EP0665407A1 - System for the injection of sludge for incineration in an incinerating oven, corresponding method of operation, use and oven - Google Patents

Abstract

Muds are burnt in an incinerator burning domestic waste on an incineration floor. The muds are sprayed into the incinerator, above the floor, so they are fed, at least partly, by gravity.

Description

The field of the invention is that of eliminating sludge or other pasty waste of the same type, such as greasy waste, and in particular sludge of the type originating from industrial processes or from purification plants for drinking water. or wastewater.

More specifically, the invention relates to a system for injecting sludge or other pasty waste of the same type to be incinerated in an incineration furnace, as well as a corresponding method and furnace. The invention finds particular application in combi ovens of household refuse (or other urban or industrial waste) and of sludge and / or greasy waste. It applies to ovens with very different types of combustion (for example with fixed or mobile incineration hearth, grates, rollers, fluidized bed, etc.).

Sludge, and in particular that from the dewatering workshops of wastewater treatment plants, generally has a non-negligible content of organic materials that are difficult to biodegrade. They therefore constitute a nuisance for the environment, which should be eliminated. In addition, due to the increasing number of water treatment plants, there is an increasing amount of sludge to be treated.

A first known solution for eliminating sludge is to landfill it. But this solution, widely used before, is not ecologically acceptable and therefore tends to be eliminated.

A second known solution, namely the reuse of this sludge in agriculture, would represent an ideal solution. Unfortunately, the high costs of storage, transport, spreading, and the very nature of the sludge very often constitute major obstacles to the implementation of such a solution.

Finally, the third and last known solution for eliminating sludge is incineration, which results in purely mineral waste. This solution seems to be the one that is currently developing the most. However, when such incineration is envisaged on the site of the treatment plant, using a specific oven, it can present a high cost. This is why, when an incinerator exists near the treatment plant, for example an oven originally intended for another use such as the incineration of household waste, it can be economically advantageous to burn the sludge treatment plant in this existing incinerator.

If this principle of incineration of sludge mixed with other products to be incinerated - such as household waste - is known, its implementation however poses many problems.

Thus, in the prior art, the injection of sludge into the combustion chamber of a household refuse incineration furnace is generally carried out continuously, in the form of a cylinder of mud.

However, with this type of injection, the sludge does not disperse in the combustion chamber during their injection and their combustion is therefore not optimal. In other words, the unburnt contents of bottom ash and fly ash from the incineration of the household waste / sludge mixture can become higher than the maximum values imposed by legislation (for example, a maximum of 5% of unburnt in bottom ash).

In addition, the sludge is not distributed with household waste evenly. There therefore occurs phenomena of sub-cooling or overheating of the combustion chamber, depending on whether the incinerated mixture contains more or less sludge. These phenomena can disturb the operation of the oven, or even cause combustion to stop.

Finally, the variable quality of the sludge to be incinerated, in particular depending on the quantity of dry matter it contains and its calorific value, can also cause overheating or sub-cooling phenomena causing defusing of the boiler.

The invention particularly aims to overcome these various drawbacks of the state of the art.

More specifically, one of the objectives of the present invention is to provide a system for injecting sludge to be incinerated in a mixed waste incineration oven household and dehydrated sludge, this system making it possible to avoid stopping the oven by crossing the high temperature limits (in the case of overheating) or low (in the case of under cooling).

The invention also aims to provide such a system which does not increase the rate of unburnt in bottom ash, nor the rate of unburnt in fly ash.

Another object of the invention is to provide such a system which does not create significant new labor requirements in terms of the daily operation of the oven or in terms of maintenance and upkeep of the heating system. injection itself.

A complementary objective of the invention is to provide such a system that can be implemented with any type of oven (including an oven specifically designed to incinerate sludge), while allowing optimal combustion of the injected sludge.

Another object of the invention is to provide an optimized method for operating such a system.

These various objectives, as well as others which will appear subsequently, are achieved using a system for injecting sludge to be incinerated, or other pasty waste of the same type, in an incineration oven, said furnace comprising an incineration hearth onto which said household waste is dumped in order to be incinerated, the system comprising means for injecting said sludge to be incinerated into the furnace, disposed essentially above said incineration hearth so as to allow a sludge supply to said bottom at least partly by gravity, said injection means being provided with means for spraying the sludge during their injection into the furnace.

According to the invention, the injection means comprise an injection body forming a spraying chamber comprising a sludge supply inlet, and an outlet nozzle for injecting sludge into the furnace, said chamber being traversed by a gas injection tube, such as air or water vapor, under pressure, the end of which is provided with a diffuser in the region of the nozzle of said chamber, said pressurized gas injection tube cooperating with means for moving the diffuser relative to the injection nozzle of the chamber, so as to allow adjustment of the spraying of sludge and / or cleaning of said chamber.

Thus, according to the invention, the sludge is divided into droplets or pancakes before being dispersed on the incineration hearth. This has an important advantage, especially when the incineration oven is a combi-type oven used to incinerate something else, in particular household waste, or other waste. This allows optimal combustion of the sludge by creating an exchange surface significant and a homogeneous distribution of this sludge on the waste resting on the incineration bottom. This optimal sludge combustion, not disturbing that of waste, does not increase the unburnt content of bottom ash and smoke. For this, the droplets or slabs of sludge obtained by spraying must be neither too fine nor too coarse. Too fine, these droplets or pancakes would be drawn too quickly into the stream of combustion fumes and would enrich the unburnt content of the fly ash. Too large, they would have too long a burning time, would disturb combustion phenomena, and would risk increasing the content of unburnt ash in the bottom ash.

The percentage of sludge injected in relation to the waste, as well as the dryness of this sludge are variable and chosen according to the desired objective, for example taking into account the thermal availability of the day, namely either to eliminate a maximum of sludge, or to supply l 'energy.

Furthermore, the sludge, by being injected continuously and burning almost perfectly, does not create any problem of overheating or subcooling. It suffices that the waste / sludge mixture remains self-combustible.

In an advantageous embodiment of the invention, said incineration hearth comprises at least two successive distinct zones, namely a combustion zone and a finishing zone, and said injection means are located essentially above said zone combustion.

In another preferred embodiment of the invention, said incineration hearth comprises at least three successive distinct zones, namely a zone of drying, a combustion zone and a finishing zone, and said injection means are situated essentially above said drying zone and said combustion zone.

In these two embodiments of the invention, the sludge is distributed over the zone or zones of the incineration hearth allowing optimum combustion of this sludge. In other words, the duration and the temperature must be sufficient for the sludge, after homogeneous distribution by spraying, to be completely burnt.

These two embodiments correspond to the most frequent configurations of the soles of incineration ovens for household waste. But it is clear that the invention is also compatible with other types of ovens, in particular with ovens whose hearths have only a single combustion zone - case for example of ovens with low flow rates and / or operating in " batch "(in successive batches) -, or a number of zones greater than three.

Advantageously, said injection body is mounted on a ball joint and cooperates with at least one telescopic rod for adjusting the inclination of said injection body by rotation around said ball joint.

This adjustment of the spraying of the sludge is generally done in conjunction with that of the injection pressure in the spraying means, these values being adjusted for example at start-up.

Preferably, said injection tube is covered at least partially with a protective sheath. This sheath makes it possible to limit the abrasion of the injection tube and the attachment of the tow.

In this way, the trajectory of the droplets or slabs of sludge inside the oven can be adjusted. Thus, the system of the invention can be adapted to any type of oven and the sludge can be injected at the right place, that is to say on the hearth, in particular avoiding any projection of sludge on the walls of the chamber. combustion.

Preferably, said chamber is provided with a cleaning fluid inlet.

Advantageously, said cleaning fluid inlet is located at the level of the sludge inlet, so as to allow cleaning of the entire chamber before the cleaning fluid is discharged through the injection nozzle.

Advantageously, the system includes means for controlling the internal temperature of the furnace, controlling the flow of injected sludge.

Thus, the combustion of sludge is enslaved to that of household waste. In other words, the sludge injection rate is slaved to the temperature of the furnace.

Preferably, the system comprises means for controlling a movement back and forth from the tube for injecting gas under pressure into the spraying chamber, in order to prevent any blockage of the chamber by the sludge.

In this way, the injection tube and the diffuser allow cleaning of the spray chamber.

Advantageously, the injection means also cooperate with a sweeping air supply duct preferably provided near the diffuser and thus making it possible to protect the latter from the radiant heat of the oven.

The invention also relates to a mixed incineration oven for household waste and sludge provided with a system as presented above.

The invention also relates to a method of operating a system as presented above, this method comprising an operating cycle starting with a start-up phase in which the supply of sludge to the spray chamber is carried out after establishment of a nominal gas injection regime such as pressurized air, and ending with a stop phase in which the interruption of the supply of sludge to the spraying chamber precedes the establishment of a low regime injection of pressurized gas, said stopping phase being preceded by a cleaning phase of the spraying chamber, in which a cleaning fluid passes into the spraying chamber and is evacuated by the sludge injection nozzle in the oven.

During the shutdown phase, the gas sweep is therefore maintained, with a low pressure value in order to prevent any risk of deterioration of the injection means by radiation. Furthermore, the cleaning phase is a generally brief and infrequent operation, for example two minutes every six hours.

The system of the invention can advantageously be used for the incineration of sludge or other pasty waste such as greasy waste from a wastewater treatment plant. wastewater treatment.

Preferably, said sludge undergoes a preliminary treatment of at least partial dehydration before their injection for incineration.

• la figure 1 présente un schéma simplifié d'un four d'incinération mixte d'ordures ménagères et de boues dans lequel est mis en oeuvre en système d'injection de boues selon l'invention ; et
• la figure 2 présente un schéma du mode de réalisation préférentiel du système d'injection de boues apparaissant sur la figure 1.
• les figures 3 et 4 représentent le diffuseur du système d'injection montré à la figure 2 respectivement en coupe transversale et en vue de dessous.

Other characteristics and advantages of the invention will appear on reading the following description of a preferred embodiment of the invention, given by way of non-limiting example, and the appended drawings, in which:

• FIG. 1 shows a simplified diagram of a mixed incineration oven for household waste and sludge in which a sludge injection system according to the invention is used; and
• FIG. 2 presents a diagram of the preferred embodiment of the sludge injection system appearing in FIG. 1.
• Figures 3 and 4 show the diffuser of the injection system shown in Figure 2 respectively in cross section and in bottom view.

The invention therefore relates to a sludge injection system intended to be used in a mixed incineration oven for household waste and sludge.

Such an oven, a simplified diagram of which is presented in FIG. 1, is in fact a conventional oven for incinerating household waste to which a sludge injection system is added.

A grapple 1 attached to an overhead crane 2 makes it possible to seize household waste in a storage pit (not shown) and to discharge it (a) into an inlet hopper 3. This household waste arrives (b) on a floor d incineration 4.

• une zone de séchage 5 des ordures ménagères, destinée à faciliter leur combustion ultérieure ;
• une zone de combustion 6 ; et
• une zone de finition 7.

In this classic example, the incineration hearth 4 comprises three successive zones (or steps) each consisting of rollers:

• a household refuse drying zone 5, intended to facilitate their subsequent combustion;
• a combustion zone 6; and
• a finishing area 7.

After the household waste has passed over this incineration hearth, clinkers 13 are obtained which are collected (c), via an outlet hopper 8, in a bucket 9 (or any other storage means) in order to to be evacuated.

Other outlet hoppers 10, 11, 12 can also be placed under the different zones 5, 6, 7 of the incineration hearth 4, so as to recover (d), (e), (f) the bottom clinkers passing through this sole 4.

The incineration of household waste, mainly in the combustion zone 6, generates not only bottom ash 13 but also smoke containing fly ash. Generally, these fumes pass (g) through an energy recovery boiler 14. At the outlet of this boiler 14, part of the fly ash 17 is recovered (h) in a bucket 15 and the resulting fumes undergo (i) a new treatment, for example in an electro-filter 16. This electrofilter 16 makes it possible to recover (j) fly ash 17 while the filtered fumes are discharged (k) through a chimney 18.

The invention therefore consists in injecting sludge into this furnace, without substantially disturbing the thermal equilibrium of the furnace, or even the operating balance of the furnace (a household waste incineration furnace which in principle produces energy under vapor or even electricity sold to a customer).

The sludge generally comes from a wastewater treatment plant and has undergone a dewatering treatment, for example with mechanical means of the band filter or centrifugal decanter type. These dehydrated sludges have a dryness of, for example, between approximately 13 and 40% by mass of free water, typically between 20 and 30%. It is subsequently considered that the sludge is dehydrated. However, it is clear that the invention relates to the incineration of all types of sludge.

The sludge injection system comprises a buffer silo 19, withdrawal means 20, a feeding hopper 21 and injection means 22.

The sampling means 20 for example consist of a volumetric pump with thick material.

The dehydrated sludge, stored in the buffer silo 19, is removed by this positive displacement pump 20 and supplied to the injection means 22 without risk of entrainment of air pockets.

The injection means 22 are arranged on a wall 24 of the furnace (the roof or the side walls), so as to allow a supply of sludge to be incinerated, by gravity, from the incineration hearth 4. More specifically, the sludge is injected (1) onto the household waste bed resting on this hearth 4. Thus, the sludge is co-incinerated with household waste.

In addition, these injection means 22 are provided with spraying means. Thus, the sludge arrives on the sole in the form of droplets or pancakes. Sludge dispersion is optimized and caking is avoided due to the water. This allows drying and complete combustion of the sludge by increasing the exchange surface between the fuel (i.e. the sludge) and the oxidant (i.e. the oxygen in the air ) in the combustion chamber. Consequently, the operation of the oven is not disturbed (no overheating or sub-cooling), without appreciable influence on the rates of unburnt in the bottom ash 13 and in the fly ash 17.

In this example, the injection means 22 are placed overhanging the combustion zone 6. It is clear that these injection means 22 can also be placed overhanging the drying zone 5.

In addition, even if, in FIG. 1, the injection means 22 constitute a single injector, the invention is not limited to this embodiment but also relates to the case where there is a plurality of injectors. A person skilled in the art is capable, in this case, of choosing the number of injectors required as well as the spacing between two successive injectors, depending in particular on the flow rate and the nature of the sludge injected, on the surface of the sole d 4, etc ...

FIG. 2 presents a diagram of the preferred embodiment of the sludge injection system.

In this preferred embodiment, the injection means 22 comprise an injection body 25 forming a spraying chamber 23 comprising a supply inlet 28 for sludge and an outlet nozzle 33 for injecting the sludge into the furnace . According to the invention, the injection system comprises means 29 for moving the diffuser 27 relative to the nozzle 33.

The tube 50 makes it possible to permanently inject a gas at low pressure, for example air, to protect the end of the injector from radiation from the oven.

Thus, the tube 26 can be moved longitudinally inside the chamber 25 thanks to these displacement means 29, which makes it possible to modify the opening angle of diffusion of the droplets or slabs of sludge. Such longitudinal displacement (back and forth movement) also allows the chamber to be cleaned if necessary. These displacement means consist, for example, of a wheel connected to the tube 26 to be used manually, or else a motorized device for driving the tube, advantageously with position memorization. According to the back-and-forth movement, the diffuser, in the lower lower position, protrudes from the nozzle, which allows effective cleaning of the chamber.

According to the invention, the injection means 22 are mounted on orientable means 30. These means 30 consist of a ball joint 35 on which the injection body 25 is mounted and telescopic rods for adjusting the inclination of the injection body 25 relative to the hearth 4 of the furnace. The means 30 make it possible in particular to precisely regulate the positioning of the injection means before the implementation of the oven and thus to optimize the operation of these.

The outlet nozzle 33, which is here profiled, does not completely pass through the wall 24 of the furnace, which makes it possible to avoid heating and drying of the sludge to be injected by thermal transfer into the injection body 25. The man of the trade may provide a more or less high angle for the injection nozzle 45.

The spray chamber 23 is crossed by a tube 26 for injecting air (or other gas) under pressure, the end of which is provided with a diffuser 27 situated in the region of the nozzle 33.

The gas injection tube 26 is connected, via a valve 31 to means (not shown) for supplying gas under pressure. The injection body 25, forming the chamber 23 inside which the gas injection tube 26 is placed, is connected, via a valve 32, to the positive displacement pump 20.

When the sludge flows into the chamber 23, it is sprayed at the outlet, in the form of fine droplets or pancakes, thanks to the gas leaving the diffuser 27.

The gas injection tube 26 may comprise a protective sheath 34, limiting the abrasion of this tube, and the diffuser may comprise a chamfer, preventing the attachment of any tows contained in the sludge.

According to FIGS. 3 and 4, the diffuser 27 has, for example, seven equidistant orifices 41 inclined by 5 ° on two axes making it possible to give the gas a helical movement making it possible to fractionate the sludge more effectively.

• la position du tube d'injection de gaz 26 dans le corps d'injection 25 ;
• la pression du gaz d'injection et son débit ; et
• l'inclinaison des moyens d'injection 22 par rapport à la sole du four.

The overall adjustment of the injection means 22 in particular during their installation in a particular furnace (as regards its shape and dimensions), and for a particular quality of sludge, therefore consists in determining:

• the position of the gas injection tube 26 in the injection body 25;
• injection gas pressure and flow rate; and
• the inclination of the injection means 22 relative to the bottom of the oven.

One can for example make a first cold setting, with a control of the angle of the spray cone at the outlet of the injection means, so that the droplets or slabs of mud do not strike the side walls of the oven while dispersant over a large area of the incineration hearth. The position of the tube, the air pressure and the inclination of the injection means corresponding to this first adjustment are then memorized. Then, a second, finer adjustment is carried out, when the oven is hot, possibly by a visual control of the injection and / or by a control of the rate of unburnt in the bottom ash and the fly ash.

In an alternative embodiment, one can imagine varying the inclination of the injection means during the spraying process. It is thus possible to carry out a transverse and longitudinal cyclic sweeping of the sludge projection area (and / or the cleaning fluid), which makes it possible to work on a larger incineration surface, or which makes it possible to distribute in space and over time the sludge load (or the cleaning fluid) assigned to the different zones of the incineration hearth.

• on ouvre la vanne 31 d'arrivée de gaz, jusqu'à l'obtention d'une valeur nominale de pression et/ou de débit de gaz ;
• on ouvre la vanne 32 d'arrivée de boues ;
• on met en marche la pompe volumétrique 20 (d'amenée de boues).

The method of starting the injection system comprises the following successive steps:

• the gas inlet valve 31 is opened, until a nominal pressure and / or gas flow value is obtained;
• the sludge inlet valve 32 is opened;
• the positive displacement pump 20 (slurry supply) is started.

• on arrête la pompe volumétrique 20 ;
• on ferme la vanne 32 d'arrivée de boues ;
• on ferme partiellement la vanne 31 d'arrivée de gaz jusqu'à l'obtention d'une faible valeur de pression de gaz (et non pas une valeur nulle), de façon à prévenir tout risque de détérioration des moyens d'injection 22 par rayonnement.

The injection system shutdown process includes the successive steps following:

• the positive displacement pump 20 is stopped;
• the valve 32 for sludge arrival is closed;
• the gas inlet valve 31 is partially closed until a low gas pressure value is obtained (and not a zero value), so as to prevent any risk of deterioration of the injection means 22 by radiation.

The operation of the system during start-up and shutdown is then fully automatic. It is clear however that these methods can also be carried out manually.

It should be noted that the injection body 25 may include an inlet 40 for a cleaning fluid (for example rinsing water), associated with an inlet valve 38 which can also be controlled by the automatic control means 37 By placing the inlet 40 for cleaning fluid at the level of the inlet 28 for supplying sludge, it is possible to clean the entire spray chamber 23, before the cleaning fluid is discharged through the nozzle. Injection case 33. In this case, the stopping method comprises an additional step, preceding the step of partially closing the air inlet valve 3, and consisting, for a predetermined period, in opening the valve 38 cleaning fluid inlet.

By connecting the means 29 for moving the diffuser to control means (corresponding here to the automatic control means 37), the cleaning of the injection body 25 can also be carried out automatically (as soon as a jam is detected, or periodically , Prevention).

The system may also include means for controlling the internal temperature of the furnace, so as to allow regulation of the operation of the furnace, that is to say controlling the flow of sludge at this temperature.

This process for regulating the operation of the oven, which can be carried out manually or else be controlled by the automatic control means 37 (if these receive the internal temperature information of the oven), comprises a step of controlling the sludge flow at internal oven temperature.

• nul lorsque la température interne du four est inférieure à une température minimale prédéterminée de fonctionnement du four (850°C par exemple) ;
• égal à une valeur maximale (1600 kg de boues humides / h par exemple) lorsque la température interne du four est supérieure à une valeur haute prédéterminée de fonctionnement du four (1100°C par exemple).

For example, this control step is such that the sludge flow is:

• zero when the internal temperature of the oven is lower than a predetermined minimum operating temperature of the oven (850 ° C for example);
• equal to a maximum value (1600 kg of wet sludge / h for example) when the internal temperature of the oven is higher than a predetermined high operating value of the oven (1100 ° C for example).

• un débit de 400 kg de boues humides / h pour une température de 900°C ;
• un débit de 1200 kg de boues humides / h pour une température de 1000°C, ce qui correspond au régime nominal pour des boues entre 20% et 30% de siccité (ce débit pouvant être modifié en fonction de la siccité).

In order to improve the quality of the servo-control, it is also possible to provide pairs of intermediate values, and in particular for example:

• a flow rate of 400 kg of wet sludge / h at a temperature of 900 ° C;
• a flow rate of 1200 kg of wet sludge / h at a temperature of 1000 ° C, which corresponds to the nominal speed for sludge between 20% and 30% dryness (this flow rate can be modified depending on the dryness).

The quantities of sludge that can be injected into a mixed household waste / sludge oven depend on local constraints. Thus, for an oven with an incineration capacity of 100 T / day of household (wet) waste, provision can be made to incinerate 10 to 20% of dehydrated sludge between 20% and 30% of dryness, i.e. 10 to 20 T / day of wet sludge. These values are however only illustrative, and can be revised up or down, depending in particular on the main objective of the oven. In certain cases, it is possible to go as far as providing a mass flow rate of sludge of the order of that of household waste, or even higher.

Prototypes of the injector were produced and tested, and made it possible to validate the effectiveness of the invention. The prototype presented a spraying chamber with an internal diameter of approximately 80 mm, over a useful length of approximately 300 mm. The injector outlet nozzle had a diameter of the order of 50 mm. It was possible to spray on site with this injector mud flow rates of the order of 400 to 1600 kg / h, by injecting air at a flow rate of 20 to 100 Nm³ / h, under a pressure of 1 to 3 bars about.

Claims (16)

System for injecting sludge or other pasty waste of the same type, to be incinerated in an incineration oven, said oven comprising an incineration hearth (4) onto which household waste is dumped in order to be incinerated, and comprising means (22) for injecting said sludge to be incinerated in the furnace, arranged essentially above said incineration hearth (4) so as to allow a sludge supply to said hearth at least in part by gravity, said said injection means (22) being provided with means for spraying the sludge during their injection into the furnace, characterized in that said injection means (22) comprise an injection body (25) forming a spraying chamber ( 23) comprising a sludge supply inlet (28), and an outlet nozzle (33) for injecting the sludge into the furnace, said chamber (23) being traversed by a tube for injecting pressurized gas ( 26), the end of which is provided a diffuser (27) in the region of the nozzle (33) of said chamber (23), said pressurized gas injection tube (26) cooperating with displacement means (29) of the diffuser (27) by relative to the injection nozzle (27) of the chamber (23), so as to allow adjustment of the spraying of sludge and / or the cleaning of said chamber. System according to claim 1, characterized in that said incineration hearth (4) comprises at least two successive distinct zones, namely a combustion zone (6) and a finishing zone (7), and in that said means injection (22) are located essentially above said combustion zone (6). System according to claim 1, characterized in that said incineration hearth (4) comprises at least three successive distinct zones, namely a drying zone (5), a combustion zone (6) and a finishing zone (7 ), and in that said injection means (22) are situated essentially above said drying zone (5) and said combustion zone (6). System according to one of claims 1 to 3, characterized in that said injection body (25) is mounted on a ball joint (35) and cooperates with a telescopic rod (36) for adjusting the inclination of said body of injection (25) by rotation around said ball joint (35). System according to claim 4, characterized in that said injection tube (26) is covered at least partially with a protective sheath (34). System according to any one of claims 1 to 5, characterized in that said chamber (23) is provided with a cleaning fluid inlet (40). System according to claim 6, characterized in that said cleaning fluid inlet (40) is located at the level of the sludge inlet (28), so as to allow cleaning of the entire chamber ( 23) before the evacuation of the cleaning fluid by the injection nozzle (33). System according to any one of Claims 1 to 7, characterized in that it comprises means (39) for controlling the internal temperature of the furnace, controlling the flow of injected sludge. System according to any one of Claims 1 to 8, characterized in that it comprises control means (29) for a reciprocating movement of the gas injection tube (26) in the spraying chamber ( 23), in the event of the chamber jamming with mud. System according to any one of claims 1 to 9, characterized in that it comprises means for varying the inclination of the injection means during the very process of spraying, so as to allow a cyclic scanning of the sludge and / or cleaning fluid projection area. System according to any one of Claims 1 to 10, characterized in that the said injection means cooperate with a sweeping air supply duct (50) preferably provided near the said diffuser. Incineration furnace provided with a system according to any one of Claims 1 to 11. Mixed incineration furnace for household waste and sludge provided with a system according to any one of Claims 1 to 11. Method of operating a system according to any one of Claims 6 to 11, characterized in that it comprises an operating cycle starting with a start-up phase in which the supply of sludge to the spraying chamber (23) is carried out after establishment of a nominal regime pressure gas injection, and ending with a shutdown phase in which the interruption of the supply of sludge to the spraying chamber precedes the establishment of a low pressure gas injection regime ,
and in that said stopping phase is preceded by a cleaning phase of the spraying chamber, in which a cleaning fluid passes into the spraying chamber and is discharged by the nozzle for injecting sludge into the furnace. Use of a system according to any one of claims 1 to 11 for the incineration of sludge from a water treatment station. Use according to claim 15, characterized in that said sludge undergoes a preliminary treatment of at least partial dewatering before their injection for incineration.

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