Patent Publication Number: US-2013245345-A1

Title: Apparatus and method for extracting hydrocarbons by staged heating

Description:
FIELD OF THE INVENTION 
     The present invention relates to apparatus and a method for processing a raw material in order to extract required constituents of the material. In particular but not exclusively the invention relates to apparatus and a method for extracted required organic and inorganic chemical constituents. 
     BACKGROUND 
     It is known to process raw material containing organic compounds such as plastics, rubber and the like in order to extract condensable and non-condensable hydrocarbon compounds such as methane, ethane, propane, butane and oils including light oils and heavy oils. 
     In one known process the raw material is extracted by pyrolysis. Pyrolysis involves heating of the raw material in a low oxygen environment in order to extract the hydrocarbon compounds without burning the compounds. 
       FIG. 1  shows a know processing plant  100  for extracting organic compounds from a raw material by pyrolysis. The plant  100  has a substantially cylindrical reactor vessel  110  oriented with its cylinder axis substantially horizontal. 
     The reactor vessel  110  is in the form of a chamber  112  surrounded by a jacket  113 . Raw material may be placed in the chamber  112  and the chamber heated by a gas burner  116 . The chamber  112  is arranged to be sealed in a substantially air tight manner in order to prevent oxygen ingress to the raw material during the heating process. 
     Combustion products from burning of gas by the gas burner  116  flow around the chamber  112  within the jacket  113 . The jacket  113  has an exhaust pipe  121  coupled thereto which conveys the combustion products to an exhaust gas purification portion  120  arranged to remove environmental toxins from the exhaust gas before exhausting it to atmosphere through a flue  129 . 
     An extraction conduit  141  is coupled to the chamber  112  at one end of the vessel  110  in order to allow extraction of gases evolved from the raw material during pyrolysis of the raw material. The extraction conduit  141  conveys the evolved gas to a water-cooled condenser portion  140  of the plant. Here the evolved gas is cooled. Hydrocarbons condensing in the condenser are fed to a storage tank  145  for storage. 
     Some hydrocarbons that evolve such as methane, ethane, propane and butane have boiling points below the temperature of the condenser. These gases therefore pass through the condenser without condensing. A portion of these gases are fed back to the gas burner  112  of the reactor  110  whilst excess gas is burned in an auxiliary burner  149 . 
     Once the hydrocarbons of interest have been removed from the raw material the raw material is removed from the chamber  112 . If pyrolysis is allowed to progress until substantially all hydrocarbons have been removed, the pyrolysed material will typically contain carbon black and any non-pyrolysable matter present in the raw material. In the case of pyrolysed rubber tyres the material may contain grit and steel. 
     The pyrolysed material is transferred from the reactor vessel  110  to a storage vessel  130 . 
     In use the raw material in the chamber  112  is heated by the gas burner  116  to a temperature of around 400° C. As the vessel  110  is heated hydrocarbons begin to evolve from the raw material. Lighter hydrocarbons such as methane, ethane, propane and butane typically evolve first, followed by light oils such as petroleum and subsequently heavier oils such as kerosene and diesel. 
     It is desirable to provide improved apparatus and an improved method of extracting hydrocarbons from waste materials such as plastics materials and rubber. 
     STATEMENT OF THE INVENTION 
     Embodiments of the invention may be understood with reference to the appended claims. 
     In an aspect of the invention there is provided apparatus for extracting hydrocarbons from hydrocarbon-containing material by pyrolysis, the apparatus comprising:
         a first reactor arranged to heat the material to a first temperature, the apparatus being operable to extract from the first reactor gaseous hydrocarbons evolved from the material therein; and   a second reactor having an inlet coupled to an outlet of the first reactor wherein material in the first reactor may be transferred to the second reactor substantially without exposure to oxygen, the second reactor being arranged to receive material heated in the first reactor and to heat the material to a second temperature greater than the first temperature,   the apparatus being operable to extract from the second reactor gaseous hydrocarbons evolved from the material therein.       

     Embodiments of the invention have the advantage that because the first and second reactors are arranged to extract hydrocarbons at different respective temperatures they may extract hydrocarbons having different respective boiling points. It is therefore not necessary to perform post-extraction re-processing of the extracted hydrocarbons in order to separate them into their respective fractions. 
     This is in contrast to known extraction apparatus in which a single reactor is heated to a temperature at which a range of fractions are evolved and the fractions must subsequently be subjected to post-extraction fractionation. Thus the evolved hydrocarbons must be re-heated. This has the disadvantage that decomposition of the fractions can occur, resulting in loss of valuable hydrocarbon resource. Furthermore, a substantial amount of energy must be used in the re-heating process. 
     Accordingly, by connecting a plurality of reactors in series, a number of surprising benefits may be enjoyed. Embodiments of the invention are ideally suited to operation in a substantially continuous mode of operation in which material to be pyrolysed is introduced substantially constantly into the first reactor and material that has passed through the first reactor is introduced substantially constantly into the second reactor. 
     In some embodiments the flow of material into the first reactor and from the first reactor to the second reactor may be performed in a substantially batch-wise manner whereby material that has been pyrolysed in the second reactor is transferred out therefrom either before or during transfer of material that has been pyrolysed in the first reactor from the first reactor to the second reactor. 
     Advantageously the apparatus is operable to convey the material from the first reactor to the second reactor by means of a conduit connecting the first and second reactors. 
     Further advantageously the apparatus is operable to introduce raw material into the first reactor without exposure of the first reactor to atmosphere. 
     This feature has the advantage that the apparatus may accommodate substantially continuous extraction of hydrocarbons from material introduced into the apparatus. In particular the introduction of material may be made without cooling the first reactor. It is to be understood that it is advisable not to heat material to be pyrolysed in the presence of oxygen due to a risk of burning the material including hydrocarbons present in the material. 
     Further advantageously the apparatus is operable to heat material in the first and second reactors substantially in the absence of oxygen. 
     This feature has the advantage that reaction of evolved hydrocarbons with oxygen may be substantially prevented. 
     Optionally the apparatus is operable in a substantially continuous mode in which material introduced into the first reactor is heated to the first temperature and subsequently transferred into the second reactor. 
     As noted above this feature has the advantage that the first reactor does not need to be cooled to ambient temperature before fresh material can be introduced. Furthermore, the first reactor does not need to be exposed to ambient atmospheric oxygen levels in order to introduce fresh material. 
     This allows highly efficient operation, reducing an amount of stress cycling to which the apparatus is subject and thereby reducing a risk of failure due to fatigue. 
     Advantageously the apparatus comprises means for determining a weight of material within a reactor. 
     The apparatus may be operable to control a rate of flow of material through the reactor responsive to a rate of loss of weight of material in the reactor. 
     This feature has the advantage that the reactor may be maintained in an operating condition in which a rate of supply of material into the reactor is sufficient to enable the reactor to operate at an optimum rate of evolution of hydrocarbons as a function of time. The optimum rate may be a maximum rate in some embodiments. 
     Advantageously the apparatus is operable to control a temperature of material in the reactor responsive to a rate of loss of weight of material in the reactor. 
     This feature has the advantage that the reactor may be maintained in an operating condition in which a temperature of material in the reactor is such as to provide an optimum rate of loss of weight of material in the reactor. The optimum rate may depend on the particular hydrocarbon fraction it is desired to extract using a given reactor. 
     The apparatus may be operable to control a rate of flow of material through the reactor responsive to a temperature of the material in the reactor. 
     The rate of flow may therefore be increased if the temperature is too high, or decreased if the temperature is too low. 
     Advantageously the means for determining the weight of material comprises one or more loads cells arranged to measure a weight of the reactor. 
     Further advantageously an upper internal surface of the reactor is sloped thereby to promote rising of evolved hydrocarbon gas to a gas outlet of the reactor. 
     This feature reduces a risk that hydrocarbon gases collect in a stagnant region of an internal environment of the reactor and become heated to an excessive temperature. 
     Advantageously the reactor comprises a substantially cylindrical vessel. 
     Further advantageously a longitudinal axis of the vessel is tilted thereby to promote flow of evolved gases towards one end of the vessel. 
     Optionally the reactor is operable to heat the material by mechanically working the material. 
     Further optionally at least one of the reactors comprises a plurality of perforated, concentric drum members, the apparatus being operable to feed material into an inner one of the drum members and to rotate the drum members whereby material may pass from one drum member to the next in a radially outward direction. 
     Advantageously respective adjacent drum members are arranged to rotate in opposite directions. 
     This feature has the advantage that shear and other mechanical forces imposed on material passing through the reactor may be increased. 
     The drum members may be arranged to rotate at different respective speeds. 
     Optionally at least one of the reactors comprises a rotary grinding member, the reactor being operable to trap material to be pyrolysed in a channel region between the grinding member and a guide member wherein the material may be mechanically worked by the grinding member. 
     Advantageously the reactor is arranged to cause a flow of material through the channel region as the grinding member rotates. 
     Further advantageously the grinding member comprises a substantially conical or frusto-conical body, the guide member having a shape corresponding to that of the grinding member wherein the channel may be defined therebetween. 
     Advantageously at least one of the guide member and grinding member are provided with raised formations thereby to enhance mechanical working of material passing through the reactor. 
     The grinding member may be provided radially inward of the guide member. 
     Alternatively the grinding member may be provided radially outward of the guide member. 
     Advantageously the apparatus is operable to apply pressure to one or both of the grinding member and guide member thereby to urge the members together. 
     The apparatus may be operable to vary a size of the channel region by varying a distance between the guide member and grinding member. 
     The apparatus may comprise electrical heating means for heating at least a portion of the reactor. 
     Advantageously at least a portion of one or more of the reactors may comprise a catalytic material. 
     Optionally the catalytic material is arranged to promote at least one selected from amongst decomposition of evolved hydrocarbons and reaction of evolved hydrocarbons. 
     The catalytic material may comprise at least one selected from amongst aluminium, alumina, tantalum, tungsten, silver, and nickel. 
     Advantageously the apparatus comprises cooling means for cooling material to be pyrolysed, the apparatus being operable to freeze material to be pyrolysed and subsequently to subject the material to a dividing process in which the material is divided into smaller pieces. 
     This feature has the advantage that liquid or liquid-containing material such as medical waste matter may be processed without splashing. Furthermore, the medical waste material as well as polymeric materials such as rubber (for example in the form of tyres) may be broken up into smaller pieces for more efficient pyrolysis. 
     The apparatus may be operable to flood at least the first reactor with a gas thereby to displace oxygen. 
     Advantageously the apparatus is operable to flood at least the first reactor with a gas product of the cooling means. 
     In a further aspect of the invention there is provided a marine vessel having apparatus as claimed in any preceding claim onboard, the vessel being arranged to receive raw material for extraction of hydrocarbons therefrom and to perform extraction of hydrocarbons by means of the apparatus. 
     In a still further aspect of the invention there is provided a method of extracting hydrocarbons from hydrocarbon-containing material by pyrolysis, the method comprising:
         heating the material in a first reactor to a first temperature and extracting gaseous hydrocarbons evolved from the material therein; subsequently   transferring the material to a second reactor substantially without exposure to oxygen; subsequently   heating the material in the second reactor to a second temperature higher than the first temperature and extracting gaseous hydrocarbons evolved from the material therein.       

     Advantageously the step of heating the material in the first and second reactors comprises heating the material substantially in the absence of oxygen. 
     The method may comprise the step of cooling material to be pyrolysed by cooling means thereby to freeze the material and subsequently subjecting the material to a dividing process in which the material is divided into smaller pieces. 
     The method may comprise the step of flooding at least the first reactor with a gas thereby to displace oxygen. 
     Advantageously the gas comprises at least one selected from amongst nitrogen and carbon dioxide. The gas may be evolved from liquid nitrogen or dry ice (solid carbon dioxide). Other sources of gas are also useful. Hydrogen may be useful in some embodiments. In some embodiments a mix of hydrogen and methane may be useful. 
     Advantageously the method comprises the step of flooding at least the first reactor with a gas product of the cooling means. 
     Thus the gas product may serve a useful purpose in enhancing pyrolysis. 
     Advantageously the cooling means comprises means for cooling by at least one of liquid nitrogen and solid carbon dioxide. 
     The material to be pyrolysed may comprise medical waste. 
     The material to be pyrolysed may comprise biological material. 
     The material to be pyrolysed may comprise polymeric material. For example rubber such as rubber obtained from rubbery tyres. 
     Optionally the method further comprises the steps of:
         retrieving hydrocarbon-containing floating waste material from a body of water to a vessel; and   extracting hydrocarbons from the waste material by pyrolysis onboard the vessel.       

     In a further aspect of the invention there is provided a method of extracting hydrocarbons from hydrocarbon-containing material by pyrolysis, the method comprising:
         heating the material in a first reactor to a first temperature substantially in the absence of oxygen and extracting gaseous hydrocarbons evolved from the material therein; subsequently   transferring the material to a second reactor substantially without exposure to oxygen; subsequently   heating the material in the second reactor substantially in the absence of oxygen to a second temperature higher than the first temperature and extracting gaseous hydrocarbons evolved from the material therein.       

     In an aspect of the invention there is provided a reactor vessel for use in a process of pyrolysis of hydrocarbon-containing material wherein the reactor vessel is an electrically heated reactor vessel. 
     This has the advantage that combustion of hydrocarbons in order to heat the reactor vessel is not required. This can be important in certain locations where it is desirable to extract hydrocarbons from hydrocarbon-containing raw materials such as plastics and rubber. 
     In one aspect of the invention there is provided a reactor vessel for use in a process of pyrolysis of hydrocarbon-containing material wherein raw material in the reactor vessel is arranged to be heated by means of a microwave generator. This has the advantage that in some embodiments heating of the raw material may be arranged to be performed in a more efficient manner in which less energy is consumed in the process of heating the raw material. 
     In a further aspect of the invention there is provided plant for extracting hydrocarbons from hydrocarbon-containing material in which gas fractions evolved from raw material processed by the plant are collected, optionally condensed, and stored in storage tanks. 
     This has the advantage that the gas fractions may be used for purposes other than heating of reactor vessels of the plant or burned in a flare stack in order to dispose of the gases. Thus for example petroleum gas (LPG) may collected and sold as a motor fuel or domestic fuel. 
     In one aspect of the invention there is provided a reactor vessel for use in a process of pyrolysis of hydrocarbon-containing material wherein the vessel is shaped or tilted to promote flow of evolved gases to a first end of the vessel that is higher than a second end of the vessel and out from the vessel through an exhaust aperture provided at or near the first end. 
     This feature has the advantage that evolved gas passes out from the vessel with a reduced dwell time within the vessel. This reduces the number of dead spots of the vessel, being locations of the vessel at which flow of evolved hydrocarbons may stagnate resulting in overheating of the hydrocarbons. Overheating can result in the conversion of aliphatic chains of hydrocarbons to hydrocarbon rings which is undesirable in some embodiments. Formation of rings can be undesirable because the resulting compounds may have a lower available energy content and/or burn in a manner that produces environmental toxins. 
     The vessel may have an inlet for raw material at the first end and an outlet for pyrolysed raw material at the second end. 
     This has the advantage that flow of raw material through the vessel from the inlet to the outlet may be promoted by the tilt of the vessel. 
     Other arrangements are also useful. Thus the inlet for raw material may be provided at the second end and the outlet for pyrolysed raw material may be provided at the first end. 
     Optionally embodiments of the invention are employed only for pyrolysing substantially solid material. Optionally embodiments of the invention are employed only for pyrolysing materially consisting essentially of substantially solid material. Optionally embodiments of the invention are employed for pyrolysing material comprising substantially solid material, such as a mixture of solid material and liquid. 
     Optionally embodiments of the invention are employed for pyrolysing only liquid material. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Embodiments of the invention will be described with reference to the accompanying figures in which: 
         FIG. 1  is a schematic diagram of a known plant for extracting hydrocarbons from hydrocarbon-containing raw materials such as plastics and rubber by pyrolysis; 
         FIG. 2  is a schematic illustration of a reactor vessel according to an embodiment of the present invention; 
         FIG. 3  is a schematic illustration of an inlet/outlet conduit arrangement of a reactor vessel according to an embodiment of the present invention; 
         FIG. 4  is a schematic illustration of a plant according to an embodiment of the present invention for extracting hydrocarbons from hydrocarbon-containing raw materials such as plastics and rubber by pyrolysis; 
         FIG. 5  is a schematic illustration of a plant according to an embodiment of the present invention for extracting hydrocarbons from hydrocarbon-containing raw materials such as plastics and rubber by pyrolysis; 
         FIG. 6  is a plot of raw material weight as a function of temperature during a process of heating waste tyre rubber; 
         FIG. 7  shows a rotating drum reactor according to an embodiment of the present invention in (a) cross-sectional side view and (b) cross-sectional end view at section X-X of (a); 
         FIG. 8  shows a conical grinding reactor according to an embodiment of the present invention; and 
         FIG. 9  shows a variety of different conical grinding members suitable for use with a reactor of the type illustrated in  FIG. 8 . 
     
    
    
       FIG. 2  is a schematic illustration of a reaction vessel  210  according to an embodiment of the invention. The vessel  210  has a substantially cylindrical chamber  212  having a cylinder axis A thereof tilted with respect to the horizontal. In the embodiment shown the vessel  210  is tilted at an angle of around 15°. However other angles are also useful. 
     The vessel  210  has a raw material inlet  214  at a first end  212 ′ and a pyrolysed material outlet  218  at a second end  212 ″ opposite the first end  212 ′. The inlet  214  is arranged to receive raw material  10  to be processed. A worm screw  217  is provided within the vessel  210  and arranged to promote flow of raw material  10  from the first end  212 ′ to the second end  212 ″. 
     A gas outlet  215  is provided in an upper region of the vessel  210  at the first end  212 ′ through which evolved hydrocarbon gases  15  may flow out from the vessel  210 . 
     The vessel  210  is arranged to be heated by an electrical heating element  216 . 
     The vessel  210  has the advantage over known vessels  110  that a dwell time of evolved gases within the vessel  210  is reduced because as the gas rises it is directed by sides of the vessel  210  towards the gas outlet  215 . A path of the gas within the vessel  210  continuously rises towards the outlet  215 . In contrast in the known vessel  110  gas can stagnate in an upper volume of the vessel  110  and become overheated. 
     In some embodiments a worm screw or the like is provided at each of the inlet  214  and outlet  218  in order to promote flow of material through the vessel  210 . 
     In some embodiments the reactor vessel  210  is arranged to be rotated relative to the worm screw  217 . In some alternative embodiments the worm screw  217  is arranged to be rotated relative to the reactor vessel  210 . 
     In some embodiments the reactor vessel  210  is rotated regardless of whether or not the worm screw  217  is rotated in order to promote agitation/turning of the raw material and promote contact between the raw material and an inner wall of the reactor vessel  210 . In some embodiments the reactor vessel  210  is rotated at a rate of around four revolutions per minute. 
     In a further aspect of the invention there is provided a reactor vessel for use in a process of pyrolysis of hydrocarbon-containing material wherein the vessel has a screw member for promoting flow of material through the reactor, the screw member comprising a catalyst for catalysing a change to hydrocarbons evolved during pyrolysis. 
     The catalyst may be arranged to promote decomposition of evolved hydrocarbons. 
     The catalyst may alternatively or in addition be arranged to promote reaction of evolved hydrocarbons. 
     The screw member may be formed substantially entirely from the catalyst. 
     The screw member may comprise at least one selected from amongst aluminium, alumina, tantalum, tungsten, silver or any other suitable catalyst. 
     In one embodiment the screw member is formed from aluminium. This has the advantage that a layer of aluminium oxide may be formed over the surface of the screw member providing a surface capable of catalysing a change to evolved hydrocarbons. 
     It is to be understood that the screw member may alternatively be coated with catalyst, for example a layer of aluminium which may oxidise to form alumina. Thus in some embodiments a screw made from steel or other screw material may be coated with aluminium or alumina. 
     In some embodiments the catalyst surface increases the proportion of aliphatic and lower molecular weight products produced by a plant and also reduces the temperature and residence time of evolving hydrocarbons in the reactor therefore increasing the production rate and efficiency of the process. 
     In a still further aspect of the invention there is provided a reactor vessel for use in a process of pyrolysis of hydrocarbon-containing material wherein a sidewall of the reactor vessel comprises a catalyst for catalysing a change to hydrocarbons evolved during pyrolysis. 
     This has the advantage that in situations where the presence of a catalyst is essential or desirable, loose catalyst need not be placed within the reactor vessel thereby contaminating pyrolysed material expelled from the outlet of the reactor vessel. It is to be understood that loose catalyst may be required to be separated from the expelled pyrolysed material before the expelled material is suitable for sale as carbon black, fuel or other product. 
     The catalyst may be arranged to promote decomposition of evolved hydrocarbons. 
     The catalyst may alternatively or in addition be arranged to promote reaction of evolved hydrocarbons. 
     Alternatively or in addition the catalyst may be arranged to promote release of hydrocarbons contained in the raw material. For example, the catalyst may be arranged to weaken cross-linked bonds thereby to promote release of hydrocarbons. 
     The sidewall may be formed substantially entirely from the catalyst. 
     The sidewall may be formed from nickel or aluminium or an alloy thereof. 
     The sidewall material may comprise an inorganic clay, chalk or aggregate material, for example a bentonite clay. These materials lower the reaction/decomposition temperature of carbonaceous materials such as plastics, rubber, wool etc. reducing the amount of energy required to be input. The materials may also reduce the time required to perform the process. 
     The bentonite clay may be mixed with catalytic metals such aluminium and/or iridium in order to promote the reaction occurring at a lower temperature. This also allows more of the low molecular weight aliphatic (chain) hydrocarbons to form rather than the higher molecular weight and aromatic (ring) hydrocarbons to form. 
     This has the advantage that clean burning of the hydrocarbons evolved is promoted. Furthermore fuels of the highest calorific value are the smaller/lighter materials in chain form and not ring form. 
     When material undergoing pyrolysis is overheated or left in the reactor too long, longer chains and rings form, for example by the Deils-Alder reaction pathway. Such hydrocarbons produce unwanted toxins when burned rather than only carbon dioxide and water as in the case of low molecular weight hydrocarbons. 
     The sidewall may comprise an outer shell portion and an inner liner portion, the inner liner portion comprising the catalyst. 
     In one aspect of the invention there is provided a liner for a reactor vessel for use in a process of pyrolysis of hydrocarbon-containing material wherein the liner comprises a catalyst for catalysing a change to hydrocarbons evolved during pyrolysis. 
     In a further aspect of the invention there is provided an element for attachment to an inner wall of a reactor vessel for use in a process of pyrolysis of hydrocarbon-containing material wherein the element comprises a catalyst for catalysing a change to hydrocarbons evolved during pyrolysis. 
     The catalyst may be a catalyst as described with respect to other aspects of the invention. 
     The reactor may be arranged to contain balls of nickel, aluminium, an alloy thereof or any other suitable catalyst that are arranged to move freely within the reactor to assist in detachment of carbon or other materials from an internal surface of the reactor. Thus in reactors having catalyst provided on an internal surface thereof the balls may assist in detaching material from the catalyst surface. The balls themselves may also act as a catalyst, promoting one or more reactions. 
     In one aspect of the invention there is provided a reactor vessel for use in a process of pyrolysis of hydrocarbon-containing material, the reactor vessel having an outlet conduit through which pyrolysed material may flow out from the reactor vessel and an inlet conduit through which raw material may flow into the reactor vessel, the inlet and outlet conduits being provided in thermal communication with one another whereby raw material flowing into the vessel may be heated by pyrolysed material flowing out from the vessel. 
     This has the advantage that waste heat borne by the pyrolysed material may be used to preheat raw material being fed into the reactor vessel. 
     The outlet and inlet conduits may be provided in a substantial coaxial arrangement, for example a concentric coaxial arrangement or any other suitable arrangement. For example, the outlet conduit may be provided within the inlet conduit or the inlet conduit may be provided within the outlet conduit. Material may be caused to flow through one or both conduits by means of a worm screw of the like. For example a worm screw may be provided within the inlet conduit, the outlet conduit or both. 
       FIG. 3  shows an outlet conduit  218 ′ of a reactor vessel  210  according to an embodiment of the invention. The outlet conduit  218 ′ is arranged to be coupled to an outlet  218  of the reactor vessel  210 . 
     An inlet conduit  214 ′ is provided around the outlet conduit  218 ′. The outlet conduit  218 ′ is provided coaxial of the inlet conduit  214 ′ and concentric therewith within the inlet conduit  214 ′. A worm screw  218 S is provided within the outlet conduit  218 ′. The worm screw  218 S is arranged to promote passage of pyrolysed material out from the reactor vessel  210 . 
     It is to be understood that the outlet conduit  218 ′ is arranged to allow passage of thermal energy through a sidewall thereof in order to allow pre-heating of raw material passing through the inlet conduit  214 ′. Pre-heating of the raw material has the advantage that less energy is required to be imparted to the raw material by the reactor vessel  210 , reducing the amount of energy consumed by the process. 
     In some embodiments the direction of flow of material through the inlet conduit  214 ′ is the same as that through the outlet conduit  218 ′. In some embodiments the directions of flow are opposite one another. 
       FIG. 4  shows a processing plant  200  according to an embodiment of the invention for extracting organic compounds from raw material by pyrolysis. 
     The plant  400  has a plurality of reactor vessels  210  as described above and oriented with their cylinder axes tilted with respect to the horizontal as shown in  FIG. 2 . 
     The vessels  210  are arranged in a parallel configuration. Hydrocarbon gases evolved from raw material  10  in the vessels  210  are piped to a condenser portion  240  of the plant where the gases are cooled. Condensation of the gases occurs, the condensate being stored in storage tanks  245 . 
     Oil in the oil tanks is then subjected to a distillation process in a distillation portion  270  to separate different respective hydrocarbon fractions for storage in respective tanks  275 . 
     In some alternative embodiments the condenser portion  240  is arranged to condense different respective hydrocarbon types (e.g. petrol, diesel) in different stages of the condenser portion and to store the hydrocarbons in different respective storage tanks. 
     Other arrangements are also useful. 
     In one embodiment of the invention a plurality of reactor vessels for use in a process of pyrolysis of hydrocarbon-containing material are connected in series. 
     That is, an outlet of a first reactor vessel is coupled to an inlet of a second reactor vessel and so forth. 
     The vessels are arranged such that material may flow out from the outlet of one vessel and into the inlet of the next vessel. 
     The reactor vessels are arranged to operate at different respective temperatures corresponding to temperatures at which different types of hydrocarbon are evolved from raw material passing from one vessel to the next. 
     For example, the first reactor vessel may be operated at a temperature suitable for driving off a gas fraction of the hydrocarbons such as methane, ethane, butane and propane. 
     The second reactor vessel may be operated at a temperature suitable for driving off petroleum. 
     A third vessel may be provided, and operated at a temperature suitable for driving off diesel. 
     A fourth vessel may be provided for driving off heavy oil fractions. 
     Other arrangements are also useful including more than four reactor vessels. 
     In one embodiment a first reactor vessel is operated at a temperature of around 150° C. 
     A second reactor vessel may be operated at a temperature of around 250° C. in order to collect fractions in the range from around 150° C. to around 250° C. 
     A third reactor vessel may be operated at a temperature of around 350° C. in order to collect fractions in the range from 250° C. to 350° C. 
     Optionally, an outlet conduit carrying gas evolved from a reactor may be arranged whereby a temperature gradient is established in the conduit such that different evolved fractions condense at different positions along a length of the conduit and are collected by respective collection means. The collection means may comprise a trap for collecting condensed vapours in a holding tank or directing the condensed vapours into a conduit for conveying the fraction to a required location. A conduit of this type may be referred to as a fractionation conduit. 
     In some embodiments a temperature control means is provided along the fractionation conduit for maintaining substantially constant temperatures at different positions along the conduit. 
     The conduit may rise at an angle away from the reactor and optionally be provided with a U-bend (which may be shallow) or other collection means for collecting any condensed vapours that seek to flow back into the reactor along the conduit. The conduit may be provided at an angle in the range of from around 5° to around 50° to the horizontal. Other angles are also useful. As described elsewhere, the reactor and/or conduit may be coated with one or more thermoelectric cells thereby to enable generation of electricity from heat passing out therefrom. The thermoelectric cells may be arranged to provide thermal insulation. 
     In some embodiments the apparatus may have a single reactor rather than a plurality of reactors in series. The single reactor may be operated at a temperature at which a plurality of fractions are evolved thereby, the fractionation conduit enabling different respective fractions to be separated. Thus in some embodiments the reactor may be operated at a temperature of around 350° C., 450° C. or any other suitable temperature. 
     It is to be understood that either the same or different respective catalysts may be employed in two or more reactor vessels arranged in series. For example liners of different respective catalytic properties may be employed, for example liners of different respective chemical composition. The catalysts may be catalysts suitable for the particular fractions evolved in a given reactor. 
     In a still further aspect of the invention there is provided a reactor vessel for use in a process of pyrolysis of hydrocarbon-containing material wherein a sidewall of the reactor vessel comprises a catalyst for catalysing a change to hydrocarbons evolved during pyrolysis. 
     It is to be understood that in some embodiments of the invention in which a single reactor is employed or a plurality of reactors in series in order to pyrolyse raw material the reactor(s) are heated and may be rotated. 
     Arrangements having a single reactor may be particularly efficient where the raw material being pyrolysed is relatively pure, for example a single type of plastic. For such materials the majority of hydrocarbons of interest may be evolved at a single temperature, the materials evolved being relatively pure and homogenous. Such materials may be efficiently processed in a substantially continuous manner in which the reactor is held at a substantially constant temperature and raw material fed through the reactor substantially continuously. 
     It is to be understood that some raw materials are of more complex composition such as rubber materials and mixed plastics. For such materials there may be a plurality of different respective temperatures at which evolution of hydrocarbons of interest occurs. 
     If only a single temperature is employed then the process of extraction of hydrocarbons may be relatively inefficient. 
     For example, if the temperature is too low then not all hydrocarbons of interest will be extracted. If the temperature is too high then some of the ‘lower’ fractions (lower molecular weight hydrocarbons, evolving at lower temperatures) may react to form undesirable complex organic compounds such as aromatic compounds. 
       FIG. 5  shows a processing plant  300  according to an embodiment of the invention for extracting organic compounds from raw material by pyrolysis. 
     The plant has three reactor vessels  310 A,  310 B,  310 C each of which is similar to that of  FIG. 2 . Like features of the reactor of  FIG. 5  to that of  FIG. 2  are labelled with like reference signs prefixed numeral  3  instead of numeral  2 . 
     In the embodiment of  FIG. 5  the reactor vessels  310 A-C are tilted such that an upper portion of an inner surface of each vessel  310 A-C is sloped so as to promote flow of evolved gas upwards to the outlet  315 A-C of each reactor. It can be seen that the gas outlets  315 A-C are provided at an opposite end of the vessels  310 A-C to the material inlet  314 A-C of each vessel  310 A-C. Thus the vessels are tilted in the opposite direction to that of the embodiment of  FIG. 2 . 
     Other arrangements are also useful. Thus in some embodiments the reactors  210  may be configured in a substantially identical manner to that of  FIG. 2 , being tilted in the same direction as the reactor  210  of  FIG. 2  and having the gas outlet  314 A-C at the same end as the material inlet  314 A-C rather than at the opposite end. 
     The reactor vessels  310 A-C each have a worm screw (not shown) provided therein in a similar manner to the reactor  210  of  FIG. 2 . The worm screws are arranged to convey material being pyrolysed through the reactor vessels  310 A-C from one vessel to the next. The vessels  310 A-C are also arranged to rotate about their cylinder axis. 
     The reactor vessels  310 A-C are controlled such that the first vessel  310 A heats the raw material to a temperature of around 200° C., the second vessel  310 B heats the raw material to a temperature of around 230° C. and the third vessel  310 C heats the raw material to a temperature of around 280° C. It is to be understood that other temperatures are also useful. Other numbers of reactor vessels are also useful. 
     In the embodiment of  FIG. 5  a separate reactor vessel is employed for each different respective hydrocarbon fraction it is required to separate. The fractions are condensed in respective condensers  343 A,  343 B,  343 C and piped directly to a corresponding storage tank  345 A,  345 B,  345 C. 
     In some embodiments several fractions may be evolved in a single reactor vessel and the fractions separated in a condenser/distillation arrangement downstream of the reactor vessel. 
     Other arrangements are also useful. 
     In some embodiments the pyrolysis process is arranged such that material output from the reactor (or the last reactor in a series in the case reactors are connected in series) is arranged to be not fully pyrolysed, i.e. to have a residual energy content. This has the advantage that the solids product of the process may be sold as a fuel, for example an outdoor catering fuel or any other suitable fuel. 
     In one aspect of the invention the solids product of the pyrolysis process is cooled using a heat exchanger and the energy extracted from the solids product used to generate electricity. For example water or other coolant fluid may be used to cool the solids product, the fluid gaining heat energy as a result. This heat energy may be used to generate electricity. In some embodiments water is converted to steam by means of heat contained within the solids product and the steam used to power a turbine generator. 
     In a further aspect of the invention there is provided a reactor vessel for use in a process of pyrolysis of hydrocarbon-containing material, the reactor vessel having means for determining a weight of material within the vessel and controlling a rate of flow of material through the vessel responsive to the weight of the vessel. 
     The means for determining the weight may comprise one or more loads cells arranged to measure the weight of the vessel, the weight of the material within the vessel being calculated by subtracting the weight of the empty vessel from the measured weight. Other arrangements are also useful. 
     In some embodiments the reactor vessel may be provided with means for monitoring a change in weight of material within the vessel. The apparatus may be operable to control a flow of material through the vessel responsive to the change in weight. The means for monitoring the weight may comprise one or more load cells. 
     The vessel is preferably arranged to allow a weight of material in the vessel to be determined or monitored during evolution of hydrocarbons. 
     The vessel may be provided in combination with a controller arranged to monitor the weight of the material. The controller may be arranged to adjust a flow rate of material through the reactor in order to maintain an optimum flow rate of material through the reactor. 
       FIG. 6  is a plot of weight of a batch of raw rubber material extracted from tyres as a function of temperature during pyrolysis. It can be seen that up until temperature T 1  a rate of change of weight as a function of temperature is relatively low. This is because only the relatively light hydrocarbon gases (e.g. methane, ethane, propane, butane) evolve at temperatures below T 1 . Between T 1  and T 2  larger hydrocarbons (light oils) evolve resulting in a more rapid drop in weight as a function of temperature. Above T 2  the rate of change of weight with temperature slows down as the heavier oils gradually evolve. 
     As the light oils are evolved, the reaction proceeds at the highest rate and may become exothermic. The reaction may be sufficiently exothermic that little or no heat is required to be input externally. 
     It is to be understood that a plot of weight as a function of time during heating of the rubber at a substantially constant rate follows a curve of similar shape. That is, the weight decreases relatively slowly initially as low molecular weight hydrocarbons evolved. As the temperature continues to rise the light oil fractions evolve relatively rapidly over a relatively narrow range of temperatures between T 1  and T 2  as shown in  FIG. 6  resulting in a relatively rapid weight loss. Above T 2  the rate of weight loss with time decreases substantially as larger molecular weight organics such as heavy fuel oils evolve. 
     It is to be understood that if a reactor is being heated in order to drive off hydrocarbons of a range of molecular weights there is a risk that the temperature of the material in the reactor may rise too quickly during the period of rapid weight loss between T 1  and T 2  such that a relatively large amount of light oil remains in the raw material as the temperature rises above T 2 . This can result in overheating of the light oils which may in turn cause higher molecular weight compounds such as aromatics to form from the light oils. 
     It is to be understood that by monitoring the weight of the material in the reactor as a function of time it is possible to determine when the exothermic reaction is occurring and to control the amount of heat input to the reactor responsive to the rate of change of weight. Thus when the reaction is proceeding in an exothermic manner the amount of heat being input to the reactor may be reduced or no further heat introduced. This has the advantage that wasting of heat energy from the external source may be prevented. Furthermore overheating of the material may also be prevented. This can increase the yield of low molecular weight aliphatic hydrocarbons. 
     It is to be understood that in a reactor where raw material is being passed through the reactor in a continuous or substantially continuous manner (as opposed to a batch process manner), if material is passed through the reactor at too slow a rate the material may become overheated. Consequently, heavier fractions may be evolved in the reactor than was intended as discussed above. 
     Likewise if the material is passed through the reactor at too high a rate there is a risk that the material will not reach a sufficiently high temperature for a sufficiently long period of time to allow the desired fraction(s) to evolve to a sufficient extent. 
     It is to be understood that by monitoring the weight of material in the vessel as a function of time, the apparatus may be controlled to ensure that material passing through the reactor vessel experiences a required amount of weight loss by adjusting a flow rate of material through the vessel. 
     Thus, if the rate of weight loss is determined to be too low, the rate of flow of material through the vessel may be reduced. If the rate of weight loss is determined to be too high, the rate of flow of material through the vessel may be increased. 
     It is to be understood that the arrangement of  FIG. 5  in which a plurality of reactors are connected in series may be configured to measure the weight of raw material in each reactor and to control the rate of flow of material through the reactor in the manner described above. The plant may be arranged to control the rate of flow of material through each reactor substantially independently of one or more other reactors of the series. Alternatively the plant may be arranged to adjust the flow rate through one or more reactors in dependence on the flow rate through another reactor. 
     Thus the temperature and flow rate of material through each chamber may be controlled to optimise conditions in each chamber. In some embodiments a gas pressure of each chamber may be monitored and controlled in order to assist in extraction of increased amounts of hydrocarbon material from raw material passing therethrough. 
     In some embodiments a lesser or greater number of reactors may be employed than that shown in  FIG. 5 , for example a fourth reactor operating at a still higher temperature in order to drive off remaining volatile organic compounds. 
     In some embodiments it is desirable to produce relatively pure carbon black at an output of the final reactor vessel, for example for manufacture of pigments for the printing industry such as inks and toner for photocopier and/or other applications. 
     In some other applications it is desirable to allow some volatile organic compounds to remain, for example where it is required to produce combustible fuel for example briquettes for fires, kilns, barbeques and so forth. 
     In some embodiments of the invention a pressure of the system is arranged to be below atmospheric pressure, for example around 0.9 to 0.05 atmosphere. A vacuum pump may be provided at an end of the process in order to achieve this. 
     This arrangement may encourage evolved gas to flow from the reactor(s) through the condenser(s). It may also help to remove any excess oxygen in air within the system that could cause undesirable side reactions to occur. 
     Furthermore, in the event of a leak in a portion of the plant a risk that hydrocarbons may flow out from the plant is reduced. Thus a risk of fire or explosion may be reduced in some embodiments. 
     In one aspect of the invention there is provided a method of pre-treatment of rubber vehicle tyres and the like before they are passed through a reactor to evolve hydrocarbons from the tyres by pyrolysis. For a typical motor vehicle tyre today, approximately 85% by weight is rubber, 13% is steel and the remainder is cotton, nylon, zinc oxide and other materials. 
     Pyrolysis of materials is most efficient when only carbonaceous material in is present in the reactor. Ideally the material should have as large a surface area as possible and there should be as little air as possible within the reactor vessel. 
     To achieve these conditions, pre-treatment of the tyres should remove the steel, cloth and other contaminants and then convert the rubber to particles of as small a diameter as possible (the particles may be collectively referred to as ‘crumb’ or ‘powder’). 
     It is to be understood that the vast majority of the power required to produce rubber crumb/powder is in the grinding and shredding of the rubber from the original tyre. There is therefore a commercial balance to be made between power expended in pre-treating rubber tyres and reactor efficiency. 
     There is also a recognised danger in the grinding of rubber due to the heat produced by the grinding. This can cause the rubber to melt onto metal components such as blades and rolls and require replacement and cleaning of the blades/grinding rolls. A fire risk also exists from high excess heat generation. 
     The most progressive and safest technology today is to use a wire stripper/de-beader followed by a rough shredding step to produce long pieces of tyre around 5 cm in width and 20 cm in length. 
     Rather than progress the shred through ever smaller grinders and cutters to obtain the small crumb required, in one aspect of the invention cryogenic technology is employed to freeze the rubber into a vitreous-like state. For example liquid nitrogen may be employed. Other coolants may be employed in addition or instead. 
     The rubber may then be mechanically broken up into pieces using nips and rolls to the smallest mesh commercially available, currently between 20 and 200 mesh, optionally between 40 and 100 mesh. 
     Additional to the benefit of substantially zero fire risk and reduced power consumption and noise, this process also produces a more pure rubber powder. It is to be understood that the freezing and mechanical processing steps also enable separation of cotton and nylon materials present in the tyre from any remaining steel or grit. 
     A vibrating screen or other separation means may be provided at the end of this stage to provide final sorting/separation of the components of the raw material. 
     Optionally a final step of the process is to employ a cyclonic separator to further purify the rubber powder. 
     The rubber powder may be sold in this form if an excess is achieved during normal production. The powder may be used as an additive to make new tyres, to road surfaces as a bulking agent, to shoes, bricks, sports surfaces etc. as a low cost filler. 
     It has been found that using powder produced using the above process a very high purity oil can be obtained directly from a reactor. The purity of the oil is comparable to that obtained using raw material processed in a non-cryogenic manner after two distillation steps following extraction from the reactor. 
     The reason for this is that the cryogenic process cools the pieces of shredded or otherwise mechanically cut or broken tyre until the pieces becomes glass-like and vitreous. The pieces may then be smashed with hammer mills allowing steel and nylon present in the tyres to be readily separated from the rubber. 
     Thus three relatively pure products may be obtained from this process: rubber, nylon and steel. 
     In contrast, if shredding and grinding is performed at ambient temperatures the rubber may be heated to relatively high temperatures by the mechanical processing. As a consequence a relatively large amount of nylon and rubber may become melted together. They may also become bonded to steel wire fragments. 
     It is to be understood that by the cryogenic processing technique rubber may be more effectively separated from the nylon, steel and other constituents. A relatively high percentage of very pure oil can therefore be obtained from the same amount of rubber. 
     It is estimated that if non-cryogenic processing is used, around 50% more raw tyre material would be required to make the same amount of oil. Notwithstanding this advantage, the cryogenic process also means that two distillation steps may be eliminated in order to obtain oil of comparable purity, avoiding loss of a further 20% of the oil produced. 
     Steel may extracted from the tyres in a single stripping process and therefore removed from the raw material before the material is pyrolysed. 
     This means that there are substantially no pieces steel or wire in the raw material that could choke or block equipment downstream of the cryogenic pre-treatment stage. 
     It is to be understood that prior art pre-treatment processes involve a system of chopping and shredding of a whole tyre, producing a mixed assortment of rubber, steel and nylon which is then subjected to a pyrolysis process. 
     The steel may be removed by use of magnetic separator beds, the nylon being separated by cyclonic separation. 
     The ability to separate steel and other metals (magnetic or non-magnetic) has the advantage that carbon pieces or particles remaining following pyrolysis may be used to make tyres (for example as a filler) without further processing to remove such metals. 
     In a further aspect of the invention there is provided a method of pre-treatment of plastics materials before being passed through a reactor to evolve hydrocarbons from the plastics by pyrolysis. 
     There are a limited number of types of plastic that can be successfully converted to fuel using pyrolysis. Some commercially used plastics have a high filler content that will reduce the fuel obtained per tonne to less than 20%. Some other types are highly cross linked, polymerised and adapted to the point where the vapour and gases obtained by heating form heavy globules that block nozzles and valves within a pyrolysis reactor and downstream from the reactor in the distillation and fractionation stages. 
     The initial pre-treatment is therefore to remove the types of plastics that cause these issues which is primarily PET (polyethylene terephthalate). Also included in this group of undesirable plastics are ABS (acrylonitrile butadiene styrene), polycarbonate, SAN (styrene acrylonitrile) and most styrene-containing plastics. These are unwelcome not because they block the system but because they produce a high amount of noxious gases and very little oil. 
     The materials that can be used (with their efficiencies per tonne for petrol production in parentheses) are—polypropylene soft (80%), polypropylene hard (50%) and low density polyethene, LDPE/high density polyethene, HDPE, (up to 80% depending on the filler content and type). 
     Acceptable plastics materials may be shredded, washed and cleaned of debris such as labels, metal pieces and contaminants using magnetic separation, vibrating screens, cyclones and sorters. Other separation methods are also useful. 
     In some embodiments the plastics materials may be shredded using a similar cryogenic technique and cyclonic separation to that described above in respect of rubber tyres. 
     It is undesirable to process rubber and plastics in the same reactor simultaneously. In some embodiments there may be configurational differences between the layout and the set up of reactors for different raw material types and the subsequent treatments of the vapours, liquids and solids produced. The configurational differences may be relatively minor. Temperatures at different stages of the process may also be different depending on the raw material. 
     In one embodiment discussed here, there are four separate processing lines producing two distinct product streams. 
     Each line has two pyrolysis reactors arranged in series. The first reactors of each line are arranged to deposit gases/condensed liquids evolved therein to a common holding tank. 
     Likewise the second reactors of each line are arranged to deposit gases evolved therein to a separate common holding tank. 
     In some embodiments, gases evolved in one or more of the reactors are subject to one or more further distillation/fractionation stages to separate evolved components according to weight, boiling point and state. 
     Pyrolysis in one embodiment is performed using heat generated by solar electrical power generators. 
     In some embodiments pyrolysis of a raw material may be performed within a period of around 12 hours, for example from around 8 hours to around 12 hours. Other periods are also useful. 
     It is to be understood that pyrolysed raw material may be conveyed to a bagging plant for packing and shipping. 
     It is to be understood that a wide range of materials may be processed by pyrolysis such as plastics and rubbers as noted above, plus carpets (wool and non-wool), wools from other waste sources, certain foodstuffs and other biological materials. 
     The temperature at which certain organic compounds are evolved from different raw material sources may differ from source to source requiring conditions in a given reactor to be optimised for a given raw material type. 
     In some embodiments, material to be pyrolysed is first cooled to a temperature sufficiently low to kill bacteria and/or viruses of concern to the user. 
     For example, in some applications biomedical waste from medical and healthcare institutions such as body parts, organs, dressings, packaging and the like may be cooled to kill bacteria, viruses and like organisms that are capable of surviving at relatively high temperatures such as those encountered during pyrolysis of organic materials. 
     It is to be understood that such organisms might otherwise still be present in waste material from a pyrolysis reactor vessel  210  such as in the carbon by-product. Thus in order to prevent spread of disease and other infections due to surviving organisms the waste material may be cooled to cryogenic temperatures in order to kill the organisms. In some embodiments the material may be cooled to around −5° C., −10° C., −20° C., −50° C., −100° C. or any other suitable temperature. In some embodiments the material may be cooled to liquid nitrogen temperatures, around 77K. Any other temperature at which the organisms of concern are unable to survive is also useful. 
     In some embodiments the material is cooled to a temperature around that of dry ice (freezing point of CO2), around −78° C. 
     In some processes, when the material is frozen it is more readily crushed into small pieces, for example into a powder making packaging (such as bagging) and handling of the material easier. Furthermore, splashing of liquids that may be comprised by the waste may be prevented. 
     It is to be understood that in some arrangements cooling also kills moulds, fungi and the like. 
     In some embodiments the feature of crushing the material before pyrolysis facilitates handling of the material when it is removed from the reactor vessel  210  since it has already been broken into manageable pieces during the cryogenic process to kill organisms present in the material. 
     It is to be understood that some organisms capable of withstanding cooling to the cryogenic temperatures may subsequently be killed in the low (or zero) oxygen, high temperature environment of the reactor during pyrolysis. In some arrangements a combination of low pressure (due to suction of gas such as air from the reactor  120 ) and heating is arranged to kill organisms that survive cooling to the cryogenic temperatures. For example, a combination of heat and low pressure may cause bacterial cells to shrink and detach from the cell walls, the cell walls then exploding, killing the bacteria. 
     In some embodiments the plant is provided with means for cooling and crushing waste as described above. The means for crushing may comprise one or more hammers, rollers or the like. 
     In some embodiments of the invention the pyrolysis process involves freezing waste such as biomedical waste; and subsequently heating the waste in a reactor to evolve organic compounds by pyrolysis as described herein. The process optionally comprises crushing the frozen waste before pyrolysis. The process may comprise shredding the frozen waste. 
     It is to be understood that, unlike rubber materials such as tyres, medical waste is preferably shredded when frozen (cryogenically cooled tyres may be smashed in a hammer mill). This is in order to prevent splashing of liquid waste which may be problematic. 
     Material to be cooled may be subject to a pre-cooling treatment in which cold gases such as nitrogen or carbon dioxide that have evolved from liquid nitrogen coolant or dry ice during a main cooling process are used to pre-cool the material. 
     Cooling of material may be performed by direct exposure to coolant or by means of a heat exchanger arrangement. It is to be understood that in some arrangements vaporised coolant may be useful in reducing an oxygen content of gases in the first reactor in which the material is heated. Thus the first reactor may be subject to an initial purging process in which vaporised coolant gas is passed into the first reactor to displace oxygen. The vaporised coolant gas may be employed to flood the first reactor during initial loading of material into the reactor and/or immediately prior to heating of the material once the material is loaded into the reactor. 
     In some embodiments one or more regions of the apparatus may be flooded with ozone gas in order to neutralise or kill harmful bacteria or other organisms in the material. This may be performed for example in the event of a malfunction of the apparatus. 
     In some embodiments, one or more other gases may be introduced into one or more of the reactors. For example in some embodiments methane and/or hydrogen may be introduced into one or more reactors in order to increase a likelihood of formation of alkanes and hydrocarbon chain molecules rather than ring molecules and alkenes. Other arrangements are also useful. 
       FIG. 7  shows a reactor  410  according to a further embodiment of the present invention. Like features of the reactor  410  of  FIG. 7  to those of the reactor of  FIG. 2  are labelled with like reference signs prefixed numeral  4  instead of numeral  2 . The reactor  410  may be referred to as a ‘counter-rotating drum’-type reactor  410 . 
     The reactor  410  has a housing  410 H in which two sets of concentric drum members D 1 -D 6  are provided. The housing  410 H may be formed from steel. It may be lined with a catalytic material on an inside thereof such as aluminium, nickel, an alloy thereof or any other suitable material. 
     A first drum support wheel  410 DS 1  is provided to which three of the drum members D 2 , D 4  and D 6  are attached at a first end of the drum members. The drum support wheel  410 DS 1  is arranged to rotate about an axis  410 DA normal to a plane of the wheel  410 DS 1 , being an axis coincident with a cylinder axis of each of the drum members D 2 , D 4 , D 6 . 
     A second drum support wheel  410 DS 2  is provided to which the three remaining concentric drum members D 1 , D 3  and D 5  are attached at a first end of the drum members. The drum support wheel  410 DS 2  is arranged to rotate about the same axis  410 DA as the first wheel  410 DS 1 , being an axis coincident with a cylinder axis of each of the drum members D 1 , D 3 , D 5 . The second drum support wheel  410 DS 2  is arranged in an opposite orientation to the first drum support wheel  410 DS 1  such that the drum members supported by the second support wheel  410 DS 2  are also concentric with those supported by the first support wheel  410 DS 1 . The drum members attached to respective support wheels  410 DS 1 ,  410 DS 2  may therefore be considered to be provided in an inter-digitated or inter-digital configuration or arrangement. 
     Each of the drums D 1 -D 6  is perforated, having apertures provided therethrough through which material may pass. An average size of the apertures in each drum decreases with increasing drum diameter. Thus the radially innermost drum D 1  has larger apertures therethrough than the radially outermost drum D 6 . 
     In some arrangements a size of apertures in one drum may be around 5 cm, whilst a diameter of apertures in an adjacent, radially outward drum may be around 4 cm. A further radially outward, adjacent drum may have apertures therein having a diameter of around 3 cm. 
     As described above, in the embodiment of  FIG. 7  the first drum member D 1  being the drum member of smallest diameter is attached to the second drum support wheel  410 DS 2 . A sixth drum member D 6  being the drum member of largest diameter D 6  is attached to the first drum support wheel  410 DS 1 . An inlet conduit  414  passes through the reactor housing  410 H coincident with the axis of rotation of the drum members  410 DA and projects into the reactor  410  as far as the second drum wheel  410 DS 2 . The inlet conduit  414  is provided radially inward and concentric with the first drum member D 1 . 
     The inlet conduit  414  is also perforated, having apertures therethrough of a size larger than those of the first drum member D 1 . A wormscrew of auger may be employed to convey material along the conduit  414 . 
     In use, the support wheels  410 DS 1 ,  410 DS 2  are arranged to rotate in opposite directions (i.e. in counter-rotation) such that immediately adjacent drum members D 1 -D 6  rotate in opposite directions. Material to be pyrolysed is passed through the inlet conduit  414  and is forced through the apertures in the inlet conduit  414 . The material then comes into contact with the first rotating drum member D 1  and becomes heated due to contact therewith. Depending on a size and shape of a given piece of material, the material may be subject to a shearing action due to contact with the first drum member D 1 , causing the material to break up into smaller pieces. It is to be understood that the material may be subject to one or more of a twisting, stretching and rubbing action generating heat in the material, for example by frictional forces. A size of a gap between the inlet conduit  414  and first drum member D 1  is set to a size allowing material passing through the inlet conduit  414  to pass into the gap and be subject to frictional heating through contact with the first drum member D 1 . 
     It is to be understood that material of sufficiently small size is able to pass through the apertures in the first drum member D 1  to the gap between the first drum member D 1  and second drum member D 2 . The material is subject to further mechanical working action as it passes through the wall of drum member D 1  and may become further heated thereby. Mechanical interactions between particles of material passing through the reactor  410  also results in heating of the material. 
     It is to be understood that as the material passes from the inlet conduit  414  through successive drum members it becomes heated to a temperature at which volatile organic compounds are evolved from the material. The reactor  410  is arranged wherein the internal environment remains substantially oxygen free and therefore burning of the material and of evolved hydrocarbons is substantially prevented. 
     The compounds rise through the reactor  410  and exit through a gas outlet  415 . The gases may then be subject to further processing (such as fractionation) and storage. 
     Pyrolysed material that exits the sixth drum member D 6  collects in a basal region of the reactor  400  where a wormscrew  417  conveys the material to an exit conduit  418 . 
     It is to be understood that in some arrangements the reactor  410  is heated by heating means in addition to heat that is generated by mechanical working of material by means of the counter-rotating drum members D 1 -D 6 . 
     It is to be understood that in some embodiments two or more reactors may be coupled in series such that material passing through an exit conduit  418  of one reactor passes into an inlet conduit  414  of another reactor. In some arrangements reactors of different types such as a counter-rotating drum-type reactor  410  and another type of reactor (such as the reactor of  FIG. 2 ) may be coupled in series. 
     It is to be understood that in some embodiments of the invention pyrolysis apparatus according to embodiments of the present invention such as those described herein may be provided with one or more thermoelectric cells on an outer surface thereof to convert waste heat into electricity. The thermoelectric cells may be arranged to provide an insulation layer to the apparatus thereby to reduce an amount of energy required to operate the apparatus. In some arrangements the cells may be arranged to provide useful sound insulation. 
     In some arrangements a reactor, pipeline or other conduit associated with the apparatus may be coated with one or more thermoelectric cells. In some embodiments the electricity generated by the thermoelectric cells may be sufficient to power one or more electrical heaters of the reactor  410  in addition to or instead of an external power source. In some situations electricity generated may be sold to an external power provider. 
     In some embodiments the reactor  410  is mounted on one or more load cells and a controller monitors a change in weight of the reactor  410  as a function of time. In some arrangements the controller is arranged to monitor weight loss and to control a temperature of the reactor  410  responsive to a rate at which evolution of hydrocarbon gas takes place. The rate of evolution of gas may be determined by reference to the weight of the reactor  410  (as determined by the one or more load cells) and a rate at which material passes into the reactor through the inlet conduit  414  (increasing a weight of the reactor  410 ) and a rate at which material passes out from the reactor through the outlet conduit  418  (decreasing a weight of the reactor  410 ). The controller may be configured to control a temperature of the reactor  410  in order to maximise a rate at which hydrocarbons are evolved from the material as discussed above with respect to  FIG. 6 . 
     In some embodiments the apparatus is arranged whereby the first drum D 1  is heated by an electrical heating means. This feature has the advantage that fresh material entering the reactor  410  through the inlet conduit  414  is heated relatively quickly so as not to reduce an efficiency of operation of the apparatus due to cooling of material that is already in the reactor  410 . 
     In some embodiments one or more scraping members and/or one or more brush members are provided between two or more of the drum members D 1 -D 6  in order to promote flow of material through the reactor  410 . One or more of the drum members D 1 -D 6  may be formed from or comprise a catalytic material. The catalytic material be arranged to catalyse evolution of hydrocarbons, and/or reduce formation of unwanted hydrocarbons. 
     In some arrangements the drum members rotating in one direction may be arranged to rotate at a higher speed than those rotating in the opposite direction. In some arrangements drum members rotating in a clockwise direction (as viewed in the direction of material entering the reactor  410  through the inlet conduit  414 ), may rotate at a higher speed than drum members rotating in an anti-clockwise direction, or vice versa. 
     In some embodiments the first drum member D 1  rotates in a clockwise direction. 
     In some embodiments the drum members D 1 -D 6  are coupled to one another by means of one or more gear wheels arranged to cause adjacent drum members to counter-rotate. 
     In some embodiments one or more surfaces (such as a radially outer surface) of one or more of the drum members D 1 -D 6  is provided with one or more raised portions to promote mechanical agitation of material passing through the reactor  410 . The one or more raised portions may include one or more blade formations to encourage twisting and grinding of material. 
       FIG. 8  shows pyrolysis apparatus  500  according to a further embodiment of the invention. Like features of the apparatus  500  of  FIG. 8  to that of  FIG. 7  are shown with like reference signs prefixed numeral  5  instead of numeral  4 . 
     The apparatus  500  has a reactor  510  having a rotatable conical grinding member  510 G that is supported by a conical ram member  510 R. A bearing arrangement  510 B is provided between the grinding member  510 G (which is substantially hollow) and the ram member  510 R, allowing relative rotation between the grinding member  510 G and ram member  510 R . The grinding member  510 G is coupled to a ram shaft  510 S that is operable to translate the ram member  510 R parallel to a longitudinal axis A thereof. The bearing arrangement  510 B may comprise a plurality of wheels, ball bearings or any other suitable arrangement. The arrangement  510 B may include a motor drive for rotating the grinding member  510 G. One or more portions of the arrangement  510 B may be formed from a catalytic material such as aluminium, nickel or an alloy thereof. An alloy of one or both of these materials with steel, or coating steel, may be useful. 
       FIG. 9(   a ) shows a side view of the grinding member  510 G. An outer surface of the grinding member  510 G is provided with teeth  510 T as shown in  FIG. 9(   a ). 
     In the embodiment of  FIG. 8  the grinding member  510 G is provided in an upright orientation for rotation about a substantially vertical axis A with an apical or tip portion  510 A of the grinding member  510 G directed substantially upwardly. Other arrangements are also useful. 
     The grinding member  510 G is positioned in close proximity to a stationary guide member  509  of corresponding shape to the grinding member  510 G. The guide member  509  bears an inner guide surface  509 S in spaced apart relationship with the grinding member  510 G. Facing surfaces of the guide member  509  and grinding member  510 G define boundaries of a substantially conical channel  510 C through which material to be pyrolysed may flow. The material may thereby be guided over the outer surface of the grinding member  510 G in a downwards direction from an inlet conduit  514  above the grinding member  510 G to an outlet conduit below the grinding member  510 G. 
     In use, material is fed to the reactor  510  via inlet conduit  514  such that the material falls onto the apical portion  510 A of the grinding member  510 G. The material then flows through the channel  510 C where it is subject to mechanical working by the grinding member  510 G in combination with the guide surface  509 S. It is to be understood that the grinding member  510 G is arranged to cause heating of the material to a temperature sufficiently high to cause evolution of volatile organics from the material. 
     It is to be understood that a width of the channel  510 C may be arranged to decrease as a function of distance from the apical portion  510 A. Thus, as material that is mechanically worked by the grinding member  510 G becomes smaller, it is able to progress through the reactor  510 . 
     In the arrangement of  FIG. 8  a portion of the inlet conduit  514  is arranged to allow hydrocarbon gases evolved in the reactor  510  to rise therethrough to a gas outlet conduit  515 . 
     A primary auger or wormscrew  517 A is provided in a material collection region below the grinding member  510 G. The primary wormscrew  517 A is arranged to convey material that has been worked by the grinding member  510 G to a secondary auger or wormscrew  517 B in an outlet conduit  518  of the reactor  510 . The secondary wormscrew  517 B conveys material through the outlet conduit  518  to an inlet conduit  514 ′ of a further reactor  510 ′ downstream of reactor  510 . As shown in  FIG. 8 , the outlet conduit  518  is inclined with respect to a horizontal direction. This feature has the advantage that a risk that hydrocarbons evolved in the downstream reactor  510 ′ pass in a reverse direction through the reactor  510  is reduced because the gases would be required to pass downwardly through the outlet conduit  518 . 
     Furthermore, this feature allows a rate at which material is conveyed from one reactor  510  to the next  510 ′ to be controlled, since pyrolysed or partially pyrolysed material collecting in one reactor  510  does not immediately fall into the next reactor  510 ′. 
     In order to encourage evolution and collection of hydrocarbons, suction may applied to the gas outlet conduit of reactors according to embodiments of the invention. This feature has the further advantage that any oxygen present in the apparatus may be removed. Furthermore, a risk of leakage of hydrocarbons from the apparatus is also reduced. 
     It is to be understood that the reactors  510 ,  510 ′ may be operated at different respective temperatures, the upstream reactor  510  being operated at a lower temperature than the downstream reactor  510 ′. The apparatus  500  may be arranged such that lighter hydrocarbons evolve in the lower temperature reactor  510  (such as methane, ethane and other relatively light hydrocarbons) whilst heavier hydrocarbons evolve in the higher temperature reactor  510 ′ (such as light and median condensable fuels). 
     It is to be understood that in use the ram member  510 R may be employed to urge the grinding member  510 G towards the guide surface  509 S thereby to apply pressure to material in the channel  510 C and increase an amount of mechanical work performed on the material. It is to be understood that a position of the ram member  510 R may be used to control a temperature of material in the channel  510 C. If the temperature is too low the ram member  510 R may be driven in a direction towards the guide surface  509 S to decrease a width of the channel  510 C and increase a rate at which mechanical work is performed on material in the channel  510 C. Conversely, if the temperature is too high the ram member  510 R may be driven in a direction away from the guide surface  509 S to increase a width of the channel  510 C and decrease a rate at which mechanical work is performed on material in the channel  510 C. Similarly, a flow rate of material through the reactor  510  may also be controlled. The flow rate may be increased by increasing a width of the channel  510 C and decreased by decreasing a width of the channel  510 C. 
     In some arrangements the guide member  509  may be movable towards and away from the grinding member  510 G in addition or instead of the grinding member  510 G being movable. 
     In the embodiment shown the ram member  510 R may be heated by means of an electrical heating element in order to increase an amount of heat to which material in the channel  510 C is subjected. This can be particularly useful during initial starting of a process of pyrolysis when the apparatus is relatively cold. 
     In some embodiments the guide member  509  may be arranged to rotate instead of or in addition to the grinding member  510 G. In some embodiments the guide member  509  may be arranged to rotate with respect to the grinding member  510 G in an opposite direction thereto. In some embodiments the guide member  509  may be operable to rotate at a different speed to the grinding member  510 G. 
     The guide surface  509 S may optionally be provided with one or more protruding tooth formations such as ridged tooth formations, bladed tooth formations or any other suitable formations to promote mechanical working of material passing through the channel  510 C. The guide surface  509 S may be provided with the one or more tooth formations in addition to or instead of the grinding member  510 G. Thus the teeth provided on the grinding member  510 G as shown in  FIG. 9(   a ) may be provided on the guide surface  509 S in addition or instead, in some embodiments. 
     In the arrangement of  FIG. 9(   a ) the teeth are substantially straight and run in a direction normal to a circumferential direction of the conical member  510 G along the outer surface thereof. This arrangement may be referred to as a radial arrangement of teeth since the teeth are arranged radially as viewed along a cone axis A of the member  510 G. 
       FIG. 9(   b ) shows a sweeping tooth arrangement in which the teeth T are oriented at a non-zero and non-normal angle to a circumferential direction and describe a substantially helical shape over the surface of the grinding member. 
       FIG. 9(   c ) shows a horizontal arrow tooth arrangement in which, with the grinding member  510 G oriented with its conical axis A substantially vertical as shown, the teeth T describe arrows pointing in a generally horizontal (circumferential) direction. 
       FIG. 9(   d ) shows an upright vertical arrow tooth arrangement in which the teeth T describe arrows pointing in a generally upward (radially inward) direction. 
       FIG. 9(   e ) shows an inverted vertical arrow tooth arrangement in which the teeth T describe arrows pointing in a generally downward (radially outward) direction. 
     In some arrangements, a height of the teeth T above a major surface M of the grinding member  510 G varies as a function of distance from the apical portion  510 A. In some arrangements the height of the teeth T decreases with distance from the apical portion  510 A, since it is expected that a size of particles of material moving through the reactor  510  will decrease as the material moves through the reactor  510 . The decrease in height may be arranged to have the additional benefit of increasing a temperature of material as a function of distance along the grinding member from the apical portion  510 A. It is undesirable to heat the material too quickly before the lighter hydrocarbon fractions have evolved in order to avoid decomposing the lighter fractions. Therefore the ability to heat the material to higher temperatures as a function of distance travelled along a given grinding member  510 G as the material passes through a reactor  510  is advantageous. 
     In some embodiments, different arrangements of teeth on a surface of a grinding member  510 G are employed in different reactors arranged in series. The arrangement selected may be arranged such that material passing through a successive one or more reactors is subject to increased mechanical working in order to increase the temperature of the material to a temperature above that of the previous reactor. A swirling tooth pattern ( FIG. 9(   b )) or arrow-shape pattern ( FIG. 9(   c )-( e )) may be advantageous in some embodiments in achieving higher material temperatures. 
     In some embodiments waste material passing into a reactor  510  is processed to remove certain foreign objects such as metals and glasses. Magnetic devices, vibrating screens, slotted screens and/or a cyclone device may be employed to remove foreign objects. In some arrangements waste pyrolysed material may also be subject to processing to increase a purity thereof, for example in cases where the material is to be processed to form carbon black, or sold as a fuel or other material such as an agricultural material. 
     In some arrangements the feed material is cut into pieces of a size of around 5 cm or less, optionally around 1 cm. Smaller sized pieces are advantageous in that a surface area to volume ratio is increased, increasing a rate at which the material is able to break down in the reactor. This has the advantage that a probability that all of the hydrocarbons of a given fraction contained in a material are evolved before the material moves to a further (higher temperature) reactor is increased. This has the advantage that a purity of gases output by a given reactor is increased. 
     As noted above, one or more components that are exposed to material being processed may be coated with, comprise or be otherwise formed from a catalytic material. A combination of steel (for strength and durability) and a catalytic material such as aluminium, nickel or any other suitable material may be employed. 
     In one application of the technology described herein, apparatus according to an embodiment of the invention is installed onboard a marine vessel. The vessel may be employed to travel between ports collecting hydrocarbon-containing waste. When at a given port the vessel may be operated so as to take onboard the waste. The vessel may be employed to subject the waste to a process of pyrolysis either whilst at the port (in which case extracted hydrocarbons may be stored in a storage facility at the port) or whilst at sea. Embodiments of the invention have the advantage that remote locations may enjoy the benefit of waste disposal and recovery of valuable resources from the waste. 
     In another application a vessel having apparatus according to an embodiment of the invention may be employed to retrieve floating hydrocarbon-containing waste from a body of water such as in an area where climatic conditions are such that waste tends to collect there. The vessel may be provided with extraction means for extracting the waste, such as nets, scoops or the like which may for example be deployed by means of extended boom members projecting from the vessel. Collector vessels may be employed to collect waste from a region and deliver the waste to the vessel having the pyrolysis apparatus. 
     A cost of the operation may be funded by sale of extracted hydrocarbons. Extracted hydrocarbons may be employed to fuel the vessel or vessels. 
     Throughout the description and claims of this specification, the words “comprise” and “contain” and variations of the words, for example “comprising” and “comprises”, means “including but not limited to”, and is not intended to (and does not) exclude other moieties, additives, components, integers or steps. 
     Throughout the description and claims of this specification, the singular encompasses the plural unless the context otherwise requires. In particular, where the indefinite article is used, the specification is to be understood as contemplating plurality as well as singularity, unless the context requires otherwise. 
     Features, integers, characteristics, compounds, chemical moieties or groups described in conjunction with a particular aspect, embodiment or example of the invention are to be understood to be applicable to any other aspect, embodiment or example described herein unless incompatible therewith.