Fuel generation system and method

Abstract

Fuel generation systems and methods for the generation of hydrogen or syncrude from solid waste are described. The systems comprises a gasifier stage, a catalytic methanation stage, a plasma torch stage and a Fischer-Tropsch reactor or a water gas shift (WGS) reactor stage. The WGS reactor stage and the catalytic methanation reactor stage connect to a different one of three Benfield columns via respective output gas flows; the WGS reactor stage, catalytic methanation reactor stage and plasma torch stage each connect to a different one of the three Benfield columns via their respective input gas flows; and wherein the input gas flow of the first Benfield column is connected to the output gas flow of each of the second and third Benfield columns in a recycle loop for the removal of acid gas, and to the output gas flow of the gasifier. Where a Fischer-Tropsch reactor stage replaces the WGS stage a single Benfield column is used.

Description

The present invention relates to a fuel generation system and method for the generation of hydrogen and / or sulphur-free syncrude from solid waste. Over the last few years, the environmental impact of carbon dioxide emissions from a wide variety of sources has become increasingly apparent, with climate change and the need for carbon neutral operations and a reduced carbon footprint at the forefront of business and legislation in many countries. There are two major contributors to the growth (and therefore reduction) in carbon emissions: combustion of fossil fuels and dumping of solid waste in landfill sites. The processing of organic material typically disposed of in landfill from solid waste is a major factor in carbon dioxide emission reduction, since appropriate processing can reduce carbon dioxide emissions, as well as the secretion of various chemicals and toxins into the surrounding environment. The "What a Waste" report from the World Bank (Hoornweg, Daniel; Bhada-Tata, Perinaz. 2012. What a Waste: A Global Review of Solid Waste Management. Urban development series; knowledge papers no. 15. World Bank, Washington, DC. © World Bank. https: / / openknowledge.worldbank.org / handle / 10986 / 17388 License: CC BY 3.0 IGO) highlights three definitions of solid waste, otherwise known as "Municipal Solid Waste" or "MSW" from the IPCC (Intergovernmental Panel on Climate Change), OECD (Organisation for Economic Co-operation and Development) and PAHO (Pan American Health Organisation). Of these, the IPEC definition concentrates on the type of waste: "food waste; garden and park waste; paper and cardboard; wood; textiles; nappies; rubber and leather; plastics; metal; glass (and pottery and china); and other (for example ash, dirt, dust, soil, electronic waste)", and the OECD and PAHO definitions concentrate on the origin of the waste "solid waste collected and treated by or for municipalities (waste from households, including bulky waste, similar waste from commerce and trade, office buildings, institutions and small businesses, yard and gardens, contents of litter containers and market cleansing" is the OECD definition, for example. Disposal of such solid waste therefore remains an issue in preventing the carbon compounds in the waste from decomposing eventually to carbon dioxide and other greenhouse gases (such as methane) or from incineration. The second issue highlighted above is that of combustion of fossil fuels. Burning hydrocarbons creates an immediate release of carbon dioxide into the atmosphere (internal combustion and jet engines, power generation), and the process of obtaining such hydrocarbons is also far from carbon neutral. Although it may be feasible to capture carbon dioxide from waste incineration plants, this suffers from difficulties due to the high nitrogen content of the offgas since waste incineration requires an excess of air to work. Alternatives to using traditional hydrocarbon fuel stocks derived from crude oil, such as petrol and diesel, for transport include hydrogen, natural gas or replacing internal combustion engine vehicles with EVs (electric vehicles), but each of these has its own drawbacks. Natural gas must still be drilled at great expense and whilst lower in emissions, still retains a high carbon footprint when used in transportation; EVs require electricity, which may still be generated using fossil fuels; and hydrogen generation from typical hydrocarbon sources is costly in terms of finance and carbon dioxide generation. The majority of hydrogen supplied to depots of fuel cell electric buses (FCEBs) or other fuel cell transportation vehicles, for example, is produced from natural gas using a Steam Methane Reforming (SMR) reactor stage. This is used typically in series with Water-Gas Shift (WGS) reactor stages, Pressure Swing Adsorption (PSA), and generally a catalytic methanation process. The amount of carbon dioxide produced per kg of hydrogen according to literature data is a minimum of 9.3kg, indicating that this still has a relatively high carbon cost. Aside from the carbon cost, fuels produced from crude oil contain sulphur, which creates further environmental issues when the fuel is burned. Whilst systems exist to reduce the amount of carbon dioxide emitted by transportation, the presence of sulphur impairs the effectiveness of such emission control systems and contributes to air pollution, forming sulphur oxide gases. These gases react with water in the atmosphere to form sulphates and acid rain, creating highly acidic soils that contribute to deforestation and ecosystem loss. There is therefore a need for an industrial-scale system that can both generate low-carbon footprint hydrogen for vehicle use and / or low sulphur or sulphur-free hydrocarbon fuels from solid waste, thus producing an overall solution to lowering carbon emissions. The embodiments of the present invention aim to address these issues by providing, in a first aspect, a fuel generation system for the generation of hydrogen from solid waste, the system comprising: a gasifier stage having an input comprising solid waste and an output gas flow of a syngas comprising carbon monoxide and hydrogen; a water-gas shift reactor stage having an input gas flow comprising carbon monoxide and water and an output gas flow comprising carbon dioxide and hydrogen; a catalytic methanation reactor stage having an input gas flow comprising carbon monoxide, carbon dioxide and hydrogen and an output gas flow comprising methane, water and carbon dioxide; and a plasma torch stage having an input gas flow comprising methane and an output gas flow comprising hydrogen; wherein the water-gas shift reactor stage and catalytic methanation reactor stage each connect to a different one of three Benfield process columns via their respective output gas flows; wherein the water-gas shift reactor stage, catalytic methanation reactor stage and plasma torch stage each connect to a different one of the three Benfield process columns via their respective input gas flows; and wherein the input gas flow of the first Benfield process column is connected to the output gas flow of each of the second and third Benfield process columns in a recycle loopforthe removal of acid gas, and to the output gas flow of the gasifier. By removing the acid gas (carbon dioxide) at each stage this can be routed to the catalytic methanation reactor stage for methanation and further use within the fuel generation system, thus lowering the overall carbon footprint of the hydrogen produced. Preferably, the plasma torch stage further comprises an output gas flow connected to an input gas flow of the catalytic methanation reactor stage, and an output for the recovery of carbon black. Preferably, the water-gas shift reactor stage comprises a high temperature shift catalysis reactor stage and a low temperature shift catalysis reactor stage. Preferably, the water-gas shift reactor stage further comprises a steam input and the water-gas shift reactor stage output gas flow enters the third Benfield process column via a water condenser; and the catalytic methanation reactor stage further comprises an input gas flow from an output gas flow of the plasma torch stage, an input gas flow from the hydrogen separation membrane, and wherein the output gas flow of the catalytic methanation reactor stage enters the second Benfield process column via a water condenser. Preferably, the fuel generation system further comprises a Fischer-Tropsch reactor stage comprising an input gas flow connected to the output gas flow of the gasifier, an output liquid flow of syncrude, an output liquid flow of water, and an output off-gas gas flow connected via a water condenser to the input gas flow of the first Benfield process column. Preferably, the syncrude is sulphur free. Preferably, the fuel generation system further comprises an output gas flow of hydrogen from the plasma torch stage to be recycled as an input gas flow to the Fischer-Tropsch reactor stage. In a second aspect, embodiments of the present invention provide a fuel generation system for the generation of syncrude from solid waste, the system comprising: a gasifier stage having an input comprising solid waste and an output gas flow of a syngas comprising carbon monoxide and hydrogen; a Fischer-Tropsch reactor stage comprising an input gas flow connected to the output gas flow of the gasifier and an output gas flow of reduced hydrogen and carbon monoxide off-gas; a catalytic methanation reactor stage having an input gas flow comprising carbon monoxide, carbon dioxide and hydrogen and an output gas flow comprising methane, water and carbon dioxide; and a plasma torch stage having an input gas flow comprising methane and an output gas flow comprising hydrogen; wherein the Fischer-Tropsch reactor stage and catalytic methanation reactor stage each connect to a Benfield process column via their respective output gas flows; wherein the catalytic methanation reactor stage and plasma torch stage each connect to the Benfield process column via their respective input gas flows; and wherein the output gas flow of the catalytic methanation reactor stage forms an additional syngas flow to the input gas flow of the Fischer-Tropsch reactor stage. This arrangement enables the production of sulphur-free syncrude for transportation use. Preferably, the plasma torch stage further comprises an output gas flow connected to an input gas flow of the catalytic methanation reactor stage, and an output for the recovery of carbon black. Preferably, the catalytic methanation reactor stage further comprises an input gas flow from an output gas flow of the plasma torch stage, an input gas flow from the hydrogen separation membrane, and wherein the output gas flow enters syngas input into the Fischer-Tropsch reactor via a water condenser. Preferably, the syncrude is sulphur-free. Preferably, the fuel generation system further comprises a hydrogen separation membrane through which all input gas flow to the plasma torch stage is passed. Preferably, the gasifier is a pyrolyser. Preferably, the solid waste is municipal solid waste. The solid waste may comprise material having a low oxygen content, a high oxygen content or an intermediate oxygen content. In a third aspect, embodiments of the present invention provide a method of generating hydrogen from solid waste, the method comprising: a) gasifying solid waste to generate a syngas comprising carbon monoxide and hydrogen; b) generating carbon dioxide and hydrogen from carbon monoxide and water using a water-gas shift reactor; c) generating methane, water and carbon dioxide from using a catalytic methanation reactor; and d) generating hydrogen from methane using a plasma torch; wherein the water-gas shift reactor and catalytic methanation reactor each connect to a different one of three Benfield process columns via their respective output gas flows; wherein the water-gas shift reactor, catalytic methanation reactor and plasma torch each connect to a different one of the three Benfield process columns via their respective input gas flows; and d) recycling the output gas flow of each of the second and third Benfield process columns by removing acid gas, wherein the input gas flow of the first Benfield process column is connected to the output gas flow of each of the second and third Benfield process columns. Preferably, the plasma torch comprises an output gas flow connected to an input gas flow of the catalytic methanation reactor, and an output for the recovery of carbon black. Preferably, the water-gas shift reactor comprises a high temperature shift catalysis reactor and a low temperature shift catalysis reactor. Preferably the water-gas shift reactor further comprises a steam input and wherein the output gas flow enters the third Benfield process column via a water condenser; and the catalytic methanation reactor further comprises an input gas flow from an output gas flow of the plasma torch, an input gas flow from the hydrogen separation membrane, and wherein the output gas flow enters the second Benfield process column via a water condenser. Preferably, the method further comprises generating syncrude using a Fischer-Tropsch reactor comprising an input gas flow connected to the output gas flow of the gasifier and an output off-gas gas flow connected via a water condenser to the input gas flow of the first Benfield process column. The syncrude is preferably sulphur free. The method may further comprise recycling hydrogen from the plasma torch as an input gas flow to the Fischer-Tropsch reactor. In a fourth aspect, embodiments of the present invention provide a method of generating syncrude from solid waste, the method comprising: a) gasifying solid waste to generate a syngas comprising carbon monoxide and hydrogen; b) generating a reduced hydrogen and carbon monoxide off-gas using a Fischer-Tropsch reactor; c) generating methane, water and carbon dioxide from using a catalytic methanation reactor; and d) generating hydrogen from methane using a plasma torch; wherein the Fischer-Tropsch reactor and catalytic methanation reactor each connect to a Benfield process column via their respective output gas flows; wherein the catalytic methanation reactor and plasma torch each connect to the Benfield process column via their respective input gas flows; and wherein generating an additional syngas flow to the input gas flow of the Fischer-Tropsch reactor using the catalytic methanation rector. Preferably, the plasma torch further comprises an output gas flow connected to an input gas flow of the catalytic methanation reactor, and an output for the recovery of carbon black. Preferably, the catalytic methanation reactor further comprises an input gas flow from an output gas flow of the plasma torch, an input gas flow from the hydrogen separation membrane, and wherein the output gas flow enters the syngas input to the Fischer-Tropsch reactor via a water condenser. Preferably, the syncrude is sulphur-free. Preferably, the method also comprises passing all input gas flow to the plasma torch via a hydrogen separation membrane. Preferably, the gasifier is a pyrolyser. Preferably, solid waste is municipal solid waste. The solid waste may contain material that is low, intermediate or high oxygen content. The present invention will now be described by way of example only, and with reference to the accompanying drawings, in which: Figure 1 is a schematic illustration of a fuel generation system in accordance with a first embodiment of the present invention; Figure 2 is a schematic illustration of a fuel generation system in accordance with a second embodiment of the present invention; and Figure 3 is a schematic illustration of a fuel generation system in accordance with a third embodiment of the present invention. The embodiments of the present invention take an approach in which the integration of three disruptive technologies is used to generate hydrogen with a very low carbon footprint and / or sulphur-free syncrude. Syncrude is a synthetic hydrocarbon that may include, when produced by a Fischer-Tropsch reaction, naphtha (about C6 - C9); Kerosene (about CIO - Cl 5); Diesel (about C16 - C21); and a heavy fraction (about C22 - C100). One approach takes solid waste and over a number of stages ultimately produces hydrogen with a very low carbon footprint. This deals with the issues surrounding hydrogen production and also prevents carbon dioxide decomposition of solid waste that would otherwise go to landfill. Firstly, gasifier stage having an input comprising solid waste and an output gas flow of a syngas comprising carbon monoxide and hydrogen is included. A water-gas shift reactor stage having an input gas flow comprising carbon monoxide and water and an output gas flow comprising carbon dioxide and hydrogen, is also provided, along with a catalytic methanation reactor stage having an input gas flow comprising carbon monoxide, carbon dioxide and hydrogen and an output gas flow comprising methane, water and carbon dioxide. A plasma torch stage having an input gas flow comprising methane and an output gas flow comprising hydrogen is also used. The water-gas shift reactor stage and catalytic methanation reactor stage each connect to a different one of three Benfield process columns via their respective output gas flows. In addition, the water-gas shift reactor stage, catalytic methanation reactor stage and plasma torch stage each connect to a different one of the three Benfield process columns via their respective input gas flows. The input gas flow of the first Benfield process column is connected to the output gas flow of each of the second and third Benfield process columns in a recycle loop for the removal of acid gas, and to the output gas flow of the gasifier. Other embodiments of the present invention also produce fuel from solid waste. This is intended to deal with the impact of both carbon emissions from solid waste disposal and the consumption of non-recycled fossil fuels. This may be done using a Fischer-Tropsch reactor stage, which produces liquid hydrocarbons using the Fischer-Tropsch process. Typically, a syngas (comprising carbon monoxide and hydrogen) is used to enrich a carrier wax and contacted with a catalyst in a three-phase reaction process. Whilst this process has been available for a century, despite the proliferation of industrial techniques (slurry reactor stages, fixed-bed reactor stages, microchannel reactor stages, for example), the conversion rate of solid waste to liquid hydrocarbon fuel remains low, with difficulties including pressure drops within the reactor stage, reactor stage size and low catalyst productivity due to water diluting the concentration of carbon monoxide and hydrogen in the gas phase. A different approach is taken in reactor stages using a two-phase reaction, such as that described in WO2014 / 122421 and GB2216567.4, both of which are incorporated herein by reference. Syngas is generated from gasification of solid waste that would otherwise go to landfill. Alternating gas-enrichment zones and reaction zones are provided, with the syngas enriching a liquid wax carrier in each gas enrichment zone, and a catalyst is retained in structure packaging in the reaction zone. Water produced from the catalytic reaction in one reaction zone is desorbed in the next gas enrichment zone, removing the need for interstage condensation. The structure of the reactor stage also results in a much lower pressure drop between the syngas inlet and syngas outlet when compared with fixed-bed reactor stages. This results in a conversion rate of approximately 80-90% far in excess of any conversion available with conventional slurry-, fixed-bed- or microchannel-based systems. Such a Fischer-Tropsch reactor stage may be included in a system arrangement described above to produce a combination of both sulphur-free syncrude and very low carbon footprint hydrogen from solid waste. Alternatively, such a Fischer-Tropsch reactor stage may be used to produce sulphur-free syncrude from solid waste in a system that does not employ a water-gas shift reactor stage. In this situation, a gasifier stage having an input comprising solid waste and an output gas flow of a syngas comprising carbon monoxide and hydrogen is used to provide an input to a Fischer-Tropsch reactor stage comprising an input gas flow connected to the output gas flow of the gasifier and an output gas flow of reduced hydrogen and carbon monoxide off-gas. A catalytic methanation reactor stage having an input gas flow comprising carbon monoxide, carbon dioxide and hydrogen and an output gas flow comprising methane, water and carbon dioxide is provided with a plasma torch stage having an input gas flow comprising methane and an output gas flow comprising hydrogen. In addition, only a single Benfield process column is required, since both the Fischer-Tropsch reactor stage and catalytic methanation reactor stage each connect to the Benfield process column via their respective output gas flows. The catalytic methanation reactor stage and plasma torch stage each connect to the Benfield process column via their respective input gas flows. The output gas flow of the catalytic methanation reactor stage forms an additional syngas flow to the input gas flow of the Fischer-Tropsch reactor stage. Each of these embodimentswill now be described in more detail below. In the description, the following definitions for solid waste comprising materials having low, intermediate and high oxygen content apply. Table 1 and Appendix 1 of Boumanchar I, Chhiti Y, M'hamdi Alaoui FE, et al. Municipal solid waste higher heating value prediction from ultimate analysis using multiple regression and genetic programming techniques. Waste Management &Research. 2019;37(6):578-589. doi:10.1177 / 0734242X18816797, list the %C, %H, %N, %S and %O for a wide variety of waste materials. Taking the mean values for %O from the groups of materials indicated in Table 1 of this reference, the ranges low, intermediate and high oxygen content materials may be defined as: Material Mean %O (ash-free dry weight basis) Oxygen Content Definition Plastics / rubber 17.7 Low Textiles 36.7 Intermediate Food 40.1 Forest and fibre processing 45.9 Paper 50.2 High Other (mixed waste) 50.3 Solid waste incinerator ash 65.5 Table 1: Oxygen content definitions in embodiments of the present invention Figure 1 is a schematic illustration of a fuel generation system in accordance with a first embodiment of the present invention. Such a fuel generation system is suitable for use with solid waste comprising material having a low oxygen content. The fuel generation system 1 has a gasifier stage 2 having an input 3 comprising solid waste 4 and an output gas flow 5 of a syngas 6 comprising carbon monoxide and hydrogen. Carbon dioxide, methane and ethane are also present in the syngas 6, as described further below. A water-gas shift reactor stage 7 is provided, having an input gas flow 8 comprising carbon monoxide and water and an output gas flow 9 comprising carbon dioxide and hydrogen. A catalytic methanation reactor stage 10 has an input gas flow 11,12 comprising carbon monoxide, carbon dioxide and hydrogen and an output gas flow 13 comprising methane, water and a small amount of carbon dioxide. A plasma torch stage 14 has an input gas flow 15 comprising methane and an output gas flow 16 comprising hydrogen. The gasifier stage 2 is preferably a pyrolyser, which uses electric power from a local or national grid to produced syngas by pyrolysis of solid waste comprising material with a low oxygen content, as defined in Table 1 above. The water-gas shift reactor stage 7 comprises a high temperature shift catalysis reactor stage and a low temperature shift catalysis reactor stage with a steam input 17. The high temperature shift catalysis reactor stage employs an Fe2O3-Cr2O3-MgO-based catalyst, and the low temperature shift catalysis reactor stage employs a CuO-ZnO-A^Os-based catalyst. The high temperature shift and low temperature shift reactor stages may be separate, or successive adiabatic stages with intersystem cooling in a single reactor stage. The water-gas shift reaction creates a reversible reaction between carbon monoxide and water vapour to form carbon dioxide and hydrogen: CO + H2O O CO2 + H2 The water-gas shift reactor stage 7 output gas flow is via a water condenser 18. The catalytic methanation stage 10 takes an input of both carbon monoxide and carbon dioxide, along with hydrogen, and generates methane via the reactions: CO + 3H2 -» CH4 + H2O CO2 + 4H2^CH4 + 2H2O using a metal catalyst, such as nickel. The resulting gas stream is output via a water condenser 19, and a carbon dioxide purge may take place prior to the input gas flow 12. The plasma torch stage 14 produces hydrogen by flowing the input gas stream between two electrodes at high temperatures (6000°C) to create a plume of ionised gas generating high purity hydrogen. The plasma torch stage 14 further comprises an output gas flow 20 connected to an input gas flow 11 of the catalytic methanation reactor stage 10, and an output 21 for the recovery of carbon black. A hydrogen separation membrane 22 is also provided, through which all input gas flow to the plasma torch stage 14 is passed. A key feature of the fuel generation system 1 is the use of Benfield process columns. The water-gas shift reactor stage 7 and catalytic methanation reactor stage 10 each connect to a different one 23 of three Benfield process columns 23, 24, 25 via their respective output gas flows 9,13. The water-gas shift reactor stage 7, catalytic methanation reactor stage 10 and the plasma torch stage 14 each connect to a different one of the three Benfield process columns 24, 25 via their respective input gas flows 8,12,15. The input gas flow 26 of the first Benfield process column 23 is connected to the output gas flow 27, 28 of each of the second 24 and third 25 Benfield process columns in a recycle loop for the removal of acid gas, and to the output gas flow 5 of the gasifier 2. The acid gas removal takes place using potassium carbonate as an alkali in an adsorption solvent: K2CO3 + CO2 + H2) = 2HCO3 + 2K+ The Benfield process columns 23, 24, 25 are also provided with a solvent regeneration column (not shown), and gas blowers and condensate tanks are provided where necessary (not shown). The output gas flow 9 of the water-gas shift reactor stage 7 enters the third Benfield process column 25 via the water condenser 18, the catalytic methanation reactor stage 10 further comprises an input gas flow 11 from the hydrogen separation membrane 22, and wherein the output gas flow 13 of the catalytic methanation reactor stage 10 enters the second Benfield process column 24 via a water condenser 19. The advantage of doing this is that by removing the acid gas (carbon dioxide) at each stage this can be routed to the catalytic methanation reactor stage 10 for methanation and further use within the fuel generation system. The embodiment illustrated in Figure 1 may also be used with solid waste comprising material having a high oxygen content, as defined in Table 1 above, with the addition of a second steam input (not shown) to the water-gas shift reactor stage 7. The following gas flows take place within the fuel generation system 1: • syngas (comprising carbon monoxide and hydrogen) flows from the gasifier stage 2 to the water-gas shift reactor stage 7 via the first Benfield process column 23; • carbon dioxide and hydrogen (with water vapour removed via condensation) flows from the water-gas shift reactor stage 7 via the third Benfield process column 25 to both the first Benfield process column 23 (carbon dioxide) and the hydrogen separation membrane 22 (hydrogen); • carbon dioxide flows from the first Benfield process column 23 to the catalytic methanation reactor stage 10; • unreacted carbon dioxide and carbon monoxide and methane (via water vapour removal via condensation) flow from the catalytic methanation reactor stage 10 to the second Benfield process column 24; • carbon dioxide flows from the second Benfield process column 24 to the first Benfield process column 23; • methane flows from the second Benfield process column 24 to the hydrogen separation membrane and into the plasma torch stage 14; • carbon monoxide flows from the second Benfield process column 24 to the hydrogen separation membrane and into the plasma torch stage 14; • hydrogen flows from the plasma torch stage 14 to the catalytic methanation stage 10; and • hydrogen is output from the water-gas shift reactor stage 7 and the plasma torch stage 14. Analysis of the input syngas indicated that it contains hydrogen, carbon monoxide, carbon dioxide, nitrogen, methane, ethane, propane, butane and pentane and water in varying amounts. The same components were also present, in varying amounts, in the gas feed to either the hydrogen separation membrane 22 (in the embodiments of the present invention illustrated in Figures 1 and 2) or the enriched syngas (in the embodiment of the present invention illustrated in Figure 3). Figure 2 is a schematic illustration of a fuel generation system in accordance with a second embodiment of the present invention. Reference numerals for the same components as in Figure 1 are omitted for clarity. The general layout of the fuel generation system 29 is the same as that shown in Figure 1 with the addition of a Fischer-Tropsch reactor stage 30. The Fischer-Tropsch reactor stage 30 comprises an input gas flow 31 connected to the output gas flow 3 of the gasifier 2, an output liquid flow 32 of syncrude, an output liquid flow 33 of water, and an output off-gas gas flow 34 connected via a water condenser 35 to the input gas flow 26 of the first Benfield process column 23. An output gas flow 36 from the plasma torch stage 14 is connected to the input gas flow 31 of the Fischer-Tropsch reactor stage and the syngas input 6. This increases the level of hydrogen in the syngas 6 as part of a recycle loop. The syncrude produced is sulphur-free, which is not achievable with conventional crude oil hydrocarbon-based fuels. Again, the advantage of using multiple Benfield process columns 23, 24, 25 is that by removing the acid gas (carbon dioxide) at each stage this can be routed to the catalytic methanation reactor stage 10 for methanation and further use within the fuel generation system. The gas flows between the other stages illustrated in Figure 1 are the same as those outlined above. The layout illustrated in Figure 2 is suitable for use with solid waste comprising materials having a high oxygen content as defined in Table 1 above. Figure 3 is a schematic illustration of a fuel generation system in accordance with a third embodiment of the present invention. Again, reference numerals for the same components as in Figures land 2 are omitted for clarity. The general layout of the fuel generation system 37 differs to that illustrated in Figures 1 and 2 as the water-gas shift reactor stage 7 is absent. This also means that only a single Benfield process column 23 is required, and the hydrogen output by the plasma torch stage 14 is split between a hydrogen output 38 and the catalytic methanation reaction stage 10 output gas flow 13 to create enriched syngas 39 (following water vapour removal via condensation) flowing into the input gas flow 31 of the Fischer-Tropsch reactor stage 30. The layout illustrated in Figure 3 is suitable for use with solid waste comprising materials having an intermediate oxygen content as defined in Table 1 above. Suitable reactor stages (unless otherwise mentioned above) may be obtained as follows: Pyrolyser: Environmental Power International Limited, 256 Martin Way, Mor den, Surrey, SM4 4AW, UK; Benfield process: UOP Honeywell, Honeywell International Inc, 300 South Tryon Street Charlotte, NC United States; Plasma torch stage: HiiROC, 303 National Avenue, Ideal Business Park, Hull, HU5 4JB, UK. Table 2 below is a summary of the main reactants and products for each of the embodiments of the present invention illustrated in Figures 1, 2 and 3 using a simulation in gPROMS based on experimental data gathered from individual reactor stages studied at pilot or demonstrator scale. In order to compare the carbon footprint from the various chemical reactions in each embodiment of the present invention with the standard, most commonly used SMR-based technology, a high fidelity simulation of carbon dioxide generation in SMR-based technology was carried out using the gPROMS modelling platform, available in the United Kingdom (www.sie mens.com / uk / en.htmI) from Siemens plc. Figure 4 is a screenshot of a typical SMR-based system modelled in gPROMs. The SMR system 40 includes a combustion zone 41 and three catalyst pellet zones 42,43, 44, linked by a series of heat exchangers 45, 46, 47, 48, coolers 49, 50 and pressure changers 51, 52. Inputs of oxygen, water, hydrogen, fuel (for combustion), steam and waste feed are provided, without outputs of syngas (carbon monoxide and hydrogen) and flue gas (from combustion). The modelling indicated that if the overall carbon footprint of the SMR process is taken to be 10kg of CO2 per lkh of H2 produced, 80% is generated on the process side and 20% is generated on the combustion side. The embodiments of the present invention therefore also tackle the 20% generated on the combustion side by utilising electricity in the pyrolysis of the solid waste and the operation of the plasma torch stage. Taking the example of the United Kingdom, electricity taken from the National Grid is a combination of renewable, fossil fuel and nuclear origin. For example, in 2020 of the electricity consumed in one year, 43.1% was generated from renewables, 40.8% was generated from fossil fuels and 16.1% was gener ated from nuclear power. Figure 1 Figure 1 Figure 2 Figure 3 Solid Waste Cat egory Low oxygen High oxygen High oxygen Intermediate oxygen Hydrogen (kg / h) 191 38 in 10* Syncrude (kg / h) 0 0 74 160 Process-side CO? Footprint (kg CO2 / kg H2) 0.13 0.91 1.27 Carbon Black (kg / h) 541 346 284 157 Net Water (kg / h) +26 +316 +251 +321 Steam Input to WGS Reactor stages(kg / h) 81 450 130 0 *not automotive grade 5 Table 2: summary of the main reactants and products for each of the embodiments of the present invention illustrated in Figures 1, 2 and 3. Other embodiments of the present invention provide a method of generating hydrogen from solid waste. Figure 5 is a flow chart illustrating a method in accordance with 10 a fourth embodiment of the present invention. The method 500 initially comprises, at step 502, gasifying solid waste to generate a syngas comprising carbon monoxide and hydrogen. Next, at step 504, carbon dioxide and hydrogen are generated from carbon monoxide and water using a water-gas shift reactor 7. At step 506, methane, water and a small amount of carbon dioxide are generated using a catalytic methanation reactor 10, 15 and at step 510, hydrogen is generated from methane using a plasma torch 14. As above, the water-gas shift reactor 7 and catalytic methanation reactor 10 each connect to a different one of three Benfield process columns 23, 24, 25 via their respective output gas flows. The water-gas shift reactor 7, catalytic methanation reactor 10 and plasma torch 14 also each connect to a different one 24, 25 of the three Benfield process columns via their respective input gas flows. At step 512, the output gas flow of each of the second 24 and third Benfield 25 process column is recycled by removing acid gas, wherein the input gas flow of the first Benfield process column 23 is connected to the output gas flow of each of the second 24 and third 25 Benfield process columns. The plasma torch 14 comprises an output gas flow connected to an input gas flow of the catalytic methanation reactor stage 10, and an output 21 for the recovery of carbon black. As in Figure 1 described above, the water-gas shift reactor 7 comprises a high temperature shift catalysis reactor stage and a low temperature shift catalysis reactor stage. The water-gas shift reactor 7 further comprises a steam input 17 and the output gas flow enters the third Benfield 25 process column via a water condenser 18. The catalytic methanation reactor 10 further comprises an input gas flow 11 from an output gas flow of the plasma torch 14, an input gas flow 11 from the hydrogen separation membrane 22, and the output gas flow enters the second Benfield 24 process column via a water condenser 19. The method 500 may also comprise an intermediate step, step 503, of generating syncrude using a Fischer-Tropsch reactor 30 comprising an input gas flow 31 connected to the output gas flow 5 of the gasifier 2 and an output off-gas gas flow 34 connected via a water condenser 35 to the input gas flow 26 of the first Benfield process column 25. Using this method generates syncrude that is sulphur free and a small amount of hydrogen. It may also be desirable, at step 511 to recycle hydrogen from the plasma torch 14 as an input gas flow to the Fischer-Tropsch reactor 30. Figure 6 is a flow chart illustrating a method in accordance with a fifth embodiment of the present invention. The method 600 generates syncrude from solid waste. Initially, at step 602, solid waste is gasified to generate a syngas comprising carbon monoxide and hydrogen. Next, at step 604, a reduced hydrogen and carbon monoxide off-gas is generated using a Fischer-Tropsch reactor 30. At step 606, methane, water and carbon dioxide are generated using a catalytic methanation reactor 10, and at step 608, hydrogen are generated from methane using a plasma torch 14. The Fischer-Tropsch reactor and catalytic methanation reactor each connect to a Benfield process column 23 via their respective output gas flows. The catalytic methanation reactor 10 and plasma torch 14 each connect to the Benfield process column 23 via their respective input gas flows. An additional syngas flow to the input gas flow of the Fischer-Tropsch reactor 30 is generated using the catalytic methanation rector 10. The plasma torch 14 further comprises an output gas flow 20 connected to an input gas flow of the catalytic methanation reactor 10 and an output 21 for the recovery of carbon black. The catalytic methanation reactor 10 further comprises an input gas flow from an output gas flow of the plasma torch 14 and an input gas flow from the hydrogen separation membrane 22. The output gas flow of the catalytic methanation reactor 10 enters the input gas flow of the Fischer-Tropsch reactor 20 via a water condenser. Using this method, the syncrude generated is sulphur-free. In both of the methods of the fourth and fifth embodiments of the present invention, all input gas flow to the plasma torch is passed via a hydrogen separation membrane. As above, the gasifier is a pyrolyser and the solid waste is municipal solid waste. The solid waste may comprise materials having a low, intermediate or high oxygen content. It can be seen that in each embodiment of the present invention producing hydrogen that the carbon footprint of the process-side is much lower than that of the existing SMR process, with the embodiment of the present invention illustrated in Figure 1 having a carbon footprint almost a factor of 100 smaller. Whilst the embodiment of the present invention illustrated in Figure 3 produces a small amount of hydrogen that is not of good enough quality for automotive use, it does produce an amount of sulphur-free syncrude unobtainable from conventional fossil fuel hydrocarbons. The inclusion of the Fischer-Tropsch reactor stage in Figure 2 offers the best balance between high-quality low carbon footprint hydrogen production and sulphur-free syncrude production.

Claims

1. Fuel generation system for the generation of hydrogen from solid waste, the system comprising:a gasifier stage having an input comprising solid waste and an output gas flow of a syngas comprising carbon monoxide and hydrogen;a water-gas shift reactor stage having an input gas flow comprising carbon monoxide and water and an output gas flow comprising carbon dioxide and hydrogen;a catalytic methanation reactor stage having an input gas flow comprising carbon monoxide, carbon dioxide and hydrogen and an output gas flow comprising methane, water and carbon dioxide; anda plasma torch stage having an input gas flow comprising methane and an output gas flow comprising hydrogen;wherein the water-gas shift reactor stage and catalytic methanation reactor stage each connect to a different one of three Benfield process columns via their respective output gas flows;wherein the water-gas shift reactor stage, catalytic methanation reactor stage and plasma torch stage each connect to a different one of the three Benfield process columns via their respective input gas flows;and wherein the input gas flow of the first Benfield process column is connected to the output gas flow of each of the second and third Benfield process columns in a recycle loop for the removal of acid gas, and to the output gas flow of the gasifier.

2. Fuel generation system as claimed in claim 1, wherein the plasma torch stage further comprises an output gas flow connected to an input gas flow of the catalytic methanation reactor stage, and an output for the recovery of carbon black.

3. Fuel generation system as claimed in claim 1 or 2, wherein the water-gas shift reactor stage comprises a high temperature shift catalysis reactor stage and a low temperature shift catalysis reactor stage.

4. Fuel generation system as claimed in any of claims 1 to 3, wherein: the water-gas shift reactor stage further comprises a steam input and wherein the output gas flow enters the third Benfield process column via a water condenser; and the catalytic methanation reactor stage further comprises an input gas flow from an output gas flow of the plasma torch stage, an input gas flow from the hydrogen separation membrane, and wherein the output gas flow enters the second Benfield process column via a water condenser.

5. Fuel generation system according to any preceding claim, further comprising a Fischer-Tropsch reactor stage comprising an input gas flow connected to the output gas flow of the gasifier, an output liquid flow of syncrude, an output liquid flow of water, and an output off-gas gas flow connected via a water condenser to the input gas flow of the first Benfield process column.

6. Fuel generation system according to claim 5, wherein the syncrude is sulphur free.

7. Fuel generation system according to claim 5, further comprising an output gasflow of hydrogen from the plasma torch stage to be recycled as an input gas flow to the Fischer-Tropsch reactor stage.

8. Fuel generation system for the generation of syncrude from solid waste, the system comprising:a gasifier stage having an input comprising solid waste and an output gas flow of a syngas comprising carbon monoxide and hydrogen;a Fischer-Tropsch reactor stage comprising an input gas flow connected to the output gas flow of the gasifier and an output gas flow of reduced hydrogen and carbon monoxide off-gas;a catalytic methanation reactor stage having an input gas flow comprising carbon monoxide, carbon dioxide and hydrogen and an output gas flow comprising methane, water and carbon dioxide; anda plasma torch stage having an input gas flow comprising methane and an output gas flow comprising hydrogen;wherein the Fischer-Tropsch reactor stage and catalytic methanation reactor stage each connect to a Benfield process column via their respective output gas flows;wherein the catalytic methanation reactor stage and plasma torch stage each connect to the Benfield process column via their respective input gas flows;and wherein the output gas flow of the catalytic methanation reactor stage forms an additional syngas flow to the input gas flow of the Fischer-Tropsch reactor stage.

9. Fuel generation system as claimed in claim 8, wherein the plasma torch stage further comprises an output gas flow connected to an input gas flow of the catalytic methanation reactor stage, and an output for the recovery of carbon black.

10. Fuel generation system as claimed in claim 8 or 9, wherein the catalytic methanation reactor stage further comprises an input gas flow from an output gas flow of the plasma torch stage, an input gas flow from the hydrogen separation membrane, and wherein the output gas flow enters the syngas input to the Fischer-Tropsch reactor via a water condenser.

11. Fuel generation system as claimed in claim 8, 9 or 10, wherein the syncrude is sulphur-free.

12. Fuel generation system as claimed in any preceding claim, further comprising a hydrogen separation membrane through which all input gas flow to the plasma torch stage is passed.

13. Fuel generation system as claimed in any preceding claim, wherein the gasifier is a pyro lyse r.

14. Fuel generation system as claimed in any preceding claim, wherein the solid waste is municipal solid waste.

15. Fuel generation system as claimed in claim 1, wherein the solid waste comprises material having a low oxygen content.

16. Fuel generation system as claimed in claim 1 or 5, wherein the solid waste comprises material having a high oxygen content.

17. Fuel generation system as claimed in claim 8, wherein the solid waste comprises material having an intermediate oxygen content.

18. Method of generating hydrogen from solid waste, the method comprising:a) gasifying solid waste to generate a syngas comprising carbon monoxide and hydrogen;b) generating carbon dioxide and hydrogen from carbon monoxide and water using a water-gas shift reactor;c) generating methane, water and carbon dioxide from using a catalytic methanation reactor; andd) generating hydrogen from methane using a plasma torch;wherein the water-gas shift reactor and catalytic methanation reactor each connect to a different one of three Benfield process columns via their respective output gas flows;wherein the water-gas shift reactor, catalytic methanation reactor and plasma torch each connect to a different one of the three Benfield process columns via their respective input gas flows;andd) recycling the output gas flow of each of the second and third Benfield process columns by removing acid gas, wherein the input gas flow of the first Benfield process column is connected to the output gas flow of each of the second and third Benfield process columns.

19. Method as claimed in claim 18, wherein the plasma torch comprises an output gas flow connected to an input gas flow of the catalytic methanation reactor, and an output for the recovery of carbon black.

20. Method as claimed in claim 18 or 19, wherein the water-gas shift reactor comprises a high temperature shift catalysis reactor and a low temperature shift catalysis reactor.

21. Method as claimed in any of claims 18 to 20, wherein:the water-gas shift reactor further comprises a steam input and wherein the output gas flow enters the third Benfield process column via a water condenser; andthe catalytic methanation reactor further comprises an input gas flow from an output gas flow of the plasma torch, an input gas flow from the hydrogen separation membrane, and wherein the output gas flow enters the second Benfield process column via a water condenser.

22. Method according to any of claims 18 to 21, further comprisinggenerating syncrude using a Fischer-Tropsch reactor comprising an input gas flow connected to the output gas flow of the gasifier and an output off-gas gas flow connected via a water condenser to the input gas flow of the first Benfield process column.

23. Method according to claim 22, wherein the syncrude is sulphur free.

24. Method according to claim 21 or 22, further comprising recycling hydrogen from the plasma torch as an input gas flow to the Fischer-Tropsch reactor.

25. Method of generating syncrude from solid waste, the method comprising:a) gasifying solid waste to generate a syngas comprising carbon monoxide and hydrogen;b) generating a reduced hydrogen and carbon monoxide off-gas using a Fischer-Tropsch reactor;c) generating methane, water and carbon dioxide from using a catalytic methanation reactor; andd) generating hydrogen from methane using a plasma torch;wherein the Fischer-Tropsch reactor and catalytic methanation reactor each connect to a Benfield process column via their respective output gas flows;wherein the catalytic methanation reactor and plasma torch each connect to the Benfield process column via their respective input gas flows;and wherein generating an additional syngas flow to the input gas flow of the Fischer-Tropsch reactor using the catalytic methanation rector.

26. Method as claimed in claim 25, wherein the plasma torch further comprises an output gas flow connected to an input gas flow of the catalytic methanation reactor, and an output for the recovery of carbon black.

27. Method as claimed in claim 25 or 26, wherein the catalytic methanation reactor further comprises an input gas flow from an output gas flow of the plasma torch, an input gas flow from the hydrogen separation membrane, and wherein the output gas flow enters the syngas input into the Fischer-Tropsch reactor via a water condenser.

28. Method as claimed in claim 25, 26 or 27, wherein the syncrude is sulphur-free.

29. Method as claimed in any of claims 18 to 28, further comprising a passing all inputgas flow to the plasma torch via a hydrogen separation membrane.

30. Method as claimed in any of claims 18 to 29, wherein the gasifier is a pyrolyser.

31. Method as claimed in any of claims 18 to 30, wherein the solid waste is municipalsolid waste.

32. Method as claimed in claim 18, wherein the solid waste comprises material having a low oxygen content.

33. Method as claimed in claim 18 or 22, wherein the solid waste comprises material having a high oxygen content.5 34. Method as claimed in claim 25 wherein the solid waste comprises material havingan intermediate oxygen content.

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