US2363942A - Fuel burner - Google Patents

Description

Nov. 28, 1944. Q F, CAMPBELL- 2,363,942

` FUEL BURNER Filed Feb. 17, 1942 2 sheets-sheet 1 INVENTOR 0in/er fampdl Nov.- 28,1944. o. F. CAMPBELL 'I v 2,363,942

FUEL BURNER .Filed Feb. 17, 1942 2 sheets-sheet 2 4INVEN'roR O Zz'ver 556203055X/ BY 1 fmmwms Patented Nov. 28,1944

UNITED STATES PATENT OFFICE FUEL BURNER oiiverr. campbell, Whiting. Ind., miglior-tn Sinclair Refining Company, New York, N. Y., a corporation of Maine Application February 17, 1942, Serial No. 431,233 A (ci. 11o- 104) Claims.

This invention relates to fuel burners and more particularly relates to an improved burner especially adapted to the burning of finely divided solid fuels, such as powdered coal, and capable of operating efficiently over a broad range of capacities.

The improved burner of my present invention is especially designed to inject into the com bustion zone of the furnace with which it is used a, relatively broad,- thin stream o f a suspension of solid fuel in a gaseous medium, for example powdered coal suspended in air. This fuel stream may be directed along a generally horil zontal or verticalplane or Vat an angle there-- with and a particular advantage of my improved burner is its .ability to direct and to shape the resultant flame in a manner best suited to the design of thefparticular furnace with which it is used.

In the burning of nely divided solid fuels, the fuel is usually supplied to the burner suspended in air. The stream'of air in which the fuel is suspended-constitutes 'a portion of the air required for combustion of the fuel. However, ad-

ditional air is required for combustion and this additionalair is 'herein designated secondary air Y l A serious disadvantage of conventional burners for burning a powdered solid fuel has -been the narrow range 'of capacities at which the burner could be operated at maximum eiliciency. For efficient operation, it is essential that the relative proportions of fuel and air be maintained at an optimum value and that the fuel and air be intimately admixed upon entering the combustion zone.

Some fuel burners are adapted to' operate sufficient that the optimum proportions of fuel and air be maintained.v It is also essential to efficient combustion that the fuel and air be properly mixed, that the fuel be highly dispersed in the combustion air.

One of the major defects of conventional `burners has been their failure to accomplish too 'low to accomplish adequate mixing, and

poor' combustion results.v If an attempt is made still further to decrease the capacity of such burners, a lower limit is soon reached. beyond which ignition cannot be maintained.

Burners vhaving air ducts of xed cross-sectional area may, of course, be designed for low capacity operation. However, if one attempts to operate such low capacity burners at considerably higher capacities either suillcient air cannot be supplied for efficient combustion or the velocity of the air stream is apt to be so great as to extinguish the flame.

Numerous attempts have been made to overcome the capacity range deficiency ofconventional fuel burners'. Fortinstance, it has been proposedto increase the flexibility of the burners with respect to capacity range by providing mechanical means for varying the cross-sectional efficiently only at a given capacity or at a. capacity which cannot be changed while the burner is in operation. The capacity of other conventional burners may be changed vat will over a limited range by varying the amount of fuel and combustion air injected thereby into the combustion zone. In the latter type of burner, when it `becomes desirable to increase themate of heating cfa boiler, for instance, the rate at' by the burner, is increased and, when al lower rate of heating is desired, the rate at which the fuel is supplied is decreased.

If ecient operation is to be maintained over a range of heating rates, these variations in. the rate of fuel upply must be accompanied by the appropriate change in the amount of air supplied by the burner. However, it isvnot alone .which fuel is'supplied to the combustion zone area o f the air duct at the point where it enters the mixing zone. Thus, when decreased volumes ofv air are required, the cross-sectional area of the air duct exit would be decreased so as to maintain velocity and `turbulence of the air stream at the point where it meets with the fuel stream. One of the primary difficulties with such previously proposed arrangements has been the necessity of having moving parts located withinthe zone of high temperature where vthey soon cease to :function and another has been .their inability adequately to extendthe range of emcient operating capacities.

Further attempts to extend the capacity 'range of conventional burners have led to the suggestion that a plurality of air ducts be proidded with means removed from the heating zone for ccntrolling the passage of air through the respec-f tive ducts. However, such suggestions, so `far as I am aware, have not heretofore resulted in a burner having the exibility and other advantageous characteristics combined in the burner of my present invention.

In my co-pending application Serial No.

'389,518, med April 21, 1941, (now Patent No.

2,334,314 issued November 16, 1943) I have described and claimed an improved burner provided with a, plurality-of co-axially arranged ducts of annular cross-section and co-ai'dally positioned with respect to the fuel injection means. The passage of air through the respec t-ive ducts of the burner there described is conltrolled by a damper adapted to permit the passage of air first through the innermost duct only and progressively through additional adjacent outer ducts as the damper is moved from the closed to the open position. The burner of the present invention in some respects resembles that of my said co-pending application but it Apossesses certain additional advantages as will hereinafter appear.

generally rectangular shape, as shown in Fig. 2

of the drawings. A

Above and below the nozzle 5 are laminated banks of air ducts 9 each consisting of a plurality of parallel airv ducts formed by a plfurality of parallel plates I9 and side plates II. These banks of dructs are so positioned that the parallel planes of the respective ducts form acute In the operation of the burner of my present invention a stream of finely divided solid fuel suspended in a gaseous medium is injected into the combustion zone of the furnace through a nozzle having an exit port of considerably greater dimension along one plane than along the plane perpendicular thereto, such, for example, as a iishtail or fan-shaped nozzle, so that the fuel suspension enters the combustion zone in a relatively broad, thin stream. The secondary air is supplied through `laminated banks of air duets arranged on each of the broad sides of the fuel nozzle and so positioned with respect thereto as to direct the streams of the secondary air issuing therefrom toward the fuel stream from above and below. The passage of air through the respective ducts is so controlled by dampers, without the high temperature zone, that, when operating at minimum capacity, the secondary air is admitted through the innermost ducts only and, as the operating rate is increased, additional fuel and secondary air being supplied, the secondary air is admitted, progressively through additional adjacent outer ducts. l

The invention will be further described with reference to the accompanying drawings which represent a specic embodiment of my invention. It will be understood, however, that my invention is not limited to the specific arrangement shown.

Fig. 1 of the drawings isa vertical cross-sectional view of the burner along the line I--I of Fig. 2 of the drawings which is a front elevation view thereof. the drawings. .like parts numerals.

In the drawings-the burner housing I is shown are indicated by like angles with the plane of the nozzle and intersect that plane in lines perpendicular to the axis of the nozzle beyond the exit end of the nozzle.

These banks of air ducts 9 are sealed into the firing port 3 by means of plates I2 and side-seal plates I8 so as to avoid the uncontrolled -entrance of air to the combustion chamber through openings in the firing port. Extending through the side-seal plates I3 are the lighter ports I4.

The outer ends of these ducts 9 terminate in a register or grating I5 to which the parallel plates II) are fastened so that the respective ducts register with the openings in the gratings. These registers are in turn supported by the nozzle 5 and the supporting members I8.

The passage of air through the several ducts ls controlled by the damper plates Il adapted to be moved across the registers I5 in the'direction of the furnace by means of 'the rack and 40 pinions I8, shafts i9, bevel gears 20, shafts 2l and the handwheels 22. A r

In Fig. 1 of the drawings, the dampers I1 are show n in the extreme left position. .In this position the entrances to all of the secondary air ducts are closed. As the dampers are moved froml this position toward the furnace, the entrancesto the innermost ducts only are first opened and, as the damper is moved still further toward theright entrances tokv successive additional outer ducts, are progressively opened.

It is sometimes desirable, in order better to forming the duct. These division members may In the respective figures of attached to the wall 2 ofV a furnace at the firing port 3 by means of-brackets 4. Within the burner housing and supported thereby is the burner nozzle 5 through which the fuel suspension is injected into the combustion chamber 6. The fuel suspension is supplied to the burner nozzle 5 in variable quantities, depending upon the operating. capacityldesired, from any convenient source, not shown, through the conduit 1. .v

The usual practice in the operation of burners of this type is to `reduce the solid fuel to the `desired fineness by conventional grinders Aor the like and to suspend the 'finely ydivided fuel in ail be generally parallel to the vertical plane through the axis of the burner and may be staggered as shown. I f desired, these division members may be placed at an angle with said vertical plane so as to concentrate the secondary air at theA inner portion or at the outer edges of the flame.

ducts may be supported by gratings or registers,`

as indicated in the drawings at 28,-'fer the innercrease the velocity -of the air stream passing therefrom. This increased velocity is sometimes If desired, the parallel plates-forming n housing I.

aaeaua The outer ends of the ducts 9 terminate in the v air chamber or windbox 23 formed by the burning Air may be supplied to the windbox through a suitable opening such as the conduit 24. Where the furnace is to be operated under forced draft conditions, the conduit 24 may be connected with a conventional air propulsion means.v not shown, and where natural draft conditions are to be used, the windbox 23 or the conduit 24 may be open to the atmosphere.

In the operation of the burner shown, the fuel suspension supplied to the burner through the conduit 1 under pressure passes through the nozzle 5 and is injected into the'combustion zone 6 in a relatively -thin fan-shaped stream. This fuel suspension includes a portion of the air required for combustionof the suspended fuel but not the entire requirement. Secondary air is' supplied through the laminated duct banks 9 and for maximum combustion eiliciency this secondary air must become intimately admixed with the suspended fuel in the combustion zone.

The thoroughness of this mixing is dependent lupon the volume of secondary air required,

velocities inadequate for proper mixing would result when the volume of secondary airis reduced to meet reduced fuel injection. In the operation of my improved burner, .optimum velocities of the secondary vair for proper mixing i.

are obtained over a wide range of operating capacities by increasing or decreasing the number of ducts through which the secondary air is supplied in accordancewith the amount of fuel being burned and consequently the amount of secondary air required. V

However, vcontrol of velocity alone o f the entering secondary air stream or streams is not sumcient to effect optimum mixing. Thel point of 4introduction of the secondary air stream or streams and the shape of the injected fuel stream are also of major importance. iIn my improved burner, the secondary air ducts are so positioned with respect to the fuel nozzle `as to direct the air streams therefrom into the thin, laterally extended fuel stream from above and below at points near ,its exit from. the fuel nozzle. The amounts of secondary air so directed against the upper and lower sides of the fuel stream vmay be equal or may be so proportioned as to direct or shape the flame to meet special.furnace conditions. i I

When operating at minimum capacity, the velocity of the incoming fuel stream is naturally reduced. Under such conditions, better mixing is obtained by directing the reduced amount -of stream having a large surface area per unit of volume and the introduction of the secondary airat the optimum velocity and at the optimum point with respect to `thefuel stream.

These dampers as shown in the drawings, are adapted to be individually controlled manually. If desired, the movement o'f .the upper and lower dampers may be correlated by suitable linkages not shown' or their movement may be automatically controlled by conventional means responsiveto the amount of fuel supply, or the like.

' In the drawings, I have shown my improved burner so positioned that the fan-shaped-fuel stream therefrom is injected into the combustion chamber in a generally horizontal plane. It will be understood, however, that the position of the burner may be varied to meet the firing or flameshaping requirements of particular furnaces with which it is to be used.

I claim:

1. In a fuel burner for burning finely-divided vsolid fuel suspended in a gaseous medium the improvement which comprises a fuel injection nozzle having a relatively broad, thin exit port, two banksof air ducts each bankcomprising a plurality of substantially parallel air ducts substantially co-extensive in breadth with the breadth of the nozzle exit port, one bank being positioned on each of the opposite broad sides solid fuel suspended in a gaseous medium theimprovement which comprises a fuel injection nozzle having a relatively broad, thin exit port.

two banks of air ducts each bank comprising a plurality of substantially parallel air ducts sub.v stantiallyco-extensive in breadth with thev breadth of the nozzle exit port, one bank being positioned on each of the opposite broad sides of 65 the nozzle exit port so that the parallel planes of secondary air into the fuel stream at a lpoint v:lust beyond the exitof the latter from the fuel nozzle. Even when operating at higher capacities, it is desirable to introduce a portion of the j bination of `advantages derived from the injection of the fuel into the combustion chamber` in a the respective ducts form acute angles with the longitudinal plane of the nozzle exit port and intersect said longitudinal plane extended inwardly from said port, a damper for each -bank of air Vprising a sliding plate member adapted to close each of the ducts of the bank when in the` extreme closed position, to admit air through each of the ductsy of the' bank when in the extreme open position and to open first the innermost duct only of the respective banks and progressively to open additional successively outer ducts thereof as the sliding plate member is moved from the closed tothe open position.

3. In a fuel burner for burning finely-divided solid fuel suspended in a gaseous medium the improvement which comprises a fuel injection nozzle having a relatively broad, thin exit port, two banks of air ducts each bank comprising a ofl air ducts for controlling the passage of air ducts for controlling the passage of air lthrough the respective ducts thereof, said damper complurality of substantially parallel air ducts substantially co-extensive in breadthwith the breadth oi! the nozzle exit port, one bank being positioned on each ofthe opposite broad sides oi' the nozzle exit port so that the parallel planes oi the respective ducts form acute angles with the longitudinal plane of the nozzle exit port and intersect said longitudinal plane extended inwardly from said port beyond the exit port in. lines substantially parallel to the verticalplane of said port, a damper for each bank of air ducts for controlling the passage oi' air through the respective ducts thereof, 'said damper comprising a member adapted'to close each of the ducts of the bank whenin the extreme closed position, to

admit air through each of the ducts of the bank when in thel extreme open position and to open ilrst the innermost duct only of the respective banks and 'progressively to open additional successively outer ducts thereof as' the damper member is moved from the closed position to the open position.

4. Ina fuelburner for burning tlne1ydlvided solid fuel suspended in a gaseous medium the improvenient which vcomprises a fuel ,injection nozzle having a relatively broad, thin exit port, two banks of air ducts each bank comprising a plurality of substantially parallel air ducts sub.- stantially co-extensive in breadth with the breadth of the nozzle exit port, one'bank. being positioned on each ofthe opposite broad sides of the nozzleexit port so that the parallel planes oi' the respective ducts form acute angles with the longitudinal plane oi.' the nozzle exit port and intersect said l ngitudinal plane extended inwardly from sai port, division members extending through the respective ducts so as to divide the ducts into a plurality oi passages running toward the exit ends thereof, a damper for each bank of air ducts for controlling the passage oi' air through the respective ducts thereof,

damper comprising a member adapted to close each oi' the ducts of the-bank when in the extreme dosed position, to admitan through each or the ducts oi the bank when in the extreme open position and to open first the innermost duct only of the respective banks `and progressively to open additional successivelyouter ducts thereof as the damper member is mved from the closed position to the open position.

5. In a fuel burner for burning iinely-divided solid fuel suspended in a gaseous medium the improvement which comprises a fuel injection nozzle having a relatively broad, thin exit port, two banks of air ducts each bankcomprising a plurality o! substantially parallel air ducts substantially cao-extensive in breadth with the breadth of the nozzle exit port, one bank being positioned on each of the opposite broad sides of the nozzle exit port so that the parallel planes of the respective ducts form acute-angles with the longitudinal plane of the nozzle exit port and the bank when in the extreme closed position, to

admit air through each of the ducts of the bank when in the extreme open position and to open first the innermost duct only oi.' thev respective banks and progressively to open additional successively outer ducts thereof'as the damper member is moved from the closed position to the open position.

' OLIVER r'. CAMPBELL.

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