CA2164439A1 - Apparatus and process for cleaning polluted ground material - Google Patents

Abstract

The present invention concerns an apparatus and a process for cleaning polluted ground material which is finely divided in a first step and heat-treated in a second step. The apparatus for cleaning polluted ground material has a pre-dividing device (4 5, 6) and a heat treatment station. To provide an apparatus and a process of the above-indicated kind which permit highly efficient removal of volatile substances from the ground material at a comparatively low energy consumption and at low cost it is proposed in accordance with the invention that in regard to the process the ground material is heated in the second step without contact with an open flame by way of heat exchangers to a temperature above the boiling temperature of water and below a temperature of 400°C and then the heated fine-grain ground material is exposed to hot, possibly superheated steam which removes the volatile constituents from the ground material grain. In regard to the apparatus it is proposed that the heat treatment station is an evaporator (10) at which there are provided heating devices (21, 11) circulating and conveying devices (11) and at a spacing from an intake of material into the evaporator (10) a steam feed device (12) for the feed of steam which is heated above the water condensation temperature to the ground material which is also heated in that region above the condensation temperature.

Description

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Apparatus and process for cleaning polluted ground material The present invention concerns an appa~lus and a process for cleaning polluted ground material, wherein primarily volatile pollutants are to be removed from the ground material. It will be noted in this respect that the term volatile pollutants also includes those pollutants which have a boiling point beyond 200C such as for example high-molecular hydrocarbon compounds and other organic compounds.
Various metals, metal compounds and other organic substances are also included

2~q~q among such volatile substances which are often highly toxic and which threaten the water table and generally the environment. Polluted ground materials ot that kind are frequently to be found at existing or abandoned industrial sites at which the most widely varying solvents, oils and other of the above-mentioned pollutants have been 5 much too carelessly handled in the past. The ground in the region of former or still existing legal or illegal dumps frequently suffers from the most widely varying pollutants with more or less volatile substances. In order to clean up such areas the ground in such pieces of land, depending on the depth of penetration of the polluting materials, must be removed at the surface or even down to a depth of several meters 10 and either dumped elsewhere or, which is to be preferred in particular when dealing with very large amounts, cleaned.
A ground cleaning apparatus of the general kind set forth generally has a pre-dividing device and a heat treatment station. In addition it will be noted that ground cleaning apparatuses and processes are also known in which the ground is not treated 15 with heat, or is not treated with heat to any marked extent, but is mixed or "inoculated" with micro-org~ni~mc, such as for example bacteria etc. which however can only break down a limited range of pollutants, which moreover under some circumct~nces may also take up a very long period of time. In accordance with the app~ s of the general kind set forth, the process of the general kind specified 20 provides in a first step for pre-division of the ground material, followed by a heat treatment step. In regard to the heat treatment step a coarse distinction can be made between so-called pyrolysis, that is to say heating with the exclusion of air, in which case by virtue of the heating effect the pollutants contained in the ground are intended to be partially destroyed, and taken off as waste gases and the waste gases can then 25 be subjected to further treatment, and a thermal tre~tment with the effect of a flame, the ground material being exposed to a burner flame.
Both processes however suffer from the disadvantage that, in part due to the relatively high temperatures above 500C at which those processes take place, they result in chemical conversion processes, in which case in part new and even more30 dangerous pollutants such as for example dioxines can be produced. Processes in which the dioxines in turn are to be destroyed by producing even higher tempelalures :

~l~qA39 above 1000C are relatively expensive and complicated in terms of process management because the cooling operation which follows the heating and combustion phases must be effected very quickly and under controlled conditions so that dioxines or other critical compounds are not freshly formed. In addition those known apparatuses and processes are relatively energy-expensive, which makes the ground material cleaning procedure correspondingly costly.
In colllpalison therewith the object of the present invention is to provide an appalaLus and a process of the above-indicated kind, which permit highly effective removal of volatile substances from the ground at a co~llpal ~lively low level of energy expenditl-re and at low cost.
In terms of the apparatus that object is att~ined in that the heat treatmen~
station is an evaporator at which there are provided heating devices, circulating and conveying devices, and at a predetermined spacing from the material intake a steam feed device for the feed of steam which is heated above the water condensation temperature to the ground material which is also heated in that region above thecondensation temperature of water. In this respect the term evaporator is essenti~lly used to denote a container in which moisture is driven out of the ground material by heating, that is to say a piece of equipment in which the ground material is heated to over 100C, for example to up to 300C.
In regard to the process set forth in the opening part of this specification theobject of the present invention is attained in that the ground material is heated without contact with an open flame by way of moved heat exchangers to a temperature above the boiling temperature of water and in any event below 500C and that then the heated fine-grain ground material is exposed to hot steam which removes the volatile constituents from the ground material grain in accordance with vapor pressure and steam volatility, or displaces them by the formation of a single- or multi-molecular layer.
In that respect the heating operation or the trea~ment operation is effected in such a way that there are no longer any ground material agglomerates, that is to say the individual ground material grain is open.
In the pre-dividing installation the ground material is divided up or reduced in ~1~443~

size to afford relatively small lumps or pieces of a size of typically less than 10 mm in diameter, and larger pieces of stone or rock are sorted out. If now those small lumps of ground material are heated in the evaporator without the effect of an external flame but only by virtue of contact with heating devices and/or convection and heat S conduction, the water which is contained in the lumps and which ultimately also forms the binding agent for the ground material lumps that generally comprise a relatively fine-grain material ls driven out. As a result of that, and also because of the conveying and circulating movements, the lumps of ground material which have already been pre-divided disintegrate still further in the evaporator to form a very fine-grain material which is brought by the heating devices in the evaporator to a desired temperature in the specified temperature range, preferably to a temperature of between 110 and 350C. Heated or superheated steam is then fed to that fine-grain heated material, in which respect that steam, because of the fine-grain nature of the ground material, has a very large surface area that it can attack, and it removes from the exposed ground material grain any volatile conctituentc~ in particular if the evaporation temperature thereof is below the temperature attained. In that respect, at a temperature of up to 350C, high-molecular hydrocarbon compounds are also driven out or stripped from the ground material grain. They are dissolved in the steam and are entrained by same. This also applies in the same manner for metals, in particular for mercury and other metals with a low melting point such as for example cadmium or certain kinds of metal alloys. Thus the ground material is already very substantially liberated of the toxic substances contained therein and it can be discharged from the evaporator and cooled and is brought again to a normal desired ground consistency by the addition of moisture.
Particular configurations of the apparatus and the process for cleaning ground material, for specific purposes of use and in particular also preferred embo~im~ntc and configllrations are set forth by the features of the appendant claims which are briefly described hereinafter. In this respect it is expressly pointed out that the features from the appendant claims can also be combined individually with each other and with the features of the main claims insofar as it is not clearly app~ent from the context that certain features can only be embodied in a group-wise manner jointly with each other.

Thus it is for example desirable if the heating device of the app~lus according to the invention has partially moved hollow elements through which flows a heat carrier which is capable of flow, which hollow elements come into contact with the ground material7 with their outside surfaces which are remote from the heat 5 carrier. In that way the heat carrier which is capable of flow can be heated at another location and brought to a uniform temperature so that the heating devices also have a uniform temperature at a desired level. The heat stored in the heat carrier can then be transmitted by way of the walls of the hollow elements, on the basis of the heat exchanger principle, to the ground material which in that way is also brought in a 10 highly uniform manner to a given temperature level.
In specific terms the heating devices may have for example hollow rotatable shafts which are provided with circulating and conveying blades or vanes, and the circulating and conveying blades may also be partially hollow and may have the heat carrier flowing therethrough. In particular the circul~ting and conveying blades may 15 also be in the form of U-shaped loop members through which the heat carrier material flows in a predetermined direction.
In that respect the heat carrier which is capable is guided in a circuit and after being cooled down in the evaporator is returned again to a heating boiler and heated again to a desired temperature. Oil has proven to be desirable as a specific heat 20 carrier, in which respect special synthetic oils with a very high boiling point are to be preferred in order to be able to heat the ground material to suitably high telllpelatllres.
Besides a heating device or a boiler for heating the oil, also provided outside the evaporator is a steam generator which generates the steam which is then blown 25 into or through the ground material preferably in the downstream region of the transit section of the ground material through the evaporator, more specifically as far as possible, from the underside thereof.
Desirably, a demineralisation device is provided in the water feed for the steamgenerator, so that dissolved substances and in particular lime are not deposited in the 30 interior of the steam generator and in the steam feed conduits. The steam feed devices should be provided in the last third of the evaporator.

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At least one waste gas conduit is provided preferably at the top side of the evaporator, that conduit primarily receiving the steam which as so-called "strip steam"
is caused to flow through the ground material and which has removed the pollutants from the ground material grain. Insofar as this can be reconciled with relevant safety 5 requirements, added carrier steam can possibly also additionally be introduced into the evaporator and discharged through the waste gas conduit in order more effectively to entrain the strip steam in which the pollutants are dissolved. This additional carrier steam can be blown in in the upper region of the evaporator and does not have to flow - through the ground material. The evaporator is generally not vacuum-tight so that, 10 if the evaporator is operated in accordance with the invention at a slightly reduced pressure of between 2 and S0 mbar below normal pres~ure, due to leaks, in particular through the intake and discharge devices, there is a flow of so-called leakage air which also escapes together with the steam through the waste gas conduit and is passed to a waste gas cleaning apparatus. It will be appreciated that a design of the 15 evaporator for vacuum operation is also readily possible.
The intake and the outlet of the evaporator are preferably provided with lock-type intake and outlet devices, such as for example cell wheel lock devices or the like, whereby the leakage rate can be kept at a relatively low level.
Connected downstream of the outlet for the ground material or the discharge 20 device for the ground material from the evaporator are a cooling screw and a dry cooler in which the dry ground material is cooled and moistened with water to a moisture content of about 10% to 15%. The ground is discharged from the dry cooler and is then ready for use again, for example also for applying to fields or the ground in wooded areas. The addition of moisture in the dry cooler is in that respect such 25 that the ground material which is finally discharged has the same moisture content as normal topsoil and in particular therefore is neither dusty nor of a muddy fluid COnCictfncy .
Desirably, connected upstream of the waste gas treatm~nt there is also a dust filter or separator such as for example an impingement-type separator, a cyclone30 separator or an electrostatic filter, the best being a combination of the impingement-type separator and an electrostatic filter which is operated with alternating current.

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The waste gas treatment or waste gas separation device has at least one condçncer which is preferably operated just below the dew point of water. That provides that the steam which comes from the evaporator and which contains pollutants as well as ground pollutants which have been driven out are conden~ed out 5 to a certain degree. The conde~cate produced as well as entrained deposited dust are passed into a gravitational separator and separated into solid and liquid phases. The steam which has not yet condensed out is passed to a second condenser which is operated at a significantly lower temperature of about 40C and the con~ensate of which is also fed to the gravitational separator. In the separator, organic, aqueous and 10 solid phases are separated from each other and discharged. The organic phases are either disposed of or they can possibly be re-processed and re-used.
The gaseous phase which remains after the second condenser is cooled, optionally cooled to a very low temperature (for example below the melting point of mercury) and passed through coolers and activated carbon filters until finally there lS essenti~lly remains leakage air which is discharged to the exterior. It will be appreciated that the activated carbon filters have to be regenerated from time to time and that then the substances which are retained in the activated carbon filters must in turn be disposed of.
The process according to the invention is distinguished in particular in that 20 there is no direct contact between a flame and the ground material, but that the ground material is heated indirectly by means of a heat carrier or by way of heat exchangers.
That affords very accurate control over the temperature which the ground material finally attains and at which it is exposed to the so-called strip steam. The heating and evaporation operations are effected in the same container but in different portions 25 while conveying and circulating devices move the ground material slowly from an intake to an outlet of the container, in which case it is firstly heated up and then, as already mentioned, exposed to the steam. After the ground material has been put into very flne-grain form by virtue of the effect of the heat and because of the simultaneous circulation effect, the steam removes therefi~m practically all relevant 30 pollutants, such as for example the usual organic compounds in the form of solvents, chemical basic substances, oils, tar, benzine, etc. but also many inorganic substances, 2:~ 64~3~

such as for example easily volatile metals and metal alloys. When the ground - material has reached the outlet of the evaporator it is cleaned and then only needs to be cooled and brought to the normal moisture content of ground material. The waste heat which is liberated in the cooling and moi~tçning operations can possibly be used 5 for further treatment of the waste gas which is liberated from the evaporator.A particularly preferred embodiment of the process is one in which a superheating operation which can optionally be brought into effect is also conducte~l downstream of the above-mentioned dust or dry filter and upstream of the condenser.
In that way, if necess~ry, it is also possible to crack various fractions and other 10 compounds which are possibly difficult to handle or which are toxic and the cor,~ ue~tc of which can be more easily deposited after having been superheated to telllperalules into the region of 550C or 600C, in the condenser or following stations.
Besides "normal" ground, the process according to the invention can also be 15 used to clean ground materials which are of an extremely fine-grain, poor-quality clay and clayish nature. A further particular advantage of the present invention is that the tre~tment temperature in the evaporator can be m~tched to the specific pollutants involved. Thus the treatment temperature can be kept in part clearly below the possible maximum temperature in the evaporator if for example only low-molecular20 hydrocarbons and other solvents, as essenti~l pollutants, are to be driven out of the ground. The process and the apparatus can therefore be adapted to the actual pollutants involved, in the optimum manner. That contributes to complete cleaning with the minimum level of energy expenditure.
In regard to the waste gas issuing from the first evaporator, the treatm~nt is 25 conducted in a first spray condenser, in which case in accordance with the invention that tre~tmçnt is effected in the spray condenser just below the dew point of water, that is to say above 90C and preferably in the range between 95 and 96C.
Temperature control in the spray condenser is in that respect preferably effected by way of an electronically regulated cooling water through-put in the cooler. Operation 30 of the spray condenser at such a high temperature contributes inter alia to the point that the con~en~te produced contains in a higher level of concentration at least the

3 9 g pollutants which are not gaseous in that temperature range, as at that temperature the - waste gas which occurs in the form of steam only partially condçnces while a part of the waste gas which now predomin~ntly contains the particularly easily volatile substances is passed to a second condenser which is now operated at a significantly S lower condencation temperature below 60C and preferably of the order of magnitude of 25 to 30C.
The substances which are also still gaseous thereafter are subjected to further cooling and filtering by means of activated carbon filters. The condçn.c~tes are fed to a gravitational separator in which they are separated into solid, organic and aqueous phases. The light products from the gravitational separator such as for example liquid hydrocarbon compounds (benzine, oil etc.) can possibly be subjected to use, possibly even as an energy carrier in the installation or they can be subjected to further separation and refining. The aqueous phase from the gravitational sepalator is succçccively passed through a fine filter, a stripping column which is operated with air and a final activated carbon filter, when it is drained from the inct~ tion. A part of the water from the sepalator is passed into the cooling circuit of the first condenser upstream or downstream of the stripping inct~ tion.
Desirably an on-line control is provided for the entire inct~ tion, that is to say the installation is automatically controlled and monitored on the basis of predeterminable or also fixedly programmable parameters, in which respect it will be appreciated that suitable sensors for example for temperature, pressure, flow quantities etc. are provided at the applopliate locations, while deviations in respect of the sensors from the predetermined or pre-programmed values are adapted by suitable control of the parameters of the parts of the inct~ tion acting thereon.
Further advantages, features and possible uses will be appdrenl from the following description of a preferred embodiment of the inct~ tion and the procedure of the process of the invention, as are diagr~mm~tic~lly illustrated by means of the single Figure. J
The core of the ground cleaning inct~ tion is an evaporator 10 which is diagramm~tically shown in the left-hand part of the drawing by outlines and withcombined circulating/heating devices 11.

~36~39 , The entire inct~ tion essçnti~lly comprises a preparation portion, the element~sof which are essentially identified by reference numerals 1 to 7, a ground treatment portion comprising the evaporator 10 and the associated components identified byreference numerals 10 through 26, and the waste gas tre~tment portion whose S components are essenti~lly identified by reference numerals above 30 and which çssenti~lly constitutes the right-hand half of the Figure.
The polluted or cont~min~ted ground firstly passes into a sel)ald~llg device forcoarse material of a typical diameter of for example clearly more than 50 mm such as stones or rocks which are collected in a container 2 and which can possibly be l O cleaned at the surface mechanically and by means of flushing water, in which case the cle~ning waste matter can be added again to the polluted ground material upstream of or downstream of the separation device l or 5. Reference 3 denotes a magnet which sorts m~gnetic materials out of the polluted ground. A shredder is identified byreference numeral 4 and divides the lumps which are initially still relatively coarse 15 and of which polluted ground usually consists. The divided ground then passesthrough a further separation device S by way of the path or conduit 7 to an intake device 13 for the evaporator 10. The material which was sorted out in the separation device S as being excessively coarse because it is possibly too hard to be reduced in size in the shredder 4 is firstly passed into a crusher 6 which also crushes the hard 20 coarse material and delivers it again upstream of the magnet 3 into the path or conduit to the shredder 4.
The intake device 13 may be for example a supply bin or bunker with cell wheel lock device.
The material which passes into the evaporator from the device 13, for example 25 by way of a cell wheel lock device, is kept colls~llly in movement by circulating devices 11 and in so doing is guided slowly from the intake device 13 to a cell wheel lock device 16 at the outlet of the evaporator 10. The evaporator 10 can be in the form of a so-called "blade drier", that is to say the circulating elements 11 are for example in the form of rotatable shafts which have distributed along their periphery 30 vanes or blades which pass over at least the major part of the volume of the vessel which closes the evaporator relative to the exterior and which thus continuously loosen ~lB443~

up the material in the interior thereof, keep it in movement and gradually transport - it from left to right in the Figure. It will be appreciated that for that conveying action the blades may be disposed inclinedly in one direction so that, when the blades rotate about the shafts, a forward thrust force is developed in the axial direction of the shafts S at the front surfaces of the blades. The forward thrust force however is also already produced by a fall or gradient in the ground material being treated, which fall or gradient occurs due to the preferably continuous intake of material at the end of the evaporator which at the left in the Figure, and the discharge of material at the right-hand end. The container which closes off the evaporator can be a cylindrical drum, 10 the length of which is preferably clearly greater than its diameter, but the cross-sectional shape of this container may also be oval or it may comprise two partially mutl~lly penetrating cylinder portions if, as diagrammatically illustrated, the arrangement has two parallel shafts with blade elements which extend in the longitudinal direction through the evaporator container.
As indicated by virtue of the thick broken line which extends towards the left from the heating device 21, a heat carrier, preferably oil, is axially introduced into the circulating elements 11 or the shafts thereof which for that purpose are in the form of hollow shafts, in which respect the circulating blades may also be at least partially in the form of hollow elements. In that way heat energy is tr~ncmitt~d to the ground 20 material from the oil circulation which is shown in thick broken line and which passes through the heating device 21 and the circulating devices 11. A circulating pump 26 provides that cooled oil at the other end of the shaft is passed back to the heating device 21, heated up there and re-introduced at the front into the hollow shafts of the circul~ting ~lçment~ 11.
The residence time of the material in the evaporator 10 can be adjusted by the feed and discharge quantities, the speed of rotation of the circ~ ting elements 11 and the specific design configuration thereof (inclined positioning of blades or the inclined positioning of the evaporator (2 - 3)). By way of the residence time and the temperature of the oil which is discharged from the heating device 21, it is then possible to set a desired temperature for the ground material which that material is intended to attain for example after having passed through half the extent of the ~6~43~

evaporator.
It is only in the last third of the evaporator 10 that hot steam conduits 12 open therein, more specifically in the lower region or bottom of the evaporator, so that the steam issuing there must necessarily pass through the bottom. The ground material 5 which has been previously circulated and heated while being circulated has in the me~ntime lost the ground moisture contained therein and is therefore generally in powder but at least fine-grain form. The so-called strip steam which issues from the conduits 12 therefore has a very large surface area which it can attack on the ground material and can almost completely remove or strip from the ground material grain 10 the pollutants which adhere to the ground material grain and diffuse therefrom.
The hot steam is generated by a steam generator 20 which can either be operated from the same boiler as the heating device 21 or which can be operated with the waste heat from the heating device 21, as inflicated by a connecting arrow between the heating device 21 and the steam generator 20. The generally superheated steam 15 is passed by the steam generator into a steam conduit 14 which branches, a part of the steam, as already mentioned, being urged through the connections 12 into the evaporator 10 while another part is introduced into the evaporator from the top side (see the thin broken lines) and in that case escenti~lly serves as a carrier gas which also entrains the strip steam which has picked up pollutants from the ground material, 20 through a waste gas conduit 15.
A further br~nching of the steam conduit 14 goes to activated carbon filters 47,50 in the waste gas treatment portion and serves for regeneration from time to time of those activated carbon filters.
Water is fed to the steam generator 20 from a water conduit 25 by way of a 25 demineralisation device 19, the purpose of the demineralisation procedure being to prevent deposits of lime and the like in the steam generator 20.
The conduit 24 which is shown by a thick line and which leads to the heating device 21 carries combustion air while a suitable fuel such as for example gas or oil is supplied through the line 23. The cleaned ground material is discharged at the end 30 of the evaporator 10 by way of a cell wheel lock device 16 and fed to a dry cooler 18 by way of the path or conduit 17. The dry cooler 18 receives an addition of water 2~ 6443~

from the conduit 25 or the conduit 43 for final moistening of the ground material so - that the cleaned ground material 8 can then finally be discharged at the desired con~i~tency, re-used and possibly put into intermedi~te storage. The steam which is liberated in that operation in the cooler 18 is conden~ed and re-introduced. Water S issuing from the filter is drained off or can be partially used as feed water (depending on the composition loading) for the steam generator.
The steam passing from the conduit 15 into the spray condenser 30 at least partially condenses, in which case the pollutants which are of a volatility that is comparable to water or more difficult also undergo an increase in concentration in the 10 conden~te. The uncondensed steam as well as also a certain proportion of air in the system is passed on to the second condenser 31. A certain proportion of leakage air is already present in the waste gas conduit lS for the reason that the intake and discharge devices 13 and 16 as well as the shaft sealing arrangements cannot be of a hermetically sealing nature, or can be so only at considerable cost. As moreover the lS evaporator is operated at a slightly reduced pressure in the range of for example from S to 10 mbar below normal pressure a corresponding amount of leakage air is sucked in and passed through the waste gas conduit lS into the conden~ers 30 and 31.
After the discharge from the evaporator and u~ ealll of the condenc~r however there is firstly provided a dust filter, more specific~lly in the form of an 20 impingement-type separator which is combined with an ac voltage electrical filter.
Reference numeral 28 denotes a superheating device which is brought into operation only when required and which is otherwise by-passed or through which the gas passes without being superheated. Depending on the respective nature of the ground pollutants to be removed however superheating at that location for example to a 25 temperature of SS0 or 600C may be al)propl iate in order to crack certain constituents of the gas and thus make them more readily accessible to further treatment.
The individual steps and blocks illustrated diagrammatically in the right-hand part of the diagr~mm~tic drawing are generally to be in~el~leled such that a heavier, liquid or solid fraction is drawn off in each case at the lower end of the 30 diagrammatically illustrated containers while a lighter fraction issues further upwardly laterally from the respective containers. Accordingly the heavy fraction from the 2:1 6~3~

condenser 30 passes into a se~iment separator 32 and that sediment is then passed into - the outlet 9 which in turn communicates with the intake device 13. That sedimçnt is therefore freshly subjected to the cleaning operation in the evaporator. Generally that involves relatively small particles in dust form, which have been entrained in the 5 evaporator 10 by the strip steam (if the dust filter 27 is omitted or they have possibly passed the dust filter 27), but of those particles a part can be recovered as ground material 8, in a renewed pass through the assembly.
The lighter fraction from the sediment separator 32 then passes into a gravitational separator 36 into which the heavier fraction of the second condenser 31 10 is also passed. From the gravitational separator 36, the heavier fraction is in turn passed into the particle filter 37 which is disposed therebeneath, and the very fine slurry which is retained in that situation is passed into the sediment separator 32 again by way of the conduit shown in dash-dotted line, from the sand filter 37. If necec~ry the aqueous phases are then neutralised at 29 by the addition of a neutralisation agent 15 and then pass through the particle filter 37 and pass into a two-stage stripping column 39 with an air feed conduit 41. The air in turn entrains volatile constituents from the liquid in the stripping column 39 and is passed by way of pump 38 into an activated carbon filter group 50. The rem~ining residue passes through the stripping column to an activated carbon filter 40 from which the water which has now been cleaned is 20 passed into the conduit 43; that water, depending on the salt content, can be in part mixed with the feed water of the steam generator. Excess water is removed through the conduit 53.
The air in the conduit 41 for the stripping column 39 is in part fresh air from the conduit 45 but in part also waste or exhaust air 42 which issues from the activated 25 carbon filters 47 and 50.
The second condenser 31 is operated at a conflencation temperature of about 40C, with the rem~ining gaseous conctit~entc passing into a cooler 34 by way of the conduit 33. A cooling tower 46 is connected into a cooling circuit for the condenser 31 in order to be able to operate the condenser 31 at the desired low condencation 30 temperature, in spite of the supply of relatively hot waste gases from the first condenser 30. The coolant circulation is m~int~inecl by the pump 35. The cooler 34 21 6A43~

lS
also acts as a separation device, in which the case the conctitu~nt~ of the waste gas, - which are put into fluid form in the cooler 34, are also passed into the gravitational sepa,ator 36 while the gaseous constituents can pass through various activated carbon filters and cooling devices. Finally, the cleaned waste gas which ec~nti~lly now only S consists of the leakage air which was previously sucked in is discharged from the activated carbon filters 47, S0 by way of the waste or exh~--st air conduit 42; in that case, as already mentioned, that waste or exhaust air can then be supplied to the two-stage stripping column 39.
In the regeneration mode of operation of the activated carbon filters 47, S0, 10 hot steam is supplied thereto by way of the conduit 14 and dissolves out the pollutants which have been absorbed in the activated carbon filter. The vapor is then passed through connected coolers 49 and the material which is put into fluid form in that phase of operation is supplied to the gravitational sep~ator 36, as also in the case of the other liquid fractions. It will be appreciated that in this mode of operation the lS valves 48 are closed.
~ n that way the polluted ground material which was originally introduced into the evaporator 10 becomes cleaned ground as indicated at 8, wherein the volatileorganic and inorganic solvents and compounds can be recovered at least in regard to a considerable part thereof at the outlet of the gravitational sep~ator 36 and, 20 depending on the respective nature of the pollutants, they can be directly re-used, subjected to further tre~tment or possibly also disposed of or dumped, while a part of the waste or exhaust air can also still issue at the conduit 42 and also the slurry or sludge from the se~liment separator 32 can be selectively fed again to the intake device 13 of the evaporator 10 or can be discharged by way of the conduit 52 for the 25 purposes of definitive dumping thereof.
The process according to the invention has the advantage that it can comprehensively and completely remove pollutants whose boiling point is below a predeterminable limit value from polluted ground materials, while coll~p~ati-tely little energy and cost has to be applied for that purpose. The process further has the 30 advantage that it operates in a purely physical manner, that is to say there are subst~rlti~lly no chemic~l reactions whatsoever such as combustion procedures or the al.6443~

like. The pollutants can be recovered in part and depending on the respective nature of the ground con~min~tion, in more or less pure form. The rem~ining residues which are suitable for being dumped and which cannot be used in some other way occur only in a very small amount so that for this reason also, but in particular 5 because of the low level of specific energy requirement, the inct~ tion according to the invention and the corresponding process are very inexpensive to operate.

Claims (23)

1. Apparatus for cleaning polluted ground material, comprising a pre-dividing device (4, 5, 6) and a heat treatment station, in the form of an evaporator (10) at which there are provided heating devices (21, 11), circulating and conveying devices (11) and at a spacing from an intake of material into the evaporator (10) a steam feed device (12) for the feed of steam which is heated above the water condensation temperature to the ground material which is also heated in that region above thecondensation temperature, and comprising at least one hollow shaft (11) which isprovided with circulating and conveying blades and which extends in the longitudinal direction of an elongate evaporator container, characterised in that there are provided two or more hollow shafts provided with circulating and conveying blades and that the steam feed device (12), in the flow direction of the ground material flowingthrough the evaporator (10), is provided in the last third of the evaporator (10).

2. Apparatus according to claim 1 characterised in that the heating devices (21, 11) have hollow elements through which flows a heat carrier that is capable of flow and which are in contact with the ground material with their outside surfaces that are remote from the heat carrier.

3. Apparatus according to one of claims 1 and 2 characterised in that a dry cooler (18) is connected downstream of the ground material outlet of the evaporator (10).

4. Apparatus according to one of claims 1 through 3 characterised in that a waste gas separation device (30, 31, 32, 47) is connected downstream of the waste gas outlet of the evaporator.

5. Apparatus according to claim 4 characterised in that a dust separator (27) is provided between the evaporator (10) and the waste gas separation device (30, 31, 32, 47).

6. Apparatus according to claim 5 characterised in that a superheating device (28) which can be selectively brought into operation is provided downstream of the dust separator (27) and upstream of the waste gas separation device (30, 31, 32, 47).

7. Apparatus according to one of claims 4 through 6 characterised in that the waste gas separation device has a sediment and/or gravitational separator (32, 36) or another phase separation device for solid and liquid fractions.

8. Apparatus according to claim 7 characterised in that there is provided a sediment slurry recycling conduit (9) to the intake of the evaporator (10).

9. Apparatus according to one of claims 1 through 8 characterised in that a neutralisation agent addition means is provided downstream of the sediment slurry discharge conduit from the condensers (30 and/or 31).

10. Apparatus according claim 9 and one of claims 5 through 9 insofar as they are appendant to claim 11 characterised in that there is provided a waste vapor conduit (43) which leads from the dry cooler (18) to the condenser (30).

11. A process for cleaning ground material which is polluted with volatile substances and which is divided in a first step and heat-treated in a second step, wherein in the second step the ground material is heated without contact with an open frame by way of heat exchangers to a temperature above the boiling temperature of water and below a temperature of 400°C and then the heated ground material is exposed to hot, possibly superheated steam which removes the volatile constituents from the ground material grain, characterised in that the ground material is first exposed to the steam after the ground material has been put into very fine-grain form by virtue of the effect of heat and simultaneous circulation, wherein the heating temperature of the ground material is adjustable and regulatable in the intendedtemperature range.

12. A process according to claim 11 characterised in that the ground material isheated to a temperature below 300°C, preferably in the range between 110°C and 250°C.

13. A process according to one of claims 11 and 12 characterised in that the operation of heating the ground material and the subsequent steam moistening operation are effected in the same substantially closed-off container (10) and preferably under a slightly reduced pressure in a range of between about 10 and 50 mbar below ambient pressure.

14. A process according to one of claims 11 through 13 characterised in that theground material after the vapor treatment is discharged from the evaporator (10), then dry cooled and then moistened.

15. A process according to one of claims 11 through 14 characterised in that thewaste gas which is produced in the steam treatment operation is exposed to at least one condensation step.

16. A process according to claim 15 characterised in that in addition to the treatment steam further heated steam is fed to the evaporator (10), as a carrier gas for substances which are driven out of the ground material.

17. A process according to claim 15 or claim 16 characterised in that the waste gas which issues from the evaporator (10) is passed into a spray condenser which is operated preferably just below the dew point of water.

18. A process according to claim 17 characterised in that the operating temperature of the spray condenser (30) is preferably kept by electronic regulation of the water circulation in the condenser in the range of between 90 and 98°C, preferably between 95 and 96°C.

19. A process according to one of claims 15 through 18 characterised in that after the first condensation step a second condensation step is effected in a condenser which is operated at a temperature of below 60°C, preferably at a temperature 40°C.

20. A process according to one of claims 14 through 19 characterised in that theliquid which is produced in the spray condenser and/or a downstream-disposed condenser is exposed to sedimentation and/or gravitational sepalation, wherein the organic phases which are liberated after phase separation, such as for example sedimentation and/or gravitational separation, are fed to a further processing operation.

21. A process according to claim 15 or one of claims 30 through 38 appended thereto characterised in that the waste gas of the evaporator is superheated prior to the condensation operation to a maximum of 550 to 600°C.

22. A process according to claim 15 or one of claims 30 through 38 appended thereto characterised in that the waste gas is passed through a dust separator (27) after issuing from the evaporator and prior to the condensation operation.

23. A process according to claim 15 or one of claims 30 through 38 appended thereto characterised in that the addition of a neutralisation agent is provided for the liquid and/or muddy separation materials downstream of the condenser (30).