GB2621637A

GB2621637A - Method and system for processing waste material

Info

Publication number: GB2621637A
Application number: GB2212142.0A
Authority: GB
Inventors: Meyer James
Original assignee: Getgo Recycling Ltd
Current assignee: Getgo Recycling Ltd
Priority date: 2022-08-19
Filing date: 2022-08-19
Publication date: 2024-02-21
Anticipated expiration: 2042-08-19
Also published as: GB202212142D0; GB2621637B; WO2024038208A1

Abstract

A method for processing human and/or animal digestive waste and/or plant derived waste that has undergone a process of anaerobic and/or aerobic digestion, is provided. The method comprises: receiving an input of waste material into a reactor pressure vessel, wherein the waste material comprises biomass and water; heating and pressuring the reactor pressure vessel to perform a hydrothermal carbonization process of the biomass; separating at least a portion of the liquid from solid components of the products produced through the hydrothermal carbonization process; performing a gasification process on the solid components, to produce syngas. A system for performing the method is also provided.

Description

Method and system for processing waste material

Technical Field

The present disclosure relates to a method and system for processing waste material comprising human and/or animal digestive waste and/or plant derived waste that has gone through anaerobic and/or aerobic digestion.

Background

Human digestive waste is typically treated through processes of anaerobic, and optionally aerobic, digestion, to produce digestate sludge and biogas. The digestate sludge typically comprises at least 80% water and biomass containing solids.

The digestate sludge may then be treated to destroy any pathogens present in the sludge and to reduce the weight and/or volume of the sludge, in order to reduce transportation and disposal costs. In particular, water may be removed from the sludge, e.g. through centrifugation, filtration; and/or evaporation processes Gasification is a process used to convert fuels, such as biomass fuels, to synthesised gas (syngas), which can in turn be used to produce energy, e.g. via a gas generator. Syngas typically comprises nitrogen, carbon monoxide, hydrogen, carbon dioxide, and may be generated as a mixture with hydrocarbons, e.g. volatile hydrocarbons. However, it is undesirable for syngas to contain high concentrations of nitrogen. The biomass in digestate sludge is therefore considered unsuitable for use in gasification processes to produce syngas, due to its high nitrogen content in the form of urea, ammonia and/or other nitrogen containing compounds.

Statements of Invention

According to an aspect of the present disclosure, there is provided a method of processing waste material, wherein the waste material comprises human and/or animal digestive waste and/or plant derived waste that has undergone a process of anaerobic and/or aerobic digestion. The method comprises: receiving an input of waste material into a reactor pressure vessel, wherein the waste material comprises biomass and water; heating and pressurising the reactor pressure vessel to perform a hydrothermal carbonization, or aqueous carbonization, process, of the biomass; separating at least a portion of a liquid from solid components of the products produced through the hydrothermal carbonization process; performing a gasification process on the solid components, e.g. remaining solid components, to produce syngas, and optionally hydrocarbons, e.g. volatile hydrocarbons.

The waste material may comprise a digestate sludge, e.g. produced through anaerobic and/or aerobic digestion of human and/or animal digestive waste and/or plant derived waste. The digestate sludge may be treated with a flocculant or coagulant.

The reactor pressure vessel may be heated to a reaction temperature greater than 180 degrees Celsius, for example 200 degrees Celsius, to perform the hydrothermal carbonization process. The reactor pressure vessel may be maintained at the reaction temperature for approximately 4 hours. Reaction temperature and pressure of the reactants within the reactor pressure vessel may be maintained to achieve subcritical conditions for water within the reactor pressure vessel, e.g. so that the water behaves a subcritical fluid. The reaction temperature and pressure of the reactants within the reactor pressure vessel maybe configured to reduce a dielectric constant of water within the reactor pressure vessel to less than 40, such as between 20 and 30, e.g. between 20 and 25.

The hydrothermal carbonization process may be performed as a continuous series of batch operation process, performed using a plurality of the reactor pressure vessels configured to receive the waste material sequentially and perform the hydrothermal carbonization process at time periods offset from one another by less than a total duration of the hydrothermal carbonization process.

The method may further comprise discharging the products of the hydrothermal carbonization process to an expansion vessel at a lower pressure than the reactor pressure vessel. For example, prior to the step of separating the liquid from the solid components.

The method may comprise circulating gases from the expansion vessel through a gas heat exchanger configured to transfer heat from the expansion vessel gases to the input waste material, e.g. prior to the waste material being received in the reactor pressure vessel. Additionally or alternatively, the method may comprise circulating the separated liquid through a liquid heat exchanger configured to transfer heat from the separated liquid to the input waste material, e.g. prior to the waste material being received in the reactor pressure vessel. The gas heat exchanger may be arranged downstream of the liquid heat exchanger, relative to the passage of the input waste material to the reactor pressure vessel.

The liquid may be separated from the solid components through a physical separation process. For example, the liquid may be separated from the solid components using a filter press or a solids/liquids centrifuge. The separated liquid may be output as liquid fertiliser and stored separately.

The method may further comprise combusting the syngas, and optionally hydrocarbon gases, e.g. volatile hydrocarbons. produced though the gasification process in a gas generator to generate electricity. The electricity generated by the gas generators may be used to power a heater for the reactor pressure vessel, e.g. during steady state performance of the method. The method may comprise providing electricity from a source separate from the gas generator to heat the reactor pressure vessel during a start-up procedure. Optionally, the electricity generated by the gas generators may be used to power other electrical equipment at a plant in which the method is performed.

The method may further comprise delivering a portion of the produced syngas as an input to the gasification process. The portion of the produced syngas may be combusted in order to heat the reactants of the gasification process. The method may further comprise providing combustible gas from a source separate from the gasification reactor, such as natural gas, as an input to the gasification process, e.g. during a start-up procedure of the method of processing waste material. The combustible gas may be combusted in order to heat the reactants of the gasification process during the start-up procedure for the method of processing waste material. The combustible gas may no longer provided as an input to the gasification process once the syngas is available to be combusted for heating the reactants.

The method may further comprise circulating the combustion gases resulting from the combustion for heating the reactants of the gasification process to the heat the input 35 waste material upstream and/or within the reactor pressure vessel. The method may further comprise cleaning the syngas produced through the gasification process prior to the syngas being used for other purposed as part of the method of processing waste, in order to remove contaminants from the syngas.

The method may further comprise recirculating at least a portion of the contaminants removed from the syngas as an input to the gasification process.

According to another aspect of the present disclosure, a system for processing waste material, wherein the waste material comprises human and/or animal digestive waste and/or plant derived waste that has undergone a process of anaerobic and/or aerobic digestion. The system comprises: a reactor pressure vessel assembly comprising one or more reactor pressure vessels for receiving an input of waste material and heating and pressurising the waste material within the vessels to perform a hydrothermal carbonization process of the waste material; a separating unit, for separating liquid from solid components produced though the hydrothermal carbonization process; a gasification reactor vessel for receiving the solid components and performing a gasification process on the separated solids within the gasification reactor vessel to produce syngas.

The reactor pressure vessel assembly may further comprise one or more expansion vessels for receiving the products of the hydrothermal carbonization process from the one or more reactor pressure vessels at a lower pressure than the reactor pressure vessels.

The system may further comprise a gas heat exchanger configured to receive gases from the one or more expansion vessels and transfer heat from the gases to the input waste material. The system may further comprise a liquid heat exchanger, configured to receive the liquid separated by the separating unit and transfer heat from the liquid to the input waste material. The gas heat exchanger may be arranged downstream of the liquid heat exchanger, relative to the passage of the input waste material to the reactor pressure vessel assembly, e.g. through the heat exchangers.

The system may further comprise a gas generator for using the syngas produced by the gasification reactor to produce electricity. The reactor pressure vessel assembly may comprise one or more electric heaters, for heating the reactants within the reactor pressure vessels. The electric heaters may be electrically connected to the gas generator.

The system may further comprise a syngas cleaning unit for removing contaminants from the syngas produced in the gasification reactor vessel. The syngas cleaning unit may be provided between the gasification reactor vessel and the gas generator relative to the flow of syngas. The syngas cleaning unit may comprise a wetted wall scrubber.

The wetted wall scrubber may comprise a plurality of spray nozzles for spraying water in order to increasing the contact surface area between the syngas and the water. The syngas cleaning unit may further comprise one or more baffles configured to promote turbulent flow of the gas passing through the cleaning unit. The system may further comprise a contaminant recirculation duct for recirculating at least a portion of the contaminants, such as tar, removed from the syngas to the gasification reactor.

The gasification reactor may comprise one or more burners for burning a gas to heat reactants in the gasification process. The system may comprise a syngas supply duct, for supplying syngas output by the gasification reactor to the one or more burners, e.g. from downstream of the syngas cleaning unit.

The reactor pressure vessel assembly may comprise a plurality of reactor pressure vessels and one or more expansion vessels. The reactor pressure vessels may be configured to store reactants and products at a higher pressure than the expansion vessels, The expansion vessels may be configured to receive products of the reaction within the respective reactor pressure vessels.

The reactor pressure vessel assembly may be configured to operate in a continuous series of batch procedures in which reactants are input to the plurality of reactor pressure vessels sequentially. Products of the reactions within the reactor pressure vessels may be output to expansion vessels sequentially. The hydrothermal carbonization procedure may be conducted over staggered time periods within the sequential reactor pressure vessels.

The reactor pressure vessel assembly may further comprise one or more ducts for conducting gases from the expansion vessels to one or more heat exchangers for heating reactants input to respective ones of the reactor pressure vessels. The ducts may be arranged so that that gases from the expansion vessels are conducted to the heat exchanger configured to heat the reactant within the next of the reactor pressure vessels to receive reactants in the continuous series of batch procedures.

The system may comprise a combustion gas duct, for conducting combustion gases from the gasification reactor to the reactor pressure vessel assembly. The system may further comprise one or more combustion gas heat exchangers for transferring heat from the combustion gases to the waste material input to the reactor pressure vessel assembly.

According to another aspect of the present disclosure, there is provided a reactor pressure vessel assembly comprising a plurality of reactor pressure vessels and one or more, e.g. a single or a corresponding number of, expansion vessels, wherein the reactor pressure vessels are configured to store reactants and products at a higher pressure than the expansion vessels, optionally wherein each of the expansion vessels is associated with a different one of the reactor pressure vessels, wherein the expansion vessels are configured to receive products of the reaction within the reactor pressure vessels, e.g. respect reactor pressure vessel.

The reactor pressure vessel assembly may further comprise one or more ducts for conducting gases from the expansion vessels to one or more heat exchangers for heating reactants being input to or within respective ones of the reactor pressure 20 vessels The reactor pressure vessel assembly may be configured to operate in a continuous series of batch procedure in which reactants are input to the plurality of reactor pressure vessels sequentially, products of the reactions within the reactor pressure vessels are output to the expansion vessels sequentially, and the hydrothermal carbonization procedure is conducted over staggered time periods within the sequential reactor pressure vessels.

The ducts may be arranged so that that gases from the expansion vessels are conducted to the heat exchanger configured to heat the reactant within the next of the reactor pressure vessels to receive reactants in the continuous series of batch procedures.

Each of the reactor pressure vessels may be associated with a heater for heating the reactants within the reactor pressure vessel. Each of the reactor pressure vessels may be associated with a heat exchanger for receiving combustion gases and transferring heat from combustion gases to the reactants within the corresponding reactor pressure vessel.

To avoid unnecessary duplication of effort and repetition of text in the specification, certain features are described in relation to only one or several aspects or embodiments of the invention. However, it is to be understood that, where it is technically possible, features described in relation to any aspect or embodiment of the invention may also be used with any other aspect or embodiment of the invention. For example, features described in relation to the first mentioned aspect may be combined with the features of the second mentioned aspect.

Brief Description of the Drawings

For a better understanding of the present invention, and to show more clearly how it may be carried into effect, reference will now be made, by way of example, to the accompanying drawings, in which: Figure 1 is a schematic diagram of a system for processing a waste material comprising human and/or animal digestive waste and/or plant derived waste that has gone through anaerobic and/or aerobic digestion, according to an arrangement of the present invention; and Figure 2 is a flow diagram depicting a method for processing a waste material comprising human and/or animal digestive waste and/or plant derived waste that has gone through anaerobic and/or aerobic digestion, according to an arrangement of the present invention.

Detailed Description

With reference to Figure 1, a system 2 for processing waste material comprising human and/or animal digestive waste and/or plant derived waste that has gone through anaerobic and/or aerobic digestion, will now be described. The system comprises a reactor pressure vessel assembly 10, comprising one or more reactor pressure vessels 12. The system 2 further comprises a separating unit 20 and a gasification reactor assembly 30.

The reactor pressure vessel assembly 10 comprises an input for receiving digestate sludge. For example, digestate sludge comprising the metabolites of aerobic or anaerobic digestion of human, animal, and/or plant waste. It may also comprise both dead and live bacteria. The sludge provided at the input may be produced through a sludge concentration process, in which a water concentration of the sludge has been brought, e.g. reduced, to approximately 80%. Accordingly, the sludge input to the reactor pressure vessel assembly 10 may comprise approximately 20% solids, e.g. biomass containing solids, and approximately 80% liquid, e.g. water. In some arrangements, the digestate sludge may be treated with a flocculant or coagulant. The digestate sludge input the reactor pressure vessel assembly 10 may be received within one or more of the one or more reactor pressure vessels 12.

The reactor pressure vessel assembly 10, may be configured to heat and pressurise the sludge within the reactor pressure vessels 12 in order to perform a hydrothermal carbonization process, which may also be referred to as an aqueous carbonization process, of the sludge. During the hydrothermal carbonization process, the solid, e.g. biomass containing, components of the sludge may be converted into carbon containing molecules more suitable for use as reactants, e.g. suitable to be pyrolyzed, in a gasification process, as described below. More particularly, to perform the hydrothermal carbonization process, the sludge may be heated to a reaction temperature greater than 170 degrees Celsius or greater than 180 degrees Celsius, such as approximately 200 degrees Celsius, and may reach a reaction pressure of greater than 1.5MPa, or greater than or equal to 2MPa, such as between 2 and 2.5 MPa. The sludge may be maintained at the reaction temperature and pressure for longer than 3 hours, such as approximately 4 hours, or longer than 4 hours.

The reactor pressure vessel assembly 10 may comprise a plurality of reactor pressure vessels 12. In the arrangement depicted in Figure 1, the reactor pressure vessel assembly 10 comprises four reactor pressure vessels 12. The reactor pressure vessel assembly 10 may be configured to perform the hydrothermal carbonization process of the sludge in a series of batch operating modes resembling that of a continuous process. For example, processing, e.g. heating and pressurising, of the sludge within each of the reactor pressure vessels may be staggered by a period of time less than the total duration for which the sludge is process in the reactor pressure vessels. For example, when the sludge is processed, e.g. maintained at the reaction temperature and pressure, for approximately 4 hours, and the reactor pressure vessel assembly comprises 4 reactor pressure vessels, heating of the sludge within each of the pressure vessels may begin approximately 1 hour after heating of the sludge within a another of the pressure vessels began.

During a start-up procedure of the system, each of the reactor pressure vessels 12 may be filled with the input sludge. However, it will be appreciated that due to the staggered initiation of the process in each reactor pressure vessel, the completion time of the process in each of the reactor pressure vessels 12 will be staggered and filling of the reactor pressure vessels for future batches, e.g. during steady state operation of the system, can also be staggered, e.g. so that the reactor pressure vessels are filled sequentially.

The reactor pressure vessel assembly 10 may comprise a one or more heaters 11 for heating the waste material within the reactor pressure vessels, e.g. the reactants of the hydrothermal carbonization process. For example, the reactor pressure vessel assembly 10 may comprise a heater 11 associated with each respective reactor pressure vessel 12. The heaters may be electrical heaters. During the start-up procedure of the system 2, electrical power may be supplied to one or more of the heaters from an electrical source external to the system, such as an electrical supply grid, in order to heat the reactor pressure vessels 12 to the reaction temperature.

However, as described below, during steady state operation of the system 2, electrical power may be generated within the system 2 for powering the one or more heaters 11.

At the reaction temperature and pressure, a dielectric coefficient of the water within the sludge may be reduced to less than 40 or less than 30, such as between 20 and 30 or between 20 and 25. Accordingly, a solubility/miscibility of macronutrient substances, such as nitrogen and/or nitrogen containing compounds in the water may be increased compared to at atmospheric temperatures and pressures. Further, the hydrothermal carbonization process may lead to nitrogen and/or nitrogen containing components being released from the solid components of the sludge. Accordingly, the conditions of the hydrothermal carbonization process may lead to nitrogen and nitrogen containing compounds, such as ammonia, within the sludge being dissolved in the water, optionally after having been released from the solids.

In some arrangements, a reactive, e.g. nucleophilic substance, such as calcium oxide, may be added to the reactor pressure vessel during the hydrothermal carbonization process, in order to promote the release of ammonia from the sludge. The released ammonia may then become dissolved within the water.

In addition to facilitating nitrogen and nitrogen containing compounds being dissolved in the water and optionally release from the solids of the sludge, the carbonization reaction conditions may similarly lead to the release of other organic and/or inorganic substances, e.g. macronutrient substances, such as phosphorous, potassium (and phosphorous and potation containing compounds) from the solids and/or the dissolving of such substances in the water.

The reactor pressure vessel assembly 10 may comprise one or more expander vessels 14. The products from the hydrothermal carbonization process may be output from the reactor pressure vessels 12 into the one or more expander vessels 14 at a lower pressure than within the reactor pressure vessels. For example, the pressure within the expander vessels may be approximately atmospheric. The reduction in pressure, e.g. rapid reduction in pressure, of the hydrothermal carbonization products within the one or more expander vessels may lead to rupturing of the structure of the solid components of the products, which may in turn release further amounts of nitrogen, phosphorous, potassium (and nitrogen, phosphorous and potassium containing compounds) and organic substances from the solids, e.g. into the liquid and/or gaseous phase of the products. Additionally, discharging the products of the hydrothermal carbonization process into the expansion vessels 14 may cause any bacteria, e.g. pathogenic bacteria, present in the products to rupture. The products of the hydrothermal carbonization process within the expansion vessel may therefore be sterile.

In the arrangement shown in Figure 1, the reactor pressure vessel assembly 10 comprises a single expansion vessel 14 configured to receive the hydrothermal carbonization products from each of the reactor pressure vessels 12. However, in other arrangements, any other number of expansion vessels 14 may be provided. For example, a number of expansion vessels 14 may be provided corresponding to a number of reactor pressure vessels 12. In such arrangements, the expansion vessels may be associated with, e.g. configured to receive the products from, one or more, e.g. respective ones of the reactor pressure vessels 12.

The system 2 may further comprise a gas heat exchanger 4. The gas heat exchanger 4 may be configured to receive gases from the expansion vessels 14 and transfer heat from the gases to the waste material to be input to the reactor pressure vessel assembly 10. The system 2 may comprise one or more ducts 16 for conducting gases, such as water vapour, from the expansion vessels 14 to the gas heat exchanger 4.

The separation unit 20 may be provided downstream of the reactor pressure vessel assembly 10. The separation unit 20 may be arranged to receive the products of the hydrothermal carbonization process. For example, the separation unit 20 may arranged to receive the products of the hydrothermal carbonization process from the reactor pressure vessels 12 or the expansion vessels 14 Of present).

The separation unit 20 may be configured to separate at least a portion of the liquid present in the products of the hydrothermal carbonization process from the solid components. For example, the separation unit 20 may be configured to separate at least a portion of the water present in the products together with any substances dissolved in the water.

The separation unit 20 may be configured to separate the liquid from the solid components through a physical separation process, such as a physical dewatering process. For example, the separation unit 20 may comprise a filter press. Alternatively, the separation unit 20 may comprise any other device suitable for separating at least a portion of the liquid, e.g. water, present in the hydrothermal carbonization products from the solid components, such as a solids/liquids centrifuge.

The system 2 may comprise a liquid heat exchanger 6. The liquid heat exchanger 6 may be configured to receive the liquid separated by the separation unit and transfer heat from the liquid to the waste material to be input to the reactor pressure vessel assembly 10. The liquid heat exchanger 6 may be arranged upstream of the heat exchanger 4 relative to the flow of wate material through the heat exchanger 4 and the liquid heat exchanger 6. In some arrangements, the system 2 may comprise a buffer tank 7, which may be heat insulated. The buffer tank 7 may be configured to store the liquid separated by the separation unit 20 until required to heat the waste material being input to the reactor pressure vessel, e.g. when a next batch of sludge is input to one or more of the reactor pressure vessels 12. The system 2 may further comprise a pump 8 for pumping the liquid from the separator unit 20 and/or buffer tank 7 to the liquid heat exchanger 6.

The system 2 may further comprise one or more liquid ducts 18, for carrying the liquid separated by the separation unit 20 to the liquid heat exchanger, e.g. via the buffer tank 7 and/or pump 8.

As described above, one or more substances, e.g. macronutrient substances, such as nitrogen, potassium, phosphorus, nitrogen containing compounds, potassium containing compounds, phosphorus containing compounds, and organic compounds, e.g. soluble organic compounds, may be dissolved or mixed with the liquid products of the hydrothermal carbonization process. Such substances may be undesirable to include as reactants in a gasification process for producing syngas, as described below. Hence, by separating at least a portion of the liquid from the solid components of the hydrothermal carbonization products, the concentration of such substances may be reduced in the solid phase products.

The liquid separated from the products of the hydrothermal carbonization process may be stored for use in another method. For example, the stored liquid may be used in a process for producing a fertiliser.

The gasification reactor assembly 30 comprises a gasification reactor vessel 32 arranged to receive the solid components separated from the products of the hydrothermal carbonization process and remaining liquid that was not separated. The gasification reactor assembly 30 is configured to perform a gasification, e.g. pyrolysis, process on the solid components within the gasification reactor to produce syngas and hydrocarbons, e.g. volatile hydrocarbon carbons. In other words, the gasification process may produce a mixture of syngas and hydrocarbons, e.g. volatile hydrocarbons. The solid components separated from the products of the carbonisation process and remaining water may form the reactants for the gasification process within the gasification reactor.

During the gasification process, the water present in the reactants may be superheated to steam and may react with carbon containing substances within the solid components. More particularly, the water may react with solid carbon to produce hydrogen and carbon monoxide in a water gas reaction, the water may react with carbon monoxide to form hydrogen and carbon dioxide in a water gas shift reaction and the water may react with hydrocarbons to produce carbon monoxide and hydrogen in a steam reformation reaction.

The gasification reactor assembly 30 may comprise an indirectly heated rotary kiln.

Alternatively, the gasification reactor assembly may comprise a fixed bed gasifier. Alternatively again, the gasification reactor assembly may comprise any other suitable gasifier.

The gasification reactor assembly 30 may comprise one or more burners 34 configured to heat the reactants, e.g. to produce the superheated steam. The burners may be multi-fuel burners, which may be configured to operate using natural gas, e.g. methane, or syngas (or a mixture of syngas and hydrocarbons, e.g. volatile hydrocarbons). The gasification reactor assembly 30 may comprise a combustion air inlet 36 for oxygen or air, e.g. atmospheric air, to be supplied to the burner 34.

During a start-up procedure of the system 2, natural gas may be supplied from a source external to the system 2, e.g. from the grid, to be burned by the burners of the gasification reactor assembly to heat the reactants. However, during steady state operation of the system 2, syngas produced through the gasification process may be supplied the burner, as described below, and may be used to heat the reactants within the gasification reactor vessel.

In addition to syngas, a product of the gasification process may be biochar, which may be removed from the system 2. Due to the nature of the gasification process, the biochar may be free from microplasfics and/or antibiotics. In some arrangements, the biochar may be mixed with the liquid separated from the products of the hydrothermal carbonization process.

The system 2 may further comprise a syngas cleaning unit 40. The syngas cleaning unit 40 may be arranged downstream, e.g. immediately downstream, of the gasification reactor assembly 30 relative to the flow of syngas from the gasification reactor assembly, in order to receive the syngas produce through the gasification reaction.

The syngas cleaning unit 40 may be configured to remove contaminants from the syngas produced by the gasification reactor assembly 30. In particularly, the syngas cleaning unit may be configured to remove hydrogen chloride, hydrogen sulphide and tar. The syngas cleaning unit 40 may comprise a wetted wall scrubber. The syngas cleaning using may comprise a plurality of spray nozzles to increase the contact surface area between the syngas and the circulated water in order to improve the rate of contaminant removal. Additionally or alternative, the syngas clearing unit may comprise any other devices suitable for removing one or more contaminants from the syngas, such as baffles to promote turbulent gas flow.

The system may further comprise a condenser 46, for condensing water vapour from the syngas produced by the gasification reactor assembly. As depicted, the condenser 46 may be provided downstream of the syngas cleaning unit 40, relative to the flow of syngas. Water condensed from the syngas by the condenser 46 may be combined with the contaminants removed from the syngas by the syngas cleaning unit 40.

The system 2 may comprise a syngas supply duct 42 for supplying syngas to the burner of the gasification reactor assembly. The syngas supply duct 42 may extend from a position downstream of the syngas cleaning unit 40, and optionally downstream of the condenser 46, relative to the flow of syngas, to the burner 34. As described above, during steady state operation of the system 2, the cleaned syngas may be burned by the burner 34 in the gasification rector assembly 30 in order to heat the reactants for the gasification process. In this way, fuel for the burner may not be required from a source external to the system when the system 2 is operating in a steady state.

The system 2 may comprise a combustion gas recirculation duct 38 configured to recirculate the products of combustion of the natural gas or syngas at the burner 34 to a combustion gas heat exchanger 19 provided on the reactor pressure vessel assembly. The combustion gas heat exchanger 19 may be configured to transfer heat from the combustion gases to the reactor pressure vessels 12. After passing through the combustion gas heat exchanger, the combustion gases may be exhausted from the system.

The system 2 may further comprise a contaminant recirculation duct (not shown) for recirculating at least a portion of the contaminants, such as tar, that have been removed from the syngas in the syngas cleaning unit 40 to the gasification reactor vessel 32 as reactants for the gasification process. Alternatively, the contaminants may be removed from the system.

The system 2 may further comprise an electrical generator 50. The electrical generator may be configured to receive the syngas produced by the gasification reactor assembly 30, e.g. after being cleaned by the syngas cleaning unit 40 and optionally after passing through the condenser 46, and burn the syngas to produce electricity. The electrical generator may be any suitable generator. For example, the electrical generator may comprise a gas turbine for burning the syngas to drive the generator.

The electrical generator 50 may be electrically connected to the reactor pressure vessel assembly 10, e.g. to the heaters 11 of the reactor pressure vessel assembly 10. During steady state operation of the system, electrical power from the electrical generator 50 may be used to heat the reactants within the reactor pressure vessels 12 to perform the hydrothermal carbonization process of the waste material. In some arrangements, the electricity generated by the gas generators may be used to power other electrical equipment at a plant in which the system 2 is provided.

In some arrangements, an electrical power generated by the electrical generator 50 by consuming, e.g. burning, the syngas produced by the gasification reactor assembly may be greater than an electrical power required for heating the reactor pressure vessels 12 to perform the hydrothermal carbonization process of the waste material. In such arrangements, electrical power may be supplied to an electrical system outside the system 2, e.g. an electrical grid or electrical energy storage system, such as a battery system. Accordingly, the system 2 may comprise an electrical terminal 52 for electrically connecting the electrical generator 50 to an external electrical system.

As described above, during steady state operation of the system, the energy input requirements of the hydrothermal carbonization procedure and the gasification procedure may be met by combusting the syngas (or mixture of syngas and hydrocarbons, e.g. volatile hydrocarbons) produced by the system. Accordingly, the system 2 may not require energy from an external source to continue operating in a steady stage and may output energy as excess syngas and/or as electricity via the terminal 52 during steady state operation.

With reference to Figure 2, a method 200 of processing waste material will now be described. The method may be performed using the system 2 described above. One or more of the steps of the method 200 may be performed sequentially, e.g. during a start-up procedure of the system 2. Alternatively, the steps of the method 300 may be performed substantially simultaneously and continuously, e.g. in a continuous series of batches, during steady state performance of the method 200.

The method comprises a first step 202, in which an input of waste material is received into a reactor pressure vessel, e.g. of the reactor pressure vessel assembly 10. The waste material comprises biomass and water. For example, the waste material may comprise digestate sludge. In a first example, approximately 4167 kg of sludge is input to the reactor pressure vessel assembly per hour. In the first example, the sludge comprises 20% solids.

The method further comprises a second step 204, in which the reactor pressure vessel is heated to perform a hydrothermal carbonization process, e.g. a hydrothermal carbonization process, of the biomass. In particular, the reactor pressure vessel may be heated to a reaction temperature greater than 170 degrees Celsius or greater than 180 degrees Celsius, such as approximately 200 degrees Celsius, and may reach a reaction pressure of greater than 1.5MPa, or greater than or equal to 2MPa, such as between 2 and 2.5 MPa. The waste material may be maintained at the reaction temperature and pressure for longer than 3 hours, such as approximately 4 hours, or longer than 4 hours.

The hydrothermal carbonization process may be performed as a continuous series of batch operation process, performed using a plurality of the reactor pressure vessels configured to receive the waste material sequentially.

In the first example, 2778 kg of hydrothermal carbonization products are output from the reactor pressure vessel assembly per hour. The hydrothermal carbonization products comprise may comprise 20% or more solids, such as 30% solids. In the first example, the hydrothermal carbonization products leave the reactor pressure vessel assembly at a temperature of approximately 100 degrees Celsius or higher.

The method further comprises a third step 206, in which liquid, e.g. water and substances dissolved in the water, is separated from solid components produced through the hydrothermal carbonization process. In the first example, approximately 1496kg of liquid per hour is separated from the products and 1282 kg per hour of semidried (65%) solids remain.

The method further comprises a fourth step 208, in which a gasification. e.g. pyrolysis, process is performed on the separated sold components, to produce syngas.

The method 200 may further comprise discharging the products of the hydrothermal carbonization process, e.g. from the reactor pressure vessel, to an expansion vessel, such as the expansion vessel 14 described above, prior to the step of separating the liquid from the solid components. The products of the hydrothermal carbonization process may be at a lower pressure within the expansion vessel than within the reactor pressure vessel.

The method 200 may further comprise circulating gases from the expansion vessel, such as water vapour, through a gas heat exchanger, such as the gas heat changer 4, configured to transfer heat from the expansion vessel gases to the input waste material, e.g. prior to the waste material being received in the reactor pressure vessel. In the first example, approximately 1389 kg of water per hour may be extracted from the expansion vessel and passed through the gas heat exchanger.

The method 200 may further comprise circulating the separated liquid, e.g. from the third step, through a liquid heat exchanger, such as the liquid heat exchanger 6, configured to transfer heat from the separated liquid to the input waste material, e.g. prior to the waste material being received in the reactor pressure vessel. The gas heat exchanger may be arranged downstream of the liquid heat exchanger, relative to the passage of the input waste material to the reactor pressure vessel assembly.

The input waste material may be at ambient temperature before passing through the gas heat exchanger and the liquid heat exchanger and, in the first example, may be at a temperature of approximately 100 degrees Celsius and comprise and may comprise approximately 20% saturated vapour when leaving the gas heat exchanger.

The method 300 may further comprise combusting the syngas produced though the gasification process in a gas powered electrical generator, such as the electrical generator 50, to generate electricity. The electricity generated by the electrical generator may be used to power a heater for the reactor pressure vessel, e.g. during steady state performance of the method. The method may further comprises providing electricity from a source separate from the electrical generator to heat the reactor pressure vessel during a start-up procedure.

The method may further comprise providing combustible gas, such as natural gas, from a source separate from the gasification reactor as an input to the gasification process during a start-up procedure of the method of processing waste material. The combustible gas may be combusted, e.g. at the burner 54 of the gasification reactor assembly 30, in order to heat the reactants of the gasification process during the start-up procedure for the method of processing waste material. In the first example, 4 MW of natural gas may be provided to the burners of the gasification reactor assembly in order to heat the reactants during the start-up procedure.

The method may further comprise delivering a portion of the produced syngas as an input to the gasification process. The portion of the produced syngas may be combusted, e.g. by the burner 34 of the gasification reactor assembly, in order to heat the reactants of the gasification process. During steady state operation of the method, the combustible gas may no longer provided as an input to the gasification process, e.g. once the syngas is available to be combusted for heating the reactants. In the first example, 4 MW of syngas gas may be provided to the burners of the gasification reactor assembly in order to heat the reactants during steady state performance of the method.

The method 300 may further comprise recirculating the combustion gases, produced from the combustion at the burner for heating the reactants of the gasification process, to heat the input waste material upstream and/or within the reactor pressure vessels of the reactor pressure assembly.

During steady state performance of the method, the waste material within the reactor pressure vessels may be heated using the gas heat exchanger, the liquid heat exchanger, the recirculated combustion gases resulting from the combustion at the burner for heating the reactants of the gasification process, and using heaters, e.g. electrical heaters 11, provided in the reactor pressure vessel assembly. In the first example, during steady state operation of the method approximately 2MW of heat may be transferred to the input waste material at the gas heat exchanger and the liquid heat exchanger, approximately 0.5MW of heat may be transferred to the input waste material from the recirculated combustion gases and approximately 0.5MW of heat maybe supplied by the heaters of the reactor pressure vessel assembly. As described above, the heaters 11 may be powered using electrical power generated by the electrical generator 50.

However, during the start up procedure of the method, the heat may be supplied to the reactor pressure vessel using the heater of the reactor pressure vessel assembly only. In the first example, 3MW of heat may be supplied to the reactor pressure vessel by the heater.

The method may further comprise cleaning the syngas produced through the gasification process, in order to remove contaminants from the syngas. The syngas may be cleaned prior to the syngas being used for other purposes as part of the method of processing waste. In particular, the syngas may be cleaned prior to being combusted by the gas generator to produce electricity and/or supplied to the burner of the gasification reactor assembly. The syngas may be cleaned using the syngas cleaning unit described above. The method may further comprise recirculating at least a portion of the contaminants removed from the syngas as an input to the gasification process.

Additionally or alternatively, the method may comprise passing the syngas through a condenser to remove water vapour from the syngas, e.g. prior to the syngas being used for other purposes as part of the method. The syngas may be passed through the condenser after contaminants are removed.

It will be appreciated by those skilled in the art that although the invention has been described by way of example, with reference to one or more exemplary examples, it is not limited to the disclosed examples and that alternative examples could be constructed without departing from the scope of the invention as defined by the appended claims.

Claims

Claims 1. A method of processing waste material, wherein the waste material comprises human and/or animal digestive waste and/or plant derived waste that has undergone a process of anaerobic and/or aerobic digestion, wherein the method comprises: receiving an input of waste material into a reactor pressure vessel, wherein the waste material comprises biomass and water; heating and pressurising the reactor pressure vessel to perform a hydrothermal carbonization process of the biomass; separating at least a portion of a liquid from solid components of the products produced through the hydrothermal carbonization process; performing a gasification process on the solid components, to produce syngas.
2. The method of claim 1, wherein the waste material comprises a digestate sludge, e.g. produced through anaerobic and/or aerobic digestion of human and/or animal digestive waste and/or plant derived waste.
3. The method of claim 1 or 2, wherein the reactor pressure vessel is heated to a reaction temperature greater than 180 degrees Celsius, for example 200 degrees Celsius, to perform the hydrothermal carbonization process.
4. The method of claim 3, wherein the reactor vessel is maintained at the reaction temperature for approximately 4 hours.
5. The method of any of the preceding claims, wherein reaction temperature and pressure of the reactants within the reactor pressure vessel are maintained to achieve subcritical conditions for water within the reactor pressure vessel.
6. The method of claim 5, wherein the reaction temperature and pressure of the reactants within the reactor pressure vessel are configured to reduce a dielectric constant of water within the reactor pressure vessel to less than 40, such as between 20 and 30, e.g. between 20 and 25.
7. The method of any of the preceding claims, wherein the hydrothermal carbonization process is performed as a continuous series of batch operation process, performed using a plurality of the reactor pressure vessels configured to receive the waste material sequentially and performed the hydrothermal carbonization process at time period offset from one another by less than a total duration of the hydrothermal carbonization process.
8. The method of any of the preceding claims, wherein the method further comprises: discharging the products of the hydrothermal carbonization process to an expansion vessel at a lower pressure than the reactor pressure vessel prior to the step of separating the liquid from the solid components.
9. The method of claim 8, wherein the method comprises: circulating gases from the expansion vessel through a gas heat exchanger configured to transfer heat from the expansion vessel gases to the input waste material prior to the waste material being received in the reactor pressure vessel.
10. The method of the preceding claims, wherein the method comprises: circulating the separated liquid through a liquid heat exchanger configured to transfer heat from the separated liquid to the input waste material prior to the waste material being received in the reactor pressure vessel.
11. The method of claims 9 and 10, wherein the gas heat exchanger is arranged downstream of the liquid heat exchanger, relative to the passage of the input waste material to the reactor pressure vessel.
12. The method of any of the preceding claims, wherein the liquid is separated from the solid components through a physical separation process.
13. The method of any of the preceding claims, wherein the liquid is separated from the solid components using a filter press.
14. The method of any of the preceding claims, wherein the method further comprises combusting the syngas produced though the gasification process in a gas generator to generate electricity.
15. The method of claim 14, wherein the electricity generated by the gas generators is used to power a heater for the reactor pressure vessel, e.g. during steady state performance of the method.
16. The method of claim 14 or 15, wherein the method comprises providing electricity from a source separate from the gas generator to heat the reactor pressure vessel during a start-up procedure.
17. The method of any of the preceding claims, wherein the method further comprises: delivering a portion of the produced syngas as an input to the gasification process, wherein the portion of the produced syngas is combusted in order to heat the reactants of the gasification process.
18. The method of any of the preceding claims, wherein the method further comprises: providing combustible gas from a source separate from the gasification reactor, such as natural gas, as an input to the gasification process during a start-up procedure of the method of processing waste material, wherein the combustible gas is combusted in order to heat the reactants of the gasification process during the start-up procedure for the method of processing waste material.
19. The method of claims 17 and 18, wherein the combustible gas is no longer provided as an input to the gasification process once the syngas is available to be combusted for heating the reactants.
20. The method of any of claims 16 to 19, wherein the method further comprises: circulating the combustion gases resulting from the combustion for heating the reactants of the gasification process to the heat the input waste material upstream and/or within the reactor pressure vessel.
21. The method of any of the preceding claims, wherein the method further comprises: cleaning the syngas produced through the gasification process prior to the syngas being used for other purposed as part of the method of processing waste, in order to remove contaminants from the syngas.
22. The method of claim 21, wherein the method further comprises: recirculating at least a portion of the contaminants removed from the syngas as an input to the gasification process.
23. A system for processing waste material, wherein the waste material comprises human and/or animal digestive waste and/or plant derived waste that has undergone a process of anaerobic and/or aerobic digestion, wherein the system comprises: a reactor pressure vessel assembly comprising one or more reactor pressure vessels for receiving an input of waste material and heating and pressurising the waste material within the vessels to perform a hydrothermal carbonization process of the waste material; a separating unit, for separating liquid from solid components produced though the hydrothermal carbonization process; a gasification reactor vessel for receiving the solid components and performing a gasification process on the separated solids within the gasification reactor vessel to produce syngas.
24. The system of claim 23, wherein the reactor pressure vessel assembly further comprises one or more expansion vessels for receiving the products of the hydrothermal carbonization process from the one or more reactor pressure vessels at a lower pressure than the reactor pressure vessels.
25. The system of claim 24, wherein the system further comprises: a gas heat exchanger, configured to receive gases from the one or more expansion vessels and transfer heat from the gases to the input waste material.
26. The system of any of claims 23 to 25, wherein the system further comprises: a liquid heat exchanger, configured to receive the liquid separated by the separating unit and transfer heat from the liquid to the input waste material.
27. The system of claims 25 and 26, wherein the gas heat exchanger is arranged downstream of the liquid heat exchanger, relative to the passage of the input waste material to the reactor pressure vessel assembly.
28. The system of any of claims 23 to 27, wherein the system further comprises: a gas generator for using the syngas produced by the gasification reactor to produce electricity.
29. The system of claim 28, wherein the reactor pressure vessel assembly comprises one or more electric heaters, for heating the reactants within the reactor pressure vessels, wherein the electric heaters are electrically connected to the gas generator.
30. The system of any of claims 23 to 29, wherein the system further comprises a syngas cleaning unit for removing contaminants from the syngas produced in the gasification reactor vessel.
31. The system of claims 29 and 30, wherein the syngas cleaning unit is provided between the gasification reactor vessel and the gas generator relative to the flow of syngas.
32. The system of claim 30 or 31, wherein the syngas cleaning unit comprises a wetted wall scrubber.
33. The system of any of claims 30 to 32, wherein the system further comprises a contaminant recirculation duct for recirculating contaminant removed from the syngas to the gasification reactor.
34. The system of any of claims 23 to 33, wherein the gasification reactor comprises one or more burners for burning a gas to heat reactants in the gasification process, wherein the system comprises a syngas supply duct, for supplying syngas output by the gasification reactor to the one or more burners.
35. The system of any of claims 23 to 34, wherein the reactor pressure vessel assembly comprises a plurality of reactor pressure vessels and one or more expansion vessels, wherein the reactor pressure vessels are configured to store reactants and products at a higher pressure than the expansion vessels, wherein the expansion vessels are configured to receive products of the reaction within the respective reactor pressure vessels.
36. The system of claim 35, wherein the reactor pressure vessel assembly is configured to operate in a continuous series of batch procedures in which reactants are input to the plurality of reactor pressure vessels sequentially, products of the reactions within the reactor pressure vessels are output to expansion vessels sequentially, and the hydrothermal carbonization process is conducted over staggered time periods within the sequential reactor pressure vessels
37. The system of claim 36, wherein the reactor pressure vessel assembly further comprises one or more ducts for conducting gases from the expansion vessels to one or more heat exchangers for heating reactants input to respective ones of the reactor pressure vessels.
38. The system of claim 37, wherein the ducts are arranged so that that gases from the expansion vessels are conducted to the heat exchange configured to heat the reactant within the next of the reactor pressure vessels to receive reactants in the continuous series of batch procedures.
39. The system of any of claims 23 to 38, wherein the system comprises a combustion gas duct, for conducting combustion gases from the gasification reactor to the reactor pressure vessel assembly, and one or more combustion gas heat exchangers for transferring heat from the combustion gases to the waste material input to the reactor pressure vessel assembly.