WO1997033840A1 - Method for the vitrification processing of harmful fibre waste, particularly asbestos-containing waste from buildings, and plant therefor - Google Patents

Abstract

A method and a plant for the vitrification processing of harmful fibre waste, particularly asbestos-containing waste from buildings, are disclosed. The waste to be processed is first coarsely ground and mixed to give a mass in which the fuel fraction is substantially uniformly distributed, whereafter the mass (9) is preheated (10) substantially to 800-1000 °C to cause combustion of the plastic and other materials in the mass, evaporate the water, and at least partially oxidise the metals. The preheated mass is fed into a melting chamber (12) to form a melt at around 1400 °C. The remaining metal fragments in the mass are allowed to settle in a solid or pasty state in an upstream portion (16) of the melt, while the vitrified fraction continuously flows towards a downstream portion (17) of said melt and is recovered by casting after processing.

Description

 Process for the treatment by vitrification of waste of harmful fibers, in particular asbestos waste from the building, and installation for implementing said process.

The present invention relates to the treatment by vitrification of waste of harmful fibers, in particular asbestos-bearing waste from the building, including a non-zero proportion of water, metallic materials, and plastics or other combustible materials.

Waste of harmful fibers, the treatment of which is envisaged in the context of the invention mainly comprises asbestos waste from the building, but also other waste such as ceramic fiber waste (in particular that from industrial furnaces) and industrial fibrous insulation.

Asbestos waste, and in particular that which comes from the decontamination of buildings, poses a particular and increasingly acute problem of treatment to make it harmless. In fact, asbestos has been widely used in industry and construction because of its low cost and its well-known properties of temperature resistance and insulation. It was only about 20 years ago that the dangers of asbestos fibers for the respiratory tract (asbestosis, different variants of lung cancer) were highlighted, which led to the ban on the varieties more harmful asbestos, as well as the flocking of buildings. It is recalled that the harmfulness of asbestos is essentially linked to its morphology in the form of extremely fine fibers, and not to its chemical composition which is itself quite banal.

In the case of asbestos waste from the decontamination of buildings, this waste is extremely heterogeneous because asbestos has often been combined with other materials to achieve the insulation of buildings, and also due to a very high water content imposed by the conditions of removal of this waste. Such asbestos-containing waste generally arrives from yards in bags of around fifty liters, plastic, and they contain a proportion of mineral matter (asbestos, plaster, cement, mineral wool), a proportion of water (asbestos is almost always watered during removal, to stabilize the dust, and in addition, certain methods of cleaning with water under pressure saturate the fibrous mass with water), a proportion of combustible materials (in particular plastics originating in large part from the confinement films, generally made of polyethylene, but also a proportion of other plastic materials such as carpet polyamide, materials to which wood or other combustible materials are added), and also metallic materials (mainly steel used for the suspen¬ false ceilings, and the support grids of the flocking of great thickness, with in addition possibly some quantities of copper or aluminum). This great heterogeneity of asbestos waste makes it considerably difficult to treat.

As a reminder, mention may be made of the processes used in certain countries of stabilization before landfilling, consisting in diluting the fibers in a large mass of hydraulic binder, the residue obtained being sent to landfill after drying. Such methods are costly since they require pre-sorting and large quantities of binder, and moreover the durability over a long period is not certain, so that safety ultimately remains questionable.

Various attempts have also been made towards thermal decomposition processes consisting in heating the asbestos to a certain temperature (500 ° C. to 900 ° C.), so as to decompose the ibres to form other constituents. Reference may in particular be made to documents EP-A-0.484.866 and EP-A-0.344.563. However, such processes have encountered significant difficulties in terms of transport and the valuation of a actually very powdery product, whose safety is also strongly contested by specialists.

Finally, it appears that vitrification alone ensures complete destruction of the harmful fibers while allowing total trivialization of the residue.

Document DE-U-93 02137 illustrates a technique for melting asbestos-containing waste which is very combustible and contains little or no water. According to this technique, the waste penetrates as it is, without prior treatment, at the entrance to a rotary kiln with a burner where combustion is carried out. Then this waste passes through a collector, the base of which opens at the entrance of a screw conveyor leading the waste to a glass-type melting chamber. The metal fragments arriving in the molten bath can decant upstream of the bath, be heated and poured by a nozzle with integrated induction heating system. It should however be noted that the hot gases from the rotary kiln are conveyed to the melting chamber (by the intermediate manifold and an associated tube opening at the top of the melting chamber). As such, as the load passes through the collector and is then conveyed by a screw conveyor, the latter must accommodate the metallic waste leaving the rotary kiln and which may block the screw. Finally, it should also be noted that the combustion in the rotary kiln is in this case necessarily incomplete combustion in the absence of air, with an end of oxidative combustion of the gases in the melting chamber (otherwise, there would be either an excessive temperature affecting the operation of the rotary kiln, ie an insufficient temperature cooling the melting chamber) so that the metal portions do not undergo any oxidation (the preheating chamber is indeed in a reducing atmosphere). Various other vitrification techniques have have been tested, and a frequent distinction is made between plasma torch processes, conduction processes, and induction processes.

The plasma torch process uses a prestigious but extremely expensive tool which allows very high temperatures (over 2000 ° C) to be reached. We can for example refer to document EP-A-565,420. The general principle of such a process is based on the fact that all of the components of the waste are globally melted thanks to the extremely high temperatures concerned, whether they be plastics or metallic materials including steel fragments. However, the investment of such an installation is very heavy and the maintenance costs are high due to the sophistication of the equipment. In addition, the very high temperatures developed locally as well as the permanent thermal shocks, adversely affect the good behavior of the refractories. It is therefore a comprehensive and theoretically satisfactory process for rendering asbestos-containing waste inert, including that originating from the building, but at the cost of considerable expenditure.

The conduction or induction processes (see for example documents FR-A-2,668,726 and US-A-5,032,161) are also expensive. In addition, conduction processes would not be suitable for treating asbestos-containing waste from the building, since the need for a reducing atmosphere would make it problematic to use such processes for waste containing combustible materials. Finally, the known vitrification processes, even if they use advanced technologies, do not yet have sufficient reliability, and they do not lend themselves to the treatment of very heterogeneous waste, which is precisely the case of asbestos waste from building decontamination sites, unless naturally to implement extremely high processing costs.

There are of course other vitrification techniques have been tried to treat various types of waste other than waste amiantifè ^¬ res generally toxic waste including hospital waste and fume residues incinéra¬ tion household waste (REFIOM). As such, it should be noted that the incineration ash is very homogeneous waste, unlike the waste that the invention aims to treat, and that their treatment is not accompanied by any combustion.

We can for example refer to document FR-A-2,704,047 for the treatment of hospital waste using a plasma torch, and to documents FR-A- 2,692,178 and FR-A-2,689,213 illustrating vitrification techniques of waste in rotary kiln and electroburner or plasma torch. Reference may also be made to documents EP-A-0 626 349, EP-A-0 590 479, EP-A-0 575 874, EP-A- 0 627 270, EP-A-0 359 003, EP -A-0515 792 and DE-A-4 301 353. The technological background is also illustrated by the document FR-A-2,711,078 illustrating a versatile technique for treating waste by vitrification, intended to treat simultaneously toxic products and residues suitable for vitrification. Vitrification is then mainly used for its ability to trap toxic substances in a glassy matrix. The toxic products and residues suitable for vitrification which are mentioned in this document have in common the fact that they are not very combustible, so that the heat pre-treatment which is mentioned aims principally at reducing the volume of the residues without 'there is truly a combustion of these. The residues in the form of ashes are either pyrolyzed in a rotary furnace which brews them, or admitted directly by a screw supply in a melting chamber. Such an installation would, however, be unsuitable for the treatment of asbestos-containing waste from the building: in fact, if bags of residue were put into the rotary kiln, this would generate considerable puffs of smoke containing unburnt residues, forcing oversizing smoke treatment installations, and moreover the absence of air injection would not allow satisfactory combustion of the plastics present in the charges. If this waste was brought in by the other route, namely the direct charging screw into the melting chamber, then the bath temperatures indicated show that the metal fragments such as the steel fragments would remain solid and not oxidized, and would disturb the molten bath (the drawdown in the lower part of the melter is limited to liquid metals, that is to say, aluminum, lead, zinc, copper portions). In addition, plastics decompose at very high temperatures with the formation of harmful pollutants, such as dioxynes and nitrogen oxides NO _x .

Finally, to be completely complete, we can mention various other treatments of hazardous waste, in particular radioactive, illustrated in documents EP-A-0 417 520, EP-A-0 622 140, OA-94 24060 and FR -A-2,593,092. The object of the invention is precisely to design a treatment technique by vitrification of waste of harmful fibers, in particular asbestos waste from the building, not having the drawbacks and / or limitations of the aforementioned known techniques. The object of the invention is therefore to design a processing technique which is both simple, reliable and of low operating cost.

This object is achieved in accordance with the invention by a method of treatment by vitrification of waste of harmful fibers, in particular asbestos waste. res, from building, including a non-zero proportion of water, metallic materials, and plastics or other combustible materials, characterized in that the waste to be treated, bagged in plastic bags, is first shredded roughly and mixed to produce a charge, the combustible part of which is distributed in a substantially homogeneous manner, after which this charge is subjected to preheating in a preheating chamber at a temperature substantially between 800 ° C and 1000 ° C in order to carry out the combustion plastic or other materials present in the charge, evaporation of water, and at least partial oxidation of metallic materials also present in said charge, before arriving in a melting chamber where a bath is produced the temperature of which is close to 1400 ° C., the hot fumes from the melting chamber passing against the current in the pre-heating by transmitting their thermal energy to the charge subjected to preheating, said melting chamber being arranged to allow the metal fragments still present in the charge to settle in the solid or pasty state in an upstream part of the fusion bath, while that the vitrified material flows continuously to a downstream part of said melt to be recovered by casting at the end of treatment.

Thus, the aforementioned process takes full account of the composition and the heterogeneous nature of the waste of harmful fibers, especially if it is asbestos waste: the preliminary phases of grinding and mixing allow a charge to be produced, the combustible part of which is distributed very satisfactorily despite the very heterogeneous nature of the waste to be treated. In addition, the preheating treatment of the waste requires very little energy, the heat necessary for the preheating of the mineral matter and for the evaporation of water is in fact provided by the combustion of plastics present in the load. It is therefore possible to reserve the noble energy for the actual melting treatment, thereby limiting the temperature ranges since the metallic fragments still present, especially in steel, are decanted upstream of the melting bath and can be extracted. Finally, a very good recovery of the energy used is obtained, which makes it possible to considerably reduce the cost of the preliminary stage of preheating the ground and mixed waste. This energy recovery also makes it possible not only to limit energy consumption, but also to reduce the volume of smoke produced, and therefore to work with a smoke treatment unit which can be small in size. .

Preferably, the air required for the combus ^¬ plastics during preheating of the burden eεt heated by the fumes of the preheater chamber. Advantageously also, the decanted metal fragments are intermittently heated to a temperature sufficient to complete their fusion, then removed from the fusion bath by casting. The decantation of scrap in a solid or pasty state makes it possible to limit the temperature of melting and pouring of mineral materials, and therefore to reduce in considerable proportions the corrosion of refractories. Thus, as soon as the layer of decanted metal fragments reaches a predetermined level, it suffices to heat these fragments to complete their fusion, and to organize their pouring to empty the tank.

Advantageously also, the vitrified material remains at the level of the downstream part of the melt until a homogeneous vitrified material is obtained before being removed by continuous casting. This residence time will for example be substantially between 30 and 60 minutes. This improves notably the homogeneity of the vitrifi t, and therefore its flowability.

The invention also relates to an installation for implementing the aforementioned treatment method, said installation being remarkable in that it comprises: a crusher supplied with bagged waste to be treated;

- a mixer arranged downstream of the mill;

- A preheating chamber supplied with milled and mixed feed, said chamber being equipped with air-gas burners and means for injecting hot air;

a melting chamber, the inlet of which communicates directly with the outlet of the preheating chamber through a common opening serving both for the charging of materials into the melting chamber under the action of mechanical pushing means, and at the countercurrent passage of the fumes from this melting chamber, said melting chamber comprising an upstream settling tank and a downstream homogenization tank above which the oxy-gas burners are arranged;

- a vitrified recovery tank outside the fuεion chamber and communicating with the downstream tank of the latter, said recovery tank being equipped with a closable casting means; - means for recovering and treating smoke in communication with the upper part of the preheating chamber.

The presence of such a common opening is particularly advantageous insofar as it allows the use of the passage of smoke from the melting chamber against the current to participate in the heat exchanges developed in the preheating chamber.

Preferably, the preheating chamber is inclined εucε εucceεεives, each provided with mechanical means for pushing the products therein, at minus the upstream suns, which have orifices used for injecting hot air into said preheating chamber. In particular, the hot air injection orifices are connected to an associated air circuit, for reheating the injected air, to the smoke recovery means.

Preferably then, the preheating chamber is supplied in the upper part by a charging screw distributing the load on the upper floor. It may prove advantageous to provide that the preheating chamber is laterally equipped with means for injecting cooling water. Such cooling may in particular prove necessary when the proportion of plastics is abnormally high. According to another particular characteristic, the upstream tank of the melting chamber can be equipped with heating electrodes and an interruptible casting nozzle, which makes it possible to organize in a simple and controllable manner the melting and intermittent recovery of scrap. .

More preferably, the downstream tank of the melting chamber is separated from the upstream tank of said chamber by a low wall, and it communicates by a corridor forming a siphon with the external vitrification recovery tank. In particular, the downstream tank and / or the associated wall are equipped with means for injecting air bubbles.

Preferably, finally, the vitrified glass recovery tank is produced in the form of a closed chamber fitted laterally with at least one oxy-gas burner, and it comprises a closable pouring means constituted by a flow nozzle which is partly supported. and a mechanized punch ensuring regulation of the flow rate.

Other characteristics and advantages of the invention will appear more clearly in the light of the description which follows and of the appended drawings, nant a particular embodiment, with reference to the figures of the accompanying drawings where: Figure 1 schematically illustrates a complete installation according to the invention for implementing the treatment process according to the invention, in order to vitrify waste harmful fibers, in particular asbestos-containing waste from the building, -

- Figure 2 is a section illustrating on a larger scale the preheating chamber of the incineration oven forming part of the above-mentioned installation;

- Figure 3 is a section on a larger scale of the melting chamber of the same incineration oven, and Figure 4 is the associated section according to IV-IV (without the fuεion bath). FIG. 1 illustrates an installation 1 for treatment by vitrification of waste of harmful fibers, more particularly but not exclusively adapted to the treatment of asbestos-containing waste from the building, which includes a non-zero proportion of water, metallic materials, and plastics or other combustible materials. The waste to be treated arrives at a feed station 2 equipped with a conveyor belt 3, in the form of bags 4, for example bags of 50 liters of polyethylene of the type well known for use on construction sites. As indicated above, this waste comes in a very heterogeneous form, containing at the same time mineral materials, water, combustible materials, and metallic materials, the latter being essentially made of steel. . In accordance with a first step of the process, and as shown by arrow 5, the waste to be treated, bagged in plastic bags 4, is first coarsely ground in a crusher 6, for example a hammer crusher, then these crushed waste is brought, as shown by line 7, to a mixer vertical 8 of large capacity. This preliminary grinding and mixing phase is essential in the context of the treatment process of the invention, since it aims to distribute the combustible part of the waste in a substantially constant manner, thereby correcting the very heterogeneous nature of this waste. . In practice, the plastic confinement films, which are made of polyethylene or polyvinyl chloride, will constitute the main part of this combustible part, that is to say will represent a proportion of about 2 to 6% by weight. . Coarse grinding will be sufficient, and in practice a particle size of 5 to 30 mm may be suitable. The intimate mixing of the crushed waste thus makes it possible to obtain a charge the combustible part of which is distributed in a substantially homogeneous manner. As shown diagrammatically by line 9, this charge is brought to an incineration oven 10, and more precisely to a preheating chamber 11 there of this incineration oven. The incineration furnace 10, the structure of which will be described in more detail with reference to FIGS. 2 to 4, basically comprises an upstream preheating chamber 11 and a downstream melting chamber 12 communicating directly with the preheating chamber 11. In the chamber preheating 11, the load is subjected to preheating at a temperature substantially between 800 ° C and 1000 ° C in order to carry out the evaporation of water, the combustion of plastic or other materials present in the load, and the at least partial oxidation of metallic materials also present in said charge. This oxidative combustion step, which is very different from a preliminary pyrolysis that could be encountered in certain techniques for treating toxic waste, is essential in the context of the invention. The preheating of the duly ground and mixed waste in fact makes it possible in this preheating chamber to both burn the plastic materials present in the charge, evaporation of water, and oxidation of metallic materials, as well as the rise in temperature of the mineral materials with complete dehydration of these, and also possibly an exothermic decomposition (it is known in particular that chrysotile is decomposes into silica and forsterite between 800 ° C and 900 ° C). Preheating to a temperature appreciably between 800 ° C and 1000 ° C, and more particularly between 800 ° C and 900 ° C, will in practice be sufficient. The combustion of plastics provides the heat necessary for the preheating of the mineral materials and for the evaporation of water, so that the preheating of the waste requires minimal energy consumption, which is a very important advantage. Unlike the aforementioned known techniques for vitrifying asbestos-containing waste, using a plasma torch for melting the waste at temperatures above 1600 ° C., a continuous treatment is carried out, the charge arriving gradually in the incineration oven 10 from the mixer 8. For good regularity of the supply, preferably use a supply screw 14 mounted in the upper part of the preheating chamber 11 of this oven d 'incineration. The control of the charging screw 14 ensures a regular supply of the charge in the preheating chamber 11. It is therefore far from the prior techniques according to which the bags of waste were directly charged into the fusion bath, according to a supply of course discontinuous. The heat resulting from the combustion of plastics is therefore here used optimally during this preheating step. In FIG. 1, there is shown diagrammatically one of two air-gas burners 40 serving to ensure the desired thermal level inside the preheating chamber 11. During the next step, the charge thus pre-heated arrives in the melting chamber 12 where a fusion bath 15 is produced, the temperature of which is close to 1400 ° C. The melting chamber 12 is further arranged to allow the metal fragments still present in the charge to settle in the solid or pasty state in an upstream part 16 of the fusion bath, while the vitrified material flows continuously towards a part downstream 17 of said melt to be recovered by casting at the end of treatment. The noble energy, brought by oxy-gas burners 60 equipping the melting chamber 12, ensure the desired thermal level for obtaining a fusion bath whose temperature remains close to 1400 ° C., which is infé¬ at least 200 ° C at the temperature encountered in the abovementioned techniques for vitrification of asbestos waste using a plasma torch.

In accordance with another characteristic of the invention, the inlet of the melting chamber 12 communicates directly with the outlet of the preheating chamber 11, at a common opening 13. As will be seen later, the melting chamber 12 has a completely closed sky, so that the hot fumes from this melting chamber can only pass through the common opening 13 to penetrate against the current in the preheating chamber 11, so that the energy of the hot fumes is then directly transferred to the load which is being preheated in the chamber. The exhaust of the hot smoke is in fact only provided at the level of the preheating chamber 11, here by at least one outlet 27 provided in the upper part, and communi¬ as to a circuit 28 leading to means 29, 30 for recovery and which will now be described in more detail.

As in any incinerator, there is a post-combustion chamber 31 which is necessary for ensure complete combustion of the gases before discharge to the atmosphere. Inside this chamber 31 furnished with refractories, several successive narrowing and widening can be provided, in order to promote the settling of residual dust. According to an interesting aspect of the process according to the invention, provision is made to use the thermal energy of these burnt gases in order to heat not only the air which must be directed to the preheating chamber for the combustion of combustible materials, but also the combustion air arriving at the air-gas burners equipping said preheating chamber. Thus, the burnt gases pass through a pipe 32 leaving the post-combustion chamber 31, to enter a recuperator 33, from which they leave via a pipe 34. leading to a conventional type smoke treatment device 30

There is successively a set of filters 35 used to trap all the dust, including the finest (absolute filtration), a water cooler 36 (often called cooling quench by spraying water), then a column 37 for neutralizing the acids by sprinkling with soda water, and finally a general draft fan 38 also serving to ensure the vacuum in the installation, and an exhaust chimney 39. These smoke treatment means are good known and need not be described in more detail

A hot air circuit 26 is associated with the preheating chamber 11 of the incineration oven 10, which circuit ends at the level of branches, here three in number, denoted 26.1, 26.2, 26.3, supplying the inclined floors of the preheating chamber 11 This hot air circuit 26 also has a branch branch 41 associated with the supply of combustion air to air-gas burners 40 of the preheating chamber 11 It is important to note that the supply circuit receiving fresh air at its inlet passes through the recuperator 33, the latter thus ensuring the heating of the air. This therefore uses all the advantages of recovering the energy of the flue gases from the preheating chamber by means of an exchanger which heats the combustion air injected into this chamber. We can for example use a recuperator 33 of tubular type, and the smoke thus cooled downstream of the recuperator 33 are then sent to the smoke treatment equipment 30 previously described. In addition, a temperature sensor 64 and an oxygen measurement probe 65 have been shown schematically on the pipe 32 at the outlet of the post-combustion chamber 31. In fact, the measurement of the temperature of the fumes before the recuperator 33 serves to control the power of the air-gas burner 40 of the pre-heating chamber 11 in the case where an energy supply is necessary, or conversely to control a rate of injection of cooling water in the case where such cooling of the preheating chamber turns out to be necessary (the means for injecting cooling water equipping the preheating chamber will be described later with reference to FIG. 2). The oxygen measurement probe 65 is used to control the flow of hot air injected into the preheating chamber 11. In the melting chamber 12, there is an upstream part 16 of the melting bath at a decantation tank and a downstream part 17 of said fusion bath at the level of a homogenization tank, so that this will be described in more detail with reference to FIGS. 3 and 4. A vitrified recovery tank 18 (often called "feeder "by the specialists) external to the melting chamber 12 is also provided, this recovery tank communicating with the downstream tank of the melting chamber 12, and it is equipped with a closable casting means with a lower orifice 19 allowing pour the vitrifiât liquid upstream of the recovery means 20 whose agen ^¬ cement is classic. These means 20 comprise successive ^¬ an inclined metal channel 21, preferably by circulating water, a buffer tank 22 regulated in level and temperature, wherein there is present a liquid refroi¬ dissement, an inclined conveyor belt 23 for reassemble the solidified products in the form of a silica granule, to pour into a receiving hopper 24 with a swiveling passage towards the residue skips (not shown here) thus receiving the inert product 25 at the end of treatment.

The direct flow of metallic fragments decanted into the upstream part 16 of the melt chamber has been shown diagrammatically by arrow 66, these fragments mainly made of steel being, intermittently, heated to a temperature sufficient to complete their fusion, in order to to be able to be removed from the melt 15 by casting. They will in fact be the most massive metal fragments, the finest fragments being fully oxidized during preheating. This principle of decanting scrap in a solid or pasty state is very advantageous, insofar as it makes it possible to limit the temperature of melting and casting of mineral materials, and therefore to reduce the corrosion of refractories in considerable proportions. This is how we can be satisfied with having a fusion bath which is at a temperature close to 1400 ° C. to 1450 ° C. At this temperature, the steel fragments present in the mixture are not yet in the liquid state, so that they settle out at the bottom of the tank, while the vitrified material flows towards the downstream part of the chamber. of fusion. It is then sufficient to organize, on request, the fusion of these fragments in order to evacuate them by casting. The downstream part 17 of the melt 15 corresponds to a homogenization of the vitrified material, and this part must preferably remain at this level until obtaining a homogeneous vitrified material before being removed by continuous casting. The vitrified product may for example remain for a period of approximately 30 to 60 minutes in the downstream part 17 of the molten bath, which contributes to the homogenization of the vitrified material, and of course improves the flowability of said vitrified material.

We will now describe in more detail the preheating chamber 11 and the melting chamber 12 of the aforementioned incineration furnace with reference to FIGS. 2 to 4.

FIG. 2 illustrates on a larger scale the preheating chamber 11 which is constituted by an enclosure entirely lined with refractory and insulating materials. In the upper part of the preheating chamber 11, there is the charging screw 14, as well as two smoke outlets 42 of which only one is visible here. One also distinguishes one 40 from the two air-gas burners supplied from the line 41 in combustion air The preheating chamber 11 is further equipped with means 26 for injecting hot air, in accordance with a circuit whose upstream has been previously described with reference to FIG. 1 The preheating chamber 11 is at successive inclined floors, here three in number, referenced 44 1, 44 2, 44 3 Mechanical means for pushing the products, noted 46.1, 46 2, 46 3 are associated with each of these inclined floors 44 1, 44.2, 44.3, these mechanical means being actuated by control members controlled in the general context of the process, by conventional means not shown here. The load 50 is present on each of the successive soles can then be pushed below, to a lower hearth, and, for the last hearth (referenced 44 3) towards the direct entry into the melting chamber 12, passing through the common opening 13. This common opening 13 thus serves both to the charging of materials under the action of mechanical means 46.3 for pushing the hearth lower 44.3, and the discharge and counter-current passage of smoke from the melting chamber. Screw ^¬ fournement 14 is arranged to the right of the upper sole

44.1, in order to distribute the load on this upper floor. Holes for the injection of hot air are provided in at least some of the inclined floors of the preheating chamber. In the diagrammatic view of FIG. 1, provision was made to supply hot air to each of the three inclined hearths from the branches of circuits 26.1, 26.2, 26.3. A variant has been illustrated in FIG. 2 according to which only the upper sole 44.1 and the middle sole 44.2 are equipped with injection orifices 45.1,

45.2, the lower plate 44.3 having no hot air injection orifice. In addition, means 43 have been shown for injecting cooling water laterally equipping the preheating chamber 11. Injections of water spray may prove to be necessary when the proportion of plastics is abnormally high. It is thus possible to control the progress of the process by monitoring the thermal level prevailing in the preheating chamber, this level being able to fluctuate depending on the proportions of combustible plastics present in the charge.

The preheating chamber 11 is connected by the common opening 13 to the melting chamber 12, and the arrow illustrated here symbolizes the passage against the current of the hot fumes coming from the melting chamber, and which transmit their energy to the load. passing through the preheating chamber. The fumes produced in the preheating chamber 11 are collected by the fumes outlets 42. Typically, these hot fumes are at a temperature of 850 ° C to 950 ° C, and will heat the air to a temperature of 300 ° C to 500 ° C. Such recovery makes it possible to significantly limit energy consumption and reduce the volume of smoke produced, so that the unit of the aforementioned smoke treatment may have a minimum dimension.

FIGS. 3 and 4 make it possible to better distinguish the structural arrangement of the melting chamber 12 also made of refractory and insulating materials. This melting chamber 12 comprises an upstream tank 47 called a settling tank and a downstream tank 48 called a homogenization of the vitrified material, above which a plurality of oxy-gas burners 60 is arranged. In practice, provision will be made for two to four pairs of such oxy-gas burners. As is best seen in Figure 4, we can use a staggered arrangement of the pairs of burners 60. The downstream tank 48 is separated from the upstream tank 47 by a wall 49 thus separating the bottom of the chamber into two separate portions , the upstream portion of which is used for the settling of metal fragments in the solid or pasty state, and the downstream portion for the homogenization of the vitrifiate and of the parts not yet melted contained in this vitrified material. The wall 49 thus raises the lower level of the bath, delimiting a downstream well which communicates, through a corridor 56 forming a siphon, with the outer tank 18 for recovering the vitrified material. The upstream tank 47 has at its bottom an interruptible pouring nozzle 54 closing a flow orifice 53 through which it is possible, intermittently, to let the decanted metal fragments flow after their heating to a temperature sufficient to complete their fusion. The heating means serving to bring these fragments to fusion can for example consist of several electrodes 52, preferably made of graphite. We have also provided, here both at the level of the wall 49 and at the bottom of the downstream tank 48, a series of means 55 for injecting air bubbles, such means being often called bubblers by the specialist. of glass technology. These injections of air bubbles promote the circulation of convective currents and thus participate in the homogenization of the vitrified material. A wall 51 forms a barrier between the downstream tank 48 and the recovery chamber 18, the lower edge of this wall delimiting the corridor forming the abovementioned siphon 56. This wall 51 makes it possible to block access to the casting to the parts not yet melted, and also participates in the homogenization of the vitrifiât whose flowability is thus significantly improved. Note also the presence of a drain nozzle 57 at the right of the corridor forming a siphon 56.

The vitrified material recovery chamber 18 is preferably arranged to form a funnel for receiving the vitrified material produced by the melting chamber, this funnel ending at a pouring bowl the bottom of which has a pouring orifice 19 closed by a drain nozzle 58 easily removable. There is also preferably provided a punch 59 mechaniεé, serving to ensure the regulation of the flow rate. This punch extends beyond the upper face of the chamber delimiting the tank 18, so as to be able to couple it to associated control means (not shown). Finally, in 70, two small oxygen-gas burners have been illustrated, serving to ensure the maintenance of the temperature of the vitrified material, or even to heat the vitrified material after a prolonged shutdown. Preferably, the tank containing the molten bath will consist of prefabricated refractory elements, resistant to corrosion, and a curved vault will be provided. We can also surround the whole with a thick layer of insulating material. A number of measurement sensors are provided to control the operation and regulation. We have already mentioned above the sensors or probes 64, 65 associated with the preheating chamber insofar as they serve to control the power of the air-gas burners 40 in the case where an energy supply is necessary. re, and possibly the water injection flow rate through the injectors 43 into the caε where the chamber must be cooled. The flow of hot air injected into the preheating chamber 11 through the associated orifices of the inclined hearths is controlled by flow by the oxygen measurement probe 65 placed at the outlet of the post-combustion chamber ion 31. D ' other temperature measurement probes could naturally also be provided in the incineration oven and in the adjacent vitrified oil recovery tank. Schematically illustrated here is a temperature sensor 61 arranged in the upper part of the preheating chamber 11, a temperature sensor 62 arranged in the upper part of the melting chamber 12, and a temperature sensor 63 arranged in the upper part of the tank. recovery 18 of the vitrified material. The temperature measurement in the melting chamber makes it possible to control the power of the oxygen gas burners 60 associated with the melting of the vitrified material. In addition, as far as the operating pressure is concerned, the whole of the installation is maintained in slight depression, as is usual in incineration furnaces, and particularly in the case of waste emitting dust. harmful. This vacuum is maintained by the general draft fan 38, and it will be advantageous to be able to regulate the speed of this fan, in order to adjust the pressure in the oven enclosure.

We have thus managed to carry out a treatment process, with an installation for implementing said process, making it possible to carry out a treatment of waste of harmful fibers, and in particular asbestos-bearing waste, in particular from the building, which is both simple. , reliable, and economical. In addition, this technique makes it possible to carry out a clean and controlled casting in temperature and in flow rate for the vitrified product obtained, which makes it possible to reduce the wear of the refractories, the corrosion of which is already considerably reduced compared to the techniques. known aforementioned using a plasma torch and a temperature regime greater than 1600 ° C. The technique according to the invention is of very satisfactory reliability, because it takes full account of the composition and the heterogeneous nature of the actual asbestos-containing waste coming from the decontamination sites of buildings. This technique also takes particular account of the thermal aspect of the treatment of this asbestos-containing waste from the building, which makes it possible to achieve truly industrial reliability and reduced operating cost.

The invention is not limited to the embodiment which has just been described, but on the contrary encompasses any variant incorporating, with equivalent means, the essential characteristics stated above.

Claims

1. Process for the treatment by vitrification of waste of harmful fibers, in particular of asbestos waste from the building, including a non-zero proportion of water, metallic materials, and plastics or other combustible materials, characterized in that waste to be treated, bagged in plastic bags, is first crushed and mixed in order to produce a charge, the fuel part of which is distributed in a substantially homogeneous manner, after which this charge is subjected to preheating in a preheating chamber ( 11) at a temperature substantially between 800 ° C and 1000 ° C in order to achieve the combustion of plastics or other materials present in the feed, the evaporation of water, and the at least partial oxidation of metallic materials also present in said charge, before arriving in a melting chamber (12) where a fusion bath (15) is made, the temperature is close to 1400 ° C., the hot fumes from the melting chamber (12) passing against the current in the preheating chamber (11) by transmitting their thermal energy to the charge subjected to preheating, said melting chamber being arranged to allow the metal fragments still present in the charge to decant in the solid or pasty state into an upstream part (16) of the molten bath, while the vitrified material flows continuously towards a downstream part (17) of said bath to be recovered by casting at the end of treatment. 2. Method according to claim 1, characterized in that the air necessary for the combustion of plastic materials during preheating of the charge is heated by the smoke from the preheating chamber (11). 3. Method according to claim 1, characterized in that the decanted metal fragments (150) are intermittently heated to a temperature sufficient to complete their fusion, then evacuated from the fusion bath (15) by casting. 4. Method according to one of claims 1 to 3, characterized in that the vitrified material remains at the downstream part (17) of the molten bath until a homogeneous vitrified material is obtained before being removed by continuous casting . 5. Method according to claim 4, characterized in that the time of stay of the vitrified stone in the downstream part (17) of the molten bath is substantially between 30 and 60 minutes. 6. Installation for implementing the treatment method according to at least one of claims 1 to 5, characterized in that it comprises: - a crusher (6) supplied with bagged waste to be treated; - a mixer (8) arranged downstream of the mill (6); - A preheating chamber (11) supplied with milled and mixed charge, said chamber being equipped with air-gas burners (40) and means (26) for injecting hot air; - a melting chamber (12), the inlet of which communicates directly with the outlet of the preheating chamber (11) through a common opening (13) used both for charging materials into the melting chamber under the action of mechanical pushing means (46.3) and at the counter-current passage of the fumes from this melting chamber, said melting chamber comprising an upstream settling tank (47) and a downstream homogenization tank (48) at - above which are arranged oxy-gas burners (60), - - a vitrified oil recovery tank (18) external to the melting chamber (12) and communicating with the downstream tank (48) of the latter, said tank recovery being equipped with a closable pouring means (58, 59); - Means (29, 30) for recovering and treating the smoke in communication with the upper part of the preheating chamber (11). 7. Installation according to claim 6, charac¬ terized in that the preheating chamber (11) is with successive inclined soles (44.1, 44.2, 44.3), each provided with mechanical means (46.1, 46.2, 46.3) of product powering which are there, at least the most upstream soles having orifices (45.1, 45.2) used for the injection of hot air danε said preheating chamber. 8. Installation according to claim 7, charac¬ terized in that the hot air injection orifice (45.1, 45.2) are connected to an air circuit (26) which is associated, for heating the air. injected, to the means (29) for recovering the fumes. 9. Installation according to claim 7 or claim 8, characterized in that the preheating chamber (11) eεt supplied in the upper part by a charging viε (14) distributing the load εur εole εupérieur (44.1). 10. Installation according to one of the claims 6 to 9, characterized in that the preheating chamber (11) is laterally equipped with means (43) for injecting cooling water. 11. Installation according to one of revendicationε 6 to 10, characterized in that the upstream pit (47) of the fuεion chamber (12) is provided with electrodes chauf ^¬ wise (52) and a casting nozzle interruptible (54). 12. Installation according to one of claims 6 to 11, characterized in that the downstream tank (48) of the melting chamber (12) is separated from the upstream tank (47) of said chamber by a wall (49), and it communicates by a corridor forming a siphon (56) with the outer tank (18) for recovering vitrified material. 13. Installation according to claim 12, characterized in that the downstream tank (48) and / or the wall (49) associated are equipped with means (55) for injecting air bubbles. 14. Installation according to one of claims 6 to 13, characterized in that the tank (18) for recovering vitrified material is produced in the form of a closed chamber fitted laterally with at least one oxy-gas burner (70) . 15. Installation according to one of claims 6 to 14, characterized in that the closable casting means (58, 59) of vitrified material comprises a flow nozzle (58) in the lower part and a mechanized punch (59) ensuring the regulation of the flow rate.