GB1592846A - Fluid-bed furnaces - Google Patents

Description

(54) FLUID-BED FURNACES (71) We, G. P. WORSLEY & COM PANY LIMITED, A British Company of Haydock Lane, Haydock, St. Helens, 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: The invention relates to fluid bed furnaces where combustion promoting gas, normally air, is forced through and "fluidises", that is maintains in motion, a bed of particulate incombustible material, into which fuel is fed, normally a solid fuel, such as coal, but possibly a liquid fuel, such as oil.

One requirement of fluid bed furnaces is to maximise heat output and thus the rate at which the combustible material is burnt in the bed. To do this, the bed should burn at a high temperature but that temperature should not rise so high that the combustible material or incombustibles therefrom fuse, either generally or locally, to destroy the fluidised nature of the gas/material mixture.

A sometimes conflicting requirement arises in providing a satisfactory gas supply which, particularly on ignition, should not cool the bed excessively and unevenly, and yet which is required to supply sufficient gas subsequently to maintain proper motion of, and burning within, the bed.

It is an object of the invention to improve operation of fluid bed furnaces, preferably with a contribution to mitigating one or other, if possible both, of the above problems, such fluid bed furnaces being characterised by being for generating heat as hot exhaust gases from combustion of fuel added to a bed of incombustible particulate material fluidised by combustion promoting gas supplied via fluidisation means serving to introduce that gas into the bed material for admixture therein with said fuel to consume the latter by self-sustaining burning after heating up of the bed material. Preferably fuel is added to the bed from a different position to the fluidisation means, such as from a position above the bed.

According to the invention there is pr vided a fluid bed furnace serving to generate heat as hot exhaust gases from combustion of fuel added to a bed of incombustible particulate material fluidised by combustion promoting gas supplied via fluidisation means serving to introduce that gas into the bed material for admixture therein with said fuel to consume the latter by self-sustaining burning after heating up of the bed material, the furnace having means serving to supply said fuel to the bed, at least one auxiliary heating burner separate from said means serving to supply fuel and free of the bed material to generate heat or hot gas for application to the bed material to pre-heat the latter prior to said combustion of fuel in the bed, and a combustion promoting gas supply system which is common both to the or each auxiliary heating burner and to the bed fluidisation means.

Implementing the invention, for example using fuel gas or oil burners to ignite the bed, means that only a part of the total amount of available gas will be supplied to the bed while the auxiliary heating system itself is using gas. Generally, after ignition, the auxiliary heating system will be turned down and a greater proportion of the gas will pass to the bed as required for efficient burning of the combustible material.

A suitable combustion promoting gas supply system has a plenum chamber, preferably formed between the furnace exhaust system and the furnace proper, and with communication both to pipes or ducts feeding the bed and to pipes or ducts feeding the auxiliary system. The latter pipes or ducts may conveniently be formed or provided against or adjacent to the furnace walls, for example to feed pressure jet oil burners operative through the furnace walls immediately above the bed.

Such a plenum chamber will have gas pumped into it and will achieve a desired degree of preheating of the gas in order to enhance efficiency of the furnace as a whole in utilizing otherwise waste heat output.

Additionally or alternatively according to the invention there is provided a fluid bed furnace in which one or more gas release pipes or ducts are, for gas supply thereto, connected to one or more pipes or ducts that traverse the bed itself.

Preferably, a plurality of gas release pipes or ducts are individually connected to corresponding ones of a plurality of the pipes or ducts that traverse the bed itself and at least the latter have a substantially even distribution over the area of the bed.

The or each such connecting or bed-traversing duct or pipe may be wholly or partially within, or immediately below the combustible material of the bed which will usually be formed in the upper parts of a layer of incombustible particulate material such as sand.

The or each gas release pipe or duct, or each of at least some thereof, is preferably disposed below at least some of the connecting pipes or ducts, conveniently its corresponding connecting pipe or duct.

Implementing this feature of the invention provides two advantages in that, prior to its release into the bed, the gas serves to cool the bed by extracting heat therefrom which, in turn, causes the gas to be preheated for release into the bed. Also, selective opening or closing of a plurality of connecting pipes or ducts distributed over the area of the bed allows a part or parts only of the bed to be operational at any one time.

In implementing the invention it is further preferred to form the connecting or gas release passageways, conveniently from junctions therebetween, to positions above the bed so as to promote combustion at the upper part or surface thereof.

One embodiment of the invention will now be described, by way of example, with reference to the drawings in which: Figure 1 is a sectional view through a fluid bed furnace; Figure 2 is a sectional view along the lines A--A of Figure 1; Figure 3 is a sectional plan view taken on the lines B-B of Figure 2; and Figure 4 shows details of interconnected fluid-bed traversing gas supply and release ducts.

A furnace chamber 10 is shown with a fluid bed 11. An exhaust duct 12 is shown extending substantially parallel with the furnace chamber 10 and in communication therewith via an upper communicating flue or passageway 13.

Between the exhaust duct and the furnace chamber there is a plenum chamber 15 to which air is supplied from a fan 16 driven by an electric motor 17. Air from the fan will be pre-heated, in operation of the furnace by wall 18 of the furnace, wall 19 of the exhaust duct, and wall 20 of the flue 13. From the plenum chamber 15 the air is passed via connecting ducts 21 which traverse the full width of the fluid bed to end chambers 22 from which it is returned via lower gas release ducts 23 from which it is injected into the fluid bed. This achieves both cooling of the fluid bed by passage of air along the upper ducts 21 and preheating of the air prior to its injection from the ducts 23. The connecting ducts 21 are shown as being at least partially within the bed which is formed above a layer of sand 24.

The end chambers 22 are also shown connected by passageways 25, under the control of dampers 26, to a position above the fluid bed to enhance burning thereof.

A coal supply hopper is shown at 30 with a rotary feeder 31 positioned below the hopper and supplying the furnace via a downwardly inclined feed passage or passages 32 extending through wall 33 of the furnace chamber 10.

As noted above, the fluid bed of the furnace and the ducting 21, 23 is shown situated above a static sand bed 24 which shares a common pit for ash. (The fluid bed includes sand and coal). Access doors to the furnace are indicated at 34. A temperature sensing probe 35 is shown at the upper part of the furnace chamber and may form part of an automatic control system, or simply act as an indicator for operator control purposes. Similiarly, tem perature sensing probes 36 are shown for obtaining indications of the bed temperature at desired positions.

The furnace is shown as having an auxiliary heating system comprising pressure jet oil burners 38 in the ends 39, 40 of the furnace chamber. These pressure jet burners 38 are supplied with air via ducting 41 taken from the ends of the plenum chamber 15. For ignition of the furnace, the pressure jet burners are first lit and will take fan-driven air from the plenum chamber 15 and so will relatively starve the supply of air to the fluid bed via ducting 21, 23. As the fluid bed ignites, the oil pressure jets will be turned down so that more air will pass directly to the fluid bed until, eventually, the oil pressure jet burners are extinguished and the fluidised coal bed is fully alight.

Ash and grit may be removed from the furnace exhaust via one or more access doors 45 as shown in Figure 3.

As is best seen from Figures 2 and 3, the air supply and release ducting 21, 23 is evenly distributed over the area of the bed 12 so that its effect is spread in as even a manner as is, practicable. Individual aperture control for the ducting 21, 23 or group control, allows part or parts, only of the furnace bed to be active at any one time and, further, gives a fine control facility for the bed, particularly in conjunction with the surface supply control dampers 26 and an overall air control damper shown at 46 in Figure 1.

The furnace described may have its wall thicknesses differ and be designed with a view to achieving a particular degree of air preheating in the plenum chamber.

Embodiments of the invention have particular but not exclusive, application to furnaces having shallow layers of combustible material to be fluidised and burnt. An overall or alternative aspect of the invention can be viewed as the provision of a fluid-bed furnace with a large area of bed compared with the depth of combustible material to be burnt.

Although reference has been made to the combustible material being particulate, no interference is to be taken that such material has to be finely comminuted as substantial lumps, at least in the case of coal, can be burnt at least in shallow bed furnaces.

WHAT WE CLAIM IS: 1. A fluid bed furnace serving to generate heat as hot exhaust gases from combustion of fuel added to a bed of incombustible particulate material fluidised by combustion promoting gas supplied via fluidisation means serving to introduce that gas into the bed material for admixture therein with said fuel to consume the latter by self-sustaining burning after heating up of the bed material the furnace having means serving to supply said fuel to the bed, at least one auxiliary heating burner separate from said means serving to supply fuel and free of the bed material to generate heat or hot gas for application to the bed material to pre-heat the latter prior to said combustion of fuel in the bed, and a combustion promoting gas supply system which is common both to the or each auxiliary heating burner and to the bed fluidisation means.

2. A fluid bed furnace as claimed in claim 1 wherein fuel is added to the bed from a different position to the fluidisation means.

3. A fluid bed furnace as claimed in claim 2 wherein fuel is added from a position above the bed.

4. A fluid bed furnace as claimed in claim 1, 2 or 3 wherein the or each burner is above the bed.

5. A fluid bed furnace according to any one of claims 1 to 4 wherein the or each auxiliary heating burner is a fuel gas or oil burner and the combustion promoting gas supply system is adapted for supply of part only of the total available combustion promoting gas to the bed fluidisation means with the remainder supplied to the burner or burners at least during said heat up.

6. A fluidmbed furnace according to any one of claims 1 to 4 wherein the gas supply system is adapted to reduce or substantially eliminate gas suppiy to the burner or burners after said heat up and initiation of fuel burning in the bed.

7. A fluid-bed furnace according to any preceding claim, wherein the gas supply system comprises a plenum chamber common to feeds both for the auxiliary heating system and the bed fluidisation means.

8. A fluid-bed furnace according to claim 7, wherein said plenum chamber is located between a furnace combustion chamber and a furnace exhaust system.

9. A fluid-bed furnace according to any preceding claim, wherein the bed fluidisation means comprises pipes or ducts traversing the bed and adapted for gas release into the par ticulate material thereof.

10. A fluid-bed furnace according to claim 9, comprising further pipes or ducts traversing the bed and connected to supply the gas release pipes or ducts.

11. A fluid-bed furnace according to claim 10, wherein further pipes or ducts are individually connected to supply different ones, respectively, of the gas release pipes or ducts.

12. A fluid-bed furnace according to claim 10 or claim 11, wherein at least the supply pipes or ducts have a substantially even distribution over the area of the bed.

13. A fluid bed furnace according to claim 10, 11 or 12 wherein at least some of the supply pipes or ducts are above at least some of the gas release pipes or ducts.

14. A fluid-bed furnace according to claim 13, wherein each supply pipe or duct is above a corresponding one of the gas release pipes or ducts.

15. A fluid-bed furnace according to any one of claims 9 to 14, wherein at least some of the gas release pipes or ducts have communication to a level above that for the bed material when static and for gas release thereat.

16. A fluid-bed furnace arranged and adapted to operate substantially as herein described with reference to and as shown in the accompanying drawings.

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

Claims (16)

**WARNING** start of CLMS field may overlap end of DESC **. Although reference has been made to the combustible material being particulate, no interference is to be taken that such material has to be finely comminuted as substantial lumps, at least in the case of coal, can be burnt at least in shallow bed furnaces. WHAT WE CLAIM IS:

1. A fluid bed furnace serving to generate heat as hot exhaust gases from combustion of fuel added to a bed of incombustible particulate material fluidised by combustion promoting gas supplied via fluidisation means serving to introduce that gas into the bed material for admixture therein with said fuel to consume the latter by self-sustaining burning after heating up of the bed material the furnace having means serving to supply said fuel to the bed, at least one auxiliary heating burner separate from said means serving to supply fuel and free of the bed material to generate heat or hot gas for application to the bed material to pre-heat the latter prior to said combustion of fuel in the bed, and a combustion promoting gas supply system which is common both to the or each auxiliary heating burner and to the bed fluidisation means.

2. A fluid bed furnace as claimed in claim 1 wherein fuel is added to the bed from a different position to the fluidisation means.

3. A fluid bed furnace as claimed in claim 2 wherein fuel is added from a position above the bed.

4. A fluid bed furnace as claimed in claim 1, 2 or 3 wherein the or each burner is above the bed.

5. A fluid bed furnace according to any one of claims 1 to 4 wherein the or each auxiliary heating burner is a fuel gas or oil burner and the combustion promoting gas supply system is adapted for supply of part only of the total available combustion promoting gas to the bed fluidisation means with the remainder supplied to the burner or burners at least during said heat up.

6. A fluidmbed furnace according to any one of claims 1 to 4 wherein the gas supply system is adapted to reduce or substantially eliminate gas suppiy to the burner or burners after said heat up and initiation of fuel burning in the bed.

7. A fluid-bed furnace according to any preceding claim, wherein the gas supply system comprises a plenum chamber common to feeds both for the auxiliary heating system and the bed fluidisation means.

8. A fluid-bed furnace according to claim 7, wherein said plenum chamber is located between a furnace combustion chamber and a furnace exhaust system.

9. A fluid-bed furnace according to any preceding claim, wherein the bed fluidisation means comprises pipes or ducts traversing the bed and adapted for gas release into the par ticulate material thereof.

10. A fluid-bed furnace according to claim 9, comprising further pipes or ducts traversing the bed and connected to supply the gas release pipes or ducts.

11. A fluid-bed furnace according to claim 10, wherein further pipes or ducts are individually connected to supply different ones, respectively, of the gas release pipes or ducts.

12. A fluid-bed furnace according to claim 10 or claim 11, wherein at least the supply pipes or ducts have a substantially even distribution over the area of the bed.

13. A fluid bed furnace according to claim 10, 11 or 12 wherein at least some of the supply pipes or ducts are above at least some of the gas release pipes or ducts.

14. A fluid-bed furnace according to claim 13, wherein each supply pipe or duct is above a corresponding one of the gas release pipes or ducts.

15. A fluid-bed furnace according to any one of claims 9 to 14, wherein at least some of the gas release pipes or ducts have communication to a level above that for the bed material when static and for gas release thereat.

16. A fluid-bed furnace arranged and adapted to operate substantially as herein described with reference to and as shown in the accompanying drawings.