Abstract:
Apparatus for the treatment of volatile material(s) in contaminated material(s) including a retort assembly which includes a rotatable retort disposed at least partially within a combustion chamber with a heater to indirectly heat the contents of the rotatable retort. A feeder feeds the contaminated material(s) to the retort. The apparatus further includes a pathway for passing contaminated material(s) to the retort and a conduit for passing the combustion gases from an afterburner to the retort assembly to provide additional heat for heating the contaminated material in the retort. The apparatus may also include a high temperature filter which can filter the volatiles before entering the afterburner.

Description:
RELATED APPLICATION 
     This application is a continuation of Ser. No. 09/051,004, filed May 3, 1999, now U.S. Pat. No. 6,213,030, filed as PCT/AU96/00628 on Oct. 4, 1996. 
    
    
     BACKGROUND OF THE INVENTION 
     a) Field of the Invention 
     This invention relates to the treatment of volatile contaminants. The invention is particularly suitable for, but not limited to, the removal of contaminants from solids and liquids. 
     The contaminants may include, but are not limited to, petroleum products (eg. petrol, oils, greases); phenols; coaltar; cyanide; pesticides; PCB&#39;s; HCB&#39;s, organochlorine pesticides and arsenics. 
     The treatment of contaminated soils and liquid wastes is a worldwide problem. Often, the contaminated soils or liquids are simply removed and transferred to a toxic waste dump or pond. This does no more than move the problem. For contaminants such as PCB&#39;s, the environmental protection authorities around the world specify strict conditions for their disposal in very high temperature incinerators, eg. found in the vessel “Vulcanus”. 
     b) Description of the Prior Art 
     International Patent Application No. PCT/AU93/00646 (International Publication No. WO 94/15150) (Robertson) discloses a stationery retort where toxic waste and other contaminants are removed from soil, the soil being agitated and being brought into contact with the retort walls to cause the wastes and contaminants to be desorbed. The retort has proved successful in the removal of toxic waste and contaminants from many types of soil. 
     SUMMARY OF THE INVENTION 
     It is an object of the present invention to provide improved methods and apparatus for use in removing volatile contaminants from solids or liquids. 
     According to one aspect of the present invention there is provided a method for the treatment of volatile material(s) in contaminated material(s) including the steps of: 
     feeding the contaminated material(s) to a retort assembly which includes a rotatable retort at least partially disposed within a combustion chamber which is heated by heating means; 
     causing the contaminated material(s) to contact the wall(s) of the retort to cause the volatile material(s) to be given off as gases; 
     discharging the treated material from the retort; 
     transferring the gases to an afterburner for combustion; and 
     returning the combustion gases from the afterburner to the retort assembly to provide assistance in heating the contaminated material(s) being treated in the retort. 
     According to another aspect of the present invention there is provided apparatus for the treatment of volatile material(s) in contaminated material(s) including a retort assembly which includes a rotatable retort disposed at least partially within a combustion chamber with heating means to indirectly heat the rotatable retort; said rotatable retort include a feed end through which the contaminated material(s) are fed to the retort and a discharge end from which the materials are discharged from the retort; an afterburner; means to transfer the volatile material(s) given off as gases to the afterburner for combustion; and means for passing the combustion gases from the afterburner to the retort assembly to provide additional heat for use in the heating of contaminated material(s) in the retort. 
     Preferably, the apparatus includes a high temperature filter through which the gaseous volatile material(s) pass after leaving the retort and prior to entering the afterburner. 
     According to yet another aspect of the present invention there is provided a high temperature filter which is suitable for use but not limited to the treatment of volatile gaseous contaminated material, the filter including a main body having first and second chambers therein which chambers when the filter is in its operative position include an upper region and a lower region, an opening providing communication between the chambers, said opening being at the lower region of the chambers, an inlet for delivering gaseous contaminated material to the first chamber in the upper region thereof, an outlet for discharging the gaseous material from the second chamber, a solids collection zone adjacent the opening, a solids discharge outlet for discharging solids from the solids collection zone, a baffle opposite to and spaced from the inlet upon which incoming gases impinge and filter means for filtering the gaseous material passing out of the second chamber via the outlet. 
     According to another aspect of the present invention there is provided a retort for use in the treatment of volatile material, the retort including a cylindrical body which is mounted for rotation about its longitudinal axis, said body having an infeed end and an outlet end, a combustion chamber, said cylindrical body being at least partially located within the combustion chamber, a plurality of balls or like elements disposed within the cylindrical body arranged to interact with contaminated material when the cylindrical body is rotating to break down the material and dislodge carbonised material which may form on the internal wall of the cylindrical body. The retort is particularly suitable for use in apparatus of the type described herein. 
     Preferably the retort includes a cage within the cylinder which retains the balls in the region of the wall of the cylindrical body. Preferably, the balls are arranged in groups, the groups being at spaced intervals along the interior of the cylindrical body. The cage includes spaced apart peripherally extending members which are adapted to assist in retaining the balls in each group at a particular location within the cylindrical body. Preferably, the balls are made of ceramic material. Preferably, the cage is mounted for rotation in the opposite direction to the cylindrical body. 
     In one embodiment of the invention the combustion gases are passed through the interior of the retort. In another embodiment the combustion gases are passed to the heating means. 
     When the contaminated material to be treated is in the form of solids, the solids are preferably passed through a grizzly or sieve prior to entering the retort to remove oversized material. If desired the solids may in addition to or alternatively to the above be passed through a mill prior to entering the retort so as to reduce the particle or granule size of the solids. 
     When the contaminated material is in the form of liquid, the water content of the liquid is preferably reduced prior to entering the retort. To this end the liquids may be preheated to boil off the water prior to entering the retort. 
     Preferably, the rotary retort rotates about an axis inclined at a small angle to the horizontal and is substantially surrounded by a combustion chamber to enable indirect heating of the retort 
     Preferably, the combustion gases pass through a scrubber before being released into the atmosphere after passing through the retort. The gases from the high temperature filter may be passed through a condenser, where the condensate contains hydrocarbon fractions such as fuel oil and lubrication oil fractions. 
     In the high temperature filter according to the invention, the baffle is preferably defined by a wall which separates the said first and second chambers. Preferably, the wall extends from an upper internal wall of the chambers and terminates at a point spaced from a lower internal wall of the chambers, the space between the free end of the wall and the lower internal wall of the filter defining the opening. The wall may have fins thereon. 
     Preferably, the discharge outlet comprises a plurality of outlet ports in the upper wall of said second chamber. Preferably, the filter means comprises a plurality of ceramic candles, each ceramic candle being associated with a respective outlet, the ceramic candles extending into the second chamber. 
     There may further be provided a gas collecting chamber for receiving the gaseous material from the outlets and a discharge outlet for discharging the gaseous material from the gas collecting chamber. Fan suction means may be provided for drawing the gaseous material from the second chamber through the outlets. 
     The filter may further include pulsing means for delivering a gas under pressure to the filter means in the opposite direction of normal flow for cleaning the filter means. Preferably, the gas used in the pulsing means is nitrogen. 
     A heat jacket is preferably provided which at least partially surrounds the main body of the filter. 
     A further embodiment of the invention is particularly suited for the treatment of material containing organochlorine pesticides such as DDT, DDE and DDD and various arsenic based compounds. Such material is found in soil from cattle dip sites. 
     According to this aspect of the present invention there is provided a method for treatment of volatile material(s) in contaminated material(s) including organochlorine pesticides and arsenic based compounds including the steps of: 
     feeding the contaminated material(s) to a retort assembly which includes a rotatable retort at least partially disposed within a combustion chamber which is heated by heating means; 
     causing the contaminated material(s) to contact the wall(s) of the retort to cause the volatile material(s) to be given off as gases; 
     discharging the treated material from the retort into a high temperature filter; 
     thereafter transferring the gases to an afterburner for combustion and at the same time introducing water vapour into the afterburner. 
     According to yet another aspect of the present invention there is provided apparatus for treatment of volatile material(s) in contaminated material(s) including organochlorine pesticides and arsenic based compounds including 
     a retort assembly which includes a rotatable retort having an infeed end through which material is fed to the retort and an outlet, the retort being at least partially disposed within a combustion chamber which is heated by heating means, whereby in use, the contaminated material(s) is caused to contact the wall(s) of the retort to cause the volatile material(s) to be given off as gases; 
     a high temperature filter which receives the material from the retort, an afterburner for combustion of the gases and means for introducing water vapour into the afterburner. 
     In this particular process the contaminated material is preferably firstly pretreated to remove water from the material. This may be done by the use of a preheater. The material is then transferred to a retort where the contaminant compounds are vaporised. The contaminants in the gas stream so formed are then transferred to a high temperature filter which may be of the type described earlier where further particulate matter is separated from the gas. The remaining gaseous component is transferred to an afterburner. The afterburner thermally destructs the organochlorine pesticides to produce simple products of combustion and hydrogen chloride gas. The arsenic component of the gas will pass through the afterburner primarily as arsenic trioxide. 
     If desired water vapour which may be conveniently drawn from the preheater is fed into the afterburner. The introduction of the water vapour causes a water/gas reaction which assists in the production of hydrogen chloride and arsenates. 
     The gas stream then passes to a condenser wherein the gas is rapidly cooled so as to condense the arsenates for collection as particulate matter. After the gas stream leaves the condenser calcium carbonate can be added to the stream to neutralise the hydrogen chloride. 
     The gas can be finally passed through a dust collector device whereafter the gas can pass to atmosphere. 
     As mentioned earlier the gases leaving the afterburner are cooled so as sublimate (condense) the arsenic and arsenic trioxide. Two alternative systems are envisaged 
     1. indirect air cooled; or 
     2. evaporative cooling through injection of water into the gas stream. 
     The gas stream leaving the afterburner is cooled to preferably about 110° C. in the condenser and then may be dosed with calcium carbonate (CaCO 3 ) (lime). The calcium carbonate reacts with the constituents of the gas stream to neutralise the hydrochloric acid and absorb moisture in the gas stream. The lime assists in minimising moisture problems on the filter bags, and can be collected in a dust collection bin. 
     The dust collector which may be in the form of a baghouse will remove the particulate arsenic trioxide which condenses below at approximately 120° C. and collects on the filter media. The gas stream will exit the baghouse at approximately 100° C. and be vented to atmosphere. An auxiliary fan on the baghouse will be used in conjunction with the high temperature filter fan in order to overcome the additional pressure loss in the system. The fans will be balanced using dampers in the system. The contaminated particulate (arsenic trioxide, spent lime) can be collected in plastic lined 200 L drums for disposal at authorized landfills. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     To enable the invention to be fully understood, preferred embodiments of the invention in its various aspects will now be described with reference to the accompanying drawings in which: 
     FIG. 1 is a schematic circuit diagram of a first embodiment for the treatment of contaminated solids; 
     FIG. 2 is a schematic view of the retort of the first embodiment; 
     FIG. 3 is a more detailed schematic view of the retort of the first embodiment; 
     FIG. 4 is a schematic sectional side view of a high temperature filter according to the present invention; 
     FIG. 5 is a schematic side view of an afterburner for use in the present invention; 
     FIG. 6 is a schematic view of a second embodiment for the treatment of contaminated liquids; 
     FIG. 7 is a schematic view of a third embodiment for the treatment of contaminated liquids; 
     FIG. 8 is a schematic view of a further embodiment particularly suited for the treatment of organochlorine pesticides and arsenic compounds; 
     FIG. 9 is a schematic side elevation of a part of a high temperature filter according to another form of the invention; 
     FIG. 10 is a side elevation of a manifold as shown in FIG. 9; 
     FIG. 11 is a schematic side elevation of one form of condenser which can be used in the embodiment of FIG. 8; 
     FIG. 12 is a schematic side elevation of another form of condenser which can be used in the embodiment of FIG. 8; 
     FIG. 13 is a sectional view of a retort according to one embodiment of the invention; and 
     FIG. 14 is a modified form of the retort shown in FIG.  13 . 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Referring to FIGS. 1-3, the rotary retort  10  has a cylindrical retort wall  11  rotatably journalled within a combustion chamber  12  heated by a plurality of burners  13  to provide indirect heating to the interior of the retort  10 . 
     Ceramic seals form an airproof seal between the moving retort wall  11  and the fixed ends of the combustion chamber  12  (or of a support structure for the retort), and also act as an explosion vent in case of a volatile mix release caused by oxygen in the retort. (Preferably, a nitrogen purge is provided for the retort to prevent the oxygen levels becoming dangerous.) 
     As shown in FIG. 3, fins, blades or the like  14  are provided on the inner face of the retort wall  11  to increase the agitation of materials passing through the retort and to improve the heat transfer from the retort wall  11  to the materials. 
     Contaminated solids  20  are transferred via conveyor  21  to a grizzly  22  where oversized particles are removed. The acceptable particles are fed to the interior of the retort  10  via a rotary valve  23 . As the contaminated solids move through the retort  10 , volatile contaminants are given off as gases and are transferred via a gas line  15  to a high temperature filter  30  to be hereinafter described in more detail. The high temperature filter  30  is heated by the combustion gases from the combustion chamber  12  (being transferred via a line  16 ). 
     A rotary valve  17  discharges the treated solids to a product bin  18  and a conveyor  19  may be provided to transfer the treated solids from the product bin  18  to a dump pile  19 A. 
     Referring now to FIG. 4, the high temperature filter  30  is maintained above 500° C. above the combustion gases from the retort being fed via line  16  to a heat jacket  31  to prevent condensation of the volatile gases  32 . The volatile gases enter a first chamber  33  and impinge on a wall  34  which acts as a baffle and separates the first chamber  33  from a second chamber  35 . The wall  34  may have fins or plates  34   a  the transfer of heat as well as to slow the gas stream down. As the volatile gases  32  sharply change path when passing from the first chamber  33  to the second chamber  35 , most of the particulates  36  in the volatile gases  32  collect at the bottom of the high temperature filter  30  and can be selectively discharged by a rotary valve  37  and line  38  to the product bin  18 . The combustion gases  32  then pass through ceramic candles  39  which capture particles down to −1 micron. The candle outlets  39   a  (FIG. 4) constitute outlet ports from chamber  35 . The interiors of the ceramic candles  39  are connected to a plenum or chamber  40  and the volatile gases  32  are drawn from the plenum by a suction fan  41 . The suction fan generates a partial vacuum in the high temperature filter  30  (and the retort  10 ) and assists in causing the ceramic seals to seal against the ends of the retort wall  11 . An explosion vent in the form of a door  63  may be provided in the wall of the filter the door being arranged to open in tie event of an explosion. 
     To prevent the oxygen level in the high temperature filter  30  reaching dangerous levels, sensor means (not shown) monitor the oxygen levels and if required, nitrogen from a supply tank  42  is injected into the line  15  via one or more nozzles connected to a valve  43 . 
     To remove the particulates  36  which tend to coat the exterior of the ceramic candles  39 , an air compressor  44  is connected to a manifold  45  via a valve  46 . A respective pipe  47  extends from the manifold  45  into the interior of each ceramic candle  39  and sensor means (not shown) which monitor the gas flow through the ceramic candles, operate the valve  46  so that a blast of air is injected into the interior of the ceramic candles, via the pipes  47  to cause a countercurrent flow to the flow of the volatile gases  32  to dislodge the particulates from the candles for collection in the bottom of the high temperature filter  30 . 
     FIGS. 9 and 10 show a modified form of apparatus for introducing nitrogen into the high temperature filter as well as for removing the particles from the candles. In the apparatus as shown nitrogen is fed from a manifold  401  having a plurality of outlets  402  to  406 . Each outlet is connected to a transfer tube  407  which extends into the filter at a position above the candles  39 . The tube has a series of downwardly facing holes  408  each hole being associated with a respective candle. The arrangement is such that a blast of nitrogen can be directed downwardly to clear the candles and at the same time deliver nitrogen to the filter. 
     The volatile gases  32  are conveyed via a line  48  to an afterburner  50  (see FIG. 5) in which combustion air is injected via a number of inclined injection pipes  51  to create a vortex for efficient combustion of the volatile gases. In one embodiment the combustion gases  52  from the afterburner pass through a plenum  53  to a line  54  which is connected to a pipe or conduit  55  extending through the interior of the retort  10 . In another embodiment the gases can pass along line  54  and instead of passing through the retort can be fed to the burners  13  as shown by dash line  62  in FIG.  1 . 
     The pipe  55  has a plurality of helical flights  56  to further promote the agitation of the laminated solids  50  in the retort  10 , and to promote the transfer of heat from the combustion gases to the solids. As shown in FIG. 1, the flow of the combustion gases  52  from the afterburner is concurrent with the flow of solids through the retort  10  and the heat from the combustion gases  52  reduces the heat requirements for the retort provided by the burners  13 , thereby reducing the input energy demand and cost. (This means that the volatile contaminants in the soil are used to provide a portion of the energy demands for the treatment of the soil and so the volatile materials, which normally have a highly negative economic value, are given at least a partial positive economic value.) From the pipe  55 , a line  57  transfers the combustion gases  52  to a scrubber  58  and thereby to the end stack  59  for release to the atmosphere. 
     Referring now to a second embodiment of FIG. 6, liquid contaminants from a pond  120  are fed to a concentrator  121  where the water content of the liquids is minimised and the concentrated contaminated liquid is transferred to a tank  122 . The contaminated liquid is pumped via a pump  122   a  to spray nozzles  123  which inject the contaminated liquid into the retort  10 . The contaminated liquid comes into contact with the interior of the retort wall  11  and the conduit  55  to cause the volatile contaminants to be given off as gases as hereinbefore described and any non-volatile solids are discharged via rotary valve  17  to the product bin  18 . 
     It will be noted that line  54  connects the afterburner  50  to the conduit  55  so that the flow of combustion gases  52  from the afterburner is countercurrent to the flow of the contaminated liquids through the retort  10 . 
     In the embodiment of FIG. 7, which is particularly suitable for the treatment of refinery tank bottoms, the contaminated refinery products containing, eg. 50-80% water, is pumped from a refinery tank  220  to a preheater  222  where the water and light hydrocarbon fraction(s) are boiled off at, eg. 120° C. plus and fed by line  260  to the afterburner  50 . A hot filtering device  261  removes particulates from the water/gas stream and feeds them to the high temperature filter  30  via a rotary valve  262 . The concentrated liquid from the preheater  122  is sprayed into the retort  10  as hereinbefore described. The preheater  122  is heated by combustion gases from the retort  10  via line  223 . 
     From the retort, the non-volatile solids are discharged via rotary valve  17  to the bin  18 , and the volatile gases are transferred to the high temperature filter  30 . The volatile gases are transferred from the filter  30  to a condenser  270  via line  271  at a temperature of, eg. 500° C. The gases are cooled and the condensate is collected as fuel oil, which is drawn off to tank  272  via line  273 . By arranging the Condenser  270  as a “fractional distillation unit”, the condensate may be separated into a lubrication oil component (drawn off at, eg. 300-500° C.) to tank  274  via line  275 , and a diesel substitute component (at, eg. 200-300° C.) via line  273  to tank  272 . 
     The remaining volatiles from the condenser  270  are fed to the afterburner  50  via line  48 . These volatiles, and the  222  water/light HC fraction from the preheater, may be burnt at, eg. 1200° C. with a residence time of, eg. 20 seconds. The energy from the afterburner  50  is recycled to heat the preheater  223  and the high temperature filter  30 . The high temperature filter and pre-treatment feed and product lines are surrounded by a heating jacket to maintain temperature and the heat is sourced from the combustion chamber excess gases. 
     This method markedly reduces the costs of treating the refinery tank bottoms, and the costs are offset by the recovery of the valuable condensates(s). 
     FIG. 8 shows a further embodiment of the invention which is particularly suited for the treatment of material containing organochlorine pesticides such as DDT, DDE and DDD and various arsenic based compounds. Such material is found in soil from cattle dip sites. 
     In this particular arrangement the contaminated material is preferably firstly pretreated to remove water from the material. This may be done by the use of a preheater  501 . The material is then transferred to retort  503  where the contaminant compounds are vaporised. The contaminants in the gas stream so formed are then transferred to high temperature filter  504  which may be which may be of the type described earlier where further particulate matter is separated from the gas. The remaining gaseous component is transferred to afterburner  506 . The afterburner thermally destructs the organochlorine pesticides to produce simple products of combustion and hydrogen chloride gas. The arsenic component of the gas will pass through the after burner primarily as arsenic trioxide. 
     If desired water vapour which may be conveniently drawn from the preheater  501  is fed into the afterburner  506  via line  510 . The introduction of the water vapour causes a water/gas reaction which assists in the production of hydrogen chloride and arsenates. 
     The gas stream then passes to condenser  512  wherein the gas is rapidly cooled so as to condense the arsenates for collection as particulate matter at vessel  514 . After the gas stream leaves the condenser  512  calcium carbonate can be added to the stream via hopper  516  to neutralise the hydrogen chloride. 
     The gas can be finally passed through a dust collector device  518  whereafter the gas can pass to atmosphere. The dust collector  518  which may be in the form of a baghouse will remove the particulate arsenic trioxide which condenses below at approximately 120° C. and collects on the filter media. The gas stream will exit the baghouse at approximately 100° C. and be vented to atmosphere. An auxiliary fan on the baghouse will be used in conjunction with the high temperature filter fan in order to overcome the additional pressure loss in the system. The fans will be balanced using dampers in the system. The contaminated particulate (arsenic trioxide, spent lime) will be collected in plastic lined 200 L drums for disposal at authorised landfills. 
     Two examples of condensers which can be used are shown in FIGS. 11 and 12. FIG. 11 shows an evaporate cooling arrangement wherein the gases leave the afterburner and travel along an inverted U-tube  601 . Water is fed from reservoir  602  to spray heads  603  by pump  604  so as to rapidly cool the gas before it leaves the condenser. 
     FIG. 12 shows an indirect air cooled arrangement where gases enter the top of the condenser  700 . A series of fans  701  create an air flow across the condenser thereby cooling the gases before they exit at the bottom. 
     FIGS. 13 and 14 show two arrangements of a retort which is suitable for use in various forms of apparatus described herein. Referring to the drawings the retort  800  includes a cylindrical body  801  which is mounted for rotation about its central axis for example on shaft  810 . The retort  800  is disposed within a combustion chamber (not shown) the ends being sealed by ceramic seals (not shown). The retort has an infeed end  802  through contaminated material is fed into the retort and an outlet  803 . A plurality of flights  808  are formed on the internal wall of the cylindrical body  801  the flights preferably having a 5° pitch. 
     The retort  800  further includes a cage  815  which is mounted within the cylindrical body  801 . The cage  815  comprises a series of horizontal elements or rods  816  and a series of circumferential elements  817  connected together to form a unitary structure. The circumferential elements  817  are arranged in pairs on the region of the space between adjacent flytes  808 . The cross-sectional diameter of the cage  815  is less than that of the internal cross-sectional diameter of cylindrical body  801  thereby forming an annular space  818  between the cylindrical body  801  and the cage  815 . 
     The cage  815  is mounted for rotation and preferably is arranged to rotate in the opposite direction to that of the cylindrical body. 
     A plurality of balls  806  or like elements are disposed in the space  818  and are arranged to interact with contaminated material when the parts are rotating to break down the material and dislodge carbonised material which may form on the internal wall of the cylindrical body  801 . The balls  806  are arranged in groups disposed at spaced intervals along the cylindrical body and are retained in position by respective pairs of circumferential elements  817   
     In the embodiment shown in FIG. 14 there is further provided a series of arms  820  which can assist in moving the balls during rotation of the parts. The arms  820  can either rotate with the cage on shaft  810  or can be fixed to the internal wall of the cylindrical body  801 . 
     The balls are arranged in groups each group which are held in place by the cage  815  and more particularly by the element  817  projecting into space  818 . The groups of balls are being disposed at spaced intervals along the cylindrical body. 
     NB: For both contaminated solids or liquids, the flow of the combustion gases  52  through the retort may be either concurrent or countercurrent to the flow of the contaminated materials. 
     The recycling of the afterburner gases back into the retort  10  via the tube, pipe or conduit  55  minimises the energy input to the retort by the burners. 
     The provision of the heat fins or flights  56  on the pipe or conduit  55  not only increases the radiant surface area of the retort, but also assists in breaking up any large particles. In addition, the recycling pipe or conduit also helps create a convection environment with improves the volatile removal process, the convection improvement being created by the moving retort wall and by rotation of the pipe or conduit  55 . 
     The energy sources for the burners  13  may include liquid petroleum gas, propane, natural gas, recycled hydrocarbons or other readily available energy sources. 
     The volatiles which may be treated by the method and apparatus of the present invention include hydrocarbons, organo-chlorides, arsenics, hydrogenated hydrocarbons, PCB&#39;s, coaltars and the like. 
     The operating temperature in the retort will be dependent on the volatile contaminants being treated and the retort may be operated at different temperatures to enable different volatiles to be treated on a fractional basis. 
     Various changes and modifications may be made to the embodiments described without departing from the present invention.