GB2162083A - Improvements in or relating to fluidised bed apparatus - Google Patents

Abstract

A distributor plate 1 for a fluidised bed apparatus includes a plurality of trough members 6 which overlap one another to provide apertures 12 for the passage of a fluidising medium. <IMAGE>

Description

SPECIFICATION Improvements in or relating to fluidised bed apparatus This invention concerns improvements in or relating to fluidised bed apparatus.

In particular, although not exclusively, the present invention has reference to such apparatus when used for the combustion or gasification of solid fuel, e.g. coal.

Fluidised bed apparatus incorporates a distributor plate which functions as a supportforthe bed and provides flow paths there through for the passage of a fluidising medium. The distributor plate must, therefore, be gas permeable and various designs have been evolved over the years. For example, the Applicants devised such a plate provided with stand-pipes extending vertically above the plate and having perforate ends for the issuance of fluidising gas therefrom at a predetermined height in the bed which latter generally comprises sand. The sand beneath the perforations remains static during operation of the fluidised bed and effectively insulates the plate from the hot fluidised bed in which combustion or gasification takes place. In the absence of such an insulating layer, the plate would be subject to thermal stressing resulting in distortion.

In an alternative design, water cooling has been adopted where hot gas is used to effect start-up of the fluidised bed, this costlier construction being off-set by savings from the use of less gas or oil to effedt start-up for coal burning.

The current designs of distributor plates are expensive to manufacture and generally of undue size. A further disadvantageous factor is that they do not readily permit the removal of large quantities of oversize material, e.g. ash, which tends to accumulate in the bed and thus there is an inhibition on the use of high ash coals.

An object of the present invention is thus to provide an improved distributor plate which obviates the disadvantages of conventional designs.

According to the invention, a distributor plate for fluidised bed apparatus includes a plurality of trough members adjacent margins of which overlap in spaced relation one to the other to provide apertures therebetween, the plate in use being horizontal or substantially horizontal. Conveniently, the trough members may be angle iron bars each of which may be of Form, each limb of the bar being inclined to the horizontal to provide in use a trough for retaining a static layer of bed material which assumes a natural angle of repose therein. The longer limbs of the L-shaped angle iron bars are parallely orientated with respect to each other as are the relatively shorter limbs, the longer limb of one bar overlapping the end of the shorter limb of an adjacent bar.The ends of the shorter limbs of the bars are spaced from the overlapping longer limbs of adjacent bars to provide the apertures which constitute slots through which in use a fluidising medium is passed in an upwards direction, but through which substantially no fluidised material can pass in a downwards direction. The dimension of the slots may be determined or varied by the provision of spacers disposed intermediate the overlapping limbs.

The ends of the angle shaped members may conveniently be in a support structure which may be orientated at a small angle to the horizontal taken laterally of the distributor plate and the expression "substantially horizontally" is to be construed accordingly. The angular orientation may be in the range 1 10 . The distributor plate may, therefore, be inclined in position within a fluidised bed apparatus thereby assisting flow of material, e.g.

oversize particles, in the downward direction of the inclinations.

In an alternative embodiment, the trough members may be concave in form.

The invention also includes a fluidised bed apparatus incorporating a distributor plate of the kind described.

By way of example only, one embodiment of distributor plate according to the invention is described below with reference to the accompanying drawing which is an end sectional view.

Referring to the drawing a distributor plate (shown only in part) is disposed within a fire tube 2 of a boiler (not shown) and is spaced therefrom to define a plenum chamber 4.

The distributor plate 1 comprises a plurality of angle iron bars 6 of substantially L-shape, the relatively longer limbs 8 of which are parallely orientated with respect to each other as are the relatively shorter limbs 10. The angle iron bars 6 are inclined to the horizontal and are secured at their ends (now shown), the structure and thus the general plane of the plate 1 being inclined art a small degree, e.g. 2", to the horizontal. The angle iron bars 6 effectively constitute troughs for the retention in use of a static layer of fluidised bed material.

The angle iron bars 6 overlap one another, the longer limbs 8 of one bar 6 overlapping the shorter limbs 10 of an adjacent bar, there being defined a slot 12 at the overlapforthe passage of a fluidising gas. The size of the slot 12, which extends continuously along the length of the bars 6 may be varied by the use of spacers 14.

In operation, and for the purposes of start-up of a fluidised bed combustion process, a shallow bed of sand is established on the distributor plate 1, the orientation of the bars 6 preventing the discharge of the sand through the slots 12, since the sand assumes a natural angle of repose and is retained in the troughs constituted by the L-shaped bars 6.

Coal is sprinkled over the shallow bed and ignition is initiated, for example by a torch orfirelighters, along a marginal edge of the plate 1, combustion sustaining gas (shown by arrows A) being directed via the plenum chamber 4 through the slots 12. The coal is then progressively ignited, using the directional nature of the slots 12, across the whole of the plate 1 after which further sand is introduced to establish a fluidised bed 20, the bars 6 of the plate 1 being insulated by the static layers 21 of sand on each bar. Once full fluidised bed combustion proceeds, large ash particles generated in the bed tend to be swept by the air issuing through the slots 12 to one side, the slight inclination of the plate assisting the flow of such particles which can then be removed and passed to a classifer in the absence of any build-up in the fluidised bed. This enables coal of high ash content to be burnt within a fluidised bed without the difficulties normally associated therewith.

The distributor plate of the present invention is of simple construction and its vertical dimension is substantially less than those that of conventional plates. The cost is therefore correspondingly reduced, but with the operational advantage associated with large ash withdrawal.

Claims (15)

1. A distributor plate for fluidised bed apparatus including a plurality of trough members adjacent margins of which overlap in spaced relation one to the other to provide apertures therebetween, the plate in use being horizontal or substantially horizontal.

2. A distributor plate according to claim 1 in which the trough members are angle iron bars.

3. A distributor plate according to claim 2 in which the angle iron bars are L-shaped.

4. A distributor plate according to claim 3 in which each limb of each angle iron bar is inclined to the horizontal to provide a trough for the retention in case of a static layer of bed material.

5. A distributor plate according to claim 4 in which the relatively longer limbs of the L-shaped angle iron bars are parallely orientated with respect to one another and the relatively shorter limbs are parallely orientated with respect to one another.

6. A distributor plate according to claim 5 in which the longer limb of one bar overlaps the shorter limb of an adjacent bar.

7. A distributor plate according to claim 6 in which the ends of the shorter limbs of the bars are spaced from the overlapping limbs of adjacent bars to provide the apertures.

8. A distributor plate according to claim 6 in which the apertures so provided constitute slots extending along the length of adjacent bars.

9. A distributor plate according to any one of the preceding claims in which the dimension of the apertures is determined by or varied by the provision of spacers disposed intermediate the overlapping members.

10. A distributor plate according to any one of the preceding claims in which the ends of the trough members are secured in a support structure.

11. A distributor plate according to claim 10 in which the support structure is orientated to the horizontal at a small angle.

12. A distributor plate according to claim 11 in which the angle lies in the range 1 to 100.

13. A distributor plate according to claim 1 in which the trough members are concave in form.

14. A distributor plate substantially as hereinbefore described with reference to the accompanying drawing.

15. A fluidised bed apparatus incorporating a distributor plate according to any one of the preceding claims.