GB2565831A - Apparatus for depolymerisation of waste plastics - Google Patents

Apparatus for depolymerisation of waste plastics Download PDF

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Publication number
GB2565831A
GB2565831A GB1713664.9A GB201713664A GB2565831A GB 2565831 A GB2565831 A GB 2565831A GB 201713664 A GB201713664 A GB 201713664A GB 2565831 A GB2565831 A GB 2565831A
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United Kingdom
Prior art keywords
zone
screw
extrusion barrel
water
barrel
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GB1713664.9A
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GB201713664D0 (en
Inventor
Windsor Hamilton Stephen
Scott Dawson Gregory
Graham Allan George
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Individual
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Individual
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Publication of GB201713664D0 publication Critical patent/GB201713664D0/en
Priority to PCT/EP2018/059782 priority Critical patent/WO2018197269A1/en
Publication of GB2565831A publication Critical patent/GB2565831A/en
Withdrawn legal-status Critical Current

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    • C—CHEMISTRY; METALLURGY
    • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
    • C08J—WORKING-UP; GENERAL PROCESSES OF COMPOUNDING; AFTER-TREATMENT NOT COVERED BY SUBCLASSES C08B, C08C, C08F, C08G or C08H
    • C08J11/00—Recovery or working-up of waste materials
    • C08J11/04—Recovery or working-up of waste materials of polymers
    • C08J11/10—Recovery or working-up of waste materials of polymers by chemically breaking down the molecular chains of polymers or breaking of crosslinks, e.g. devulcanisation
    • C08J11/14—Recovery or working-up of waste materials of polymers by chemically breaking down the molecular chains of polymers or breaking of crosslinks, e.g. devulcanisation by treatment with steam or water
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
    • B01J19/00—Chemical, physical or physico-chemical processes in general; Their relevant apparatus
    • B01J19/18—Stationary reactors having moving elements inside
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
    • B01J3/00—Processes of utilising sub-atmospheric or super-atmospheric pressure to effect chemical or physical change of matter; Apparatus therefor
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
    • B01J3/00—Processes of utilising sub-atmospheric or super-atmospheric pressure to effect chemical or physical change of matter; Apparatus therefor
    • B01J3/008—Processes carried out under supercritical conditions
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
    • B01J8/00—Chemical or physical processes in general, conducted in the presence of fluids and solid particles; Apparatus for such processes
    • B01J8/18—Chemical or physical processes in general, conducted in the presence of fluids and solid particles; Apparatus for such processes with fluidised particles
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
    • B01J8/00—Chemical or physical processes in general, conducted in the presence of fluids and solid particles; Apparatus for such processes
    • B01J8/18—Chemical or physical processes in general, conducted in the presence of fluids and solid particles; Apparatus for such processes with fluidised particles
    • B01J8/20—Chemical or physical processes in general, conducted in the presence of fluids and solid particles; Apparatus for such processes with fluidised particles with liquid as a fluidising medium
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B09—DISPOSAL OF SOLID WASTE; RECLAMATION OF CONTAMINATED SOIL
    • B09B—DISPOSAL OF SOLID WASTE NOT OTHERWISE PROVIDED FOR
    • B09B3/00—Destroying solid waste or transforming solid waste into something useful or harmless
    • B09B3/40—Destroying solid waste or transforming solid waste into something useful or harmless involving thermal treatment, e.g. evaporation
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B09—DISPOSAL OF SOLID WASTE; RECLAMATION OF CONTAMINATED SOIL
    • B09B—DISPOSAL OF SOLID WASTE NOT OTHERWISE PROVIDED FOR
    • B09B3/00—Destroying solid waste or transforming solid waste into something useful or harmless
    • B09B3/40—Destroying solid waste or transforming solid waste into something useful or harmless involving thermal treatment, e.g. evaporation
    • B09B3/45—Steam treatment, e.g. supercritical water gasification or oxidation
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B29—WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
    • B29B—PREPARATION OR PRETREATMENT OF THE MATERIAL TO BE SHAPED; MAKING GRANULES OR PREFORMS; RECOVERY OF PLASTICS OR OTHER CONSTITUENTS OF WASTE MATERIAL CONTAINING PLASTICS
    • B29B17/00—Recovery of plastics or other constituents of waste material containing plastics
    • B29B17/04—Disintegrating plastics, e.g. by milling
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B29—WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
    • B29C—SHAPING OR JOINING OF PLASTICS; SHAPING OF MATERIAL IN A PLASTIC STATE, NOT OTHERWISE PROVIDED FOR; AFTER-TREATMENT OF THE SHAPED PRODUCTS, e.g. REPAIRING
    • B29C48/00—Extrusion moulding, i.e. expressing the moulding material through a die or nozzle which imparts the desired form; Apparatus therefor
    • B29C48/25—Component parts, details or accessories; Auxiliary operations
    • B29C48/275—Recovery or reuse of energy or materials
    • B29C48/276—Recovery or reuse of energy or materials of energy
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B29—WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
    • B29C—SHAPING OR JOINING OF PLASTICS; SHAPING OF MATERIAL IN A PLASTIC STATE, NOT OTHERWISE PROVIDED FOR; AFTER-TREATMENT OF THE SHAPED PRODUCTS, e.g. REPAIRING
    • B29C48/00—Extrusion moulding, i.e. expressing the moulding material through a die or nozzle which imparts the desired form; Apparatus therefor
    • B29C48/25—Component parts, details or accessories; Auxiliary operations
    • B29C48/36—Means for plasticising or homogenising the moulding material or forcing it through the nozzle or die
    • B29C48/50—Details of extruders
    • B29C48/505—Screws
    • B29C48/53—Screws having a varying channel depth, e.g. varying the diameter of the longitudinal screw trunk
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B29—WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
    • B29C—SHAPING OR JOINING OF PLASTICS; SHAPING OF MATERIAL IN A PLASTIC STATE, NOT OTHERWISE PROVIDED FOR; AFTER-TREATMENT OF THE SHAPED PRODUCTS, e.g. REPAIRING
    • B29C48/00—Extrusion moulding, i.e. expressing the moulding material through a die or nozzle which imparts the desired form; Apparatus therefor
    • B29C48/25—Component parts, details or accessories; Auxiliary operations
    • B29C48/92—Measuring, controlling or regulating
    • C—CHEMISTRY; METALLURGY
    • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
    • C08J—WORKING-UP; GENERAL PROCESSES OF COMPOUNDING; AFTER-TREATMENT NOT COVERED BY SUBCLASSES C08B, C08C, C08F, C08G or C08H
    • C08J11/00—Recovery or working-up of waste materials
    • C08J11/04—Recovery or working-up of waste materials of polymers
    • C08J11/10—Recovery or working-up of waste materials of polymers by chemically breaking down the molecular chains of polymers or breaking of crosslinks, e.g. devulcanisation
    • C—CHEMISTRY; METALLURGY
    • C10—PETROLEUM, GAS OR COKE INDUSTRIES; TECHNICAL GASES CONTAINING CARBON MONOXIDE; FUELS; LUBRICANTS; PEAT
    • C10B—DESTRUCTIVE DISTILLATION OF CARBONACEOUS MATERIALS FOR PRODUCTION OF GAS, COKE, TAR, OR SIMILAR MATERIALS
    • C10B53/00—Destructive distillation, specially adapted for particular solid raw materials or solid raw materials in special form
    • C10B53/07—Destructive distillation, specially adapted for particular solid raw materials or solid raw materials in special form of solid raw materials consisting of synthetic polymeric materials, e.g. tyres
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B29—WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
    • B29B—PREPARATION OR PRETREATMENT OF THE MATERIAL TO BE SHAPED; MAKING GRANULES OR PREFORMS; RECOVERY OF PLASTICS OR OTHER CONSTITUENTS OF WASTE MATERIAL CONTAINING PLASTICS
    • B29B17/00—Recovery of plastics or other constituents of waste material containing plastics
    • B29B17/04—Disintegrating plastics, e.g. by milling
    • B29B2017/0424—Specific disintegrating techniques; devices therefor
    • B29B2017/0496—Pyrolysing the materials
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02P—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN THE PRODUCTION OR PROCESSING OF GOODS
    • Y02P20/00—Technologies relating to chemical industry
    • Y02P20/50—Improvements relating to the production of bulk chemicals
    • Y02P20/54—Improvements relating to the production of bulk chemicals using solvents, e.g. supercritical solvents or ionic liquids
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02P—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN THE PRODUCTION OR PROCESSING OF GOODS
    • Y02P70/00—Climate change mitigation technologies in the production process for final industrial or consumer products
    • Y02P70/10—Greenhouse gas [GHG] capture, material saving, heat recovery or other energy efficient measures, e.g. motor control, characterised by manufacturing processes, e.g. for rolling metal or metal working
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02W—CLIMATE CHANGE MITIGATION TECHNOLOGIES RELATED TO WASTEWATER TREATMENT OR WASTE MANAGEMENT
    • Y02W30/00—Technologies for solid waste management
    • Y02W30/50—Reuse, recycling or recovery technologies
    • Y02W30/62—Plastics recycling; Rubber recycling

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  • Chemical & Material Sciences (AREA)
  • Engineering & Computer Science (AREA)
  • Organic Chemistry (AREA)
  • Chemical Kinetics & Catalysis (AREA)
  • Mechanical Engineering (AREA)
  • Environmental & Geological Engineering (AREA)
  • Oil, Petroleum & Natural Gas (AREA)
  • Combustion & Propulsion (AREA)
  • Physics & Mathematics (AREA)
  • Thermal Sciences (AREA)
  • Life Sciences & Earth Sciences (AREA)
  • Sustainable Development (AREA)
  • Health & Medical Sciences (AREA)
  • Medicinal Chemistry (AREA)
  • Polymers & Plastics (AREA)
  • Materials Engineering (AREA)
  • Separation, Recovery Or Treatment Of Waste Materials Containing Plastics (AREA)
  • Processing Of Solid Wastes (AREA)

Abstract

An apparatus for the depolymerisation of waste plastics comprising an extrusion barrel, at least one screw rotatably mounted within the extrusion barrel, a drive means for driving said at least one screw, a feed device for feeding waste plastics into an inlet region of said extrusion barrel, and heating means for heating at least a portion of said barrel, wherein the pitch and/or the root diameter of said at least one screw is adapted to define a feed zone adjacent said feed device adapted to feed material into the extrusion barrel, a decompression water injection zone downstream of said feed zone, whereby water can be added into the barrel via a water inlet at substantially ambient/atmospheric pressure, a compression zone downstream of said decompression water injection zone, wherein a mixture of molten waste plastic and water is heated and compressed to supercritical conditions, and a reaction zone downstream of said compression zone, wherein the waste plastics are broken down into hydrocarbon fuel products, before leaving the extruder via a discharge port at a discharge end thereof.

Description

Apparatus for depolymerisation of waste plastics
FIELD OF THE INVENTION
This invention relates to an apparatus for the depolymerisation of waste plastics and in particular an apparatus for converting waste plastics into hydrocarbon based fuels.
BACKGROUND OF THE INVENTION
The prevalence of plastic materials in modem society has led to a major problem in relation to waste plastics. Such materials are generally not biodegradable and therefore major environmental problems result from their disposal. There have been a number of attempts to create a commercially viable method for extracting fuel from waste plastics by means of depolymerisation processes.
Anhydrous pyrolysis can be used to produce liquid fuel similar to diesel from plastic waste. However, pyrolysis requires a lot of heat energy and generally comprises a batch process.
Many conventional solvents do not sufficiently dissolve cross-linked polymers to allow efficient depolymerisation. Supercritical water provides an alternative benign solvent for this application. Supercritical water oxidation and thermal degradation under supercritical water conditions provide a means to break down waste plastics into organic compounds that can then be recovered as a hydrocarbon based fuel.
US 8,980,143 discloses an apparatus for depolymerising waste plastic using supercritical water, wherein hot compressed water is injected into a reaction zone containing waste plastic. The waste plastic is extruded into the reaction zone at very high temperature and pressure. The resulting mixture is further heated in the reaction zone to conditions at or above supercritical. A spear tube is used to try and maintain the pressure within the reaction zone while permitting expulsion of the reaction products into an expansion and separation chamber. With this arrangement it is extremely difficult to control the pressure within the reaction zone while ensuring that the waste material spends sufficient time within the reaction zone for the required depolymerisation to take place.
SUMMARY OF THE INVENTION
According to a first aspect of the present invention there is provided an apparatus for the depolymerisation of waste plastics comprising an extrusion barrel, at least one screw rotatably mounted within the extrusion barrel, a drive means for driving said at least one screw, a feed device for feeding waste plastics into an inlet region of said extrusion barrel, and heating means for heating at least a portion of said barrel, wherein the pitch and/or the root diameter of said at least one screw is adapted to define a feed zone adjacent said feed device adapted to feed material into the extrusion barrel, a decompression water injection zone downstream of said feed zone, whereby water can be added into the barrel via a water inlet at substantially ambient/atmospheric pressure, a compression zone downstream of said decompression water injection zone, wherein a mixture of molten waste plastic and water is heated and compressed to supercritical conditions, and a reaction zone downstream of said compression zone, wherein the waste plastics are broken down into hydrocarbon fuel products, before leaving the extruder via a discharge port at a discharge end thereof.
In a preferred embodiment the different zones of the extruder are defined by step changes in the root diameter of the at least one screw. The at least one screw may have a first constant root diameter in said the feed zone, a stepped reduction in the root diameter defining the decompression water injection zone, and an increasing root diameter in said compression zone to increase the pressure of the mixture of molten waste plastic and water therein. The root diameter of the at least one screw preferably remains substantially constant in the reaction zone.
Preferably the mixture is compressed to a pressure of at least 217.7 atmospheres in the compression zone. More preferably the mixture is heated to a temperature of at least 374.4° C in the compression zone and/or reaction zone, thereby achieving and maintaining supercritical conditions.
The speed of the drive means and the pitch and/or root diameter of the screw in the reaction zone may be selected such that the mixture remains in the reaction zone for sufficient time for the waste plastics to be converted to one or more hydrocarbon fuels. The speed of the drive means and the pitch and/or root diameter of the screw in the reaction zone may be selected such that the mixture remains in the reaction zone for at least 10 second before leaving the extruder.
According to a further aspect of the present invention there is provided a method of depolymerising waste plastics comprising the steps of feeding waste plastic into a feed zone of an the extrusion barrel having at least one extrusion screw driven to rotate therein, at least partially melting the waste plastic and conveying the waste plastic into a decompression water injection zone of the extrusion barrel, adding water into decompression water injection zone of the extrusion barrel at substantially ambient pressure, mixing said water into the molten waste plastic in the decompression water injection zone before compressing and further heating the mixture to supercritical conditions in a compression zone of the extrusion barrel and passing the material under supercritical conditions through a reaction zone of the extrusion barrel, while further heating the extrusion barrel, so that the waste plastics are converted to hydrocarbon fuel products within the reaction zone of the extrusion barrel before exhausting the extruder via an exit port of the extrusion barrel.
The different zones of the extruder are preferably defined by step changes in the root diameter of the at least one screw within the extrusion barrel.
The method may comprise the steps of heating the waste plastic and water mixture to a temperature of at least 374.4° C in the compression zone and/or reaction zone and preferably increasing the pressure of the waste plastic and water mixture to a pressure of at least 217.7 atmospheres in the compression zone to achieve and maintain supercritical conditions in at least the reaction zone.
Preferably the method comprises maintaining the material in the reaction zone for sufficient time for the waste plastics to be converted into one or more hydrocarbon fuel products. In one embodiment the method may comprise maintaining the material in the reaction zone for at least ten seconds.
BRIEF DESCRIPTION OF THE DRAWINGS
An apparatus for depolymerisation of waste plastics in accordance with an embodiment of the present invention will now be described, by way of example only, with reference to the accompanying drawing, in which :Figure 1 is a longitudinal sectional view through an apparatus for depolymerisation of waste plastics in accordance with an embodiment of the present invention.
DETAILED DESCRIPTION OF THE DRAWINGS
The present invention provides a novel approach for converting waste plastics into a multitude of hydrocarbon based fuels.
As illustrated in Figure 1, an apparatus in accordance with the present invention utilises a constant feed extruder having a screw 4 rotatably mounted within a barrel 2 and having a drive means (not shown). While the use of a single screw it is described and shown in the drawings, it is envisaged that a dual screw extruder may be utilised.
The screw 4 comprises flights 6 extending from a screw core , the shape of the flights and the diameter of the core defining a specifically designed screw profile, said screw profile defining a feed zone “A” adjacent a feed hopper 8 feeding an inlet of the extruder barrel 2, a decompression water injection zone “B”, whereby water “W” can be added, via a water inlet 10 in the extruder barrel, at substantially ambient/atmospheric pressure, a compression zone “C”, wherein the mixture of molten waste plastic and water is heated and compressed to supercritical conditions, and a reaction zone “D”, wherein the waste plastics are broken down into hydrocarbon fuel products by the action of supercritical water, before leaving the extruder via an exit port 12.
The extruder includes heating means 14 for heating the barrel of the extruder, thereby heating material within the abovementioned zones of the extruder, in particular in the compression zone “C” and the reaction zone “D”. The heating means 14 may comprise a heat exchanger extending circumferentially around the barrel 2 of the extruder or being located within the outer wall of the barrel.
This apparatus provides an economical and continuous (as opposed to a batch process) conversion of waste plastics (and optionally other biomass) into a hydrocarbon fuel product.
The different zones of the extruder are preferably defined by step changes in the root diameter of the extruder screw 4. A first constant root diameter 16 defines the feed zone. A region following a stepped reduction in the root diameter 18 defines the decompression water injection zone “B”, wherein pressure is reduced to substantially atmospheric as water in injected into the extruder. In the compression zone “C”, the root diameter gradually increases to compress the mixture of molten waste plastic and water as the mixture is heated, achieving supercritical conditions as or before the mixture enter the reaction zone “D”, wherein the root diameter 22 of the screw 4 remains substantially constant.
Waste plastic first enters the extruder’s feed zone “A”, wherein it first makes contact with the extruder screw 4. Water is injected in a metered quantity at substantially atmospheric pressure via the water inlet 10 to mix with the at least partially molten waste plastic in the decompression water injection zone “B”. The latter eliminates the need to introduce high temperature water at high pressure, reducing energy consumption.
From the decompression water injection zone “B”, the molten plastic/water slurry enters the compression zone “C”, wherein which the screw core diameter 20 increases, increasing the pressure of the mixture to in excess of 217.7 atmospheres and increasing temperature to in excess of 374.4° C, to achieve supercritical conditions.
At this point, the melting and compression zone transitions into the metering zone whereas the extruder screw or screws maintain a flat core profile 22, allowing for the pressure to be maintained above 217.7 atmospheres while the circumferential heating means 14 maintain a temperature exceeding 374.4° C.
Also of importance is the fact that the screw flight pitch is designed in conjunction with and to accommodate the extruder screw speed to allow for sufficient reaction time within the reaction zone “D” to allow the supercritical conversion to take place (preferably around 10 seconds).
The process is tailored around the working of a single or twin screw extruder, specifically modified to deliver the optimum conditions for depolymerisation of the waste plastics are they pass through the extruder.
In use, waste plastic is fed into the extruder via the feed hopper 8, wherein it is heated and mixed prior to for water injection. The waste plastic is preferably heated to its molten state in the feed zone “A” before it enters the decompression water injection zone “B”, wherein water is added at substantially ambient pressure. The mixture is then passed through the compression zone “C”, wherein it is further heated and pressurized until the slurry mix reaches a supercritical state. From there it passes through the reaction zone “D”, maintaining supercritical pressure and temperature. The extended reaction zone “D” ensures full product conversion before exhausting the extruder via the exit port 12.
A heat exchanger may be provided downstream of the exit port 12 of the extruder for recovering heat energy before the product enters a separation tank.
The invention is not limited to the embodiment(s) described herein but can be amended or modified without departing from the scope of the present invention.

Claims (13)

1. An apparatus for the depolymerisation of waste plastics comprising an extrusion barrel, at least one screw rotatably mounted within the extrusion barrel, a drive means for driving said at least one screw, a feed device for feeding waste plastics into an inlet region of said extrusion barrel, and heating means for heating at least a portion of said barrel, wherein the pitch and/or the root diameter of said at least one screw is adapted to define a feed zone adjacent said feed device adapted to feed material into the extrusion barrel, a decompression water injection zone downstream of said feed zone, whereby water can be added into the barrel via a water inlet at substantially ambient/atmospheric pressure, a compression zone downstream of said decompression water injection zone, wherein a mixture of molten waste plastic and water is heated and compressed to supercritical conditions, and a reaction zone downstream of said compression zone, wherein the waste plastics are broken down into hydrocarbon fuel products, before leaving the extruder via a discharge port at a discharge end thereof.
2. An apparatus as claimed in claim 1, wherein the different zones of the extruder are defined by step changes in the root diameter of the at least one screw.
3. An apparatus as claimed in claim 2, wherein the at least one screw has a first constant root diameter in said the feed zone, a stepped reduction in the root diameter defining the decompression water injection zone, and an increasing root diameter in said compression zone to increase the pressure of the mixture of molten waste plastic and water therein.
4. An apparatus as claimed in claim 3, wherein the root diameter of the at least one screw remains substantially constant in the reaction zone.
5. An apparatus as claimed in any preceding claim, wherein the mixture is compressed to a pressure of at least 217.7 atmospheres in the compression zone.
6. An apparatus as claimed in any preceding claim, wherein the mixture is heated to a temperature of at least 374.4° C in the compression zone and/or reaction zone.
7. An apparatus as claimed in any preceding claim, wherein the speed of the drive means and the pitch and/or root diameter of the screw in the reaction zone are selected such that the mixture remains in the reaction zone for at least 10 second before leaving the extruder.
8. A method of depolymerising waste plastics comprising the steps of feeding waste plastic into a feed zone of an the extrusion barrel having at least one extrusion screw driven to rotate therein, at least partially melting the waste plastic and conveying the waste plastic into a decompression water injection zone of the extrusion barrel, adding water into decompression water injection zone of the extrusion barrel at substantially ambient pressure, mixing said water into the molten waste plastic in the decompression water injection zone before compressing and further heating the mixture to supercritical conditions in a compression zone of the extrusion barrel and passing the material under supercritical conditions through a reaction zone of the extrusion barrel, while further heating the extrusion barrel, so that the waste plastics are converted to hydrocarbon fuel products within the reaction zone of the extrusion barrel before exhausting the extruder via an exit port of the extrusion barrel.
9. A method as claimed in claim 8, wherein the different zones of the extruder are defined by step changes in the root diameter of the at least one screw within the extrusion barrel.
10. A method as claimed in claim 8 or claim 9, comprising heating the waste plastic and water mixture to a temperature of at least 374.4° C in the compression zone and/or reaction zone.
11. A method as claimed in any of claims 8 to 10, comprising increasing the pressure of the waste plastic and water mixture to a pressure of at least 217.7 atmospheres in the compression zone.
12. A method as claimed in any of claims 8 to 11, comprising maintaining the material in the reaction zone for sufficient time for the waste plastics to be converted into one or more hydrocarbon fuel products.
5
13. A method as claimed in claim 12, comprising maintaining the material in the reaction zone for at least ten seconds.
GB1713664.9A 2017-04-25 2017-08-25 Apparatus for depolymerisation of waste plastics Withdrawn GB2565831A (en)

Priority Applications (1)

Application Number Priority Date Filing Date Title
PCT/EP2018/059782 WO2018197269A1 (en) 2017-04-25 2018-04-17 Apparatus and method for carrying out supercritical water oxidation of a material

Applications Claiming Priority (1)

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US201762489740P 2017-04-25 2017-04-25

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GB201713664D0 GB201713664D0 (en) 2017-10-11
GB2565831A true GB2565831A (en) 2019-02-27

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Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
RU2804969C1 (en) * 2022-12-29 2023-10-09 федеральное государственное автономное образовательное учреждение высшего образования "Пермский национальный исследовательский политехнический университет" Method for producing liquid hydrocarbons from thermoplastic waste and device for its implementation

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CN112476849B (en) * 2020-11-09 2023-06-02 湖南中塑新能源有限公司 Multistage salt washing system for regenerating plastic particles
CN115555387A (en) * 2022-09-12 2023-01-03 昆明理工大学 Method for degrading plastics in waste water and sludge

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WO2006131570A2 (en) * 2005-06-10 2006-12-14 Armines Method for producing an active substance-containing composite material
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