GB2080137A - Fluidised beds - Google Patents

Abstract

A fluidised bed which has a gas distributor (2) supported from below by at least one support member (3) extending across the area of the particulate bed (4) disposed above the gas distributor (2), has deflector plates (6, 6<1>) disposed above the gas distributor (2) on both sides of the support member (3) the deflector plates (6, 6<1>) inclining upwardly from a position laterally of the support member (3) in the direction towards the support member (3). <IMAGE>

Description

SPECIFICATION Improvements relating to fluidised beds This invention relates to fluidised beds in which fluidising gas is passed through a gas distributor to fluidise a particulate bed disposed above the gas distributor.

More particularly the invention is concerned with fluidised beds of the kind in which at least one support member supports the gas distributor from below and extends across the distributor beneath the area of the particulate bed. The support members may be necessitated by the large size of a one-piece gas distributor which can not be adequately supported solely at its edges, or by reason of the gas distributor being sub-divided into a number of sections, known as plates or tiles, which have to be supported along their adjacent edges beneath the area of the bed and which therefore require a number of support members. This sub-division of the gas distributor may be desirable for mechanical convenience and/or to accommodate thermal expansion effects.

The presence of such a support member or support members beneath the gas distributor, which for example is of perforated plate construction, inevitably interrupts the gas flow through the distributor at the position of the or each support member and causes a band of unfluidised particles extending along the line of the support member. It has been found that the band can be of a depth comparable to the depth of the bed and this is particularly so in the case of shallow fluidised beds, i.e.

fluidised beds having a depth of about 6 inches or less. Such a band impedes free fluidised flow of particles between areas of the bed on either side of the band.

In operation of fluidised beds there is usually some unintended lack of symmetry which tends to cause a nett removal of particles from one area of the bed and a nett deposition of particles in another area of the bed. The presence of any unfluidised band of particles as described above can create a barrier preventing an equalising flow of fluidised particles and this in the extreme condition results in exhaustion of the bed in said one area and excessive depth in said other area.

The object of the present invention is to prevent or reduce the formation of said bands of unfluidised particles at least to the extent that the aforesaid extreme condition is avoided.

According to the present invention, in a fuidised bed of the kind described above, deflector plates are disposed above the gas distributor on both sides of the support member and incline upwardly from a position laterally of the support member in the direction towards said support member, whereby a fluidised flow of particles is caused by said deflector plates to pass over said support member. Thus the deflector plates define lean phase particle transport paths through which equalising flows between areas of the bed on either side of said support member can take place.

Said deflector plates may each be contained wholly on one side of the support member or extend from one side of the support member to a higher position on the other side of the support member.

It has been found that the deflector plates also promote a purposeful interchange of particles between neighbouring plates considerably in excess of that created by interchange due to casual assymmetry and this interchange can assist in avoiding undesirable temperature differences or undesirable buildup of contaminants in certain areas of the bed.

When the gas distributor is made in a number of sections, there will also be a number of support members, each of which has deflector plates associated with it. Selection of the number and disposition of the deflector plates inclined one way or the other can pomote desired patterns of circulation of particles around the bed as well as obviating undesirable differences in level in different areas of the bed.

The deflector plates may be mounted in position by brackets extending from the gas distributor. Alternatively in the case of heatexchanger type fluidised beds having fluidcarrying tubes extending through the bed, the deflector plates can be mounted by clips locating on said tubes.

It is an advantage of the invention, that the deflector plates can by their nature be easily fitted after installation and test of the fluidised bed in order to adjust or trim the flow of particles between different areas of the bed.

The invention will now be further explained by way of example with reference to the accompanying drawings, in which: Figures 1 to 3 show in vertical section three different fluidised bed arrangements in accordance with the invention. In the three figures the same reference numerals have been used to designate corresponding parts.

In Figs. 1 to 3 each of the fluidised beds is shown as having a plenum chamber 1, a gas distributor 2 formed from a number of perforated plates 2a, 2b etc., which are interconnected along their adjacent edges by support members 3 in the form of bars of 'T' crosssection to which the plates 2a, 2b, etc. are bolted and a particulate bed 4. Also each of the fluidised beds of Figs. 1 to 3 is shown as a heat exchanger type of fluidised bed having fluid carrying tubes 5 extending within bed 4.

Referring now to Fig. 1 this shows deflector plates 6 and 61 disposed on opposite sides of the central vertical plane 7 of the support member 3 and inclining upwardly towards the central vertical plane 7 from a position beyond the lateral extent of the support member 3, so that the lower edges of the deflector plates 6 and 67 lie over portions of the perforated plates 2a, 2b not obstructed from below by the support member 3. The deflector plates 6 and 61 are displaced along the length of the support member 3 from each other so that they overlie different portions of the support member 3.It may be necessary in order to overlie the whole length of the support member 3 for more than two deflector plates to be provided and in this case, the plates on one side of the support member 3 may be staggered along the length of the support member 3 with respect to those on the other side. The deflector plates are secured to the gas distributor by a series of brackets 8 arranged at intervals along the support member 3 and secured in position by fixing bolts 9 which are used to secure the perforated plates 2 to the support member 3.

It is to be noted that the deflector plates 6 and 6' do not extend to the central vertical plane 7 of the support member 3 but are contained wholly on one side of it.

In the absence of the deflector plates 6, an unfluidised band of particles could be formed over the support member 3 and dividing the bed into sections 4a and 4b, the band extending along the length of the support member 3 and forming a barrier separating the sections of the bed 4a and 4b. The presence of the deflector plates 6 and 61 define respective areas of lean phase particle flow as indicated by the arrows 10 for the plate 6. The lean phase particle flow associated with the plate 6 is from bed section 4ato bed section 4b. The corresponding flow associated with the plate 61 is from bed section 4b to bed section 4a.

Referring now to Fig. 2 the arrangement shown differs from that of Fig. 1 only in that the deflector plates 6 and 67 extend beyond the central vertical plane 7 of the support member 3.

In Fig. 3 deflector plates 11 and 11 a are different in shape from those of Figs. 1 and 2 and have spring clips 12 rivetted to them by which they are clipped around the tubes 5 to locate them in position. Otherwise the arrangement is basically the same as those of Figs. 1 and 2.

Claims (7)

1. A fluidised bed of the kind in which fluidising gas is passed through a gas distributor to fluidise a particulate bed disposed above the gas distributor, at least one support member supporting the gas distributor from below and extending across the distributor beneath the area of the particulate bed, wherein deflector plates are disposed above the gas distributor on both sides of the support member and incline upwardly from a position laterally of the support member, whereby a fluidised flow of particles is caused by said deflector plates to pass over said support member.

2. A fluidised bed according to Claim 1, wherein each said deflector plate is contained wholly on one side of the support member.

3. A fluidised bed according to Claim 1, wherein each said deflector plate extends from a position on one side of said support member to a higher position on the other side of the support member.

4. A fluidised bed according to any preceding claim, wherein the deflector plates are mounted in position by brackets extending from the gas distributor.

5. A fluidised bed according to any one of Claims 1 to 3 and having fluid-carrying tubes extending through the particulate bed, wherein the deflected plates are mounted on said tubes.

6. A fluidised bed according to Claim 5, wherein said deflector plates are mounted on said tubes by clips which clip around said tubes.

7. A fluidised bed substantially as hereinbefore described with reference to Fig. 1 or Fig. 2 or Fig. 3 of the accompanying drawings.