EP0746725B1 - Method and plant for waste treatment by drying, sublimation, oxidation and combustion - Google Patents

Abstract

PCT No. PCT/FR95/00223 Sec. 371 Date Jan. 17, 1997 Sec. 102(e) Date Jan. 17, 1997 PCT Filed Feb. 24, 1995 PCT Pub. No. WO95/23317 PCT Pub. Date Aug. 31, 1995Waste treatment. The installation for implementing the method comprises: a furnace (1) defining a confinement enclosure (2) for a fluidized bed (3) of particulate matter; means for recirculating the particles of the bed; means (28) for mixing, coating, and drying the recycled particles and the waste; and means for feeding the furnace from the means (28). The invention is applicable to treating moist waste.

Description

TECHNICAL AREA

The present invention relates to the technical field of waste treatment and it aims, more particularly, although in a nonlimiting manner, the treatment of wet waste and, more specifically, among these, sludge of various origins.

As an example, it is worth mentioning food sludge, stationery sludge, steel, dyeing, wastewater treatment, etc ....

Different difficulties are to be overcome when seeking to treat and to inject wet waste and, in particular, sludge. Among these difficulties and without whether it is an order of importance, it can be cited following difficulties.

The first relates to the water content which must necessarily be removed for that a suitable treatment leads to the "inerting" of dry products residual. By the neologism "inerting", it is necessary to understand any means for make such waste after treatment not liable to cause pollution by themselves or by leaching. This first difficulty is linked to the need to control energy expenditure so that the cost of treatment is acceptable.

The second difficulty is due to the pasty or muddy form of the waste which poses a difficult problem of transfer within a facility, by risks of clogging, solidification, vaulting which may occur within transfer circuits in particular.

The third difficulty relates to the establishment, conduct and control a treatment process capable of safely and completely eliminating all components of waste likely to be destroyed by incineration. This is a objective that must necessarily be achieved in order to meet the requirements of regulatory, or even legislative, texts aimed at eliminating, if not ultimately immediately, deposits and spills in uncontrolled or access dumps regulated.

PRIOR ART

The prior art has proposed a number of methods to attempt to inert the waste. These processes can be classified into two main categories, called cold process and hot process.

Cold processes consist of coating the waste in a matrix which can be bitumen, cement, or even a suitable plastic. These processes immediately appear inappropriate for wet waste and especially sludge.

Among the hot processes, one consists in vitrifying waste included in a mixture of silica or alumina. Vitrification occurs at very high temperature generated by expensive, complex and delicate technical means which do not cannot be considered for the treatment of all waste and which especially not suitable for wet waste.

The prior art has proposed a more specific method of treatment for such waste. This method, taught by US Patent 3,677,404, consists to create, in an incineration furnace, a fluidized bed of inert solid particles mineral, for example formed from silica grains, such a bed being heated to a suitable temperature, for example around 750 ° C.

The particles circulate from the bottom of the bed to the upper level from which they are recycled for incorporation into the waste. The mixture obtained is received in a filtration tower intended to allow the evacuation of at least part moisture.

A low racking device is provided to extract the mixture from the tower. filtration and to direct it to the inlet of a supply system providing, in the oven at the base of the fluidized bed, the mixture of heated particles.

In this way, it is expected that the waste-particle mixture will have the property of being put into circulation and of following, by a continuous feeding from the furnace, an upward migration in the fluidized bed within which an incineration burnable components may intervene.

This technique recommended in 1970 does not seem able in reality to do the subject of a real industrial application for wet waste and, in particular, sludge, because it suffers from various disadvantages.

The first arises from the desire to keep the mixture in the tower of filtration. This proposal is easily understood because its objective is to eliminate a important part of the water included, before entering the oven by taking advantage of the heat stored by particles. However, this procedure leads to pile up the mixture in an enclosure in which the mixture inevitably solidifies with minimal consequence, the formation of lumps, or maximum, the constitution of cakes or layers that oppose an extraction later.

The second is that the mixture from the filtration tower has a heterogeneous character which is not favorable to the progress of a process complete incineration inside the bed.

The third is due to the fact that the fluidization of the bed is ensured by gas exhaust of a burner responsible for raising and maintaining the temperature inert recyclable particles. When the bed is necessarily large height to impose sufficient residence time, as recommended, the incineration of "burnable" components cannot really and effectively intervene due to lack of oxygen.

The prior art has also proposed a different solution described in FR 73-23 383 (2 234 920). According to this publication, a cot is provided fluidized constituted by a mass of solid particles which come from the waste itself (see page 2 lines 28 to 34) and which are partly recycled to a unit mixing with waste to be treated.

Such a proposal involves particles of the same kind which, for those from the fluidized bed, can still offer an ability to amalgam with those to be treated. A risk of progressive agglomeration can therefore intervene to some of these particles whose presence will result in constituting little to small an inhomogeneous fluidized bed and, consequently, incapable of submitting the waste to the same heat treatment.

The object of the present invention is to overcome the above drawbacks listed, in order to propose a process for inerting wet waste, and more particularly sludge, which is really effective, relatively little energy consumer and which could be subject to flexibility or suppleness of driving, in particular by self-adjusting the temperature regulation of the bed taking into account the energy input resulting from the actual and complete combustion burnable components.

STATEMENT OF THE INVENTION

• créer dans l'enceinte de confinement d'un four un lit de particules inertes à la base duquel est injecté un fluide sous pression pour entretenir un lit fluidisé,
• maintenir le lit fluidisé à une température de traitement par un moyen de chauffage extérieur à l'enceinte,
• définir un niveau supérieur maximal du lit fluidisé et à extraire tout surplus à partir dudit niveau,
• mélanger les déchets avec une charge de matière minérale sous forme particulaire,
• introduire ledit mélange à la base du lit,
• soumettre le mélange à un parcours ascendant au sein du lit,
• prélever, à partir du ciel de four, les gaz produits qui sont dirigés vers une installation de traitement
• et extraire le surplus du lit fluidisé à partir du niveau supérieur,

est caractérisé en ce qu'il consiste à :

• recycler les particules inertes chaudes extraites du lit vers une section de mélange d'une unité,
• admettre en proportion appropriée les déchets humides à traiter dans ladite section,
• procéder dans la section à un mélange,
• brasser et déplacer le mélange dans une section d'enrobage séchage où les déchets s'agglomèrent en couche autour des particules pour former une gangue en partie au moins séchée,
• recycler les particules enrobées directement à la base du lit
• et entretenir la fluidisation du lit par un fluide sous pression, oxygéné, délivré au moins à la base du lit.

To achieve this objective, the method according to the invention, of the type consisting in:

• create in the containment of a furnace a bed of inert particles at the base of which is injected a pressurized fluid to maintain a fluidized bed,
• maintain the fluidized bed at a treatment temperature by means of heating outside the enclosure,
• define a maximum upper level of the fluidized bed and extract any surplus from said level,
• mix the waste with a charge of mineral matter in particulate form,
• introduce said mixture at the base of the bed,
• subject the mixture to an ascending course within the bed,
• extract, from the furnace roof, the gases produced which are directed to a treatment installation
• and extract the surplus from the fluidized bed from the upper level,

is characterized in that it consists of:

• recycle the hot inert particles extracted from the bed to a mixing section of one unit,
• admit in appropriate proportion the wet waste to be treated in the said section,
• mix in the section,
• stir and move the mixture in a drying coating section where the waste aggregates in a layer around the particles to form a gangue that is at least partly dried,
• recycle the coated particles directly at the base of the bed
• and maintain the fluidization of the bed with a pressurized, oxygenated fluid, delivered at least to the base of the bed.

Various other characteristics will emerge from the description given below in reference to the accompanying drawings which show, by way of examples of the embodiments of the subject of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

Figure 1 is a schematic view illustrating an installation for the implementation of the method.

Figure 2 is a schematic view showing an alternative embodiment of the installation.

BEST WAY TO IMPLEMENT THE INVENTION

FIG. 1 shows a first embodiment of an installation for implementing the treatment method. Such an installation comprises an oven 1 delimiting an enclosure 2 for confining a bed 3 of materials or of an inert mineral material, in particulate form. Preferably, the enclosure 2 is made so that the bed 3 can rise over a relatively large height, for example between 1 m and 2.50 m. The inert mineral material retained is chosen from silica, alumina, lime, zircon, with a particle size favorable for fluidization. The particle size is, for example, between 100 and 2000 micrometers in average diameter. The bed 3 can be formed from a single mineral material or from a composition of several compatible with each other.

The oven 1 comprises an insulating envelope 4 suitably formed to form a barrier limiting the propagation of calories from the interior of the oven to the surrounding environment. Inside the insulating envelope 4 , a tank 5 is mounted which delimits the enclosure 2 . The tank 5 has a bottom 6 and a double bottom 6a defining between them a manifold 7 of admission and pressure distribution whose function appears in the following.

The double bottom 6a is provided with fluidization nozzles 8 opening inside the collector 7 which communicates with a circuit 9 adapted to supply an oxygenated gaseous fluid, under pressure, responsible for ensuring the fluidization of the bed 3 . The gaseous fluidization fluid is, for example, supplied by a booster 10 , the outlet 11 of which can be connected to the circuit 9 , either directly or indirectly through a heating system 12 , of any suitable type, which may preferably be a heat exchanger, the second circuit of which will be described below.

The oven 1 also comprises heating means 13 which are constituted by static means capable of heating the bed 3 . Such means 13 are preferably constituted by electrical resistances, arranged between the tank 5 and the insulating envelope 4 , being distributed over the entire height corresponding to that of the bed 3 at least, but preferably also over the height a chamber 14 forming an enclosure sky and delimited inside the latter by the upper level of the bed 3 . The chamber 14 communicates at its upper part with a chimney 15 passing through the insulating envelope 4 to ensure the extraction of the fumes and other gaseous products developing in the enclosure 2 . The chimney 15 leads to a cyclone 16 for separating any dust, before being connected to the heating system 12 to take the second circuit of the latter then produced in the form of a dual-circuit exchanger. The exchanger 12 is also connected to a smoke treatment unit 17 , produced in any known manner to provide pollution control.

According to another arrangement of the invention, the circuit 9 comprises a branch branch 9a capable of passing through a heater 18 , the outlet of which is connected to means 19 for supplying an oxidant inside the enclosure 2 . The means 19 are, for example, constituted by a rod 20 , the end of which is provided with a diffuser 21 which can be located just above the upper level of the bed 3 or at least partly inside the latter. .

According to another arrangement of the invention, the upper level of the bed 3 inside the enclosure 2 is determined by extraction means 25 which can involve active means, of the type of an extraction screw endless driven by a motor or passive means, such as an overflow through a level weir.

The enclosure 2 is provided with means 26 for supplying waste to be treated. By waste, it is appropriate, within the meaning of the invention, to consider the term in its widest sense to designate wet materials and more generally sludge.

The supply means 26 may consist of a sheath containing an endless screw or also of a pneumatic transfer system. In all cases, the means 26 open out at the bottom of the tank 5 , substantially at the level of the double bottom 6a and above the outlets of the nozzles 8 . The supply means 26 are connected by a supply line 27 to a mixing unit 28 comprising a first inlet 29 reserved for the introduction of the waste to be treated and a second inlet 30 reserved for the introduction of a charge of mineral matter in particulate form directly from means 25 .

The mixing unit 28 comprises a box 32 defining a trough or gutter 33 for, at least, a mixing screw 34 of the Archimedes type driven in rotation by an actuator 35 . The gauge 33 delimits a section or zone 36 , called a mixing zone, to which the inlets 29 and 30 lead . The inlet 29 is connected upstream to a device 37 for supplying waste which may be a buffer tank provided with extraction means, a grinder, a kneader, an agitator, or even a granulator, if the wet waste has been previously frozen. The gauge 33 delimits, after the zone 36 , a zone or section 38 , called coating-drying, which is overhung by a hood 39 connected to the smoke treatment circuit, for example between the heating system 12 and the processing unit 17 . The gauge 33 is connected, opposite section 36 , to line 27 with the interposition of a launching device 40 .

The method according to the invention consists in heating the enclosure 2 by means of the means 13 so as to maintain a constant temperature, between 400 and 1000 ° C. and typically close to 900 ° C., imposed on the bed 3 .

When the desired temperature is reached and maintained by control and servo means which are not directly part of the object of the invention, the unit 28 is put into service.

In the case of a first start-up, inert mineral particles at a suitable temperature are supplied, for example by an auxiliary circuit 30a to maintain a functional mode in a closed circuit. When this functional mode has been reached, the inert particles come directly from the oven 2 by extraction from the upper level of the bed 3 .

The hot mineral particles are poured into the zone 36 where they are stirred by the rotation of the screw or screws 34 . Zone 36 also receives, via inlet 29, a proportional quantity of waste which is thus mixed with the particles in zone 36 .

The screw (s) 34 then maintain effective mixing of the mixture in the zone 38 where there is progressively a coating of the hot inert mineral particles which yield their calories to the layer of waste gradually forming into a dry gangue of relatively small thickness. Given the large specific surface area of the particles, a high drying power of the waste occurs and the vapors produced are taken up by the hood and evacuated.

At the end of the migration inside the box 28 , the waste is entirely incorporated by coating around the particles and the mixture thus obtained can be described as homogeneous.

The coated particles are then extracted from the box 28 and taken in charge by the launcher 40 to be conducted by the line 27 to the means 26 ensuring their introduction inside the bed 3 whose fluidized state is maintained by the intake oxygenated gaseous fluid, possibly heated, supplied by the booster 10 and delivered to the lower manifold of the tank 5 .

Upon their introduction to the base of the fluidized bed, the coated particles are subjected to a thermal shock bringing the gangue of waste to the temperature ambient of the fluidized bed.

This temperature rise occurs quickly, given the relatively small thickness of the gangue of dried waste surrounding the particles. The thermal shock weakens the gangue to the point of fracturing it and the temperature of the bed maintains the combustion of the burnable compounds during the upward path followed by the particles and the waste inside the fluidized bed 3 .

The ascending route is positively controlled in length of stay, given that the particles and waste are trapped in a kind of fluid matrix which homogeneity is ensured by the fact that the particles of mineral matter having been coated, are of the same nature and the same particle size as those constituting the fluidized bed.

This residence time, which is consequently relatively long due to the height of the fluidized bed 3 , can, depending on the operating parameters of the furnace, be in the region of several tens of minutes, or even several hours, during which the waste is subjected to the processing temperature.

This temperature therefore promotes the combustion of the combustible parts of the waste, the oxidation of the oxidizable parts, and even the sublimation of the sublimable parts. Thus, the leachable products partially decompose in the gaseous phase, for example, the salts in the form of chloride, and this gaseous phase is evacuated from the treatment and reaction enclosure 2 , via the chimney 15 to undergo there. possible separation of the fine particles included inside the cyclone 16 before passing through the exchanger 12 making it possible to improve the energy balance of the installation in operation. Beyond the exchanger 12 , the fumes are washed and decontaminated by the unit 17 operating in a manner known per se.

The residual part of the waste in solid form can be partly burnt and partly oxidized by the effect of the oxygen surrounding each of the particles and which comes from the gaseous fluid for fluidizing the bed 3 . It can be envisaged to improve the presence of oxygen inside the enclosure 2 by providing in particular a supply by the rod 20 to maintain, for example, in the headliner or room 14 , a partial pressure of oxygen greater than 2,000 Pascal, maintaining an oxidizing atmosphere.

The oxidation of the residual part in solid form also occurs due to the temperature maintained inside the enclosure 2 and the long residence time which is imposed on the particles following an ascending path or path inside the fluidized bed 3 .

The supply, continuously or discontinuously, of the mixture to be treated has the consequence of increasing the mass of the fluidized bed 3 , the surplus of which is taken up at a higher level by the extraction means 25 . This surplus consists of the mineral matter in inert particulate form, or even the inert inert solid fraction of the waste.

Depending on the nature of the waste, bringing it into zone 36 can involve a proportion of particulate matter of between 15 and 80% compared to the waste.

Thus within the meaning of the invention, the recommended method involves the implementation work of inert particles which can be qualified as carriers which, in the above case, operate in a closed circuit to facilitate hydrodynamics, handling and waste circulation in the installation.

The particles included also act as a vector of heat energy favoring, during mixing in the unit 28 , the drying of wet waste.

This arrangement makes it possible to treat a wide spectrum of wet waste, even going as far as direct treatment of organic and hospital waste by planning, for example to freeze it initially to allow grinding and / or granulation favoring incorporation into the inert material. recycled whose temperature at the outlet of the oven ensures rapid drying during the mixing phase in unit 28 .

In an installation according to the invention, it is possible to extend the inlet 30 by a withdrawal duct 41 provided with a valve 42 so as to eliminate from the recirculating mass a portion corresponding to the gradually increasing residual presence of the fraction solid waste treated.

FIG. 2 shows an alternative embodiment in which the recirculation means 30 are directed, optionally after passage through a cooler 43 , towards a separator 44 capable of ensuring, by any suitable means, such as centrifugation or mechanical stripping, the separation between the particulate inert material and the solid fraction of the waste together constituting the surplus extracted from bed 3 by means 25 . In such a case, the separated solid fraction is evacuated to a packaging or compacting unit for ultimate waste, such as 45 , while the inert particulate matter fraction is taken up by a line 46 to reach inlet 29 .

INDUSTRIAL APPLICATION

The invention finds a preferred application in the treatment of water sludge worn out.

Claims (12)

1. A method of treating waste by drying, subliming, oxidizing, and combustion, the method being of the type consisting in:

   creating a bed of inert particles in the confinement enclosure of a furnace, with a fluid under pressure being injected into the base of the bed to maintain a fluidized bed;

   maintaining the fluidized bed at a treatment temperature by heater means outside the enclosure;

   defining a maximum top level of the fluidized bed and extracting any surplus from said level;

   mixing the waste with a fill of mineral matter in particulate form;

   injecting said mixture into the base of the bed;

   subjecting the mixture to an upward path through the bed;

   extracting from the roof of the furnace the gases that are produced and directed to a treatment installation; and

   extracting the surplus fluidized bed from the top level;

      the method being characterized in that it consists in:

   recycling the hot inert particles extracted from the bed to a mixer section of a unit (28);

   admitting an appropriate proportion of moist waste to be treated into said section;

   performing mixing in the section;

   churning and moving the mixture through a coating-and-drying section where the waste agglomerates as a layer on each particle to form a deposit that is dried, at least in part;

   recycling the coated particles directly to the base of the bed; and

   maintaining fluidization of the bed by an oxygen-containing fluid under pressure delivered at least to the base of the bed.
2. A method according to claim 1, characterized in that the mineral matter in particulate form is selected from silica, alumina, zircon, and lime, with a grain size of mean diameter lying in the range 100 micrometers to 2,000 micrometers.
3. A method according to claim 1 or 2, characterized in that the mineral matter is mixed with the waste at a concentration lying in the range 15% to 80%.
4. A method according to claim 1, 2, or 3, characterized in that the mineral matter and the waste are subjected to a treatment temperature lying in the range 400°C to 1000°C.
5. A method according to claim 1 and 2 to 4, characterized in that the mineral matter and the waste are subjected to a transit time in the fluidized bed lying in the range a few tens of minutes to several hours.
6. A method according to claim 1, characterized in that an oxygen partial pressure is maintained in the furnace.
7. A method according to claim 6, characterized in that the oxygen partial pressure is greater than 2000 Pascals.
8. A method according to one of claims 1 to 5, characterized in that the surplus is recycled to an installation for separating the mineral fill from the residual inert dry fraction of the waste.
9. An installation for implementing the method according to one of claims 1 to 8, the installation being of the type comprising:

   a furnace (1) defining a confinement enclosure (2) for a fluidized bed (3) of matter;

   a circuit (9) for feeding a fluid under pressure, said circuit opening out into the bottom of the enclosure to fluidize the bed;

   feed means (26) for feeding substances to be treated to the base of the bed;

   means (25) for extracting surplus bed from the top level thereof; and

   a mixer unit between the waste to be treated and the surplus matter extracted from the bed ;

      the installation being characterized in that it comprises:

   a fill of inert particle matter occupying the confinement enclosure of the furnace so as to constitute the fluidized bed ;

   a mixer unit (28) comprising firstly a mixer section in which there terminate a hot inert particle inlet and a waste inlet, and secondly a coating-and-drying section ; and

   recycling means (27) connecting the outlet of the unit (28) to the base of the furnace.
10. An installation according to claim 9, characterized in that the mixer unit is implemented in the form of a box defining a trough containing at least one mixer apparatus and defining the mixing section and the coating-and-drying section.
11. An installation according to claim 9 or 10, characterized in that the coating-and-drying section is under a hood for collecting and removing vapor.
12. An installation according to one of claims 9 to 11, characterized in that the recycling means include a separator (44) for separating the inert mineral matter from the inert residual dry fraction of the treated waste.

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