EP2303996A2

EP2303996A2 - Processing of waste using a plasma processing unit

Info

Publication number: EP2303996A2
Application number: EP09769602A
Authority: EP
Inventors: Leonid Rusnac
Original assignee: Horizon Ventures Ltd
Current assignee: Horizon Ventures Ltd
Priority date: 2008-06-25
Filing date: 2009-06-25
Publication date: 2011-04-06
Also published as: WO2009156761A2; GB0811631D0; WO2009156761A3

Abstract

Processing of Waste The present invention includes a waste processing apparatus (10) comprising: a reactor vessel (11) in which waste is received and broken-down by pyrolysis to produce pyrolysis gases; and at least one plasma processing unit that treats the pyrolysis gases. The plasma processing unit comprises a plasma generator (13) that creates hot ionised plasma gases; a plasma chamber (12) in which the plasma gases and the pyrolysis gases mix; and electrodes (36, 37) within the plasma chamber that apply an electromagnetic field to the mixed plasma and pyrolysis gases to achieve decomposition of harmful waste components. The electrodes may include first and second electrodes across which a fixed or variable electrical potential is applied. There is also a method of processing waste comprising: A) thermally decomposing waste by pyrolysis to generate pyrolysis gases; B), heating the pyrolysis gases within a plasma chamber in the presence of hot ionised plasma, whilst applying an electric field to the pyrolysis gases, to decompose said gases; C) passing the decomposed gases through a catalytic process; and D) rapidly cooling the formed gases.

Description

Processing of Waste

This invention relates to waste processing. In particular, this invention is directed to apparatus for and a method of processing waste to generate useful components therefrom.

As used herein, the term waste refers to matter that contains hydrocarbons and which can be treated by pyrolysis and/or gasification. It would usually encompass material of high calorific value such as plastics and rubbers, but can apply to any matter generally containing hydrocarbons such as organic and synthetic material. Further whilst it is envisaged that the present invention will find particular use in treating rubbish and industrial byproducts (and will predominantly described with reference thereto), it is equally possible that the present invention can be used to convert non-waste material (e.g. that which is specifically made or provided for that purpose) with the correct chemistry into more useful components.

The safe disposal of waste is of great importance and is becoming increasingly pertinent due to the influence of waste emissions on climate change. Traditional waste disposal methods include landfill disposal or incineration, but these methods destroy natural resources, squander energy and cause pollution from air emissions and toxic ash. Even when a waste can be incinerated the efficiency of the energy recovery is low.

There have been many attempts at providing solutions to the problem of recovering useful components from waste as well as disposing thereof using thermal processes. The aim is to generate not only energy but also provide raw materials for reuse, for example in the chemical industry. One such thermal processing technique is pyrolysis, where hydrocarbon matter undergoes thermal decomposition in the absence of oxygen. Other processing techniques include gasification, which is often used after pyrolysis to breakdown the hydrocarbons it produces, using high temperatures and a controlled amount of oxygen. Another processing method which is more commonly being used involves plasma technology. This method uses a lot of electrical energy and a high temperature created by an electrical arc gasifier, to breakdown waste. These plasma waste technologies operate at high temperatures with high power consumptions.

Systems utilising the above technologies for the processing of waste can produce significant results, particularly as compared to landfill disposal or mere incineration, but they do not provide a total solution. In order to treat waste using these technologies the prior art systems generally expose waste to very high temperatures. These high temperatures cause evaporation of the waste including heavy metals and compounds thereof (such as oxides) contained therein, thereby releasing them into the gas stream and thereafter into the atmosphere, creating an environmental hazard.

Whilst existing waste processing systems produce desirable components such as hydrogen and carbon monoxide, they also produce a range of undesirable multinuclear molecules. These multinuclear molecules form various structures which, when cooled, can condense in pipelines, valve mechanisms, turbines and compressors, causing operating problems. Furthermore, and more importantly, a greater problem is the creation of chlorine atoms, which replace hydrogen atoms forming polychlorinated polycyclic connections. These possess powerful immunosuppressive and mutagenic effects and are carcinogenic and embryo-toxic. These molecular structures are difficult to split and they collect within human organisms, as well as in the biosphere of the planet. Full destruction of these molecular structures through a process of thermal decomposition comprising, a cycle of oxidation at high temperature and then fast cooling, is difficult and at times not totally effective. The reasons for this include insufficient and irregular activity of catalysts and insufficient speed of cooling of the gases at the point of return.

A plasma pyrolysis process for the treatment of waste is described in International Patent Publication No. 2007/000607. This describes a process of treating the waste in a pyrolysis unit to produce an off-gas and char, followed by a plasma treatment step, whereby the off-gas and char are subjected to a plasma treatment in a plasma treatment unit. This process suffers from the same problems as described above, utilising high temperatures, ultimately resulting in the evaporation of heavy metal particles within the waste stream. The process thus does not provide full decomposition of the waste and does not provide a catalytic or rapid cooling process to prevent reformation of the undesirable, multinuclear molecules.

A method of treating waste gases by means of plasma treatment is described in US Patent Publication No. 6,153158. This describes passing waste gases through an inductively coupled plasma arc torch to incinerate and oxidize any contaminants therein. In order to oxidize these contaminants, the gases are subjected to extremely high plasma temperatures. However, due to the high temperatures, this process does not remove heavy metals and their oxides from the gas stream. Consequently, this method does not prevent the release of heavy metals and their oxides into the atmosphere.

Similarly, British Patent Publication No. 2436429 describes a method and apparatus for the plasma treatment of waste using two plasma arc torches. This process also involves treating the waste at extremely high temperatures, which would cause evaporation of any heavy metal from within the waste and the formation of heavy metal oxides.

To achieve full destruction of the undesirable molecular structures through a process of thermal decomposition, comprising a cycle of oxidation at a high temperature and then fast cooling, is difficult and at times not totally effective. The reasons for this, include: the extremely large assortment of waste that is processed simultaneously; non-uniform distribution of temperature gradients in the reactor; non-uniform release and production of gases during pyrolysis; insufficient and irregular activity of catalysts; insufficient speed of cooling (of gases) at the point of return; and other factors reducing the quality and safety of the fuel produced. The application of large amounts of heat during the process, and the use of expensive catalysts preventing the reformation of these molecular structures, partially solve the problems above; however these technologies demand significant material inputs and electric energy, reducing the commercial value of the fuel produced from waste. In - A -

addition, the effectiveness and durability of catalysts are dependent upon many factors, including; the chemical compounds used as cracking products, temperatures, pressure, properties and size of the surface of the catalyst and other limiting factors.

There is thus a need for a waste processing system which overcomes the problems of prior art systems, as described above. It is therefore a principal aim of the present invention to provide a system for the processing of waste which prevents formation of undesirable components (such as those harmful to the environment or health) in the materials produced. It is a further aim to provide a system which can be easily adapted to suit a wide range of waste types, that is economic to run, efficient in use and capable not only of treating the waste but of generating, either directly or from the products thereof, a far greater amount of energy than is used in starting and maintaining the treatment process.

According to a first aspect of this invention, there is provided waste processing apparatus comprising:

- a reactor vessel that receives waste and within which the waste is broken-down by pyrolysis to produce pyrolysis gases; and

- at least one plasma processing unit that receives the pyrolysis gases, comprising:

- a plasma generator adapted to create hot ionised plasma gases;

- a plasma chamber in which the plasma gases from the plasma generator and the pyrolysis gases from the reactor vessel mix; and

- electrodes within the plasma chamber that create a variable electromagnetic field that is applied to the mixed plasma and pyrolysis gases to achieve decomposition of harmful waste components.

The problems of the prior art are avoided by the present invention's use of economic pyrolysis technologies for the gasification of waste at low temperature and the subsequent heating of vapour and gases produced, in the presence of a hot ionized plasma, a very high power variable electric field and catalysts. These conditions promote simultaneous reactions between both steam and carbon dioxide, with the hydrocarbons; producing hydrogen and carbon monoxide as follows:

C_n H_m + nH₂O ^■* nCO + (n + ^m/₂) H₂ C_n H_m + nCO₂ -> 2nCO + ^m/₂ H₂

In addition to the breaking of the C- C, and C-H bonds, there is also the possibility of carbon and hydrogen forming bonds with: chlorine, fluorine, oxygen and sulphur; thereby forming acids and oxides.

The present invention acts to destroy these under the influence of the variable electric field on a moving stream of charged particles in a heated gas stream. This influence causes add itional excitation of atoms and as a consequence breaks the intermolecular bonds, and by changing the parameters of the field, one can change the speed of reaction and interaction without changing the power capacity of the heating devices. This process may be considered in the following stages:

1. High energy plasma gases are oxidised by the application of electrical arc discharge (without electrodes) or otherwise, to create a stream of heated ionized gas and charged particles.

2. A variable electric field is created between the two electrodes located along the axis of movement of the pyrolysis gas. The electric field may have an oscillatory pattern synchronized by means of an external electrical circuit, and acts upon the ionized gas and the charged particles provided from the plasma gas stream.

3. Control of the interaction between the electrical field and charged particles of the ionized gas, may be made by measurement of the electrical parameters of: amplitude of the current, voltage, and load; and the nonelectrical parameters of: pressure, temperature, spectrum, brightness and the characteristic sound of the plasma. The waste is exposed to heat and is continuously mixed in the reactor vessel to produce pyrolysis gases. The reactor vessel may advantageously comprise a central rotating member having a helical screw configuration to enable effective mixing and transference of the waste along the length thereof, to ensure efficient generation of pyrolysis gases.

Drive means to enable rotation of the central member of the reactor vessel may be provided at a suitable location. The drive means would most conveniently be located externally of the reactor vessel. Ideally, rotation of the central member is adjustable and can be controlled. To facilitate this, the drive means may be connected to control means for the control thereof.

The waste to be processed will, if possible, be subjected to a preparation treatment process prior to its introduction to the reactor vessel. Part of the function of this could be to remove metals, as if heavy metals are subjected to extreme heat under pyrolysis they will evaporate and form heavy metal oxides. Once in a gaseous form, heavy metals are very difficult to get back to a manageable state. Even if a preparation process is performed, it is likely that heavy metal particles will remain in the waste. It is therefore important that the temperature of the reactor vessel is not too high, to ensure only organic matter turns to gas. Preferably, the heat required to effect pyrolysis is provided from the central rotating member to provide heat therethrough. This may be achieved by any suitable means, but ideally heat would be provided by a gas burner in communication with the rotating member. Thus, whilst the temperature within the central rotating region of the reactor vessel will be high, the surrounding temperature provided to the waste will be significantly lower - though high enough to enable pyrolysis of organic matter. The optimum temperature of pyrolysis will vary according to the nature of the waste but a temperature in the region of 800⁰C has been found suitable.

During the process, heat is applied in limited measure, sufficient only for the effective processing of organic waste. This has a further important advantage, as the low operating temperatures during pyrolysis prevents thermal damage to the reactor vessel and its component parts. Additionally, as the pyrolysis process with in the reactor vessel is ach ieved at low temperature, none of the waste is transformed into a molten state, thereby preventing inconsistencies in the movement of the waste caused by increased viscosity or the formation of solid structures or mass, which may otherwise cause bridging or blocking within the reactor vessel.

As detailed above, a preparation process would be beneficial . Therefore, in a preferred form of the present invention the waste processing apparatus further comprises preparation means to separate and remove metal particles. This may comprise any suitable means but preferably comprises a magnetic separator. The preparation means may further comprise apparatus, adapted to reduce the average particle size of the raw material waste before processing thereof. Reducing the average particle size ensures that the waste is not too large to be efficiently processed. Most conveniently, the particle size is reduced using a shredder. The shredder may comprise a single fixed rotor, two counter-rotating rotors or any suitable design. Ideally, the particles are shredded so that the diameter of each particle is no greater than about 10mm.

Pyrolysis gases formed from the waste in the reactor vessel are transported into the plasma chamber, where they undergo chemical-electrical processing to produce a mix of gases, as will be described in more detail below. The plasma generator heats up the plasma chamber. In the plasma chamber the pyrolysis gases are heated to temperatures in the range 1200 - 1800^°C in the presence of ionised plasma gases and a high power variable electromagnetic field. To create a high power electromagnetic field, the electrodes preferably comprise a first electrode facing a second electrode. A direct current power supply may be used, but ideally, the power supply is an alternating current power supply for the creation of an alternating electric field between the plates. In this way, the changing polarity of the electric field acts upon the macromolecular bi-polar chains of the pyrolysis gases, applying forces of alignment and turning moments of sufficient energy to overcome the internal atomic bonding energy within the molecule chain which causes fragmentation and destruction thereof. In order to ensure efficient operation the electrodes will ideally be located along the axis of movement of the pyrolysis gases so that the field is generally parallel thereto. The strength of the electric field, between the two electrodes, may preferably be greater than 10KV/cm.

A constant mixing of the gas flow is created in the plasma chamber, preventing the occurrence of an electrical discharge. Changing the parameters of the variable frequency electromagnetic field affects the movement of the electrically charged plasma gas particles, causing them to become highly excited and mobile. This creates opportunities for high energy collisions between the micro molecular plasma gas particles and the macro molecules of the pyrolysis gases, causing their subsequent fragmentation and destruction. By changing the parameters it is possible to change the speed of reaction and interaction without changing the power capacity of the heating devices.

Preferably, the waste processing apparatus further comprises control means for the control of the interaction between the electric field and charged particles of the ionised gas. The electric field has an oscillatory pattern which may be synchronised by the control means. The control means may comprise an external electrical circuit. Control of the reaction between the electric field and charged particles of the ionised gas may be made by measurement of parameters such as, but not limited to electrical parameters including the amplitude of the current, voltage and load and non-electrical parameters such as pressure, temperature, spectrum, brightness and the characteristic sound of the plasma.

The constricting effect of the induced electromagnetic field acting upon the flow within the plasma/pyrolysis gas mix may cause sharp increases in conductivity, creating an electrical discharge. The control means may also be adapted to limit the increase of current under such conditions.

The control means may also be adapted to control other parameters such as the flame and draft required for suitable combustion within the central rotating member and the speed or rotation thereof. The control means may comprise a digital controller programmed to control parameters of the apparatus such as the operating temperatures. The controller may then be programmed with different parameters dependant upon the waste being processed.

The plasma generator is specially adapted to create hot ionised plasma gases having a high temperature flame. The plasma generator may comprise any means for creating the hot ionised plasma from plasma forming gases. Preferably, the plasma forming gas comprises a steam/hydrogen mixture that is introduced into the plasma generator via an inlet thereto. The steam/hydrogen mixture is used because it maximises the calorific value of the resultant gas, though it is to be understood that any gas suitable for forming plasma may be used and this would not depart from the scope of this invention.

The steam/hydrogen gas mixture is oxidised in the plasma generator up to temperatures of 2500^°C in order to form plasma. The plasma generator may comprise an AC resonance device for the ignition and stabilisation of a burning electric arc, which heats the plasma gas flow to ionisation temperature. The plasma generator may comprise a microwave device to provide additional heat energy to the plasma gas flow.

The gases treated in the plasma chamber by such a process have undergone processing to destroy molecular structures therein. However, in order to prevent reformation of these molecular structures it is highly desirable that the gases leaving the plasma chamber undergo a catalytic process before they are subsequently cooled. The combined process of plasma treatment followed by catalyst treatment followed by rapid cooling is important in optimising prevention of the formation of harmful dioxins and other unwanted products. Preferably, therefore, the waste processing apparatus further comprises at least one catalytic chamber in communication with a plasma chamber to receive processed gases therefrom. The catalytic chamber may comprise a catalytic layer containing metal atoms which are capable of affecting the course and speed of chemical reactions.

Each plasma chamber shall have a plasma generator associated therewith and the term processing unit is used to refer to a plasma chamber and the associated generator thereof. The optimum number of processing units required is wholly dependent upon the type of waste being processed. The ratio of processing units to catalytic chambers is an important aspect but this too is dependent upon the type of waste being processed. The ratio of processing units to catalytic chambers in most cases will be 1 :1 , but of course some types of waste may require more or less than one catalytic chambers for each processing unit and vice versa, so the ratio of these components will vary depending on the application. The output of more than one processing unit may be combined and fed to the, or each, catalytic chamber.

Rapid cooling of the gases following catalytic processing is highly advantageous in preventing formation of dioxins and other unwanted products. Thus in a preferred embodiment of the present invention, the waste processing apparatus further comprises at least one cooler adapted to receive the gases from the catalytic chamber(s). The cooler may be any device suitable to provide rapid cooling of the gases, but preferably comprises a heat exchanger adapted to transfer heat to water flowing in or around the cooler. Thus, the cooling chamber acts also to recover thermal energy that may be reused within the system or externally.

There may be more than one cooling chamber. Ideally, there is one cooler associated with each catalytic chamber, though multiple coolers for each catalytic chamber may be used to ensure rapid cooling of the gases.

Following cooling the gases may need to be stored prior to use, and storage may involve compression of the gas. Preferably, therefore the waste processing apparatus further comprises a gas compressor for the compression of the gaseous product after processing. A low pressure gas reservoir may be connected to the output of the cooling chamber(s) and adapted to receive cooled gas therefrom. The gas may then be compressed by the gas compressor and stored in a high pressure gas reservoir, in communication therewith.

Some of the molecules in the gas leaving the catalytic chambers are large and liquid at normal atmospheric temperatures. These condense in the, or each, cooler and this liquid which itself is useful is collected for subsequent further processing or use.

The waste processing apparatus of this invention may be compact in size and may be capable of being operated within and/or transported by an ISO container, ideally a 40ft one. Thus, the apparatus is adaptable and mobile. The main components of the processing apparatus may be built substantially within such a container such that it may be brought to its site of operation and then set up with minimal effort. Ideally the waste processing apparatus is adaptable to connect with additional add-on modules for different end uses. These could be in additional containers that are similarly transported and then integrated with the main components of the processing apparatus.

According to a second aspect of the present invention there is provided a method of processing organic waste comprising:

A) thermally decomposing said waste by means of pyrolysis in a reactor vessel to generate pyrolysis gases;

B) within a plasma chamber, heating the pyrolysis gases in the presence of hot ionised plasma created by a plasma generator; whilst simultaneously applying a high power electric field to the pyrolysis gases, to decompose said gases;

C) passing the decomposed gases through a catalytic process to reduce the reactivity thereof; and

D) rapidly cooling the formed gases.

Preferably, the waste will be fed continuously to the apparatus at a controlled rate. In a preferred embodiment of the present invention, the waste processing apparatus further comprises a feed compression barrel connected to the reactor vessel and adapted to compress waste. Waste may be fed to the feed compression barrel after it has undergone a preparation process or simply as the initial processing step, if a preparation process is not employed. The feed compression barrel compresses the waste and continually feeds the compressed waste into the reactor vessel. In order to experience efficient pyrolysis, the waste and reactor vessel must have little or no oxygen. Any means suitable for the creation of air tight seals may be used. Preferably however, an airtight seal is provided by the constant barrier of compressed waste material being fed in. The feed compression barrel may apply a different degree of compression for different types of waste, sufficient for the removal of air and thus create the ideal gas environment inside the reactor vessel.

The waste processing apparatus and method of the present invention provides continuous, completely automated processing of fuel from waste for the production of usable products and then electrical and/or thermal energy if so required. In this way, waste can truly be considered a valuable high-energy fuel. Unlike other systems utilising plasma to treat waste, which operate at high temperatures and with a high power consumption, the low temperature of the pyrolysis process and the modified power source of the present invention reduces the overall power required to operate the apparatus, with the consequence that there will be a net surplus of energy created from operation of the apparatus. A high service life of the apparatus can be expected due to the lower temperature during pyrolysis, the application of special thermal coverings to protect against corrosion and the application of control devices to manage the system. The apparatus provides efficient processing of waste whilst, preventing the release of harmful synthetic products, heavy metals and their oxides into the atmosphere.

Some of the gases produced by the apparatus and process of the present invention may be fed back to provide heating and supply plasma forming gases.

By way of example only, one specific embodiment of the first aspect of the present invention and a method of the second aspect of this invention will now be described in detail, reference being made to the accompanying drawings in which:-

Figure 1 is a front view of a systematic representation of the waste processing apparatus of the present invention; Figure 2 is a plan view of the waste processing apparatus of Figure 1 ; and

Figure 3 is a front partially cut away view of the plasma chamber of Figures 1 and 2.

Referring to Figures 1 and 2, there is shown one embodiment of waste processing apparatus 10. For convenience some parts are not shown on both drawings. As will be discussed in more detail below, the apparatus includes a reactor vessel 11 within which waste undergoes pyrolysis to generate gaseous products, which are fed sequentially to plasma chambers 12 for plasma treatment and then to catalytic chambers 14 and coolers 15 before being stored.

Waste to be treated is pre-processed before its introduction to the reactor vessel. The nature of this pre-processing varies according to what types of material are contained within that waste. Generally however the waste is sorted in someway to remove undesirable components, such as metals, and is then shredded to reduce particle size. As shown in Figure 2 waste is introduced into a magnetic separator 20 which separates and thereafter removes metal particles - which may subsequently be passed to a suitable recycling process. The waste then passes to a shredder 19 which is adapted to reduce the particle size of the waste to a diameter no greater than 10mm. This assists the efficient thermal processing of the waste when undergoing the pyrolysis process.

The ground waste is transferred, by a belt 18 to a waste feed hopper 16. The waste particles are then compressed in a waste compression barrel 23 thereby expelling any atmospheric air which is removed by means of the exhaust fan 25. The waste compression barrel 23 has a helical drive screw 24 which is driven by a drive unit 26 to rotate and thereby to both compress the waste and force it into the reactor vessel 11. Waste is continuously feed into the waste feed hopper 16 and the arrangement within the compression barrel creates a constant stream of compressed waste to be received by the reactor vessel 11. This constant stream caused by the helical drive screw 24 combined with the constant feed of waste causes an airtight plug to the reactor vessel 11 , thus preventing or minimising the entry of air sufficient for effective pyrolysis.

The reactor vessel 11 comprises a drive member 28 (as shown in Figure 3), extending axially inside the reactor 11 and having a helical screw formation 29 thereon. The drive member 28 is rotatably driven by drive means 31 to cause the contents of the reactor vessel 11 to move therealong in a generally left to right direction (as viewed in Figures 1 to 3). A gas burner 32 is adapted to heat the drive member 28 from the inside thereof as it rotates. The gas burner 32 is adapted to burn gas derived from the process. The combustion products produced by the operation of the gas burner 32 are disposed of by means of an exhaust fan 33 mounted at the opposite end of the drive member. The drive member 28 passes in and out of the reactor vessel and seals are provided at these points.

Providing heat to the waste indirectly in a way such as that described above allows pyrolysis to be carried out at a low temperature. This lower temperature reaction is important as it reduces or prevents evaporation of any heavy metals within the waste. The heating and rotation of the waste in the reactor vessel in the absence of oxygen produces pyrolysis gases which are then transferred to the plasma chambers 12. There are three plasma chambers 12 and each leads to a catalytic chamber 14 and cooler 15. The components and operation of these are equivalent so only one set of these will be described in detail.

Pyrolysis gases flow from an upper part of the reactor vessel 11 through a plasma chamber feed pipe 30 to the plasma chamber 12. As illustrated in Figure 3, the walls of the plasma chamber 12 define a reaction space 34 in the flow path from the plasma chamber feed pipe 30 to a catalysis chamber feed pipe 35. The reaction space 34 is wider than the diameter the pipes 30 and 35. First and second electrodes 36, 37 are provided within the reaction space 34, and an AC power supply (not shown) is applied across these plates to create an alternating electromagnetic field therebetween. The orientation of this field is such that it is applied generally parallel to the flow path through the chamber. The strength, direction, frequency and other parameters of this field may be varied.

Hot ionised plasma gases are generated by a plasma generator (generally indicated 13 in Figures 1 and 2 but not illustrated in Figure 3) using a variety of techniques and are transferred to the reaction chamber 34 through a plasma fed pipe 38. The pyrolysis gases interact with the plasma gases under the influence of the electromagnetic field to enable full decomposition of the components therein. The changing polarity of the electromagnetic field causes fragmentation and destruction of the macro molecular bi-polar neutral chains of the pyrolysis gases. The reaction between the electromagnetic field and the gases can be controlled by changing parameters such as the temperature of the gasification of waste, the intensity and frequency of the electric field, the temperature in the reactor vessel; and speed of supplying and movement of the waste. The varying nature of the electromagnetic field causes the charged plasma gas particles to become highly excited and mobile causing more and stronger collisions with the macromolecular polar chains of the pyrolysis gases.

Once the gases have undergone processing in the plasma chamber 12 they have been reduced to far smaller molecules and they flow to the catalytic chambers 14 through the associated feed pipe 35. In the catalytic chambers 14 they are passed over catalytic layers having metal atoms, which are capable of affecting the course and speed of chemical reactions to ensure the formation of desirable compounds rather than undesirable ones. The out flow of gases from the catalytic chambers 14 is directed through cooler feed pipes 39 to coolers 15 to rapidly cool the gases after processing. The catalytic process followed by rapid cooling in the coolers 15 is important in the prevention of the reformation of any hydrocarbons macromolecules, including dioxins and other undesirable substances. As best shown in Figure 2, the coolers 15 comprise a heat exchanger 43 adapted to allow water circulated by coolant feed pipes 44 to rapidly cool the gases by absorbing their heat. The heat recovered by this water may be used in other applications.

During the cooling process certain constituents of the gas condense and collect in the coolers 15. This liquid is channelled though liquid pipes 41 to a liquid storage tank 42 from where it may be pumped by pump 44 for use or further processing.

Following the cooling process, the resultant clean gas is a mixture including significant proportions of H₂ and CO (often referred to as syngas) and is transferred to a low pressure gas reservoir 45. It may be subsequently compressed by a gas compressor 46 and stored in a high pressure gas reservoir 47 before use.

Remnants from the pyrolysis process within the reactor vessel are discharged therefrom through a discharge port 54 that is provided with a motor drive 55. Such material, sometimes known as char may, depending on its composition, be a useful product.

Control of the whole system's operation and the various parameters that affect it may be achieved by an integrated control means 49 (shown only in Figure 2). The control means is connected to the apparatus at many points by electric wires contained in the electrical wiring harness 51. Sensors adapted to detect conditions within the system may provide information that is used to alter parameters of various operating conditions. An electric service panel 50 may be provided. The control means can be used to control all parameters of the apparatus' operation including: the temperatures of the catalytic chambers 14; the speed of cooling in the coolers 15; the input of waste to the reactor vessel 11 , the pre-processing of the waste, such as sorting and shredder particle output size; speed of the drive member 28; the temperature in the reactor vessel; the electrical field in the plasma chamber; the plasma generated by the plasma generators; the overall process speed and many other factors. Both on large and small-scale installations the control means 49 may be programmed with different programs for the various types of waste to be processed, and the various requirements of the end-product.

Claims

1. Waste processing apparatus comprising:

- a plasma generator adapted to create hot ionised plasma gases;

- electrodes within the plasma chamber that create an electromagnetic field that is applied to the mixed plasma and pyrolysis gases to achieve decomposition of harmful waste components.

2. Waste processing apparatus as claimed in claim 1 , wherein the reactor vessel comprises a central rotating member having a helical drive screw configuration.

3. Waste processing apparatus as claimed in claim 2, wherein the central rotating member has drive means to cause rotation thereof.

4. Waste processing apparatus as claimed in any of the preceding claims further comprising a waste preparation system that treats raw waste prior to its introduction to the reactor vessel.

5. Waste processing apparatus as claimed in claim 4, wherein the waste preparation system includes a shredder or like device to granulate the waste.

6. Waste processing apparatus as claimed in claim 4 or claim 5, wherein the waste preparation system reduces the waste to a maximum particle size of 10mm.

7. Waste processing apparatus as claimed in any of claims 4 to 6, wherein the waste preparation system further comprises apparatus for the separation of metal from the raw waste.

8. Waste processing apparatus as claimed in claim 7, wherein the apparatus for the separation of metal particles comprises a magnetic separator.

9. Waste processing apparatus as claimed in any of the preceding claims, wherein the electrodes include a first electrode and an opposed second electrode across which an electrical charge is applied.

10. Waste processing apparatus as claimed in claim 9, wherein the electrodes are connected to an alternating current power supply to generate an alternating electric field.

11. Waste processing apparatus as claimed in any of the preceding claims wherein the plasma generator has one or more inlet for one or more plasma forming gas and an ignition and heating system that converts that one or more plasma forming gas into a plasma.

12. Waste processing apparatus as claimed in claim 11 , wherein the plasma forming gas comprises a mixture of steam and hydrogen.

13. Waste processing apparatus as claimed in any of the preceding claims, wherein the plasma generator includes an AC resonance device for the ignition and stabilisation of a burning electric arc, for the heating of plasma forming gas to ionisation temperature.

14. Waste processing apparatus as claimed in any of the preceding claims, wherein the plasma generator comprises or includes a microwave device to provide additional heat energy.

15. Waste processing apparatus as claimed in any of the preceding claims, further comprising a catalytic chamber receiving processed gas from the plasma chamber.

16. Waste processing apparatus as claimed in claim 15, wherein the catalytic chamber includes a catalytic layer containing metal atoms which catalyse desirable chemical reactions in the processed gas from the plasma chamber.

17. Waste processing apparatus as claimed in either of claims 15 or 16, further comprising a cooler that receives gases from the catalytic chamber.

18. Waste processing apparatus as claimed in claim 17, wherein the cooler includes a heat exchanger adapted to pass heat from the gas to a coolant flowing within the heat exchanger.

19. Waste processing apparatus as claimed in either of claims 17 or 18, wherein there is one cooler associated with each catalytic chamber.

20. Waste processing apparatus as claimed in any of the preceding claims, further comprising storage for generated gas.

21. Waste processing apparatus as claimed in claims 20, wherein the storage is pressurised and a compressor is provided to compress gas after processing.

22. Waste processing apparatus as claimed in any of the preceding claims wherein multiple plasma processing units are provided on a single reactor vessel.

23. Waste processing apparatus as claimed in claim any of claims 17 to 19, which further comprises a liquid collection system to recover and store liquid that condenses within the coolers.

24. Waste processing apparatus as claimed in any of the preceding claims further comprising one or more add-on modules adapted to perform one or more of: pre-processing of waste before pyrolysis; post treatment of products produced by the process; generation of electricity from the process products; and integration of the process products or electricity derived therefrom into local supply networks.

25. Waste processing apparatus as claimed in any of the preceding claims further comprising control means that control the operation of the apparatus.

26. A method of processing waste comprising:

B), heating the pyrolysis gases within a plasma chamber in the presence of hot ionised plasma created by a plasma generator, whilst simultaneously applying an electric field to the pyrolysis gases, to decompose said gases; C) passing the decomposed gases through a catalytic process to reduce the reactivity thereof; and

D) rapidly cooling the formed gases.

27. A method as claimed in claim 26 wherein the processing of waste is a continuous process.

28. A method of processing waste as claimed in claim 26 or 27, wherein the plasma treatment of the waste is carried out in the plasma chamber at a temperature in the range 1200-1800^°C.

29. A method of processing waste as claimed in any of claims 26 to 28, wherein the processed gases are subsequently used in a turbine, gas engine or other apparatus to generate electricity.

30. A method of processing waste as claimed in any of claims 26 to 29, wherein a proportion of products of the process or electricity generated therefrom is used to power the waste processing apparatus.

31. A method of processing waste as claimed in claim 30, wherein said proportion is approximately 10%.

32. A method as claimed in any of claims 26 to 32 wherein pyrolysis in the reactor vessel is carried out at temperatures less than about 800^°C.