WO2022133527A1 - A process for converting waste into clean energy and value-added products - Google Patents

A process for converting waste into clean energy and value-added products Download PDF

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Publication number
WO2022133527A1
WO2022133527A1 PCT/AU2021/051532 AU2021051532W WO2022133527A1 WO 2022133527 A1 WO2022133527 A1 WO 2022133527A1 AU 2021051532 W AU2021051532 W AU 2021051532W WO 2022133527 A1 WO2022133527 A1 WO 2022133527A1
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Prior art keywords
gas
carbon
gas mixture
syngas
temperature
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PCT/AU2021/051532
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French (fr)
Inventor
Garry J.A PRICE
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Clean Energy Resources Pty Ltd
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Priority claimed from AU2020904812A external-priority patent/AU2020904812A0/en
Application filed by Clean Energy Resources Pty Ltd filed Critical Clean Energy Resources Pty Ltd
Publication of WO2022133527A1 publication Critical patent/WO2022133527A1/en

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    • C10K3/00—Modifying the chemical composition of combustible gases containing carbon monoxide to produce an improved fuel, e.g. one of different calorific value, which may be free from carbon monoxide
    • C10K3/02—Modifying the chemical composition of combustible gases containing carbon monoxide to produce an improved fuel, e.g. one of different calorific value, which may be free from carbon monoxide by catalytic treatment
    • C10K3/04—Modifying the chemical composition of combustible gases containing carbon monoxide to produce an improved fuel, e.g. one of different calorific value, which may be free from carbon monoxide by catalytic treatment reducing the carbon monoxide content, e.g. water-gas shift [WGS]
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    • C01C1/04—Preparation of ammonia by synthesis in the gas phase
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    • C10B47/00—Destructive distillation of solid carbonaceous materials with indirect heating, e.g. by external combustion
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    • C10J—PRODUCTION OF PRODUCER GAS, WATER-GAS, SYNTHESIS GAS FROM SOLID CARBONACEOUS MATERIAL, OR MIXTURES CONTAINING THESE GASES; CARBURETTING AIR OR OTHER GASES
    • C10J2300/00—Details of gasification processes
    • C10J2300/18—Details of the gasification process, e.g. loops, autothermal operation
    • C10J2300/1853—Steam reforming, i.e. injection of steam only
    • C—CHEMISTRY; METALLURGY
    • C10—PETROLEUM, GAS OR COKE INDUSTRIES; TECHNICAL GASES CONTAINING CARBON MONOXIDE; FUELS; LUBRICANTS; PEAT
    • C10J—PRODUCTION OF PRODUCER GAS, WATER-GAS, SYNTHESIS GAS FROM SOLID CARBONACEOUS MATERIAL, OR MIXTURES CONTAINING THESE GASES; CARBURETTING AIR OR OTHER GASES
    • C10J2300/00—Details of gasification processes
    • C10J2300/18—Details of the gasification process, e.g. loops, autothermal operation
    • C10J2300/1861—Heat exchange between at least two process streams
    • C—CHEMISTRY; METALLURGY
    • C10—PETROLEUM, GAS OR COKE INDUSTRIES; TECHNICAL GASES CONTAINING CARBON MONOXIDE; FUELS; LUBRICANTS; PEAT
    • C10J—PRODUCTION OF PRODUCER GAS, WATER-GAS, SYNTHESIS GAS FROM SOLID CARBONACEOUS MATERIAL, OR MIXTURES CONTAINING THESE GASES; CARBURETTING AIR OR OTHER GASES
    • C10J2300/00—Details of gasification processes
    • C10J2300/18—Details of the gasification process, e.g. loops, autothermal operation
    • C10J2300/1861—Heat exchange between at least two process streams
    • C10J2300/1884—Heat exchange between at least two process streams with one stream being synthesis gas
    • C—CHEMISTRY; METALLURGY
    • C10—PETROLEUM, GAS OR COKE INDUSTRIES; TECHNICAL GASES CONTAINING CARBON MONOXIDE; FUELS; LUBRICANTS; PEAT
    • C10J—PRODUCTION OF PRODUCER GAS, WATER-GAS, SYNTHESIS GAS FROM SOLID CARBONACEOUS MATERIAL, OR MIXTURES CONTAINING THESE GASES; CARBURETTING AIR OR OTHER GASES
    • C10J2300/00—Details of gasification processes
    • C10J2300/18—Details of the gasification process, e.g. loops, autothermal operation
    • C10J2300/1861—Heat exchange between at least two process streams
    • C10J2300/1892—Heat exchange between at least two process streams with one stream being water/steam

Definitions

  • the present invention broadly relates to a process for converting waste, in particular carbonaceous waste, into clean energy and value-added products.
  • waste-to-energy plants For many years waste has been converted into energy in so-called "waste-to-energy plants".
  • a waste-to-energy plant is a waste management facility that combusts waste in order to produce electricity. However, following the combustion process, further waste is generated. This waste is typically in the form of slag which is disposed in landfill and air pollution control residues. Furthermore, waste-to-energy plants require a large input of energy to sustain the temperatures required to combust the waste.
  • the present invention provides a continuous recycling process comprising:
  • step (vi) exchanging heat from the syngas with water so as to provide superheated steam which is used in the high-temperature water-gas shift reaction in step (iv) and a cooled syngas;
  • step (viii) transferring the carbon obtained following step (iii) into a second reactor and further heating the carbon in the presence of oxygen-enriched air so as to provide a second gas mixture comprising carbon monoxide and nitrogen, wherein heat from the second gas mixture is used to heat further carbon in step (viii);
  • step (x) exchanging heat from the second gas mixture with water so as to provide superheated steam which is used in the high-temperature water-gas shift reaction in step (ix) and a cooled second gas mixture;
  • step (xii) transferring the carbon obtained following step (viii) into a third reactor and further heating the carbon in the presence of oxygen-enriched air so as to provide a fourth gas mixture comprising carbon monoxide and nitrogen, wherein heat from the fourth gas mixture is used to heat further carbon in step (xii);
  • step (xiv) exchanging heat from the fourth gas mixture with water so as to provide superheated steam which is used in the high-temperature water-gas shift reaction in step (xiii) and a cooled fourth gas mixture; (xv) subjecting the cooled fourth gas mixture to a low-temperature water-gas shift reaction so as to provide a fifth gas mixture comprising hydrogen, nitrogen and carbon dioxide;
  • the waste material may comprise a carbonaceous material.
  • the carbonaceous material may comprise plastic or a mixture of different plastics.
  • the carbonaceous material may comprise tyres.
  • the carbonaceous material may comprise coal fines.
  • the carbonaceous material may comprise biomass, such as for example a fibrous biomass.
  • the carbonaceous material may comprise municipal waste.
  • the waste material comprises palm oil waste or coconut fibre.
  • the briquettes may be produced by extrusion.
  • the briquettes may have a density between about 500 kg/m 3 and about 1000 kg/m 3 , or between about 600 kg/m 3 and about 900 kg/m 3 , or between about 650 kg/m 3 and about 750 kg/m 3 . In one embodiment the briquettes have a density of about 750 kg/m 3 .
  • the briquettes may further comprise one or more of: sewage, wood pulp or fines.
  • the briquettes may comprise at least 20% moisture (w/w).
  • the briquettes may be pyrolysed at a temperature between about 500 °C and about 1200 °C, or between about 600 °C and about 1100 °C, or between about 700 °C and about 1100 °C, or between about 800 °C and about 1000 °C, or about 900 °C.
  • the high-temperature water-gas shift reaction in step (iv) may be performed by mixing the syngas with superheated steam.
  • the high-temperature water-gas shift reactions in steps (ix) and (xiii) may be performed by mixing the second gas mixture and the fourth gas mixture respectively with superheated steam.
  • the high-temperature water-gas shift reaction in steps (iv), (ix) and (xiii) may be performed at a temperature between about 500 °C and about 1200 °C, or at a temperature between about 500 °C and about 1100 °C, or at a temperature between about 500 °C and about 1000 °C, or at a temperature between about 600 °C and about 900 °C, or at a temperature between about 600 °C and about 800 °C, or at a temperature between about 650 °C and about 750 °C.
  • Exchanging heat from the syngas with water so as to provide superheated steam may be performed after step (v).
  • the syngas may be scrubbed to remove one or more of the following contaminants: dioxins, heavy metals, furans and acid gases.
  • the cooled syngas, cooled second gas mixture and cooled fourth gas mixture may have a temperature below about 300 °C, or below about 275 °C, or below about 250 °C, or between about 200 °C and about 300 °C, or about 250 °C.
  • the low-temperature water-gas shift reaction in step (vii) may be performed by mixing the cooled syngas with superheated steam.
  • the low-temperature water-gas shift reactions in steps (xi) and (xv) may be performed by mixing the cooled second gas mixture and the cooled fourth gas mixture respectively with superheated steam.
  • the low-temperature water-gas shift reaction in steps (vii), (xi) and (xv) may be performed at a temperature above about 250 °C, or above about 300 °C, or above about 350 °C, or between about 250 °C and about 500 °C, or between about 250 °C and about 400 °C, or between about 250 °C and about 350 °C.
  • the carbon may be heated at a temperature between about 500 °C and about 1200 °C, or between about 700 °C and about 1200 °C, or between about 600 °C and about 1100 °C, or between about 700 °C and about 1100 °C, or between about 800 °C and about 1000 °C, or about 900 °C.
  • the oxygen-enriched air may have an oxygen content of at least about 23% (w/w), at least about 25% (w/w), at least about 27% (w/w), at least about 30% (w/w), at least about 35% (w/w), or at least about 50% (w/w).
  • the carbon dioxide, hydrogen and nitrogen may be separated using a positive swing adsorption (PSA) system.
  • PSA positive swing adsorption
  • the first, third and fifth gas mixtures may be combined prior to step (xvi).
  • the first, second and third reactors may be vertically stacked such that step (iii) is carried out above step (viii) which is carried out above step (xii).
  • step (iii) the briquettes may be rotated during heating.
  • the carbon may be rotated during heating.
  • the first reactor may comprise a reaction chamber and an outer gas jacket attached to at least a portion of the reaction chamber, the outer gas jacket comprising an inner wall and an outer wall defining a conduit, wherein syngas produced in the reactor is fed into the conduit so as to transfer heat to the reaction chamber to drive further pyrolysis.
  • the second reactor may comprise a reaction chamber and an outer gas jacket attached to at least a portion of the reaction chamber, the outer gas jacket comprising an inner wall and an outer wall defining a conduit, wherein the gas mixture produced in the second reactor is fed into the conduit so as to transfer heat to the reaction chamber to heat further carbon.
  • the third reactor may comprise a reaction chamber and an outer gas jacket attached to at least a portion of the reaction chamber, the outer gas jacket comprising an inner wall and an outer wall defining a conduit, wherein the gas mixture produced in the third reactor is fed into the conduit so as to transfer heat to the reaction chamber to heat further carbon.
  • the inner wall may have a thermal conductivity that is about 15 times to 25 times, or about 20 times larger than the thermal conductivity of the outer wall.
  • the thermal conductivity of the inner wall may be between about 250 W/(m.K) and about 350 W/(m.K), or between about 300 W/(m.K) and about 350 W/(m.K). In one embodiment the thermal conductivity of the inner wall may be about 327 W/(m.K).
  • the inner wall may comprise, or be made of, a copper/ceramic material.
  • the superheated steam generated in steps (vi), (x) and (xiv) may be injected into the conduit of each of the first, second and third reactors at a plurality of spaced apart points thereby enabling the high-temperature water-gas shift reaction.
  • Carbon generated in steps (iii), (viii) and (xii) may be one or more of: biochar, carbon black or activated carbon.
  • Time elapsed from commencement of pyrolsis of a briquette to removal of carbon produced from the briquette from the third reactor may be between about 60 minutes and about 120 minutes, or between about 70 minutes and about 110 minutes, or between about 80 minutes and about 100 minutes, or about 90 minutes.
  • the first, third and fifth gas mixtures may be free, or substantially free, of carbon monoxide.
  • an element means one element or more than one element.
  • the term "substantially free” is understood to mean less than about 1%, or less than about 0.5%, or less than about 0.1%, or less than about 0.01 %, or less than about 0.005%, or less than about 0.001 %, or less than about 0.0001 % of the recited entity.
  • Figure 1 Schematic diagram of a process in accordance with one embodiment of the invention.
  • the present invention provides a continuous recycling process comprising:
  • step (vi) exchanging heat from the syngas with water so as to provide superheated steam which is used in the high-temperature water-gas shift reaction in step (iv) and a cooled syngas;
  • step (viii) transferring the carbon obtained following step (iii) into a second reactor and further heating the carbon in the presence of oxygen-enriched air so as to provide a second gas mixture comprising carbon monoxide and nitrogen, wherein heat from the second gas mixture is used to heat further carbon in step (viii);
  • step (x) exchanging heat from the second gas mixture with water so as to provide superheated steam which is used in the high-temperature water-gas shift reaction in step (ix) and a cooled second gas mixture;
  • step (xii) transferring the carbon obtained following step (viii) into a third reactor and further heating the carbon in the presence of oxygen-enriched air so as to provide a fourth gas mixture comprising carbon monoxide and nitrogen, wherein heat from the fourth gas mixture is used to heat further carbon in step (xii);
  • step (xiv) exchanging heat from the fourth gas mixture with water so as to provide superheated steam which is used in the high-temperature water-gas shift reaction in step (xiii) and a cooled fourth gas mixture; (xv) subjecting the cooled fourth gas mixture to a low-temperature water-gas shift reaction so as to provide a fifth gas mixture comprising hydrogen, nitrogen and carbon dioxide;
  • the process of the present invention allows a wide range of waste materials to be converted to energy and value-added products.
  • the process differs from traditional waste-to-energy processes in that emissions are used as an energy source to drive the process and carbon is used as a catalyst to produce hydrogen.
  • the process results in zero emissions and can therefore be descried as a "closed-loop" process.
  • ammonia has been suggested as a possible fuel for electric cars and urea is used extensively as a fertiliser.
  • a portion of the hydrogen produced is used to produce base-load electricty. This may be achieved, for example, by using a solid oxide fuel cell.
  • the process also generates carbon, which is typically in the form of biochar, activated carbon or carbon black.
  • biochar is used as a soil amendment and may increase soil fertility of acidic soils, increase agricultural productivity and provide protection against some foliar and soil- borne diseases.
  • Carbon black is used as a filler in tyres and other rubber products and as a colour pigment in plastics, paints and inks.
  • Activated carbon is used in a wide range of applications, including methane and hydrogen storage, air purification, decaffeination, gold purification, metal extraction, water purification, sewage treatment and teeth whitening.
  • the type of carbon produced depends on the nature of the waste material.
  • the waste material may be selected based on the type of carbon that is sought to be produced. For example, where the waste material is tyres, a substantial quantity of carbon black is produced. Alternatively, where the waste material is a fibrous biomass, such as cocunut fibre, a substantial quantity of activated carbon is produced. Municipal solid waste can be used where it is desired to produce biochar.
  • Waste materials suitable for use in the process include any and all carbonaceous materials, including but not limited to, plastic, biomass, municipal waste, coal fines and tyres. Plastic pollution remains a major global challenge.
  • the present invention provides a convenient and efficient means for converting large amounts of plastic waste into energy and value-added products.
  • Step (i) involves providing a homogenised waste material.
  • the waste material may comprise a single type of waste or different types of waste and be homogenised using, for example, a blender.
  • step (ii) the homogenised waste material is formed into briquettes.
  • the briquettes may be about the same size and the same density, thereby having a consistent carbon content.
  • the consistent carbon content allows for consistent carbon monoxide production which translates into consistent hydrogen production following the initial high- temperature water-gas shift reaction. This provides the process with the necessary energy balance required for continuous operation and the production of base-load electricity.
  • the briquettes may have a density between about 400 kg/m 3 and about 1000 kg/m 3 , or between about 500 kg/m 3 and about 1000 kg/m 3 , or between about 550 kg/m 3 and about 1000 kg/m 3 ’ or between about 550 kg/m 3 and about 950 kg/m 3 , or between about 550 kg/m 3 and about 900 kg/m 3 , or between about 600 kg/m 3 and about 900 kg/m 3 , or between about 600 kg/m 3 and about 850 kg/m 3 , or between about 650 kg/m 3 and about 750 kg/m 3 .
  • the briquettes are then fed into a first reactor and pyrolysed so as to provide carbon and a syngas which typically comprises carbon dioxide, carbon monoxide, hydrogen, hydrocarbons and contaminants, including dioxins, heavy metals, furans and acid gases.
  • a syngas typically comprises carbon dioxide, carbon monoxide, hydrogen, hydrocarbons and contaminants, including dioxins, heavy metals, furans and acid gases.
  • the briquettes may be pyrolysed at a temperature between about 400 °C and about 1200 °C, or at a temperature between about 500 °C and about 1200 °C, or at a temperature between about 500 °C and about 1100 °C, or at a temperature between about 550 °C and about 1100 °C, or at a temperature between about 550 °C and about 1000 °C, or at a temperature between about 600 °C and about 1100 °C, or at a temperature between about 600 °C and about 1000 °C, or at a temperature between about 700 °C and about 1100 °C, or at a temperature between about 700 °C and about 1000 °C, or at a temperature between about 800 °C and about 1000 °C, or at a temperature between about 850 °C and about 1000 °C, or at a temperature between about 850 °C and about 950 °C.
  • the briquettes are pyrolysed at a
  • Heat from the syngas produced is used to drive further pyrolysis. This may be achieved using a jacketed reactor whereby syngas produced in the reactor is extracted and fed into an outer gas jacket. Heat from the syngas is transferred from the outer jacket to the reaction chamber where pyrolysis takes place.
  • the first reactor comprises a reaction chamber and an outer gas jacket attached to at least a portion of the reaction chamber, the outer gas jacket comprising an inner wall and an outer wall defining a conduit, wherein syngas produced in the reactor is fed into the conduit so as to transfer heat to the reaction chamber to drive further pyrolysis.
  • the inner wall may have a thermal conductivity that is about 15 times to 25 times, or about 20 times larger than the thermal conductivity of the outer wall. This arrangement optimises heat transfer from the syngas to the reaction chamber.
  • the inner wall may comprise, or be made of, a copper/ceramic material.
  • step (iv) the syngas is subjected to a high-temperature water-gas shift reaction.
  • the reaction may be carried out by mixing the syngas with superheated steam.
  • the high- temperature water-gas shift reaction serves to enrich the amounts of hydrogen and carbon dioxide in the syngas stream at the expense of carbon monoxide.
  • the high-temperature water-gas shift reaction may be performed at a temperature between about 500 °C and about 1200 °C, or at a temperature between about 500 °C and about 1100 °C, or at a temperature between about 500 °C and about 1000 °C, or at a temperature between about 600 °C and about 900 °C, or at a temperature between about 600 °C and about 800 °C, or at a temperature between about 650 °C and about 750 °C.
  • step (v) the syngas is scrubbed to remove contaminants including dioxins, heavy metals, furans, acid gases and particulates.
  • contaminants including dioxins, heavy metals, furans, acid gases and particulates.
  • Heat from the syngas is utilised by exchanging with water so as to provide superheated steam that is used in the high-temperature water-gas shift reaction in step (iv).
  • the heat exchange is performed after scrubbing of the syngas.
  • the heat exchange also provides a cooled syngas.
  • the cooled syngas may have a temperature below about 300 °C, or below about 275 °C, or below about 250 °C, or between about 200 °C and about 300 °C, or about 250 °C.
  • the superheated steam generated in step (vi) may be injected at a plurality of spaced apart points along the conduit thereby enabling the high-temperature water-gas shift reaction. This arrangement allows additional heat produced in the high-temperature water-gas shift reaction to be transferred to the reaction chamber to drive further pyrolysis.
  • step (vii) the cooled syngas is subjected to a low-temperature water-gas shift reaction in order to remove any residual carbon monoxide.
  • the carbon monoxide may be present as a result of methane being reduced to carbon monoxide and hydrogen in the high-temperature water-gas shift reaction according to the following reaction:
  • the low-temperature water-gas shift reaction may be performed at a temperature above about 250 °C, or above about 300 °C, or above about 350 °C, or between about 250 °C and about 500 °C, or between about 250 °C and about 400 °C, or between about 250 °C and about 350 °C.
  • step (viii) the carbon generated from pyrolysis is transferred to a second reactor and heated in the presence of oxygen-enriched air so as to provide a second gas mixture comprising carbon monoxide and nitrogen.
  • the oxygen-enriched air may be obtained from the positive swing adsorption system.
  • the oxygen-enriched air may have an oxygen content of at least about 23% (w/w), at least about 25% (w/w), at least about 27% (w/w), at least about 30% (w/w), at least about 35% (w/w), or at least about 50% (w/w).
  • Heat from the second gas mixture produced is used to heat further carbon in step (viii). This may be achieved using a jacketed reactor as described above, whereby gas produced in the reactor is extracted and fed into an outer gas jacket. Heat from the second gas mixture is transferred from the outer jacket to the reaction chamber where heating of the carbon takes place.
  • the second reactor comprises a reaction chamber and an outer gas jacket attached to at least a portion of the reaction chamber, the outer gas jacket comprising an inner wall and an outer wall defining a conduit, wherein gas produced in the second reactor is fed into the conduit so as to transfer heat to the reaction chamber to heat further carbon.
  • the inner wall of the second may have a thermal conductivity that is about 15 times to 25 times, or about 20 times larger than the thermal conductivity of the outer wall. This arrangement optimises heat transfer from the syngas to the reaction chamber.
  • the inner wall may comprise, or be made of, a copper/ceramic material.
  • step (ix) the second gas mixture is subjected to a high-temperature water-gas shift reaction.
  • the reaction may be carried out by mixing the syngas with superheated steam.
  • the high-temperature water-gas shift reaction serves to enrich the amounts of hydrogen and carbon dioxide in the second gas mixture at the expense of carbon monoxide.
  • the high-temperature water-gas shift reaction in step (ix) may be performed at the temperatures described above in connection with step (iv).
  • Heat from the second gas mixture is utilised by exchanging with water so as to provide superheated steam that is used in the high-temperature water-gas shift reaction in step (ix).
  • the heat exchange also provides a cooled second gas mixture.
  • the cooled second gas mixture may have a temperature below about 300 °C, or below about 275 °C, or between about 250 °C, or between about 200 °C and about 300 °C, or about 250 °C.
  • step (viii) When step (viii) is carried out in a jacketed reactor, the superheated steam generated in step (x) may be injected at a plurality of spaced apart points along the outer gas jacket thereby enabling the high-temperature water-gas shift reaction. This arrangement allows additional heat produced in the high-temperature water-gas shift reaction to be transferred to the reaction chamber to heat further carbon.
  • step (xi) the cooled second gas mixture is subjected to a low-temperature water-gas shift reaction.
  • This reaction serves to further enrich the amounts of carbon dioxide and hydrogen in the second gas mixture at the expense of carbon monoxide so as to provide the third gas mixture.
  • the third gas mixture may be free, or substantially free, of carbon monoxide.
  • the low-temperature water-gas shift reaction may be performed at a temperature above about 250 °C, or above about 300 °C, or about 350 °C, or between about 250 °C and about 500 °C, or between about 250 °C and about 400 °C.
  • step (xii) the carbon generated following step (viii) is transferred to a third reactor and heated in the presence of oxygen-enriched air so as to provide a fourth gas mixture comprising carbon monoxide and nitrogen.
  • the oxygen-enriched air may be obtained from the positive swing adsorption system.
  • Steps (ix) to (xi) are then repeated as described above as steps (xiii) to (xv).
  • steps (vii), (xi) and (xv) the carbon dioxide, hydrogen and nitrogen are separated. Separation may be achieved using a positive swing adsorption system.
  • the gas mixtures obtained in steps (vii), (xi) and (xv) may be combined prior to step (xvi).
  • the first, second and third reactors may be vertically stacked such that step (iii) is carried out above step (viii) which is carried out above step (xii). In this arrangement, following step (iii) the carbon is dropped into the second reactor and following step (viii) the carbon is dropped into the third reactor.
  • the amounts of carbon and hydrogen produced may be controlled.
  • the dwell time may be varied by varying the rate of rotation of the briquettes and carbon. It has been found that increasing the rate of rotation maximises the amount of carbon produced and minimises the amount of hydrogen produced. Conversely, decreasing the rate of rotation minimises the amount of carbon produced and maximises the amount of hydrogen produced.
  • the dwell time calculated from commencement of pyrolsis of a briquette to removal of carbon from the third reactor may be between about 60 minutes and about 120 minutes, or between about 70 minutes and about 110 minutes, or between about 80 minutes and about 100 minutes, or about 90 minutes.
  • FIG. 1 shows a schematic diagram of a process in accordance with one embodiment of the invention.
  • Jacketed pyrolysis reactor 1 is provided comprising briquette 2.
  • briquette 2 On heating, briquette 2 is pyrolysed liberating syngas 3 which is extracted and passes through the conduit 4 of the jacketed reactor 1.
  • Superheated steam 6 is injected into the conduit 4 at a plurality of spaced apart points 8, 9 and 10 along the conduit 4 where mixing with syngas 3 occurs thereby enabling the high-temperature water-gas shift reaction.
  • syngas 3 is scrubbed in scrubber 5 to remove contaminants.
  • the syngas 3 is then passed through heat exchanger 7 so as to provide superheated steam 6 which is piped to points 8, 9 and 10 for injection into the conduit 4, and cooled syngas 11.
  • the cooled syngas 11 is then subjected to a low temperature water-gas shift reaction 12 to provide the first gas mixture 13, which comprises carbon dioxide, nitrogen and hydrogen.
  • the resulting carbon 15 is dropped into jacketed reactor 14 where heating in oxygen-rich air is performed.
  • carbon 15 liberates the second gas mixture 16 which is extracted and passes through the conduit 17 of the jacketed reactor 14.
  • Superheated steam 19 is injected into the conduit 17 at a plurality of spaced part points 20, 21 and 22 along the conduit 17 where mixing with the second gas mixture 16 occurs thereby enabling the high-temperature water-gas shift reaction.
  • the second gas mixture 16 is then passed through heat exchanger 18 so as to provide superheated steam 19 which is piped to points 20, 21 and 22, for injection into the conduit 17, and the cooled second gas mixture 23.
  • the cooled second gas mixture 23 is then subjected to a low temperature water-gas shift reaction 24 to provide the third gas mixture 25, which comprises carbon dioxide, nitrogen and hydrogen.
  • the resulting carbon 27 is dropped into jacketed reactor 26 where heating in oxygenrich air is performed.
  • carbon 27 liberates the fourth gas mixture 28 which is extracted and passes through the conduit 29 of the jacketed reactor 26.
  • Superheated steam 31 is injected into the conduit 29 at a plurality of spaced part points 32, 33 and 34 along the conduit 29 where mixing with the fourth gas mixture 28 occurs thereby enabling the high-temperature water-gas shift reaction.
  • the fourth gas mixture 28 is then passed through heat exchanger 30 so as to provide superheated steam 31 which is piped to points 32, 33 and 34, for injection into the conduit 29, and the cooled fourth gas mixture 35.
  • the cooled second gas mixture 35 is then subjected to a low temperature water-gas shift reaction 36 to provide the fifth gas mixture 37, which comprises carbon dioxide, nitrogen and hydrogen.
  • the first gas mixture 13, third gas mixture 25 and fifth gas mixture 37 are then combined into a single gas mixture 38.
  • the single gas mixture 38 is passed through PSA 39 which separates the single gas mixture 38 into a gas stream comprising hydrogen gas and a gas stream comprising nitrogen gas and carbon dioxide gas.
  • a portion of the hydrogen gas is directed to a single oxide fuel cell 40 for generation of base load electricity (BLE).
  • BLE base load electricity
  • the gas stream comprising nitrogen gas and carbon dioxide gas is passed through PSA 41 which separates the mixture into nitrogen and gas and carbon dioxide gas.
  • a portion of the hydrogen gas is reacted with the nitrogen gas to give ammonia (NH 3 ).
  • a portion of the ammonia is reacted with the carbon dioxide to provide urea.
  • Carbon 42 (in the form of one or more of biochar, activated carbon and carbon black) is recovered from the jacketed reactor 26.

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Abstract

The invention is broadly directed to a continuous recycling process comprising: providing a homogenised waste material; forming the homogenised waste material into briquettes having a consistent size and density; feeding the briquettes into a first reactor and pyrolysing the briquettes so as to provide carbon and syngas, wherein heat from the syngas is used to drive further pyrolysis. The syngas may be subjected to a high-temperature water-gas shift reaction to enrich the hydrogen continent of the syngas, and scrubbed to remove contaminants, wherein heat is then exchanged from the syngas with water so as to provide superheated steam which is used in the high-temperature water-gas shift reaction and a cooled syngas.

Description

A process for converting waste into clean energy and value-added products
Field of the Invention
The present invention broadly relates to a process for converting waste, in particular carbonaceous waste, into clean energy and value-added products.
Background of the Invention
Across the globe the amount of waste being generated continues to grow at an alarming rate. In 2012, the worlds’ cities generated 1.3 billion tonnes of solid waste. With rapid population growth and urbanization, municipal waste generation is expected to rise to 2.2 billion tonnes by 2025.
Residents in developing countries, especially the urban poor, are more severely impacted by unsustainably managed waste. In some countries waste is often disposed in unregulated dumps or openly burned. These practices create serious health, safety, and environmental consequences. Poorly managed waste serves as a breeding ground for disease vectors and contributes to global climate change through methane generation.
For many years waste has been converted into energy in so-called "waste-to-energy plants". A waste-to-energy plant is a waste management facility that combusts waste in order to produce electricity. However, following the combustion process, further waste is generated. This waste is typically in the form of slag which is disposed in landfill and air pollution control residues. Furthermore, waste-to-energy plants require a large input of energy to sustain the temperatures required to combust the waste.
Against this background there is a need for improved processes for converting waste into energy.
Summary of the Invention
In a first aspect the present invention provides a continuous recycling process comprising:
(i) providing a homogenised waste material;
(ii) forming the homogenised waste material into briquettes having a consistent size and density; (iii) feeding the briquettes into a first reactor and pyrolysing the briquettes so as to provide carbon and syngas, wherein heat from the syngas is used to drive further pyrolysis;
(iv) subjecting the syngas to a high-temperature water-gas shift reaction so as to enrich the hydrogen content of the syngas;
(v) scrubbing the syngas to remove contaminants;
(vi) exchanging heat from the syngas with water so as to provide superheated steam which is used in the high-temperature water-gas shift reaction in step (iv) and a cooled syngas;
(vii) subjecting the cooled syngas to a low-temperature water-gas shift reaction so as to provide a first gas mixture comprising hydrogen, nitrogen and carbon dioxide;
(viii) transferring the carbon obtained following step (iii) into a second reactor and further heating the carbon in the presence of oxygen-enriched air so as to provide a second gas mixture comprising carbon monoxide and nitrogen, wherein heat from the second gas mixture is used to heat further carbon in step (viii);
(ix) subjecting the second gas mixture to a high-temperature water-gas shift reaction so as to enrich the hydrogen content of the second gas mixture;
(x) exchanging heat from the second gas mixture with water so as to provide superheated steam which is used in the high-temperature water-gas shift reaction in step (ix) and a cooled second gas mixture;
(xi) subjecting the cooled second gas mixture to a low-temperature water-gas shift reaction so as to provide a third gas mixture comprising hydrogen, nitrogen and carbon dioxide;
(xii) transferring the carbon obtained following step (viii) into a third reactor and further heating the carbon in the presence of oxygen-enriched air so as to provide a fourth gas mixture comprising carbon monoxide and nitrogen, wherein heat from the fourth gas mixture is used to heat further carbon in step (xii);
(xiii) subjecting the fourth gas mixture to a high-temperature water-gas shift reaction so as to enrich the hydrogen content of the fourth gas mixture;
(xiv) exchanging heat from the fourth gas mixture with water so as to provide superheated steam which is used in the high-temperature water-gas shift reaction in step (xiii) and a cooled fourth gas mixture; (xv) subjecting the cooled fourth gas mixture to a low-temperature water-gas shift reaction so as to provide a fifth gas mixture comprising hydrogen, nitrogen and carbon dioxide;
(xvi) separating the hydrogen, carbon dioxide and nitrogen in the first, third and fifth gas mixtures, wherein at least a portion of the hydrogen separated is used to produce base load electricity, at least a portion of the nitrogen separated is used to produce ammonia and at least a portion of the carbon dioxide separated is used to produce urea; and,
(xvii) recovering the carbon obtained following step (xii).
The waste material may comprise a carbonaceous material.
The carbonaceous material may comprise plastic or a mixture of different plastics.
The carbonaceous material may comprise tyres.
The carbonaceous material may comprise coal fines.
The carbonaceous material may comprise biomass, such as for example a fibrous biomass.
The carbonaceous material may comprise municipal waste.
In some embodiments, the waste material comprises palm oil waste or coconut fibre.
The briquettes may be produced by extrusion.
The briquettes may have a density between about 500 kg/m3 and about 1000 kg/m3, or between about 600 kg/m3 and about 900 kg/m3, or between about 650 kg/m3 and about 750 kg/m3. In one embodiment the briquettes have a density of about 750 kg/m3.
The briquettes may further comprise one or more of: sewage, wood pulp or fines.
The briquettes may comprise at least 20% moisture (w/w).
The briquettes may be pyrolysed at a temperature between about 500 °C and about 1200 °C, or between about 600 °C and about 1100 °C, or between about 700 °C and about 1100 °C, or between about 800 °C and about 1000 °C, or about 900 °C.
The high-temperature water-gas shift reaction in step (iv) may be performed by mixing the syngas with superheated steam.
The high-temperature water-gas shift reactions in steps (ix) and (xiii) may be performed by mixing the second gas mixture and the fourth gas mixture respectively with superheated steam. The high-temperature water-gas shift reaction in steps (iv), (ix) and (xiii) may be performed at a temperature between about 500 °C and about 1200 °C, or at a temperature between about 500 °C and about 1100 °C, or at a temperature between about 500 °C and about 1000 °C, or at a temperature between about 600 °C and about 900 °C, or at a temperature between about 600 °C and about 800 °C, or at a temperature between about 650 °C and about 750 °C.
Exchanging heat from the syngas with water so as to provide superheated steam may be performed after step (v).
In step (v) the syngas may be scrubbed to remove one or more of the following contaminants: dioxins, heavy metals, furans and acid gases.
The cooled syngas, cooled second gas mixture and cooled fourth gas mixture may have a temperature below about 300 °C, or below about 275 °C, or below about 250 °C, or between about 200 °C and about 300 °C, or about 250 °C.
The low-temperature water-gas shift reaction in step (vii) may be performed by mixing the cooled syngas with superheated steam.
The low-temperature water-gas shift reactions in steps (xi) and (xv) may be performed by mixing the cooled second gas mixture and the cooled fourth gas mixture respectively with superheated steam.
The low-temperature water-gas shift reaction in steps (vii), (xi) and (xv) may be performed at a temperature above about 250 °C, or above about 300 °C, or above about 350 °C, or between about 250 °C and about 500 °C, or between about 250 °C and about 400 °C, or between about 250 °C and about 350 °C.
In steps (viii) and (xii) the carbon may be heated at a temperature between about 500 °C and about 1200 °C, or between about 700 °C and about 1200 °C, or between about 600 °C and about 1100 °C, or between about 700 °C and about 1100 °C, or between about 800 °C and about 1000 °C, or about 900 °C.
The oxygen-enriched air may have an oxygen content of at least about 23% (w/w), at least about 25% (w/w), at least about 27% (w/w), at least about 30% (w/w), at least about 35% (w/w), or at least about 50% (w/w).
The carbon dioxide, hydrogen and nitrogen may be separated using a positive swing adsorption (PSA) system.
The first, third and fifth gas mixtures may be combined prior to step (xvi). The first, second and third reactors may be vertically stacked such that step (iii) is carried out above step (viii) which is carried out above step (xii).
In step (iii), the briquettes may be rotated during heating.
In steps (viii) and (xii) the carbon may be rotated during heating.
The first reactor may comprise a reaction chamber and an outer gas jacket attached to at least a portion of the reaction chamber, the outer gas jacket comprising an inner wall and an outer wall defining a conduit, wherein syngas produced in the reactor is fed into the conduit so as to transfer heat to the reaction chamber to drive further pyrolysis.
The second reactor may comprise a reaction chamber and an outer gas jacket attached to at least a portion of the reaction chamber, the outer gas jacket comprising an inner wall and an outer wall defining a conduit, wherein the gas mixture produced in the second reactor is fed into the conduit so as to transfer heat to the reaction chamber to heat further carbon.
The third reactor may comprise a reaction chamber and an outer gas jacket attached to at least a portion of the reaction chamber, the outer gas jacket comprising an inner wall and an outer wall defining a conduit, wherein the gas mixture produced in the third reactor is fed into the conduit so as to transfer heat to the reaction chamber to heat further carbon.
In the first, second and third reactors the inner wall may have a thermal conductivity that is about 15 times to 25 times, or about 20 times larger than the thermal conductivity of the outer wall.
The thermal conductivity of the inner wall may be between about 250 W/(m.K) and about 350 W/(m.K), or between about 300 W/(m.K) and about 350 W/(m.K). In one embodiment the thermal conductivity of the inner wall may be about 327 W/(m.K).
The inner wall may comprise, or be made of, a copper/ceramic material.
The superheated steam generated in steps (vi), (x) and (xiv) may be injected into the conduit of each of the first, second and third reactors at a plurality of spaced apart points thereby enabling the high-temperature water-gas shift reaction.
Carbon generated in steps (iii), (viii) and (xii) may be one or more of: biochar, carbon black or activated carbon.
Time elapsed from commencement of pyrolsis of a briquette to removal of carbon produced from the briquette from the third reactor may be between about 60 minutes and about 120 minutes, or between about 70 minutes and about 110 minutes, or between about 80 minutes and about 100 minutes, or about 90 minutes.
The first, third and fifth gas mixtures may be free, or substantially free, of carbon monoxide.
Definitions
The following are some definitions that may be helpful in understanding the description of the present invention. These are intended as general definitions and should in no way limit the scope of the present invention to those terms alone, but are put forth for a better understanding of the following description.
Throughout this specification, unless the context requires otherwise, the word "comprise", or variations such as "comprises" or "comprising", will be understood to imply the inclusion of a stated element, integer or step, or group of elements, integers or steps, but not the exclusion of any other element, integer or step, or group of elements, integers or steps.
The terms "a" and "an" are used herein to refer to one or to more than one (i.e. to at least one) of the grammatical object of the article. By way of example, "an element" means one element or more than one element.
In the context of this specification the term "about" is understood to refer to a range of numbers that a person of skill in the art would consider equivalent to the recited value in the context of achieving the same function or result.
In the context of the present specification, the term "substantially free" is understood to mean less than about 1%, or less than about 0.5%, or less than about 0.1%, or less than about 0.01 %, or less than about 0.005%, or less than about 0.001 %, or less than about 0.0001 % of the recited entity.
Brief Description of the Drawings
Figure 1 : Schematic diagram of a process in accordance with one embodiment of the invention.
Detailed Description of the Invention
In one aspect the present invention provides a continuous recycling process comprising:
(i) providing a homogenised waste material;
(ii) forming the homogenised waste material into briquettes having a consistent size and density; (iii) feeding the briquettes into a first reactor and pyrolysing the briquettes so as to provide carbon and syngas, wherein heat from the syngas is used to drive further pyrolysis;
(iv) subjecting the syngas to a high-temperature water-gas shift reaction so as to enrich the hydrogen content of the syngas;
(v) scrubbing the syngas to remove contaminants;
(vi) exchanging heat from the syngas with water so as to provide superheated steam which is used in the high-temperature water-gas shift reaction in step (iv) and a cooled syngas;
(vii) subjecting the cooled syngas to a low-temperature water-gas shift reaction so as to provide a first gas mixture comprising hydrogen, nitrogen and carbon dioxide;
(viii) transferring the carbon obtained following step (iii) into a second reactor and further heating the carbon in the presence of oxygen-enriched air so as to provide a second gas mixture comprising carbon monoxide and nitrogen, wherein heat from the second gas mixture is used to heat further carbon in step (viii);
(ix) subjecting the second gas mixture to a high-temperature water-gas shift reaction so as to enrich the hydrogen content of the second gas mixture;
(x) exchanging heat from the second gas mixture with water so as to provide superheated steam which is used in the high-temperature water-gas shift reaction in step (ix) and a cooled second gas mixture;
(xi) subjecting the cooled second gas mixture to a low-temperature water-gas shift reaction so as to provide a third gas mixture comprising hydrogen, nitrogen and carbon dioxide;
(xii) transferring the carbon obtained following step (viii) into a third reactor and further heating the carbon in the presence of oxygen-enriched air so as to provide a fourth gas mixture comprising carbon monoxide and nitrogen, wherein heat from the fourth gas mixture is used to heat further carbon in step (xii);
(xiii) subjecting the fourth gas mixture to a high-temperature water-gas shift reaction so as to enrich the hydrogen content of the fourth gas mixture;
(xiv) exchanging heat from the fourth gas mixture with water so as to provide superheated steam which is used in the high-temperature water-gas shift reaction in step (xiii) and a cooled fourth gas mixture; (xv) subjecting the cooled fourth gas mixture to a low-temperature water-gas shift reaction so as to provide a fifth gas mixture comprising hydrogen, nitrogen and carbon dioxide;
(xvi) separating the hydrogen, carbon dioxide and nitrogen in the first, third and fifth gas mixtures, wherein at least a portion of the hydrogen separated is used to produce base load electricity, at least a portion of the nitrogen separated is used to produce ammonia and at least a portion of the carbon dioxide separated is used to produce urea; and,
(xvii) recovering the carbon obtained following step (xii).
The process of the present invention allows a wide range of waste materials to be converted to energy and value-added products. The process differs from traditional waste-to-energy processes in that emissions are used as an energy source to drive the process and carbon is used as a catalyst to produce hydrogen. Importantly, the process results in zero emissions and can therefore be descried as a "closed-loop" process.
The process generates substantial quantities of hydrogen, nitrogen and carbon dioxide which are used to produce base load electricity and value-added products, i.e., ammonia and urea. Ammonia has been suggested as a possible fuel for electric cars and urea is used extensively as a fertiliser.
A portion of the hydrogen produced is used to produce base-load electricty. This may be achieved, for example, by using a solid oxide fuel cell.
The process also generates carbon, which is typically in the form of biochar, activated carbon or carbon black. Each of these forms of carbon are widely used in industry. Biochar is used as a soil amendment and may increase soil fertility of acidic soils, increase agricultural productivity and provide protection against some foliar and soil- borne diseases. Carbon black is used as a filler in tyres and other rubber products and as a colour pigment in plastics, paints and inks. Activated carbon is used in a wide range of applications, including methane and hydrogen storage, air purification, decaffeination, gold purification, metal extraction, water purification, sewage treatment and teeth whitening.
The type of carbon produced depends on the nature of the waste material. As such, the waste material may be selected based on the type of carbon that is sought to be produced. For example, where the waste material is tyres, a substantial quantity of carbon black is produced. Alternatively, where the waste material is a fibrous biomass, such as cocunut fibre, a substantial quantity of activated carbon is produced. Municipal solid waste can be used where it is desired to produce biochar.
Waste materials suitable for use in the process include any and all carbonaceous materials, including but not limited to, plastic, biomass, municipal waste, coal fines and tyres. Plastic pollution remains a major global challenge. The present invention provides a convenient and efficient means for converting large amounts of plastic waste into energy and value-added products.
Step (i) involves providing a homogenised waste material. The waste material may comprise a single type of waste or different types of waste and be homogenised using, for example, a blender.
In step (ii) the homogenised waste material is formed into briquettes. The briquettes may be about the same size and the same density, thereby having a consistent carbon content. The consistent carbon content allows for consistent carbon monoxide production which translates into consistent hydrogen production following the initial high- temperature water-gas shift reaction. This provides the process with the necessary energy balance required for continuous operation and the production of base-load electricity. The briquettes may have a density between about 400 kg/m3 and about 1000 kg/m3, or between about 500 kg/m3 and about 1000 kg/m3, or between about 550 kg/m3 and about 1000 kg/m3’ or between about 550 kg/m3 and about 950 kg/m3, or between about 550 kg/m3 and about 900 kg/m3, or between about 600 kg/m3 and about 900 kg/m3, or between about 600 kg/m3 and about 850 kg/m3, or between about 650 kg/m3 and about 750 kg/m3.
The briquettes are then fed into a first reactor and pyrolysed so as to provide carbon and a syngas which typically comprises carbon dioxide, carbon monoxide, hydrogen, hydrocarbons and contaminants, including dioxins, heavy metals, furans and acid gases.
The briquettes may be pyrolysed at a temperature between about 400 °C and about 1200 °C, or at a temperature between about 500 °C and about 1200 °C, or at a temperature between about 500 °C and about 1100 °C, or at a temperature between about 550 °C and about 1100 °C, or at a temperature between about 550 °C and about 1000 °C, or at a temperature between about 600 °C and about 1100 °C, or at a temperature between about 600 °C and about 1000 °C, or at a temperature between about 700 °C and about 1100 °C, or at a temperature between about 700 °C and about 1000 °C, or at a temperature between about 800 °C and about 1000 °C, or at a temperature between about 850 °C and about 1000 °C, or at a temperature between about 850 °C and about 950 °C. In some embodiments, the briquettes are pyrolysed at a temperature of about 900 °C.
Heat from the syngas produced is used to drive further pyrolysis. This may be achieved using a jacketed reactor whereby syngas produced in the reactor is extracted and fed into an outer gas jacket. Heat from the syngas is transferred from the outer jacket to the reaction chamber where pyrolysis takes place.
In one embodiment the first reactor comprises a reaction chamber and an outer gas jacket attached to at least a portion of the reaction chamber, the outer gas jacket comprising an inner wall and an outer wall defining a conduit, wherein syngas produced in the reactor is fed into the conduit so as to transfer heat to the reaction chamber to drive further pyrolysis.
The inner wall may have a thermal conductivity that is about 15 times to 25 times, or about 20 times larger than the thermal conductivity of the outer wall. This arrangement optimises heat transfer from the syngas to the reaction chamber. The inner wall may comprise, or be made of, a copper/ceramic material.
In step (iv) the syngas is subjected to a high-temperature water-gas shift reaction. The reaction may be carried out by mixing the syngas with superheated steam. The high- temperature water-gas shift reaction serves to enrich the amounts of hydrogen and carbon dioxide in the syngas stream at the expense of carbon monoxide.
The high-temperature water-gas shift reaction may be performed at a temperature between about 500 °C and about 1200 °C, or at a temperature between about 500 °C and about 1100 °C, or at a temperature between about 500 °C and about 1000 °C, or at a temperature between about 600 °C and about 900 °C, or at a temperature between about 600 °C and about 800 °C, or at a temperature between about 650 °C and about 750 °C.
In step (v) the syngas is scrubbed to remove contaminants including dioxins, heavy metals, furans, acid gases and particulates. Those skilled in the art will be familiar with methods for removing contaminants from a syngas stream.
Heat from the syngas is utilised by exchanging with water so as to provide superheated steam that is used in the high-temperature water-gas shift reaction in step (iv). Typically, the heat exchange is performed after scrubbing of the syngas. The heat exchange also provides a cooled syngas. The cooled syngas may have a temperature below about 300 °C, or below about 275 °C, or below about 250 °C, or between about 200 °C and about 300 °C, or about 250 °C. When pyrolysis is carried out in a jacketed reactor, the superheated steam generated in step (vi) may be injected at a plurality of spaced apart points along the conduit thereby enabling the high-temperature water-gas shift reaction. This arrangement allows additional heat produced in the high-temperature water-gas shift reaction to be transferred to the reaction chamber to drive further pyrolysis.
In step (vii) the cooled syngas is subjected to a low-temperature water-gas shift reaction in order to remove any residual carbon monoxide. The carbon monoxide may be present as a result of methane being reduced to carbon monoxide and hydrogen in the high-temperature water-gas shift reaction according to the following reaction:
CH4 + superheated steam — > CO + 3Hs
The low-temperature water-gas shift reaction may be performed at a temperature above about 250 °C, or above about 300 °C, or above about 350 °C, or between about 250 °C and about 500 °C, or between about 250 °C and about 400 °C, or between about 250 °C and about 350 °C.
The combination of high-temperature water-gas shift and low-temperature water-gas shift reactions optimises the forward direction of the following reaction:
CO + H2O - CO2 + H2
In step (viii) the carbon generated from pyrolysis is transferred to a second reactor and heated in the presence of oxygen-enriched air so as to provide a second gas mixture comprising carbon monoxide and nitrogen. The oxygen-enriched air may be obtained from the positive swing adsorption system. In some embodiments the oxygen-enriched air may have an oxygen content of at least about 23% (w/w), at least about 25% (w/w), at least about 27% (w/w), at least about 30% (w/w), at least about 35% (w/w), or at least about 50% (w/w).
Heat from the second gas mixture produced is used to heat further carbon in step (viii). This may be achieved using a jacketed reactor as described above, whereby gas produced in the reactor is extracted and fed into an outer gas jacket. Heat from the second gas mixture is transferred from the outer jacket to the reaction chamber where heating of the carbon takes place.
In one embodiment the second reactor comprises a reaction chamber and an outer gas jacket attached to at least a portion of the reaction chamber, the outer gas jacket comprising an inner wall and an outer wall defining a conduit, wherein gas produced in the second reactor is fed into the conduit so as to transfer heat to the reaction chamber to heat further carbon. As per the first reactor, the inner wall of the second may have a thermal conductivity that is about 15 times to 25 times, or about 20 times larger than the thermal conductivity of the outer wall. This arrangement optimises heat transfer from the syngas to the reaction chamber. The inner wall may comprise, or be made of, a copper/ceramic material.
In step (ix) the second gas mixture is subjected to a high-temperature water-gas shift reaction. The reaction may be carried out by mixing the syngas with superheated steam. Again, the high-temperature water-gas shift reaction serves to enrich the amounts of hydrogen and carbon dioxide in the second gas mixture at the expense of carbon monoxide.
The high-temperature water-gas shift reaction in step (ix) may be performed at the temperatures described above in connection with step (iv).
Heat from the second gas mixture is utilised by exchanging with water so as to provide superheated steam that is used in the high-temperature water-gas shift reaction in step (ix). The heat exchange also provides a cooled second gas mixture. The cooled second gas mixture may have a temperature below about 300 °C, or below about 275 °C, or between about 250 °C, or between about 200 °C and about 300 °C, or about 250 °C.
When step (viii) is carried out in a jacketed reactor, the superheated steam generated in step (x) may be injected at a plurality of spaced apart points along the outer gas jacket thereby enabling the high-temperature water-gas shift reaction. This arrangement allows additional heat produced in the high-temperature water-gas shift reaction to be transferred to the reaction chamber to heat further carbon.
In step (xi) the cooled second gas mixture is subjected to a low-temperature water-gas shift reaction. This reaction serves to further enrich the amounts of carbon dioxide and hydrogen in the second gas mixture at the expense of carbon monoxide so as to provide the third gas mixture. The third gas mixture may be free, or substantially free, of carbon monoxide. The low-temperature water-gas shift reaction may be performed at a temperature above about 250 °C, or above about 300 °C, or about 350 °C, or between about 250 °C and about 500 °C, or between about 250 °C and about 400 °C.
In step (xii) the carbon generated following step (viii) is transferred to a third reactor and heated in the presence of oxygen-enriched air so as to provide a fourth gas mixture comprising carbon monoxide and nitrogen. The oxygen-enriched air may be obtained from the positive swing adsorption system. Steps (ix) to (xi) are then repeated as described above as steps (xiii) to (xv). Following steps (vii), (xi) and (xv) the carbon dioxide, hydrogen and nitrogen are separated. Separation may be achieved using a positive swing adsorption system. In some embodiments, the gas mixtures obtained in steps (vii), (xi) and (xv) may be combined prior to step (xvi).
The first, second and third reactors may be vertically stacked such that step (iii) is carried out above step (viii) which is carried out above step (xii). In this arrangement, following step (iii) the carbon is dropped into the second reactor and following step (viii) the carbon is dropped into the third reactor.
By varying the dwell time of the briquettes and carbon in each reactor the amounts of carbon and hydrogen produced may be controlled. The dwell time may be varied by varying the rate of rotation of the briquettes and carbon. It has been found that increasing the rate of rotation maximises the amount of carbon produced and minimises the amount of hydrogen produced. Conversely, decreasing the rate of rotation minimises the amount of carbon produced and maximises the amount of hydrogen produced.
In some embodiments, the dwell time calculated from commencement of pyrolsis of a briquette to removal of carbon from the third reactor may be between about 60 minutes and about 120 minutes, or between about 70 minutes and about 110 minutes, or between about 80 minutes and about 100 minutes, or about 90 minutes.
Figure 1 shows a schematic diagram of a process in accordance with one embodiment of the invention. Jacketed pyrolysis reactor 1 is provided comprising briquette 2. On heating, briquette 2 is pyrolysed liberating syngas 3 which is extracted and passes through the conduit 4 of the jacketed reactor 1. Superheated steam 6 is injected into the conduit 4 at a plurality of spaced apart points 8, 9 and 10 along the conduit 4 where mixing with syngas 3 occurs thereby enabling the high-temperature water-gas shift reaction. Following the high-temperature water-gas shift reaction syngas 3 is scrubbed in scrubber 5 to remove contaminants. The syngas 3 is then passed through heat exchanger 7 so as to provide superheated steam 6 which is piped to points 8, 9 and 10 for injection into the conduit 4, and cooled syngas 11. The cooled syngas 11 is then subjected to a low temperature water-gas shift reaction 12 to provide the first gas mixture 13, which comprises carbon dioxide, nitrogen and hydrogen.
Following pyrolysis, the resulting carbon 15 is dropped into jacketed reactor 14 where heating in oxygen-rich air is performed. On heating, carbon 15 liberates the second gas mixture 16 which is extracted and passes through the conduit 17 of the jacketed reactor 14. Superheated steam 19 is injected into the conduit 17 at a plurality of spaced part points 20, 21 and 22 along the conduit 17 where mixing with the second gas mixture 16 occurs thereby enabling the high-temperature water-gas shift reaction. The second gas mixture 16 is then passed through heat exchanger 18 so as to provide superheated steam 19 which is piped to points 20, 21 and 22, for injection into the conduit 17, and the cooled second gas mixture 23. The cooled second gas mixture 23 is then subjected to a low temperature water-gas shift reaction 24 to provide the third gas mixture 25, which comprises carbon dioxide, nitrogen and hydrogen.
The resulting carbon 27 is dropped into jacketed reactor 26 where heating in oxygenrich air is performed. On heating, carbon 27 liberates the fourth gas mixture 28 which is extracted and passes through the conduit 29 of the jacketed reactor 26. Superheated steam 31 is injected into the conduit 29 at a plurality of spaced part points 32, 33 and 34 along the conduit 29 where mixing with the fourth gas mixture 28 occurs thereby enabling the high-temperature water-gas shift reaction. The fourth gas mixture 28 is then passed through heat exchanger 30 so as to provide superheated steam 31 which is piped to points 32, 33 and 34, for injection into the conduit 29, and the cooled fourth gas mixture 35. The cooled second gas mixture 35 is then subjected to a low temperature water-gas shift reaction 36 to provide the fifth gas mixture 37, which comprises carbon dioxide, nitrogen and hydrogen.
The first gas mixture 13, third gas mixture 25 and fifth gas mixture 37 are then combined into a single gas mixture 38. The single gas mixture 38 is passed through PSA 39 which separates the single gas mixture 38 into a gas stream comprising hydrogen gas and a gas stream comprising nitrogen gas and carbon dioxide gas. A portion of the hydrogen gas is directed to a single oxide fuel cell 40 for generation of base load electricity (BLE). The gas stream comprising nitrogen gas and carbon dioxide gas is passed through PSA 41 which separates the mixture into nitrogen and gas and carbon dioxide gas. A portion of the hydrogen gas is reacted with the nitrogen gas to give ammonia (NH3). A portion of the ammonia is reacted with the carbon dioxide to provide urea. Carbon 42 (in the form of one or more of biochar, activated carbon and carbon black) is recovered from the jacketed reactor 26.
The citation of any reference herein should not be construed as an admission that such reference is available as prior art to the present application. Further, the reference in this specification to any prior publication (or information derived from it), or to any matter which is known, is not, and should not be taken as an acknowledgement or admission or any form of suggestion that that prior publication (or information derived from it) or known matter forms part of the common general knowledge in the field of endevour to which this specification relates.
Those skilled in the art will appreciate that the invention described herein is susceptible to variations and modifications other than those specifically described. It is to be understood that the invention includes all such variations and modifications.

Claims

CLAIMS:
1 . A continuous recycling process comprising:
(i) providing a homogenised waste material;
(ii) forming the homogenised waste material into briquettes having a consistent size and density;
(iii) feeding the briquettes into a first reactor and pyrolysing the briquettes so as to provide carbon and syngas, wherein heat from the syngas is used to drive further pyrolysis;
(iv) subjecting the syngas to a high-temperature water-gas shift reaction so as to enrich the hydrogen content of the syngas;
(v) scrubbing the syngas to remove contaminants;
(vi) exchanging heat from the syngas with water so as to provide superheated steam which is used in the high-temperature water-gas shift reaction in step (iv) and a cooled syngas;
(vii) subjecting the cooled syngas to a low-temperature water-gas shift reaction so as to provide a first gas mixture comprising hydrogen, nitrogen and carbon dioxide;
(viii) transferring the carbon obtained following step (iii) into a second reactor and further heating the carbon in the presence of oxygen-enriched air so as to provide a second gas mixture comprising carbon monoxide and nitrogen, wherein heat from the second gas mixture is used to heat further carbon in step (viii);
(ix) subjecting the second gas mixture to a high-temperature water-gas shift reaction so as to enrich the hydrogen content of the second gas mixture;
(x) exchanging heat from the second gas mixture with water so as to provide superheated steam which is used in the high-temperature water-gas shift reaction in step (ix) and a cooled second gas mixture;
(xi) subjecting the cooled second gas mixture to a low-temperature water-gas shift reaction so as to provide a third gas mixture comprising hydrogen, nitrogen and carbon dioxide;
(xii) transferring the carbon obtained following step (viii) into a third reactor and further heating the carbon in the presence of oxygen-enriched air so as to provide a fourth gas mixture comprising carbon monoxide and nitrogen, wherein heat from the fourth gas mixture is used to heat further carbon in step (xii); (xiii) subjecting the fourth gas mixture to a high-temperature water-gas shift reaction so as to enrich the hydrogen content of the fourth gas mixture;
(xiv) exchanging heat from the fourth gas mixture with water so as to provide superheated steam which is used in the high-temperature water-gas shift reaction in step (xiii) and a cooled fourth gas mixture;
(xv) subjecting the cooled fourth gas mixture to a low-temperature water-gas shift reaction so as to provide a fifth gas mixture comprising hydrogen, nitrogen and carbon dioxide;
(xvi) separating the hydrogen, carbon dioxide and nitrogen in the first, third and fifth gas mixtures, wherein at least a portion of the hydrogen separated is used to produce base load electricity, at least a portion of the nitrogen separated is used to produce ammonia and at least a portion of the carbon dioxide separated is used to produce urea; and,
(xvii) recovering the carbon obtained following step (xii).
2. The process of claim 1 , wherein the waste material comprises a carbonaceous material.
3. The process of claim 2, wherein the carbonaceous material comprises plastic or a mixture of different plastics.
4. The process of claim 2, wherein the carbonaceous material comprises tyres or coal fines.
5. The process of claim 2, wherein the carbonaceous material comprises biomass.
6. The process of claim 5, wherein the biomass is palm oil waste or coconut fibre.
7. The process of claim 2, wherein the carbonaceous material comprises municipal waste.
8. The process of any one of claims 1 to 7, wherein the briquettes are produced by extrusion.
9. The process of any one of claims 1 to 8, wherein the briquettes have a density between about 500 kg/m3 and about 1000 kg/m3, or between about 600 kg/m3 and about 900 kg/m3, or between about 650 kg/m3 and about 750 kg/m3.
10. The process of any one of claims 1 to 9, wherein the briquettes further comprise one or more of: sewage, wood pulp or fines.
1 1 . The process of any one of claims 1 to 10, wherein the briquettes are pyrolysed at a temperature between about 500 °C and about 1200 °C, or between about 600 °C and 18 about 1100 °C, or between about 700 °C and about 1100 °C, or between about 800 °C and about 1000 °C, or about 900 °C.
12. The process of any one of claims 1 to 11 , wherein the high-temperature water- gas shift reactions in steps (iv), (ix) and (xiii) are performed at a temperature between about 500 °C and about 1200 °C, or at a temperature between about 500 °C and about 1100 °C, or at a temperature between about 500 °C and about 1000 °C, or at a temperature between about 600 °C and about 900 °C, or at a temperature between about 600 °C and about 800 °C, or at a temperature between about 650 °C and about 750 °C.
13. The process of any one of claims 1 to 12, wherein exchanging heat from the syngas with water so as to provide superheated steam may be performed after step (v).
14. The process of any one of claims 1 to 13, wherein in step (v) the syngas is scrubbed to remove one or more of the following contaminants: dioxins, heavy metals, furans and acid gases.
15. The process of any one of claims 1 to 14, wherein the cooled syngas, cooled second gas mixture and cooled fourth gas mixture have a temperature below about 300 °C, or below about 275 °C, or below about 250 °C, or between about 200 °C and about 300 °C, or about 250 °C.
16. The process of any one of claims 1 to 15, wherein the low-temperature water- gas shift reaction in step (vii) is performed by mixing the cooled syngas with superheated steam.
17. The process of any one of claims 1 to 16, wherein the low-temperature water- gas shift reactions in steps (xi) and (xv) are performed by mixing the cooled second gas mixture and the cooled fourth gas mixture respectively with superheated steam.
18. The process of any one of claims 1 to 17, wherein the low-temperature water- gas shift reaction in steps (vii), (xi) and (xv) is performed at a temperature above about 250 °C, or above about 300 °C, or above about 350 °C, or between about 250 °C and about 500 °C, or between about 250 °C and about 400 °C, or between about 250 °C and about 350 °C.
19. The process of any one of claims 1 to 18, wherein in steps (viii) and (xii) the carbon is heated at a temperature between about 500 °C and about 1200 °C, or between about 700 °C and about 1200 °C, or between about 600 °C and about 1100 °C, or between about 700 °C and about 1100 °C, or between about 800 °C and about 1000 °C, or about 900 °C. 19
20. The process of any one of claims 1 to 19, wherein the oxygen-enriched air may have an oxygen content of at least about 23% (w/w), at least about 25% (w/w), at least about 27% (w/w), at least about 30% (w/w), at least about 35% (w/w), or at least about 50% (w/w).
21. The process of any one of claims 1 to 20, wherein the carbon dioxide, hydrogen and nitrogen are separated using a positive swing adsorption system.
22. The process of any one of claims 1 to 21 , wherein the first, third and fifth gas mixtures are combined prior to step (xvi).
23. The process of any one of claims 1 to 22, wherein the first, second and third reactors are vertically stacked such that step (iii) is carried out above step (viii) which is carried out above step (xii).
24. The process of any one of claims 1 to 23, wherein in step (iii), the briquettes are rotated during heating.
25. The process of any one of claims 1 to 24, wherein in steps (viii) and (xii) the carbon is rotated during heating.
26. The process of any one of claims 1 to 25, wherein the first reactor comprises a reaction chamber and an outer gas jacket attached to at least a portion of the reaction chamber, the outer gas jacket comprising an inner wall and an outer wall defining a conduit, wherein syngas produced in the reactor is fed into the conduit so as to transfer heat to the reaction chamber to drive further pyrolysis.
27. The process of any one of claims 1 to 26, wherein the second reactor comprises a reaction chamber and an outer gas jacket attached to at least a portion of the reaction chamber, the outer gas jacket comprising an inner wall and an outer wall defining a conduit, wherein the gas mixture produced in the second reactor is fed into the conduit so as to transfer heat to the reaction chamber to heat further carbon.
28. The process of any one of claims 1 to 27, wherein the third reactor comprises a reaction chamber and an outer gas jacket attached to at least a portion of the reaction chamber, the outer gas jacket comprising an inner wall and an outer wall defining a conduit, wherein the gas mixture produced in the third reactor is fed into the conduit so as to transfer heat to the reaction chamber to heat further carbon.
29. The process of any one of claims 26 to 28, wherein in the first, second and third reactors the inner wall has a thermal conductivity that is about 15 times to about 25 times, or about 20 times, larger than the thermal conductivity of the outer wall. 20
30. The process of claim 29, wherein the thermal conductivity of the inner wall is between about 250 W/(m.K) and about 350 W/(m.K), or between about 300 W/(m.K) and about 350 W/(m.K).
31. The process of any one of claims 26 to 30, wherein the inner wall comprises, or is made of, a copper/ceramic material.
32. The process of any one of claims 26 to 31 , wherein the superheated steam generated in steps (vi), (x) and (xiv) is injected into the conduit of each of the first, second and third reactors at a plurality of spaced apart points thereby enabling the high- termperature water-gas shift reaction.
33. The process of any one of claims 1 to 32, wherein carbon generated in steps (iii), (viii) and (xii) is one or more of: biochar, carbon black or activated carbon.
34. The process of any one of claims 1 to 33, wherein time elapsed from commencement of pyrolsis of a briquette to removal of carbon produced from the briquette from the third reactor may be between about 60 minutes and about 120 minutes, or between about 70 minutes and about 110 minutes, or between about 80 minutes and about 100 minutes, or about 90 minutes.
35. The process of any one of claims 1 to 34, wherein the first, third and fifth gas mixtures may be free, or substantially free, of carbon monoxide.
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