Process

Abstract

Process for the production of useful liquid hydrocarbon product comprising: gasifying carbonaceous feedstock comprising waste materials and / or biomass in a gasification zone 4 to produce a first synth

Description

The present invention concerns a gasification process for the production of products such as higher molecular weight (typically liquid) hydrocarbon products, for example synthetic fuels, from waste materials and / or biomass materials in a manner which allows increased carbon conversion efficiency in comparison with conventional processes of the type. It is widely known in the art to manufacture useful products such as synthetic fuels from waste materials and / or biomass and / or gaseous material, such as natural gas. We may refer to such manufacturing methods as WTL (Waste-to-Liquids), BTL (Biomass-to-Liquids) and GTL (Gas-to-Liquid) processes. Typical WTL and BTL processes involve several reactions, for example, the gasification of waste or biomass feedstock by steam reforming processes and / or partial oxidation and / or water gas shift reaction and / or de-volatilization and / or carbon dioxide reforming and / or methanation, to produce a raw synthesis gas which may then be treated and purified in various ways before entering a chemical reaction train to generate a useful product. Typical GTL processes involve the gasification by steam methane reforming and / or autothermal reforming of natural gas feedstock to produce a raw synthesis gas which may then be treated and purified in various ways before entering a chemical reaction train to generate a useful product. Additionally, it is widely known in the art to generate hydrogen through the electrolysis of water. Typical electrolysis processes involve the decomposition of water into oxygen and hydrogen gas by passing an electric current through the water. In the case of the useful product being a synthetic fuel (for example a drop-in synthetic fuel), the chemical reaction train will typically comprise a Fischer-Tropsch (FT) reactor. The FT process is widely used to generate fuels from carbon monoxide and hydrogen and can be represented by the equation: (2n + 1)H2 + nCO -+ CnH2n+2 + nH2O For an FT process the usage ratio approximates ideally to 2 when n is a large number in the above equation. For example, when n=100 the ratio is 2.01. It will be appreciated that in a complex reaction network, side reactions may occur in which case the overall usage ratio and the primary reaction stoichiometry may not be synonymous and further both of these can be different from the ratio of reactants made available for the reaction. For example, in the case of FT the usage ratio in reality is typically in the range of 1.95 to 2.05, while the H2:CO ratio in the feed can vary significantly. Fuels derived from biomass and / or waste derived carbon are in increasingly high demand for various applications, for example aviation and marine fuel applications, to meet strict carbon emission restrictions. It is therefore desirable to provide a method that reduces undesirable carbon emissions. To date, there appears to have been little consideration given as to how the process can be optimised to increase the carbon conversion efficiency of the feedstock whilst reducing the environmental impact of the process (and reducing carbon intensity) and controlling the feed the feed H2:CO ratio to increase efficiency and improve profitability in an otherwise satisfactory WTL, BTL or GTL process. The term “Carbon Intensity” or “Cl” may also be construed in accordance with a model based on an overall lifecycle assessment, for example forest to tailpipe. For example, GREET a publicly available spreadsheet model developed at Argonne National Laboratory (ANL) or a California-specific version of Argonne National Laboratory’s GREET life cycle model used to calculate GHG emissions under the California Low Carbon Fuel Standard (LCFS) is the CA-GREET Version 3.0 (Tier 1) model. Other appropriate models are available such as the Biomethane &Biogas Carbon Calculator published by NNFCC Ltd, Biocentre, York Science Park, Innovation Way, York, YO10 5NY UK. Carbon intensity provides a measure of the overall energy efficiency of a process. Carbon intensity may be understood for example in terms of grams of CO2 equivalent to per MJ of fuel produced. It would be desirable to increase the quantity of desired product, for example synthetic fuels, without increasing carbon dioxide emissions at the WTL or BTL site. In particular, it would be beneficial to afford a more environmentally friendly process, such as through the use of clean power, recycling by-products and tailgas, in order to provide a process that generates more volume of desired produce. In turn, this may reduce the environmental impact of the process, increase carbon conversion efficiency and improve profitability in an otherwise satisfactory WTL, BTL or GTL process. The invention is concerned particularly, but not exclusively, with a gasification process utilising waste and / or biomass materials as the feedstock and recycling lesser desirable by-products and / or tailgas to increase the carbon conversion efficiency of the overall reaction. Additionally, the process may utilise an electrolysis process operated with a renewable electricity source. The recycling of tailgas, to some extent, has been addressed in the art. US2015152019 describes a process for the conversion of natural gas to hydrocarbon products comprising (a) mixing natural gas with a small amount of hydrogen, (b) purifying the mixture from (a) in a feed purification section to obtain purified natural gas, (c) mixing the purified natural gas from (b) with steam to obtain the desired steam-to-carbon (S / C) ratio, (d) mixing the natural gas / steam mixture from (c) with the tail gas from the downstream Fischer-Tropsch synthesis or a part thereof in a syngas section and converting the mixture into a synthesis gas, (e) cooling the synthesis gas from (d) and condensing out the process water from it, (f) leading the dry synthesis gas from (e) to a carbon dioxide removal section, where the CO2 is removed from the synthesis gas, and (g) sending the CO2-deprived synthesis gas to the downstream Fischer-Tropsch synthesis unit as a make-up gas. The carbon dioxide removed from the syngas in step (f) is either vented or kept for other use without any part of it being recycled. However, there is no consideration given to the recovery of CO2 for use in generating additional synthesis gas. US2008098654 describes a liquid fuel production system, comprising at least one gasification process apparatus configured to produce a synthesis gas; at least one gas clean-up process configured to remove carbon dioxide from the synthesis gas; at least one synthesis gas conversion process apparatus configured to receive at least a portion of the synthesis gas after removal of at least a portion of the carbon dioxide therefrom and to produce a carbon-containing tail gas; and at least one reactor configured to receive at least a portion of the carbon dioxide removed from the synthesis gas by the gas clean-up process and configured to receive the carbon-containing tail gas from the at least one synthesis gas conversion process apparatus. However, there is no consideration provided to supplying a recycle stream to an oxygen-fed reactor to produce a second synthesis gas stream, thereby complicating any required clean up processes. WO2022161823 describes a system for providing a hydrocarbon product stream. Also described is an electrolysis section providing a syngas stream from a first feed comprising CO2 and a second feed comprising H2O, which is then passed to an F-T section where it is converted to a hydrocarbon product stream and a tail gas stream. An electrical steam reformer section receives a tail gas stream and convert it to a second syngas stream, which is then recycled upstream the FT section. WO2022078915 describes an integrated process for the production of a useful liquid hydrocarbon product comprising the steps of feeding a gasification zone with an oxygencontaining feed and a first carbonaceous feedstock comprising waste materials and / or biomass, gasifying the first carbonaceous feedstock in the gasification zone to produce a first synthesis gas, partially oxidising the first synthesis gas in a partial oxidation zone to generate partially oxidised synthesis gas, combining at least a portion of the first synthesis gas and / or the partially oxidised synthesis gas and at least a portion of electrolysis hydrogen obtained from an electrolyser in an amount to achieve the desired hydrogen to carbon monoxide molar ratio of from about 1.5:1 to about 2.5:1, which is higher than that of the first synthesis gas, and to generate a blended synthesis gas, wherein the electrolyser operates using green electricity; and subjecting at least a portion of the blended synthesis gas to a conversion process effective to produce the liquid hydrocarbon product. US2011168605 describes a method and system for reforming a carbonaceous feedstock comprising reforming the feedstock to produce a first synthesis gas, subjecting a portion of the first synthesis gas to catalytic conversion, separating from the synthesis gas conversion product at least one by-product, and utilizing at least a portion of the at least one by-product during reforming of additional carbonaceous material. The object of the present invention is to provide an improved process for manufacturing a useful product, such as synthetic fuel, from waste materials and / or biomass materials in which the carbon conversion efficiency is improved in comparison to conventional processes for producing high molecular weight synthetic fuel. One way in which this is achieved is with the recycling of recovered carbon dioxide combined with by-products and / or tailgas produced during the process of the present invention. Additionally, the present invention utilises renewable energy sources that are implemented in an optimised way. It is a further object of the present invention to increase the conversion of feedstock into the desired product without increasing harmful emissions, such as carbon dioxide emissions, at the site of process. According to a first aspect of the present invention, there is provided a process for the production of a useful liquid hydrocarbon product comprising the steps of: gasifying a carbonaceous feedstock comprising waste materials and / or biomass in a gasification zone to produce a first synthesis gas, supplying at least a portion of the raw synthesis gas to a clean-up zone to produce carbon dioxide and clean synthesis gas comprising hydrogen and carbon monoxide, recovering at least a portion of the carbon dioxide from the clean-up zone; subjecting at least a portion of the clean synthesis gas to a conversion process effective to produce the liquid hydrocarbon product, by-product(s) and tailgas; combining at least a portion of the by-product(s) and / or tailgas with at least a portion of the recovered carbon dioxide to produce a recycle stream; and supplying the recycle stream to an oxygen-fed reactor to produce a second synthesis gas stream. The inventors of the present invention have surprisingly found that a process according to the invention provides an effective method for both increasing the carbon conversion efficiency from the feedstock and in providing a more environmentally friendly route compared to conventional processes in the art. This is because the present invention utilises at least a portion of carbon dioxide that is recovered during the process of the reaction, in combination with by-products and / or tailgas produced during the process for recycled use within the process to generate more of the desired product. Furthermore, the process of the present invention preferably utilises renewable (ie. green) feedstock. The inventors have found that a process of the present invention may produce useful liquid hydrogen products comprising a carbon content that is equal, or substantially equal, to the carbon contained in the biomass and / or waste feedstock. Furthermore, the inventors have found that supplying the recycle stream to an oxygen-fed reactor to produce a second synthesis gas stream simplifies the synthesis gas clean-up process compared to conventional processes in the art. Preferably, at least a portion of the recycle stream is not supplied to the gasification zone supplied with the waste and / or biomass feedstock materials, nor the optional partial oxidation zone where the first raw synthesis gas may be supplied. The generation of a second synthesis gas stream has been found to reduce the complexity of the synthesis gas purification equipment. For example, the purification of the first raw synthesis gas may require different purification conditions to the recycle stream. Therefore, providing separate streams simplifies the overall process and decreases the size and cost of the synthesis gas purification equipment, therefore also providing an economical advantage. Furthermore, the provision of separate streams advantageously allows control of the H2:CO ratio. At least a portion of the first raw synthesis gas and / or clean synthesis gas may be combined with at least a portion of the second synthesis gas to create a blended synthesis gas prior to the conversion process. The second synthesis gas may be supplied to a reactor, for example an FT unit, different to the first synthesis gas. The present invention utilises recycling processes to provide improved carbon recovery, thereby increasing the carbon conversion efficiency of the feedstock. The present invention aims to generate additional synthesis gas from the same amount of feedstock, therefore in turn, increase the amount of desired product generated (ie. fuel). The invention achieves this by utilising recovered carbon dioxide, by-products and / or tailgas that would otherwise be classified as waste or sequestered, for example. The conversion process effective to produce the liquid hydrocarbon product, for example a Fischer-Tropsch reaction, generates by-product(s) and tailgas. The by-products may include, for example, naptha (comprising C5 to C8 components), liquefied petroleum gas (LPG) comprising C3 and C4 components, diesel and kerosene. The inventors of the present invention have found that not all of the by-products and / or byproducts after upgrading are suitable for use as a fuel. Therefore, these components may not be considered to be a desired product for the production of aviation fuel. The process of the present invention utilises lesser desired products to advantageously generate additional synthesis gas suitable for use in conversion processes, for example Fischer-Tropsch process. For example, tailgas from the conversion process is be recycled to an oxygen-fed reactor to achieve a high carbon conversion efficiency to diesel or jet fuel, for example. The inventors have advantageously found that recycling at least a portion of tailgas from the conversion process, for example a Fischer-Tropsch synthesis unit, externally to an oxygen-fed reactor, maximises the use of waste products and can be used to generate additional synthesis gas. Furthermore, the inventors have found that the resulting tailgas from the process according to the present invention may comprise a low inert gas content, therefore allowing the tailgas to be recycled straight to the oxygen-fed reactor. Tailgas may optionally be purged prior to being fed to the oxygen-fed reactor. Therefore, in some embodiments at least a portion of the tailgas may be purged to remove non-reactive species. Tailgas may comprise inerts as well as uncondensed light hydrocarbons, typically C1 to C4. Tailgas is typically burned and used as fuel gas. Alternatively, tailgas may be processed to produced pure hydrogen by using a water gas shift reactor, followed by hydrogen separation, for example in a pressure swing adsorption (PSA) unit. The off-gas from the PSA unit may then be available for fuel gases. The process of the invention utilises the tailgas to generate an increased amount of synthesis gas by recycling at least a portion of the tailgas to an oxygen-fed reactor. Therefore, the process of the present invention aims to reduce unnecessary waste. It is also within the scope of the invention to recycle a portion of the tailgas to the gasification zone. The recycle stream comprising tailgas may be at a pressure which allows flow back to the synthesis gas reactor without the need for further compression. In some embodiments, it may be preferable to feed the by-products and / or tailgas via a hydrogenator and / or pre-reformer to the oxygen-fed reactor. This advantageously limits the formation of soot. Combustible gases present in the tailgas may react with oxygen in the oxygen-fed reactor to reach a temperature of at least 800°C, at least 900°C, or at least 1000°C. The inventors have advantageously found that an equilibrium gas composition is achievable at these temperatures without the need for a catalyst. Preferably, the temperature reached is at least 1000°C. At equilibrium, the content of carbon dioxide may be substantially low. A low carbon dioxide content is preferable for some synthesis reactions, such as a Fischer-Tropsch reaction, where cobalt catalysts are used because carbon dioxide is a non-reactive inert gas. In other embodiments, catalytic partial oxidation may be used to achieve equilibrium. Catalytic partial oxidation may achieve equilibrium with a shorter residence time. The second synthesis gas stream (ie. from the recycle stream) may be cooled and any solids removed. The second synthesis gas may be fed to a reactor operating the conversion process. The reactor may be the same or different to the first synthesis gas stream (ie. the raw synthesis gas and / or clean synthesis gas and / or optionally partially oxidised synthesis gas). Unless the context dictates otherwise, the terms “raw synthesis gas”, “clean synthesis gas”, “blended synthesis gas”, “partially oxidised synthesis gas” and any other phrase containing the term “synthesis gas” are to be construed to mean a gas primarily comprising hydrogen and carbon monoxide. Other components such as carbon dioxide, nitrogen, argon, water, methane, tars, acid gases, higher molecular weight hydrocarbons, oils, tars, volatile metals, char, phosphorus, halides and ash may also be present. The concentration of contaminants and impurities present will be dependent on the stage of the process and carbonaceous feedstock source. It is to be understood that carbonaceous material, for example, CH4 and inert gas such as N2 present in the raw synthesis gas generated is expected to be carrier forth through each of the subsequent steps and may not be explicitly mentioned. The process of the invention is further concerned with the practicality of generating consistently and efficiently useful products from variable energy sources, preferably where the feedstocks are renewable. For example, non-recyclable waste is conventionally sent to landfill or incineration and woody biomass is conventionally left on a forest floor and / or may contribute to forest fires. The process according to the present invention advantageously provides a lower emissions route to process waste than incineration or landfill. Instead of being burnt, the carbon waste may be converted into a useful product such as sustainable fuel for use in aircraft or vehicles. The carbonaceous feedstock may comprise at least one of woody biomass, municipal solid waste and / or commercial and industrial waste or a combination of these and the moisture content of the feedstock is reduced to below 20% w / w, preferably below 15% w / w, most preferably below 10% w / w prior to gasification by drying with at least a portion of steam gained from downstream processes. Preferably, the process of the present invention is a continuous process wherein carbonaceous feedstock, of whatever nature provided it is derived from waste materials and / or biomass, is continuously fed to a gasification zone for gasifying the carbonaceous feedstock. The gasification zone may be continuously fed with an oxygen-containing feed comprising oxygen generated from a renewable source, such as electrolysis. The inventors have advantageously found that the use of high purity oxygen (ie. electrolysis oxygen) for synthesis gas generation decreases the tailgas purge in the downstream processes, relative to oxygen that has been derived from an air separation unit. The resulting tailgas of the present invention comprises a lower inert gas content. Furthermore, the inventors of the present invention have found that the use of an oxygen-fed reactor, preferably a separate secondary oxygen-fed reactor, to process at least a portion of the tail gas and / or by-products with at least a portion of the recovered carbon dioxide stream simplifies the gas purification process compared to conventional methods in the art, thereby providing an improved process. The simplification is a result of providing a separate second synthesis gas stream that is not supplied to the same stream as the first synthesis gas stream entering the clean-up zone (for example, the first raw synthesis gas), which would otherwise complicate the purification stage. The recycle stream supplied to the secondary oxygen-fed reactor may produce synthesis gas with a low concentration of carbon dioxide. By “oxygen-fed” is meant that the reactor is supplied with a stream comprising oxygen. The stream may be an oxygen stream. The oxygen-fed reactor may be a partial oxidation zone (POx zone). Reactants / synthesis gas in the partial oxidation zone will undergo partial oxidation reactions. The process may comprise the operation of one or more partial oxidation zones. Conventional partial oxidation zones known in the art are typically catalytic or non-catalytic. The partial oxidation zone may partially combust tailgas from a downstream synthesis unit and / or syngas generated in the process and / or light gases from upgrading and / or natural gas with preheated oxygen. The partial oxidation zone may optionally comprise a burner to produce a stream of hot oxygen. The partial oxidation zone may operate at a temperature of least about 1100°C, at least about 1200°C, at least about 1300°C. Preferably, the partial oxidation zone operating temperature is at least about 1300°C, most preferably in the range of from about 1200°C to about 1350°C. The partial oxidation zone may optionally operate at a pressure slightly or somewhat lower than that of the gasification zone (to avoid any intermediate compression requirements). The partial oxidation zone may operate at a pressure of between about 2 and 3 bar for a gasification process that operates around 3.5 bar, for example. The partial oxidation zone may convert residual methane, naphthalene, higher hydrocarbons and tar components into carbon oxides, hydrogen and water. Synthesis gas leaving the partial oxidation zone may be construed to be equilibrated synthesis gas or partially oxidised synthesis gas. The partial oxidation zone may operate at a pressure slightly or somewhat lower than that of the gasification zone (to avoid any intermediate compression requirements). The partial oxidation zone may operate at a pressure of between about 2 and 3 bar for a gasification process that operates around 3.5 bar, for example. At least a portion of the raw synthesis gas from the gasification zone may be recovered and at least a portion of the recovered raw synthesis gas may optionally be supplied to an oxygen-fed reactor, for example a partial oxidation zone (POx). At least a portion of the recycle stream may be fed to a partial oxidation zone. The process according to the present invention may include a first oxygen-fed reactor and a second oxygen-fed reactor. Accordingly, the process according to the present invention may comprise a first partial oxidation zone and a second partial oxidation zone. Preferably, the oxygen-fed to the primary and / or secondary oxygen-fed reactor is from a renewable source. Preferably, the source of oxygen is from an electrolyser. Hydrogen may be supplied to the process. Preferably, the source of hydrogen is green hydrogen or blue hydrogen. In the above “green hydrogen” is meant hydrogen obtained from the electrolysis of water using renewable energies such as wind or solar. In the above “blue hydrogen” is meant hydrogen produced from natural gas, usually via steam reforming, with associated carbon capture storage. Preferably, renewable energy is used to provide the energy necessary for natural gas reforming. The products formed by a process according to the present invention may constitute cleaner versions of fuels formed by conventional processes. For example, the process may further comprise an electrolyser configured to generate electrolysis hydrogen and electrolysis oxygen. Therefore, electrolysis may be used in the present invention to generate electrolysis hydrogen and oxygen. Advantageously, water electrolysis is an efficient and clean hydrogen production technology. When renewable electricity is used to power the electrolyser and electrolysis reaction, the resulting products are considered carbon-neutral and do not contribute to harmful emissions, thereby having a significant impact on carbon intensity and greenhouse gas emissions. Electrolysis hydrogen may be combined with at least a portion of the recovered carbon dioxide, by-products and / or tailgas. Electrolysis hydrogen may be combined with the raw synthesis gas and / or clean synthesis gas and / or optionally partially oxidised synthesis gas. Electrolysis hydrogen may be combined with the raw synthesis gas and / or clean synthesis gas and / or second synthesis gas stream. The electrolysis hydrogen may be added to control the desired molar H2 to CO ratio for the conversion process. The inventors of the present invention have advantageously found that the combination of providing a recycle stream to generate additional synthesis gas with the addition of oxygen and / or hydrogen from electrolysis increases the carbon efficiency of the overall process in a manner which is more environmentally friendly than conventional processes in the art. Technologies that may be utilised in accordance with the present invention to produce the electrolysis hydrogen and oxygen may for example comprise an electrolyser which may undergo at least one of alkaline water electrolysis, solid polymer water electrolysis, high temperature solid oxide water electrolysis. The process of the invention may obtain electrolysis hydrogen and electrolysis oxygen through the electrolysis of water in an electrolyser. Advantageously, water electrolysis is an efficient and clean hydrogen production technology. The electrolyser may be operated using an external source of electricity. Preferably, the source of electricity is from a renewable (green) source. The electrolyser may operate using green technology, for example, low carbon power. The electrolyser may operate using low carbon electricity, also termed green electricity. Low carbon power is a result of processes or technologies that produce power with substantially lower amounts of carbon dioxide emissions than is emitted from conventional fossil fuel power generation. For example, low carbon power may include power generation from wind power, solar power, hydroelectric power, geothermal power, and / or nuclear power. Typically, the power consumption of an electrolyser is high and can be costly, therefore it is important to utilise “clean” energy and to minimise, or preferably obviate, the importation of external “dirty” energy, which has a significant impact on the carbon intensity of the overall process. It is important to utilise all by-products generated within the plant facility to optimize the process and reduce any waste products, thereby impacting the carbon intensity of the overall process. The source of green electricity supplied to the electrolyser may for example be wind power, solar energy, or a renewable reformer fuel such as biogas, ethanol or renewable natural gas, such as bio-diesel. Advantageously, the use of a renewable electricity source for electrolysis will make the generation of electrolysis oxygen and hydrogen virtually carbon-neutral and thus will not contribute to the overall carbon intensity of the process. The process of the invention therefore provides a lower emissions route to the production of a useful product, particularly when compared to processes that utilise hydrogen generated from fossil hydrocarbons. It is therefore desirable to use renewable electricity sources where possible thereby reducing the carbon dioxide and greenhouse gas levels and thus reducing carbon intensity of the overall process. The process according to the present invention therefore does not require the importation of hydrogen generated from fossil fuels. In an embodiment where electrolysis hydrogen is not sufficient, hydrogen may be generated from a different renewable source. For example, electrolysis hydrogen and oxygen produced in the present invention may be substantially pure. By substantially pure we mean at least about 98% pure, at least about 99% pure, at least about 99.5 % pure, about 99.8% pure. Therefore, in preferred embodiments this may obviate the need for additional external feeds to supplement the synthesis gas of the first and / or second stream, and / or additional external processes to remove waste, that may otherwise be associated with conventional BTL and WTL processes. This has a significant impact on carbon intensity. The electrolysis hydrogen and electrolysis oxygen may be used in upstream and / or downstream processes. Advantageously, using both the products of the electrolysis reaction within the plant facility reduces, and in preferable embodiments obviates, the requirement to import hydrogen and oxygen from other non-renewable and / or external sources. Additionally, the use of both major products within the plant facility ensures that there are no waste products, or extra processes required to remove components from the plant. Therefore, providing both electrolysis hydrogen and oxygen to existing processes in the plant facility can advantageously reduce the carbon intensity associated with the plant. For example, electrolysis oxygen may be used in upstream processes, such as supplying a feed into the gasification zone and partial oxidation zone(s). The inventors have found that the use of electrolysis oxygen for synthesis gas generation advantageously decreases the tailgas purge relative to when oxygen is supplied by an air separation unit. This is as a result of a concentration of inert gas in the tailgas. For example, electrolysis hydrogen may be combined with synthesis gas (i.e. raw synthesis gas) and / or the second synthesis gas steam prior to entering the reaction unit (i.e. FT reaction unit), in an amount to achieve the desired ratio. The inventors have found that the supply of pure hydrogen may obviate or reduce the need for additional downstream processes, such as a water gas shift reaction, to obtain the desired molar ratio, as is conventionally used. This has the advantage that the process of producing useful products, such as transportation fuels, is optimised and reduces the complexity of the process in comparison with conventional processes of the type. Accordingly, in one embodiment, the process according to the present invention does not include a water gas shift reaction. The absence of a water gas shift reaction further reduces the complexity and cost of a clean-up zone, for example a Rectisol™ unit, as there will no longer be any requirement to remove CO2 produced by a water gas shift reactor. Additionally, or alternatively, electrolysis hydrogen may be used as a feed to a reverse water gas shift (RWGS) reactor. When hydrogen is used to adjust the H2:CO molar ratio of synthesis gas, the hydrogen will preferably be from a green or renewable source. Thus, if the supply of electrolysis hydrogen does not satisfy the demand of the process and / or achieve the desired H2:CO molar ratio, green hydrogen from a separate feed may optionally be additionally supplied. Accordingly, in some embodiments the process may comprise a green hydrogen feed. The green hydrogen feed may be separate to the electrolysis hydrogen feed. The green hydrogen gas may therefore be combined with at least one of electrolysis hydrogen and / or partially oxidised synthesis gas and / or clean synthesis gas and / or second synthesis gas. The use of green hydrogen therefore does not negatively impact the carbon intensity of the overall process. Electrolysis oxygen may be used as a feed to the gasification zone. The electrolysis oxygen may be used to supplement the quantity of oxygen otherwise supplied by other means to the gasification zone, for example via an air separation unit (ASU). In preferred embodiments, the oxygen demand of the gasification zone may be achieved without the requirement of an air separation unit It has been found that the use of an electrolyser in combination with a gasifier enhances the carbon intensity score when compared to conventional processes. For example, electrolysis oxygen integration within the plant facility maximises the utility of the electrolyser, optimises the overall process and eliminates the requirement of an air separation unit. In some embodiments, the electrolysis process and the gasification zone may be integrated. Furthermore, it has been found that suppling at least one renewable source of hydrogen, preferably substantially pure hydrogen, helps in obtaining specific hydrogen to carbon monoxide feed ratios and simplifies the overall process. Additionally, supplying a renewable source of hydrogen to the second synthesis gas stream aids in the generation of synthesis gas suitable for downstream processes. This arrangement allows the rest of the facility to be simplified, thereby benefitting the economics of the process. However, if electrolysis oxygen supply is limited or does not meet the demand, some air separation unit capacity may be included. Accordingly, in one embodiment, the process according to the present invention does not include an air separation unit. Advantageously, the integration of feeding the electrolysis oxygen into the gasification zone and / or optional partial oxidation zone and combining electrolysis hydrogen with synthesis gas, maximizes the utility of the electrolyser and in some embodiments, obviates the need of a separate air separation unit and / or water gas shift reaction, thereby reducing costs and increasing simplicity of the plant. Thus, the complexity of the process according to the present invention is reduced when compared to conventional processes in the art. The process according to the invention therefore may provide a process that combines a gasification process with an electrolysis process which has the potential to overcome environmental issues associated with oxygen and hydrogen which would otherwise be supplied to the plant by alternative non-renewable sources and / or methods. The process according to the present invention may be integrated. The process according to the present invention may include combining the second synthesis gas with the first synthesis gas stream (ie. first raw synthesis gas and / or optionally partially oxidised synthesis gas and / or clean synthesis gas) to achieve the desired H2:CO molar ratio . Preferably, the process of the present invention is a continuous process wherein carbonaceous feedstock, of whatever nature provided it is derived from waste materials and / or biomass, is continuously fed to a gasification zone for gasifying the carbonaceous feedstock. For example, the feedstock, preferably renewable feedstock, fed to the plant may comprise at least one of waste, bio-feed, green electricity, green hydrogen and / or renewable natural gas. The feedstock may be supplied as the same, or different, feed within the plant facility. The gasification zone may be continuously fed with an oxygen-containing feed comprising oxygen generated from a renewable source, such as electrolysis. Preferably, the majority, if not all, of the oxygen-containing feed fed to the gasification zone is from a renewable source. If the demand cannot be met solely with an oxygen-containing feed from a renewable source, supplementary oxygen from a traditional oxygen unit, such as an air separation unit, may be used. In preferred embodiments, the oxygen demand of the gasification zone may be achieved without the requirement of an air separation unit Preferably, an electricity source, of whatever nature provided it is considered “green” or renewable, is continuously fed, either simultaneously or separately to an electrolyser for the electrolysis of water. It is to be understood that the terms “renewable”, “green” and / or “clean” when used to describe feedstock and / or energy sources are construed to mean that they are from a natural resource or source of energy that is not depleted by use. They are produced with little-to-no environmental impact and do not contribute greenhouse gases into the air the way fossil fuels do. At least a portion of the synthesis gas (for example, clean synthesis gas) is fed into a synthesis unit. Non-limiting examples of suitable syntheses include Fischer-Tropsch, ammonia synthesis, methanol synthesis, alcohol synthesis or hydrogen production. The useful product may be produced by subjecting at least part of the first raw synthesis gas and / or clean synthesis gas and / or second synthesis gas and / or blended synthesis gas to a Fischer-Tropsch synthesis or ammonia synthesis or methanol synthesis. Synthesis reactions require specific hydrogen to carbon monoxide ratio in feed gas (“desired ratio”) for optimum performance to meet process requirements, maximise conversion and product yield. As a non-limiting example, it is generally needed to increase the hydrogen to carbon monoxide ratio of the synthesis gas generated from waste-derived gasification when wanting to supply clean synthesis gas to a Fischer-Tropsch reactor. As a result, at least part of the synthesis gas from, for example, a clean-up zone (ie. clean synthesis gas) may be combined with at least a portion of electrolysis hydrogen from the electrolyser and / or synthesis gas from the recycle stream and / or at least a portion of green hydrogen to adjust the hydrogen to carbon monoxide ratio to the desired range. As a non-limiting example, the Fischer-Tropsch synthesis feed (i.e. blended synthesis gas) may have a hydrogen to carbon monoxide ratio of about 2. As a non-limiting example, the Fischer-Tropsch synthesis H2:CO ratio may from about 1.5:1 to about 2.5:1, or preferably from about 1.7:1 to about 2.2:1, or more preferably from about 1.95:1 to about 2.05:1, typically about 2. It has been found that by combining at least a portion of the waste derived synthesis gas (i.e. low H2 to CO molar ratio) with at least a portion of pure hydrogen (i.e. electrolysis hydrogen and / or green hydrogen and / or blue hydrogen) and / or the synthesis gas from the recycle stream, a blended synthesis gas may be produced with a desired H2 to CO molar ratio for the required synthesis, for example Fischer-Tropsch synthesis. Preferably, the adjusting of the H2 to CO molar ratio of the waste derived synthesis gas is achieved by the combination of feedstocks which are from renewable sources. This has a significant impact on both the carbon intensity and economics of the process. The useful product may optionally be produced by subjecting at least part of the synthesis gas to a Fischer-Tropsch synthesis. According to the embodiment relating to Fischer-Tropsch synthesis, the optionally blended synthesis gas may be fed into a FT reactor. The synthesis unit may be a FT unit comprising FT reactors. The FT reactors may comprise microchannels. Filters may be used to remove any particulates. The FT reactor may convert at least part of the carbon monoxide and hydrogen of the optionally adjusted fine synthesis gas into mainly linear hydrocarbons. The blended synthesis gas may be converted by Fischer-Tropsch synthesis into liquid hydrocarbons. The conversion of synthesis gas into liquid hydrocarbons may optionally be in the presence of a catalyst. The chain length distribution will be dependent on the properties of the catalyst used and the operating conditions. Fischer-Tropsch reactions are exothermic and release heat that must be removed to keep the temperature of the reaction approximately constant. Localised high temperatures in the catalyst bed have been found to adversely affect the FT product mix, yield and potentially reduce catalyst life. Therefore, it is desirable to keep the temperature constant. The temperature may be controlled by varying pressure of a steam drum associated with the FT reactor used in conjunction with circulating cooling water. The operating temperature for the FT synthesis may be between about 125 and 350°C, between about 150 and 300°C, between about 170 and 250°C, between about 180 and 240°C. Preferably, the operating temperature is between about 180 and 240°C for a low temperature FT technology. The catalyst may be a metal or compounded metal catalyst with a support. In one embodiment, the metal is cobalt. The support may be made from silica and / or titania. The products that may be obtained in the FT synthesis, for example, said hydrocarbons, may include heavy FT liquid (HFTL), light FT liquid (LFTL), FT process water, naphtha, and tail gas comprising of inerts as well as uncondensed light hydrocarbons, typically C1 to C4. The liquid hydrocarbons may be upgraded to make a useful product. At least part of the liquid hydrocarbons may be upgraded by at least one of hydroprocessing, hydrotreating, product fractionation, hydrocracking and / or hydroisomerisation for example. The FT liquid upgrading unit may for example produce high quality naphtha and Synthetic Paraffinic Kerosene (SPK). Other upgraded products may for example include gasoline, diesel and waxes. The unit may for example be configured as a recycle hydrocracker. The useful product may for example be sustainable liquid transportation fuel or a gasoline blendstock. The transportation fuel or gasoline blendstock may for example be used for aviation and / or vehicles. The sustainable liquid transportation fuel may for example comprise high quality diesel and / or SPK. As a result of the supply of high purity electrolysis hydrogen provided to combine with waste and / or biomass derived synthesis gas and / or recycle stream synthesis gas, the desired molar ratio may be achieved without the requirement of a water gas shift reaction, as is conventionally used. Accordingly, in one embodiment, the process according to the present invention does not include a water gas shift reaction. Accordingly, in this embodiment, the clean up zone may further be simplified as a result of no longer requiring the removal of carbon dioxide produced by a water gas shift reactor. However, if renewable natural gas and / or electrolysis hydrogen supply is limited as the feedstock, some water gas shift capacity may be included. At least a portion of the first synthesis gas is decontaminated in a clean-up zone. This step will alleviate poisoning of any catalyst utilised in a subsequent conversion process. The synthesis gas may optionally remove ammoniacal, sulphurous and carbon dioxide (and other acid gases) impurities, preferably sequentially, in the clean-up zone. The overall process according to the invention may optionally include additional stages. Therefore, the synthesis gas cleaned by sequentially removing ammoniacal, sulphurous and carbon dioxide impurities may be, for example, raw synthesis gas and / or partially oxidised synthesis gas. The conversion process will typically result in a high molecular weight (e.g. liquid) hydrocarbon whereas a separation process may be used to produce hydrogen or carbon dioxide, for example. The process of the present invention is configurable to generate additional synthesis gas by combining by-product(s), recovered carbon dioxide and optionally green hydrogen. Furthermore, the addition of hydrogen is configurable to control the molar H2 to CO ratio of the synthesis gas. In some embodiments, the resulting second synthesis gas stream is combined with the first synthesis gas stream and / or green hydrogen to provide a blended synthesis gas with the desired molar H2 to CO. The “first synthesis gas stream” is to be understood to mean the synthesis gas stream generate by the waste and / or biomass feedstock. Therefore the first synthesis gas stream may for example comprise the first raw synthesis gas and / or optionally partially oxidised raw synthesis gas and / or clean synthesis gas. The “second synthesis gas stream” is to be understood to mean the synthesis gas stream resulting from the by-products and / or tailgas and / or recovered carbon dioxide and / or green hydrogen. The clean-up process may, for example, be a physical absorption process, for example a solvent-based process. Suitable processes include low steam processes such as the Rectisol™ or Selexol™ processes, for example. In one embodiment, the physical absorption unit may be configured to operate a dual stage process with two separate absorber columns that contact the synthesis gas stream with methanol comprising a common methanol regeneration system. The first absorber column may selectively remove sulphur and may use a CO2 saturated solvent to minimise CO2 absorption in the sulphur removal column. The second absorber column may recover CO2. This arrangement allows for the selective removal of sulphur from the synthesis gas, followed by the subsequent removal of CO2. This technology is further described elsewhere; for example, in Fossil Fuel Emissions Control Technologies, Bruce Miller, 2015. At least a portion of the carbon dioxide is recovered. The carbon dioxide may optionally be in substantially pure form. The carbon dioxide may for example be essentially sulphur free. The recovered carbon dioxide may be at least about 60%, at least about 70%, at least about 80%, at least about 85% pure. At least a portion of the recovered substantially pure carbon dioxide may optionally be sequestered. Sequestering carbon dioxide may involve separating, compressing, and transporting carbon dioxide to an appropriate geologic formation, where it is injected and stored permanently underground. This advantageously reduces the carbon intensity of the process. Carbon dioxide produced may also contribute to the carbon intensity and economics of the overall process. The source and the nature of the carbon dioxide produced will affect the carbon intensity of the process. Alternatively, the clean-up process may, for example, be a chemical process such as an amine wash. The resulting synthesis gas is referred to herein as “clean synthesis gas”. At least a portion of the optionally partially oxidised synthesis gas may be fed to a clean-up zone to remove contaminants. In variants of the invention which do not utilize a partial oxidation zone for the first synthesis gas it is also desired to remove tars either by condensation prior to the sulphur removal bed or by using the physical absorption solvent to absorb tars and recovering them from the solvent regeneration stage. The conversion process will typically result in a high molecular weight (e.g. liquid) hydrocarbon whereas a separation process may be used to produce hydrogen or carbon dioxide, for example. It has been found that suppling at least one renewable source of hydrogen, preferably substantially pure hydrogen helps in obtaining specific hydrogen to carbon monoxide feed ratios and simplifying the overall process. Advantageously it has been found that a process according to the present invention has the ability to utilise the by-products and tailgas to produce additional synthesis gas that is suitable for the conversion process. A preferred embodiment of the invention is described below by way of example only with reference to Figures 1 of the accompanying drawings, wherein: Figure 1 is a simplified schematic diagram of a process for undertaking FT synthesis by the integration of an electrolyser with a gasification zone and a recycling stream in accordance with the present invention; Referring to Figure 1, a carbonaceous feedstock is supplied in line 1 to Fuel Conditioning Facility (FCF) 2 and on in line 3 to gasification zone 4. Raw synthesis gas from gasification zone 4 is passed on in line 5 to partial oxidation zone 6. Partially oxidised raw synthesis gas passes on in line 7 to gas clean-up zone 8, generating clean synthesis gas in line 9. Electricity and water are supplied in lines 10 and 11 respectively to the electrolyser 12. Several different sources of electricity could be considered for electrolyser 12, with the most preferable being green electricity, for example solar or wind. Electrolysis oxygen from electrolyser 12 is passed in line 13 to gasification zone 4. It is possible in some embodiments to solely use electrolysis oxygen to supply the gasification zone 4 without the need for a separate air separation unit. If electrolysis oxygen supply is limited, it is possible that some ASU oxygen is included in order to meet the gasification zone 4 requirements. Electrolysis hydrogen from electrolyser 12 is passed in line 14 to combine (line 15) with the clean synthesis gas from line 9. All or a portion of the blended synthesis gas in line 15 is fed to Fischer-Tropsch (FT) reactor train 16 and the resulting FT products are fed in line 17 to upgrading zone 18, generating a useful product stream in line 19. Means are provided, for controlling the amount of electrolysis hydrogen that is combined with the waste or biomass derived synthesis gas from clean-up zone 8. This embodiment involves the supplementing of waste-derived synthesis gas (which has a low H2:CO ratio of approximately 1.0 when leaving partial oxidation zone 6) with pure electrolysis hydrogen from the electrolyser 12. Thus, the low H2:CO ratio synthesis gas from waste gasification is combined with pure electrolysis hydrogen from the electrolyser 12 to produce a syngas that meets the H2:CO of approximately 2.00 requirement for Fischer-Tropsch synthesis. At least a portion of the by-products and / or tailgas from line 21 is fed to oxygen-fed reactor 22 in line 21, optionally via a hydrogenator and / or pre-reformer 20. This is combined with CO2 recovered from the synthesis gas clean up zone 8 in line 23 and electrolysis hydrogen 24. The oxygen-fed reactor is fed with electrolysis oxygen 25. A secondary synthesis gas stream 26 which is suitable for Fischer-Tropsch synthesis may be recovered from oxygen-fed reactor 22.

Claims

1. A process for the production of a useful liquid hydrocarbon product comprising the steps of:gasifying a carbonaceous feedstock comprising waste materials and / or biomass in a gasification zone to produce a first raw synthesis gas,supplying at least a portion of the raw synthesis gas to a clean-up zone to produce carbon dioxide and clean synthesis gas comprising hydrogen and carbon monoxide,recovering at least a portion of the carbon dioxide from the clean-up zone;subjecting at least a portion of the clean synthesis gas to a conversion process effective to produce the liquid hydrocarbon product, by-product(s) and tailgas;combining at least a portion of the by-product(s) and / or tailgas with at least a portion of the recovered carbon dioxide to produce a recycle stream; andsupplying at least a portion of the recycle stream to an oxygen-fed reactor to produce a second synthesis gas stream.

2. The process according to Claim 1 wherein the by-products and / or tailgas are further combined with hydrogen.

3. The process according to Claim 2 wherein the hydrogen comprises green and / or blue hydrogen.

4. The process according to Claim 2 or Claim 3 wherein the oxygen-fed reactor is fed with green oxygen.

5. The process according to any one of Claims 2 to 4 wherein the hydrogen and / or oxygen comprises hydrogen and / or oxygen obtained from an electrolyser.

6. The process according to any one of Claims 1 to 5 wherein at least a portion of the first raw synthesis gas and / or clean synthesis gas is combined with at least a portion of the second synthesis gas to create a blended synthesis gas prior to the conversion process.

7. The process according to any one of Claims 1 to 6 wherein the by-products comprise at least one of naphtha and liquified petroleum gas.

8. The process according to any one of Claims 1 to 7 wherein the process further comprises partially oxidizing the first synthesis gas in an oxygen-fed reactor to generate a partially oxidized synthesis gas.

9. The process according to any one of Claims 1 to 8 wherein the clean-up zone comprises the removal of ammoniacal, sulphurous and carbon dioxide impurities, preferably sequentially.

10. The process according to any one of Claims 1 to 9 wherein the recovered carbon dioxide is substantially pure.

11. The process according to Claim 10 wherein the pure carbon dioxide is at least about 60%, at least about 70%, at least about 80%, at least about 85% pure.

12. The process according to any one of Claims 1 to 11 wherein at least a portion of the carbon dioxide is captured and sequestered.

13. The process according to any one of Claims 1 to 12 wherein the useful liquid hydrocarbon product is produced by subjecting at least portion of the clean synthesis gas and / or recycled synthesis gas to a Fischer-Tropsch synthesis.

14. The process according to any one of Claims 1 to 13 wherein the clean synthesis gas and / or recycled synthesis gas synthesis gas is converted by Fischer-Tropsch synthesis into liquid hydrocarbons.

15. The process according to any one of Claims 1 to 14 wherein the liquid hydrocarbons are upgraded into the useful liquid hydrocarbon product.

16. The process according to any one of Claims 1 to 15 wherein at least a part of the liquid hydrocarbons are upgraded by at least one of hydroprocessing, product fractionation, hydrocracking and / or hydroisomerisation to produce the useful liquid hydrocarbon product.

17. The process according to any one of claims 1 to 16 wherein the useful liquid hydrocarbon product comprises synthetic paraffinic kerosene and / or diesel.

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