EP0138692B1 - Device for the combustion in a fluidized bed of low-grade fuels, especially black batt or bind - Google Patents

Abstract

An apparatus for the combustion of a poorly combustible fuel in a fluidized bed comprises a vertical front wall through which the poorly combustible fuel is delivered in particulate form and two lateral walls extending rearwardly from the front wall. A fixed grate extends from a front input end towards a rear discharge end between the lateral walls, and the two sides and the front input end of the grate define spaces with the lateral walls and the front wall, respectively. The fixed grate is upwardly inclined over at least a portion of its length from the input end to the discharge end whereby the discharge end is disposed above the input end, and the particulate fuel is delivered to the input end for forming a fluidized bed on the grate. A series of windboxes disposed under the grate along the length thereof blast combustion gas through the grate for fluidizing and burning the fuel while generating ashes moving rearwardly along the fluidized bed to the discharge end, and the discharge end constitutes a weir over which the ashes flow for easy removal. Plane surfaces are arranged in the spaces for supporting heaps of the particulate fuel.

Description

The subject of the present invention is a device for combustion in a fluidized bed of poor fuels, in particular coal shale or bituminous, comprising a substantially vertical front wall, provided with a fuel supply means in the form of particles, two side walls, a grid extending from the front towards the rear and inclined upward over at least part of its length, said grid being arranged between said side walls and at a certain distance from them, and a plurality of boxes air vents arranged under the grid.

In the article "The Ignifluid process among the combustion processes in a fluidized bed" by P. COSAR published in the General Review of Thermics, vol. 21, N ° 241 of January 1982, the author describes a device of this type used for the combustion of fuels with agglomeration of the ashes, settling of the agglomerates which are deposited on the grid and are transported out of the bed by the grid which is mobile . This device is incapable of burning fuels whose combustion temperature in a fluidized bed is insufficient to cause agglomeration of the ashes.

A fluidized bed hearth with a movable mechanical grid of the IGNIFLUID type is also described by FR-A-2 528 543 (published 16.12.83).

Document EP-A-6307 describes a fluidized bed combustion device of the type concerned in which the fluidized bed is limited towards the rear by a solid wall, and the ashes are evacuated at the front of the bed by an orifice provided in the bottom of the bed at the lowest point of the grid. So that the proportion of unburnt matter extracted with the ashes is not too high, the fluidized bed must essentially consist of inert materials, ashes and additives, which makes it necessary to give the bed a volume much greater than the useful volume, it i.e. the volume occupied by the fuel.

The object of the invention is to allow the combustion, in a device of the type concerned, of fuels the combustion of which in a fludized bed does not cause the agglomeration of the ash, without it being necessary to give the fluidized bed a clearly defined volume. greater than the useful volume.

The combustion device which is the subject of the invention is characterized in that the grate is fixed and in that the blowing boxes extend over the entire length of the grate, including under its rear end, so that in operation the fluidized bed covers the entire grid and the ash formed from the fuel having traveled the entire length of the bed overflows above the upper end of the grid forming a weir.

The grid advantageously has, at the level of the spillway, a short horizontal section forming an overflow threshold.

The device includes means for evacuating agglomerates which could accidentally form.

Said means may comprise a horizontal sliding register cooperating with an orifice drilled in a flat surface bordering the grid in the vicinity of its front end.

According to a particular arrangement, the grid is first horizontal, then has an inclined section which optionally connects to the section constituting the overflow threshold.

A single blowing box is advantageously provided under each section.

Whatever the embodiment, the grid has a decreasing permeability from front to back.

• La figure 1 est une vue schématique, en coupe longitudinale du dispositif, suivant la ligne B-B,de la figure 2.
• La figure 2 en est une coupe transversale faite au niveau où le lit fluidisé atteint sa profondeur maximale, suivant la ligne A-A de la figure 1.
• La figure 3 illustre une variante de réalisation.

The invention will be better understood by referring to the description which follows, given with reference to the appended drawings, concerning a particular embodiment given by way of nonlimiting example.

• FIG. 1 is a schematic view, in longitudinal section of the device, along line BB, of FIG. 2.
• FIG. 2 is a cross section made of it at the level where the fluidized bed reaches its maximum depth, along line AA of FIG. 1.
• Figure 3 illustrates an alternative embodiment.

In Figures 1 and 2, the reference 1 designates the front wall of the fireplace, and the references 2 and 3 its side walls. The wall 1 is provided with a chute 4 for supplying raw or previously crushed coal.

The bottom of the chamber delimited by said walls is constituted by a fixed grid 5 inclined upwards from front to back. The longitudinal profile of the grid 5 has substantially the shape of a straight line, at least over most of its length.

The reference 6 designates the fuel slope formed against the wall 1, while the references 7 and 8 respectively designate the fuel slope formed against the side walls 2 and 3. These slopes rest, of course, on flat surfaces, respectively 6 ', 7' and 8 ', bordering the grille 5 at the front and on these sides.

Below the latter are boxes for blowing oxidant gas. As shown in FIG. 2, two boxes 9a and 9b are juxtaposed, each of them extending over a half-width of the grid 5. Tubes 10a and 10b, arranged in opposition, supply the boxes 9a and 9b respectively, A plurality of twin boxes, such as 9a and 9b, are provided over the entire length of the grid 5, below the latter. It goes without saying that each pair of boxes could be replaced by a single box supplied on one or both sides.

The reference 11 designates the fluidized bed which forms above the grid 5 under the effect of the blowing.

As and when the coal is poured through the chute 4 into the bed 11, the latter overflows at the upper end of the grid 5 forming a weir 12. In fact the materials discharged essentially consist of ash formed from the coal having traveled the entire length of the bed. These ashes are removed by tubing 13.

According to the arrangement shown in Figure 1, the grid 5 has at the weir 12 a short horizontal section 5 'forming the overflow threshold. A minimum blowing is provided under this section in order to maintain the mobility of the ash by fluidization.

In principle, no agglomeration of ash should occur. If, for an accidental reason, some agglomerates were formed, they would deposit at the deepest part of the bed, at the base of the slope 6. At this location, there is a horizontal sliding register 14 controlled by a rod 15. This register cooperates with an orifice drilled in the flat front surface 6 '. It is normally in the closed position. Opening for a very short period of time causes the slope 6 to collapse partially and the agglomerates to be evacuated by piping 16.

In FIG. 3, the same references have been used as in the preceding figures to designate the identical or equivalent elements.

Here the grid 5 is horizontal over most of its length, while the section 5 'is arranged at a higher level; the grid is connected to said section by a 5 "inclined intermediate section.

The permeability of the grid (ratio of voids and full) is advantageously chosen to be different, more precisely decreasing, from front to rear, so as to adapt to the carbon concentration of the bed which varies in the same direction. .

In the case of FIG. 3, it is possible to provide only three boxes 9a, 9b arranged respectively under the three sections 5, 5 ′, 5 ". This therefore gives a limited number of boxes and a larger bed volume for a given surface. .

In the case of FIGS. 1 and 2, it is also possible to provide a grid with variable permeability under the same conditions. The number of boxes 9a, 9b can possibly be reduced and the blowing regime must then be suitably adapted.

Claims (7)

1. Device for the combustion, in a fluidized bed, of low-grade fuels especially coal or oil shales, consisting of a nearly vertical front wall (1) fitted with a fuel particles feeding system, two side walls (2, 3), a grate extending from the front to the rear and sloping upwards on, at least, part of its length, the said grate being located between the said side walls and at a certain distance from them, and several wind-boxes (9a, 9b) below the grate (5), characterized by the fact that the said grate is stationary and that the wind-boxes (9a, 9b) extend all along the grate (5), including below its rear end, in such a way that, when operating, the fluidized bed covers the whole grate and that the ash formed from the fuel having crossed the whole length of the bed overflows the grate upper end forming a weir (12).

2. Device according to claim 1, characterized by the fact that the grate (5) is provided, next to the weir (12), with a short horizontal section (5') forming an overflow threshold.

3. Device according to claim 1 or 2,
characterized by the fact that it includes means (14,15,16) for discharging any agglomerates which could form accidentally.

4. Device according to claim 3, characterized by the fact that the said means include a horizontal sliding damper (14) in conjunction with a hole provided into a plane surface (6) bordering the grate in the vicinity of its front end.

5. Device according to any of the claims 2 to 4, characterized by the fact that the grate (5) is first horizontal then presents an inclined section (5").

6. Device according to claim 5, characterized by the fact that it has one single wind-box below each section (5,5' and 5").

7. Device according to any of the preceding pc claims, characterized by the fact that the grate (5, 5' and 5") has a permeability which decreases from the front to the rear.

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