WO2025008613A1

WO2025008613A1 - Electromagnetic pyrolysis apparatus and a method of use thereof to recycle waste materials to obtain separated hydrocarbon chemical components

Info

Publication number: WO2025008613A1
Application number: PCT/GB2024/051702
Authority: WO
Inventors: John MCGREEVY
Original assignee: Sylatech Ltd
Current assignee: Sylatech Ltd
Priority date: 2023-07-04
Filing date: 2024-07-01
Publication date: 2025-01-09
Anticipated expiration: 2026-01-04
Also published as: GB202409456D0; GB2633189A; GB202310201D0

Abstract

The invention relates to apparatus and a method for performing pyrolysis of a material by electromagnetic travelling wave transmission such as a microwave transmission to process material, such as plastics material or biomass material and allow components of the material to be separated collected and provided for subsequent uses, thereby providing and environmentally friendly processing of waste material. The material may be pre-processed by drying and/or forming prior to placing the same into a chamber with a susceptor material to and into which the electromagnetic waves are introduced to create an interface between the susceptor material and material to be processed and at which pyrolysis occurs, with the interface progressing through the said material and processing the same.

Description

Electromagnetic Pyrolysis Apparatus and a Method of use thereof to recycle waste materials to obtain separated hydrocarbon chemical components The invention to which this application relates is a method for performing pyrolysis of a material by electromagnetic transmission and an apparatus thereof and, in particular, pyrolysis induced by microwave transmission. The invention is particularly, although not necessarily exclusively, related to the pyrolysis of plastics material. Global plastic use has grown significantly since the late 20^th century due to its affordability, versatility and durability. These materials are typically moulded, extruded or pressed from synthetic or semi-synthetic materials including polymers that can take centuries to degrade. Plastic materials in unregulated disposal sites may be blown by wind into wildlife areas or enter water ways, causing significant environmental damage as the material is difficult to break down. Plastic recycling methods, such as mechanical recycling, are generally underused due to the number of factors that may reduce the quality of the recycled product, such as impurities in the materials to be recycled. Industries have therefore looked to alternative plastic waste management methods, such as pyrolysis. Plastic pyrolysis is the process of breaking down the hydrocarbon chains of plastics material by suitably heating the material to a required temperature in an inert environment so as to prevent oxidation of the same. This allows the material to be converted back to usable oils, gases and other substances. The oil fractions typically contain between 8 and 30 carbon atoms, with the naphtha fractions being the majority, if the process is sufficiently controlled. A benefit of plastic pyrolysis is that the purity of the input material is not as significant a factor as other recycling methods. Plastic pyrolysis is often carried out in industry by heating a chamber containing the plastic by conventional means, such as by burning wood or oil, until the plastic reaches a temperature suitable to undergo pyrolysis. However, it has been found that this method of heating the plastic is highly inefficient, as the heat from the burning fuel is often absorbed by the chamber, or lost to the surrounding atmosphere and/or the inert gas within the chamber. An aim of the present invention is therefore to provide a method and apparatus for performing pyrolysis on a volume of material, wherein the pyrolysis of the material is performed in a manner more efficient than conventional methods. In a first aspect of the invention there is provided a method of performing pyrolysis on a volume of material, said method comprising the steps of: locating the volume of material intermediate a susceptor material and an electromagnetic wave transmitter, wherein an interface is formed between the volume of material and susceptor material; and directing an oscillating electromagnetic wave from the transmitter to generate a travelling electromagnetic wave through the volume of material, towards the said interface such that the temperature of the said susceptor material is increased to induce pyrolysis of the volume of material at the said interface and to move the interface through the said volume of material. In one embodiment the pyrolysis is induced progressively through the volume of material. In one embodiment the volume of material is a plastic material and, as plastic material is substantially transparent to the electromagnetic waves, the said waves can be directed through the said plastic material to reach the interface with the susceptor material. Typically the volume of material is pre-processed so as to be provided in a form suitable for pyrolysis, such as brickettes, compaction of the material or extruding the material. Typically the volume of material is dried to remove moisture before the electromagnetic wave is directed towards the material. Typically the drying step occurs before the pre-processing stage. Typically the electromagnetic wave will not raise the temperature of the plastic material directly due to the effective transparency of the plastic material. In other words, the plastic molecules are not excited by the microwave. As such, the susceptor material which is a material with a high tan delta value is heated by the microwave, and the heat energy is transferred to the plastic material at the interface to first melt and then pyrolyze the same. Typically the plastic material that is pyrolyzed is broken down into at least a susceptor material which includes at least a substantially solid carbon component. Thus, the depth of the susceptor material increases as pyrolysis is performed and so said interface at which pyrolysis occurs progresses towards the transmitter. In one embodiment of the invention the electromagnetic wave is directed at the said interface as the interface progresses through the volume of material so as to maintain the condition of the interface as pyrolysis is performed on the quantity of material. In one embodiment the wavelength of the electromagnetic wave is within the ISM microwave band of the electromagnetic spectrum, due to regulatory requirements but technically could fall outside that range if permitted to be used. Typically the electromagnetic wave directed through the volume of material is adjusted so as not to be a standing wave, such that substantially all of the interface is subjected to the wave. In one embodiment the said chamber is substantially devoid of oxygen. Typically the interface progresses through the volume of material in a direction towards the transmitter as pyrolysis occurs. In one embodiment the electromagnetic wave is adjustable, and the resultant travelling wave solution is at least the distance between the transmitter and the interface. In one embodiment the method includes the step of adjusting the electromagnetic wave such that the heat energy received from the same is primarily at the said interface so as to maintain the condition of the interface as it progresses through the volume of material. In one embodiment the volume of material comprises plastic material. In one embodiment the method includes the step of drying the plastic material prior to being located in the chamber, so as to remove moisture from the plastic material. In one embodiment the plastic material is pre-processed to a form suitable for the pyrolysis process. Typically the plastic material is pre-processed into brickettes, formed by extrusion or formed by compaction. In one embodiment the travelling wave power can be varied to change the rate of movement of the interface throughout the plastic material. The length of the carbon-carbon bonds of the plastic material varies depending on the plastic material. In one embodiment the selected power and hence rate of movement of the interface through the plastic material is suitable for breaking down the carbon-carbon bonds of the plastic material treated and bonds of the plastic material with the longest carbon-carbon bonds if there are different plastic materials being treated. In one embodiment the plastic material will pyrolyze into solid, liquid and gas products. In one embodiment the method includes the step of capturing the liquid and/or gas products to prevent the same from affecting the pyrolysis of the volume of material. Typically the captured liquid and/or gas products are removed from the chamber and prevented from re-entering the said volume of material in the chamber. In one embodiment the susceptor priming element and subsequent susceptor carbon comprises a material with polar bonds, such that the molecules may be vibrated by the microwave to heat the same. Typically the susceptor priming element is or includes carbon. Preferably the susceptor priming element is carbon black, or char, recovered from previous cycles of operation of the apparatus and/or silicon carbide may be used as the priming element. Typically the travelling wave solution used varies with the power supplied to the wave generator. In one embodiment, the power and hence travelling wave solution selected is suitable for the susceptor material used at that time and/or desired rate of pyrolysis. In one embodiment the location of the interface is detected by measuring the capacitance of the material in the chamber above and below the interface, i.e. the waste plastic and susceptor material respectively. In one embodiment the pyrolysis products are removed from the chamber. In one embodiment an inert gaseous fluid is passed through the chamber to remove the droplets of liquid and gas products. The inert gas and pyrolysis products are then passed through a condenser such that the liquid products may be collected. Preferably the inert gas is or includes nitrogen. In one embodiment the temperature of the chamber is controlled by the temperature of the gaseous fluid via a feedback loop. Typically the temperature of the chamber is such that excess solid products are not present in the collected liquid and/or gas products. Preferably the temperature of the chamber does not exceed 250 °C at the outside of the chamber, but in other circumstances such as, for example, to separate other components, potentially higher temperatures can be used. Typically the plastic material is any of, or includes, polyethylene or polypropylene, but in other embodiments other plastic feedstocks may be used, with the exception of PVC and PTFE, and/or biomass material may be used as the feedstock. In a second aspect of the invention there is an apparatus for performing pyrolysis on a volume of material, said apparatus comprising: a chamber for the reception of said volume of material therein, said chamber including at least one susceptor priming element located at or proximal a base of the chamber; an electromagnetic travelling wave transmitter connected to a waveguide with an outlet located such that an oscillating electromagnetic wave passes from the transmitter and into the chamber and directing said oscillating electromagnetic wave from the transmitter to an interface between the susceptor priming material and the volume of material and generate a travelling electromagnetic wave through the volume of material, towards the said interface such that the temperature of the said susceptor material is increased to induce pyrolysis of the volume of material at the said interface and to move the interface through the said volume of material. In one embodiment the waveguide outlet is located at or adjacent to the opposing side of the volume of material from the susceptor element. In one embodiment the electromagnetic wave is within the microwave band of the electromagnetic spectrum. In one embodiment the transmitter is controlled by a control unit. In one embodiment the transmitter includes a power source, automatic stun tuner, wave guide and an antenna. In one embodiment the apparatus includes a number of capacitance probes, such that the location of the interface between the volume of material and the products of the pyrolysis may be determined. Typically, the volume of material will have a lower capacitance than the pyrolysis products. In one embodiment, the travelling wave provided by the electromagnetic wave may be adjusted by the transmitter control unit and is applicable at least at the location of the interface between the volume of material and the products as determined by the capacitance probes. In one embodiment the chamber includes a capturing means to capture the liquid and/or gas products emitted from the volume of material during pyrolysis and prevent the same from re-entering the said volume of material in the chamber. In one embodiment the capturing means includes a channel located with an angled wall of the chamber. In one embodiment the apparatus includes a plurality of sensors so as to provide feedback data to the control means for the apparatus as the pyrolysis occurs and thereby allow adjustment of the parameters of the operation of the apparatus, if required so as to maintain a substantially uniform pyrolysis. Typically the control means includes means to allow user input of data relating to one or more parameters of the apparatus, the said volume of material and/or the separated components of the material so as to allow the apparatus operation to be set for the specific pyrolysis operation which is to be performed. In one embodiment the processing means includes the ability for a learning function to be performed based on the input data and received data. In one embodiment the apparatus includes sealing means to prevent the leakage of microwave emissions to the environment external of the apparatus. In one embodiment the microwave transmitter and/or waveguide include at least one filter assembly. In one embodiment the said volume of material is a plastics material such as agricultural plastic waste, agrifleece or may be a biomass material. Specific embodiments of the invention are now described with reference to the accompanying drawings wherein: Figures 1a-d illustrate the steps of inducing pyrolysis of a plastic material in accordance with one embodiment of the invention; Figure 2 illustrates a plastic pyrolysis system in accordance with one embodiment of the invention; Figure 3 illustrates a sample of plastic material that has partially undergone the process in accordance with one embodiment of the invention; Figure 4 illustrates a schematic of a pyrolysis system in accordance with one embodiment of the invention; Figure 5 illustrates a section view of a chamber for the reception of a volume of material to be pyrolyzed; Figure 6 illustrates a perspective view of a power combiner for an electromagnetic transmitter in accordance with one embodiment of the invention; Figures 7a-d illustrate exploded, front, side and rear views of a radiofrequency window of the electromagnetic transmitter in accordance with one embodiment of the invention; Figure 8 illustrates a series of temperature sensors located with the wall of a chamber in accordance with one embodiment of the invention; Figure 9 illustrates a schematic of a system for condensing the pyrolysis products in accordance with one embodiment of the invention; Figure 10 illustrates an electromagnetic filter in accordance with one embodiment of the invention; Figure 11 illustrates a char removal grid in accordance with one embodiment of the invention; Figure 12 illustrates the chromatography results of pyrolysis products produced from a plastic feedstock; Figures 13a-d illustrate the chromatography results of liquid and gas pyrolysis products produced from a dirty plastic feedstock; Figure 14 illustrates the components of the gas pyrolysis products of the trial represented in Figures 13c-d; and Figure 15 illustrates the effect of a pyrolysis process on polypropylene bonds. In Figures 1a-d there is illustrated the steps of a method of inducing pyrolysis of a volume of material, in this example, plastic material 2 by an electromagnetic wave 4 in accordance with the invention. Pyrolysis is heating of an organic material in the absence of oxygen to a temperature suitable to break down the carbon bonds of the material. In plastics, pyrolysis typically breaks down the mater into usable oil and other products. Plastic typically has a relatively low tan delta value, that is the tangent of the field between an alternating field vector and a material’s loss component. As such an oscillating electromagnetic wave, in this case a microwave 4, is unable to excite the plastic molecules so that the plastic material is effectively “transparent” to the microwave 4. Similarly, any inert gas or air is further unlikely to be directly excited by the microwave 4. As shown in Figure 1a, the volume of material 2 is located in a chamber 6 which further contains a number of susceptor elements 8. The susceptor elements 8 are composed of materials with a high tan delta value, such as carbon or silicon carbide, and as such have relatively high levels of emissivity and relatively high thermal radiation characteristics. Alternatively, these susceptors elements can be replaced by a layer of susceptor powder, for example carbon black power, silicon carbide (carborundum) grit or char from the process itself. The microwave 4 causes oscillation of the susceptor molecules, generating kinetic energy which is transferred to heat energy, increasing the temperature of the susceptor material which is initially provided by the susceptor element and subsequently includes carbon from the pyrolyzed plastics material. In Figure 1b it can be seen that this heat energy is transferred to neighbouring plastic material 2, as indicated by lines 10. The heat energy raises the temperature of the plastic material 2 beyond melting point to form a layer of molten plastic 12, as seen in Figures 1c. Further heat transfer from the susceptor elements 8 causes the molten plastic 12 to undergo pyrolysis, breaking down the plastic to liquid oil, and carbon-rich solid char. These pyrolysis products inherently have a high tan delta value, and as such absorb the microwave power, increasing their temperature. An interface 14 is formed between the pyrolysis products 12 and the plastic material yet to be melted 2. As the pyrolysis products absorb microwave power and generate more heat across the interface 14, proximal plastic material 2 will increase in temperature and melt, and subsequently undergo pyrolysis. As such, the interface 14 increases through the plastic material 2 until substantially all of the plastic material 2 has undergone pyrolysis. The movement can be likened to the progression of the burning interface of a cigarette with the carbon layer progressing upwardly through the chamber and being led by the interface. To improve the efficiency of the system, the electromagnetic wave 4 may be adjusted such that the travelling wave is applicable beyond the interface 14, as shown in Figure 1d. This may be done by altering the phase of the transmitted wave 4 to minimise the reflected wave, or by other means. While theoretically the limit of the range of frequencies in which the wave may be varied is determined by the operating parameters of the wave generator, in practice the frequency band is limited by international standards, such as Industrial Scientific and Medical (ISM) standards. As such, the wave generator typically operates at the frequency band of 896MHz – 915 MHz or more typically 2450MHz. It has been found that it is possible to induce pyrolysis of 1kg of plastic in this way for 1.5kW/hour. It has further been found that approximately 60% of light oils may be extracted from the plastic material using this process. In Figure 2 there is illustrated a system for inducing pyrolysis of a plastic material 2 by an electromagnetic wave 4 in accordance with the invention. The plastic material 2 is contained in a chamber 6 containing susceptor elements 8 or a layer of susceptor powder. The plastic material 2 and susceptors 8 rest on a mesh interface 16. The plastic 2 is deposited into the chamber through an inlet chute 18 which is then sealed with a cap 20. An electromagnetic transmitter 22 is controlled by a control unit 24 to transmit the electromagnetic wave 4 within the chamber 6 to the susceptor materials 8. The transmitter 22 may include a power source, automatic stub tuner, wave guide and antenna. A series of capacitance probes 26 determine the carbon content of the chamber 6 at a given distance from the transmitter 22. As such, the interface 14 distance from the transmitter 22 may be determined and the control unit 24 will adjust the phase of the electromagnetic wave 4 to minimise the reflected power such that the effectiveness of the wave is applicable to an area which is typically just further than the location of the interface 14. As such, the electromagnetic power is directed to the location of the pyrolysis reaction and the efficiency of the system is increased. In this embodiment, the detection of carbon content and corresponding adjustment of the electromagnetic wavelength is carried out by the system. The system may further include oxygen probes, temperature probes and/or pressure probes. It is found that when the chamber temperature does not exceed 250 °C, wax and other impurities are less likely to be present within the liquid products. As the plastic material 2 undergoes pyrolysis, resultant products become present in the chamber 6. These products may be solid, such as char 28; liquid, such as oil 30 or gas as indicated by arrow 32. Oil vapour 30 suspended in the chamber and any gas products may be removed from the chamber by passing through an inert gas 34, such as nitrogen. The pressurised gas 34 is introduced into the chamber through an inlet 35 and through the mesh interface 16 and acts as a medium by which to expel the vaporised pyrolysis products from the chamber through an outlet 36. The outlet may include a condenser 38 to induce condensation of the oil 30 which is collected in a container 40. The remaining products may be exhausted or collected for separation from the nitrogen gas 34. The remaining solid char 28 may be removed and used in, for example, cementitious materials. A portion of this char maybe used as the initial susceptor in the equipment in future operational runs either on a batch or continuous basis. Gas chromatography–mass spectrometry (GC-MS) tests have been performed by the applicant on the extracts from the apparatus and method as described herein and test results are reproduced below with three experiments performed and tested using a GCMS apparatus manufactured by Agilent and Model 7890B with a 5977 MSD on three samples, 11.4.1, 11.4.2 and 11.4.3, which is the order that the liquids came off the condenser, so that, for example, 11-4-1 was replaced by 11-4-2 and so on. This apparatus allows analysis to begin with a gas chromatograph, in which the sample is effectively vaporized into the gas phase and separated into its various components using a capillary column coated with a stationary (liquid or solid) phase material. Area %

From these test results it can be seen that the liquid oil content produced from the plastics material as a result of the use of process as herein described is comprised of at least 40% mono-olefins and at least 22% paraffin and with further smaller percentage components also identifiable. The chromatography test results 200, 202, 204 for the samples 11.4.1, 11.4.2 and 11.4.3 are illustrated in Figure 12. A further liquid and gas sample produced from dirty waste plastic film feedstock, in this example waste agricultural covering plastic commonly referred to as agrifleece, was tested by the applicant. The chromatography test results for the liquid products 206 and gas products 208 from the dirty plastic film feedstock are illustrated in Figures 13a-b and Figures 13c-d respectively. Figure 13b illustrates a spike 207 indicting the presence of a plasticiser component from external source, such as tubing in the reactor. Figure 13d is a reduced scale graph of Figure 13c. In this test, it was found that the gas content was comprised of at least 32% propene, 21% butene and 9% ethene. A table 212 breaking down the constituents of the gas product is detailed in Figure 14. The major component of the liquid was found to be 2,4-dimethyl-1-heptene, as indicated by spike 210. The process by which the microwave induces pyrolysis of the plastic feedstock is illustrated in Figure 15, where it can be seen that the polypropylene chain 212 is broken down into smaller hydrocarbon components 214 by the microwave, most commonly 2,4-dimethyl-1- heptene. Figure 3 shows a sample of plastic feedstock that has partially undergone plastic pyrolysis in accordance with the present invention. It can be seen that the plastic feedstock 2 has partially been broken down into black carbon or char 28 and light- coloured wax components 30; remaining plastic 2 is visible. The material 28 clearly shows the boundary layer at which the pyrolysis reaction is occurring on the plastics material as the process interface moves and passes through the plastics material to cause the separation of the components of the plastics material for subsequent extraction and use. A system schematic for a 20 kW microwave pyrolysis system 100 operating at 2450 MHz is illustrated in Figure 4. The system comprises a reaction chamber 106, herein after referred to as a chamber, for the reception of a volume of plastics material, hereinafter referred to as plastic feedstock 102, therein. The chamber is illustrated in section view in Figure 5. The chamber 106 is formed of an electrically conductive material to prevent microwave power loss through the walls of the chamber. In this embodiment, the chamber is formed of a copper-clad steel. Alternatively, the internal walls of the chamber may be plated in silver or formed of stainless steel if power loss is acceptable during the reaction. Additionally, by adding more generators and power combiners the operational power of the system can be increased. The chamber 106 can be formed of separate compartments that are assembled at the desired location. The chamber includes a tapered roof compartment 107, a main compartment 109 and a feedstock inlet 118. The separate compartments include fixing points (not shown) to allow a crane to manoeuvre the compartments to be assembled to form the chamber 106. Swing bolts (not shown) are provided to allow sealing between the compartments. Channels are provided along the edges of the compartments for the reception of graphite rope there along to produce leak tight thus ensuring the chamber is airtight and can maintain an inert atmosphere. Additionally since graphite rope is conductive, this ensures that good electrical contact is maintained between the lid, walls and base of the reaction chamber where the electromagnet field is present. Guide dowels ensure correct alignment between the compartments and ensure there is a good seal for the prevention of microwave leakage from the reactor 106. The feedstock inlet 118 is in communication with a plastic feedstock former 120 for providing a pre-processing step. The former 120 forms the plastic feedstock 102 into a manner suitable for pyrolysis such as by shredding or compacting the feedstock into pellets or brickettes to increase the surface area of the feedstock and increase the rate at which the same is melted. In this embodiment, the former 120 includes a mechanical screw compactor. The plastic feedstock 102 is dehydrated prior to being formed, and any metal debris is removed from the feedstock prior to being formed. Although it should be noted the presence of metal within the feedstock will not substantially affect the pyrolysis process. Dirt and other contaminants are a major contributor to the dielectric loss of the plastic feedstock 102 and so the feedstock 102 is monitored for contaminants as it is input to the chamber 106, and the microwave generators adjusted accordingly. The IEC, ICES, IEEE and CENELEC have defined a maximum permissible microwave emission density of 5W per m^-2 at 5cm away from the external surface of a microwave oven operating at 2450MHz, this has been adopted as a design parameter for the safe operation of the equipment. (The control of Electromagnetic fields at Work Regulations 2016, Table AL3 define an alert level of 50W per m^-2 .) A filter is included along the feedstock inlet 118 to absorb the microwaves input to the chamber 106 and prevent leakage to the external environment of the same. The filter includes a series of ceramic rods resonators 105 located along the walls of the inlet 118, as illustrated in Figure 10. This filter provides the advantage that plastic feedstock 102 may pass through the inlet 118 unimpeded, whilst preventing excess microwave leakage from the chamber 106. If lower emission limits are required by the regulatory authorities, then additional resonators can be added to the filter to provide further attenuation. A microwave fuse (not shown) is further fitted to the walls of the inlet 118. The fuse comprises a diode covered by a window so as not to be covered by plastic feedstock 102, and is arranged to continuously measure the radiofrequency power within the inlet. If the power exceeds a predetermined safe limit, it will trip a power supply 146 of the microwave system. Carbon is provided as the susceptor element 108 for the chamber 106. At 2450 MHz the loss tangent of carbon black exceeds that of carbon, thus allowing better energy coupling at the boundary between the susceptor element and the waste plastic feedstock 102. Approximately 5% of the product from the reaction will be carbon, providing the advantage that the susceptor element for further pyrolysis processes is provided by a portion of the products of the preceding processes. The carbon generated during the pyrolysis is a loose powder, which provides an advantage over other possible susceptor elements such as silicon carbide which forms a hard, solid material that can be difficult to handle in further processes. During the pyrolysis process, a temperature gradient is formed between the reaction zone and the walls of the chamber. Typically, the reaction zone temperature is 450 deg C, while the external walls of the main compartment 109 of the chamber is 300 deg C and the external walls of the roof compartment 107 is 100 deg C. As the syngas from the pyrolysis reaction rises from the reaction zone, it condenses on the walls of the chamber and can run back into the chamber, cracking the reaction. A channel 122 is provided along the interface between the roof compartment 107 and the main compartment 109 of the chamber to collect the condensed products that may otherwise pass back into the chamber and affect the pyrolysis reaction. The channel 122 removes the liquid products to collection points 121. Excess syngas production may also be relieved with the provision of a thermocouple and ball valve installed in the chamber. A gas outlet 124 is provided in the chamber 106 and consists of a large bore pipe with a globe valve fitted so that the flowrate, and hence residence time, can be adjusted. The outlet 124 pipe diameter is small enough to prevent microwave propagation therethrough. If necessary, the gas outlet 124 is formed of multiple pipes connected to a manifold. The gas outlet 124 is connected to a condenser system, shown in more detail in Figure 9. The gas outlet 124 includes a series of thermocouples fitted to monitor the syngas temperature at the outlet, as this is a function of the number of carbon atoms in a molecule. These sensors are connected to a programmable logic controller (PLC) 126 and used to determine the operating power setting. The products from the pyrolysis process are flushed from the chamber 106 by the provision of an inert gas into the chamber. A nitrogen generator 128 is in communication with the chamber. The nitrogen gas is heated by a heater 130 prior to being supplied to the chamber 106 to prevent the gas supply affecting the pyrolysis of the feedstock. The nitrogen gas further provides the benefit of suppressing arcing from the microwave system. The nitrogen circuit includes a controllable solenoid valve or an adjustable flowmeter to control the flow into the chamber. The nitrogen gas is provided by the generator 128 at a typical rate of 4 l/minute. The reaction chamber 106 is sealed to maintain an inert atmosphere. The reaction chamber 106 includes a series of burst disks that are set to fail at 0.5 barg, to prevent the risk of explosion from excessive internal pressure. To ensure the inert atmosphere within the chamber 106, rotary airlocks, sealed hoppers and/or a nitrogen blanket may be provided. The system includes a microwave system to induce pyrolysis of the feedstock 102. The system operates at a frequency of 2450 MHz, as this is optimal for the dielectric properties of the carbon susceptors. Conversion efficiency, that is energy per unit mass, of a 2450 MHz system is approximately three times greater than that of an 896-915 MHz system. The microwave system includes a waveguide formed of copper or aluminium that is 10m in length. If Aluminium, the waveguide may be silver plated. The microwaves are generated by two 10kW generators 132 which are combined by a 2:1 combiner 134 to obtain a 20 kW system. If a higher power system is required multiple generators can be combined together. The power combiner 134 is illustrated in Figure 6, and includes two microwave generator inputs 136 and a combined output 138. The microwave loss for this combiner is approximately 455W, and therefore the combiner is water cooled. A water load 139 is connected to port 140. The power combiner is manufactured from silver plated aluminium. A stub tuner 142 is fitted with the combiner output 138. The microwave circuit is connected to the nitrogen circuit to supply the microwave waveguide with a dielectric gas. An arc detector 144 is fitted within the microwave system such that any arcs detected within the system can be detected, and the PLC 126 may be triggered to reduce or disconnect the power supplied from a supply 146 to the microwave system. The detector 144 is arranged to detect arcs in the output port 138 of the power combiner 134 and also to detect arcs from the stub tuner 142. These components will be the points of maximum electric fields and therefore the point at which an arc would propagate. If the arc detector 144 detects the occurrence of an arc or large reflections, the power from the supply 146 is reduced by the PLC 126 and restated after any ionised gases have been dissipated. The PLC 126 includes a user interface so as to be accessed by a user. A series of fault sensors throughout the sensor are controlled and readable by the PLC 126. The generated microwave is input to the chamber 106 through a radiofrequency window 148, shown in detail in Figures 7a-d. The window 148 is formed of a front plate 150 and back plate 152 and a fused quartz windowpane 154 located therebetween. Two seals 156 are provided between the windowpane 154 and plates 150,152. Water cooling can also be incorporated into the window if required. The system is controlled by the measured temperature of the pyrolysis interface within the chamber 106. However, thermocouples cannot be activated at the pyrolysis interface where microwaves are directed, as the activated component will act as an antenna for radiofrequency energy which will couple to it. In the best case, this will result in an inaccurate measurement and in the worst case this may damage the circuitry of the component. Therefore, a series of thermocouples are located on an external wall of the chamber 106, as shown in Figure 8. In this embodiment, a series of thermocouples 158 of the type known as Type K thermocouples are placed at 50mm intervals along a centreline 160 of the main compartment 109 of the chamber 106. A grid of thermocouples 158 are also positioned at the base of the main compartment. The temperature readings from the thermocouples 158 are provided to the PLC 126 to control the microwave generators 132, and the data is stored in a suitable database for analysis purposes. The database is accessible by a user through the user interface of the PLC. Thermocouples are also provided at the outlets for the syngas products 124, the outlets for the liquid products 122, the radiofrequency window 148, the water load supply 139, and the cooling water input 140. Suitable sensors are also provided to measure temperature, pressure, O2 levels, waterflows, gas flows, extraction volumes and flare. Data from these sensors is input to the PLC. Output sensors are also provided on the stub tuner 142 which are connected to the PLC 126. These sensors measure the forward and reflected power, and the output frequency. This data is used to determine the voltage standing wave ratio (VSWR) return/loss ratio and the electrical efficiency of the system. The condensing system 162 is illustrated in detail in Figure 9. The syngas containing oil 164 from the outlet 124 is provided into a oil separator 166. Heavy oil is removed from the separator into a container 168. The remaining gas and oil vapour is passed through a cooling system 170, with the condensed oil and non-condensable gas passing into a pyrolysis container 172. The liquid oil is removed from this container 172 to an end container 174 whilst the remaining non-condensable gas is input to an anti-tempering system 176, before passing to an exhaust gas combustion chamber 178. The condensing system 162, in alternative embodiments, includes a scrubber to remove chlorine, fluorine, hydrochloric and hydrofluoric acids from the products. A cyclone is included in alternative embodiments to remove entrained solids such as carbon. In alternative embodiments the non-condensable gases may be stored or used to generate electricity. Flare is used to ensure no residual gases are exhausted to the atmosphere, and trace heating is applied as appropriate on the pipework and collection vessels. On completion of the pyrolysis process, a check is performed to ensure the feedstock 102 within the chamber 106 is exhausted and has been completely pyrolyzed. This is done by monitoring the carbon content within the chamber, by taking a capacitance measurement, as the dielectric constant of carbon is an order of magnitude greater than that of plastic. Additionally, by measuring the susceptance and the equivalent series resistance of the remaining contents of the chamber, it is possible to determine the Q and hence the tan delta, which is five orders of magnitude greater between plastic and carbon. Alternatively, a perturbed cavity could be used to measure the dielectric constant of the remaining char, as there is a linear relationship between the percentage plastic in the char and the dielectric constant. Following the pyrolysis process, the remaining char is removed from the chamber 106 through a char output grid 180 located at the base of the main compartment 109 of the chamber, as illustrated in Figure 11. The grid is composed of a series of 30mm x 30mm square apertures located opposite the feedstock inlet 118. The aperture size and wall thickness are such that there is no significant microwave leakage therethrough. The char is able to pass through this grid on completion of the pyrolysis due to its powder composition, and can then be removed by an auger. Bulk metal contaminants that have been ground down to a suitable size in the forming process 120 or have been melted down during the pyrolysis to a suitable size may be removed through the grid 180. Larger contaminants that are unable to be removed through the grid 180 may be periodically removed through the inlet 118 or by removing the roof compartment 107 from the main compartment 109.

Claims

CLAIMS 1. A method of performing pyrolysis on a volume of material, said method comprising the steps of: locating the volume of material intermediate a susceptor material and an electromagnetic wave transmitter, wherein an interface is formed between the volume of material and susceptor material; and directing an oscillating electromagnetic wave from the transmitter to generate a travelling electromagnetic wave through the volume of material, towards the said interface such that the temperature of the said susceptor material is increased to induce pyrolysis of the volume of material at the said interface and to move the interface through the said volume of material. 2. A method according to claim 1, wherein the pyrolysis is induced progressively through the volume of material such that the said interface progresses through the volume of material. 3. A method according to any of the preceding claims, wherein the said wave is directed through the said plastic material to reach the interface with the susceptor material. 4. A method according to any of the preceding claims, wherein the volume of material is pre-processed by any of compaction or extrusion. 5. A method according to any of the preceding claims, wherein the volume of material is dried to remove moisture before the electromagnetic wave is directed towards the material. 6. A method according to any of the preceding claims, wherein the electromagnetic wave is a microwave. 7. A method according to claim 6, wherein the microwave is adjusted so as not to be a standing wave. 8. A method according to any of the preceding claims wherein the said chamber is substantially devoid of oxygen. 9. A method according to any of the preceding claims wherein the electromagnetic wave is adjustable, and the resultant travelling wave is at least the distance between the transmitter and the interface. 10. A method according to claim 9, wherein the method includes the step of adjusting the electromagnetic wave such that the heat energy received from the same is primarily at the said interface so as to maintain the condition of the interface as it progresses through the volume of material. 11. A method according to claim 10, wherein travelling wave power is varied to change the rate of movement of the interface throughout the volume of material. 12. A method according to any of the preceding claims wherein the method includes the step of capturing the separated liquid and/or gas products to prevent the same from affecting the ongoing pyrolysis of the remaining volume of material. 13. A method according to any of the preceding claims wherein the susceptor priming element is or includes carbon. 14. A method according to any of the preceding claims wherein the said volume of material is a plastics material or biomass material. 15. Apparatus for performing pyrolysis on a volume of material, said apparatus comprising: a chamber for the reception of said volume of material therein, said chamber including at least one susceptor priming element located at or proximal a base of the chamber; an electromagnetic travelling wave transmitter connected to a waveguide with an outlet located such that an oscillating electromagnetic wave passes from the transmitter and into the chamber and directing said oscillating electromagnetic wave from the transmitter to an interface between the susceptor priming material and the volume of material and generate a travelling electromagnetic wave through the volume of material, towards the said interface such that the temperature of the said susceptor material is increased to induce pyrolysis of the volume of material at the said interface and to move the interface through the said volume of material. 15. Apparatus according to claim 15 wherein the waveguide outlet is located at or adjacent to the opposing side of the volume of material from the susceptor element. 16. Apparatus according to claim 14 wherein the electromagnetic wave is within the microwave band of the electromagnetic spectrum. 17. Apparatus according to any of claims 14-16 wherein the transmitter is controlled by a control unit. 18. Apparatus according to any of claims 14-17 wherein the transmitter includes a power source, automatic stub tuner, wave guide and an antenna. 19. Apparatus according to any of claims 14-18 wherein the apparatus includes a number of capacitance probes to allow the location of the interface between the volume of material and the products of the pyrolysis to be determined. 20 Apparatus according to any of the claims 14-19 wherein the travelling wave provided by the electromagnetic wave may be adjusted by the transmitter control means and is applicable at least at the location of the interface between the plastic material and the products as determined by the capacitance probes. 21 Apparatus according to any of the claims 14-20 wherein the chamber includes a capturing means to capture the liquid and/or gas products emitted from the plastic during pyrolysis and prevent the same from re-entering the said volume of material in the chamber. 22. Apparatus according to claim 21 wherein the capturing means includes a channel located with a wall of the chamber. 23 Apparatus according to any of the claims 14-22 wherein the apparatus includes a plurality of sensors so as to provide feedback data to the control means for the apparatus as the pyrolysis occurs and thereby allow adjustment of the parameters of the operation of the apparatus, if required, so as to maintain a substantially uniform pyrolysis. 24. Apparatus according to any of the claims 14-23 wherein the control means includes means to allow user input of data relating to one or more parameters of the apparatus, the said volume of material and/or the separated components of the material so as to allow the apparatus operation to be set for the specific pyrolysis operation which is to be performed. 25. Apparatus according to claims 23 and 24 wherein the control means includes the ability for a learning function to be performed based on the input data and received data. 26. Apparatus according to any of the claims 14-25 wherein the apparatus includes sealing means to prevent the leakage of microwave emissions to the environment external of the apparatus. 27. Apparatus according to any of the claims 14-26 wherein the electromagnetic wave transmitter and/or waveguide include at least one filter assembly. 28. Apparatus according to any of the claims 14-27 wherein the said volume of material is a plastics material such as agricultural plastic waste, agrifleece or may be a biomass material.