US2361117A - Powdered fuel burner - Google Patents

Description

Oct. 24, 1944. F.. E. MILLETT POWDERED FUEL BURNER 2 sheets-sheet r1 Filed DeC. 16, 1941 Patented Oct. 24, 1944 nutren STATES* PATENT ortica 2,361,117 I* POWDERED IFUEL BURNER Fernley E. Millett, Blairmore, Alberta, Canada Application December 16, 1941, Serial No. 423,215

The present invention burning pulverized fuel.

It has been proposed to burn pulverized coal in domestic heating furnaces. However, the ignition. problem has always been a source of difficulty. In an average domestic pulverized fuel furnace, only a fraction of a pound of coal dust is in suspension at any time. It has been found that spark ignition 'is virtually impossible when starting without the admixture of a secondary fuel such as gas or oil which must be supplied for ignition and used to keep theV re going until the furnace has been heated to normal operating temperature, whereupon the supply of secondary fuel can be cut'olf.

A primary object of the invention is to provide a pulverized fuel burning furnacein which\ the pulverized fuel-air mixture may be ignited with electrical ignition without the use of secondary fuels such as gas,4 or oil.

Another object of the invention is to provide a pulverized fuel burningfurnace with an electrically heated ignition chamber.

relates to furnaces for Another object of the invention is to provide a pulverized fuel burner with an electrically heated ignition chamber and a fuel delivery member movable withrespect to the ignition chamber so as to be out of range of the ignition chamber during normal operation following ignition.

A further object of the invention is to provide' a pulverized fuel burner with electrically oper- 'ated ignition means capable of supplying a large amount of sensible heat to the mixture of powdered coal and air delivered to the ignition chamber so Aas to raise the same to ignition temperature when starting the burner into operation.

A still further object of the invention is to provide for automatic operation of the ignition means and relative movement between the ignition means and fuel delivery member to remove the ignition means from the fire zone after the flame is self-sustaining.

Other objects and advantages of the invention will become evident during the course of the following detailed description of a preferred embodiment of the 'invention as illustrated by the accompanying drawings which form a part i hereof yand in which:

Fig.'k l is vertical section through a furnace 'i 'equipped with a powdered fuel burner embodyn i gthe invention,

Figi-f2; isv an axial section through vthe burner IQ proper, and

'Figiy is a'wiriii'g diagram for the system.

A blower 26 operatedby 5 claims. (ci. 11o-2s) the invention is shown applied to a hot air furnace 5 having an inner bottom walls of which are provided with a refractory lining 1. 'I'he products of combustion pass from the main re chamber within the casing S through an economizer 8 to a ue 9. While a hot air furnace has been illustrated it will be understood that any other type such as a hot water or steam boiler type could be provided with the invention.

The burner assembly comprises a refractory lined tubular combustion chamber II which extends into the fire chamber within the casing 6 through an -opening I2 opposite the re wall formed bythe refractory lining v, which opening may be the usual re door opening. A mounting plate I3 closes the space around the casing 6, the back and chamber I I which is slanted at an angle of about An ignition chamber It is mounted coaxially of the tubular combustion chamber II at the I upper and-outer end thereof and vin communication therewith. The chamber I4 is provided with a refractory lining I5 and mounted therein is electric heating element or elements I8 which may be of nickel-chrome wire or other material having suitable electrical and physical properties to withstand high temperatures. The heating element 6 ls preferably partially embedded in the surface of the refractory lining I 5. The ignition chamber I4 is substantially conical in axial section opening at its base or large end into the lcombustion chamber II and provided at its small end with an axially disposed tubular guide bushing Il for the outer tube I8 of a double tube powdered fuel burner 'I'he burner I 9 includes a T-tting 20 mounted on the outer end of tube I8 to which secondary air is supplied through a branch pipe 22 which may be provided with a regulating valve tube 24 concentric with tube I8 is supported by fitting 20 and is supplied with a mixture of powdered coal and air through a flexible hose 25 from a mixing an electric motor 26'. At its discharge end, which is, substantially coincident with the inner or delivery end of tube I8; the fuel-air delivery tube 2li is provided with a propeller shaped whirler 21 for insuring intimate mixture of the powdered coal and air emerging therefrom.

The burner I9 is axially slidable in the bushing Il so that it may be adjusted to shift its disposed to radiant charge end more or less into and out ofthe ignition chamber I4, that is, it may be adjusted to a retracted position in which the fuel and air must pass through the ignition chamber after leaving the tubes I3 and 24 or to a projected position in which the tubes extend through the i8- nition chamber I4 and discharge directly into the combustion chamber I I.

Shifting of the burner between its two extreme positions of adjustment preferably is eifected by means of a two position control electric motor 23, of a type commonly used for damper controls and preferably provided with reduction gears giving an output shaft speed of 180 degrees in about 105 seconds and equipped with limit switches providing for 180 degrees output shaft rotation each time energized. A crank arm 23 mounted on the output shaft of motor 28 is connected by a connecting rod 30 to the T-fitting of burner I3 so that with each successive 180 degrees of rotation of the motor shaft 30', the burner is shifted from one end to the other of its limits of movement. In one end position, shown in Fig. 2, the burner is retracted so that it discharges the powdered fuel and air into the end of the ignition in which the air and powdered fuel pass entire- 1y through the ignition chamber and being exheat in the ignition chamber are raised to ignition temperature thereby. In the otherpend position, indicatedby dotted lines in Fig. 2, the burner is in the projected position wherein the tubes I8 and 24 extend through the ignition chamberand discharge powdered fuel and air directly into the combustion chamber II. This is the running position to which the burner is shifted after operating in starting position long enough to insure self -sustained combustion with- .out the aid of the heat supplied in the ignition chamber. Shifting of the burner to discharge directly into the combustion chamber, starting, saves wear and tear on the heating coils and lining of the ignition chamber by protecting them from the full heatv of the pulverized fuel ilame during normal running of the furnace.

The electrical control system for the burner is shown diagrammaticaily in Fig. 3. A definite time relay 3| controls a pair of double throw switches 32 and 33 operated in unison by a solenoid 34. In one position switch 32 energizes burner shifting motor 28 and switch 33 energizes ignition heating coil I6. In the other position switch 32 energizes' burner shifting motor 28 again and switch 33 energizes fuel supply motor 26'. A speed control rheostat 35 provided with an adjusting handle 35' 'is placed in series with motor 26 and a, thermostat 36 controls 'a shunt around th'e speed controller. This system provides for continuous operation of the burner on a high-low principle, the thermostat 36 shunting out the rheostat 35 when the temperature falls to a point requiring more heat than is being supplied on low re so that the motor runs at high speed until the demand is satisfied. A manual on-off switch 31 is provided for starting or stopping operation of the burner entirely. If automatic on-off operation is desired, the thermostat 36 and rheostat 35 are eliminated and manual switch 31 is replaced by a thermostat or pressure responsive switch, as desired.

In the operation of the burner, to put the burner into operation switch 31 is closed to energize time delay relay 3|. Relay 3l immediately operates to energize solenoid 34 to throw switches chamber remote from theco'mbustion chamber. This is the starting position after 32 and 33 to the start position to energize electric heating element I6 and burner shifting motor 28, which latter operates to rotate its output shaft to shift the burner to the retracted starting position. After elapse of the deilnite time for which the relay 3I is adjusted, which time is suillcient for the heating coil I6 to become incandescent and raise the temperature of the refractory lining I5 of ignition chamber to incandescence, the relay breaks the circuit of solenoid 34 and the switches 32 and 33 are thrown to the opposite or run position to break the heating coil circuit and energize the fuel supply blower motor 26' and again energize the burner shifting motor 28. l

When the switches 32' and 33 are thrown to the run position, fuel and air are supplied to the burner i9 which fuel and air mixture in its passage through the incandescent ignition chamber absorbs heat therefrom and is raised to the ignition temperature so that the fire is started. At the same time, the motor 2B being energized starts operation through another 180 cycle to shift the burner tubes I8 and 24 slowly toward the run position. 'As the burner advances, the fuel-air mixture is heated to maintain combustion and by the time the burner reaches regular running position. the flame is self-sustaining in combustion chamber II. The burner then continues in operation in this position until a shutdown calis for a new cycle of operation when again starting up.

Although a preferred embodiment of the invention has been shown and described by way of illustration, itI will be understood that the same is not limited to the precise details of construction shown and that various modifications may be resorted to without departing from the spirit of the invention withinthe scope of the appended claims.

I claim:

1. In a powdered fuel burner, a combustion chamber, an ignition chamber opening into the combustion chamber, electrical heating means within said ignition chamber, a fuel delivery means movably mounted with respect to said ignition chamber and said combustion chamber and adapted to be moved to one position to der 2. In a powdered fuel burner, a combustionchamber, an ignition chamber opening at onev end into said combustion chamber, electrical heating means withinsaid ignition chamber, a fuel-air delivery tube movably mounted with respect to and extending into said ignition chamber at a point remote from 1the combustion chamber, and means for shifting said fuel-air delivery tube with respect to said combustion and ignition chambers between a retracted position in which fuel and air delivered through said tube passes through the ignition chamber to the combustion chamber and a projected position in which fuel and air delivered through said tube is discharged directly into the 'combustion chamber.

3. In a powered fuel burner, a combustion chamber, an ignition chamber opening at one end into said combustion chamber; electrical heating means within said ignition chamber; a fuelair delivery tube movably mounted with respect to and extending into said ignition chamber at a `point remote from the combustion chamber;

means for shifting said fuel-air delivery tube with respect to said combustion and ignition chambers betweenl a retracted position in which fuelv and air delivered through said tube passes througlr the ignition chamber to the combustion Chamberland a projected position in which fuel and airdelivered through said tube is discharged directly` into. the combustion chamber, and

Q means for controlling the supply vof heating current 4to said electrical heating means, for actuating said shifting 'means to move said fuel-air delivery tube to the retracted position'when starting said burner into operation, for controlling supply of fuel and air to said delivery tube, for

advancing said tube to projected position and for cutting oil the supply of heating current to said electrical heating means after a predetermined starting period.

4. In a powdered fuel burner, an openA ended combustion chamber, an ignition chamber mounted at one end of and opening into said combustion chamber, a bushing at the end of said ignition chamber opposite said combustion chamber, a burner tube slidable through said bushing,

,- "electrical heating means within said ignition. l chamber, means for supplying powdered fuel and air through said burner tube, and means for moving said burner tube through said bushing to a retracted position in which fuel and air delivered thereby is caused to pass through the ignition chamber to the combustion chamber or to a projected position in which fuel and air delivered thereby passes directly into the combustion chamber.

5. In a powdered fuel burner, an open ended combustion chamber, an ignition chamber mounted at one endy of and opening into said combustion chamber, a bushing at the end of said ignition chamber opposite said combustion chamber, a burner tube slidable through said bushing, electrical heating means within said ignition chamber, means for supplying powdered fuel and air through said burner tube, and means for moving said burner tube through said bushing f to a retracted position in which fuel and air delivered thereby is caused to pass through the ignition chamber to the combustion chamber or to a projected position in which fuel and air delivered thereby passes directly into the combustion chamber, and control mechanism operative to actuate said burner tube moving means to shift the burner tube to retracted position and to energize said electrical heating means `when starting the burner into operation and operative after a predetermined time interval to aetuate said burner tube moving means to shift said burner tube to projected position, actuate the fuel aj'nd air supply means and to deenergize the electrical heating means. l

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