuel and of said at least one second fuel is performed to minimise or reduce the fossil carbon content of said fuel mix and / or of emissions produced by combustion of said fuel mix in said at least one combustion process.

[0018] In some embodiments, said at least one second fuel comprises one or more type of fuel, preferably any one or more of: hydrogen, methane (in particular biomethane and e-methane), ammonia, syngas, e-fuel(s) and biogenic carbon-containing fuel(s).

[0019] In some embodiments, said at least one other type of fuel used to produce one or more of said at least one second fuel comprises any one or more of water, biomass, glycerine (or glycerol), biodiesel, ammonia, forestry & agricultural wastes, solid recoverable fuel (SRF), municipal solid waste (MSW), wastewater sludge and meat & bonemeal (MBM).

[0020] In some embodiments, said at least one other type of fuel incorporated into the fuel mix comprises any one or more of biomass, glycerine (or glycerol), biomass, biodiesel, ammonia, forestry & agricultural wastes, solid recoverable fuel (SRF), municipal solid waste (MSW), wastewater sludge and meat & bonemeal (MBM).

[0021] Optionally, the method includes adding oxygen to the fuel mix and / or said at least one combustion process in order to increase combustion efficiency and / or to reduce or minimize the respective quantity of said at least one first fuel and / or of said at least one second fuel in the fuel mix.

[0022] Typically, controlling the fuel mix is performed depending on one or more input received from any one or more of: said combustion system; one or more fuel production system; one or more fuel supply system, optionally in real-time, and / or based on historic data relating to the combustion system, said one or more fuel production system and or said one or more fuel supply system.

[0023] Preferably, the method includes optimizing the composition of the fuel mix in order to minimise or reduce the carbon content of said fuel mix and / or of emissions produced by combustion of said fuel mix by said combustion system while satisfying said at least one operating condition, conveniently using one or more suitable optimization algorithm and / or using artificial intelligence (Al) and / or machine learning (ML). Said optimizing may involve determining which of the available fuel(s) is to be converted to a different type of fuel, in particular a different type of fuel having a higher adiabatic flame temperature than the respective fuel being converted, for use in the fuel mix. Said optimizing may involves determining which of the available fuel(s), and / or what quantity of the available fuel(s), is to be used to heat said fuel mix, or at least one fuel for inclusion in said fuel mix, prior to combustion by said combustion system.

[0024] In typical embodiments, the method includes controlling the supply of a plurality of different types of combustible fuel and / or feedstock for producing combustible fuel from at least one fuel supply, and / or feedstock supply, directly or indirectly to said combustion system, for example to said one or more combustion location and / or to a mixing device, and / or to one or more fuel production system for converting one or more type of fuel, or feedstock, to a different type of fuel.

[0025] From a second aspect, the invention provides a method of controlling a combustion system for performing at least one combustion process in one or more combustion location, the method including the method of controlling a fuel mix for the combustion system according to the first aspect of the invention.

[0026] From a third aspect the invention provides an optimization system for providing a fuel mix to a combustion system, the optimization system including a control system configured to perform the method of the first aspect of the invention and / or the method of the second aspect of the invention.

[0027] From another aspect, the invention provides a method of controlling a fuel mix for use in a combustion system, the fuel mix comprising different types of combustible fuels with different carbon content. The method involves controlling the composition of the fuel mix in order to minimise or reduce the carbon content of the fuel mix and / or of emissions produced by combustion of the fuel mix. The method preferably involves minimising the use of high combustion temperature fuels and maximising the use of low temperature combustion fuels. The method may involve converting feedstock into high temperature combustion fuels.

[0028] From a further aspect the invention provides a method, typically a computer-implemented method, of controlling a fuel mix for use in a combustion system for performing at least one combustion process in one or more combustion location, the fuel mix comprising a plurality of different types of combustible fuels, the method including controlling the composition of the fuel mix based on a grade of each fuel, wherein the grade is indicative of the respective fuel’s suitability for combustion at a target combustion temperature, which may be based on one or more thermophysical and / or one or more thermodynamic property of the respective fuel, preferably being based at least on the adiabatic flame temperature of the respective fuel, and wherein, preferably, said controlling involves minimising or reducing the respective quantity of the, or each, fuel that is suitable for or capable of combustion at said target combustion temperature, and preferably increasing, or maximising, the quantity of the, or each, fuel that suitable for or capable of combustion at a respective temperature lower than said target combustion temperature.

[0029] From a still further aspect the invention provides a method, typically a computer-implemented method, of controlling a fuel mix for use in a combustion system for performing at least one combustion process in one or more combustion location, the fuel mix comprising a plurality of different types of combustible fuels, the method including controlling the composition of the fuel mix based on the carbon content, preferably the fossil carbon content, of the respective fuel, by adjusting the respective amounts of fuels that are of the same grade, wherein the grade of each fuel is indicative of the respective fuel’s suitability for combustion at a target combustion temperature, which may be based on one or more thermophysical and / or one or more thermodynamic property of the respective fuel.

[0030] Preferred embodiments involve optimizing fuel mix composition to enable high temperature combustion processes, high temperature chemical reaction processes, high temperature combustion processes facilitating high temperature reaction(s) or other high temperature heating processes and systems while minimising or reducing the quantity of fossil fuel used and / or reduce or minimise the amount of fossil carbon exhaust gases produced. Typically, such high temperature processes have an operating temperature of at least 500°C. For example, cement production and glass production each involve processes occurring at 800 to 1600°C, while steel production involves processes occurring at 700 - 1700°C (wherein direct reduction of iron ore (typically a mixture of iron oxide and other susbstance(s)) from hydrogen occurs at 800°C).

[0031] Methods embodying the invention are advantageously computer-implemented.

[0032] Preferred systems and methods embodying the invention are configured to use renewable energy to convert feedstocks having a low, or relatively low, calorific content (or calorific value) and / or low, or relatively low, adiabatic flame temperature (e.g. unrefined biomass, municipal solid wastes and so on) to combustible fuel(s) having a high, or relatively high, calorific content (or calorific value) and / or high, or relatively high, adiabatic flame temperature (e.g. hydrogen) and to use the resulting fuel(s) in a high temperature combustion or heating process or system, particularly in combination with one or more other type of combustible fuel, typically one or more fossil fuel such as coal, oil, natural gas and / or other hydrocarbon containing material. Typically, fuels or feedstocks with a calorific value less than 25 MJ / kg are defined as low calorific, while fuels or feedstocks with a calorific value greater than 25 MJ / kg are defined as high calorific. Typically, fuels or feedstocks with an adiabatic flame temperature greater than 1000 °C are defined as high adiabatic flame temperature fuels, while fuels or feedstocks with an adiabatic flame temperature less than 1000 °C are defined as low adiabatic flame temperature fuels. Examples of fuels / feedstocks for use with or production by typical embodiments of the invention are provided in Table 1 below. For example, hydrogen has a high calorific value (120 MJ / kg) compared to coal (25-30 MJ / kg) and lower calorific sustainable fuels e.g. solid recovered fuels (SRFs) (approx. 16-24 MJ / kg). Hydrogen may be produced from lower calorific sustainable fuels e.g. solid recovered fuels (SRFs) and used in combination with one or more fossil fuel to provide the energy requirements for any given target combustion or heating process or system, thereby minimizing, or at least reducing, the amount of fossil fuel that is used.

[0033] *Net calorific value of fuel source vary due to composition differences which is reflected in the range of values.

[0034] ** The methane may be from any source including natural gas, biomethane and e-methane.

[0035] *** The biomass may be from any source including lignocellulosic, hemicellulosic and cellulosic sources.

[0036] TABLE 1

[0037] Lower calorific content sustainable fuel(s) may be injected or otherwise included in the fuel mix, optionally in combination with high calorific content fuel(s) to improve the fuel efficiency of the relevant combustion and / or heating process. Advantageously, optimization of fuel composition is performed to achieve the appropriate energy requirements and operational conditions of the relevant combustion or combustion system or process (which can vary from system to system or process to process), while minimizing or reducing the amount of fossil that is used.

[0038] Advantageously, an appropriate fuel composition can be achieved through optimisation of process parameters and / or post-production separation techniques, to achieve the appropriate operational conditions of the desired, or target, combustion process, in particular to reduce fossil fuel emissions, especially CO2. Examples of the process parameters include any one or more of flow rate, temperature, pressure, ratio of reactants, catalyst type and activity. Examples of the separation techniques include pressure swing adsorption (PSA), vacuum swing adsorption (VSA), temperature swing adsorption (TSA), membrane separation, electrostatic separation, chemical separation, condensation separation.

[0039] Optionally, oxygen may be added to the fuel mix or otherwise to the combustion process (for ‘oxycombustion’) in order to increase combustion efficiency, and as such may be said to be an additive to the combustion process, and reduces overall fuel mass requirements for the relevant application, which creates a more sustainable and efficient process.

[0040] Preferred embodiments control, and advantageously optimize, one or more characteristic, or parameter, of the fuel mix (for example any one or more of: composition; calorific value (calorific value may be used as an indication of calorific content, or energy content); combustion temperature (or adiabatic flame temperature) and difference between lower heating value (LHV) and higher heating value (HHV)) and / or of the combustion process (e.g. to control the air / fuel ratio and / or the exhaust products (in particular the composition of the exhaust product(s))) to reduce fossil carbon emissions (especially CO2) whilst maintaining key operating parameter(s) (or condition(s)) of the process, such as any one or more of: operating temperature; energy level; power level; adiabatic flame temperature; flame position and exhaust composition (e.g. maintaining a target level of carbon in the exhaust gas for steel production). In this connection it is noted that combustion temperature, or adiabatic flame temperature, is often higher than desired operating temperature to allow for thermal losses in the system. Operating temperature can also vary at different points of the process. Preferably, the control is performed using model-based control methods. Typically, the energy content or calorific value of the fuel mix is controlled (calorific value may be used as an indication of calorific content, or energy content). In preferred embodiments, the fuel mix is controlled to create a target energy level and / or temperature in the combustion process or other heating process (e.g. at one or more location such as a combustion chamber or reaction zone). Controlling the energy level may involve controlling the calorific value of the fuel mix, which depends on the individual calorific values of the fuels in the mix and so may be controlled by controlling the type of fuels in the mix and / or the ratio of fuels in the mix. Controlling the temperature may involve controlling the adiabatic flame temperature of the fuel mix, which depends on the individual adiabatic flame temperatures of the fuels in the mix and so may be controlled by controlling the type of fuels in the mix and / or the ratio of fuels in the mix. Some fuels (e.g. hydrogen) may have both a high adiabatic flame temperature and a high calorific value, while other fuels (e.g. syngas) may have a high adiabatic flame temperature and a low calorific value. The types of fuels included in the mix may depend on the application, e.g. syngas is suited to steel production as it provides carbon to the process.

[0041] Some embodiments involve reforming or gasification of relatively low calorific content biomass to produce higher calorific content fuel(s) (such as hydrogen) or relatively high flame temperature fuel(s) (such as syngas) as a pre-process step before adding the resulting fuel(s) to the fuel mix.

[0042] Sustainable fuels (e.g. SRF(s) which may for example be formed from any one or more of paper, card, wood, textiles and plastics) may be injected or otherwise included in the fuel mix, optionally in combination with high calorific content fuel(s) to minimize or reduce consumption of fossil fuels.

[0043] Oxygen-enriched air may be added to the fuel mix or otherwise to the combustion process to facilitate replacement of fossil fuel, and to facilitate further use of sustainable fuel(s), e.g. SRF(s) and / or hydrogen.

[0044] Some embodiments use thermochemical cycle(s) for hydrogen production and / or the production of low-carbon, high calorific content fuels, advantageously in a reactor, preferably a recirculating reactor, configured to utilise waste heat recovery within the reactor or production system.

[0045] Some embodiments use compression and dispensing technology to deliver low carbon high calorific content fuels to the process.

[0046] Preferred embodiments include, or involve the use of, a control system configured to regulate volume flows of fuels into the combustion process.

[0047] Preferred embodiments involve the Integration of any one or more of the above-identified features to produce a total system approach for the minimization or removal of fossil fuels from any given high temperature combustion process or system.

[0048] Further advantageous aspects of the invention will be apparent to those ordinarily skilled in the art upon review of the following description of specific embodiments and with reference to the accompanying drawings.

[0049] BRIEF DESCRIPTION OF THE DRAWINGS

[0050] Embodiments of the invention are now described by way of example with reference to the accompanying drawings in which:

[0051] Figure 1 is a schematic diagram of a system embodying the invention for optimizing fuel for a combustion system; Figure 2 is a schematic diagram illustrating how a fuel mix is created from available fuel inputs; and

[0052] Figure 3 is a schematic diagram of a preferred embodiment of a control system for use with the system of Figure 1.

[0053] DETAILED DESCRIPTION OF THE DRAWINGS

[0054] Referring now to Figure 1 of the drawings there is shown, generally indicated at 10, an optimization system for providing fuel, in particular a fuel mix comprising two or more different types of combustible fuel, to a combustion system 12. The optimization system 10 embodies one aspect of the invention and is configured to implement an optimization method embodying another aspect of the invention. In typical embodiments, the combustion system 12 comprises one or more combustion apparatus 14 configured to perform one or more combustion process, e.g. the combustion of fuel in one or more combustion stages at one or more combustion location. The combustion stage(s) may comprise a main combustion stage (or high temperature combustion stage) and one or more lower temperature combustion stage (e.g. a pre-heating, preparatory or preliminary combustion stage). Each combustion stage may be performed by the same combustion apparatus 14 or by a different combustion apparatus 14, i.e. the, or each, combustion apparatus 14 may perform one or more combustion stage.

[0055] The combustion process (typically the, or each stage of the combustion process) is typically associated with target values for one or more operating parameters (or conditions), which may include any one or more of (and typically all of): required energy; required adiabatic flame temperature, or combustion temperature; operating temperature; gas composition, in particular exhaust gas composition; required moisture content; air to fuel ratio. Each stage of the combustion process may have the same target value(s), or different target value(s) depending on the application. By way of example, in typical embodiments, the required adiabatic flame or combustion temperature may be 900-2200°C, but may alternatively be in the range 500-2500°C . Typically, the exhaust gas may comprise a mixture of any one or more of: H2O, O2, CO2, CO, SOx, NOx, N2, PM5.25. The target gas composition may stipulate required concentrations of any one or more of these products, or other products produced by the combustion.

[0056] The combustion system 12 may be part of an industrial system implementing an industrial process for manufacturing one or more products. Examples of such industrial systems include, but are not limited to, systems for manufacturing cement, glass, steel or other metals. In typical embodiments, the combustion system 12 is configured to implement a relatively high heat process that involves high heat combustion of fuel. Typically, such high temperature processes have an operating temperature of at least 500°C. For example, cement production and glass production each involve processes occurring at 800 to 1600°C, while steel production involves processes occurring at 700 - 1700°C (wherein direct reduction of iron ore (typically a mixture of iron oxide and other susbstance(s)) from hydrogen occurs at 800°C). The heat generated by the combustion system 12 may be used at the combustion location (e.g. at the respective combustion apparatus 14) and / or may be delivered to one or more other location (e.g. a chemical reactor or chemical reaction zone) in the system 12 and / or in the industrial system of which the system 12 is part.

[0057] The combustion apparatus 14 typically comprises one or more furnace, a boiler or other heater. The combustion apparatus 14, e.g. the or each furnace or other heater, typically comprises one or more burner 16 for combusting fuel, typically mixed with air and / or oxygen. In typical embodiments, combustion apparatus 14 includes at least one burner 16 of a type that receives fuel in a flowable form, for example comprising fuel that is fluid (liquid or gaseous) and / or that comprises particulate material (e.g. entrained in air or other gas(es)). Alternatively, or in addition, the combustion apparatus 14 may include one or more solid fuel burner 16. In some embodiments, the combustion apparatus 14 may comprise one or more solid fuel burner and one or more flowable, or gaseous, fuel burner, wherein one or more solid fuels are combusted by the solid fuel burner(s) to produce some of the heat energy required by the application, and one or more flowable or gaseous fuels are combusted by the flowable or gaseous fuel burner(s) to produce the remainder of the heat energy required by the application. For example, solid fuel(s) (e.g. SRF(s)) having a low or relatively low adiabatic flame temperature may be combusted to produce heat energy at a relatively low temperature (i.e. lower than is required by the application) and gaseous fuel(s) (e.g. hydrogen) having high or relatively high adiabatic flame temperature may be combusted to produce heat energy at a higher temperature such that the combined heat energy reaches the target temperature for the application. In typical embodiments, the fuel comprises a mix of different types of fuel, each of which may be in flowable form or solid form, i.e. the fuel mixture may comprise one or more flowable fuel and / or one or more solid fuel. Some or all of the different types of fuel may be mixed together prior to combustion. The combustion system 12 may be configured to mix fuels, as required, prior to combustion, and / or fuels may be mixed elsewhere in the system 10 (e.g. in the fuel supply system(s) 22). Alternatively, or in addition, some fuels may be provided to the fuel supply system(s) 22 or otherwise to the system 10 premixed. Alternatively, or in addition, one or more of the different types of fuel (or a mixture of two or more fuels) may be combusted and one or more other type of fuel may be added to the combustion flame and / or to the combustion chamber. Accordingly, while the combination of fuels is referred to as a mix or mixture, this does not imply that all of the fuels are mixed together prior to combustion (although all of the fuels may be mixed together prior to combustion in some embodiments) or otherwise all mixed together to form a single mixture of fuels. The fuel mix, or fuel mixture, may therefore be said to comprise a combination of different types of fuel for use in the combustion process(es) performed by the combustion system 12. Optionally, fossil fuel(s) may be used to provide the pilot flame only. Optionally, gaseous fuel(s) may be used to provide the pilot flame only. Liquid or solid fuels may be delivered to the combustion chamber. By way of example, hydrogen (or other gaseous fuel) may be combusted and pulverised solid fuel may be added to the combustion flame (which increases the radiant heat transfer from the flame). Liquid fuels may be injected into combustion chamber. Alternatively or in addition, one or more of the different types of fuel may be combusted at different locations in the combustion system 12, e.g. by different combustion apparatus 14 or by different burners 16. Optionally, the combustion system 12 includes one or more fuel processing unit 13 for performing one or more processing operation, e.g. pulverising, shredding, drying and / or mixing, on fuel prior to combustion by the combustion apparatus 14. The fuel processing unit(s) 13 may be of any suitable conventional type, and for example comprise any one or more of a solid fuel mixing device, a flowable / gaseous fuel mixing device, a kiln (or other drying apparatus). The fuel processing unit(s) 13 are preferably electrically-powered, but may alternatively be powered by fuel combustion, in which case a portion of the fuel mixture may be used to power the fuel processing unit(s) 13.

[0058] Optionally, the combustion system 12 includes one or more pre-heating apparatus 15 for heating the fuel mixture, or any component fuel of the fuel mixture, prior to combustion by the combustion apparatus 14. The fuel pre-heating apparatus 15 may be of any suitable conventional type, for example a furnace (e.g. a tube furnace), oven or kiln. The pre-heating apparatus 15 is preferably electrically-powered, but may alternatively be powered by fuel combustion, in which case a portion of the fuel mixture may be used to power the pre-heating apparatus 15.

[0059] The preferred system 10 includes one or more fuel production system 18 for producing fuel(s), in particular fuel(s) having a low or relatively low carbon content (in particular a low or relatively low fossil carbon content) and / or a high adiabatic flame temperature and / or a high calorific value (which fuel(s) may be referred to as high quality fuel(s) or low carbon high quality fuel(s)), from any suitable feedstock material, typically low calorific content (or calorific value) feedstock, for example biomass or water. The calorific value (sometimes called the heating value) of a fuel may be used as an indication of its calorific content, or energy content. In preferred embodiments the fuel production system(s) 18 are configured to produce any one or more of hydrogen, syngas, methane or e-fuels, although the fuel production system(s) may be configured to produce, or synthesise, any other suitable fuel (typically in liquid or gaseous form). Any suitable conventional production or synthesis process(es) may be used depending on the available feedstock. Suitable conventional production or synthesis process(es) include, but are not limited to, any one or more of biomass reforming, steam reforming, water splitting, electrolysis, thermal H2generation, the Fischer-Tropsch process, anaerobic digestion, pyrolysis, gasification, fermentation, enzymatic generation, thermochemical water-splitting cycle(s) (e.g. the sulphur-iodine cycle, cadmium carbonate cycle, hybrid sulphur cycle, hybrid copper chloride cycle, carbon-sulphur cycle, nickel-manganese ferrite cycle, ISPRA series, vanadium chloride cycle), fermentation steam reforming, autothermal reforming, partial oxidation reforming, aqueous-phase reforming or supercritical water reforming as applicable. For example, the fuel production system(s) 18 may be configured to produce hydrogen from biomass and / or water using any one or more of the above-identified processes as applicable. The fuel production system(s) 18 may be configured to use the produced hydrogen (and / or other source of hydrogen available to the system(s) 18) to produce methane and / or syngas using any suitable conventional process. The fuel production system(s) 18 may be configured to use the produced syngas (and / or other source of syngas available to the system(s) 18) to produce e-fuel, typically comprising liquid hydrocarbon(s), using any suitable conventional process, typically comprising the Fischer-Tropsch process. The fuel production system(s) 18 may take any conventional form for producing the respective fuel(s) from the respective feedstock(s). In preferred embodiments, the fuel production system(s) 18 are powered using renewable or green energy, for example electrical power, or other energy, obtained from wind, water and / or solar power. Fuel produced by the fuel production system(s) 18 may be supplied directly to the combustion system 12, e.g. to a burner 16, or mixing device 13 or storage container (not shown) from which it can be dispensed for use in the combustion system 12 as required. Optionally, one or more fuel produced by the fuel production system(s) 18 is stored (e.g. in a suitable storage container included in the combustion system 12 or elsewhere in the system 10) and is made available for use in the combustion system 12 (e.g. via any suitable arrangement of conduits, valves, pumps and / or injectors etc.) when required. This allows the system 10 to produce and store such fuel(s) in periods when renewable energy is available to power the fuel production system(s) 18, and to use the stored fuel(s) in periods when there is insufficient available renewable energy, and so to limit the impact that a variable renewable energy supply may otherwise have on the operation of the system 10. The system 10 may be configured to determine the composition of the fuel mixture depending on the intermittency of the renewable energy supply, for example by selecting to use one or more liquid fuel in the fuel mixture rather than gaseous fuel(s) in applications where there is an intermittent or unreliable renewable energy supply since it is easier to store liquid fuel than it is to store gaseous fuel, or conversely to select to use one or more gaseous fuel in the fuel mixture rather than liquid fuel(s) in applications where there is reliable or relatively constant renewable energy supply, e.g. because producing the gaseous fuel(s) requires less energy. For example, in embodiments where the system 10 uses a highly intermittent renewable energy source, it may be advantageous for the system 10 to produce a liquid fuel (e.g. a e-fuel) than to produce pure hydrogen due to storage implications for hydrogen, even if the liquid fuel requires more energy to produce. Hence, when optimising the fuel mixture, the system 10 may be configured to take into account the intermittency of the renewable energy supply in conjunction with the system’s ability to store respective fuel types and / or the energy required to produce the respective fuel types.

[0060] One or more optional separation step can be applied to fuel produced by the fuel production system 18 to ensure desired fuel composition. For example if the fuel production system 18 produces a mixture of H2, CO, CO2and CH4and hydrogen injection is desirable, PSA or membrane separation can be applied to separate hydrogen from the product stream. For example in glass production excess moisture in the exhaust gas is undesirable so the fuel mixture can be optimised to limit moisture content below acceptable levels. For example fuels which produce water upon combustion, such as hydrogen, may need to be limited. Separation techniques may be traditional or emerging technologies, including but not limited to the separation methods identified hereinbefore.

[0061] The system 10 includes a control system 20 configured to control, and advantageously optimize, one or more characteristic, or parameter, of the fuel mix that is used by the combustion system 12. For example, the control system 20 may be configured to control or select any one or more of the following aspects of the fuel mixture: composition of the fuel mixture (e.g. the type(s) of fuel used in the fuel mix and / or their relative quantity in the mix); calorific value of the, or each, fuel included in the mixture; energy content of the fuel mixture (calorific value may be used as an indication of calorific content, or energy content); adiabatic flame temperature of the, or each, fuel in the fuel mixture, and difference between lower heating value (LHV) and higher heating value (HHV) of the or each fuel in the fuel mixture. The control system 20 may be configured to control one or more aspect of the combustion process(es) in the combustion apparatus 12, for example to control the air / fuel ratio and / or the exhaust product(s), in particular the composition of the exhaust product(s). In preferred embodiments, the operation of the control system 20 is configured with the aim of reducing fossil carbon emissions (especially CO2) by the combustion system 12, whilst maintaining key operating parameter(s) of the combustion process (and / or other process(es) performed by the combustion system 12), such as operating temperature, adiabatic flame temperature and / or the target energy level.

[0062] Typically, the control system 20 comprises one or more suitably programmed or configured hardware, firmware and / or software controllers, e.g. comprising one or more suitably programmed or configured computing device, microprocessor, microcontroller or other processor, for example an IC processor such as an ASIC, DSP or FPGA (not illustrated) or PLC. The control system 20 may be configured to implement feedback control and / or predictive control. Preferably, the control system 20 is configured to control the system 10, more particularly to control the fuel mix, using model-based control, wherein the control system 20 is programmed with a mathematical model of the system 10 that allows it to determine or predict the behaviour of the system 10, for example depending on measured values of one or more relevant system parameters and / or one or more set points for those parameters. Relevant system parameters may include any one or more of: composition of the fuel mix, composition of the exhaust products, air / fuel ratio, combustion temperature, adiabatic flame temperature, calorific value(s) and any of the other characteristics or parameters described herein.

[0063] The preferred system 10 includes one or more fuel supply system 22 for supplying one or more fuel and / or one or more feedstock, to the combustion system 12 and / or to the fuel production system(s) 18. In typical embodiments, the fuel supply system(s) 22 comprises means for supplying one or more type of fossil fuel, for example coal, oil, natural gas and / or other hydrocarbon containing material to the combustion system 12. In typical embodiments, the fuel supply system(s) 22 are configured to supply one or more other type of fuel as required by the combustion system 12 and / or to the fuel production system(s) 18. For example, the fuel supply system(s) 22 may comprise means for supplying one or more low, or relatively low, calorific content fuel, e.g. any one or more of glycerol, MSW and SRF. In some embodiments, instead of producing any given low carbon high quality fuel using fuel production system(s) 18, such fuel, e.g. hydrogen, syngas, methane or e-fuels, may be supplied (ready-made) by one or more fuel supply system 22. The fuel production system(s) 18 may be omitted or provided in addition to one or more fuel supply system 22 as suits the application. The fuel supply system(s) 22 may take any conventional form for supplying the respective fuel, for example comprising one or more tank, canister or other storage container (pressurized or nonpressurized as applicable), and any associated equipment such as valve(s), pump(s), feeder(s) and conduit(s) required to supply the respective fuel to the combustion system 12. For fuels that are to be supplied in particulate form (e.g. coal), the system 22 may include any suitable conventional means for pulverizing the solid fuel and / or for entraining it in air or other gas. A respective fuel supply system 22 may be provided for each type of fuel, or each fuel supply system 22 may be configured to supply a mixture of one or more fuels. Fuel supply systems 22 may be co-located with each other or distributed around the system 10 as is convenient.

[0064] Preferably, the system 10 includes an oxygen supply system 28, which may take any conventional form, e.g. comprising one or more suitable storage container with means for delivering oxygen to the system. In use, oxygen may be added to the fuel mix or otherwise to the combustion process (for ‘oxycombustion’) in order to increase combustion efficiency, and as such may be said to be an additive to the combustion process, and reduces overall fuel mass requirements for the relevant application, which creates a more sustainable and efficient process.

[0065] Optionally, one or more Carbon Capture Utilisation and / or Storage (CCUS) device or system 24 may be incorporated into the combustion system 12 and / or included elsewhere in the system 10. The, or each, CCUS device or system 24 may be configured to increase decarbonisation within the system 10 and may for example be performed using one or more conventional point source carbon capture technologies, and / or by using process additives to capture carbon in-situ (e.g. metal oxides including iron oxide, and / or calcium looping). Inclusion of CCUS can impact the optimisation process to enable most efficient capture of carbon. The control system 20 may be optimised with respect to the CCUS system, in particular the control system may be configured to control the composition of the exhaust gas to increase the efficiency of the CCUS system.

[0066] The control system 20 may control the operation of any one or more of the fuel production system(s) 18, the fuel supply system(s) 22, the combustion system 12, the oxygen supply system 28 and the CCUS device(s) / system(s) 24, as required, to control the operation of the system 10, and in particular to control, and advantageously optimize, one or more characteristic, or parameter, of the fuel mix that is used by the combustion system 12.

[0067] The fuels that are available to the system 10 may be available for supply via one or more of the fuel supply source(s), or system(s) 22, e.g. for supply directly to the combustion system 12 or to a premixing device for supply to the combustion system 12, and / or to one or more of the fuel production system(s) 18 for conversion, or upgrading, to a different type of fuel for supplying directly to the combustion system 12 or to a pre-mixing device for supply to the combustion system 12. The fuel mixture 40 may therefore comprise a mixture of two or more different types of fuel. The fuels may differ from each other with respect to one or more thermophysical parameters, including any one or more of the following thermophysical parameters: calorific value (or heating value); hydrocarbon ratio (or hydrogen / carbon ratio); ash and / or moisture content; carbon content; biogenic-to-fossil carbon content; carbon to oxygen ratio; physical state (solid, liquid, gas); laminar flame speed. The fuels may differ from each other with respect to one or more combustion or thermodynamic parameters, including any one or more of the following combustion or thermodynamic parameters: adiabatic flame temperature (or adiabatic combustion temperature or just combustion temperature); higher heating value (HHV); lower heating value (LHV); carbon dioxide production; air-to-fuel mass ratio; pre-combustion fuel temperature; pre-combustion air temperature.

[0068] Figure 2 is a schematic diagram illustrating how a combustible fuel mixture 40 for use in the combustion system 12 is created from available fuels 30. In preferred embodiments, each available input fuel 30 is graded based on one or more of its thermodynamic parameters and / or one or more of its thermophysical parameters, whereby the grade is an indication of the respective fuel’s quality, or suitability, for combustion, especially in the combustion system 12 in which it is intended to be used. In preferred embodiments, the grade is an indication of the fuel’s quality for combustion at relatively high temperatures, for example between 900°C- 2200°C. The fuels 30 may be graded into any one of a plurality of grades which, in the illustrated embodiment, comprise grades A, B and C. In preferred embodiments, the grades are indicative of the fuel’s suitability for combustion at different temperature ranges, including a highest temperature range (corresponding to grade A in this example), a lowest, or lower, temperature range (corresponding to grade C in this example), and optionally one or more intermediate temperature range (corresponding to grade B in this example). More generally, there may be two or more grades as suits the application, including a relatively high, or highest, grade, and one or more lower grade. Alternatively, or in addition, the grading of each available fuel 30 may include an indication of its suitability or readiness for being upgraded to a higher grade, e.g. from grade C to grade B, or from grade B to grade A in the present example, wherein the upgrading may be performed by one or more of the fuel production system(s) 18 in the present example. For example SRF and glycerine (or glycerol) may be graded in grade B, with glycerine (or glycerol) indicated as being particularly suitable for upgrading to hydrogen (grade A), as a result of which the controller 20 may decide to upgrade the glycerine (or glycerol) to hydrogen rather than to combust it without conversion (upgrading) in order to support higher combustion temperatures and optionally reduced fossil carbon content if paired with, for example, SRF.

[0069] It is assumed that the combustion system 12, in particular the combustion apparatus 14, requires combustion at temperatures in temperature range A, and it is assumed that fuel(s) that are graded in grade A are inherently suitable for providing combustion at the required temperature range A, and as such may be added directly to the fuel mixture 40. As indicated at block 34 in Figure 2, fuel(s) that are graded in a lower grade, e.g. grade B in this example or more generally in an intermediate grade, e.g. medium or low-to-medium grade, are not capable by themselves to provide combustion in the required temperature range A, but may be added directly to the fuel mixture 40 in order to contribute heat energy to the combustion process, in particular to facilitate reaching combustion at a temperature lower than the required temperature range A; such fuels are provided in the fuel mixture 40 together with one or more higher temperature fuel (i.e. graded in grade A in this example) in order that the fuel mixture 40, when combusted, causes the combustion system 12 to reach required combustion temperature, and as such may be referred to as bulking fuels. As indicated at blocks 32 and 36 in Figure 2, fuel(s) that are graded in a lower grade, e.g. grades B or C in this example or more generally in an intermediate or low grade, are not capable by themselves to provide combustion in the required temperature range A, but may be used to produce a different type of fuel for adding to the fuel mixture 40. In particular, such lower grade fuel(s) may be used to produce a fuel having a higher combustion temperature, e.g. a grade A fuel in the present example. Production of one type of fuel from another may be performed using any suitable conventional process(es), typically comprising chemical and / or biological process(es), and in the illustrated embodiment may be performed by the fuel production system(s) 18. In typical embodiments, such lower grade fuel(s), e.g. biomass, and / or water, are used to produce hydrogen, syngas, methane or e-fuels using any suitable conventional production process, for example including any one or more of biomass reforming, electrolysis, thermal H2generation, anaerobic digestion, pyrolysis, gasification, thermochemical cycle(s), fermentation steam reforming, autothermal reforming, partial oxidation reforming, aqueous-phase reforming or supercritical water reforming (and / or any other process(es) as outlined above) as applicable.

[0070] As indicated at block 38 of Figure 2, fuel(s) that are graded in a lower grade, e.g. grade C in this example, may be used for ancillary purposes, e.g. to facilitate the production of different type(s) of fuel (as outlined with reference to blocks 32 and 36) as a source of heat energy for the fuel production process, and as such may be provided to the fuel production system(s) 18, or to provide heat energy for other applications within the system 10, e.g. heating, drying or pre-heating, which may be required by any of the systems 12, 18, 22, e.g. by any one or more of the fuel processing apparatus 13 and / or pre-heating apparatus 15. Other grades of fuel may be used for such ancillary purposes if required.

[0071] In typical embodiments, the available fuels 30 includes, but are not limited to, any one or more of the following types of fuel: coal, peat, fuel oil(s), diesel, gasoline, kerosene, methane (natural gas, biomethane, e-methane), syngas, e-fuel, hydrogen, biomass, biodiesel, ammonia, forestry & agricultural wastes, solid recoverable fuel (SRF), glycerine (or glycerol), municipal solid waste (MSW), wastewater sludge and meat & bonemeal (MBM), liquid fraction from AD digestate, dairy waste and wastewater including whey, lactose and lactic acid, brewing wastes including wastewaters, brewer’s spent grain, hot trub, brewer’s yeast, distilling wastes including wastewaters, distillery sludges, draff, pot ale, spent lees. Fuels that may be graded in the highest grade (grade A in the present example) include: coal, fuel oil(s), diesel, gasoline, kerosene, methane (natural gas, biomethane, e-methane), syngas, e-fuel, hydrogen, biodiesel. Fuels that may be graded in a lower or medium grade (grade B in the present example) include biomass, recoverable fuel (SRF), glycerine (or glycerol), meat & bonemeal (MBM), peat. Fuels that may be graded in a still lower, or lowest, grade (grade C in the present example) may include MSW and wastewater sludge. The following fuels may be indicated as being suitable for upgrading (and / or for any or the ancillary purposes mentioned above): biomass, forestry and agricultural wastes, glycerol, MBM, SRF, wastewater sludge. In preferred embodiments, the system 10, in particular the control system 20, is configured to use the grading of the available fuels 30 to determine how to use the available fuels 30, including determining which fuel(s) are directly included in the fuel mixture 40, which fuel(s) are upgraded for use in the fuel mixture 40, and which fuel(s) are used for ancillary purposes. In preferred embodiments, the control system 20 determines the composition of the fuel mixture 40 in order to meet the operating requirements of the application (e.g. with respect to required energy level and combustion temperature), advantageously while minimising the amount of carbon fossil fuel used in the combustion process and / or the amount of carbon fossil emissions produced by the combustion process.

[0072] By way of specific example, it is assumed that coal, glycerine (or glycerol), SRF and MSW are available to the system 10 as input fuels 30. The coal is a relatively high temperature fuel (and would be graded in grade A in the illustration of Figure 2) and may be added directly to the fuel mixture 40. The glycerine (or glycerol) is a lower temperature fuel (and would be graded in grade B in the illustration of Figure 2). The glycerine (or glycerol) may be used to produce hydrogen (which is a higher temperature fuel, i.e. grade A in the illustrated example) by any suitable conventional process such as steam reforming, autothermal reforming, partial oxidation reforming, aqueous-phase reforming or supercritical water reforming, and the produced hydrogen may be added to the fuel mixture 40. The SRF is a lower temperature fuel (and would be graded in grade B in the illustration of Figure 2) and may be added directly to the fuel mixture 40 to facilitate reaching a combustion temperature below the required temperature. The MSW is a relatively low combustion temperature fuel (and would be graded in grade C in the illustration of Figure 2) and may be used to provide heat energy for the production of hydrogen from the glycerine (or glycerol).

[0073] It is desired to minimize, or at least reduce, the quantity of fossil fuel that is included in the fuel mixture 40, and so to minimize or reduce the quantity of fossil carbon emissions produced by combustion of the fuel mixture 40. In the foregoing example, by producing hydrogen and adding to the mixture 40, the quantity of coal that is required to obtain the required combustion temperature is reduced, and by adding SRF to the mixture 40 the quantity of coal that is required to obtain the required combustion temperature is reduced. In particular, by using the SRF (or other suitable lower temperature fuel as outlined above) to provide combustion at a temperature lower than the required combustion temperature, the required quantity of coal (or other fossil fuel(s) as applicable)) needed to uplift the combustion temperature to the required combustion temperature is less than would be required in the absence of the SRF. Similarly, by adding hydrogen (or other non-fossil high temperature fuel such as syngas, methane or e-fuels) the required quantity of coal (or other fossil fuel(s) as applicable)) needed to obtain the required combustion temperature is less than would otherwise be required in the absence of the hydrogen.

[0074] More generally, it is desired to minimize or reduce the carbon content (fossil based carbon or otherwise), and in particular the CO2, produced by combustion of the fuel mixture 40. In preferred embodiments, the control system 20 is configured to control, and advantageously to optimize, one or more characteristic of the fuel mixture 40 and / or of the combustion of the fuel mixture 40 to reduce fossil carbon emissions (especially CO2), and preferably carbon emissions (especially CO2) generally, produced by combustion of the fuel mixture 40 while maintaining one or more target operating parameter (or condition) of the combustion process, or heating process, performed by the combustion system 12 or combustion apparatus 14. As such, the control system 20 may be said to decarbonise the operation of the combustion system 12 by optimizing the fuel mixture 40.

[0075] In typical embodiments, the target operating parameters (or conditions) of the combustion system 12 includes any one or more of (and typically all of): required energy (e.g. the total energy required to be produced by the combustion process(es) performed by the combustion system 12 and / or consumed by the combustion system 12; energy rate (or power) (e.g. the total energy rate, or power, required to be produced by the combustion process(es) performed by the combustion system 12 and / or consumed by the combustion system 12); required adiabatic flame temperature or combustion temperature (e.g. the flame temperature or combustion temperature in the, or each, combustion location, combustion apparatus 14 and / or at the burner(s) 14); operating temperature; exhaust gas composition; required moisture content of the fuel mixture and / or the combustion products; air to fuel ratio. The target operating parameter(s) may be provided as inputs to the control system 20. The control system 20 is provided with data indicating the available fuels 30 and the respective thermophysical parameter values and thermodynamic parameter values for those fuels 30. The control system 20 may also monitor, during operation of the system 10, any relevant operating parameters such as combustion temperature, composition of the combustion exhaust gas, energy consumption, power consumption and / or combustion efficiency. Using the available information, the control system 20 may control and optimize the fuel mixture 40.

[0076] In preferred embodiments, the control system 20 is configured to assess each of the available fuels 30 based on one or more of their thermophysical properties (e.g. calorific value, H:C ratio, ash and moisture content, carbon content, biogenic:fossil carbon ratio etc.). Each of the available fuels 30 is also assessed for their combustion behaviour based on one or more of its thermodynamic properties (e.g. adiabatic flame temperature, Higher and Lower Heating Values, carbon dioxide production, air to fuel mass ratio etc.), typically using first principles and empirical combustion equations, as would be apparent to a skilled person. The assessments allow the control system 20 to grade the available fuels 30, in particular with respect to their suitability, or quality, for combustion at the desired, or target, temperature range of the combustion system 12, i.e. temperature range A in the above example which corresponds to the highest temperature range of the required combustion. More generally, the assessments allow the control system 20 to determine the suitability, or quality, of each fuel 30 for combustion at the desired temperature range of the combustion system 12. For example, assuming that the available fuels 30 include coal, glycerine (or glycerol), SRF and hydrogen, the control system 20 may determine that coal and hydrogen are higher grade fuels than glycerine (or glycerol) and SRF based on one or more of the parameters indicated below:

[0077] Higher grade fuels:

[0078] • Coal: high LHV (or high energy content / calorific value), low moisture content, high adiabatic flame temperature, high fossil carbon content.

[0079] • Hydrogen: high LHV (or high energy content / calorific value), high adiabatic flame temperature, zero fossil carbon content.

[0080] Lower grade fuels:

[0081] • Glycerine (or glycerol): low LHV (or high energy content / calorific value), high moisture content, high H:C ratio, low adiabatic flame temperature, zero fossil carbon content.

[0082] • SRF: low LHV (or high energy content / calorific value), high moisture content, low adiabatic flame temperature, high waste variability.

[0083] The control system 20 thus determines which fuel(s) 30 are suitable for combustion at the required, or target, temperature (temperature range A in this example), i.e. the higher grade / quality fuel(s), and which fuel(s) are not suitable, i.e. the lower grade / quality fuels that are determined to have relatively poor combustion properties as outlined above.

[0084] The control system 20 is configured to assess which of the lower grade fuels are suitable for use in producing a higher grade fuel, preferably using renewable electricity, as outlined above. This assessment may include assessing which feedstock(s) are available and in what quantities, and on which fuel production processes are supported by the fuel production system(s) 18. For example, glycerine (or glycerol) can be readily converted to hydrogen and biogenic carbon monoxide via reformation which can be driven by renewable electricity, thereby converting a lower quality fuel into a higher quality fuel (hydrogen) and a byproduct (carbon monoxide). Steam reforming of glycerine produces a mixture of hydrogen, carbon monoxide, carbon dioxide and methane. Hydrogen can subsequently be separated by any suitable separation technique including those identified above. Separation techniques may also target a syngas mixture (Hydrogen and carbon monoxide) leaving methane and carbon dioxide as byproducts.The upgraded fuel (hydrogen in this example) is suitable for combustion at the required temperature and so can be added to the list of fuels that are available for adding to the fuel mixture 40. The assessment may also depend on any one or more of: which produced fuel(s) are suitable for use in the relevant combustion process(es); how much of the respective fuel can be produced; the rate at which the respective fuel can be produced; the availability of electrical energy to operate the fuel production system(s).

[0085] If a fuel cannot be upgraded such that it is suitable for combustion at the required temperature (temperature range A in this example), the control system 20 may determine if the fuel can be used in another application, typically a relatively low temperature application, within the system 10, such as drying and / or preheating or other ancillary purpose(s) identified above. For example, SRF can be pretreated (dried, shredded etc.) to improve its combustion characteristics improving its usefulness as a fuel. SRF, having been pretreated, may be used in preheating stage(s) of the heating process of system 12 to provide initial uplift in temperature to the limit of its combustion properties in lower temperature areas of the process and / or in high temperature areas to provide bulking energy.

[0086] More generally, any fuel 30 that is not suitable for combustion at the required temperature (temperature range A in this example) and / or which is not suitable for upgrading such that it is suitable for combustion at the required temperature may be used in any one or more of the following ways: added to the fuel mixture 40 to provide lower temperature energy during combustion (e.g. as described in relation to block 34 of Figure 2); used in other process(es), e.g. for the ancillary purposes identified above, performed by the system 10 (e.g. by any one or more of the systems 12, 18, 22) that require energy for heating, drying, pre-heating, lower temperature combustion and so on. Such fuels can also be used for indirect heating, or pre-heating, in any part of the systems 12, 18, 22, especially where the emissions produced exit as a separate stream. Furthermore, fuels that are suitable for upgrading may be added to the fuel mixture or used for any of the ancillary purposes without being upgraded, and / or upgraded fuels may be added to the fuel mixture or used for any of the ancillary purposes depending on the requirements of the application. The control system 20 may be configured to take into account any one or more of the above-identified options as part of the control / optimisation process. For example, the control system 20 may use of a portion of one or more of the fuels (irrespective of grade and whether upgraded or not) or fuel mixture for pre-heating (e.g. to be used to power the pre-heating apparatus 15) upon determining that it would reduce the overall carbon emissions and / or carbon consumption of the combustion process e.g. to use a low calorific value low temperature low carbon fuel to pre-heat one or more other fuels, or the fuel mixture 40, to minimise the use of high calorific value high temperature high carbon fuel.

[0087] The control system 20 may be configured to assess using renewable energy for electrically powered indirect heating (induction, radiative etc.) in order to increase the precombustion temperature of the fuel(s).

[0088] Using lower grade fuel(s) to provide lower temperature energy during combustion (e.g. as described in relation to block 34 of Figure 2) enables the control system 20 to use higher grade fuels only for higher temperature combustion. In particular, the higher grade fuel(s) may be blended or otherwise included in the fuel mixture 40 with the lower grade fuel(s) such that the higher grade fuel(s) only provide the high temperature combustion energy, with the ‘bulker’ lower grade fuel(s) providing the lower temperature energy to the combustion reaction. In the above example, pre-processed SRF may be used as a lower grade ‘bulking’ fuel in the fuel mixture 40 in combination with the higher grade fuels hydrogen and coal for use in the high temperature combustion process to reduce the amount of hydrogen and coal needed such that the higher grade fuels (hydrogen and coal in this example) provide only the high temperature combustion energy, with SRF providing the energy to the combustion process at lower temperatures. In preferred embodiment, the control system 20 is configured to reduce or minimise the use of higher quality, or grade, fuel(s) in the mixture 40 and to increase or maximise use of lower quality, or grade, fuel(s), while ensuring that the fuel mixture 40 provides, when combusted in the relevant combustion process, the required amount of energy at the required conditions (e.g. temperature, exhaust gas characteristics etc.). In preferred embodiments, the control system 20 optimises the composition of the fuel mixture 40 based on the respective grade of the respective fuels, in particular on the respective fuel’s suitability for combustion at the target combustion temperature range, which in turn depends on one or more thermophysical and / or one or more thermodynamic property of the respective fuel (in particular any one or more of: energy content or calorific value; adiabatic flame temperature; fossil carbon content), and / or on the fuel’s suitability for being upgraded. This optimisation facilitates the system 10 in efficiently producing the correct product.

[0089] Advantageously, the control system 20 is configured to optimize the composition of the fuel mixture 40 based on the fossil carbon content of the respective fuel(s), in order to reduce or minimize the fossil fuel used in the fuel mix and / or the fossil carbon content released from combustion of the fuel mixture 40. As such, the control system 20 may optimize the composition of the fuel mixture 40 based on one or more thermophysical and / or one or more thermodynamic property of the respective fuel, in particular any one or more of: fossil carbon content; carbon content; biogenic-to-fossil carbon ratio; carbon dioxide production. Alternatively or in addition, the control system 20 is configured to optimize the composition of the fuel mixture 40 based on the overall carbon content of the respective fuel(s) and / or the amount of carbon (particularly in the form of CO2) that is released by combustion of the fuel, in order to reduce or minimize the carbon content of fuel used in the fuel mix and / or the carbon content released from combustion of the fuel mixture 40. The control system 20 may optimize the composition of the fuel mixture 40 based on one or more thermophysical and / or one or more thermodynamic property of the respective fuel, in particular any one or more of: fossil carbon content; carbon content; biogenic-to-fossil carbon ratio; carbon dioxide production.

[0090] Advantageously, the optimisation based on fossil carbon content and / or carbon content more generally involves adjusting the respective amounts of fuels that are of the same grade, e.g. on the respective fuel’s suitability for combustion at the target combustion temperature range. For example the optimization may involve adjusting the respective amounts of high grade low carbon fuel(s) (e.g. hydrogen, methane, syngas and / or e-fuel) and high grade high carbon fuel(s) (e.g. coal, oil and / or natural gas).

[0091] In preferred embodiments, higher grade fuel(s) with relatively low or zero fossil carbon content (such as hydrogen, ammonia, or biogenic carbon containing fuels) are assessed for suitability to displace the fossil carbon fuel(s) in the fuel mixture 40, and the fuel mixture 40 is correspondingly adjusted. The optimisation is such that the displacing higher grade fuel still produces the required process conditions established previously. In the above example, hydrogen and coal are then assessed as the available higher grade fuels, with the optimal fossil carbon aim being minimal use of coal, and maximum use of hydrogen while maintaining combustion characteristics that enable the combustion process to function correctly.

[0092] In preferred embodiments, the optimisation based on carbon and or fossil carbon content is performed after the optimisation based on combustion temperature. This is advantageous since the carbon-based optimization does not unduly compromise the optimization based on combustion temperature. In particular, in cases where the higher grade fuel is a fossil fuel such as coal, oil or natural gas, the overall amount of higher grade fuel is already reduced or minimised by the temperature-based optimisation and the carbon-based optimisation does not affect this assuming that it is performed with respect to other high grade fuel (e.g. hydrogen).

[0093] Carbon-based optimisation may be performed for each grade of fuel included in the fuel mixture 40, preferably to ensure minimal fossil carbon containing fuels are used to ultimately minimise the overall process fossil carbon emissions.

[0094] Depending on the available fuels 30 (typically including the respective available quantities and / or rate at which they can be supplied) and the requirements of the combustion process (e.g. required amount of energy at the required conditions (e.g. temperature, exhaust gas characteristics etc.)), the control system 20 is able to determine an optimal fuel mixture 40 for the combustion process, in particular a fuel mixture 40 that minimizes or reduces the amount of higher grade fuel used in the mixture 40 (which tends to be scarce, relatively expensive and / or have high fossil carbon content), and more particularly to reduce the carbon content (especially the fossil carbon content) of the fuel mixture 40 and / or the combustion emissions.

[0095] Optionally, the optimisation processes may begin based on an initial fuel mixture 40 composition, which may be based on historic data provided to the control system 20 in respect of the system 10.

[0096] The, or each, optimisation performed by the control system 20 may be performed using any conventional optimisation algorithm(s) and / or may be performed iteratively. The, or each, optimisation may be performed multiple times, for example periodically, during operation of the system 12. The, or each, optimisation may be performed based on real-time data provided to the control system 20 (e.g. from any one or more of the sensors or measurement devices provided to monitor operation of the system 10) and / or on historic data provided to the control system 20 that pertains to the application. Optionally, the control system 20 may be configured to use Artificial Intelligence (Al) and Machine Learning (ML) techniques, e.g. by means of one or more Artificial Neural Network (ANN), to perform the optimisation and control described herein. Typically, the optimisation begins with an initial fuel mixture composition (e.g. obtained from historical data relating to the relevant application) and involves adjusting the fuel mixture composition using the available fuels and / or the fuels that can be produced from the available fuels in order to minimise or reduce the carbon content of the fuel mixture and / or of emissions produced by combustion of said fuel mixture by said combustion system, while satisfying the relevant operating conditions of the combustion system (e.g. energy level and adiabatic flame temperature). Any of the methods described herein may be used in the optimisation, including not only methods for determining the composition of the fuel mixture, but also methods for determining which of the available fuel(s) should be upgraded for use in the fuel mixture and / or which of the available fuel(s) an / or what quantity of the available fuel(s) should be used for pre-heating as described above.

[0097] During use, the system 10, and in particular the control system 20, may record a range of process conditions and product characteristics to further optimise fuel blend for minimal fossil carbon content, enabling minimal fossil carbon released per unit of product. This enables response to nonequilibrium operation e.g. change in feedstock(s) qualities, process condition changes, feedback data trending out of specified conditions etc.

[0098] By way of example, a conventional fuel mixture for an industrial combustion process may comprise 90% coal and 10% of another fuel such as wood chips. By employing the optimisation process described herein, hydrogen may be used to displace coal such that the mixture comprises 70% coal, 21% of the other fuel and 9% hydrogen, and further optimisation can result in a mixture comprising 51% coal, 40% of the other fuel and 9% hydrogen.

[0099] In preferred embodiments, the optimisation performed by the control system 20 takes into account one or more parameter that is indicative of a physical characteristic (e.g. indicative of the energy loss in sending fuel or energy to a given part of the system) of the system 10, particularly in order to determine how to allocate fuel or energy within the system 10. As such the control system 20 may be configured to consider fuel and / or energy delivery location and impacts from this in the optimisation.

[0100] Referring to Figure 3 in particular, a preferred embodiment of the control system 20 is shown. The control system 20 comprises a master controller 52 in communication with the relevant components of the system 10 by a control network 53, which may comprise a network of wired and / or wireless connections as is convenient, and which is capable of sending control signals from the controller 52 to the relevant components of the system 10, and receiving feedback signals from the relevant components of the system 10 required.

[0101] Each component of the system 10, in particular the components of the fuel production system(s) 18, the fuel supply system(s) 22, the oxygen supply system 28 and the combustion system 12 may include one or more controllable device, e.g. one or more local controller (e.g. PLC), sensor, fan, blower, pump, heater, furnace, fluid injector, valve, feeder, pulveriser and / or actuator, that is used during operation of the respective component. In this regard, the particular configuration of any given component depends on its type. For example, a liquid or gas storage vessel (as may be found in the system(s) 22) may include one or more valve, level controller and / or pressure sensor, while the fuel production system(s) 18 may comprise one or more controller, sensor, fan, blower, pump, heater, furnace, fluid injector, level controller and / or valve for performing the relevant chemical reaction(s). The fuel production system(s) 18 may comprise a chemical reactor. The configuration of the respective chemical reactor depends on the respective reaction(s) to be performed.

[0102] In preferred embodiments, the control network 53 includes a control signal network 53A for delivering control signals from the master controller 52 to the relevant components of the system 10, e.g. to the respective local controller and / or to the relevant controllable devices.

[0103] In preferred embodiments, the control network 53 includes a feedback network 53B by which feedback signals can be sent from the relevant components of the system 10 to the master controller 52. The feedback signals may be sent from the respective local controller and / or from one or more measurement device or other sensor associated with the respective system component. Each component of the system 10 may include one or more other sensor for sensing one or more parameter that is indicative of the status of the respective system component. For example, for components that implement one or more chemical reaction, one or more sensors may be provided to detect the temperature in the reaction zone, the pressure in the reaction zone, the fluid flow rate in the reaction zone, the quantity and / or composition of the reactant(s) in the reaction zone. For storage components, e.g. reservoirs, vessels, tanks and so on for storing and / or supplying feedstock or fuel, one or more sensors may be provided to detect or monitor the current available capacity of the storage component to store the respective product and / or to deliver or dispense the respective product, or delivery flow rate or feed rate.

[0104] In preferred embodiments, the control system 20 is configured to perform raw material control 56, which may involve controlling the supply of feedstock to the fuel production system(s) 18 (e.g. from the fuel supply system(s) 22), and / or the supply of fuel to the combustion system 12 (e.g. from the fuel supply system(s) 22 and / or the fuel production system(s)) using the control signal network 53A depending on feedback signals received via the feedback network 53B, e.g. from one or more sensor for detecting feedstock or fuel feed rate 57 to and / or from any one or more of the fuel production system(s) 18, the fuel supply system(s) 22), and / or the combustion system 12.

[0105] In preferred embodiments, the control system 20 is configured to perform fuel mass flow control 58, which may involve controlling the flow of fuel (typically in liquid or gaseous form), especially higher grade fuels (e.g. with zero or relatively low carbon content, relatively high calorific value and / or relatively high combustion temperature) such as hydrogen, methane, syngas and / or e-fuel, from the fuel production system(s) and / or from another source such as a fuel supply system(s) 22 to the combustion system 12 and / or to a fuel mixing apparatus, via the control signal network 53A depending on feedback signals received via the feedback network 53B, e.g. from one or more sensor for detecting mass flow rate and / or production rate 59 to and / or from any one or more of the fuel production system(s) 18, the fuel supply system(s) 22), and / or the combustion system 12.

[0106] In preferred embodiments, the control system 20 is configured to perform fuel mass flow control 58, which may involve controlling the temperature of the, or each, combustion process using the control signal network 53A depending on feedback signals received via the feedback network 53B, e.g. from one or more sensor for detecting the flame and / or burner temperature 61 , and optionally from a flame location sensor 63. Flame location can be important for practical production of material, e.g. to ensure proper operation of equipment and prevent damage, as well as maintaining temperature zones at the required conditions.

[0107] The controller may also be configured to perform safety control 62, which may involve receiving alarm signals from one or more alarm sensors (not shown), e.g. gas sensors or leak detectors or emergency stops that may be included in the system 10, and provide alarm information to the master controller 52 based on the alarm signals received from the alarm sensors.

[0108] In preferred embodiments, the control system 20 is configured to support computer modelling of any one or more of: the overall operation of the system 10; the operation of the fuel production system(s) 18, the operation of the fuel supply system(s) 22; the operation of the combustion system 12.

[0109] The preferred control system 20 supports computer modelling of the system 10 (in particular any one or more of the of the fuel production system(s) 18, the fuel supply system(s) 22; the combustion system 12) in order to monitor and / or predict the fuel consumption and / or fuel requirements of the system 10, in particular the combustion system 12, in order to control, and adjust as necessary, the composition of the fuel mixture 40, particularly in order to reduce the consumption of fossil fuel and / or the production of fossil carbon emissions while maintaining the required combustion operating parameters (e.g. flame temperature and / or energy level) of the combustion process.

[0110] In order to support the computer modelling, the control system 20 is configured to use at least one respective mathematical model of the relevant system(s) 10, 12, 18, 22 (including mathematical model(s) of their individual respective components as required). Optionally, the control system 20 is configured to use Artificial Intelligence (Al) and Machine Learning (ML) techniques, e.g. by means of one or more Artificial Neural Network (ANN), to train and / or optimise the mathematical model(s), e.g. the mathematical model(s), or algorithms, may be trained and / or optimized using supervised and / or unsupervised machine learning techniques, preferably using internal or external data obtained by the system during use, and / or historical data. Alternatively or in addition the control system 20 may be configured to use Model Predictive Control (MPC).

[0111] The control system 20 typically comprises one or more suitably programmed or configured hardware, firmware and / or software controllers (which may include the master controller 52 and any local controllers), e.g. comprising one or more suitably programmed or configured microprocessor, microcontroller, PLC or other processor, for example an IC processor such as an ASIC, DSP or FPGA (not illustrated). The master controller 52 and local controllers may be implemented in any convenient manner, for example as one or more separate hardware, firmware and / or software components of the overall control system 20. The local controllers may act as slaves to the master controller 52, or may act as stand-alone controllers with interface signals to the master controller 52. In preferred embodiments, the control system 20, and more particularly the master controller 52, is configured to implement system modelling logic, e.g. by supporting mathematical modelling software or firmware, for enabling the control system 20 to mathematically model the behaviour of the system 10, or any relevant part thereof, as described above. The control system 20 may be configured to implement Model Predictive Control (MPC). Suitable mathematical models can be written in Matlab, Simulink, or Labview (by way of non-exhaustive examples) and executed by the master controller 52.

[0112] To manage the appropriate energy requirements and operational conditions of the combustion system 12, the control system 20 may receive, during use, input signals providing data in relation to any one or more of the following aspects: inputs and feedback relating to the combustion process including internal temperatures (e.g. combustion temperature, flame temperature or burner temperature), flame position, oxygen post combustion concentration, production rate and so on; inputs indicating the expected fuel required (from a user or through analysis of historic fuel consumption data for the relevant combustion process); inputs from feedstock storage (and / or storage or other fuel(s)) indicating fuel availability; inputs from low-quality fuel feed to determine the required temperature uplift needed from combustion of high-quality fuel and / or oxygen input to implement the combustion process correctly; prioritisation data for assets, e.g. fuel resources, based on pre-determined priority ranking (or through calculated priority based on a “cost” function); any additional factors such as availability of feedstocks for the system.

[0113] The input data may be used by the control system 20 to make decisions relating to the composition of the fuel mixture and / or in relation to oxygen amounts.

[0114] Optionally, data mining activities may be performed using Al and ML tools to identify trends to support optimised operation especially around available renewable energy supply and potential lack of sufficient electrical power.

[0115] In preferred embodiments, the control system 20 is configured to control the operation of the system 10 process by: determining how much high flame temperature fuel and / or oxygen is required at any time during operation; determining when additional feedstock will be required to ensure continued production of high-calorific fuels and / or oxygen; balancing the high-quality:low-quality fuel ratio to provide sufficient combustion temperatures and energy transfer within the process; adjusting the fuel mixture based on operability factors such as availability of feedstock, continuity of critical operations, asset prioritisation and so on.

[0116] The control system 20 may then optionally monitor high-calorific value fuel, and / or other high grade fuel (e.g. fuel with a high adiabatic flame temperature), fuel and / or oxygen consumption relative to forecasted feedstock / power availability and operation and adjust production rates for this instance, or for future instances accordingly to allow for short term storage of excess production to allow continued operation. Embodiments of the invention may be be applied to high temperature combustion applications to reduce the use of fossil fuels and / or reduce fossil carbon emissions. Optimisation of fuel composition can achieve the relevant energy requirements and operational conditions for the given application. This can involve optimal utilisation of available feedstock to maximise decarbonisation.

[0117] By way of example, suitable applications include: cement kilns; glass furnaces; steel production; thermal power generation. Details relating to some of these applications is provided below. It is noted that the details relating to cement kilns are also suitable for use with other applications including metal refining.

[0118] Cement Kilns

[0119] In a cement kiln, high temperatures (circa. 1250 °C) are required to initiate the decomposition of limestone to produce clinker. This requires a high-quality combustible fuel (such as coal) to enable the process to occur. Pilot injection of lower calorific sustainable fuels has been developed to reduce the amount of coal used in the main burner, complemented by oxy-combustion trials. However, this approach is unable to replace coal due to the limited flame temperature evolving from combustion of the sustainable fuel. The conversion of low calorific feedstocks to high calorific value fuels can enable high temperature applications. Injection of these converted fuels in relatively small amounts, in combination with lower calorific sustainable fuels increases the quality of the fuel mixture enabling a much higher combustion temperature to be achieved.

[0120] Cement kilns also use iron ore (Fe2C>3) as an additive in the clinker production process. Other forms of iron ores including ‘black iron oxide’ or Fe3O4 have an enhanced capability to react with CO2 to produce iron carbonate, a filler material used in cement. This means addition of black iron oxide in place of iron ore could increase the amount of the CO2 released from thermal decomposition of limestone that is sequestered into the cement product itself, decreasing the overall carbon intensity of the cement produced. This form of iron oxide can be created by oxidation of iron metal in other applications and also naturally occurs but in smaller forms.

[0121] By way of example a cement kiln, or more generally a cement production plant, may have a fuel of grade A classification e.g. coal and a fuel of a grade B classification e.g. wood chips. Prior to optimisation the process may comprise 90 % coal and 10 % wood chips. Typically process operation limits use of grade B fuels, due to the low adiabatic flame temperature. Through the optimisation process as per Figure 2, the fuel mix can be optimised to achieve the required adiabatic flame temperature, whilst reducing the grade A coal use. The grade B wood chips can be upgraded to a grade A fuel e.g. hydrogen through several thermochemical reactions e.g. pyrolysis, gasification, and subsequent separation. This allows greater than 10 % wood chip utilisation across the process, decreasing the proportion of coal used and by extension the proportion of fossil fuel used by the system. By employing the optimisation process described herein, hydrogen may be used to displace coal such that the mixture comprises 70% coal, 21 % of the wood chips and 9% hydrogen, and further optimisation can result in a mixture comprising 51 % coal, 40% of the wood chips and 9% hydrogen.

[0122] Glass Furnaces

[0123] Glass blast furnaces require high temperatures to melt sand (silica) and other additives to create molten glass. Due to the fine level of control necessary, a clean burning fuel such as natural gas is favoured for the process. Replacement of natural gas with sustainable alternative sources of methane, hydrogen or syngas is considered the only feasible way to improve the sustainability of glass manufacture as less clean burning liquid and solid biomass fuels are unsuitable. The conversion of low calorific feedstocks to high calorific value and clean burning fuels can provide the high temperatures required. Current burner technology can only tolerate injection of 20%vol hydrogen due to material constraints. This limits the potential of hydrogen to be a total replacement for natural gas as the main source of energy. This limit would result in circa 7% of energy into the furnace being supplied from hydrogen combustion and 93% from natural gas leaving a significant proportion of energy delivery from fossil fuels in the process. Further optimisation of fuel composition can enable >20 %vol. replacement of natural gas in the furnace without retrofitting.

[0124] By way of example a glass production plant may have a fuel of grade A classification, typically natural gas provided by a gas grid connection. Glass production requires temperature ranges of 800 to 1600 °C and specific considerations for moisture content and combustion gas composition dependant on the product desired e.g. tempered glass, float glass. These process conditions limit use of grade B / C fuel types without upgrading to a subset of grade A fuels that exhibit the correct combustion behaviour for example ash content, particulate formation, moisture content. For example, grade C fuels such as MSW can be utilised in an anaerobic digestion process to produce a fuel of a higher grade such as biogas (mixture of carbon dioxide and methane) which can then be further upgraded to a grade A fuel such as hydrogen through processes such as steam methane reforming (SMR). Post-optimisation this enables a 7 % use of hydrogen in the fuel mix, therefore reducing fossil fuel emissions by 7 %.

[0125] Steel Production - Blast Furnace

[0126] In blast furnace-basic oxygen furnace steel production utilises fossil fuels for several reasons: high temperature combustion is required to facilitate the chemical reactions necessary to produce steel; removal of excess carbon in the liquid metal (“pig iron”) to produce steel; and to provide a reductant agent (C) to reduce iron oxide as a key reaction step:

[0127] • 2Fe20a + 3C -> 4Fe + 3CO2

[0128] The conversion of low calorific feedstocks to high calorific value and / or high temperature fuels can enable high temperature applications, reducing the requirement for fossil fuel use. Combustion of these high calorific value fuels can often produce a higher adiabatic flame temperature than fossil fuels. Combustion of these fuels can provide alternative reductant agents to facilitate the reduction of iron oxide as a key reaction step, generating water as a by-product instead of carbon dioxide. Furthermore, optimisation of the fuel composition can provide the correct carbon to hydrogen ratio. This can improve the efficiency of the process by reducing the requirement of excess carbon to be removed from the liquid metal.

[0129] By way of example a steel production plant may have a fuel of grade A classification, typically coking coal. Steel production requires temperature ranges of 700 to 1700 °C and specific considerations for combustion gas composition specifically carbon monoxide concentration. These process conditions limit use of grade B / C fuel types without upgrading to a subset of grade A fuels that exhibit the correct combustion behaviour for example adiabatic flame temperature, post-combustion carbon monoxide concentration. For example, grade B fuels for example forestry and agricultural wastes can be upgraded to a grade A fuel such as syngas (a blend of hydrogen and carbon monoxide) through processes such as gasification and pyrolysis. This grade A fuel can be optimised through post-production separation to provide the minimal amount of carbon monoxide required to produce steel while providing hydrogen as an alternative to coking coal for energy delivery to the system minimising the need for coking coal. Through introduction of only the required amount of carbon monoxide and reduction of coking coal, the total carbon dioxide produced by the process is minimised while maintaining the necessary process conditions for operation.

[0130] Steel Production - Electric Arc Furnace

[0131] Electric arc furnaces (EAF) utilise high-current electric arcs to melt steel (usually scrap) and convert it into liquid steel. Due to the use of alternating current cold spots can occur in the furnace. Here fossil fuel (typically natural gas) is injected to provide additional heating to these cold spots. EAF steel production utilising direct-reduced iron the conversion of low calorific feedstocks to high calorific value fuels with subsequent optimisation of composition can provide low-carbon sources of reductant agents. Similarly, the injection of these high calorific value fuels can provide a low-carbon source of heating to cold spots.

[0132] The invention is not limited to the embodiment(s) described herein but can be amended or modified without departing from the scope of the present invention.

Claims

CLAIMS:

1. A method of controlling a fuel mix for use in a combustion system for performing at least one combustion process in one or more combustion location, the fuel mix comprising a plurality of different types of combustible fuels including at least one first fuel and at least one second fuel, wherein said at least one first fuel has a higher carbon content than said at least one second fuel, and wherein the method comprises controlling the composition of the fuel mix depending on at least one operating condition of the combustion system, said controlling involving controlling the respective quantity of said at least one first fuel and / or of said at least one second fuel in order to minimise or reduce the carbon content of said fuel mix and / or of emissions produced by combustion of said fuel mix by said combustion system.

2. The method of claim 1 , including controlling the composition of the fuel mix based on a grade of each fuel, wherein the grade is indicative of the respective fuel’s suitability for combustion at a target combustion temperature, which may be based on one or more thermophysical and / or one or more thermodynamic property of the respective fuel, preferably being based at least on the adiabatic flame temperature of the respective fuel, and wherein, preferably, said controlling involves minimising or reducing the respective quantity of the, or each, fuel that is suitable for or capable of combustion at said target combustion temperature, and preferably increasing, or maximising, the quantity of the, or each, fuel that suitable for or capable of combustion at a respective temperature lower than said target combustion temperature.

3. The method of claim 2, wherein the grade of each fuel depends on the combustion temperature, or adiabatic flame temperature, of the respective fuel, and wherein controlling the composition of the fuel mix based on the respective grade of each fuel involves minimising or reducing the respective quantity of one or more fuel of one or more relatively high grade, and preferably in maximizing or increasing the respective quantity of one or more fuel of one or more relatively low grade, wherein the or each relatively high grade corresponds to one or more respective combustion temperature, or adiabatic flame temperature, that is higher than one or more respective combustion temperature, or adiabatic flame temperature, associated with the or each relatively low grade.

4. The method of claim 3, wherein controlling the composition of the fuel mix based on the respective grade of each fuel involves minimising or reducing the respective quantity of one or more fuel of a highest grade, and preferably in maximizing or increasing the respective quantity of one or more fuel of one or more lower grade, wherein the highest grade corresponds to one or more combustion temperature, or adiabatic flame temperature, that is higher than one or more respective combustion temperature, or adiabatic flame temperature, associated with the or each lower grade.

5. The method of any preceding claim, wherein controlling the fuel mix is performed depending on one or more input received from any one or more of: said combustion system; one or more fuel production system; one or more fuel supply system, optionally in real-time, and / or based on historicdata relating to the combustion system, said one or more fuel production system and or said one or more fuel supply system.

6. The method of any preceding claim, comprising optimizing the composition of the fuel mix in order to minimise or reduce the carbon content of said fuel mix and / or of emissions produced by combustion of said fuel mix by said combustion system while satisfying said at least one operating condition, conveniently using one or more suitable optimization algorithm and / or using artificial intelligence (Al) and / or machine learning (ML).

7. The method of claim 6, wherein said optimizing involves determining which of the available fuel(s) is to be converted to a different type of fuel, in particular a different type of fuel having a higher adiabatic flame temperature than the respective fuel being converted, for use in the fuel mix.

8. The method of claim 6 or 7, wherein said optimizing involves determining which of the available fuel(s), and / or what quantity of the available fuel(s), is to be used to heat said fuel mix, or at least one fuel for inclusion in said fuel mix, prior to combustion by said combustion system.

9. The method of any preceding claim, wherein said at least one operating condition comprises a required energy level and / or a required combustion temperature, and wherein said required energy level may comprise total energy required to be produced by said at least one combustion process and / or total energy consumed by the combustion system.

10. The method of any preceding claim, wherein said at least one operating condition comprises any one or more of: a required adiabatic flame temperature; a required gas composition, in particular exhaust gas composition; a required moisture content, in particular moisture content of the fuel mix and / or of the exhaust gas composition; a required air-to-fuel ratio; energy rate, for example a total energy rate required to be produced by said at least one combustion process and / or consumed by the combustion system.11 . The method of any preceding claim, further including producing one or more of said at least one second fuel from at least one other type of fuel, preferably using renewable energy, and using the, or each, produced second fuel in the fuel mix.

12. The method of claim 11 , wherein said at least one other type of fuel has a lower calorific value and / or a lower combustion temperature than the, or each, produced second fuel, and preferably has a lower combustion temperature than said at least one first fuel.

13. The method of claim 11 or 12, wherein producing one or more of said at least one second fuel from said at least one other type of fuel involves using one or more fuel production process or fuel conversion process, preferably including any one or more of: biomass reforming, steam reforming, water splitting, electrolysis, thermal H2generation, the Fischer-Tropsch process, anaerobic digestion,pyrolysis, gasification, fermentation, enzymatic generation, thermochemical water-splitting cycle(s) (e.g. the sulphur-iodine cycle, cadmium carbonate cycle, hybrid sulphur cycle, hybrid copper chloride cycle, carbon-sulphur cycle, nickel-manganese ferrite cycle, ISPRA series, vanadium chloride cycle), fermentation steam reforming, autothermal reforming, partial oxidation reforming, aqueous-phase reforming and supercritical water reforming.

14. The method of any preceding claim, further including incorporating at least one other type of fuel into said fuel mix, wherein said at least one other type of fuel has a lower combustion temperature than said at least one first fuel and said at least one second fuel.

15. The method of claim 14, wherein said controlling the composition of the fuel mix depending on at least one operating condition of the combustion system involves controlling the respective quantity of said at least one other type of fuel incorporated into the fuel mix to minimise or reduce the individual or combined quantity of said at least one first fuel and of said at least one second fuel in the fuel mix.

16. The method of claim 15, further including using said at least one other type of fuel to provide relatively low temperature energy during said at least one combustion process, and using said at least one first fuel and said at least one second fuel only for higher temperature energy during said at least one combustion process.

17. The method of claim 15 or 16, including adjusting the respective quantity of said at least one first fuel and of said at least one second fuel in said fuel mix in order to minimise or reduce the carbon content of said fuel mix and / or of emissions produced by combustion of said fuel mix in said at least one combustion process.

18. The method of any preceding claim, including controlling the composition of the fuel mix based on the carbon content, preferably the fossil carbon content, of the respective fuel, which may be based on one or more thermophysical and / or one or more thermodynamic property of the respective fuel, for example any one or more of: fossil carbon content; carbon content; biogenic-to-fossil carbon ratio; carbon dioxide production rate, and wherein, preferably, said controlling involves minimising or reducing the carbon content, preferably the fossil carbon content, of said fuel mix and / or of emissions produced by combustion of said fuel mix in said at least one combustion process.

19. The method of claim 18, wherein controlling the composition of the fuel mix based on carbon content, in particular fossil carbon content, involves adjusting the respective amounts of fuels that are of the same grade, wherein the grade of each fuel is indicative of the respective fuel’s suitability for combustion at a target combustion temperature, which may be based on one or more thermophysical and / or one or more thermodynamic property of the respective fuel.

20. The method of claim 19, wherein the grade of each fuel depends on the combustion temperature, or adiabatic flame temperature, of the respective fuel.

21. The method of claim 19 or 20, wherein said adjusting the respective amounts of fuels that are of the same grade is performed in respect of each grade of fuel.

22. The method of any one of claims 18 to 21 when dependent on any one of claims 2 to 4, wherein said controlling the composition of the fuel mix based on the carbon content is performed after controlling the composition of the fuel mix based on a grade of each fuel.

23. The method of claim 11 , and any other claim when dependent on claim 11 , further including identifying said at least one other type of fuel for use in production of said one or more of said second fuel based on a respective grade of each fuel, wherein the respective grade is indicative of the respective fuel’s suitability for conversion to said one or more second fuel and / or of the respective fuel’s suitability for conversion to a fuel type having a higher adiabatic flame temperature than the respective fuel, preferably in order to minimise or reduce the carbon content of said fuel mix and / or of emissions produced by combustion of said fuel mix by said combustion system.

24. The method of any preceding claim, further including determining, in respect of at least one type of fuel, either to incorporate said at least one type of fuel into the fuel mix or to use said at least one type of fuel to produce another type of fuel, preferably to produce one or more of said at least one second fuel, depending on the suitability of said at least one type of fuel for being converted to a different type of fuel having a higher adiabatic flame temperature than said at least one type of fuel, preferably in order to minimise or reduce the carbon content of said fuel mix and / or of emissions produced by combustion of said fuel mix by said combustion system.

25. The method of any preceding claim, further including heating said fuel mix, or at least one fuel for inclusion in said fuel mix, prior to combustion by said combustion system.

26. The method of claim 25, including combusting at least one fuel available to said combustion system to provide heat for heating said fuel mix, or said at least one fuel for inclusion in said fuel mix, preferably using a combustion heating apparatus such as a furnace or boiler, and preferably in order to minimise or reduce the carbon content of said fuel mix and / or of emissions produced by combustion of said fuel mix by said combustion system.

27. The method of any preceding claim, wherein said at least one first fuel comprises one or more type of fossil fuel, for example any one or more of: coal, oil, peat, fuel oil, diesel, kerosene and natural gas.

28. The method of claim 27, wherein said controlling the respective quantity of said at least one first fuel and of said at least one second fuel is performed to minimise or reduce the fossil carbon content of said fuel mix and / or of emissions produced by combustion of said fuel mix in said at least one combustion process.

29. The method of any preceding claim, wherein said at least one second fuel comprises one or more type of fuel, preferably any one or more of: hydrogen, methane (in particular biomethane and e-methane), ammonia, syngas, e-fuel(s) and biogenic carbon-containing fuel(s).

30. The method of claim 11 , and any other claim when dependent on claim 11 , wherein said at least one other type of fuel used to produce one or more of said at least one second fuel comprises any one or more of water, biomass, glycerine (or glycerol), biodiesel, ammonia, forestry & agricultural wastes, solid recoverable fuel (SRF), municipal solid waste (MSW), wastewater sludge and meat & bonemeal (MBM).31 . The method of claim 14, and any other claim when dependent on claim 14, wherein said at least one other type of fuel incorporated into the fuel mix comprises any one or more of biomass, glycerine (or glycerol), biomass, biodiesel, ammonia, forestry & agricultural wastes, solid recoverable fuel (SRF), municipal solid waste (MSW), wastewater sludge and meat & bonemeal (MBM).

32. The method of any preceding claim, further including adding oxygen to the fuel mix and / or said at least one combustion process in order to increase combustion efficiency and / or to reduce or minimize the respective quantity of said at least one first fuel and / or of said at least one second fuel in the fuel mix.

33. The method of any preceding claim, including controlling the supply of a plurality of different types of combustible fuel and / or feedstock for producing combustible fuel from at least one fuel supply, and / or feedstock supply, directly or indirectly to said combustion system, for example to said one or more combustion location and / or to a mixing device, and / or to one or more fuel production system for converting one or more type of fuel, or feedstock, to a different type of fuel.

34. A method of controlling a combustion system for performing at least one combustion process in one or more combustion location, the method including the method of controlling a fuel mix for the combustion system as claimed in any one of claim 1 to 33.

35. An optimization system for providing a fuel mix to a combustion system, the optimization system including a control system configured to perform the method of any one of claims 1 to 33 or the method of claim 34.

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