US2573910A - Method for burning pulverized coal - Google Patents

Description

1951. H. KREISINGER 2,573,910

METHOD FOR BURNING PULVERIZED c0111 Filed Aug. 21, 1945 v s Sheets-Sheet 1 FY INVET OB ATTORNEY- NOV. 6, 1951 KRE|SINGER 2,573,910

METHOD FOR BURNING PULVERIZED com.

Filed Aug 21, 1945 5 Sheets-Sheet 2 lllllllllllgllillnlm ATTORNEY$ Nov. 6, 1951 H. KREISINGER 2,573,910

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Filed Aug. 21, 1945 3 Sheets-Sheet 3 ATTORNEY! Patented Nov. 6, 1951 2,573,910 METHOD FOR BURNING PULVERIZED COAL Henry Kreisinger, Piermont, N. Y., assignor to Combustion Engineering-Superheater, Inc., a

corporationoi Delaware Application August 21, 1945, Serial No. 611,762 3 Claims. (01. 110- 28) This invention relates to a method and apparatus whereby solid fuel such as pulverized high ash coal and anthracite coal dust may be burned at extremely high rates of heat liberation in a very small cyclone burner or furnace, while at the same time solid residues of combustion are effectively handled. The process and apparatus are particularly useful where the available space for generating steam is relatively very small, as in naval vessels.

In general, I propose to promptly ignite and burn the coal under conditions such that extremely rapid combustion is achieved with B. t. u. liberation as much as 1,000,000 B. t. u. per cubic foot of of furnace volume per hour or even higher, and this in a very small furnace whose dimensions are, for example, on the order of three feet in diameter and six feet in length. The conditions are also such as will result in the effective handling, collection and disposition of the solid products of combustion.

The process is effective when burning fine or coarsely pulverized coal. The coal should be fine enough to be kept in suspension by the velocity of the rotating gas streams hereinafter referred to and should not contain particles so coarse as to drop out of the stream by gravity without being consumed. Such coal is finely enough divided for carrying out the invention. The coal dust obtained in the mining of anthracite, for example, a

may be effectively burned.

I accomplish the foregoing, together with such other objects and advantages as may hereinafter appear or are incident to my invention, by a method illustrated more or less diagrammatically in the accompanying drawing, wherein Figure 1 is a vertical cross section through a steam generating installation embodying my invention;

Figure 2 is a section taken on the line2-2 of of Figure 1; 1

Figure 3 is an enlarged section taken on the line 3--3 of Figure l, and V Figure 4 illustrates a modification of the invention.

Referring now to the drawings, the reference character A indicates the furnace proper or primary combustion chamber, B the outlet thereof, C a secondary combustion chamber located therebelow, and D an upward pass leading to the stack.

The primary combustion chamber or furnace is lined with relatively closely spaced upright tubes 1 having plastic refractory material 8 therebetween, as shown in Figure 3, whereby a portion of the surface of the tubes is exposed.

In this instance, the primary combustion chamber is circular in cross section and is approximately three feet in diameter andsix feet in length. The outlet B of the chamber, however, is restricted, being approximately inches in diameter, to which end the wall is carried in and the tubes 1 are bent, as shown.

The secondary combustion chamber C is likewise lined with tubes 9, in this instance desirably horizontally disposed, and there are steam generating coils and superheater tubes or similar apparatus (not shown) located in the pass D.

The coal is preferably introduced centrally into the upper end of the primary combustion chamber at very high velocity, say from about 6000 to about 24,000 feet per minute (depending upon the then outwardly, as shown in Figure 1. Surrounding the burner l 0 is a ring of spaced pivoted vanes l3 which may be adjusted to impart a swirling or rotating movement to the secondary air admitted around the burner from duct l3.

By introducing the coal in this form with surrounding secondary air, there is a tendency for the coal to concentrate in an annular band adjacent to the wall of the furnace, external eddying and mixing occurs as indicated at I4, and internal eddying and mixing as indicated at 15. The swirling secondary air tends to impart swirling movement to the entering stream of coal and primary air and to initiate eddying. In consequence, the entering coal is promptly ignited, once the furnace is in operation, and burning takes place substantially as high as the lower end of the burner, particularly in the region of the eddies, this further assisting in ensuring prompt ignition of the entering fuel.

Located at about the level where unconsumed fuel particles tend to concentrate in a band adjacent to the wall of the furnace, due to the admission of the fuel in flaring or hollow conical form, are tertiary air inlets l6, preferably four in number, and desirably equally annularly spaced from one another. These inlets are accommodated in the wall of the furnace, as shown in Figure 3, and they are directed desirably at substantially the angle indicated in said rlgure. In consequence, at four annularly spacedpoints, peripheral portions of the body of fuel, flame and gas are driven inwardly toward the region which is relatively lean in fuel and relatively rich in oxygen. At the same time, a further rotary motion is imparted to the said body. In consequence, very turbulent and intimate admixture of unconsumed fuel and oxygen occurs, promoting rapid and effective combustion. At the same time, there is a tendency of the portions of the body next to the wall to become fuel lean and oxygen rich. The angles of the inlets may be varied so long as the above characteristics are obtained.

By reason of the rotary motion imparted to the body of fuel, flame and gases, there is a tendency, in the region just below the levelof the air inlets ii, for unconsumed fuel particles again to move outwardly toward the wall of the furnace to the oxygen rich area, which, among other things. facilitates combustion. The movement of unconsumed particles outwardly again tends to make the central portion of the body relatively rich in oxygen and lean in fuel. Because of the draft, the body of fuel, flame and gas moves helically.

The peripheral portions of the helically rotating body of fuel, flame and gas are now again driven inwardly toward the center by a second series of tertiary air inlets Ii, located at a level sufliciently below the level of the inlet ll to bring about the just above described action to take place. There preferably are four of the air inlets IO', desirably staggered with respect to the inlet Ii. The air delivered by these inlets thus tends to bring about turbulent intimate admixture at the level of such inlets, again driving unconsumed fuel into a relatively oxygen rich zone. The air also tends to impart and maintain the rotary movement of the body of fuel, flame and gas.

As before, there is a zone below the level of the inlet 18 in which, because of centrifugal force, unconsumed particles again tend to move outwardly to the periphery, which is relatively oxygen rich from the air introduced through the inlet ii.

A third series of inlets l6", preferably staggered with respect to the other inlets II and i6, is provided at a suitable level below the level of inlet l8, which again drive peripheral portions of the fuel, flame and gas inwardly, producing turbulent and intimate admixture while at the same time imparting and maintaining rotary movement of the body.

The tertiary air is supplied to inlets ll, 16' and it" from branch I!" of duct l3, which discharges into the casing l3' surrounding chamber A. The air thus is preheated.

I prefer to admit about of the air required as-primary air with the coal, about around the nozzle as secondary air, and about 20% through each of the series of inlets l6, l8 and l6" as tertiary air.

ondary combustion chamber.

Thus, it will be seen that ignition of entering fuel occurs practically instantaneously, and that, in approximately the upper half of the combustion chamber, there is repeated turbulent mixing of unconsumed fuel and oxygen, with intervening zones wherein solid particles of fuel (and of incombustibles) move outwardly into relatively oxygen rich regions. In consequence of this, the combustion in the upper half of the furnace is very rapid and effective. reliance being placed upon the lower half to consume the unconsumed combustible volatiles and such few solid particles as were not previously consumed.

The secondary and tertiary air admitted to the inlets l2, l8, l8 and ii" (at from about 12,000 to about 60,000 feet per minute, depending upon the rate of firing and upon whether the air is preheated and the extent of preheating), the relatively high velocity of the entering fuel and primary air, and the restriction afforded by the relatively small outlet throat B, cause the combustion to take place under superatmospheric pressure, ranging from about 2 inches to about 110 inches of water, depending on the rate of flring. (750 F. air, for example, occupies a relatively large volumei) This operation under superatmospheric pressure also tends to increase the rapidity of combustion.

It will be clear from the above that the temperature of combustion is well above the fusion temperature of the ash of the coal, despite the fact that the tubes 1 are partly exposed. In consequence; the solid incombustibles are reduced to a molten -state. In the upper half ofv the combustion chamber, because of the eddying and the turbulent mixing, the tiny droplets of molten incombustibles have opportunity to contact with one another and form larger droplets which, by reason of the rotary movement, move outward to the wall. This outward movement of molten particles also takes place in the region below the inlets l6". Thus, the inner face of the wall of the furnace is covered with a sticky deposit of moltenslag. The centrifugal force drives by far the greater part of the incombustible solids (molten droplets and ash particles, if any) against this sticky deposit which holds the same. Thus solid residues are separated out, there being in the upper half alternating zones of violent mixing and of separating. Below the inlets l6",

there is separation without marked disturbance or mixing. Any fuel particles which lodge on the deposit will burn.

The temperature within the furnace is sufficientto cause the slag to continually run down the upright wall of the furnace and drip off the wall portions defining the outlet throat B. Thus the incombustible solids are removed. This action is facilitated by reason of the increased velocity of the gaseous products of combustion passing through the discharge throat. The slag discharged from the outlet collects on the walls and floor of the secondary combustion chamber wherein the heat is still sumcient to maintain the same in a molten condition, in which condition it is removed through the slag hole II which may be located at any desirable point in the secondary combustion chamber floor. Such solid incombustibles not removed in the main combustion chamber as above described, are largely removed from the gases in the secondary combustion chamber by the velocity of the discharging gases which causes such incombustibles to contact and adhere to the slag on the bounding surfaces of the secondary chamber.

Thus it will be seen that the incombustible solid residues are effectively removed, collected and handled before the up pass is reached. The relatively small amount which may be left in the gases makes no trouble in the up pass for by this time the temperature is below the fusion point.

Heat is usefully abstracted from the gaseous products of combustion( and also from the slag),

for the generation of steam, superheating and the like, in the secondary combustion chamber and in the up pass D.

It is to be understood that the boiler preferably has forced circulation.-

While I have described the furnace as being circular in cross section, it may be of other shape, as, for example, rectangular. While I prefer to admit the coal and primary air and secondary air as described, the same may be admitted tangentially', generally considered, as shown in Figure 4. The nozzles, which may vary in number, are directed at approximately the same angle as the air inlets it.

The arrangement of Figure 1 is best suited for the burning of pulverized coal, such, for example, as coal 80% of which would pass through a 200 mesh screen. For heavier coals the arrangement of Figure is better suited.

At a B. t. u. liberationof 500,000, the velocity in the furnace of the size hereinbefore indicated would be approximately 60 feet per second and at the B. t. u. liberation of 1,000,000, the velocit would be approximately 120 feet per second. Thus there is ample opportunity for the effective burning of the fuel. By way of illlustration, buckwheat No. 4 which is a size which passes through a 3% inch round hole but is retained on a 4, inch round hole screen, is burnable on a stoker. Anything smaller than inch is unsuitable for burning on the stoker. These fines passing through a inch have heretofore been pulverized. By my improvements, however they may be burned without the need for pulverization.

I claim:

1. The process which comprises delivering at high velocity a rotating annular mixture of finely divided high ash coal and primary air in a downward direction in flaring form and toward the wall of a vertically disposed small cyclone furnace to concentrate fuel in an ansnular zone adjacent the furnace wall, igniting the fuel at entry into the furnace and burning it while imparting to and continuously maintaining rotary movement of the body of fuel, flame and gases about a vertical axis, whereby unconsumed particles of fuel and ash are caused by centrifugal force to move towards the furnace wall during such rotation and whereby the central portion or core of such body tends to become oxygen rich and fuel lean and said annular zone adjacent the wall to become fuel rich, repeatedly driving peripheral portions of fuel in said zone inwardly away from the wall of the furnace into the oxygen rich core by continuously supplying high velocity, high pressure air in a direction inwardly and tangentially at a plurality of vertically spaced levels in the furnace and at a plurality of circumferentially spaced points at each level, said levels being a substantial vertical distance apart whereby high turbulence and intensive mixing over the entire cross section are provided at said levels by which unconsumed fuel and oxygen are mixed and whereby said air also serves to impart and maintain said rotary movement of said body, said rotary movement intermediate said levels being by itself relatively non-turbulent, maintaining furnace temperatures sufliciently high to produce molten slag on the furnace wall, collecting incombustible solids by said slag, gravity discharging the slag from the bottom of the furnace, burning adjacent said wall any solid combustible particles adhering to said slag covered wall, maintaining a pressure within said furnace substantially above atmospheric to produce extremely high rates of combustion, substantially completing combustion within said furnace, and collecting said slag for discharge below the said furnace.

2. The process of claim 1 in which the fuel and primary air are admitted at a velocity of from about 6000 to about 24,000 feet per minute, the other air at from about 12,000 to about 60,000 feet per minute,'the furnace pressure being maintained at from about 2 inches to about inches of water, and the rate of combustion being from substantially 500,000 B. t. u. and up- .ward, liberated per cubic foot of furnace volume per hour.

3. The process which comprises delivering finely divided fuel into the upper part of a vertically disposed small cyclone furnace in a swirling movement in a horizontal plane to concentrate the fuel in an "annular zone adjacent the wall of the furance, igniting the fuel at entry into the furnace and burning it while imparting to and continuously maintaining rotary movement of the body of fuel, flame and gases about a vertical axis, whereby unconsumed particles of fuel and ash are caused by centrifugal force to move towards the furnace wall during such rotation and whereby the central portion or core of such body tends to become oxygen rich and fuel lean and said annular zone and adjacent the wall to become fuel rich, repeatedly driving peripheral portions of fuel in said zone inwardly away from the wall of the furnace into the oxygen rich core by continuously supplying high velocity high pressure air in a direction inwardly and tangentially at a plurality of vertically spaced levels in the furnace and at a plurality of circumferentially spaced points of each level, said levels being a substantial vertical distance apart whereby high turbulence and intensive mixing over the entire cross section are provided at said levels by which unconsumed fuel and oxygen are mixed and whereby said air also serves to impart and maintain said rotary movement of said body, said rotary movement intermediate said levels being by'itself relatively nonturbulent, maintaining furnace temperatures suificiently high to produce molten slag on the furnace wall, collecting incombustible solids by said slag, gravity discharging the slag from the bottom of the furnace, burning adjacent said wall any solid combustible particles adhering to said slag covered wall, maintaining a pressure within said furnace substantially above atmospheric to produce extremely high rates of combustion, substantially completing combustion within said furnace, and collecting said slag for discharge below the said furnace.

HENRY KREISiNGER.

REFERENCES CITED The following references are of record in the file of this patent:

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