Method and device for thermal destruction of organic compounds by an induction plasma

Abstract

A method and device for chemical destruction of at least one feed comprising at least one organic compound are provided. The device comprises at least one inductive plasma torch, means for introducing at least one plasma-forming gas into the torch, optionally when the plasma gas(es) comprise(s) no or little oxygen, means for bringing oxygen gas into the plasma or into the vicinity of the plasma, means for introducing the feed into the torch, a reaction enclosure capable of allowing thermal destruction of the gases flowing from the torch, a device allowing mixing of the gases flowing out of the reaction enclosure to be carried out, means for introducing air and/or oxygen gas into the mixing device, a device allowing recombination by cooling of at least one portion of the gases from the mixing device, the torch, the reaction enclosure, the mixing device and the recombination device being in fluidic communication.

Claims

1. A method for thermal destruction of at least one feed comprising at least one organic compound by at least one induction plasma formed by at least one plasma-forming gas ionized by an inductor, wherein the following successive steps are carried out: a) introducing only said feed into the plasma and achieving a supply of oxygen gas in said at least one plasma-forming gas, and/or in the plasma or in the vicinity of the plasma, by means of which gases are obtained in which decomposition into atomic elements can be induced, wherein said feed is not mixed with water before its introduction into the plasma; b) in a reaction enclosure, carrying out a first operation for thermal destruction of only a portion of said gases in which decomposition of only a portion of said gases into atomic elements has been induced; c) carrying out a second operation for thermal destruction of the gases having undergone the first operation for thermal destruction by mixing, in a mixing device, said gases from the first operation for thermal destruction, with air and/or with oxygen; d) achieving a recombination of the atomic elements into gases by cooling at least one portion of the gases from the mixing; and e) discharging the gases.

2. The method according to claim 1, wherein the supply of oxygen gas is achieved by using pure oxygen as a single plasma-forming gas.

3. The method according to claim 1, wherein the at least one plasma-forming gas is not composed of oxygen, does not comprise oxygen, or comprises little oxygen, and the supply of oxygen gas is achieved by bringing oxygen gas into the plasma or into the vicinity of the plasma.

4. The method according to claim 3, wherein the supply of oxygen gas is achieved by introducing oxygen gas into the plasma at a location identical or close to the location where the feed is introduced and simultaneously with the latter.

5. The method according to claim 3, wherein a molar ratio of the oxygen gas supplied to the organic compound(s) is greater than a stoichiometric combustion ratio.

6. The method according to claim 1, wherein the mixing device comprises a venturi device into which air and/or oxygen gas is injected.

7. The method according to claim 1, wherein, in step c), mixing is achieved by an air and/or oxygen distribution ring which injects air and/or oxygen gas towards the main axis of the reaction enclosure.

8. The method according to claim 1, wherein at the end of step d) at least one step d1) is provided for chemical treatment of the gases.

9. The method according to claim 8, wherein said at least one step d1) for chemical treatment of the gases is selected from the group consisting of a dehalogenation or neutralization step, a step for deoxidation of nitrogen oxides, and a desulfuration step.

10. The method according to claim 8, wherein the feed further comprises at least one mineral filler and a gas filtering step is provided after step d) and before step d1).

11. The method according to claim 8, wherein at the end of the step for chemical treatment of the gases d1), the gases are treated in a droplet catcher condenser.

12. The method according to claim 1, wherein several identical or different feeds are treated with several plasmas.

13. The method according to claim 1, wherein the feed further contains at least one mineral filler.

14. The method according to claim 7, wherein the feed further contains at least one mineral filler.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 is a schematic vertical sectional view of the device for carrying out the method described in document [8] which uses water as an oxidizer, comburent;

(2) FIG. 2 is a graph which gives the maximum flow rate for treating C.sub.xH.sub.yCl compounds with water as an oxidizer, comburent. The maximum treatment flow rate (in g/h/kW) is plotted in ordinates and the number of carbon atoms x of the compound is plotted in abscissae.

(3) FIG. 3 is a graph which shows the change in the formation of phosgene COCl.sub.2 versus the amount and the nature of the oxidizer, comburent, used, respectively water or oxygen, during destruction of chloroform. The amount of formed COCl.sub.2 (in moles) is plotted in ordinates and the amount of oxidizer, comburent, for one mole of chloroform is plotted in abscissae.

(4) FIG. 4 is a graph which shows the change in the formation of chlorine Cl.sub.2 versus the amount and the nature of the oxidizer, comburent used, water or oxygen respectively, during the destruction of chloroform. The amount of formed Cl.sub.2 (in moles) is plotted in ordinates and the amount of oxidizer, comburent for one mole of chloroform is plotted in abscissae.

(5) FIG. 5 is a graph which shows the power required for treating 100 g/h of a compound C.sub.xH.sub.yCl versus the number of carbon atoms x of the compound, for water and oxygen oxidizers, comburents, respectively. The treatment power for 100 g/h (in W) is plotted in ordinates, and the number of carbon atoms x of the compound C.sub.xH.sub.yCl is plotted in abscissae.

(6) A positive ordinate corresponds to power absorption and a negative ordinate corresponds to power production.

(7) FIG. 6 is a schematic vertical sectional view of a device for carrying out the method according to the invention in an embodiment where the plasma-forming gas is composed of pure oxygen.

(8) FIG. 7 is a schematic sectional view of a device for carrying out the method according to the invention in an embodiment where the plasma-forming gas comprises no oxygen or little oxygen.

(9) FIG. 8 is a schematic vertical sectional view showing the structure of a specific rod designed in order to introduce a fluid feed into the core of a plasma, and its application in a plasma torch.

(10) FIG. 9 is a schematic vertical sectional view showing the structure of a specific rod designed for introducing a fluid feed and an oxidizing gas, such as oxygen, into the core of a plasma, and its application in a plasma torch.

(11) FIG. 10 is a schematic vertical sectional view which illustrates the whole of a device for carrying out the method according to the invention.

DETAILLED DISCUSSION OF CERTAIN ILLUSTRATIVE EMBODIMENTS

(12) Let us specify first of all that the method and the device according to the invention are defined as being a method and a device for thermal destruction of a load, feed, charge, comprising at least one organic compound.

(13) Preferably, the feed is composed of (consists of) said at least one organic compound.

(14) According to the invention, the treated feed is generally a fluid feed, i.e. it is in liquid, gas or powdery form (i.e. in the latter case it forms a flowable powder).

(15) By organic compound is generally meant a compound comprising, preferably composed of, consisting of, carbon and hydrogen atoms and optionally atoms selected from oxygen, nitrogen, sulfur atoms and from halogen atoms such as chlorine, bromine, iodine and fluorine atoms.

(16) The organic compound(s) to be destroyed are generally toxic, harmful or dangerous organic compounds for example explosive compounds; and/or radioactive compounds.

(17) These compounds may for example be organo-halogenated solvents, notably organochlorinated solvents, oils, aromatic or aliphatic hydrocarbons, toxic gas products such as chlorofluorocarbons CFC or hydrochlorofluorocarbons HCFC, warfare gases, solid explosives etc.

(18) A preferred feed which may be treated by the method according to the invention is a radioactive liquid feed comprising halogenated organic compounds, the structure of which includes radioactive tracers such as .sup.14C or .sup.3H.

(19) By destruction is meant that at the end of the method, i.e. generally in the discharge gases, the organic compounds initially present in the feed and the removal of which is sought are no longer present or present with a content of less than 10% by mass, preferably less than 5% by mass, or even that these compounds are no longer detectable and that their content may then be considered as zero. The organic compounds to be destroyed are transformed in the method into molecules of smaller size, for which the harmfulness, toxicity, dangerousness is less than that of the compounds to be destroyed, initially present in the feed, or even for which the toxicity, harmfulness may be considered as nil.

(20) FIG. 6 illustrates a device for carrying out the method according to the invention in an embodiment where the plasma-forming gas is composed of, consists of, pure oxygen. The device of this figure is substantially similar to the one of FIG. 1 (the same reference symbols are used), however except that the oxygen is used as plasma-forming gas and is introduced into the reactor through the duct (1) opening out into the plasma torch, and that only the feed to be treated (5) is introduced, fed, into the plasma and not a mixture of the feed and of water. Further, advantageously, the introduction, feeding, system (4) of the device of FIG. 1 may optionally be replaced in the device according to the invention by a specific introduction rod, tube (14), and/or the venturi (11) of the device of FIG. 1 may be suppressed and replaced by a gas distribution ring for injecting air and/or oxygen (15) towards the centre of the reactor as this is described in more detail below.

(21) FIG. 7 illustrates a device for carrying out the method according to the invention in an embodiment wherein the plasma-forming gas is not pure oxygen, or wherein the plasma-forming gas(es) comprise(s) no oxygen or little oxygen.

(22) It is therefore necessary to provide an oxygen supply which may be accomplished by directly bringing the gas into the core of the reactor or by bringing it simultaneously and jointly with the feed for example the liquid or gas feed to be treated. In the first case, and as this is illustrated in FIG. 7, tapping of a traditional type (16) gives the possibility of ensuring the arrival of oxygen into the reactor as close as possible to the plasma or into the plasma, while another separate duct (1) allows introduction of a plasma-forming gas into the plasma torch. As for the remainder, the device of FIG. 7 is substantially similar to the one of FIG. 6.

(23) FIG. 10 shows the whole of a device for carrying out the method according to the invention.

(24) From upstream to downstream, the installation is equipped with an induction plasma torch (102) powered by an electric generator (101) connected to the mains (380V/50 Hz) which delivers a high frequency current adapted to the geometry of the torch (102).

(25) Supplying power to the torch (102) with the generator (101) is generally accomplished via a control panel (not shown).

(26) Starting of the torch (102) is ensured at atmospheric pressure by setting up tungsten filaments (103) in the torch (102) which, when they are subjected to the high frequency electromagnetic field, initiate the plasma.

(27) In the case of an oxygen plasma, the starting may be accomplished according to other means avoiding oxidization of the electrodes.

(28) The torch (102) generally consists of one single coil, of a turn, generally cooled by air, which is supplied with oxygen by means of suitable inlets (104) and which is supplied with a feed by suitable means (105) which introduce the feed into the inside of the plasma.

(29) Preferably and notably in the case when the feed is liquid, the means for introducing the feed into the plasma consist of a specific rod for introducing liquids into the core of the plasma.

(30) This specific rod, tube is illustrated in more detail in FIG. 8.

(31) Indeed, a plasma is a viscous medium into which it is difficult to introduce fluids.

(32) The rod (81) plunges into the core of the plasma (82) and opens out (83) into the lower portion of the single inductive coil, inductive turn (84) where the feed (85) sent from the top (86) of the rod is thereby introduced.

(33) If reference is made to FIG. 8, this rod consists of: a tube (87) made of a refractory material such as alumina, which ensures the mechanical structure; a packing or wick (88) composed of a textile made of fibers of a refractory material such as a glass, alumina, or zirconia in which the feed (85), generally fluid, is introduced through one of the ends of the rod, which is generally its upper end (86) because the rod is generally positioned vertically.

(34) In this structure, the textile fibers packing (88) prevents the formation of drops falling through the plasma (82). It ensures a regular flow rate by capillary impregnation.

(35) When the fluid is a liquid, the high temperatures attained by the rod in its middle portion ensure vaporization and the organic material is essentially treated in gas form.

(36) However, this rod may also be used with fluids which are not liquid.

(37) As this was already indicated above, the provision, supply of oxygen may be accomplished in several ways. Thus, in the case when the plasma-forming gas is composed of oxygen, then the oxygen supply naturally consists of the supply of this plasma-forming gas (FIG. 6).

(38) Or else, if the plasma-forming gas comprises no oxygen or little oxygen, then the provision, supply of oxygen may be accomplished by bringing the oxygen gas directly into the core of the reactor or by bringing it together with the feed.

(39) In the first case, a tapping of the traditional type ensures arrival of oxygen into the torch which produces the plasma (FIG. 7).

(40) The feed is brought into the plasma through the rod described in FIG. 8.

(41) In the second case, oxygen may be brought in via the rod described above and in FIG. 8, this rod being modified so as to allow passage of oxygen.

(42) This modified rod or dual, double rod (91) is shown in FIG. 9.

(43) As oxygen cannot be mixed with the organic compounds of the feed before their arrival into the reactor for safety reasons, a tube, generally a capillary tube (92), may be set up in the center of the rod (91) which retains its textile or fibrous packing (88) described above. The oxygen (93) is then introduced into the capillary (92) while the feed (85) comprising the organic compounds is introduced through one of the ends of the rod, generally its upper end (86) at the periphery in the annular space defined between the wall (94) of the tube bringing the oxygen and the wall (87) of the rod.

(44) The plasma formed in the plasma torch (102) burns in a reactor or in a reaction enclosure (106).

(45) This reaction chamber (106) generally includes a double wall in which the cooling water circulates. This double wall may be made of steel. The inner surface of the double wall is covered with a protective refractory material.

(46) The external walls of the reactor are generally cooled by circulation of water.

(47) The chemical species from the plasma oxidized in the reactor, reaction enclosure, (106) by means of the oxygen introduced into the torch (102) notably when pure oxygen is used as a plasma-forming gas. The reaction chamber has the function of confining the heat produced in the plasma torch in order to thereby allow complete destruction of the waste. The gas from this reaction enclosure may thus attain a temperature above 1,500° C.

(48) The reaction chamber is generally in the form of a vertical cylinder shape at the top of which is positioned the plasma torch. Generally, the walls of the reaction enclosure are thermally insulated by a refractory material.

(49) Said oxidation is promoted by means of a mixing device (107) such as a venturi, located at the lower portion of the reaction enclosure. An introduction of oxidizing, comburent gas for example air and/or oxygen (108) may be provided at this device.

(50) In the case when the mixing device is a venturi, there is always introduction of air and/or of oxygen into the mixing device.

(51) If the venturi is suppressed, only an introduction of air and/or oxygen by means of a distribution ring is retained.

(52) The structure of the venturi is described in detail in document [8] to the description of which reference may be made.

(53) The venturi by means of a supply of oxidizing gas such as air and/or oxygen allows generation of a second combustion or post-combustion between this oxidizer, comburent and the gases from the reaction enclosure. With this device it is thus possible to destroy the compounds, notably the toxic compounds which would have escaped the first destruction stage in the reaction enclosure (106).

(54) In other words, the purpose of the venturi is to generate significant turbulence of the reaction gases from the reaction chamber (106) by means of a cold air and/or oxygen supply (108). This mixture of gases consisting of cold air and/or oxygen and reaction products, allows without any provision of additional heat, generation of post-combustion of the gases from the reaction chamber. It is thus possible to complete the destruction of the possible reactive gases which have not been transformed in the reaction chamber (106). In the venturi, the different gas species such as H.sub.2, CO, C . . . will react with air according to the following reaction:
CO+H.sub.2+O.sub.2.fwdarw.CO.sub.2+H.sub.2O

(55) The harmful gas CO is thus transformed into a less harmful gas.

(56) It may be stated that the venturi notably ensures mixing for improving the recombination rates, speeds and cooling by addition of air and/or oxygen (108).

(57) In the case when the fluid includes mineral fillers, the venturi is suppressed, introduction of air also ensures quenching of the gases and of the particles found therein.

(58) According to the invention, the geometry of the reactor, reaction enclosure, may be modified, at the mixing device (107), in order to allow the reactor to more easily accept mineral fillers.

(59) Indeed, the method according to the invention is generally dedicated to the treatment of fluids without any mineral fillers.

(60) However, for example, the treatment of used solvents having been used for dissolving materials containing minerals results in the concentration of these mineral fillers in the form of particles which may form deposits.

(61) The presence of the venturi, present in order to ensure substantial mixing of the gases risks being at the origin of the formation of deposits and of a plug. This is why the treatment of liquids loaded with minerals should preferably be carried out with a reactor of a different design.

(62) In this embodiment, the venturi is removed in order to avoid unwanted deposits at its level. It is replaced by a ring for distributing gases, for example air which may be enriched in oxygen. Said ring injects air and/or oxygen towards the axis of the reactor (which generally appears as a vertical cylinder) in a direction which may be tilted upwards. This tilt will depend on the geometry of the reactor and on the power of the plasma torch used. It may range from 0° to 70° relatively to the horizontal depending on the case.

(63) The gas, the injection pressure of which may be modulated according to the geometry of the reactor and the power of the plasma, will have the function of generating a rupture area in the flow and of imposing the turbulence required for proper mixing. It will also ensure quenching of the gases and of the liquid particles which may be found therein in order to limit the formation of coherent deposits which may degrade the operation of the method. The gas distribution ring ensures post-combustion as this is the case in the venturi.

(64) The treatment of liquids which may contain mineral fillers should involve a filtration step downstream from the reactor. A filter (112) will therefore have to be introduced into the chain for treating gases.

(65) This configuration of the reactor with a gas distribution ring is shown in FIGS. 6 and 7. The additional filter is not illustrated but is included in the treatment of the gases.

(66) Downstream from this mixing device (107) the gases penetrate into a cooler (109) which brings the gases to a temperature compatible with the treatment device positioned downstream.

(67) This cooler (109) also allows the gases to finish their recombination process which has already begun in the venturi. By recombination is meant that the organic compounds which have been destroyed in the plasma, oxidized by oxygen, are recombined in small molecules forming a gas which may generally be discharged into the atmosphere after treatment, for example, a neutralization treatment for removing certain species such as HCl or Cl.sub.2.

(68) This cooler (109) which may also be called a recombination space, generally consists in a double wall chamber cooled by water. In this space, the temperature of the gases rapidly drops so as to attain for example 200° C. at the outlet. Unlike the reaction enclosure (106), the recombination space is not thermally insulated and its double wall is cooled by circulation of water from a central cooling unit. In this space, the gases flow and cool by natural convection close to the walls.

(69) At the outlet of the cooler, or recombination space (109), the gases are analyzed for example by mass spectrometry or by infrared spectroscopy (118). With this analysis it is possible to check the efficiency of the heat treatment and to know the composition of the gases after this heat treatment, but especially with the analysis, it is possible to know whether the gases additionally have to undergo at least one chemical treatment.

(70) The temperature of the gases may be adjusted by spraying water (111) at the inlet of an oversleeve (110) before directing the gases towards the gas treatment installation (113). It is thus possible to lower the temperature of the gases in the case of excess heat notably for protecting the system for neutralization of the halogens.

(71) This gas treatment installation (113) is adapted according to the compounds which have to be treated. In this installation, it is possible to carry out one or several chemical treatments of the gases, selected for example from a dehalogenation treatment or treatment for removing the halogens, a treatment for removing nitrogen oxides, and a desulfuration treatment.

(72) Generally the installation for treating the gases (113) may thus comprise a unit for neutralizing the halogens and/or a so-called DENOX system allowing catalytic denitrification of the gases notably in the case when the plasma-forming gas comprises nitrogen, and/or optionally a desulfuration unit.

(73) Neutralization of the halogens present in the form of HCl or of chlorine gas is carried out generally by standard washing with spraying of soda water according to the following reaction:
HCl+NaOH.fwdarw.NaCl+H.sub.2O,
or according to the following reaction:
Cl.sub.2+2NaOH.fwdarw.NaCl+NaClO+H.sub.2O

(74) Denitrification of nitrogen oxides is for example carried out by reaction with ammonia:
NO+NO.sub.2+2NH.sub.3.fwdarw.2N.sub.2+3H.sub.2O
4NO+4NH.sub.3+O.sub.2.fwdarw.4N.sub.2+6H.sub.2O
2NO.sub.2+4NH.sub.3+O.sub.2.fwdarw.3N.sub.2+6H.sub.2O

(75) In the case when the effluents are loaded with minerals, these gases as this has already been specified above, pass through a filter placed upstream (112) of the washing system (113).

(76) When the effluents are radioactive, this filter (112) will be of the VHE (Very High Efficiency) type.

(77) This type of filter is currently distributed commercially.

(78) Once they are washed, the gases pass through a droplet catcher condenser (114) with which the transport of liquid towards the element (116) and the chimney (117) may be limited.

(79) The gases circulate in the installation from upstream to downstream by means of an extractor (115) maintaining a slight depression in the system.

(80) On-line analysis means (118, 119), for example of the infrared spectroscopy or mass spectrometry type, ensure monitoring of the quality of the gases at the outlet of the cooler (109) and at the chimney (117) in order to determine every time whether the gases may be discharged into the atmosphere.

(81) Finally, it should be noted that several plasma torches may be placed on a same reactor. This arrangement may allow treatment of substantial flow rates of fluids and/or simultaneous treatment of different immiscible or chemically incompatible fluids.

(82) Further, the device according to the invention may be a mobile device, placed on a vehicle.

REFERENCES

(83) [1] U.S. Pat. No. 4,438,706 [2] U.S. Pat. No. 4,479,443 [3] U.S. Pat. No. 4,644,877 [4] U.S. Pat. No. 4,886,001 [5] U.S. Pat. No. 5,505,909 [6] U.S. Pat. No. 5,288,969 [7] FR-A-2765322 [8] FR-A-2866414