EP0763384A1 - Centrifugal separator, in particular for a circulating fluidized bed boiler - Google Patents

Abstract

The separator consists of an upper section (1) of constant cross-section with an inlet (3) for the mixture of gas and solid particles and an outlet (4) for the gas, and a lower section (2) which tapers towards its lower end, where it has an outlet (5) for the solid particles. The inner surface of the separator walls have at least one groove (6, 7) for trapping the solid particles and guiding them towards the outlet. The depth of each groove is between 1 and 20 per cent of the upper section's inner diameter, and a width of between 2 and 10 per cent of its inner perimeter.

Description

The present invention relates to a centrifugal separator for a circulating fluidized bed boiler.

• une partie supérieure de section sensiblement constante constituée d'une première paroi et comportant en partie haute une conduite d'entrée d'un mélange de gaz et de particules solides et une conduite de sortie du gaz et
• une partie inférieure de section décroissante vers le bas constituée d'une seconde paroi et comportant en partie basse une conduite de sortie des particules solides.

It relates more precisely to a gas-solid mixture separator for a circulating fluidized bed boiler comprising

• an upper part of substantially constant section consisting of a first wall and comprising, at the top, an inlet pipe for a mixture of gas and solid particles and an outlet pipe for the gas and
• a lower part of decreasing section downwards consisting of a second wall and comprising in the lower part an outlet pipe for solid particles.

The function of the separator is the separation of the phases of the mixture of gases and solid particles suspended in it. A gas vortex is formed creating a centrifugal force in the enclosure of the separator. The efficiency of a separator is linked to the speed of the mixture in the inlet pipe, the internal diameter and the height of the separator which determines the residence time.

In order to reduce the cost of such a separator and in particular of a separator associated with a circulating fluidized bed boiler, it is therefore possible to increase the speed of the mixture at the inlet and in the body of the separator, which makes it possible to reduce its diameter.

However, a high speed can have harmful effects, especially in the case where the mixture has a high concentration of solid particles as in the circulating fluidized beds. Gas at high speed tends, in fact, to re-entrain solid particles already deposited on the wall of the separator and therefore to cause a loss of efficiency.

Excessive speed likewise leads to an increase in erosion and an increase in pressure losses.

The present invention solves this problem of re-entrainment of solid particles and, to do this, in accordance with the invention, said walls are provided on their internal face with at least one groove for collecting solid particles directed downwards, of depth included. between 1 and 20% of the internal diameter of the upper part and of width between 2 and 10% of the internal perimeter of the upper part.

This groove serves on the one hand as a capture groove for solid particles and on the other hand as a guide groove for the collected particles downwards, while protecting them from the gas vortex.

In general, the inlet pipe for the mixture of gases and solid particles is tangential to the first wall and, according to the preferred embodiment, the upper end of said groove is disposed opposite this inlet pipe, allowing the direct capture upon entry of a large quantity of solid particles.

Said groove can be vertical or inclined at an angle of about 60 ° relative to the vertical.

The angle can be variable over the height of the separator.

The separator can have several said grooves and these grooves can be distributed around its perimeter or distant from each other by an increasing pitch in the direction of the flow of gas mixture and solid particles.

In order to improve this capture effect, said groove can be partially covered over part of its width by a wall integral with its edge opposite the direction of the flow of gas mixture and solid particles.

Preferably, said groove opens into the outlet pipe for solid particles.

In order to eliminate the re-entrainments of solid particles in the lower part, said groove can be completely covered by a closure wall in the lower part of the lower part.

The invention has the advantage of effecting the separation of solids in two stages, that is to say by gravity drop and centrifugation, which is well suited to CFL boilers where the high loads of solids at the inlet of the separator tend to create a dilute phase overcoming a dense phase on the wall.

The dense phase can be immediately separated from the main flow in the inlet of the separator and not disturb the rest of the flow of solids and therefore reduce the retraining.

This separation therefore makes it possible to increase the speed field used in the centrifugation and therefore to improve the compactness of the separator.

These embodiments can be applied to cased or uncased separators, of circular or polygonal shape.

The total width of the grooves is between 5 and 33% of the internal perimeter of the upper part.

The invention is described below in more detail using figures showing only a preferred embodiment of the invention.

Figure 1 is a vertical sectional view of a first embodiment of a separator according to the invention.

Figure 2 is an elevational view in partial vertical section of a separator of a separator according to the invention according to a second embodiment.

Figure 3 is an elevational view in partial vertical section of a separator according to the invention according to a third embodiment.

FIG. 4 is a view in horizontal section along III-III of FIG. 1.

Figure 5 is a similar sectional view of a fourth embodiment of a separator according to the invention.

Figure 6 is a cross-sectional view of a groove.

Figure 7 is a sectional view of a fifth embodiment according to the invention.

• une partie supérieure 1 de section sensiblement constante, par exemple cylindrique de section circulaire ou octogonale, constituée d'une première paroi 1A et comportant en partie haute une conduite d'entrée 3 d'un mélange de gaz et de particules solides, en général tangentielle à la première paroi 1A, et une conduite de sortie 4 du gaz constituée en général d'un tube plongeur et
• une partie inférieure 2 de section décroissante vers le bas, par exemple conique ou prismatique, constituée d'une seconde paroi 2A et comportant en partie basse une conduite de sortie 5 des particules solides, en général verticale.

The centrifugal separator shown in the figures includes:

• an upper part 1 of substantially constant section, for example cylindrical of circular or octagonal section, consisting of a first wall 1A and comprising in the upper part an inlet pipe 3 of a mixture of gas and solid particles, generally tangential to the first wall 1A, and a gas outlet pipe 4 generally consisting of a dip tube and
• a lower part 2 of decreasing section downwards, for example conical or prismatic, consisting of a second wall 2A and comprising in the lower part an outlet pipe 5 for solid particles, generally vertical.

These walls 1A, 2A are provided on their internal face with grooves 6, 7 for collecting solid particles directed downwards, of depth, constant or increasing as they descend, ranging between 1 and 20% of the diameter internal of the upper part 1 and of width, constant or variable, between 2 and 10% of the internal perimeter of the upper part 1.

According to the embodiment shown in Figure 1, the grooves 6, 7 are vertical.

According to the embodiment shown in Figure 2 where a single groove 6 is shown for clarity, the grooves are inclined at an angle α less than 60 ° relative to the vertical. According to another embodiment (Figure 3) the angle may be 45 ° in one area and 0 degrees in another.

According to these embodiments, the grooves 6, 7 start in the first part 1, preferably substantially at the level of the horizontal plane of symmetry of the inlet pipe 3 and open into the outlet pipe 5 solid particles in the lower part of the lower part 2.

The grooves 6, 7 are completely covered by a closure wall 14 in the lower part of the lower part 2. Advantageously, they are thus covered over a height substantially equal to half the height of the lower part 2 where the quantity of solid particles in the grooves is large and is therefore completely protected from any re-entrainment and where the small quantity of separated particles can flow along this closure wall 14.

According to an improvement, the separator may also be provided with outlet orifices 13 for the solid particles arranged along the grooves 6, 7 which constitute intermediate outlets upstream from the conventional outlet pipe 5.

On the periphery of the separator, the grooves 6 to 9, as shown in Figure 4, are spaced from each other by an increasing step in the direction of the flow of gas mixture and solid particles, represented by the arrows. There are four of them here. It is possible to arrange one to eight such grooves, regularly distributed or thus offset, the total width of the grooves being between 5 and 33% of the internal perimeter of the upper part 1.

FIG. 5 represents an embodiment of a separator with a single groove 6 ', where the latter has its upper end disposed opposite this inlet pipe 3. According to this embodiment, the groove 6' n ' is not radial but of transverse axis parallel to the longitudinal axis of the inlet pipe 3. This groove 6 ′ is thus located at the point of impact of the flow of gas mixture and solid particles directly at the outlet of the line 3 where the speed is maximum and the quantity of solid particles separated by centrifugal force also.

According to an improvement shown in FIG. 6, the groove or grooves 6 are partially covered over part of their width by a wall 10 integral with their edge 6A opposite to the direction of the flow of gas mixture and solid particles. During the vortex of the flow of gas and solid particles mixture shown diagrammatically by the arrow 12, the solid particles are entrained in the groove 6 according to the arrow 11 and are maximum protected there from any re-entrainment by the vortex.

According to the embodiments described, the groove or grooves extend over the upper part 1 and over the lower part 2. The cyclone may comprise a number of grooves of one type and a number of grooves of the other type .

FIG. 7 represents an embodiment of a separator of octagonal upper section made up only of planar faces 20 connected to each other by grooves 21.

The wall consists of cooling tubes 22 internally traversed by a cooling fluid and internally covered with a lining of refractory materials.

The separator according to the invention is in particular intended to equip a circulating fluidized bed boiler.

Claims (12)

Separator for gas-solid mixtures for a circulating fluidized bed boiler comprising - an upper part (1) of substantially constant section consisting of a first wall (1A) and comprising in the upper part an inlet pipe (3) of a mixture of gases and solid particles and an outlet pipe (4 ) gas and a lower part (2) of decreasing downward section consisting of a second wall (2A) and comprising in the lower part an outlet pipe (5) for solid particles, characterized in that said walls (1A, 2A) are provided on their internal face with at least one groove (6 to 9) for collecting solid particles directed downwards, with a depth between 1 and 20% of the internal diameter of the upper part (1) and of width between 2 and 10% of the internal perimeter of the upper part (1). Separator according to claim 1, the inlet pipe (3) of the mixture of gases and solid particles is tangential to the first wall (1A), characterized in that the upper end of said groove is arranged opposite this inlet pipe (3). Separator according to claim 1 or 2, characterized in that said groove is vertical. Separator according to claim 1 or 2, characterized in that said groove is inclined at an angle (α) less than 60 ° relative to the vertical. Separator according to one of the preceding claims, characterized in that said groove (6 ') is partially covered over part of its width by a wall (10) integral with its edge (6A) opposite the direction of the flow of gas mixture and solid particles. Separator according to one of the preceding claims, characterized in that said groove opens into the outlet pipe (5) for solid particles. Separator according to claim 6, characterized in that said groove is completely covered by a closure wall (14) in the lower part of the lower part (2). Separator according to one of the preceding claims, characterized in that it comprises several said grooves (6 to 9). Separator according to claim 8, characterized in that said grooves are distributed around its perimeter. Separator according to claim 8, characterized in that said grooves are spaced from each other by an increasing pitch in the direction of the flow of gas mixture and solid particles. Separator according to one of claims 8 to 10, characterized in that the total width of the grooves is between 5 and 33% of the internal perimeter of the upper part (1). Separator according to claim 1, characterized in that the upper part consists of planar faces (20) arranged so as to constitute an octagonal section, said faces being connected together by grooves (21).

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