GB1601212A

GB1601212A - Start up arrangements for fluidized bed combustion furnaces

Info

Publication number: GB1601212A
Application number: GB186877A
Authority: GB
Original assignee: Worsley & Co Ltd G P
Current assignee: Worsley & Co Ltd G P
Priority date: 1978-04-17
Filing date: 1978-04-17
Publication date: 1981-10-28

Description

(54) START UP ARRANGEMENTS FOR FLUIDISED BED COMBUSTION FURNACES (71) We, G. P. WORSLEY & Co.

LIMITED, a British Company of Haydock Lane Works, Haydock, St. Helens, Merseyside WAll 0UU, 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 material including combustible solid fuel, normally coal. or even a liquid fuel such as oil.

Attainment of fuel ignition conditions for such a furnace is usually by preheating particulate incombustible material of the bed prior to normal substantially continuous supply of the fuel to be burnt. We have recently filed patent applications disclosing various systems for such preheating, for example over-firing using oil or even gas, burners above the bed. underfiring with burners below the bed, and firing of burners effectively within the bed.

It is an object of this invention to provide a further alternative preheating system for the bed material.

According to the invention there is provided a fluid-bed furnace having means for providing a hot stream of combustion promoting gas to preheat and fluidise at least a portion of incombustible particulate bed material, the hot gas stream being heated or generated by means of a burner prior to reaching the vicinity of the bed and duct- ing to take that stream to a desired position of the bed which ducting takes the hot gas stream through the bed material prior to release in or below the bed.

Preferably the desired position is substantially centrally of the bed.

The furnace cf the invention preferably further comprises fluidising inlets to the bed material for the hot gas stream from said ducting.

A particularly efficient furnace is obtained where substantially the whole of the duct passes through the furnace chamber proper from above the bed and that ducting also serves to house the burner itself. Thus, the duct may pass from the top of the furnace downwards and through the bed, say with a side exit or flue for the heated gas output of the furnace.

The use of a centrally fluidised bed area for pre-heating purposes allows separation of supply of fluidising combustion promoting gas to surrounding areas of the bed either by way of sparge pipes passing through the bed material or, and preferably, via pipes extending from below the bed.

One embodiment of the invention will now particularly described, by way of example, with reference to the accompanying drawing, which is a sectional view through a fluid bed furnace.

In the drawing, a combustion chamber 10 has side walls 12 formed from andlor lined with refractory material and having an upwardly extending throat part 14 from which a side exit flue 16 is shown. At its lower part, the combustion chamber 10 has a suitable support 18 for particulate bed material 20, Extending from a top part 20 of the throat portion is a duct 22 passing at its lower end through the bed support and being ported at 24 to communicate with a plenum arrangement 26 and gas injector pipes 28 extending through the bed support and having appropriate release heads 30.

The downwardly extending duct 22 has at its upper part a gas, or preferably oil, burner 32 and a combustion promoting gas supply 34 in order to provide a flow of heated gas into the bed material for fluidising and heating purposes.

The remaining outer areas of the bed support are shown having further gas inlet pipes 36 passing therethrough and equipped with gas release heads 38 for the supply, from a plenum chamber 40, of combustion promoting and fluidising gas.

The combustion chamber itself may be of generally circular shape or of any other desired construction, such as a long sub stantially rectangular chamber in which case it may be advantageous to have either an elongated duct 22 equipped with more than one burner or a plurality of ducts spaced along and within a middle region thereof.

In operation, air from a pressurising fan will be fed through the duct 22 and its burner 32 supplied with fuel oil via pipe 42 will be ignited. The gasses issuing from the lower end of the duct will be heated to a predetermined extent depending upon burner output and the speed of combustion promoting air supply and can readily be arranged both to fluidise and preheat the inner regions of the bed material to a temperature at which fuel such as oil, but preferably coal, delivered to the furnace chamber via means not shown will spontaneously ignite. Clearly, if the only gas supply at this time is via the duct from the burner, an excess of oxygen will be required over and above requirements of the burner 32 in order to allow the promotion of combustion of added fuel material in the bed itself. However, it would also be feasible for the relatively peripheral ducts to be simultaneously supplied with combustion promoting gas for fluidising purposes and for ignition to start substantially at the interface between that gas and the gas issuing from the duct.

If desired, the plenum chamber 40 for supply to the peripheral inlet pipes 36 could be partitioned to allow sectional working of a bed either in bands outwardly from the central region of the bed or in sections along the length of an elongated combustion chamber, i.e. through the plane of the paper.

It would also be possible for communication to be selectively permitted between the plenum chamber arrangement for the outer fluidising bed pipes 36 and the inner fluidising pipes 30, say at least after the preheating stage.

Damper provisions are shown at various points in the drawing so as to allow for fine tuning, or general adjustment of the furnace in order to obtain optimum operating conditions. Perhaps particularly with circular section combustion chambers, it may also be preferred to provide for cyclonic action within the combustion chamber and at least above the bed material thereof via suitably inclined combustion promoting gas inlets through the furnace side walls.

If the oil burner in the duct is kept going throughout furnace operation there may well be a useful heat transfer through the ducting itself, i.t. between the results of bed material combustion and the preheated air from the burner 32. Such burner action could of course be at a lower level than for preheating purposes, or it might even allow alternative fuel operation of the furnace.

WHAT WE CLAIM IS: 1. A fluid-bed furnace having means for providing a hot stream of combustion promoting gas to preheat and fluidise at least a portion of incombustible particulate bed material, the hot gas stream being heated or generated by means of a burner prior to reaching the vicinity of the bed and ducting to take that stream to a desired position of the bed which ducting takes the hot gas stream through the bed material prior to release in or below the bed.

2. A fluid-bed furnace according to claim 1, wherein said desired position is substantially central of the bed.

3. A fluid-bed furnace according to claim 1 or 2, further comprising fluidising inlets to the bed material for the hot gas stream from said ducting.

4. A fluid-bed furnace according to claim 1, 2 or 3, wherein said ducting passes through the furnace chamber proper above the bed material.

5. A fluid-bed furnace according to claim 4, wherein the ducting houses the burner and substantially the whole of the ducting is within the furnace chamber proper and the bed material.

6. A fluid-bed furnace according to claim 5, wherein the ducting comprises a cylindrical duct from the. top of the furnace chamber to and through the bed material.

7. A fluid-bed furnace according to claim 6, wherein the furnace chamber has a side exit or flue for exhaust gas output of the furnace.

8. A fluid-bed furnace according to claim 7, wherein the burner is in a top part of the duct.

9. A fluid-bed furnace according to any preceding claim, having separate means for supplying combustion-promoting gas to the bed material.

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

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

Claims

**WARNING** start of CLMS field may overlap end of DESC **. stantially rectangular chamber in which case it may be advantageous to have either an elongated duct 22 equipped with more than one burner or a plurality of ducts spaced along and within a middle region thereof. In operation, air from a pressurising fan will be fed through the duct 22 and its burner 32 supplied with fuel oil via pipe 42 will be ignited. The gasses issuing from the lower end of the duct will be heated to a predetermined extent depending upon burner output and the speed of combustion promoting air supply and can readily be arranged both to fluidise and preheat the inner regions of the bed material to a temperature at which fuel such as oil, but preferably coal, delivered to the furnace chamber via means not shown will spontaneously ignite. Clearly, if the only gas supply at this time is via the duct from the burner, an excess of oxygen will be required over and above requirements of the burner 32 in order to allow the promotion of combustion of added fuel material in the bed itself. However, it would also be feasible for the relatively peripheral ducts to be simultaneously supplied with combustion promoting gas for fluidising purposes and for ignition to start substantially at the interface between that gas and the gas issuing from the duct. If desired, the plenum chamber 40 for supply to the peripheral inlet pipes 36 could be partitioned to allow sectional working of a bed either in bands outwardly from the central region of the bed or in sections along the length of an elongated combustion chamber, i.e. through the plane of the paper. It would also be possible for communication to be selectively permitted between the plenum chamber arrangement for the outer fluidising bed pipes 36 and the inner fluidising pipes 30, say at least after the preheating stage. Damper provisions are shown at various points in the drawing so as to allow for fine tuning, or general adjustment of the furnace in order to obtain optimum operating conditions. Perhaps particularly with circular section combustion chambers, it may also be preferred to provide for cyclonic action within the combustion chamber and at least above the bed material thereof via suitably inclined combustion promoting gas inlets through the furnace side walls. If the oil burner in the duct is kept going throughout furnace operation there may well be a useful heat transfer through the ducting itself, i.t. between the results of bed material combustion and the preheated air from the burner 32. Such burner action could of course be at a lower level than for preheating purposes, or it might even allow alternative fuel operation of the furnace. WHAT WE CLAIM IS:

1. A fluid-bed furnace having means for providing a hot stream of combustion promoting gas to preheat and fluidise at least a portion of incombustible particulate bed material, the hot gas stream being heated or generated by means of a burner prior to reaching the vicinity of the bed and ducting to take that stream to a desired position of the bed which ducting takes the hot gas stream through the bed material prior to release in or below the bed.