EP0326442B1 - Ash pit for a fireplace of a boiler with an easy-to-clean ash extraction box - Google Patents

Abstract

An ashbox for the hearth of a furnace adapted to burn solid fuel, descending along in inclined grate as it burns. The ashbox comprises an extractor chamber having a concave bottom which is part-cylindrical with horizontal generatrices. This chamber is normally filled with water to a level below the upper edge of the chamber. A vertical clinker well terminates at a lower lip below the upper edge of the chamber and is immersed in the water in the chamber. A scraper blade is reciprocated perpendicularly to the generatrices of the concave bottom. An inclined wall merges at its lower end with the concave bottom of the chamber and has an overflow at its upper end above the normal level of the water in the chamber. The arrangement is such that the scraper blade pushes ash up over the overflow lip. The extractor chamber is in two parts and can be opened by relative displacement of these parts to provide vertical access to the ash well. One part of the chamber is a tilting part comprising the concave bottom and the scraper blade.

Description

The invention relates to an ashtray for a solid fuel boiler hearth, such as urban waste, where the fuel, loaded in the upper part of an inclined grate, descends along this grate to a downstream end during its combustion, this ashtray comprising, below the downstream end of the grate, a vertical well, known as bottom ash, which ends with a lower lip in an extraction box filled with water below an upper edge, up to a level higher than that of the lip of the well, the box comprising a concave bottom in a portion of cylinder with horizontal generatrices equipped with a scraper blade carrying on the bottom according to a generator and movable back and forth perpendicular to the generators for discharging the ashes on a wall in a rising inclined plane, from a connection at the bottom along a generator to a discharge edge at a level higher than that of the water in the he box, from which the ashes are poured into a hopper. Such an ashtray is known from US-A 4,520,738.

This conventional arrangement allows the ash to be evacuated practically continuously without disturbing the fuel combustion regime, the water seal in the box making it possible to isolate the hearth from the outside atmosphere, so that the combustion gases are not diverted from their circulation in the boiler towards the flue gas exhaust pipes, if the hearth is in overpressure relative to the external atmosphere, and that the combustion air intake under the grate is not short-circuited by an air inlet through the ashtray, if the fireplace is in depression compared to the outside atmosphere.

Furthermore, by falling into the water, the hot ashes are cooled, and the incandescent clinkers in particular are extinguished and possibly disintegrated by thermal shock.

It is recalled that generically called ashes, everything that reaches the downstream end of the grate, whether it is mineral residue, unburnt material, non-combustible elements such as metal parts, and, more particularly, partially vitrified bottom ash or ash aggregates.

It happens, and this is relatively frequent with urban waste, that large noncombustible objects are mixed with solid fuel when the grid is loaded; in urban waste, we find, in a non-exceptional way, bicycle frames, stove elements or household electrical appliance machines that are no longer in use; there are also tree stumps, where the soil trapped between the roots protects these roots from complete combustion, and remains in a block state.

These foreign objects can get stuck in the box, and in any case do not lend themselves to raising the wall in plan; a packing jam occurs.

To remedy this, it is then necessary to stop the fireplace and empty the box of its water, then to extract the cause of the jam, either by inspection doors of the box, or along the inclined wall, by dividing or cutting up the object that got stuck on the spot when necessary.

These are difficult operations, extremely painful, and likely to cause a relatively long shutdown of the boiler hearth.

Document FR-A-1 477 877 has proposed to provide the lip of the bottom ash well with a wall mounted hanging with a counterweight at its lower part, so that a large foreign body, pushed by the scraper blade can release by lifting the hanging wall towards the wall in an inclined plane.

This arrangement makes it possible to avoid a certain number of jams; in return, the water seal may be insufficient.

In addition, this arrangement does not avoid jams if the foreign object gets caught between a wall of the box and the scraper blade, or if this object cannot be removed by the wall in an inclined plane. In this case, the difficulties mentioned above are repeated.

According to this document FR-A-1 477 877, it is planned to accelerate the return of the movable wall using a spring or the like, to prevent too much combustion gas and hot ashes from escaping while the foreign object is released; but this spring increases the risk of jamming.

The object of the invention is to allow efficient cleaning, whatever the shape of the foreign body which causes the jam, by reducing to a minimum the intervention time and disturbances of the operating regime of the boiler hearth.

The invention proposes in this sense an ashtray for a solid fuel boiler hearth, such as urban waste, where the solid fuel, loaded in the upper part of an inclined grid descends along this grid to a downstream end during its combustion, this ashtray comprising, below the downstream end of the grate, a vertical well, known as bottom ash, which ends with a lower lip in an extraction box filled with water below an upper edge up to '' at a level higher than that of the well lip, the box comprising a concave bottom in a portion of cylinder with horizontal generators equipped with a scraper blade carrying on the bottom according to a generator and movable back and forth perpendicular to the generators for discharging the ashes on a wall in an inclined rising plane, from a connection at the bottom along a generator to a discharge edge at a level higher than that of water u in the box, from which the ashes are poured into a hopper, characterized in that the box is opening and consists of two adjoining parts according to a sealed joint surface in the closed position, a fixed part comprising the wall in inclined plane and the upper edge of the box, and a tilting part comprising the bottom and the scraper blade and pivotally mounted about an axis parallel to the bottom cylinder generators to an open position where the plumb of the lip bottom ash is cleared.

When a blockage occurs, the activity of the hearth is reduced so that this hearth is in slight depression compared to the external atmosphere. and that the unloading of the ashes from the grate is substantially stopped. The box is emptied of most of the water it contains, then the box is opened above an appropriate receptacle; the wet ashes and the foreign body which caused the jam generally clear and fall into the receptacle, since this foreign body is offered a substantially vertical passage at least equal to the passage it has passed through the bottom ash pit. If, however, an oblong foreign body has become stuck, the opening of the box allows easy access to intervene and clear the jam.

Preferably, the joint surface extends along a dihedral with two half-planes on either side of an edge parallel to the generators of the bottom cylinder and situated substantially at water level in the box on the side of the well closest to the wall in inclined plane, the dihedron being protruding for the tilting part and returning for the fixed part.

This arrangement makes it possible to increase the surface of the side walls of the tilting part of the box, in which opening inspection doors have been arranged in order to be able to carry out certain interventions in the box. The surface of these doors can thus be increased.

The preferred arrangement of the dihedral joint surface is that in which one of the half-planes of the dihedral is directed downwards substantially perpendicular to the wall in an inclined plane to pass substantially through the generatrix connecting the bottom to this wall, while the Another half goes up from the edge to the upper edge of the box, which it cuts on the side of the well farthest from the wall in an inclined plane.

The fixed and tilting parts of the box can be joined by flanges extended in the half-planes of the dihedral towards the outside, with the interposition of a seal. Locking means are provided associated with the flanges for tightening the joint. Advantageously, these locking means are operated by hydraulic jacks, which can be controlled remotely.

According to a preferred arrangement of the invention, the pivot axis of the tilting box part is located above the upper box edge on the side of the bottom ash well farthest from the wall in inclined plane. For the opening of the box to be possible, it is necessary that no point of the dihedral joint of the tilting part has a trajectory which would pass through the dihedral joint of the fixed part. The aforementioned position of the joint dihedral is the most favorable.

According to a preferred arrangement, the scraper blade is fixed to the end of push arms coupled to cranks wedged on a scraper shaft disposed above the water level in the box parallel to the bottom generators, and on the side from the bottom clinker well furthest from the wall in an inclined plane, the scraper shaft being driven back and forth by at least one hydraulic cylinder disposed approximately horizontally outside the box, between a joint on the fixed part of the box and a crank pin at the end of a control crank wedged on the scraper shaft, with a setting, relative to the cranks where the thrust arms are harnessed, such as, the retracted cylinder, the scraper blade is farthest from the wall in an inclined plane. The cylinder thus works in expansion to push the ash on the wall in an inclined plane, with the hydraulic pressure applied on the side of the cylinder piston which has the maximum effective surface, or side opposite to the cylinder rod.

• Le manchon de manivelle de commande ayant une trajectoire qui passe entre l'axe d'arbre de racleur et l'axe de pivotement de la partie basculante de caisson, des moyens de verrou, disposés entre arbre de racleur et partie basculante du caisson sont aptes, en état actif, à bloquer la rotation de l'arbre de racleur, avec la lame racleuse au plus loin de la génératrice de fond où se raccorde la paroi en plan incliné.

In addition, this arrangement, together with the position of the pivot axis of the tilting part above the upper edge of the box, as defined above, allows a significant development as follows:

• The control crank sleeve having a trajectory which passes between the scraper shaft axis and the pivot axis of the tilting part of the box, latch means, arranged between scraper shaft and tilting part of the box are suitable , in active state, to block the rotation of the scraper shaft, with the scraper blade as far as possible from the bottom generator where the wall is connected in an inclined plane.

Normally, the latch means are in the passive state and the expansion of the jack pushes the ashes onto the wall in an inclined plane. If a jam occurs, the cylinder is retracted to bring the scraper blade as far as possible from the connection of the bottom with the wall in an inclined plane and the locking means are put in the active state. The water contained in the box is drained and the tilting part is separated from the fixed part of the box. Then the expansion of the jack, applied to the fictitious crank arm which extends from the pivot axis of the tilting part to the crank pin of the control crank, causes the opening of the box.

In a preferred arrangement, the latch means comprise, on the scraper shaft outside the box, a radial finger, and, on the tilting part, a stop against which the radial finger comes to bear when the scraper blade is at the furthest from the generator for connecting the bottom to the wall in an inclined plane, and a pusher actuated by a cylinder aligned in the direction of the stop with an extended position, corresponding to the active state of the latch means, where it presses the finger on the stop , and with a retracted position away from the passage of the finger. Thus, it is possible to control remotely, without loss of time, the switching of the function of the jack, from the operation of the scraper blade to the opening of the box.

In preferred arrangement, the grid comprises, at its downstream end, a flap tilting around a shaft transverse to the grid; the thickness of the fuel layer can be adjusted downstream of the grid, by raising this flap more or less relative to the plane of the grid. By raising it perpendicularly to the grate plane, and by reducing the combustion rate and the displacements of the movable grate bars, the ash fall is stopped in the bottom ash well, for cleaning operations.

The box is conventionally equipped with water evacuation pipes to a drain manifold, with overflow holes in the water in the box, and drain ports in the lower part, provided with valves. associated, so that the water level in the box cannot drop pass the height just necessary to maintain a water seal, and that we can empty the box to unclog it. In a preferred arrangement, these evacuation pipes are mounted on the tilting part of the box and end at a low point with at least one flow nozzle, with a fixed chute disposed below the flow nozzle when the box is closed. It will be understood that the movements of the scraper blade accumulate the ashes in the fixed part, the wall of which they rise in an inclined plane, so that the overflow and drain orifices located in the tilting part hardly risk being engorged. by the ashes.

• la figure 1 représente, en élévation partiellement arrachée, un cendrier selon l'invention en situation de marche normale ;
• la figure 2 représente le cendrier de la figure 1, en préparation d'ouverture ;
• la figure 3 représente le cendrier des figures 1 et 2, en position d'ouverture ;
• la figure 4 représente les canalisations d'évacuation d'eau du cendrier de l'invention, omises sur les figures 1 à 3 pour des raisons de clarté.

Secondary characteristics and advantages of the invention will emerge from the description which follows by way of example, with reference to the appended drawings in which:

• Figure 1 shows, in partially cutaway elevation, an ashtray according to the invention in normal walking situation;
• 2 shows the ashtray of Figure 1, in preparation for opening;
• Figure 3 shows the ashtray of Figures 1 and 2, in the open position;
• 4 shows the water drainage pipes of the ashtray of the invention, omitted from Figures 1 to 3 for reasons of clarity.

According to the embodiment chosen and shown in Figure 1, at the downstream end of a combustion grate 1 is disposed a bottom ash well 2 generally vertical. The grid is of the type where bars, made up of elements joined laterally are alternately fixed and movable back and forth longitudinally in a descending succession from an upstream loading end to the downstream end. The grid is supplied with oxidizing air from below, which passes through the grid through orifices made in the bar elements. At the downstream end of the grid 1 is disposed a flap 1a, movable around an axis transverse to the grid. This component 1a can be more or less inclined relative to the grid plane 1, to adjust the level of ash at the downstream end of the grid and to improve the combustion of the last combustible fractions.

The bottom ash 2 is of rectangular section, with its large dimension transverse to the grid, and comprises, in the upper part, hopper walls to connect the large dimension of the well 2 to the width of the grid 1. The well 2 is connects to an extraction box 3 as a whole, which has in the upper part a duct 2 ′ in extension of the bottom ash 2. The box 3 is filled with water up to a level 10a below an upper edge 11 a. The duct 2 'is defined, parallel to the plane of the figure, by the vertical side walls of the box 3, and perpendicular to this plane of the figure by two partitions directed downwards. One of these partitions, not referenced as a whole, ends, at a level below the level 10a of the water 10 in the box 3, by a horizontal lip 2a, while the opposite partition 2b descends more deeply into the water 10.

The immersion of the lip 2a in water 10 forms a water seal which decouples the pressure in the focus from atmospheric pressure, so as not to disturb the paths of the combustion gases.

These arrangements are conventional and the description of their structure is incidental. It will be noted that the duct 2 ', which structurally forms part of the casing 3, behaves functionally as a downward extension of the bottom ash well 2, whether it is the guiding of the ashes towards the bottom of the casing, or the tightness of the fireplace above the water seal.

It will therefore be considered, in the present description, that functionally the well 2 is extended, by the conduit 2 ', up to the lip 2a, below the level 10_a of the water in the box 3.

The box 3 has a concave bottom 13, in the form of a portion of cylinder with horizontal generatrices, here perpendicular to the plane of FIG. 1, the bottom is connected, according to a connection generator 19, to a wall in inclined plane 11b, which ends with a discharge edge 11c, at an intermediate level between the water level 10a and the upper edge 11a of the box 3.

The concave bottom 13 is equipped with a raking blade 14, which bears on this bottom along a cylinder generator. This scraper blade is mounted at the end of a thrust arm 14a articulated on cranks 15a of a scraper shaft 15 disposed parallel to the generatrices of the bottom cylinder 13, above the water level 10a and the side of the well 2 which is furthest from the wall in inclined plane 11b.

The scraper shaft 15 has, outside the box 3, a control crank 15b. A hydraulic cylinder 16 is disposed close to a horizontal between a hinge yoke 16a fixed to the box 3 and a crank pin 16_b of the control crank 15b. As can be seen in the figure, the control crank 15b is directed upwards, while the cranks 15a are directed rather downwards. The relative timing of the cranks 15a and 15b is such that, the jack 16 fully retracted (see FIG. 2) the scraper blade 14 is as far as possible from the connection generator 19, and approaches this generator by extension of the jack.

In fact, there are two jacks 16, on either side of the box 3, to avoid torsional forces on the box 3.

The wall in inclined plane 11 has its discharge edge 11c inside a hopper 4. At the bottom of the hopper is an ash removal device 5, suggested here by a bucket, but which can be a conveyor belt, for example.

• Les cendres et mâchefers résultant de la combustion du combustible solide chargé à l'amont de la grille 1, parvenus à l'extrémité aval de cette grille sont poussés sur le volet mobile la convenablement incliné pour se déverser, par-dessus le bord terminal de ce volet 1 a, où ils tombent dans le puits à mâchefers 2, soit librement, soit par un guidage par les parois en trémie.

All of the arrangements described so far differ from conventional arrangements only in construction details, and operate as follows:

• The ashes and bottom ash resulting from the combustion of the solid fuel loaded upstream of the grid 1, which have reached the downstream end of this grid, are pushed onto the movable flap, the inclination suitably inclined to pour out, over the terminal edge of this flap 1a, where they fall into the bottom ash 2, either freely, or by guidance through the walls in the hopper.

The lower lip 2a being embedded below the level 10a of the water 10, the pressures in the hearth and in the external atmosphere are independent, the water 10 forming a seal. It will be recalled that the pressure in the hearth is determined by the composition of an overpressure caused by the blowing of the combustion air through the grid 1 and possibly of secondary air, and the draft vacuum caused by a draft fan and the fireplace.

The ashes and bottom ash therefore fall into the water 10, which extinguishes the still incandescent fractions, and will deposit on the bottom 13. It goes without saying that the level of the water 10a is kept substantially constant, to compensate for the losses by evaporation on contact with hot ashes, and entrainment with ashes.

The scraper blade is, for part of the time, at rest on the bottom 13 as far as possible from the connection generator 19, the jack 16 being retracted. Periodically, the rod of the jack 16 is put in progressive extension, and the scraper blade 14 runs through the bottom 13 to push the ashes and bottom ash towards, then on the wall in inclined plane 11 b from which they pour out beyond the edge 11 c in the hopper 4 to reach the evacuation device 5. After full extension of the jack rod 16, the latter is retracted and the scraper blade 14 returns to its rest position. Of course, the ashes and bottom ash rise on the wall in an inclined plane takes place by the succession of displacements of the scraper blade 14. Furthermore, it will be appreciated that the thrust of the ashes and bottom ash is obtained by the extension of the jack 16. Thus, the stroke of the scraper blade which requires a high effort corresponds to the pressurization of the chamber of the jack 16 which does not contain the rod, where the effective cross-section of the piston is greatest.

We will now also refer to Figures 2 and 3.

The essential characteristic of the extraction box 3 according to the invention is to be made up of two parts, a fixed part 11, and a tilting part 12, which are joined along a joint surface, in the form of a dihedron with two half -plans 18 and 18 _' on either side of an edge 18 ", parallel to the bottom generators and substantially at the level of the level 10a of the water in the box 3.

The dihedral 18, 18 ′ is protruding for the tilting part 12, and re-entering for the fixed part 11. The half-plane 18 starts from the edge 18 "downward, substantially perpendicular to the wall or inclined plane 11 b, for pass substantially through the generatrix connecting the bottom 13 to the wall in an inclined plane 11b. The half-plane 18 ′ starts from the edge 18 ", going up until cutting the plane of the upper edge 11a of the box 3 on the side clinker well 2 furthest from the wall in inclined plane 11 b. It will be noted that the half-plane 18 ′ cuts the entire width of the well 2 at an angle.

The fixed part 11 comprises the upper edge 11g of the box 3 and the wall in inclined plane 11b. The tilting part includes the concave bottom 13 and contains the scraper blade 14 and the scraper shaft 15: it can pivot around an axis 17 located above the level of the upper edge 11g of the box 3, and on the side of the well. clinker 2 furthest from the wall in inclined plane 11 b.

In addition, the axis 17 is located approximately above the scraper shaft 15 and high enough for the trajectory of the crank pin 16b of the control crank 15b to pass between the axis of the scraper shaft 15 and l pivot axis 17 of the tilting part 12.

The fixed 11 and tilting 12 parts comprise, along the joint dihedral 18, 18 ′, flanges 18a, 18b extended towards the outside of the box 3, between which is a seal, maintained on the flange 18a of the fixed part. The seal is held tight, in normal situation, by latch means 18c, constituted by hooks articulated on the fixed part 11, and which engage under protruding plugs on the tilting part 12, under the action of jacks hydraulic.

In the side wall of the tilting part 12, an inspection door 12a is arranged, located in alignment with the bottom ash 2 and below the level 10a of the water in the box. This inspection door is placed in the corner of the dihedral 18, 18 ′, projecting into the tilting part 12 of the box 3.

The scraper shaft 15 is fitted, substantially in the extension of the control crank 15b, with a finger 15c, which comes to bear, when the scraper blade 14 is at the furthest from the connection generator 19 between the bottom 13 and the wall in inclined plane 11b on a fixed stop 20 (see in particular Figure 2). Opposite the stop 20 is arranged a cylinder push button 21, aligned with the stop 20. In the retracted position (FIG. 1) the cylinder push button 21 is away from the movement of the finger 15c. In the extension position (FIGS. 2 and 3), the actuator with a jack 21 blocks the finger 15c bearing on the stop 20. Under these conditions, the extension of the jack 16 will apply to the lever arm ( virtual) formed between the pivot axis 17 of the tilting part 11 and the sleeve 16b of the control crank 15b, secured to the tilting part 12 by blocking the finger 15c between the stop 20 and the actuator 21.

• On réduit le régime du foyer en supprimant, ou tout au moins en réduisant notablement le soufflage d'air sous la grille 1 de façon que le foyer soit en dépression par rapport à l'atmosphère extérieure; on réduit parallèlement la cadence de va-et-vient des barreaux mobiles de grille, on relève le volet 1 a en position sensiblement perpendiculaire au plan de grille pour interrompre l'arrivée de cendres par le puits à mâchefers 2.

When a jam occurs, resulting for example from the fall into the box 3 of a large incombustible object which has been loaded on the grid with the fuel, and manifested in particular by a blocking of the scraper blade 14, it is maneuvered in the manner next:

• The speed of the hearth is reduced by eliminating, or at least significantly reducing the blowing of air under the grid 1 so that the hearth is in depression with respect to the external atmosphere; the rate of reciprocation of the movable grating bars is reduced in parallel, the flap 1 a is raised to a position substantially perpendicular to the grating plane in order to interrupt the arrival of ash by the clinker well 2.

The water is drained from the extractor box 3.

At the same time, the scraper blade 14 is brought back to its position furthest from the connection generator 19 from the bottom 13 to the wall in inclined plane 11b, then the actuator pusher 21 is extended to block the finger 15c between the stop 20 and the pusher 21.

We retract the cylinders of the latch means 18c, so as to release the plugs from the movable part 12 from the hooks articulated on the fixed part 11. FIG. 2 represents the ashtray at this stage of the maneuver.

We can then gradually extend the actuator 16 to open the box 3 as shown in Figure 3. Of course we will have placed under the box a suitable receptacle, into which the object spills because of the jam and the accumulated ash. FIG. 3 clearly shows that the surface offered for the evacuation of the stuffing largely exceeds the plumb of the bottom ash 2.

It will have been noted that the face of the lower part of the bottom ash 2, opposite the tilting part 12 is slightly inclined on the vertical, to move away, downwards, from this tilting part. This is intended to reduce the amount of ash that may fall behind the scraper blade 14.

The cleaning done, the cylinder 16 is retracted to attach the tilting part 12 to the fixed part 11 along the dihedral joint 18, 18 '; the actuator 18c is extended in extension so that the hooks engage under the plugs, and the normal water level 10a is restored. The ram plunger 21 is retracted to release the scraper blade 14. The hearth is gradually brought back to its normal speed by lowering the flap 1a by a suitable angle, and the rate of reciprocation of the movable bars is resumed while '' We restore normal blowing and draft.

It happens, when incombustible objects of great length, such as for example metallic box springs, have been introduced on the grid, that these objects are able to cross, while being placed in length, the bottom ash 2 to come to get stuck bias in the casing 3. The opening of the casing can then be prevented, or be only ineffective in effecting a suitable cleaning.

It is then necessary to open the door 12a after emptying the box to try to extract the jammed object, if necessary by splitting it with a thermal lance. It is therefore advantageous to have an inspection door 12a of sufficient size for such an intervention.

We will now specify, with reference to FIG. 4, how the level 10a of the water in the box 3 is kept constant in normal operation, and can be reduced to practically nothing before the opening of the box.

This figure schematically represents the rear part of the tilting part 12 of the box 3, with the pivot axis 17, the finger 15c lockable between the stop 20 and the actuator 20, and the inspection door 12a.

Conventionally, the water is brought to the casing 3 using pipes and valves, which ensure either a complete stop of the water supply, or a high-flow filling if the actual level of the water in the casing is significantly lower than the desired level 10a, ie a maintenance rate set when the actual level is close to level 10a; it is desirable to minimize the amount of water escaping through the overflows.

The tilting part 12 is equipped with water evacuation pipes 25 which comprise, stitched into a vertical rear wall of this tilting part of the overflow orifices 26, at the required level 10a of the water in the box 3, and drain orifices 27, located in the lower part of the casing 3, between the inspection door 12a and the end of the cylinder plunger 21. The overflow orifices 26 are connected to a flow nozzle 29 located at point bottom (when the box is closed) by a pipe 26a. The drain orifice 27 is connected to the flow nozzle 29 through a valve 28, provided with a remote control. The flow nozzle 29, when the box 3 is closed, is located immediately above a chute 30 forming a drain manifold.

It will be noted that it is important that the overflow orifices 26 and especially the drainage 27 are located in the tilting part 12 in areas where the ash is unlikely to accumulate. However, these orifices are provided with inspection plugs to remedy a blockage.

It will be appreciated that all the cleaning operations in the event of jamming without aggravating circumstances such as a jamming of an object of great length, can be carried out remotely, and therefore be the subject of centralized commands, practically without intervention of personnel. on the ashtray. We should be able to remove a jam by putting the hearth in sleep for less than an hour, while the breaking of boxes of the state of the art often lead to sleep that can exceed a few hours.

Claims (12)

1. A furnace ash box for a boiler burning solid fuel, such as in particular urban waste, in which the fuel, loaded onto the upper part of a sloping grate (1), descends along this grate to a downstream end whilst it burns, this ash box comprising, underneath the downstream end of the grate (1), a vertical well (2), referred to as a clinker well, which terminates in a lower lip (2a) in an extraction chamber (3) filled with water (10) below an upper edge (11 a) up to a level (10a) higher than that of the lip (2a) of the well, the chamber (3) having a concave base (13) shaped like a portion of a cylinder with horizontal generatrices, fitted with a scraper blade (14) bearing on the base (13) along a generatrix and movable in a reciprocating motion at right angles to the generatrices in order to push the ash along an upwardly sloping wall (11 b), from a connection to the bottom (13) along a generatrix (19) as far as a discharge edge (11 c) at a level higher than that of the water (10a) in the chamber (3), from where the ashes are discharged into a hopper (4), characterised in that the chamber (3) is openable and consists of two parts joined together along a sealing surface (18, 18') in the closed position, a fixed part (11) comprising the sloping wall (11 b) and the upper edge (11 a) of the chamber (3) and a tilting part (12) comprising the base (13) and the scraper blade (14) and mounted so as to pivot about an axis (17) parallel to the generatrices of the bottom (13) into an open position in which the bottom of the clinker well (2) is clear.

2. An ash box according to claim 1, characterised in that the sealing surface forms a dihedron with two half-planes (18, 18') on either side of an edge (18") parallel to the generatrices of the base and located approximately at the water level (10a) in the chamber (3) on the side of the well (2) closest to the sloping wall (11 b).

3. An ash box according to claim 2, characterised in that one of the half-planes (18) of the sealing dihedron is directed downwards substantially at right angles to the sloping wall (11 b) so as to pass substan- cially through the generatrix (19) where this wall (11 b) is connected to the base (13), whilst the other half- plane (18') rises from the edge (18") to the upper edge (11 a) of the chamber (3), which it intersects on the side of the well (2) furthest from the sloping wall (11 b).

4. An ash box according to one of claims 2 and 3, characterised in that the fixed (11) and tilting (12) parts have respectively flanges (18a, 18b) extending along the half-planes (18, 18') of the sealing dihedron, locking means (18c) associated with these flanges (18a, 18b), being able to attach the tilting part (12) to the fixed part (11), clamping a sealing joint.

5. An ash box according to claim 4, characterised in that the locking means (18c) comprise hydraulic actuating rams.

6. An ash box according to any one of claims 1 to 5, characterised in that the pivot axis (17) of the tilting part (12) of the chamber (3) is situated above the upper edge (11 a) of the chamber on the side of the clinker well (2) furthest from the sloping wall (11 b).

7. An ash box according to any one of claims 1 to 6, characterised in that the scraper blade (14) is fixed at the end of pusher arms (14a) connected to cranks (15a) keyed onto a scraper shaft (15) disposed above the water level (10a) parallel to the generatrices of the base (13) and on the side of the clinker well (2) furthest from the sloping wall (11 b), the scraper shaft being driven in reciprocating rotation by at least one hydraulic actuator (16) disposed close to the horizontal outside the chamber (3) between an articulation (16a) on the fixed part (11) of the chamber and a crank pin (16b) at an end of a control crank (15b) keyed onto the shaft (15) with an offset with respect to the cranks (15a) to which the pusher arms (14a) are connected such that, when the actuator (16) is retracted, the scraper blade (14) is at its furthest point from the sloping wall (11 b)

8. An ash box according to claims 6 and 7 taken in conjunction, characterised in that, the crank pin (16b) on the control crank moving in a path which passes between the axis of the scraper shaft (15) and the pivot axis (17) of the tilting part (12) of the chamber, locking means (15c, 20, 21) are disposed between the scraper shaft (15) and the tilting part (12) of the chamber, and are able, when activated, to lock the rotation of the scraper shaft (15) with the scraper blade (14) at its furthest point from the generatrix (19) of the base (13) where the latter is connected to the sloping wall (11 b).

9. An ash box according to claim 8, characterised in that the locking means comprise, on the scraper shaft (15) outside the chamber (3), a radial finger (15c), and, on the tilting part (12), a stop (20) against which the radial finger (15c) bears when the scraper blade (14) is at its furthest point from the generatrix (19) where the base (13) is connected to the sloping wall (11b), and a pusher (21) moved by an actuator and aligned in the direction of the stop (20) with an extension position, corresponding to the activated state of the locking means , in which it presses the finger (15c) onto the stop (20) and with a retracted position away from the path of movement of the finger (15c).

10. An ash box according to any one of claims 1 to 9, characterised in that the combustion grate (1) is fitted at its downstream end, above the clinker wall, with a flap (1 a) moving about an axis transverse to the grate and capable of adopting an adjusted angle in order to vary the level of its end with respect to the plane of the grate.

11. An ash box according to any one of the claims 1 to 10, in which the chamber (3) is fitted with pipes (25) for draining water to a drainage outlet (30), comprising at least one overflow orifice (26) situated at the water level (10a) in the chamber (3), and at least one drain orifice (27) in the bottom part of the chamber (3) fitted with an associated valve (28), characterised in that the water drainage pipes (25) are mounted on the tilting part (12) of the chamber and terminate at a low point in at least one discharge nozzle (29), a fixed chute (30) being disposed underneath this discharge nozzle (29) when the tilting part (12) of the chamber (3) is in its closed position.

12. An ash box according to claim 11, characterised in that the valve (28) associated with the drain orifice (27) is fitted with remote control means.

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