PT629138E - MATERIAL PROCESSING - Google Patents

Abstract

A material treatment process, and particularly such a process for the destruction of waste material. The process involves pyrolysis of waste material within a plasma torch and a hot zone which receives the material stream from the torch. Waste material is injected into the torch as a fine spray and/or as a gas, and the direction of injection is generally transverse to the direction of movement of the plasma through the torch. The location of the injection is such that the waste material is injected directly into the core of the plasma. The hot zone is of a length such as to ensure complete pyrolysis of the material, and that zone is immediately followed by a cooling zone in which the material is subjected to very rapid quenching. The material stream entering the cooling zone is at a temperature above that at which CO in the material stream tends to re-form into CO2 in the material stream includes particulate carbon which is used to absorb residual toxic compounds when the material is subjected to an alkaline environment within the cooling zone and/or a scrubber following that zone.

Description

85 106 ΕΡ 0 629 138 / ΡΤ

DESCRIPTION "Material processing"

This invention relates to thermal decomposition processes, such as the destruction of toxic residual matter, and concerns both the process and the apparatus. It will be convenient to describe the invention in particular with reference to the application of the example to the destruction of waste material.

This invention relates in particular but not exclusively to the treatment of waste products resulting from chemical treatment, chemical conversion and the like. These products often contain highly toxic physiologically active substances directly or carcinogenically. By way of example, such products may include per- or polychlorinated and per- or polyfluorinated aliphatic or aromatic substances, such as chlorophenols, dioxins and furans. In addition to their toxicity, these compounds often exhibit high chemical and thermal resistance. The destruction of waste is becoming a problem of great importance all over the world. The processes of removing the contaminated material were established, in particular through landfill and high temperature combustion techniques.

In the landfill technique, which generally only applies to solids, the toxic matter is not destroyed, but simply stored in leaks. In the best case, the leachers are indicated to avoid the contamination of groundwater by the residual matter deposited in them. This technique is not suitable for some areas, such as areas where there is a potential danger of spills, seepage or the like.

In the high temperature combustion technique, temperatures generally attainable, for example up to 1500 ° C, are insufficient to destroy all toxic substances. The most stable thermally hazardous substances are thus emitted into the atmosphere. In addition, the combustion process may promote the formation of additional dioxins and furans, which are then also emitted into the atmosphere.

85 106 ΕΡ 0 629 138 / ΡΤ 2

There are thus disadvantages associated with each of the techniques described above. US-A-4644877 describes a pyrolysis waste destruction system in which the waste material is fed into a plasma burner and exits through a cylindrical element into a reaction vessel, which forms a reaction chamber. Residuals leave the chamber through outlet openings for cooling in the spray ring. The outlet chamber is for cooling the waste material subject to pyrolysis to form recombined products.

According to a first aspect of this invention, a thermal decomposition process includes the steps of forming a plasma within a pyrolysis apparatus, injecting the material to be treated as a fine spray and / or a gas within said plasma, moving said material being a stream through said pyrolysis apparatus in one direction towards the outlet end of the pyrolysis apparatus, maintaining said material at a high temperature during said movement of the material stream, so that substantially complete pyrolysis of said material and preventing the recombination of undesired by-products, moving said stream of material through said outlet end to a temperature higher than the temperature at which said recombination will occur, and subjecting said material stream to a rapid cooling at said end of exit, or adjacent to it and before the temperature thereof. the material to be lowered to a level at which recombination of said unwanted by-products will occur.

In one process form, the cooled material is subjected to an environment in which the toxic residual compounds are adsorbed onto a solid carrier substance so as to thereby be capable of separating the main body from the material. It is preferred that the above solid carrier substance is particulate carbon, and it is further preferred that the carbon is formed by treatment of the waste material in the pyrolysis apparatus. The material to be treated may be in the form of a liquid which is atomized upon introduction into the pyrolysis apparatus. Alternatively, the material may be in the form of a particulate solid or in the form of a gas.

It is preferred that the pyrolysis apparatus includes a high energy electrothermal plasma in which the atomised material is injected so as to cause dissociation of the molecules which make up the material. The rate at which such dissociation occurs is controlled, at least partially, by the temperature of the plasma. It is further preferred that the material leave the plasma arc as a stream, which passes through a hot zone, within which the temperature of the material is maintained at a sufficiently high level to facilitate the continuation of the pyrolysis, which is initiated within of the plasma. This can be achieved in a number of ways, as will be described below. The residence time within the hot zone can be determined suitably to increase the likelihood of complete dissociation of all molecules within the material stream. The greater the time during which the specific material is subjected to heating, the greater the likelihood of decomposition of compounds having higher thermal resistance. Generally, the higher the temperature, the greater the rate at which decomposition is achieved. The material stream is cooled upon being subjected to rapid cooling in a cooling zone after leaving the hot zone, and the cooling rate is preferably such as to avoid, or at least minimize, the recombination of the dissociated ions.

Residual toxic compounds which are separated from the stream of material by adsorption or adsorption on the particulate carbon, as described above, may be destroyed by subjecting the particulate carbon to suitable additional treatment.

In a preferred form of the process, the aforementioned hot zone is defined by a tube (hereinafter referred to as a tube haul), through which a current of material is displaced between the plasma arc and the cooling zone. The stream of material preferably enters that tube immediately after emerging from the plasma arc. The dimensions and construction of the tube haul may have an influence on the efficiency of the process, as will be explained hereinafter.

As described above, the pyrolysis of the material, such as waste material, can result in the production of particles of coal, such as soot or charcoal

85 106 ΕΡ 0 629 138 / ΡΤ 4, and these particles can influence the downstream processing of the material. For example, the particles may block or partially block tube haul. This is especially true in the case where the material to be treated mainly comprises hydrocarbons. However, where the material mainly comprises oxygen-containing organic compounds, there may not be a problem with excessive carbon particles.

In one form of the process, the oxygen is introduced into the plasma so as to react with carbon particles which can be formed and thereby produce gaseous carbon compounds with the concomitant evolution of heat. Such oxygen addition may therefore lower the level of solid coal within the material stream so as to further facilitate the downstream processing of such material, for example, to facilitate the passage of the material stream through the pipe lance. In addition, the released heat assists in keeping the temperature of the material stream suitably high as it passes through the tube lance to prevent recombination to form toxic compounds. The need to convert solid carbon to gaseous carbon compounds by addition of oxygen to the process material can be eliminated, or at least reduced, by diluting the material to be processed into an inert carrier liquid, which passes through the apparatus without affecting the dynamics of the reaction. The carrier liquid will have the effect of lowering the percentage by weight of carbon particles in the stream leaving the plasma. Ideally, the amount of inert carrier liquid added will be controlled so as to reduce the percentage by weight of coal particles to a level, which avoids blockages of the equipment without the addition of any oxygen.

In some circumstances the level of carbon particles in the stream of material exiting the pipe lance may be such as to cause partial blocking or blockage in the cooling zone and / or in any other part of the apparatus following the cooling zone, and this can occur notwithstanding the introduction of oxygen into the plasma, as described above. To overcome this problem, in one process form, more oxygen is added to the stream exiting the pipe lance, so as to react with the coal particles and lower the level of particles within the stream of material. The reaction of the oxygen with the coal is exothermic, which helps to maintain the current temperature of 85 106 ΕΡ 0 629 138 / ΡΤ 5

adequately high material until actual cooling of the chain is verified. High temperatures tend to resist the recombination of ions to form toxic compounds. It is preferred that a marked temperature gradient is effectively provided in the cooling zone. The cooled material may be exposed to an alkaline environment to encourage the adsorption of any toxic acidic residual compounds in the carrier substance, such as the coal particles. Thus, toxic compounds which have escaped pyrolysis, or which are formed by recombination following pyrolysis, may be isolated in the carbon particles, and these particles may be separated from the remainder of the processed material by any suitable means. As an example, such separation can be done by filtration.

The separated carbon particles with the adsorbed toxic compounds may be subjected to further treatment to decompose the toxic compounds. For example, the particles may be subjected to further treatment which causes the toxic compounds to be desorbed in a liquid, which is then recirculated through the process.

Alternatively, the coal particles may be disposed of into the landfill. The procedure adopted under any circumstance will generally be dependent on the level of the toxic compounds in the coal particles.

According to a second aspect of this invention, a thermal decomposition apparatus includes a pyrolysis apparatus, having means for generating a plasma arc and passage means for containing the plasma beyond the region of said arc, means for introducing the and are operative to introduce the material into said pyrolysis apparatus as a fine spray and / or a gas, and cooling means, located at an outlet end of said pyrolysis apparatus. wherein said pyrolysis apparatus is operative to maintain said introduced material at a high temperature so that substantially complete pyrolysis of said material is achieved and the recombination of unwanted by-products is, substantially prevented during movement of said material through the passage means to the outlet end of said apparatus pyrolysis, and the said means of

85 106 ΕΡ 0 629 138 / ΡΤ 6 are rapidly operative to effect cooling of said material leaving said outlet end, prior to the temperature of said material being lowered to a level, wherein said recombination of said by-products and wherein said passage means provides control of a boundary layer of said material to ensure a substantially consistent temperature of the material through said passage means.

Embodiments of the invention are described in detail in the following passages of the specification, which relate to the accompanying drawings. The drawings are, however, merely illustrative of how the invention may be embodied, so that specific shape and arrangement of the various aspects, as shown, should not be construed as limiting the invention.

In the drawings: FIG. 1 is a flowchart representing a form of the process according to the invention; FIG. 2 is a schematic cross-sectional view through one form of the pyrolysis apparatus for use in a process as represented by FIG. 1; FIG. 3 is a semi-schematic cross-sectional view of one form of the pipe lance, suitable for use in the apparatus shown in FIG. 2; FIG. 4 is a semi-schematic cross-sectional view of another form of the tube lance, suitable for use in the apparatus of FIG. 2; FIG. 5 is a schematic view of the apparatus according to one embodiment of the invention:

In FIG. 1 the line 1 represents the path of the material to be treated as it is introduced into the pyrolysis apparatus 2. The material can be introduced into the pyrolysis apparatus in any suitable way, but it is preferred that it is in the form of a spray fine particles of liquid and / or solid, or a gas, or a combination of such a fine spray and a gas. And still

It is preferred that the material is injected into the pyrolysis apparatus 2 under pressure.

In case the material is moved along path 1 as a stream of liquid, the stream of liquid may be atomized at or just before the injection point within the pyrolysis apparatus 2, and any injecting or other means may be used appropriate. The liquid droplets resulting from the atomization preferably have a diameter of 100 microns or less. In particular, the liquid droplets must be small enough to allow complete pyrolysis. If they are too large, the surface of the droplets may only carbonize superficially under the conditions within the pyrolysis apparatus 2.

If the material entering the pyrolysis apparatus 2 is in the form of a particulate spray or includes the same, each of these particles preferably has a suitably small size due to the above. A particle size of 100 microns or less will generally be satisfactory. The pyrolysis apparatus 2 includes means 3 for generating a plasma arc 4 so as to allow the production of a high energy electrothermal plasma. The pyrolysis apparatus 2 also includes a hot zone 6, immediately following the arc generation means 3 and which receive the material stream 5 exiting the arc generating means 3. It is preferred that the plasma gas 7 is argon or a mixture of argon, since it produces an inert plasma atmosphere in which the pyrolysis is carried out. The arc generation means 3 may be, for example, a plasma torch the same or similar to that described by the PCT patent application AU89 / 00396. In this regard, the temperature within the plasma may typically be in the range of 10,000 to 15,000 ° C. Alternatively, other types of plasma, such as a vapor plasma, may also be used. The direction in which the material to be treated is introduced into the plasma arc 4 may be selected according to preference or circumstances. As an example, the steering may generally be parallel to, or generally transverse to, the bow line 4, but the latter is generally preferred.

It is preferred that the region of the pyrolysis apparatus 2 in which the material to be treated is introduced into the plasma is maintained at a suitably high temperature, for example a temperature of 1000 ° C or , preferably, higher. The material may be injected directly into the core of the plasma arc 4, or at least near the downstream fixture 8 of the bow 4. If direct injection is not possible, the surfaces of the torch 3 in the region of introduction of the material may be heated to maintain a suitably high level of temperature. FIG. 2 provides a clearer indication of the preferred location of point 9 in which the material to be treated is introduced into the pyrolysis apparatus 2. The particular torch 3 which is shown in FIG. 2, and forms part of the pyrolysis apparatus 2, includes a cathode 10 and two anodes 11 and 12 separated by a set 13 of spacers. The anode 11 functions as a starting anode to initiate the arc 4 and, once generated, the arc 4 is then extended so that its downstream fixation 8 lies in the anode 12. Other forms of torches could be adopted.

In the specific arrangement shown in FIG. 2, the material to be treated is injected into the torch passage 14, at or near the arc connection 8. The direction of this injection is usually transverse to the longitudinal axis of the passageway 14, so as to facilitate injection into the core of the arch 4.

The molecules comprising the injected material are required to separate under the influence of the high temperatures prevailing within the plasma, and the material thereby undergoes pyrolysis, or at least substantial pyrolysis. The material leaves the plasma arc 4 as a chain 5, which is directed into and through the hot zone 6. The stream of the material 5 is, first, a gas which has associated solid carbon particles in the form of soot.

In a particular arrangement shown, the hot zone 6 is formed by an elongate hollow tube which will be identified from now on as the tube lance. The tube 6 effectively forms an extension or continuation of the torch passage 14, and the dimensions of the tube 6 will be selected to suit particular requirements and circumstances. A basic function of the pipe 6 is to provide retention of the stream of material 5 in an environment, which promotes the continuation of the pyrolysis process. That is, it may happen that the pyrolysis of the material is not complete within the torch 3, and the function of the tube 6 is to provide an extension of the environment within which the pyrolysis is effected. In particular, the tube 6 extends the residence time of the material within a suitable high temperature environment and thereby optimizes the possibility that the complete pyrolysis is achieved.

In one arrangement, which has operated satisfactorily, the tube lance is narrow and has a ratio of the diameter to length of about 2 to 25. However, in any particular circumstances, the length of the tube may be selected so as to achieve a suitable residence time of the processed material within the tube and any relation between the diameter and the length can be adopted. The nature of the toxic compounds within the material to be treated will influence the determination of a suitable residence time within the tube 6.

An important consideration in the design of the tube 6 is the need to keep the material processed at as high a temperature as possible along the length of the tube as this assists in the prevention of undesirable recombination reactions. In this aspect, the temperature of the stream 5 entering the tube 6 may be above 3000 ° C and the temperature of the stream leaving the tube may be 1200 ° C. The flow limiting layer of the fluid from the material stream which comes into contact with the surrounding surface of the tube 6 will tend to cool due to such contact. Accordingly, the tube 6 may be designed so as to allow the control of the boundary layer, so that it is kept as thin as possible. In particular, it is desirable that the temperature of the material stream be substantially consistent along that stream as it arises from the outlet end 15 of the pyrolysis apparatus 2.

An approach to the above is shown schematically in FIG. 3. The inner surface of the tube lance 6, shown in FIG. 3 is equipped with a series of lips 16 which tend to deflect the boundary layer of the material stream 5 back to the axial center of that stream. The resulting turbulence inhibits the formation of a distinct cold boundary layer, and there is a continuous mixing of the boundary layer with the relatively warm inner body of the material stream such that a substantially consistent temperature is maintained across the width of the stream.

85 106 ΕΡ 0 629 138 / ΡΤ 10 FIG. 4 shows another approach, in which the tube 6 has a coating 17, which is capable of withstanding high temperatures and, in particular, temperatures above 1000 ° C. As an example, the coating 17 may be composed of a ceramic material. If desired, such a device may be modified by introducing an external source of heat into the coating 17 at an appropriate location, such as adjacent the outlet end 15 of the pyrolysis apparatus 2. The body 18 of the tube 6, which surrounds the coating 17, can also be cooled with water (for example), which enters the inlet 19 and exits the outlet 20. A similar cooling may be desirable in other forms of the pipe 6, including that shown in FIG. 3.

As previously mentioned, the stream of material 5 exiting the torch 3 will contain particles of carbon. If the level of coal particles is relatively high, there may be a danger of the coal locking the tube 6. In order to alleviate this problem, an oxygen stream may be fed into the pyrolysis apparatus 2 to convert some of the carbon particles into gaseous carbon compounds. In the specific example shown in FIGS. 1 and 2, the oxygen is fed to the torch 3 at a location 21 adjacent to the point 9, in which the material to be treated is introduced. Other provisions are clearly possible. The reaction of the coal and oxygen is exothermic and a considerable amount of heat is released. This heat assists in maintaining the temperature of the material stream at a suitably high level to encourage the continuation of the pyrolysis and resist recombination of the dissociated ions and simple compounds to form undesirable compounds.

In one possible arrangement, the tube 6 may include a graphite coating. In such a case, it may be important to control the oxygen stream entering at 21 so as to maintain an oxygen deficient atmosphere within the tube 6. As an example, the ratio of oxygen to carbon may be maintained 30% below the values stoichiometric. If such an atmosphere is not maintained, some oxygen may react with the carbon of the tube coating, thereby attacking the coating.

An oxygen deficient atmosphere will also tend to reduce the combination of dissociated ions to form undesirable oxygen-containing compounds.

The stream of material 5, which passes out the outlet end 15 of the pyrolysis apparatus 2, is subjected to cooling in a cooling zone 22. In the arrangement shown, the material is then and / or subsequently subjected to an environment such as that described below, in which the residual toxic organic compounds are adsorbed onto a particulate carrier. As an example, the carrier substance may be provided by the non-reacted carbon particles which remain within the material stream 5. The level of the carbon particles in the material stream 5, which passes outside the outlet 15 can, for example, be 1% by weight, or greater. Such a level of carbon may cause blockage or blockage of the components of the processing apparatus, which follows the pyrolysis apparatus 2. Consequently, in some circumstances it may be desirable to further reduce the carbon content by introducing a additional oxygen stream 23 to convert some of the remaining coal particles into gaseous carbon products. The carbon content of the material stream entering the cooling zone 22 is preferably in the range of 0.5% by weight. The introduction of the additional oxygen stream 23 may have a different effect. That is, the heat generated by the reaction of that oxygen with the coal can assist in keeping the material stream 5 at a suitably high temperature until cooling is done. In this regard, it is desirable that the temperature of the material stream 5 just before cooling is at least 1500Â ° C and it is preferred that the temperature is in the range of 1800Â ° C to 2000Â ° C .

As mentioned above, higher temperatures resist the recombination of the dissociated ions to form toxic compounds, such as dioxins. It is generally believed that it is desirable to maintain the temperature in the material stream 5 until the time of cooling to a level that is high enough to avoid the possibility of the CO in the stream 5 to be reconverted to CO2.

As indicated above, the introduction of additional oxygen stream 23 will not be necessary in all applications of the invention.

85 106 ΕΡ 0 629 138 / ΡΤ 12

In the particular configuration shown, the cooling zone 22 includes a set of sprayers 24, arranged to produce a cold barrier 25, through which the stream of material 5 has to pass. That is, the stream 5 is confined to a passage 26, which is completely filled at the location of the sprayers 24 by the barrier 25. The arrangement is such that the cooling of the stream of material is complete and this results in the existence of a sudden sharp drop in material temperature. In the example shown, the passage 26 is formed as an extension of the passage through the pipe 6. The cooled material exiting the cooling zone 22 can be passed through a scrubber 27, as shown. The pH of the scrubber 27 will generally be alkaline, for removal of acidic compounds from the material received. The carbon particles within that material may be dispersed within a body 28 of the alkaline solution of the scrubber, so that the acidic organic compounds are encouraged to be adsorbed onto the carbon particles. Optimal process parameters, such as pH and temperature of the scrubber solution, which are required to achieve the maximum adsorption of toxic organic compounds, may be determined by routine experimentation.

In one particular example, the scrubber solution is a sodium hydroxide solution, but other types of solutions may be used. Furthermore, in the configuration illustrated by FIG. 1, the same solution can be used in the cooling sprayers 24 and scrubber sprayers 29. To that end, a pump 30 can operate to aspirate the solution from the body of the solution 28, to feed the sprayers 24 and 29. The line 31 in FIG. 1 represents the solution feed to the scrubber 27, and the line 32 represents the withdrawal of spent solution from the scrubber 27.

The carbon particles may be separated from the scrubber solution by a simple filtration process, which is identified in FIG. 1 by block 33. Such filtration may be performed on a continuous basis or on a batch basis.

The toxic organic compounds adsorbed on the carbon particles can be separated from the coal particles by a desorption process, which is represented by block 34 in FIG. 1. That is, the adsorption process 85 106 ΕΡ 0 629 138 / ΡΤ 13

effected in the scrubber 27 is inverted. The compounds are typically desabsorbed in water, which can be recycled in the process, as part of the inflow of material 1.

In the particular construction shown in FIG. 2, the scrubber 27 has a rectangular configuration and is substantially larger than the tube which forms the cooling zone 22. A plurality of scrubber sprayers 29 are located in the upper operative region of the scrubber 27 to direct the scrubber solution as a fine spray or mist. The direction of this spray or mist is preferably downward. The apparatus may include an explosion drain 35, as shown in FIG. 5, to purge the system in the event of the formation of an explosive gas mixture. This is an important safety feature to reduce the risk of explosion. Explosion purge has a known shape and construction. In the example shown, the purge 35 is located adjacent to the scrubber 27. The material, which remained in gaseous form and which has not been purified from the gas in the scrubber 27, can be passed to the atmosphere by means of a chimney 36, shown in FIG. 5. The chimney 36 may, for example, include a number of chimney sprayers 37, which act to remove any remaining traces of gaseous compounds having an affinity for an aqueous alkaline environment. In the specific arrangement shown, the chimney sprayers 37 are supplied with solution by means of the pump 30.

Specifically the pyrolysis apparatus 2, and the entire apparatus, more generally, form a very compact unit, which is suitable for use in the field. The apparatus may, for example, be integrated into an existing process so that there is no net production of toxic waste. This is an important advantage, since the transport of toxic substances is dangerous.

A unique feature of the process described is the deliberate retention of particulate carbon within the material stream and the control of the process conditions such that the carbon particles act as a carrier substance for the toxic organic compounds which survived the process pyrolysis step. That is, the organic compounds, which survived the processing steps prior to the cooling process, are effectively retained by the fixation or adsorption on the carbon particles. The surviving organic compounds are thus retained in a manner which facilitates convenient clearance or, alternatively, subsequent processing, when deemed appropriate, depending on the level of toxic organic compounds. This is contrary to the accepted practice of inhibiting the formation of coal in the existing processes of destruction of toxic compounds. Analysis of the material leaving the scrubber has shown that the level of destruction of the toxic products in the process steps prior to the scrubber is in the order of 99.9999%. Further treatment of the separated carbon particles allows the level of destruction to be increased beyond 99.9999%. A process according to the invention is useful for the effective destruction of a wide range of toxic products, including chlorophenols and dioxins. The process is robust and secure. Various modifications, modifications and / or additions may be introduced into the constructions and arrangements of the previously described parts without departing from the invention as defined by the appended claims.

By COMMONWEALTH SCIENTIFIC AND INDUSTRIAL RESEARCH ORGANIZATION and SIDDONS RAMSET LIMITED

Claims (35)

A thermal decomposition process comprising the steps of forming a plasma inside a pyrolysis apparatus (1), injecting the material (1) to be treated as a fine spray and / or a gas within said plasma, moving said material as a stream (5) through said pyrolysis apparatus in one direction to the outlet end (26) of the pyrolysis apparatus, maintaining said material at a high temperature during said movement of the material stream so that substantially complete pyrolysis of said material is achieved and the recombination of unwanted by-products is avoided, movement of said stream of material through said outlet end to a temperature higher than the temperature at which said recombination will occur, and subjecting said stream of material to a rapid cooling (22, 24, 25) at said outlet end (26) or adjacent to the month and before the temperature of said material stream is lowered to a level at which recombination of said undesired by-products occurs. A process according to claim 1, wherein the temperature of said material stream just prior to said cooling is such that the CO in said material stream has not begun to be converted to CO2. A process as claimed in claim 1 or claim 2, wherein said plasma is formed by the use of a gas, which is a noble gas. A process according to claim 3, wherein said gas is argon or a mixture of argon. A method according to any one of claims 1 to 4, wherein said plasma is generated by an electric arc (4), created between two electrodes (10, 12), and said material (1) is injected into the electrode said plasma, at a location adjacent the connection (8) of said arc to the electrode (12) forming the anode. A method according to any one of claims 1 to 4, wherein said plasma is generated by an electric arc (4) created between two electrodes (10, 12), and said material is injected into the core of said arc . 85 106 ΕΡ 0 629 138 / ΡΤ A method as claimed in claim 5 or claim 6, wherein said material is injected in a direction extending generally transverse to the direction in which said arc extends between said electrodes. A process according to any one of claims 1 to 7, wherein said material is injected into the pyrolysis apparatus in the form of atomised liquid. A method according to claim 8, wherein the dimension of? droplets of liquid forming said atomized liquid is 100 microns or less. A process according to any one of claims 1 to 7, wherein said material is injected into said pyrolysis apparatus in the form of solid particles. A process according to claim 10, wherein the size of each said particle is 100 microns or less. A process according to any one of claims 1 to 11, wherein the oxygen (21) is introduced into said pyrolysis apparatus at the location of said adjacent or adjacent material injection. A process according to any one of claims 1 to 11, wherein there is a partially oxidizing atmosphere within said pyrolysis apparatus. A method according to any one of claims 1 to 13, wherein said pyrolysis apparatus includes a plasma torch (2) and a hot zone extending between said torch and the location in which said cooling is effected . A method according to claim 14, wherein said hot zone is formed within a tube (6), and a boundary layer of said material, contacting the surrounding surface of said tube, is controlled so that the material within said material stream is at a substantially consistent temperature at the time it is subjected to said cooling. 85 106 ΕΡ 0 629 138 / ΡΤ 3/5 A method according to any one of claims 1 to 13, wherein said pyrolysis apparatus includes a tube (6), through which said material passes to the outlet end, and a boundary layer of said material, which comes into contact with the surrounding surface of said tube, is controlled so that the material within said material stream is at a substantially consistent temperature at the time it is subjected to said cooling. A method according to claim 15 or claim 16, wherein said boundary layer is controlled by inducing turbulent flow in said boundary layer. A method as claimed in claim 15 or claim 16, wherein said boundary layer is controlled by deflecting inwardly toward the center of said material stream. A method as claimed in claim 15 or claim 16, wherein said boundary layer is controlled by maintaining a suitably high temperature in a wall of said tube, which forms said surrounding surface. A process according to any one of the preceding claims, wherein the cooled material is subjected to an environment in which the residual toxic compounds are absorbed into a carrier substance, and said substance is then separated from said material. A process according to claim 20, wherein said carrier substance is particulate carbon. A method according to claim 21, wherein said carbon particles are formed by said pyrolysis. A method as claimed in claim 21 or claim 22, wherein said toxic compounds are desorbed from said carrier substance. 85 106 ΕΡ 0 629 138 / ΡΤ 4/5 A process according to any one of the preceding claims, wherein the temperature of the material just before cooling is at least 1500Â ° C. A process according to claim 24, wherein the temperature of the material just before cooling is at least 1100 ° C. A thermal decomposition apparatus, comprising a pyrolysis apparatus (2), having means (10, 11, 12) for generating a plasma arc (4) and passage means (6) for containing the plasma for therein, means for introducing the material (1), located in the region of said arc, or adjacent thereto, and which are operative to introduce the material into said pyrolysis apparatus as a fine spray and / or gas, and cooling means (22, 24, 25) located at or adjacent the exit end of said pyrolysis apparatus, wherein said pyrolysis apparatus is operative to keep said material introduced at a high temperature, so that substantially complete pyrolysis of said material is achieved and recombination of undesired side products is substantially avoided during the movement of said material through the passage means (6) to the outlet end of said apparatus and said cooling means is rapidly operative to effect cooling of said material (5), which leaves said outlet end, prior to the temperature of said material that is lowered to a level in which the recombination of said unwanted by-products, and wherein said passage means (6) provides control of a boundary layer of said material to ensure a substantially consistent temperature of the material through said passage means. The apparatus of claim 26, wherein said generating means includes a plasma torch having a passageway (14) therethrough, and said material introducing means (1) are arranged to introduce the torch material in said passageway in a direction which is substantially transverse to the longitudinal direction of said passageway. The apparatus of claim 27, wherein said means containing the plasma includes a tube (6), which forms a continuation of said passage of the plasma torch. 85 106 ΕΡ 0 629 138 / ΡΤ 5/5 Apparatus according to any one of claims 26 to 28, wherein said generating means includes a cathode (10) and an anode (12) arranged in spaced relationship to said cathode, and said material introduction means (1) are located at said anode. Apparatus according to any one of claims 26 to 29, wherein said cooling means (24, 25) are located on said outlet end and are operable to produce a cold barrier, through which the material exiting from the outlet said pyrolysis apparatus has to pass. Apparatus according to any one of claims 26 to 30, wherein said passage means includes means (16) for inducing turbulent flow in a boundary layer of the material stream. Apparatus according to claim 31, wherein the turbulent flow inducing means comprises a plurality of lips (16) for deflecting a boundary layer of the material stream to the axial center of the passage means (6), for mixing the current of material. Apparatus according to any one of claims 26 to 30, wherein the boundary layer is controlled by means which maintains a suitably high temperature in said wall of said passage means (6). Apparatus according to claim 33, wherein the means for maintaining a suitably high temperature comprises a coating of material. The apparatus of claim 34, wherein said material coating is heated. Lisbon, - " 3. MOV. 2000 By COMMONWEALTH SCIENTIFIC AND INDUSTRIAL RESEARCH ORGANIZATION and SIDDONS RAMSET LIMITED - THE OFFICIAL AGENT -