GB2033561A - Method of controlling the level of a fluidised bed - Google Patents

Abstract

In a fluidised bed combustor means (13,14) is provided to determine the level (12) of the bed (11), and in response to the bed dropping below the desired level, to operate a servo- operated valve to allow bed material to pass from a hopper for that material into the bed. <IMAGE>

Description

SPECIFICATION Method of controlling the level of a fluidised bed This invention relates to fluidised bed combustors, and is particularly concerned with the feed of material to the fiuidised bed.

In the feed of material into a fluidised bed combustor for combustion therein, difficulty has been experienced in achieving reliable flow of material into the bed.

The invention provides means for feeding material into the bed, to control the level of the bed during operation.

Accordingly in a fluidised bed combustor means is provided to determine the level of the bed, and in response to the bed dropping below the desired level, to operate a servo-operated valve to allow bed material to pass from a hopperforthat material into the bed.

Preferably in order to determine the level of a fluidised bed in a combustorforthe purposes of controlling the depth of the bed, fluid pressure detector devices are inserted in the bed at points which are spaced vertically one from another, and the pressure difference between those points is measured to determine the height of the bed.

In orderto promote the flow of such bed material, means is provided to fluidise the bed material at the base of the hopper therefor, just above the servooperated valve.

By this means reliable flow of bed material, which may be sand or other similar granular material into the combustor may be achieved to control the level of the bed to a desired height in operation as ashing from the bed and combustion of material takes place.

In order to promote a fuller understanding of the above and other aspects of the invention, one embodiment will now be described, by way of example only, with reference to the accompanying drawing which shows in schematic cross-section a fluidised bed combustor.

The drawing shows a fluidised bed combustor having a sloping air diffuser 10 supporting fluidised bed 11 having a surface level 12. Pressure detectors are inserted at 13 and 14, the points 13 and 14 being spaced vertically from one another. Pressure sensors are provided to measure the pressures at the points 13 and 14 and means is provided for determining the pressure difference. It has been found that this pressure difference gives a very effective correlation with the depth of the bed, and thus the pressure difference determined may be used in controlling the supply of additional material to the bed, or the removal of material from the bed, to control its depth.

A hopper 15 is provided for the temporary storage of bed material and a feed chute 16 is arranged to direct material from the hopper to the bed. A valve 17 which is operable by means of an electrical servo-motor 18, is provided at the outlet of the hopper to control the supply of material to the chute 16.

An electrical control system, not shown, is provided, in known mannerperse, to control the servo-motor 18 in dependence upon the bed depth measurement derived from the detectors 13 and 14, so as to maintain the depth of the bed constant.

1. A fluidised bed combustor including a feed hopper for material to be fluidised in the bed and a servo motor operable valve arranged to control the supply of material from the hopper to the bed in response to measurement of the depth of the bed so as to maintain the level of the bed substantiaily constant.

2. A fluidised bed combustor as claimed in Claim 1, in which two fluid pressure detectors are provided to experience fluid pressure in the bed at points which are spaced vertically from one another and means is provided to determine the difference in pressure at those points in operation of the bed such difference being used as a signal to control such servo motor as a measurement of the depth of the bed.

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

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

Claims (3)

**WARNING** start of CLMS field may overlap end of DESC **. SPECIFICATION Method of controlling the level of a fluidised bed This invention relates to fluidised bed combustors, and is particularly concerned with the feed of material to the fiuidised bed. In the feed of material into a fluidised bed combustor for combustion therein, difficulty has been experienced in achieving reliable flow of material into the bed. The invention provides means for feeding material into the bed, to control the level of the bed during operation. Accordingly in a fluidised bed combustor means is provided to determine the level of the bed, and in response to the bed dropping below the desired level, to operate a servo-operated valve to allow bed material to pass from a hopperforthat material into the bed. Preferably in order to determine the level of a fluidised bed in a combustorforthe purposes of controlling the depth of the bed, fluid pressure detector devices are inserted in the bed at points which are spaced vertically one from another, and the pressure difference between those points is measured to determine the height of the bed. In orderto promote the flow of such bed material, means is provided to fluidise the bed material at the base of the hopper therefor, just above the servooperated valve. By this means reliable flow of bed material, which may be sand or other similar granular material into the combustor may be achieved to control the level of the bed to a desired height in operation as ashing from the bed and combustion of material takes place. In order to promote a fuller understanding of the above and other aspects of the invention, one embodiment will now be described, by way of example only, with reference to the accompanying drawing which shows in schematic cross-section a fluidised bed combustor. The drawing shows a fluidised bed combustor having a sloping air diffuser 10 supporting fluidised bed 11 having a surface level 12. Pressure detectors are inserted at 13 and 14, the points 13 and 14 being spaced vertically from one another. Pressure sensors are provided to measure the pressures at the points 13 and 14 and means is provided for determining the pressure difference. It has been found that this pressure difference gives a very effective correlation with the depth of the bed, and thus the pressure difference determined may be used in controlling the supply of additional material to the bed, or the removal of material from the bed, to control its depth. A hopper 15 is provided for the temporary storage of bed material and a feed chute 16 is arranged to direct material from the hopper to the bed. A valve 17 which is operable by means of an electrical servo-motor 18, is provided at the outlet of the hopper to control the supply of material to the chute 16. An electrical control system, not shown, is provided, in known mannerperse, to control the servo-motor 18 in dependence upon the bed depth measurement derived from the detectors 13 and 14, so as to maintain the depth of the bed constant. CLAIMS

1. A fluidised bed combustor including a feed hopper for material to be fluidised in the bed and a servo motor operable valve arranged to control the supply of material from the hopper to the bed in response to measurement of the depth of the bed so as to maintain the level of the bed substantiaily constant.

2. A fluidised bed combustor as claimed in Claim 1, in which two fluid pressure detectors are provided to experience fluid pressure in the bed at points which are spaced vertically from one another and means is provided to determine the difference in pressure at those points in operation of the bed such difference being used as a signal to control such servo motor as a measurement of the depth of the bed.

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