US3756201A

US3756201A - Industrial boilers

Info

Publication number: US3756201A
Application number: US00182808A
Authority: US
Inventors: R Williams
Original assignee: BOILERS Ltd
Current assignee: THORN EMI INDUSTRIAL BOILERS Ltd; Thorn EMI Energy Developments Ltd
Priority date: 1970-09-22
Filing date: 1971-09-22
Publication date: 1973-09-04
Anticipated expiration: 1990-09-04
Also published as: CA934622A; AU3370371A; GB1355054A; FR2112975A5; DE2148065A1; AU432939B2

Abstract

An industrial boiler including a fluid-fired burner and having means for feeding solid fuel to the combustion chamber, and there being a control means which is operable to control the burner and the feed means so that the burner can operate whilst the feed means is inoperative, and the feed means can operate whilst the burner is inoperative, and the burner can operate whilst the feed means is operative.

Description

[ 1 Sept. 4, 1973 INDUSTRIAL BOILERS 4/1966 Kloecker.......

1,616,960 2/1927 Johanson...... 1'22 2 3,066,655 12/1962 Jakobsson......................... ll0/22X Inventor: Robert Spencer Williams, Upper Arley near Bewdley, England [73] Assignee: G. W. B. Boilers Limited, Worcester County England Primary Examiner-Kenneth W. Sprague Sept. 22, 1971 Attorney-George H. Spencer et all.

4 Appl. No.: 182,808

[22] Filed:

ABSTRACT 373/70 An industrial boiler including a fluid-fired burnerand having means for feeding solid fuel to the combustion [52] US. 122/2, 110/10 chamber and there being a comm] means which is [51] Int. F22b 33/00 erable to control h burner and the feed means so ha [58] Field of Search 110/10, 22; 122/2, the burner can operate whilst the feed means is inoper 122/235 P I ative, and the feed means can operate whilst the burner is inoperative, and the burner can operate whilst the feed means is operative. I

[5 6] References Cited UNITED STATES PATENTS 3,536,049 10/1970 Agrest..........................=..110/235 P 13 Claims, Drawing Figures PATENTEDsEP 4 I975 SHEET 3 BF 3 INDUSTRIAL BOILERS BACKGROUND OF THE INVENTION This invention relates to industrial boilers. It is an object of the present invention to provide a new industrial boiler.

SUMMARY OF THE INVENTION The present invention consists broadly in an industrial boiler including a fluid-fired burner communicating with a combustion chamber containing a grate, air supply means for delivering air to said chamber and feed means for feeding solid fuel to said chamber so as to fall onto or towards the grate and control means operable to control said burner and said feed means whereby, in operation of the boiler, said burner can operate whilst the feed means is inoperative, said feed means can operate whilst the burner is inoperative and said burner can operate whilst said feed means is operalive.

The solid fuel may be saw dust, wood chippings, wool shavings, or other waste material similar to wood such as cotton seed husks and similar vegetable waste and all referred to herein as wood waste The control means of the boiler of the present invention preferably operates in such way that, on starting up of the boiler and actuation of the air supply means, the burner is operated after a predetermined time interval, the feed means is rendered operative after a further predetermined time interval and the burner is rendered inoperative after another predetermined time interval.

Said time intervals are preferably adjustable.

The burner is preferably arranged to operate selectively with either a first lower output or a second higher output, the burner operating initially with said first output and then with said second output. The arrangement is preferably such that prior to the feed means being rendered operative, said burner is operating at said second output and such that, on said feed means being rendered operative, the burner then operates at said first output and subsequently ceases to operate.

The solid fuel feed means preferably includes a storage hopper for containing the solid fuel, said storage hopper including a primary conveyor for feeding solid fuel to an output pipe along which the fuel is fed pneumatically to the conduit which depends downwardly from the top of the shell of the boiler and a secondary conveyor for feeding the fuel from the interior of the hopper to the primary conveyor.

The primary conveyor is preferably a screw-conveyor and the secondary conveyor may comprise an endless belt conveyor which extends over the full width of the hopper or the secondary conveyor may comprise a series of parallel screw-conveyors extending from end to end of the hopper transverse to the axis of the screw of the primary conveyor.

Means are preferably provided for feeding air into the combustion chamber so as to pass up through the grate, the flow of air through the grate being such as to maintain particles of solid fuel which drop onto the grate in a fluidised state.

BRIEF DESCRIPTION OF THE DRAWINGS The invention will now be described by way of example with reference to the accompanying drawings wherein,

FIG. 1 is a perspective view, partly broken away, of

a wood-fired/oil-fired boiler embodying the invention, FIG. 2 is a perspective view, partly broken away, of part of the boiler of FIG. 1,

FIGS. 3A-3D are diagrammatic illustrations of the control system of the furnace of FIG. 1.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring to FIGS. 1 and 2 of the drawings, the solid fuel, which, in the present example is wood waste, is contained within a hopper l0 and is fed from the hopper 10 into a pipe 11 which communicates to a conduit 12 leading downwardly from the top of the boiler 13 into a combustion chamber 14 within the boiler. A shut-off valve 15 is contained within the pipe 11.

The base of the hopper 10 is constituted by an endless belt, conveyor 16 which extends over the whole of the base of the hopper 10 and is arranged to deliver wood into the trough 17 of a screw-type conveyor 18. The conveyor 18 has its axis of transport at right angles to the axis of movement of the endless belt conveyor 16 and is arranged to deliver the wood to a pneumatic blower 19 in the feed pipe 11 which extends between the blower l9 and the conduit 12 so that the wood is fed pneumatically into the boiler.

A level controller, not shown, is provided in the trough 17 so that the endless belt conveyor 16 is operated to maintain a predetermined level of wood continuously in the trough.

The combustion chamber 14 within the boiler 13 is of generally cylindrical form and the lower end portion 20 of the conduit 12 which extends downwardly into the chamber 14 is of frusto-conical form.

The conduit 12 is surrounded concentically by a cylindrical tube 22 into which is fed air under pressure from the pipe 11. The compressed'air passes through tangential air nozzles 21 at the top and bottom of the tube 22 to induce the fuel to distribute evenly over the grate 25. The lower end of the fuel conduit 12 is of frusto-conical shape as indicated at 20 and the inner face of the cone is provided with ribs, not shown.

The cylindrical combustion chamber 14 is provided at its inlet end 26 with the nozzle of an oil burner 27 to which oil is fed under pressure from an oil tank through a line 28 containing a pump 29 and an electrical pre-heater 30. A burner air supply duct 31 extends from the blower 24 and is arranged to feed burner air into the chamber 14 along a horizontal axis coincident with the axis of the oil burner 27.

The grate 25 within the combustion chamber 14 is arranged at a horizontal level below the axis of the oil burner 27 and refractory rubble is supported on the grate 25. The flame from the oil burner 27 serves to heat the refractory rubble which acts as a back radiator and provides continuous ignitiion of the wood fed in through the conduit 12 extending downwardly from the top of the boiler. Primary air is fed through a duct 32, which branches from the duct 31, into the bottom of the combustion chamber 14 so as to pass up through the rubble on the grate 25, as shown by the arrows A. Thus, when wood is being burned and lumps or chips of wood drop onto the rubble, these lumps or chips are maintained in a fluidised state so as to assist combustion thereof.

The products of combustion pass from the combustion chamber 14, as shown by the: arrow B, into a reversing chamber 33 from which they pass through a series of smoke tubes 34 arranged parallel to the axis of the combustion chamber 14 to a chamber 35 at the front of the boiler. There is then a further series 36 of smoke tubes extending from the front of the boiler to a chamber 37 at the rear of the boiler and this chamber contains a grit arrester 28 for separating grit from the combustion products which then pass through a flue 39.

A part of the out-put of the blower 24 is supplied to a conduit 40 extending to the combustion chamber 14 above the fire grate 25.

At the grit arrest 28 the conduit 40 has a narrow portion 41 to provide a high velocity pass, and a conduit 42 connects the bottom of the grit arrester 28 to the narrow portion 41 so that venturi action produces suction from the grit arrester 28 into the conduit 40.

Referring now particularly to FIG. 3 of the drawings, a control system controlling operation of the boiler is provided and this includes a pair of

photoelectric cells

45 and 46. The two

photoelectric cells

45, 46 are arranged with one (45) directed along the flame tube of the oil burner 27 so as to sense combustion in the combustion chamber 14, i.e., the solid fuel flame 47 and the oil flame 48. The other photoelectric cell 46 is arranged transverse to the flame tube and is shielded from the combustion chamber 14 so as to sense only the oil flame 48 within the flame tube. The control system also includes means for controlling operation of the oil supply valve and the valve in the wood deliv ery pipe 11.

In use, the arrangement is that, on starting up the boiler, the air delivery blower 24 is first operated to deliver air into the combustion chamber to act as a purge. The oil valve is then opened and the pump 29 in the oil feed line 28 is operated, whereby oil is fed into the burner 27 and the rate of oil supplied is such that a first, low, thermal output is obtained. After a predetermined adjustable time interval the rate of oil supply is increased so as to increase the thermal output of the oil burner. This second output corresponds to the intended operational output of the boiler.

FIG. 3A illustrates the state of the control system at this stage. Because the

photoelectric cells

45 and 46 both sense a flame the oil supply is maintained. No wood is supplied as the timer 49 is set for oil supply only.

After a predetermined adjustable time interval the timer 49 causes the rate of oil supplied to the burner to be reduced and the valve 15 in the wood feed pipe 11 is opened and the rate of feed of wood is correlated to the rate of oil supplied so that the total thermal output of the boiler remains substantially the same.

Again, the

photoelectric cells

45 and 46 both sense a flame and so the oil and wood are maintained switched on as the timer is in condition for feed of both fuels, as shown in FIG. 3B.

After a further predetermined time interval, the timer causes the supply of oil to the burner 27 to be cut off and the rate of wood supply is increased to maintain a uniform thermal output of the boiler. The time for which the higher oil delivery rate is maintained is dependent on the fineness of the wood and on the initial temperature of the boiler. If, for example, fine sawdust is being used and the initial temperature of the boiler is quite high, the time for which the maximum oil feed is maintained may be of the order of one minute whereas, if the boiler is initially cold and coarse sawdust is used, the maximum oil delivery rate may be obtained for half an hour or longer. The time for which both oil and wood are being burned is also adjustable and can again be varied dependent on the nature of the wood being burned.

When wood is being burned alone then, as shown in FIG. 36, the photo-electric cell 45 looking along the length of the oil burner flame tube is arranged to respond to a failure of the flame 47 within the combustion chamber. If, for any reason, the light output of the flame 47 should fall below a predetermined level, the photo-electric cell, on sensing said fall in light output, causes closure of the valve 15 in the wood delivery pipe, and opening of the valve in the oil delivery line 28 after a predetermined time interval, as shown in FIG. 3D. During this time interval air alone is fed to the combustion chamber of the boiler to act as a purge. The boiler then operates in the same way as described above in relation to starting up of the boiler and, if for any reason, wood is not supplied at the required time, the boiler continues to re-cycle with the oil burner op erating.

The electrical circuit of the control system also includes a switch which is responsive to the level of water within the shell in the boiler fallin to a predetermined low level and, when the water in the boiler reaches this low level, the switch in the electrical circuit of the control system opens and the boiler is shut off. If, for any reason, there is a failure in the oil supply, the photoelectric cell arranged transverse to the axis of the flame tube of the boiler will sense the absence of a flame at the required time in the flame tube to shut off the boiler.

The feed means whereby the solid fuel is fed down through the steam and/or water spaces of the shell of the boiler to feed the grate 25 comprises the conduit 12 and surrounding tube 22. The solid fuel is carried by the stream of air along the pipe 11 and enters the conduit 12. The fuel then falls down the conduit past the group of nozzles 20 and 21 which impart to the fuel a giratory motion which is augmented by the vanes on the first conical part 20 of the conduit 12 and producing a throwing out action at the inlet to the furnace.

The above described arrangements have the practical advantage that a single tube is utilised for the admission to the conduit of both solids and compressed air for retarding the velocity of descent of the solids through the conduit and for ensuring that the solid fuel is spread out over the grate 25.

Combustion of the solid fuel in the furnace causes grits to be entrained in the gases leaving the boiler and these grits are held in the grit arrester 38 and then are sucked through the conduit 42 into the conduit 40. They are then carried by the air flow in the conduit 40 and are blown into the furnace in a direction which is substantially transverse to the main gas flow in the furnace and to one side thereof.

In this manner a great deal of the ash is kept in circulation until such time as it is settled on the grate and in addition the unburnt carbon is collected and returned to the fire for burning. Thus, the benefits are two-fold; firstly, the amount of ash leaving the actual boiler is greatly reduced and, secondly, there is very little fuel wasted as the unburnt carbon loss is very low indeed.

Although a boiler in which the solid fuel is wood waste has been described hereinbefore, it should be appreciated that the invention can be applied to other similar forms of solid fuel as described hereinbefore.

if desired, the solid fuel feed conduit 12 may comprise simply a cylindrical tube without any conical lower end portion and without any surrounding tube 22. in this case no extra air is introduced into the conduit 12 except that used to transport the solid fuel through the pipe 11. Such an arrangement is particularly suitable for use with very fine solid fuel.

I claim:

1. An industrial boiler including a combustion chamber, a fluid fuel fired burner to cause combustion of said fluid fuel in said combustion chamber, a grate contained in said combustion chamber, air supply means for delivering air to said combustion chamber, feed means for feeding solid fuel to said combustion chamber so as to fall towards said grate and control means operable to control supply of fluid fuel to said burner and solid fuel by said feed means, said control means including a first sensing means to detect the presence of combustion of both fluid fuel and solid fuel, said first sensing means being effective to control operation of said feed means to control feed of solid fuel to said combustion chamber and to control supply of fluid fuel to said burner, and a second sensing means to detect the presence of combustion of the fluid fuel alone, said second sensing means being effective to control supply of fluid fuel to said burner, whereby said burner can operate whilst the feed means is inoperative, said feed means can operate whilst the burner is inoperative and said burner can operate whilst said feed means is operative.

2. A boiler according to claim 1, including an envelope, a steam/water space of the boiler contained within said envelope, said envelope comprising a shell through which extends at least one set of fire tubes for passage of products of combustion from said combustion chamber, said grate being totally enclosed within the overall dimensions of said shell, and means for continuously supplying solid fuel passing down through the steam/water space of the boiler to said grate.

3. A boiler according to claim 2, wherein the combustion gases flow from the combustion chamber in a first direction and the boiler includes a grit arrester, located close to the gas outlet from the boiler, arranged to extract grit entrained in the combustion gases, and a means for supplying air to said combustion chamber, to withdraw grit from the grit arrester and to return the grit to the combustion chamber.

4. A boiler according to claim I, wherein the boiler includes a conduit extending upwardly from said combustion chamber through the shell of the boiler, means for feeding fuel to said conduit above the lower end thereof and distributing means for imparting an outwards throwing action to fuel leaving an outlet of said conduit, whereby there is obtained a substantial even distribution of fuel over said grate.

5. A boiler according to claim 4, wherein said outlet of said conduit is spaced above the grate of the boiler and a single tube is provided to transport and supply both solid fuel and compressed air into said conduit, and wherein said distributing means comprises a plurality of tangential air nozzles associated with said conduit.

6. A boiler according to claim 1,. wherein the control means is operative so that, on starting up of the boiler and actuation of the air supply means, the burner is operated after a predetermined time interval, the feed means is rendered operative after a further predetermined time interval and the bumer' is rendered inoperative after another predetermined time interval.

7. A boiler according to claim 6, wherein the control means causes the burner to operate initially with a first, lower, output and then with a second, higher, output.

8. A boiler according to claim 7, wherein in use prior to the feed means being rendered operative, said burner is operating at said second output and such that, on said feed means being rendered operative, the burner then operates at said first output and subsequently ceases to operate.

9. A boiler according to claim 1, wherein the solid fuel is wood waste and the grate supports a refractory material so that in use, the grate and refractory material are heated by the combustion product from said burner.

10. A boiler according to claim 1, wherein the solid fuel feed means includes a storage hopper for containing the solid fuel, said storage hopper including a primary conveyor for feeding solid fuel to an output pipe along which the fuel is fed pneumatically to a conduit which depends downwardly from the top of the shell of the boiler and a secondary conveyor for feeding the solid fuel from the interior of the hopper to the primary conveyor.

11. A boiler according to claim 10, wherein the primary conveyor is a screw-conveyor and the secondary conveyor is an endless belt conveyor which extends over the full width of the hopper.

12. A boiler according to claim 11, wherein the primary conveyor is a screw-conveyor and the secondary conveyor comprises a series of parallel screwconveyors extending from end to end of the hopper transverse to the axis of the screw of the primary conveyor.

13. A boiler according to claim ll, wherein means are provided for feeding air into the combustion chamber so as to pass up through the grate, the flow of air through the grate being such as to maintain particles of solid fuel which drop onto the grate in a fluidised state. l

. UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3,756 ,201 Dated September 4th. 1973 l Robert Spencer Williams It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

In the heading of the patent, line 3, after "Bewdley," insert County of Worcester; line 4, after "Limited," insert --Dudley--.

Signed and sealed this 12th day of February 1974 (SEAL) Attest:

EDWARD'M. FLETCHER,JR. c MARSHALL DANN Attestlng 0ff1Ce Commissioner of Patents FORM Po-msouo-ss) USCOMM-DC suave-Poo 1! ,5. GOVERNMENT PRINTING OFFICE: l9! O-QES-Slh

Claims

4. A boiler according to claim 1, wherein the boiler includes a conduit extending upwardly from said combustion chamber through the shell of the boiler, means for feeding fuel to said conduit above the lower end thereof and distributing means for imparting an outwards throwing action to fuel leaving an outlet of said conduit, whereby there is obtained a substantial even distribution of fuel over said grate.

6. A boiler according to claim 1, wherein the control means is operative so that, on starting up of the boiler and actuation of the air supply means, the burner is operated after a predetermined time interval, the feed means is rendered operative after a further predetermined time interval and the burner is rendered inoperative after another predetermined time interval.

12. A boiler according to claim 11, wherein the primary conveyor is a screw-conveyor and the secondary conveyor comprises a series of parallel screw-conveyors extending from end to end of the hopper transverse to the axis of the screw of the primary conveyor.

13. A boiler according to claim 1, wherein means are provided for feeding air into the combustion chamber so as to pass up through the grate, the flow of air through the grate being such as to maintain particles of solid fuel which drop onto the grate in a fluidised state.