WO2018197269A1

WO2018197269A1 - Apparatus and method for carrying out supercritical water oxidation of a material

Info

Publication number: WO2018197269A1
Application number: PCT/EP2018/059782
Authority: WO
Inventors: Stephen Windsor HAMILTON; Gregory Scott DAWSON; George Graham Allan
Original assignee: Hamilton Stephen Windsor; Dawson Gregory Scott; George Graham Allan
Priority date: 2017-04-25
Filing date: 2018-04-17
Publication date: 2018-11-01
Also published as: GB2565831A; GB201713664D0

Abstract

An apparatus for carrying out super critical water oxidation of a material in an extrusion process, said apparatus comprising an extrusion barrel, at least one screw rotatably mounted within the extrusion barrel, a drive means for driving said at least one screw, 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 within the extrusion barrel a feed zone, wherein the mixture of the material to be treated and water can be passed into said extrusion barrel via one or more inlet ports at substantially ambient/atmospheric pressure, a compression zone downstream of said feed zone, wherein the mixture of material to be treated and wateris compressed to supercritical pressure, a heating zone downstream of said compression zone,wherein the mixture of material to be treated and wateris heated to supercritical temperature, and a reaction zone downstream of said compression zone, whereinsupercritical water oxidation of the material takes place, before the treated material leaves the extruder via a discharge port at a discharge end thereof.

Description

Apparatus for carrying out supercritical water oxidation of a material

FIELD OF THE INVENTION This invention relates to an apparatus for carrying out supercritical water oxidation of a material and in particular for the depolymerisation of waste plastic, for example for converting waste plastics into hydrocarbon based fuels.

BACKGROUND OF THE INVENTION

The prevalence of plastic materials in modern 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, which is external to the extruder, 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 both the extruder and also the separate 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 carrying out super critical water oxidation of a material in an extrusion process, said apparatus comprising an extrusion barrel, at least one screw rotatably mounted within the extrusion barrel, a drive means for driving said at least one screw, 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 within the extrusion barrel a feed zone, wherein the mixture of the material to be treated and water can be passed into said extrusion barrel via one or more inlet ports at substantially ambient/atmospheric pressure, a compression zone downstream of said feed zone, wherein the mixture of material to be treated and water is compressed to supercritical pressure, a heating zone downstream of said compression zone, wherein the mixture of material to be treated and water is heated to supercritical temperature, and a reaction zone downstream of said compression zone, wherein supercritical water oxidation of the material takes place, before the treated material leaves the extruder via a discharge port at a discharge end thereof.

The different zones of the extruder may be defined by changes in the root diameter of the at least one screw. In a preferred embodiment the at least one screw may have a substantially constant root diameter in said the feed zone and an increasing root diameter in the compression zone to increase the pressure of the mixture of material and water therein.

The root diameter of the at least one screw may remain substantially constant in the reaction zone.

The root diameter of the at least one screw may have a reducing root diameter and/or increasing flight spacing in the heating zone to account for thermal expansion of the mixture therein In one embodiment a mixing zone may be defined in the extruder barrel between the feed zone and compression zone wherein the material to be treated and the water is mixed.

The apparatus may further comprise cooling means for cooling the compression zone of the extrusion barrel, thereby preventing phase change of the water during compression. The extrusion barrel may have a substantially constant internal diameter in each of said feed, compression, heating and reaction zones.

Preferably the mixture is compressed to a pressure of at least 217.7 atmospheres in the compression zone.

Preferably the heating means is arranged to heat the mixture to a temperature of at least 374.4° C in the heating zone of the extrusion barrel.

The heating means may be arranged to heat the reaction zone of the extrusion barrel to maintain the temperature of the material in therein.

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 for carrying out super critical water oxidation of a material in an extrusion process comprising the steps of feeding material to be treated into a feed zone of an the extrusion barrel having at least one extrusion screw driven to rotate therein, adding water to the material in or adjacent the feed zone at substantially ambient pressure, compressing the mixture of material and water to supercritical pressure in a compression zone and heating the mixture to supercritical temperature in a compression zone of the extrusion barrel and passing the mixture of material and water under supercritical conditions through a reaction zone of the extrusion barrel wherein supercritical water oxidation of the material takes place, before exhausting the material via an discharge port of the extrusion barrel.

Preferably the different zones of the extruder are defined by changes in the root diameter of the at least one screw within the extrusion barrel.

The method may further comprise increasing the pressure of the mixture of material and water to a pressure of at least 217.7 atmospheres in the compression zone. The method may further comprise heating the mixture to a temperature of at least 374.4° C in the heating zone.

Preferably the method comprises maintaining the material in the reaction zone for at least ten seconds.

BRIEF DESCRIPTION OF THE DRAWINGS

An apparatus for carrying out super critical water oxidation of a material 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 plan view of an apparatus for carrying out super critical water oxidation of a material in accordance with an embodiment of the present invention; and Figure 2 is a longitudinal sectional view through the apparatus of Figure 1 on line A- A.

DETAILED DESCRIPTION OF THE DRAWINGS

The present invention provides a novel approach for carrying out super critical water oxidation of a material and in particular for converting waste plastics into a multitude of hydrocarbon based fuels. The apparatus and method may also be used for to neutralising and sterilising trace amounts of pharmaceuticals, such as antibiotics, antidepressants and illicit drugs, found in ground water, lakes and streams through the treatment of waste water discharge and direct treatment of expired stockpiled pharmaceuticals, for treating sewage wastewater to fuel conversation utilizing the processed sludge and/or for the treatment of crude oil for the purpose of increasing API gravity and reducing sulphur content. 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 an extrusion 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 or root 14, the shape and/or spacing of the flights 6 and the diameter of the root 14 of the screw 4 defining a specifically designed screw profile, said screw profile defining a feed zone "A" adjacent a feed hopper 8 feeding material to be treated to an inlet of the extruder barrel 2 and having an adjacent inlet port 9 for injecting water into the feed zone at substantially atmospheric or ambient pressure, a mixing zone "B", wherein the material to be treated and the water is mixed, a compression zone "C", wherein the mixture of material and water is compressed to at least 217.7 atmospheres, a heating zone "D", wherein the mixture is heated to at least 374.4 °C (i.e. supercritical conditions) by suitable heating means, and a reaction zone "E", wherein supercritical water oxidation of the material takes place, for example to break polymeric material down into fuel products within the extruder in a continuous process, before such treated material leaves the extruder via an exit port 12. The extruder includes heating means (not shown) for heating the barrel of the extruder, in particular in the heating zone "D" and preferably also in the reaction zone "E". The heating means may comprise a heat exchanger extending circumferentially around the barrel 2 of the extruder or being located within the outer wall of the barrel through which a heat exchange fluid may be passed.

This apparatus provides an economical and continuous (as opposed to a batch process) for the treatment of material by supercritical water oxidation, and in particular for the conversion of waste plastics (and optionally other biomass) into a hydrocarbon fuel product. The different zones of the extruder are preferably defined by changes in the root diameter of the extruder screw 4. A first constant root diameter 16 defines the feed zone "A" and mixing zone "B". In the compression zone "C", the root diameter 17 increases to compress the mixture of material and water to at least 217.4 atmospheres. The compression zone "C" of the extrusion barrel may be cooled to prevent the liquid water from changing phase during the pressure increase. Subsequently the pressurised mixture is heated in the heating zone "D" to achieve supercritical conditions as or before the mixture enter the reaction zone "E", wherein the root diameter 18 of the screw 4 remains substantially constant. In the heating zone "D" thermal expansion of the material may be accounted for by decreasing the root diameter 19 of the screw 4 and/or increasing the flight spacing.

Waste plastic and metered water first enters the extruder's feed zone "A" via the feed hopper 8 and water injection inlet port 9, wherein it first makes contact with the extruder screw 4. This eliminates the need to introduce high temperature water at high pressure, reducing energy consumption. The material to be treated and the water is mixed together as the mixture passes through the mixing zone "B", before entering the compression zone "C", wherein which the screw core diameter 17 increases, increasing the pressure of the mixture to in excess of 217.7 atmospheres. The pressurised mixture then passes into the heating zone "D", wherein it is heated to a temperature to in excess of 374.4° C, to achieve supercritical conditions, whilst maintaining pressure through flight spacing and/or decreasing screw root diameter to allow for thermal expansion.

At this point, the heating zone "D" transitions into the reaction zone "E, wherein the extruder screw or screws maintain a flat core profile 18, allowing for the pressure to be maintained above 217.7 atmospheres while the circumferential heating means maintains 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 "E" to allow the supercritical conversion to take place (preferably at least 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 waste plastics as they pass through the extruder.

In use, material to be treated, such as waste plastics, is fed into the extruder via the feed hopper 8, wherein water is added by water injection through the inlet port 9 at substantially ambient conditions. The mixture then passes through the mixing zone "B" and into the compression zone "C", wherein it is pressurized to very high pressure, above that required for supercritical conditions, while maintaining the water in liquid phase, preferably via cooling of the compression zone "C". The mixture is then heated to supercritical conditions in the heating zone "D before passing through the reaction zone "E", maintaining supercritical pressure and temperature. The extended reaction zone "E" ensures full conversion of the material via supercritical water oxidation before exhausting the extruder via the discharge port 12.

A heat exchanger may be provided downstream of the discharge 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

1 . An apparatus for carrying out super critical water oxidation of a material in an extrusion process, said apparatus comprising an extrusion barrel, at least one screw rotatably mounted within the extrusion barrel, a drive means for driving said at least one screw, 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 within the extrusion barrel a feed zone, wherein the mixture of the material to be treated and water can be passed into said extrusion barrel via one or more inlet ports at substantially ambient/atmospheric pressure, a compression zone downstream of said feed zone, wherein the mixture of material to be treated and water is compressed to supercritical pressure, a heating zone downstream of said compression zone, wherein the mixture of material to be treated and water is heated to supercritical temperature, and a reaction zone downstream of said compression zone, wherein supercritical water oxidation of the material takes place, before the treated material leaves 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 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 substantially constant root diameter in said the feed zone and an increasing root diameter in the compression zone to increase the pressure of the mixture of material 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 claim 2 or claim 3, wherein the root diameter of the at least one screw has a reducing root diameter and/or increasing flight spacing in the heating zone to account for thermal expansion of the mixture.

6. An apparatus as claimed in any preceding claim, wherein a mixing zone is defined in the extruder barrel between the feed zone and compression zone wherein the material to be treated and the water is mixed.

7. An apparatus as claimed in any preceding claim, further comprising cooling means for cooling the compression zone of the extrusion barrel, thereby preventing phase change of the water during compression.

8. An apparatus as claimed in any preceding claim, wherein the extrusion barrel has a substantially constant internal diameter in each of said feed, compression, heating and reaction zones.

9. 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.

10. An apparatus as claimed in any preceding claim, wherein the heating means is arranged to heat the mixture to a temperature of at least 374.4° C in the heating zone of the extrusion barrel.

1 1 . An apparatus as claimed in claim 10, wherein the heating means is arranged to heat the reaction zone of the extrusion barrel to maintain the temperature of the material in therein.

12. 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.

13. A method for carrying out super critical water oxidation of a material in an extrusion process comprising the steps of feeding material to be treated into a feed zone of an the extrusion barrel having at least one extrusion screw driven to rotate therein, adding water to the material in or adjacent the feed zone at substantially ambient pressure, compressing the mixture of material and water to supercritical pressure in a compression zone and heating the mixture to supercritical temperature in a compression zone of the extrusion barrel and passing the mixture of material and water under supercritical conditions through a reaction zone of the extrusion barrel wherein supercritical water oxidation of the material takes place, before exhausting the material via an discharge port of the extrusion barrel.

14. A method as claimed in claim 13, wherein the different zones of the extruder are defined by changes in the root diameter of the at least one screw within the extrusion barrel.

15. A method as claimed in claim 13 or claim 14, comprising increasing the pressure of the mixture of material and water to a pressure of at least 217.7 atmospheres in the compression zone.

16. A method as claimed in any of claims 13 to 15, comprising heating the mixture to a temperature of at least 374.4° C in the heating zone.

17. A method as claimed in any of claims 13 to 16, comprising maintaining the material in the reaction zone for at least ten seconds.