Method and system for pyrolysis

Abstract

A method is provided, the method comprising: decomposing, in a pyrolysis reactor, a biomass feedstock to produce a biochar and a pyrogas; receiving, by a combustion chamber, the pyrogas and an oxygen rich gas; combusting, in the combustion chamber, the pyrogas with the oxygen rich gas; and heating the pyrolysis reactor with heat from the combustion chamber.

Description

[0001] Method and System for Pyrolysis

[0002] Field of the invention

[0003] The present invention relates to a method and system for pyrolysis. The present invention is particularly, but not exclusively, applicable to pyrolysis of biomass.

[0004] The present disclosure seeks to provide more efficient and effective methods and systems for pyrolysis with reduced unwanted biproducts.

[0005] Background to the disclosure

[0006] Pyrolysis is increasingly deployed as a thermochemical conversion route for biomass, enabling the production of biochar for long-term carbon sequestration alongside pyrogas generation. The produced pyrogas can be combusted to recover thermal energy for use in the pyrolysis process, biomass drying and even electricity generation. Conventional pyrolysis systems typically rely on air-based combustion of pyrogas (also referred to herein as pyrosyngas or syngas) to generate heat, as is conventionally considered effective. It is an aim to find improved pyrolysis methods and systems.

[0007] Summary of the disclosure

[0008] Aspects and embodiments of the present invention are set out in the appended claims. These and other aspects and embodiments of the invention are also described herein.

[0009] According to a first aspect there is provided a method comprising: receiving a pyrogas; receiving an oxygen rich gas; and combusting the received pyrogas with the oxygen rich gas.

[0010] The pyrogas may be received from a pyrolysis reactor (also referred to as a pyrolysis chamber) and may be generated as a product of pyrolysis of a biomass feedstock or a carbon-rich feedstock.

[0011] The use of oxygen rich gas in the combustion of pyrogas can enable synergistic improvements to the combustion products, in particular the heat and the exhaust gases. For instance, higher heat can be achieved, which can permit more favourable pyrolysis conditions, in turn providing pyrogas with favourable characteristics for combustion. For instance, the exhaust gas from the combustion can be relatively free of or contain lower amounts of undesired combustion products that can prevent efficient use of the exhaust gas.

[0012] The method may be performed in a combustion chamber. The combustion chamber maycomprise an exhaust. The method may further comprise collecting exhaust gas at the exhaust. The exhaust gas may be collected for downstream use.

[0013] The pyrogas may be from pyrolysis (also referred to as pyrolisation) in a pyrolysis reactor heated by the combustion chamber. The pyrogas may be from pyrolysis of a biomass or a carbon-rich feedstock.

[0014] The combustion temperature may be above 600°C. The combustion temperature may be above 700°C. The combustion temperature may be above 800°C. The combustion temperature may be above 900°C. The combustion temperature may be above 1000°C. The combustion temperature may be above 1100°C. The combustion temperature may be below 1200°C. The combustion temperature may be below 1100°C. The combustion temperature may be below 1000°C. The combustion may be maintained at a pressure below 900 Pa. The combustion may be maintained at a pressure below 850 Pa. The combustion may be maintained at a pressure below 800 Pa. The combustion may be maintained at a pressure above 600 Pa.

[0015] Oxygen rich gas preferably has a higher oxygen content than air. The oxygen rich gas may be a mixture of oxygen and air. The oxygen rich gas may be a mixture of oxygen and a CO2 enriched gas. The oxygen rich gas may be a mixture of oxygen and an exhaust gas from the combustion. The oxygen rich gas may be pure oxygen. The oxygen rich gas may have more than 40% oxygen by volume (or by mole fraction), preferably more than 60% oxygen by volume (or by mole fraction), and further preferably more than 75% oxygen by volume (or by mole fraction). The oxygen rich gas may be between 90% and 100% oxygen by volume. The oxygen content of the oxygen rich gas may be variable.

[0016] The method may further comprise recovering energy from excess heat produced by the method. The method may further comprise distributing excess heat produced by the method and / or distributing energy produced from excess heat of the method.

[0017] The method may further comprise capturing an exhaust gas produced by the method. The exhaust gas may comprise 50% or more CO2 by mole fraction, optionally 70% or more CO2 or 85% or more CO2. The exhaust gas may comprise around 90% CO2 by mole fraction. The method may further comprise recycling the exhaust gas to provide a component of the oxygen rich gas. Pure oxygen may be a further component of the oxygen rich gas.

[0018] Combustion of a pyrogas with ambient air may lead to the formation of nitrogen oxides (NOX). Nitrogen oxides are well known for their negative effect on the environment and on health,and it can be beneficial to reduce such unwanted emissions. Combustion of the pyrogas with oxygen rich air has been found to reduce the amount of NOXproduced as a biproduct of pyrolysis methods.

[0019] The combusting the pyrogas with oxygen rich gas may generate a flue gas comprising NOXof between 14 to 90 mg / Nm3. The exhaust gas may comprise less than 100 mg / Nm3NOX, optionally less than 80 mg / Nm3NOXor less than 30 mg / Nm3NOXor less than 20 mg / Nm3NOX.

[0020] Conversely, combustion of the pyrogas in air may generate a flue gas comprising NOXof over 100 mg / Nm3.

[0021] The oxygen rich gas is preferably between 90% and 100% oxygen by volume and is optionally provided to the combustion chamber at between 70 and 90 kg / h.

[0022] The combustion of pyrogas in oxygen rich gas of between 90% and 100% oxygen by volume may generate a flue gas comprising NOXof between 14 to 30 mg / Nm3.

[0023] According to another aspect there is provided a pyrolysis method comprising decomposing a biomass (or a carbon-rich feedstock) with heat provided by a method as aforementioned.

[0024] The method of decomposing the biomass (or a carbon-rich feedstock) may comprise decomposing, in a pyrolysis reactor, the biomass (or the carbon-rich feedstock) and thereby producing the pyrogas. The method of decomposing the biomass may comprise: decomposing, in a pyrolysis reactor, the biomass into a plurality of first intermediate components, wherein one of the plurality of first intermediate components is the pyrogas.

[0025] According to another aspect there is provided a method, the method comprising: decomposing, in a pyrolysis reactor, a biomass feedstock (or a carbon-rich feedstock) and thereby producing a pyrogas; providing, to a combustion chamber, the pyrogas and an oxygen rich gas; and combusting the pyrogas with the oxygen rich gas. The method preferably comprises heating the pyrolysis reactor with heat from the combustion chamber or heating the pyrolysis reactor by the combustion chamber. The decomposing, in the pyrolysis reactor, may comprise producing a biochar from the biomass. The decomposing, in the pyrolysis reactor, may comprise producing a plurality of first intermediate components, wherein one of the plurality of first intermediates is pyrogas.

[0026] The method may include features according to a method as aforementioned.According to another aspect there is provided a pyrolysis system comprising: a pyrolysis reactor heated by a combustion chamber; a conduit arranged to provide a pyrogas produced in the pyrolysis reactor to the combustion chamber for combustion; and an oxygen rich gas source arranged to provide oxygen rich gas to the combustion chamber for combustion.

[0027] The heating of the pyrolysis reactor by the combustion chamber may be by direct or indirect heating. For instance, exhaust gas leaving the combustion chamber may be used to transfer heat. At least a portion of the exhaust gas may pass through an outer jacket of the pyrolysis reactor to indirectly heat the pyrolysis reactor. Heat may be transferred to a separate heat transfer fluid, and the heat transfer fluid may be used to heat the pyrolysis reactor. The heating of the pyrolysis reactor by the combustion chamber may be by converting heat energy released by the combustion to electric energy and electric heating of the pyrolysis reactor. Heat energy may be transferred to a separate energy carrier, and the energy carrier may be used to heat the pyrolysis reactor.

[0028] The use of oxygen rich gas in the combustion of pyrogas can enable synergistic improvements to the combustion products, in particular the heat and the exhaust gases. For instance, higher heat can be achieved, which can permit more favourable pyrolysis conditions, in turn providing pyrogas with favourable characteristics for combustion. For instance, the exhaust gas from the combustion can be relatively free of or contain lower amounts of undesired combustion products that can prevent efficient use of the exhaust gas.

[0029] The pyrolysis system may be adapted for a method as aforementioned.

[0030] The combustion chamber may comprise an exhaust. The pyrolysis system may comprise an exhaust gas store for collecting exhaust gas at the exhaust for downstream use.

[0031] The pyrolysis system may comprise a feedstock supply unit arranged to store a feedstock and / or supply feedstock to the pyrolysis reactor. The feedstock supply unit may be adapted to supply feedstock to the pyrolysis reactor at a controlled rate. The pyrolysis system may be adapted for pyrolysis of a biomass. The pyrolysis system may be adapted for pyrolysis of a carbon-rich feedstock.

[0032] The pyrolysis system may be adapted for a combustion temperature above 600°C, optionally above 700°C. The combustion chamber may be adapted for a combustion temperature above 800°C. The combustion chamber may be adapted for a combustion temperature above 900°C. The combustion chamber may be adapted for a combustion temperature above 1000°C. The combustion chamber may be adapted for a combustion temperature above1100°C. The combustion chamber may be adapted for a combustion temperature below 1200°C. The combustion chamber may be adapted for a combustion temperature below 1100°C. The combustion chamber may be adapted for a combustion temperature below 1000°C. The combustion chamber may be adapted for a combustion temperature a pressure below 900 Pa. The combustion chamber may be maintained at a pressure below 850 Pa. The combustion chamber may be maintained at a pressure below 800 Pa. The combustion chamber may be maintained at a pressure above 600 Pa.

[0033] The pyrolysis system may further comprise a CO2 capture unit.

[0034] Oxygen rich gas preferably has a higher oxygen content than air. The oxygen rich gas may be a mixture of oxygen and air. The oxygen rich gas may be a mixture of oxygen and a CO2 enriched gas. The oxygen rich gas may be a mixture of oxygen and an exhaust gas from the combustion. The oxygen rich gas may have more than 40% oxygen by volume or by mole fraction. The oxygen rich gas may be pure oxygen. The oxygen rich gas may be as aforementioned.

[0035] The pyrolysis system may comprise a heat recovery system arranged to store and distribute excess heat produced at the combustion chamber.

[0036] According to another aspect there is provided a biochar produced by a pyrolysis system or a pyrolysis method as aforementioned. According to another aspect there is provided a biochar produced by a method comprising: receiving a pyrogas; receiving an oxygen rich gas; and combusting the received pyrogas with the oxygen rich gas. The method may be as aforementioned.

[0037] Any apparatus feature as described herein may also be provided as a method feature, and vice versa. As used herein, means plus function features may be expressed alternatively in terms of their corresponding structure.

[0038] Any feature in one aspect of the invention may be applied to other aspects of the invention, in any appropriate combination. In particular, method aspects may be applied to apparatus aspects, and vice versa. Furthermore, any, some and / or all features in one aspect can be applied to any, some and / or all features in any other aspect, in any appropriate combination. It should also be appreciated that particular combinations of the various features described and defined in any aspects of the invention can be implemented and / or supplied and / or used independently.

[0039] The invention extends to methods, system and apparatus substantially as herein describedand / or as illustrated with reference to the accompanying figures.

[0040] As used herein, the term “pure” preferably connotes 95% or more by mole fraction, more preferably 99% or more by mole fraction. Where gas composition values of a gas mixture are provided in units of mole fraction, the same values in units of volume fraction (% by volume) can take their place (and vice versa), by virtue of assumption of ideal gas behaviour. So, for example, 95% of a gas by mole fraction is considered equivalent to 95% by volume.

[0041] As used herein, the unit mg / Nm3preferably refers to mg per m3at a temperature of 15 °C and a pressure of 101.325 kPa.

[0042] It should be noted that the term “comprising” as used in this document means “consisting at least in part of”. So, when interpreting statements in this document that include the term “comprising”, features other than that or those prefaced by the term may also be present. Related terms such as “comprise” and “comprises” are to be interpreted in the same manner.

[0043] Description of the Drawings

[0044] One or more aspects will now be described, by way of example only and with reference to the accompanying drawings having like-reference numerals, in which:

[0045] Figure 1 is a schematic of a system for pyrolysis of biomass;

[0046] Figure 2 is a schematic of an alternative system for pyrolysis of biomass;

[0047] Figure 3 is a schematic of a method of pyrolysis of biomass;

[0048] Figure 4 is a schematic of an alternative system for pyrolysis of biomass;

[0049] Figure 5 is a table outlining characteristics of the Grade A woodchip, which were used within the model;

[0050] Figure 6 is a schematic of an alternative system for pyrolysis of biomass showing a Mass and Energy Balance with Air Combustion;

[0051] Figure 7 is a schematic of an alternative system for pyrolysis of biomass showing a Mass and Energy Balance with 75% Air, 25% Pure Oxygen Combustion;

[0052] Figure 8 is a schematic of an alternative system for pyrolysis of biomass showing a Mass and Energy Balance with 50% Air, 50% Pure Oxygen Combustion;

[0053] Figure 9 is a schematic of an alternative system for pyrolysis of biomass showing a Mass and Energy Balance with Pure Oxygen Combustion;

[0054] Figure 10 is a graph showing the effect of increasing concentration in oxidant on NOXin Flue Emissions;

[0055] Figure 11 is a graph showing the effect of increasing oxygen concentration in oxidant onEnergy Recovery Potential; and

[0056] Figure 12 is a table outlining flue gas emissions and energy recovery data as oxygen concentration is increased in combustion chamber oxidant.

[0057]

[0058] embodiments

[0059] Figure 1 shows a system 10 for pyrolysis of biomass. Pyrolysis is a thermochemical decomposition of organic material at elevated temperatures (typically between 400°C and 700°C) in the absence or near-absence of oxygen. A biomass feedstock 8 is heated in a pyrolysis reactor 2 in oxygen-deprived conditions, causing the biomass to convert to a blend of hydrocarbons that can form biochar, pyrogas, and bio-oil. The raw pyrolysis product 12 including gas and particles flowing from the pyrolysis reactor 2 is processed by suitable processing units 6 and materials (e.g. cyclotron, quencher system, condenser) to separate out the biochar 14, bio-oil 16 and pyrogas 18 from the raw exhaust gas 12. The biochar 14 is rich in carbon including elemental carbon and has numerous uses, including soil improvement, carbon sequestration, and pollution reduction. The bio-oil 16 can be used as a fuel.

[0060] A combustion chamber 4 provides heat 106 to the pyrolysis reactor 2 by combustion of the pyrogas 18. The pyrogas 18 is fed to the combustion chamber 4 and combusted under addition of ambient air 20. Exhaust 22 from the combustion chamber 4 is released and may be further processed, e.g. scrubbed for release into the atmosphere, or heat recovered for further use. In some examples the bio-oil is also fed to the combustion chamber 4 and combusted with the pyrogas 18.

[0061] In an example the exhaust gas 22 from the combustion chamber 4 is brought into thermal contact with the pyrolysis reactor 2. In an example at the combustion chamber a temperature of 875°C is observed, and at the pyrolysis reactor 2 a temperature of 675°C is observed. In an example a pressure in the combustion chamber is maintained at 900 Pa (below ambient pressure).

[0062] Figure 2 shows an alternative system 100 for pyrolysis of biomass. Instead of combusting the pyrogas 18 in the combustion chamber 4 under addition of air 20, a gas 102 with a higher oxygen content than air is provided. In an example pure oxygen is used instead of air. In the system 10 for pyrolysis ambient air is used for the combustion of pyrogas; the ambient air contains nitrogen and other components alongside oxygen. In contrast, the alternative system 100 for pyrolysis utilizes oxygen rich gas or pure oxygen for the combustion process.Combustion with ambient air 20 in the system 10 introduces nitrogen into the system, leading to dilute flue gases, and the formation of nitrogen oxides (NOX). Nitrogen oxides are well known for their negative effect on the environment and on health, and it can be beneficial to reduce such unwanted emissions. The alternative system 100 can enable this and other benefits.

[0063] In an example the exhaust gas 22 from the combustion chamber 4 is brought into thermal contact with the pyrolysis reactor 2. In an example at the combustion chamber a temperature above 875°C is observed, and at the pyrolysis reactor 2 a temperature above 775°C is observed. In an example a pressure in the combustion chamber is maintained below 900 Pa (below ambient pressure).

[0064] Figure 3 shows a method 1200 for pyrolysis of biomass as can be implemented by the system 100 for pyrolysis of biomass. A biomass feedstock 8 is pyrolysed 500. The pyrolysis product 12 including gas and particles is processed and separated 600 to produce biochar 14, bio-oil 16 and pyrogas 18. The pyrogas 18 is combusted 700 with a gas with a higher oxygen content than air, in the illustrated example pure oxygen 105. The combustion 700 provides heat 106 to the pyrolysis step 500. The combustion 700 produces CO2 enriched exhaust gas 104. The CO2can be harvested and for instance sequestered or used as biogenic sourced CO2in industrial practices.

[0065] The combustion 700 may provide heat 106 to the pyrolysis step 500 by indirect heating of the pyrolysis step 500 by the exhaust gas 104 passing through an outer jacket of the pyrolysis reactor 2.

[0066] In an example, the exhaust gas 104 is 90% or more CO2 (by mole fraction). Because the exhaust gas 104 has such a high CO2 content it can provide an industrially useful CO2 source. Because the exhaust gas 104 has such a high CO2 content it can enable efficient CO2 capture and removal or storage. By harvesting the high CO2content exhaust gas 104 a high proportion of the carbon in the biomass can be captured, for instance 90% (by mole fraction) or more, in the forms of biochar 14 and exhaust gas 104. In some examples the exhaust gas is processed further for extraction and concentration of the CO2. The harvested CO2 can be upgraded and sold for offsetting non-biogenic CO2(reducing CO2used in industrial processes from having a carbon emission). The harvested CO2 can be sequestered in storage. This permits a higher proportion of the inbound biogenic carbon (from the biomass) to be utilised compared to a process where only the biochar is utilised.

[0067] The combustion of pyrogas with pure oxygen instead of air can result in an increase of thepyrolysis temperature. In an example combustion of pyrogas with air produces a temperature around 500°C, and combustion of pyrogas with pure oxygen produces a temperature above 750°C, for example in the range of 750°C to 1200°C or in the range of 750°C to 1000°C or around 800°C. For some applications a higher temperature for pyrolysis can be unsuitable, but for the envisaged pyrolysis of biomass it can be favourable.

[0068] For some low quality biomass feedstocks a higher pyrolysis temperature achieved with a pure oxygen combustion can be particularly beneficial. A low quality biomass feedstock generally has a lower carbon and hydrogen content than high quality biomass. Such a low quality biomass feedstock can create less pyrogas and poorer quality biochar at the same temperature, whereas at a higher temperature can mitigate these issues. The higher temperature may also create an enhanced bio-oil with additional use cases or lower cost refinement.

[0069] The use of pure oxygen can offer several advantages:

[0070] Enhanced Efficiency: combusting pyrogas with pure oxygen increases the combustion efficiency, resulting in a higher overall energy yield. This is because the absence of nitrogen allows for a more complete and controlled combustion process, thereby maximizing heat generation and minimizing energy loss.

[0071] Reduced Emissions: Using pure oxygen significantly reduces the production of nitrogen oxides (NOx), which are harmful pollutants commonly produced during the combustion of pyrogas with ambient air. The reduced emissions contribute to a cleaner, more environmentally friendly operation.

[0072] Improved Biochar Quality: The controlled combustion environment created by the use of pure oxygen ensures a consistent and high-quality biochar product. The absence of impurities and the optimal combustion conditions lead to a biochar with enhanced properties, including higher carbon content and improved structural stability.

[0073] Example 1

[0074] In example 1 , pyrogas 18 is fed to the combustion chamber 4 and combusted under addition of ambient air 20 (comprising approximately 21 % oxygen and 78% nitrogen by volume). The pyrogas 18 is a mixture of gases produced from pyrolysis of biomass. The mixture of gases comprises, for example: CO, CH4, C2H6 and C2H4 but it is of course understood that the combination could differ and the same principle applied to that of this illustrative example.A proportion of the combustion of the pyrogas combusted in ambient air may be combusted by incomplete combustion (for example, a proportion of the combustion of CH4, C2H6 and C2H4) and a proportion of the pyrogas may remain un-reacted (for example producing CO instead of CO2). This is illustrated in equations 1 - 3.

[0075] (1) 2CH4+ 3O22CO + 4H2O

[0076] (2) C2H6+ 2O2C + CO + 3H2O

[0077] (3) 2C2H4 + 3O22C+ 2CO + 4H2O

[0078] A proportion of the combustion may be complete as illustrated in equations 4 - 7.

[0079] (4) 2CO + O22 CO2

[0080] (5) CH4+ 2O2CO2+ 2H2O

[0081] (6) 2C2H6+ 7O24CO2+ 6H2O

[0082] (7) C2H4 + 3O22CO2+ 2H2O

[0083] Example 2

[0084] In example 2, pyrogas 18 is fed to the combustion chamber 4 and combusted under pure oxygen. Again, the pyrogas 18 is a mixture of gases produced from pyrolysis of biomass, for example: CO, CH4, C2H6 and C2H4. It is thought that a higher proportion of complete combustion can occur when combustion with pure oxygen takes place.

[0085] Example 3

[0086] In a third example, pyrogas 18 is fed to the combustion chamber 4 and combusted under oxygen enriched air. Again, the pyrogas 18 is a mixture of gases produced from pyrolysis of biomass, for example: CO, CH4, C2H6 and C2H4. It is thought that an intermediate proportion of complete combustion can occur compared with examples 1 and 2, dependent on the pressure, temperature and oxygen concentration.

[0087] The alternative system 100 for pyrolysis can include an oxygen supply system that is dedicated to supplying pure oxygen to the combustion chamber, ensuring a consistent and controlled flow. The oxygen supply system may be a cryogenic oxygen plant. Cryogenically produced oxygen is pure (typically at least 99.5% oxygen by mole fraction). The oxygen supply system may be driven by excess heat from the combustion.

[0088] The alternative system 100 for pyrolysis can include a feedstock hopper that can store the biomass feedstock and feed it into the pyrolysis reactor at a controlled rate.The alternative system 100 for pyrolysis can include a heat recovery system that can capture, store and distribute the heat generated during the combustion of pyrogas for further use, such as preheating the feedstock or generating electricity or for district heating or industrial uses otherwise. This can be useful for instance in case the combustion produces a heat at a higher temperature than is desired for pyrolysis (e.g. above 900°C), in which case a portion of the heat energy can be provided elsewhere than to the pyrolysis reactor.

[0089] The alternative system 100 for pyrolysis can include a generator to generate electricity from surplus heat energy produced by the combustion process.

[0090] The alternative system 100 for pyrolysis can include a biochar collection system to collect and store the produced biochar for further use or sale.

[0091] The alternative system 100 for pyrolysis can include an exhaust gas collection system for collecting exhaust gas from the combustion chamber. With the combustion of pure oxygen and pyrogas in the combustion chamber the exhaust from the combustion chamber may be mostly carbon dioxide and water vapour, with little NOx. In an example the exhaust is around 70-80% by mole fraction carbon dioxide. This exhaust can be more usefully captured and used as a relatively pure feedstock for other processes. Capture and use of the combustion chamber exhaust instead of release into the atmosphere can increase the proportion of carbon capture overall.

[0092] The biochar pyrolysis unit that uses pure oxygen for pyrogas combustion can represent a significant advancement in biomass conversion technology. By enhancing efficiency, reducing emissions, and improving biochar quality, the system 100 can offer a sustainable and environmentally friendly solution for biomass management and renewable energy production. As the demand for sustainable practices continues to grow, such innovative technologies will play a crucial role in addressing global environmental challenges.

[0093] Flow and pressure of the pure oxygen to the combustion chamber can be adapted to ensure the pyrogas is fully combusted and the temperature in the pyrolysis reactor is suitably maintained. For example, if pure oxygen is provided instead of air (air having only around 1 / 5thoxygen component), then the flow rate may be reduced to around 1 / 5thof the flow rate used with air combustion.

[0094] In some examples the system 100 and method 1200 for pyrolysis use a gas with a higher oxygen content than air but a lower oxygen content than pure oxygen. The enriched oxygen can increase the burn temperature making the overall system more efficient.In some examples the system 100 and method 1200 for pyrolysis use a gas with a higher oxygen content than air but a lower oxygen content than pure oxygen, with the gas having a lower N2content than air. The gas may be a mixture of pure oxygen and a CO2enriched gas. The CO2enriched gas can be an exhaust from the combustion chamber. Such a combustion can provide a CO2enriched exhaust gas 104 as described above, but avoid excessively hot temperatures in the combustion chamber. Such a variant can be beneficial for a feedstock that does not benefit from higher pyrolysis temperatures. Avoiding excessively hot temperatures in the combustion chamber can also enable a simpler system that does not include provisions to harvest excess heat energy. Avoiding excessively hot temperatures in the combustion chamber can also enable use of a simpler combustion chamber requiring less expensive materials and devices in the combustion chamber. In an example the pyrolysis is performed at a temperature in the region of 500°C to 750°C.

[0095] It will be understood that the invention has been described above purely by way of example, and modifications of detail can be made within the scope of the invention.

[0096] A wide variety of biomass feedstocks can be used, including wood chip, manure, sewage sludge, litter, grain waste, silage waste, hay, straw, fruit stones, shells, husks, compost, fabric waste, paper and cardboard. In a variant the feedstock is not a biomass but instead another carbon-rich material, whether synthetic or organic. For instance the feedstock may be a synthetic polymer. The feedstock may be used tyre material or spent rubber.

[0097] In a variant the heat energy released by the combustion is used to generate electricity, and the electricity is used to power a heater at the pyrolysis reactor (e.g. by inductive heating). This variant can suffer an efficiency penalty compared to direct heat transfer, but can permit excess energy from the combustion to be provided as electric energy for use elsewhere.

[0098] While the example described above refers to using pure oxygen in the combustion chamber, in a variant an oxygen rich gas is used with a higher oxygen content than air. Dry air (without a water vapour component) typically contains 21% oxygen by mole fraction and 78% nitrogen; or 23% oxygen by mass and 75.5% nitrogen; or 21% oxygen by volume and 78% nitrogen. In an example the oxygen rich gas comprises over 21% oxygen by mole fraction, preferably over 25% oxygen by mole fraction. In an example the oxygen rich gas comprises over 30% oxygen by mole fraction, preferably over 50% oxygen by mole fraction. In an example the oxygen rich gas comprises over 75% oxygen by mole fraction, preferably over 90% oxygen by mole fraction. For example a typical industrial grade compressed oxygen comprises at least 99.5% oxygen by mole fraction, and is considered pure in the context of the present discussion. In some examples the oxygen rich gas comprises less than 95% oxygen by molefraction, optionally less than 90% oxygen by mole fraction. In some examples the oxygen rich gas comprises less than 80% oxygen by mole fraction, optionally less than 60% oxygen by mole fraction. In some examples the oxygen rich gas comprises less than 50% oxygen by mole fraction, optionally less than 40% oxygen by mole fraction. In some examples a mixture of pure oxygen and air is used in the combustion chamber. In some examples a mixture of pure oxygen and a CO2enriched gas is used in the combustion chamber. In some examples a mixture of pure oxygen and an exhaust from the combustion chamber is used in the combustion chamber.

[0099]

[0100] A simulation of a pyrolysis plant with Grade A woodchip feedstock was modelled. A detailed steady-state process model was developed in Aspen Plus (RTM) process simulation software to represent a commercial PYREG P500 slow-pyrolysis unit. A commercial PYREG P500 slow-pyrolysis unit has a nominal fuel capacity or combustion rating of 500 kW; a representative maximum heat output of 200 kW (thermal energy); a representative maximal electricity consumption of 12 kW (electric energy); a representative annual throughput of 1100 t (dry substance; based on wood chips with 80 % dry substance and 19 MJ / kg dry substance, based on 7,000 operating hours); a representative annual biochar production of 3001 (based on wood chips with 80 % dry substance and 7,000 operating hours); and a representative size of 12 x 6 x 5 m. The model was developed to replicate major thermal and material flows within a real-world system, including biomass drying, conditioning, pyrolysis, Pyrogas combustion, and heat recovery. Pyrogas combustion may also be referred to as Pyro-syngas combustion.

[0101] The model assumes that the Grade A woodchip is pre-dried, so for the purpose of the model, the feedstock is assumed to have a moisture content, by mass, (M.C) of 10%.

[0102] Figure 4 shows a schematic of a system for pyrolysis. The system shown in Figure 4 is modelled in Aspen Plus (RTM). The system comprises a Pyrolysis reactor; a Combustion chamber; a Biochar Quenching Reactor; a Heat Offtake Unit and a Bagging and Storage Unit. The Biochar Quenching Reactor; Heat Offtake Unit; and Bagging Storage Unit are among components more generally referred to in Figure 2 as processing units 6. The pyrolysis reactor was modelled as an R-YIELD and R-GIBBS reactor operating at 650 °C, representing the decomposition of the biomass and formation of Pyrogas.

[0103] As discussed above in relation to Figure 2, the feedstock (in this case, Grade A woodchip) is heated in the pyrolysis reactor in oxygen-deprived conditions. The modelled resultingproducts were split into:

[0104] • Biochar, comprising fixed carbon, ash, and a small retained fraction of volatile matter (assumed at 8% for the model); and

[0105] • Volatile species, which were subsequently equilibrated in a Gibbs reactor to determine Pyrogas composition.

[0106] The Pyrogas was combusted in a dedicated combustion chamber, maintained at 1000 ° C to generate high-temperature flue gas. The flue gas was used to indirectly heat the pyrolysis reactor and then cooled to 180 °C in a heat exchanger, by heating a 5 barg water stream from 30 °C to 115 °C. A reference temperature of 15 °C was used consistently throughout the model for mass and energy balances, with explicit accounting for sensible and latent heat effects, including water vaporisation in the flue gas.

[0107] Figure 5 is a table outlining characteristics of the Grade A woodchip, which were used as a feedstock within the simulations. The ultimate and proximate analysis of the biomass was determined by standard methods. Figure 5 shows values from ultimate analysis (with sample preparation according to DIN 51701-3 (2006-09)) of: carbon (determined according to DIN 51732 (2014-07)); hydrogen (determined according to DIN 51732 (2014-07)); nitrogen (determined according to DIN 51732 (2014-07)); oxygen (determined according to DIN 51733 (2016-04)); sulphur (determined according to DIN 51724-3 (2012-07)); ash (determined according to DIN 51719 (1997-07)); and moisture as a percentage by weight (determined according to DIN 51718 (2002-06)). A Gross Calorific Value (GCV), dry basis (D.B), was calculated using the Boie formula in accordance with equation 8. A Gross Calorific Value of 19.26 MJ / kg was calculated for the biomass used in this model.

[0108] Equation 8: GCV (dry) [^] = 35.1600 + 116.225H + 10.465S + 6.280 / V - 11.0900

[0109] Where:

[0110] C =mass fraction of carbon

[0111] H = mass fraction of hydrogen

[0112] S = mass fraction of sulphur

[0113] N = mass fraction of nitrogen

[0114] O = mass fraction of oxygen

[0115] Figure 5 also shows values from proximate analysis of the biomass, namely fixed carbon (determined according to DIN 51734 (2008-12)); volatile matter (determined according to DIN51720 (2001-03)); and ash (determined according to DIN 51719 (1997-07)).

[0116] As touched on in the detailed description above, oxy-combustion, or oxygen enriched air combustion, in place of air for combustion, offers a potential route to improve the thermal and environmental performance of pyrolysis systems. By eliminating or reducing nitrogen from the oxidant, oxy-combustion produces a flue gas composed primarily of CO2and H2O, significantly reducing NOXemissions.

[0117] Simulations were run altering the combustion gas provided to the combustion chamber to investigate the application of pure oxy-combustion and oxygen enriched air combustion to a commercial-scale slow pyrolysis system, with particular focus on quantifying improvements in heat recovery and reductions in NOXemissions relative to conventional air-fired operation.

[0118] In all simulations, feedstock was provided to the pyrolysis reactor [100 kg / h; 10 % M.C; GCV 19.26 MJ / Kg D.B; 481 kW] and Pyrogas [75.2 kg / h; 650 °C; 16.97 MJ / Kg; 354 kW] was provided to the combustion chamber for combustion. In all simulations an air composition of 21 % oxygen, 79 % nitrogen by volume was used.

[0119] Simulation 1 - Mass and Energy Balance with Air Combustion

[0120] In a first simulation, air [367.8 kg / h; 15 °C] was provided to the combustion chamber for combustion of Pyrogas [75.2 kg / h; 650 °C; 16.97 MJ / Kg; 354 kW], The combustion of Pyrogas produced Flue gas [443.0 kg / h; 180 °C; 60.3 kW], The first simulation also produced Heat Offtake [181 kW] and Biochar [31.0 kg / h; 20 % M.C; 22.96 MJ / Kg; 158 kW] and Heat Loss [~80 kW], The specific Mass and Energy Balance for the first simulation is shown in Figure 6.

[0121] Simulation 2 - Mass and Energy Balance with 75 % Air, 25 % Pure Oxygen Combustion

[0122] In a second simulation, 75 % Air, 25 % Pure Oxygen by volume [187.7 kg / h; 15 °C] was provided to the combustion chamber for combustion of Pyrogas [75.2 kg / h; 650 °C; 16.97 MJ / Kg; 354 kW], The combustion of Pyrogas produced Flue gas [262.9 kg / h; 180 °C; 51.4 kW], The second simulation also produced Heat Offtake [190 kW]; Biochar [31.0 kg / h; 20 % M.C; 22.96 MJ / Kg; 158 kW] and Heat Loss [~80 kW], The specific Mass and Energy Balance for the second simulation is shown in Figure 7. The 75 % Air, 25 % Pure Oxygen by volume mixture corresponds to a mixture of 40.75 % oxygen and 59.25 % nitrogen by volume.Simulation 3 - Mass and Energy Balance with 50 % Air, 50 % Pure Oxygen Combustion

[0123] In a third simulation, 50 % Air, 50 % Pure Oxygen by volume [128.2 kg / h; 15 °C] was provided to the combustion chamber for combustion of Pyrogas [75.2 kg / h; 650 °C; 16.97 MJ / Kg; 354 kW], The combustion of Pyrogas produced Flue gas [203.4 kg / h; 180 °C; 48.5 kW], The third simulation also produced Heat Offtake [193 kW]; Biochar [31.0 kg / h; 20 % M.C; 22.96 MJ / Kg; 158 kW] and Heat Loss [~80 kW], The specific Mass and Energy Balance for the second simulation is shown in Figure 8. The 50 % Air, 50 % Pure Oxygen by volume mixture corresponds to a mixture of 60.5 % oxygen and 39.5 % nitrogen by volume.

[0124] Simulation 4 - Mass and Energy Balance with 100 % Pure Oxygen Combustion

[0125] In a fourth simulation, 100 % Pure Oxygen [80.5 kg / h; 15 °C] was provided to the combustion chamber for combustion of Pyrogas [75.2 kg / h; 650 °C; 16.97 MJ / Kg; 354 kW], The combustion of Pyrogas produced Flue gas [155.9 kg / h; 180 °C; 46.1 kW], The fourth simulation also produced Heat Offtake [195 kW]; Biochar [31.0 kg / h; 20 % M.C; 22.96 MJ / Kg; 158 kW] and Heat Loss [~80 kW], The specific Mass and Energy Balance for the fourth simulation is shown in Figure 9.

[0126] NOXemissions observed for Simulations 1 to 4

[0127] A substantial reduction in NOXemissions is observed when transitioning from air combustion (first simulation) to oxy-combustion (fourth simulation). In the first simulation, total NOXemissions are calculated to be 112.9 mg / Nm3(milligrams per normal cubic meter under a temperature of 15 °C and a pressure of 101.325 kPa), whereas the fourth simulation produces NOXemissions of 14.3 mg / Nm3, corresponding to an 87 % reduction in NOXconcentration from the first simulation to the fourth simulation.

[0128] On a mass flow basis, total NOXemissions decrease from 4.13 x 1O-2kg / h under air combustion to 1.75 x 1O-3kg / h under oxy-combustion. This reduction is primarily due to the elimination of nitrogen from the oxidant, which suppresses both thermal NOXand fuel-NOxformation mechanisms. The significantly lower NOXemissions demonstrate the strong environmental advantage of oxy-combustion, particularly in the context of tightening emissions regulations and low-impact plant operation. Figure 10 is a graph showing the effect of increasing oxygen concentration on NOXin Flue Emissions.Energy recovery results observed for Simulations 1 to 4

[0129] Furthermore, in the first simulation, the combustion of Pyrogas produces a flue gas flow rate of 442.97 kg / h, resulting in a recoverable heat offtake of 181 kW. In contrast, the fourth simulation produces a significantly lower flue gas mass flow of 155.92 kg / h, due to the removal of nitrogen from the oxidant stream. Despite this reduction in mass flow, the fourth simulation achieves a higher recoverable heat offtake of 195 kW. Figure 11 is a graph showing the effect of increasing oxygen concentration in oxidant on Energy Recovery Potential. Figure 12 is a table outlining flue gas emissions and energy recovery data as oxygen concentration is increased in combustion chamber oxidant. Figure 12 shows the mass fractions of NO and NO2 decrease as oxygen concentration is increased.

[0130] The modelling results from simulations 1 to 4 indicate that oxy-combustion may have the potential to improve both the thermal efficiency and environmental performance of commercial pyrolysis systems. A further advantage of oxy-combustion is production of a CO2-rich flue gas, which presents a clear opportunity for downstream carbon capture. In some examples, the system described with reference to Figure 2 may further comprise integration of CO capture technologies, such as condensation-based separation or post-combustion purification, to quantify the potential increase in overall CO2capture efficiency for the process. Beneficially, this may further enhance the carbon-negative performance of the system by complementing biochar sequestration with direct capture of process CO2 emissions. It is observed that even a 75 % air, 25 % pure oxygen by volume mixture (40.75 % oxygen and 59.25 % nitrogen by volume in the resulting gas; simulation 2) can compare favourably to combustion using air (simulation 1), with increasing benefits with increasing oxygen proportions (simulations 3 and 4).

[0131] Each feature disclosed in the description, and (where appropriate) the claims and drawings may be provided independently or in any appropriate combination. Reference numerals appearing in the claims are by way of illustration only and shall have no limiting effect on the scope of the claims.

Claims

Claims1. A method comprising:receiving a pyrogas;receiving an oxygen rich gas; andcombusting the received pyrogas with the oxygen rich gas.

2. The method of claim 1 performed in a combustion chamber, the combustion chamber comprising an exhaust.

3. The method of claim 2 further comprising collecting exhaust gas at the exhaust for downstream use.

4. The method of claim 2 or 3 wherein the pyrogas is from pyrolysis in a pyrolysis reactor heated by the combustion chamber.

5. The method of any preceding claim wherein the pyrogas is from pyrolysis of a biomass.

6. The method of any preceding claim wherein the combustion temperature is above 700°C, optionally above 800°C or above 900°C.

7. The method of any preceding claim wherein the oxygen rich gas has a higher oxygen content than air, preferably wherein the oxygen rich gas has more than 40% oxygen by volume or by mole fraction.

8. The method of any preceding claim wherein the oxygen rich gas is pure oxygen.

9. The method of any preceding claim further comprising recovering energy from excess heat produced by the method.

10. The method of any preceding claim further comprising capturing an exhaust gas produced by the method.

11. The method of claim 10, wherein the exhaust gas comprises 50% or more CO2 by mole fraction, optionally 70% or more CO2or 85% or more CO2.

12. The method of claim 10 or 11 , further comprising recycling the exhaust gas to provide a component of the oxygen rich gas, optionally with pure oxygen being a furthercomponent of the oxygen rich gas.

13. The method of any preceding claim, wherein the combusting the pyrogas with the oxygen rich gas generates a flue gas comprising NOXbelow 100 mg / Nm3, preferably between 14 to 90 mg / Nm3.

14. The method of any preceding claim, wherein the oxygen rich gas is between 90% and 100% oxygen by volume and optionally wherein the oxygen rich gas is provided to the combustion chamber at between 70 and 90 kg / h.

15. A pyrolysis method comprising decomposing a biomass with heat provided by the method of any of claims 1 to 14, wherein decomposing the biomass comprises decomposing, in a pyrolysis reactor, the biomass and thereby producing the pyrogas.

16. A method, optionally according to any of claims 1 to 14, the method comprising:decomposing, in a pyrolysis reactor, a biomass feedstock to produce a biochar and a pyrogas;receiving, by a combustion chamber, the pyrogas and an oxygen rich gas; combusting, in the combustion chamber, the pyrogas with the oxygen rich gas; and heating the pyrolysis reactor by the combustion chamber.

17. A pyrolysis system comprising a pyrolysis reactor heated by a combustion chamber; a conduit arranged to provide a pyrogas produced in the pyrolysis reactor to the combustion chamber for combustion; and an oxygen rich gas source arranged to provide oxygen rich gas to the combustion chamber for combustion.

18. The pyrolysis system of claim 17 adapted for the method according to any of claims 1 to 16.

19. The pyrolysis system of claim 17 or 18 with the combustion chamber comprising an exhaust, the pyrolysis system further comprising an exhaust gas store for collecting exhaust gas at the exhaust for downstream use.

20. The pyrolysis system of any of claims 17 to 19 further comprising a feedstock supply unit arranged to store a feedstock and / or supply feedstock to the pyrolysis reactor, preferably at a controlled rate.

21. The pyrolysis system of any of claims 17 to 20 adapted for pyrolysis of a biomass.

22. The pyrolysis system of any of claims 17 to 21, wherein the combustion chamber is adapted for a combustion temperature above 700°C, optionally above 800°C or above 900°C.

23. The pyrolysis system of any of claims 17 to 22 wherein the oxygen rich gas has a higher oxygen content than air, optionally wherein the oxygen rich gas has more than 40% oxygen by volume or by mole fraction, preferably wherein the oxygen rich gas is pure oxygen.

24. The pyrolysis system of any of claims 17 to 23 further comprising a heat energy recovery system arranged to store and / or distribute excess heat energy produced at the combustion chamber.

25. The pyrolysis system of any of claims 17 to 24, further comprising a CO2 capture unit.

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