GB1604312A - Fluidised bed combusters - Google Patents

Description

(54) IMPROVEMENTS IN OR RELATING TO FLUIDISED BED COMBUSTERS (71) We, APPA THERMAL EXCHANGES LIMITED, a British Company of City Wall House, 14-18 Finsbury Street, London EC2Y 9AQ, do hereby declare the invention for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: This invention relates to fluidised bed combustion apparatus and to furnaces and incinerators embodying such equipment. The invention is particularly concerned with provision of large capacity fluidised bed combustion apparatus.

It has been proposed to provide fluidised bed combustion apparatus in which a fluidised bed of granular material is supported in a housing on an air diffuser bed support. In such an arrangement fuel or waste material to be burnt, either to raise heat or for disposal purposes, is fed into the fluidised bed to be burnt therein, the oxygen for combustion coming at least in part and usually entirely from air fed in to the bed from the diffuser support to fluidise the bed. The diffuser is in some cases arranged to slope from one side of the bed to the other, and the supply of fluidising air to the various areas of the diffuser being selectively controlled to cause the bed materials to circulate about a generally horizontal axis extending across the slope of the diffuser.

It is an object of the present invention to provide an improved fluidised bed combustor embodying such principles.

Accordingly the present invention provides a fluidised bed combustor comprising an upright circular cylindrical combustion chamber having disposed therein a generally frusto-conical downwardly and outwardly sloping air diffuser bed support arranged to support and fluidise with air a bed of granular material in the combustion chamber, means disposed in the axis of the combustion chamber to feed material to be burnt into a bed on the bed support, and means disposed around the periphery of the bed support for removing ash and other incombustible materials from the bed in which the air diffuser bed support is supplied with air in such fashion in operation that the bed circulates in a torroidal fashion.

In order to promote a fuller understanding of the above and other aspects of the present invention, some embodiments will now be described, by way of example only, with reference to the accompanying drawings in which: Figure 1 shows an embodiment of the invention in schematic cross-section Figure 2 shows a schematic plan view of the embodiment of Figure 1.

Figure 3A shows a part cross-section of the bed support of Figure 1, and Figure 3B shows a part cross-section of an alternative bed support for the embodiment of Figure 1.

Figure 1 shows a schematic cross-sectional view of a fluidised bed combuster comprising an upright circular cross-section cylindrical combustion chamber 10, having a flue 11 at the top with associated combustion gas scrubbing and cleaning apparatus of known design per se indicated generally 12.

A generally frusto-conical air diffuser bed support 13 is disposed towards the bottom of the combustion chamber to support and fluidise a bed of granular material having an upper surface level indicated at 14. Air is supplied to the diffuser bed support to fluidise the bed in operation, by means of a motor driven blower 15.

The surface bed support 13, as seen in figures 3A and 3B, is divided into a series of rings 16 each of which has an air plenum chamber 17 below it, which is connected by way of a respective valve 18 to the supply conduit 39 from the blower 15.

As shown in figure 3A in one arrangement some of the rings 1 6A provide horizontal surfaces, whereas some of the rings 1 6B provide vertical surfaces, so that air is diffused both upwards and radially outwards.

As shown in Figure 3B in an alternative arrangement, the rings 16 lie in the frustoconical surface of the diffuser.

Preferably the supply of air to each of the rings 16 is controlled in operation so that the bed is fluidised to a varying extent radially across it and it circulates in a towoidal fashion moving preferably outwards down the slope of the support 13 and back inwards across the top of the bed.

A frusto-conical baffle 19 is disposed above the outer part of the bed extending inwards and upwards from the wall of the chamber 10, and this assists in promoting the above circulation.

The baffle 19 continues with a reverse slope 20 to define a chamber 21 around the inside of the combustion chamber above the bed.

At the centre of the diffuser bed support 13, there is an inlet duct 22 for material to be burnt in the bed. Material to be burnt is fed from a hopper 23 by way of a valve 24 to a motor driven feed screw 25 to be conveyed to the bottom of the duct 22. The duct 22 is in the form of a pneumatic elevator in which the material is elevated by means of air jets, such as that shown at 23A, supplied preferably by the blower 15, or from another source of air under pressure. A circular baffle 24a is provided over the top of the duct 22.

Thus it can be seen, particularly when the bed is caused to circulate, that material to be burnt is fed into the bed, and is carried down in the bed preventing immediate escape of the material from the bed surface, and thus ensuring that combustion is completed in the bed.

An ash trough 25A is provided around the periphery of the bed support to collect ash and other incombustible material from the bed in operation. Ash collecting in the trough 25A is released via a series of flap valves 26 spaced around the periphery of the support to a pneumatic conveyor manifold 27 arranged around the bed support in which the ash is conveyed, by means of air jets to a collection point 28.

At the collection point 28, the ash is removed by a pneumatic elevator 29 to separate apparatus to separate the ash from bed material which is then replaced in the bed, in a manner disclosed in our co-pending British Patent Applica tionNo. 18354/77. Serial No.1604221.

The inner surfaces of the combustion chamber 10 and the baffle 19 may be lined with or embody water filled heat exchange tubes to cool the structure and extract useful heat from the combustion process. Further such heat exchange tubes may be positioned in the bed as indicated at 30, and in the space above the bed as indicated at 31.

WHAT WE CLAIM IS: 1. A fluidised bed combustor comprising an upright circular cylindrical combustion chamber having disposed therein a generally frusto-conical downwardly and outwardly sloping air diffuser bed support arranged to support and fluidise with air a bed of granular material in the combustion chamber, means disposed in the axis of the combustion chamber to feed material to be burnt into a bed on the bed support, and means disposed around the periphery of the bed support for removing ash and other incombustible materials from the bed in which the air diffuser bed support is supplied with air in such fashion in operation that the bed circulates in a torroidal fashion.

2. A combustor as claimed in Claim 1, in which a generally frusto-conical baffle is provided in the combustion chamber sloping inwardly and upwardly from the wall of the chamber to cover the outer part of the bed.

3. A combustor as claimed in any one of Claims 1 or 2 in which the air diffuser bed support is formed with a series of concentric steps.

4. A combustor as claimed in Claim 3 in which the steps are right angle steps.

5. A combustor as claimed in Claim 3 or 4, in which the steps are arranged to diffuse air both upwards and radially outwards.

6. A combustor as claimed in any preceding Claim in which the means for feeding material to be bed comprises a pneumatic elevator.

7. A combustor as claimed in Claim 2, in which the baffle defines a chamber above it in the combustion chamber, in which material to be burnt may be preheated before being fed to the fluidised bed.

8. A fluidised bed combustor substantially as herein described with reference to the accompanying drawings.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims (8)

**WARNING** start of CLMS field may overlap end of DESC **. this assists in promoting the above circulation. The baffle 19 continues with a reverse slope 20 to define a chamber 21 around the inside of the combustion chamber above the bed. At the centre of the diffuser bed support 13, there is an inlet duct 22 for material to be burnt in the bed. Material to be burnt is fed from a hopper 23 by way of a valve 24 to a motor driven feed screw 25 to be conveyed to the bottom of the duct 22. The duct 22 is in the form of a pneumatic elevator in which the material is elevated by means of air jets, such as that shown at 23A, supplied preferably by the blower 15, or from another source of air under pressure. A circular baffle 24a is provided over the top of the duct 22. Thus it can be seen, particularly when the bed is caused to circulate, that material to be burnt is fed into the bed, and is carried down in the bed preventing immediate escape of the material from the bed surface, and thus ensuring that combustion is completed in the bed. An ash trough 25A is provided around the periphery of the bed support to collect ash and other incombustible material from the bed in operation. Ash collecting in the trough 25A is released via a series of flap valves 26 spaced around the periphery of the support to a pneumatic conveyor manifold 27 arranged around the bed support in which the ash is conveyed, by means of air jets to a collection point 28. At the collection point 28, the ash is removed by a pneumatic elevator 29 to separate apparatus to separate the ash from bed material which is then replaced in the bed, in a manner disclosed in our co-pending British Patent Applica tionNo. 18354/77. Serial No.1604221. The inner surfaces of the combustion chamber 10 and the baffle 19 may be lined with or embody water filled heat exchange tubes to cool the structure and extract useful heat from the combustion process. Further such heat exchange tubes may be positioned in the bed as indicated at 30, and in the space above the bed as indicated at 31. WHAT WE CLAIM IS:

1. A fluidised bed combustor comprising an upright circular cylindrical combustion chamber having disposed therein a generally frusto-conical downwardly and outwardly sloping air diffuser bed support arranged to support and fluidise with air a bed of granular material in the combustion chamber, means disposed in the axis of the combustion chamber to feed material to be burnt into a bed on the bed support, and means disposed around the periphery of the bed support for removing ash and other incombustible materials from the bed in which the air diffuser bed support is supplied with air in such fashion in operation that the bed circulates in a torroidal fashion.

2. A combustor as claimed in Claim 1, in which a generally frusto-conical baffle is provided in the combustion chamber sloping inwardly and upwardly from the wall of the chamber to cover the outer part of the bed.

3. A combustor as claimed in any one of Claims 1 or 2 in which the air diffuser bed support is formed with a series of concentric steps.

4. A combustor as claimed in Claim 3 in which the steps are right angle steps.

5. A combustor as claimed in Claim 3 or 4, in which the steps are arranged to diffuse air both upwards and radially outwards.

6. A combustor as claimed in any preceding Claim in which the means for feeding material to be bed comprises a pneumatic elevator.

7. A combustor as claimed in Claim 2, in which the baffle defines a chamber above it in the combustion chamber, in which material to be burnt may be preheated before being fed to the fluidised bed.

8. A fluidised bed combustor substantially as herein described with reference to the accompanying drawings.