EP0246147A1 - Incinerator for urban waste - Google Patents

Abstract

The incinerator comprises a combustion chamber (14) comprising a lower hearth (40) and an outer wall (34), a feeder (24-32) of the materials to be incinerated, an insufflation box (42) d primary air (44, 46) in the center of the hearth, and a secondary air circuit (50, 52) comprising insufflation nozzles (48) distributed around the periphery of the combustion chamber. At least part of said nozzles is formed of pairs of nozzles (48a, 48b) oriented at an angle above and below a horizontal plane and at a second angle on either side of a diametrical vertical plane .

Description

The present invention relates to an incinerator intended for the incineration of urban waste, in particular for capacities of between 1 and 3 tonnes / hour, such that the gases discharged include polluting emissions in quantities lower than the current installations, and to the limits imposed by the new regulations.

Typically, the incinerators commonly used consist of a hearth in the form of a chamber comprising a hearth, or lower grid under which is disposed an ash box, and an outer wall of refractory material. A feed device opens from the outside towards the chamber to introduce residues to be incinerated as the combustion progresses.

As complete combustion as possible is ensured by blowing primary air below the hearth, and secondary air above the mass in combustion, to ensure complete oxidation of the combustion gases and the solid residues they entail .

In some cases, part of the secondary air is injected into the combustion mass from the periphery of the combustion chamber, always with the aim of making combustion as complete as possible.

However, despite the precautions taken, it can be seen that the rate of gaseous or solid unburnt materials often remains clearly beyond regulatory limits.

In order to reduce this unburnt rate to a level as low as possible, and compatible with the regulations in force, the present invention provides an incinerator comprising a combustion chamber comprising a bottom or grid below which is disposed a ash and an outer wall of refractory material, a device supply for introducing materials to be incinerated, a primary air supply circuit comprising an insufflation box disposed substantially in the center of the hearth, and a secondary air supply circuit comprising insufflation nozzles distributed around the periphery of the combustion chamber and arranged along at least one stage included in the height of the combustion mass, characterized in that at least part of said nozzles is formed of pairs of nozzles oriented at a predetermined angle, l one above and the other below a horizontal plane, as well as at a second predetermined angle on either side of a diametral vertical plane of the combustion chamber.

Thus, thanks to the invention the secondary air is blown in jets directed both upward and downward relative to the horizontal and directed on one side and the other relative to the vertical, which produces multiple turbulences of the secondary air and an excellent contact between this secondary air and the solid and gaseous elements of the mass in combustion, therefore an even more complete combustion.

In addition, the device also includes another secondary air insufflation stage comprising insufflation nozzles distributed around the periphery of the combustion chamber and arranged in at least one stage above the height of the mass. in combustion.

These insufflation nozzles can be single and simply directed radially, or even consist of double nozzles having the same particulars of orientation as above. In both cases, excellent contact is obtained between the secondary air and the combustion gases escaping from the combustion mass, which allows better oxidation of these combustion gases and a reduction complementary to the unburnt rate.

The invention further provides a reaction chamber, placed above the combustion chamber, into which the combustion gases are admitted in an ascending column substantially in the center of said reaction chamber and into which air is blown reaction costs, following a helical annular flow descending around the ascending column of combustion gases.

In this way, multiple turbulences are created between the ascending column of combustion gases and the descending annular flow of fresh air, by means of which a complementary oxidation of the unburnt substances present in the combustion gases is obtained and a significant reduction in the temperature of the combustion gases before they are released to the atmosphere. As an additional advantage, it will be noted that the outer wall of the reaction chamber is cooled by the annular flow of fresh reaction air, which is blown in by a corresponding fan, which makes it possible to produce this outer wall in less material expensive while ensuring sufficient longevity.

• - la figure 1 est une vue latérale d'un incinérateur conforme à la présente invention ;
• - la figure 2 est une vue en coupe agrandie de la partie inférieure, ou chambre de combustion, de l'incinérateur de la figure 1 ;
• - la figure 3 est une vue en coupe agrandie de la partie supérieure, ou chambre de réaction, de l'incinérateur de la figure 1 ; et
• - la figure 4 est une vue schématique en perspective de l'agencement des buses d'insufflation d'air secondaire dans la chambre de combustion.

Other details and advantages of the invention will appear clearly on reading the description which follows, with reference to the appended drawings, in which:

• - Figure 1 is a side view of an incinerator according to the present invention;
• - Figure 2 is an enlarged sectional view of the lower part, or combustion chamber, of the incinerator of Figure 1;
• - Figure 3 is an enlarged sectional view of the upper part, or reaction chamber, of the incinerator of Figure 1; and
• - Figure 4 is a schematic view in perspective of the arrangement of the secondary air insufflation nozzles in the combustion chamber.

The incinerator, represented as a whole in FIG. 1, has a general cylindro-conical shape with a vertical XX axis and is successively composed, from bottom to top:
- a hopper 12 for receiving ash
- a combustion chamber 14
- a combustion chamber 16, and
- a reaction chamber 18.
The structure and operation of each of these components will be explained later. It will be noted at this stage that this staged construction of the incinerator makes it a modular assembly which can be built section by section. This constitutes an appreciable advantage for maintenance or possible repairs.

The entire incinerator is supported by a frame 20, so as to provide an elevation between the ground and the lower mouth of the ash reception hopper. The frame also has the role of supporting a certain number of gateways 22 for access to the different levels of the incinerator.

Next to the incinerator are provided a storage hopper 24, a loading hopper 26 and a feed pusher 28.

The waste to be incinerated is received in the storage hopper 24 where a conveyor 25 lifts it up to the loading hopper 26.

At the bottom of the latter is connected a vertical chute 27, controlled by a motorized hatch 30, which opens into a feed chute 29, in which the feed pusher 28 moves.

The feed chute 29 opens at the top of the combustion chamber, where it is closed by a tilting loading door 32.

Referring now to FIG. 2, it can be seen that the combustion chamber 14 has a cylindrical wall 34, made of refractory material, and an upper arch 36 providing a central opening 38 for the passage of combustion gases to the transfer chamber 16 as will be seen later.

At the base of the combustion chamber, a hearth grate 40 receives the combustion materials introduced by the pusher 28. This grate is preferably formed of oscillating bars so as to allow the evacuation of the ashes and bottom ash to the receiving hopper ashes. To simplify the figure, the bar oscillation mechanism has been omitted.

In the center of the hearth grate is disposed a blowing box 42 of primary air, which is supplied by means of a primary fan 44 via a duct 46 passing through the upper part of the ash receiving hopper, and which diffuses primary air within the combustion material, substantially in the center of the chamber and in the manner of a sprinkler, that is to say in all directions and as uniformly as possible. Preferably, one will use to make this conduit 46 one of the hollow rectangular sections forming part of the support structure of the entire incinerator.

Above the level of the grate and on several different stages are provided nozzles 48 for secondary air insufflation supplied by a secondary fan 50 via a duct 52 plated on the external wall of the combustion chamber, ensuring the distribution of air to annular collectors 62 supplying the aforesaid nozzles.

In the example illustrated, there are four stages of secondary air insufflation, that is, from the bottom to the high, three stages 54, 56 and 58 intended to breathe secondary air into the combustion material itself and put into service according to the height of the latter, then a stage 60 intended to breathe secondary air above the material in combustion within the combustion gases.

As illustrated in detail in FIG. 4, each of the stages of nozzles, at least stages 54, 56, 58 is formed by a series of nozzles distributed around the periphery of the combustion chamber, and these nozzles, or at the very at least part of them, are formed of pairs of nozzles 48a, 48b, oriented at a predetermined angle a relative to the horizontal plane, one of the nozzles 48a being oriented above this horizontal plane and the other nozzle 48b being oriented below this horizontal plane. In addition, the nozzles are oriented by a second predetermined angle b on either side of the diametrical vertical plane passing through the nozzle, that is to say that one of the nozzles is oriented by an angle b d 'one side of this diametrical plane, and the other nozzle is oriented by an angle b on the other side.

As a variant, only one nozzle out of two is formed of a pair of nozzles, as indicated above, the other nozzles being directed only radially.

The multiple jets of secondary air thus blown into the material in combustion cause, because of their particular orientations, an optimal penetration of the secondary air within the material in combustion and therefore a combustion as complete as possible while minimizing the rate of 'unburnt in the combustion gases which rise above the combustion mass.

The height of the latter is detected by means of a detector and a control device uses this information in order to activate the various stages of secondary air insufflation. successively as a function of this height, by means of valves 55, 57, 59 (Fig. 1).

The fourth stage of secondary air insufflation also consists of a series of nozzles distributed around the periphery of the combustion chamber which are also formed of pairs of nozzles 60a, 60b.

These nozzles can, like the previous ones, have the same characteristic orientations, namely:
- an angle a above / below the horizontal plane
- an angle b on one side / on the other of the diametral vertical plane
so as to cause multiple turbulences and an intense mixing of the secondary air thus blown with the combustion gases, which completes the combustion of the unburnt present in these gases.

As a variant, these pairs of nozzles can be directed in the horizontal plane (the angle a being equal to zero) and oriented by an angle b on either side of the vertical diametral plane, and thus producing an air curtain secondary above the mass in combustion. This curtain has the effect of constituting an effective barrier against the entrainment of solid particles.

According to another variant, the nozzles 60 are unique and directed only radially.

Preferably, in the context of the invention, the angles a and b are equal to or less than 15 degrees.

The conduits 62 (FIGS. 2 and 4) serving each of the stages of nozzles form rings encircling the combustion chamber and located in the thickness of the refractory material which constitutes the wall. This allows the wall to cool thanks to the secondary air circulation and the latter to be heated before it is blown into the combustion.

At the sum of the combustion chamber, the outlet opening 38 of the combustion gases is surrounded by a focusing collar 64, of frusto-conical shape, the angle of the apex c of which is such that the apex is located on the axis XX substantially at the base of the reaction chamber which will be described in detail later.

Thanks to this flange 64, the combustion gases are grouped, or focused, in the form of an ascending column 66 which passes through the transfer and exhaust chamber 16, causing at its periphery a small quantity of the gases circulating on the around this chamber, and therefore their recycling in the reaction chamber.

The reaction chamber 18 (Figure 3) also has a frusto-conical shape, with an apex angle d of the order of 14 to 24 degrees (Figure 3), preferably between 15 and 18 degrees.

The large base, located at the lower end 68, corresponds to the top of the transfer and exhaust chamber 16, and the small base, located at the upper end 70, is capped by a circuit 72 for intake of reaction air.

The reaction air intake circuit consists of a fan 74 and an intake ring 76, of annular shape and internally equipped with a series of inclined blades 78, so that the air reaction is introduced in the form of a descending annular flow "glued" to the outer wall 80 of the reaction chamber and animated by a helical and centrifugal movement having the effect of cooling the lower wall 70 of the reaction chamber and on the other hand to create a depression in the axial zone which sucks in the large base of the cone part of the blown air and the column of gases and fumes from the combustion chamber.

Numerous turbulences 86 are created between these two streams which ensure a thorough mixing between them and additional oxidation of unburnt materials possibly still present in the combustion gases, as well as a significant reduction in the temperature of the latter. As an illustrative example, the temperature of the combustion gases leaving the combustion chamber is of the order of 900 to 950 degrees C and the temperature leaving the reaction chamber, that is to say say in the annular zone on the periphery of the base thereof, is of the order of 750 to 800 degrees C.

For the adjustment of the speed of supply of fresh reaction air, the intake circuit 72 includes an adjustment plunger 73, in the form of a cylinder closed at its lower end and which can be lowered more or less in the intake crown.

At the base of the reaction chamber 18, the wall 80 has a short, approximately cylindrical section 81, so that the flow from the reaction air / combustion gas mixture is slightly bent vertically in the direction of the rising gas column. combustion in order, on the one hand to properly confine the latter in the central zone of the combustion chamber 16, and on the other hand to create in this zone some turbulence of mixing and oxidation of the combustion gases of the column.

The mixture leaving the reaction chamber 18 finally crosses the combustion chamber 16 in the annular zone 88 surrounding the column of combustion gas 66. This mixture flows in a rotating movement in the same direction as the helical movement of air reaction, then escapes through an orifice 90 tangential from where it is sucked by an extraction and rejection fan which has not been shown for simplification.

The combustion chamber has a bi-conical shape, namely: an upper frustoconical portion 92 which widens downwards from the large base of the reaction chamber, then a lower frustoconical portion 94 which narrows towards the bottom to an area surrounding the focusing collar 64 at the top of the combustion chamber. Advantageously, as illustrated in FIG. 3, the upper edge 65 of the focusing flange 64 and the upper edge 91 of the tangential orifice 90 will be placed approximately at the same level.

This therefore determines in the annular zone 88 a flow of the reaction air / combustion gas mixture first of all diverges with expansion of the mixture and formation of turbulences which increase the residence and reaction times, then a slightly convergent flow by reflection on the lower frusto-conical part which causes interface contact with the riser coming from the combustion chamber.

In addition, in the vicinity of the lower part of the combustion chamber, the mixture which is reflected on the lower frusto-conical part is again deflected on the external surface of the flange, which further increases the mixing of the gas mixture before its final evacuation. through port 90.

The materials used for the different parts of the incinerator will, for example, be as follows:

For the operation and control of the incinerator, of course, all the necessary mechanisms and detectors will be provided, as well as the prescribed safety sampling installations.

Optionally, driving can be done manually or automatically. The automatic control device can be restricted to continuous operation, the start-up and shutdown phases being controlled manually.

• a) le fonctionnement du poussoir d'alimentation sera déterminé afin de conserver une hauteur constante de la masse dans la chambre de combustion ;
• b) le nombre d'étages d'insufflation d'air secondaire mis en service correspond à la hauteur de la masse en combustion ;
• c) le variateur de vitesse du ventilateur secondaire est commandé en fonction de la température des gaz de combustion, pour maintenir cette dernière dans une plage de 900 à 950 degrés C pour éviter la fusion des verres et mâchefers dans la masse en combustion ;
• d) le variateur de vitesse du ventilateur d'admission d'air de réaction est commandé en fonction de la température des gaz dans la chambre de comburation pour maintenir cette dernière dans une plage de 750 à 800| C et favoriser la pyrolyse et la combustion complète des imbrûlés gazeux ou solides dans les gaz de combustion ;
• e) une détection de la teneur en poussières des gaz à l'échappement, au moyen d'un opacimètre, permet d'agir sur le ventilateur d'air de réaction dans le sens d'un accroissement du débit, ainsi que sur le circuit d'air secondaire par diminution du débit et mise hors service d'un ou deux étages.

In particular, whether driving is manual or automatic, there are a few important points:

• a) the operation of the feed pusher will be determined in order to maintain a constant height of the mass in the combustion chamber;
• b) the number of stages of secondary air insufflation put into service corresponds to the height of the mass in combustion;
• c) the secondary fan speed controller is controlled according to the temperature of the combustion, to maintain the latter in a range of 900 to 950 degrees C to avoid the melting of glasses and bottom ash in the mass in combustion;
• d) the speed controller of the reaction air intake fan is controlled as a function of the temperature of the gases in the combustion chamber to maintain the latter in a range of 750 to 800 | C and favor the pyrolysis and complete combustion of unburnt gases or solids in the combustion gases;
• e) detection of the dust content of the exhaust gases, by means of an opacimeter, makes it possible to act on the reaction air fan in the direction of increasing the flow rate, as well as on the circuit secondary air by reducing the flow and putting one or two stages out of service.

It will be noted from the above description that the incinerator allows semi-continuous operation, requiring a short-term shutdown (about 2 and a half hours per day) for the extraction of bottom ash and re-ignition. This ignition does not require any specific device and is carried out manually using paper and cardboard, and a minimal layer of waste. This type of incinerator is considered autonomous and works by self-combustion.

Claims (11)

1. Incinerator comprising a combustion chamber (14) comprising a bottom or grid (40) under which is disposed an ash box (12) and an outer wall (34) of refractory material, a supply device (24- 32) intended to introduce materials to be incinerated, a primary air supply circuit (44, 46) comprising an insufflation box (42) disposed substantially in the center of the hearth, and an air supply circuit secondary (50, 52) comprising insufflation nozzles (48) distributed around the periphery of the combustion chamber and arranged in at least one stage (54, 56, 58) included in the height of the mass in combustion, characterized in that at least part of said nozzles is formed of pairs of nozzles (48a, 48b) oriented at a predetermined angle (a), one above and the other below a horizontal plane, as well as a second predetermined angle (b) on either side of a diametral vertical plane of the combustion. 2. Incinerator according to claim 1, characterized in that it comprises at least two stages (54, 56) of secondary air blowing nozzles included in the height of the mass in combustion and of the valves (55, 57) controlling the secondary air blowing by said stages as a function of the height of said mass in combustion. 3. Incinerator according to either of Claims 1 and 2, characterized in that it further comprises a stage (60) of secondary air insufflation nozzles situated above the mass in combustion. 4. Incinerator according to any one of claims 1 to 3, characterized in that said predetermined angles (a) and (b) are between 0 and 15 degrees. 5. Incinerator according to any one of claims 1 to 4, characterized in that it comprises a reaction chamber (18), placed above the combustion chamber (12), into which the combustion gases are admitted in an ascending column (82) substantially in the center of said reaction chamber and into which fresh reaction air is blown, in a descending helical annular flow (84) around the ascending column of combustion gas. 6. Incinerator according to claim 5, characterized in that the reaction chamber comprises an outer wall (80) frustoconical whose large base is located at the lower end (68) and having a predetermined angle at the top (d), understood between 14 and 24 degrees. 7. Incinerator according to claim 6, characterized in that it comprises an intake circuit (72) of reaction air, located at the upper end (70) of said reaction chamber (16), composed of a fan (74) and an intake ring (76) of annular shape and covering said reaction chamber. 8. Incinerator according to claim 7, characterized in that said intake ring (76) is equipped with a series of inclined blades (78), so that the downward annular flow of reaction air is animated by 'a helical movement. 9. Incinerator according to any one of claims 5 to 8, characterized in that the combustion chamber comprises at its upper part a focusing flange (64) of frustoconical shape whose angle at the top (c) is such that the top is located substantially at the base of said reaction chamber (18). 10. Incinerator according to any one of claims 5 to 9, characterized in that it comprises a combustion chamber (16) interposed between the combustion chamber (14) and the reaction chamber (18) and traversed in its center by the riser of combustion gases from the combustion chamber to the reaction chamber, and at its periphery by the downward annular flow of reaction air, mixed with the combustion gases, coming from the reaction chamber. 11. Incinerator according to claim 10, characterized in that the combustion chamber (16) is formed of an upper frusto-conical portion (92) which widens downwards from the base of the reaction chamber (18) , then a lower frusto-conical portion (94) which tapers to the top of the combustion chamber (14) and in which is formed a tangential exhaust orifice (90).

Images