US2782738A - Control of flame length in furnaces - Google Patents

Description

Feb. 26, 1957 R. E. zoLLER 2,782,738

CONTROL oF FLAME LENGTH. 1N FuRNAcEs Filed Jan. 12, 195s IN V EN TOR. s KOA/44D E. Z 0445 illnited States Patent O CONTROL F FLAME LENGTH IN FURNACES Ronald E. Zoller, London, England, assignor to The Babcock & Wilcox Company, New York, N. Y., a corporation of New Jersey Application January 12, 1953, Serial No. 336,729

Claims priority, application Great Britain January 11, 1952 3 Claims. (Cl. 11G-28) This invention relates to combustion apparatus and particularly `to combustion apparatus of the kind including a furnace chamber comprising radiant heat exchange surfaces. In such combustion apparatus the temperature at a region adjacent the outlet from the furnace chamber varies with the rate of tiring and at any particular rate of firing is liable to vary with the quality of the fuel and in some instances with the state of the heat exchange surfaces. In modern high pressure high temperature vapor generating and superheating units temperature control of the gases at the inlet to the convection section is a matter of importance. Temperature control at a particular region or particular regions within a furnace chamber may also be of importance. An object of the invention, therefore, is to enable a measure of control of temperature variation along the gas flow path within a furnace chamber to be achieved.

The present invention includes a furnace chamber comprising radiant heat exchange surfaces `arranged to be fired by flame producing burner means, wherein means are provided for regulating the rate of combustion in an inner region of the flame and hence the llame length.

The invention also includes la furnace chamber comprising radiant heat exchange surfaces and arranged to be lred by llame producing burner means, wherein means are provided for regulating the ratio of air to fuel in an inner region of the llame and hence the llame length.

The invention furthermore includes a furnace chamber comprising radiant heat exchange surfaces and arranged to be fired by a group or cluster of two or more burner elements, wherein damper means are provided for controlling the -amount of air supplied to a region within the furnace chamber between burner elements of the group.

The invention furthermore includes a tubulous vapor generating and superheating unit comprising a furnace chamber including radiant heat exchange surfaces and arranged to be fired by flame producing burner means,

a gas pass communicating with the furnace chamber and containing a convection superheater, and means for regulating the rate of combustion in an inner region of the flame and hence the flame length.

The invention also includes the method of controlling the temperature of vapor supplied by a tubular vapor generating and superheating unit having a furnace chamber including radiant heat exchange surfaces and a gas pass communicating with the furnace chamber and containing a convection superheater which comprises supplying burner means associated with the furnace chamber with air and fuel at rates suited .to the load on the unit and regulating the length of the flame produced by the burner means to control the temperature of the vapor supplied by the unit.

The invention will now be described, by way of example, with reference to the accompanying largely diagrammatic drawings, in which:

Fig. 1 is a sectional elevation through an integral furnace type boiler to which the invention is applied, taken on the line 1--1 of Fig. 2;

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Fig. 2 is a sectional plan view taken on the line 2 2 of Fig. l, showing only details adjacent the section line;

Fig. 3 is a sectional side elevation through a pair of pulverized fuel burner elements of modified form forming part of a cluster of four such burner elements to which the invention is applied, taken on the line 3-3 of Fig. 5;

Fig. 4 is an enlarged longitudinal sectional view taken on the line iw-4 of Fig. 5 of part of the primary air and fuel pipe and an associated deilector shown in Fig. 3; and

Figs. 5 and 6 are front elevations of the cluster of burner elements shown in Fig. 3 under two different conditions of operation.

Referring first to Figs. l and 2, a cluster or group of four burner elements l of any suitable type adapted to burn fluid fuel, for example oil or pulverized coal, as shown for example in U. S. Patent No. 2,044,720, are positioned to discharge through burner ports 2 formed in the front wall 3 of the furnace chamber 4 of a tubular vapor generating and superheating unit of the integral furnace boiler type, in which the front wall 3, the rear wall 5, the side wall 6, the partition wall 7, the roof 8 and the door 9 include radiantly heated fluid cooled tubes in a well known manner. A lateral outlet it) adjacent the rear wall 5 leads from the furnace chamber 4 into a plurality of serially connected gas passes ll containing vapor generating surfaces formed by tubes l2 connecting an upper vapor and liquid drum 13 and a lower liquid drum 14. Located in the rst gas pass 1l, adjacent the outlet ttl from the furnace chamber, is a convection superheater 15 comprising tubes i6 connected at their ends to inlet and -outlet headers 17. Hot gases pass from the last gas pass 1,1 through a duct 18 to a stack (not shown).

The four burner elements l are arranged to discharge four streams of a mixture of fuel and air towards the rear wall 5 of the furnace chamber, secondary air being discharged from the ports 2 about the burner elements from a wind box 20 arranged on the outside of the furnace chamber front wall 3. An air port 2l of smaller diameter than the burner ports 2 is arranged centrally of the group of'burner ports and is supplied with air from the wind box Ztl, the amount of air discharged from the port 2l being regulated by an air register 22, arrranged at the outer end of the air port 21 and within the wind box 20. This air register is suitably of a well-known type commonly used in connection with the supply of combustion air to oil and pulverized fuel burners associated with integral furnace boilers, and comprises an imperforate cylindrical front part 23 adjacent the front wall 3 and a rear part 24 including a circular series of curved vanes 25 respectively pivotally supported on axes (not detailed) arranged normal to the plane of the furnace wall, the vanes being arranged, when in their closed positions, to form a cylindrical continuation of the front part 23. In the present inst-ance, the rear end of the `air register is closed by a plate 26, and the vanes may be rocked on their pivotal axes from their closed positions to their open positions from outside the wind box by means of a rotatable shaft 27 provided with a suitable fluid tight seal where it passes through the rear wall 28 of the wind box 20. Each of the burner ports 2 has associated with it an air register 30, which suitably may be of the type described above in connection with the air port 21, for the regulation of the amount of air discharged through the port from the wind box.

in the arrangement of burner elements shown in Figs. l .and 2, the four burner elements are placed relatively close to one another with their fuel discharge axes parallel `to'one another, so `that the elements produce a common name.

Under one condition of operation of the vapor generating and superheating unit `described above, the vanes of the air register 22 `associated with the air port 21 'are in their closed position, a-nd no air is discharged through the air port 21, the requisite amount of combustion air being supplied through the burner ports 2 by suitable adjustment of -their air registers 30.

Under another condition of operation of the unit, the vanes of the air register 22 associated with the air port 21 are at least partly opened, and air is discharged through the .air port 21. To maintain the requisite total air supply to the furnace chamber, the air registers 30 associated with the burner ports 2 are suitably adjusted. It will be seen that under this condition of operation, the airfuel ratio in the central part or inner region of the common ame has been increased, and as a result, the flame is shorter than when all the combustion air is suppliedto the bur-ner ports.

By varying the length of the ame in this manner, the

temperature of the hot products of combustion when they pass through the lateral gas outlet may be controlled within limits, and as a result an improved regulating of the final temperature of superheated vapor leaving the unit may be obtained.

Referring now to the embodiment illustrated in Figs. 3 to 6, a cluster or group of four pulverized fuel burner elements 41 is positioned in the front wall 42 of the furnace chamber of an integral furnace boiler such as that illustrated in Fig. l in which the furnace walls include radantlv heated tubes and in which the hot products of combustion after traversing the length of the furnace chamber flow through a lateral gas outlet and then flow in a generally reverse direction through convection banks of superheater and steam generating tubes. As shown in Fig. 3, each burner includes a central pipe 43 arranged normally to the plane of the furnace wall 42 within a secondary air wind box 44 and having a -downwardly curved outer end part 45 arranged to be supplied with pulverized fuel entrained in primary air from a pulverizing mill (not shown) and to discharge through a burner port 46 formed in the vfront wall 42. A part 47 of the pipe 43 near the wall 42 is enclosed in an air register 48 of well known type including an imperforate cylindrical front part 49 and a rear part 50 including a circular series of curved vanes 51 respectively pivotally supported on axes (not detailed) arranged parallel to the central axis of the pipe 43 and arranged, when in their closed positions, to form a cylindrical continuation of the front part 49. An annular plate 52 closes the rear end of the register.

Mounted rotatably and coaxially within the part 47 of the pipe 43 and extending through the rear wall 55 of the curved part 45 of the pipe 43 is a control shaft 56 provided at its rearward end with a handwheel 57. The forward end of the shaft 56 is suitably supported axially of the pipe 43 and has secured to it a deflector 58 which, during normal operation of the burner element, is positioned a short distance outside the front end 59 of the pipe 43 (as shown in Fig. 3), but which during periods when the particular burner element is out of operation may be withdrawn by thel control shaft 56 to a position within the pipe 43, where it is less exposed to the heat of the furnace chamber.

The form of this deflector is shown most clearly in Fig. 4. A central boss 60, adapted to fit onto the control shaft 56, to which it is secured by `screws such as 61, and to be held against rotation thereon by projections 62 engaging grooves 63 on the control shaft, is provided at its forward end 64 with a forwardly divergent frusto-conical rim 65, and is surrounded by three spaced but overlapping frustoconical rings 66, 67 and 68 supported relative to the boss 60'and to one .an-other by a series of radial lugs, which have been omitted from the drawing for the safe of clearness. The detlector shown has been fabricated by casting, and the casting includes a closure piece 70 extending over lsubstantially a full quadrant of the circumference of the -deflector and joining the :three rings 66, 67, and 68 and CTI the rim 65 over that quadrant so as to close the annular passages, inclined outwardly in the direction of flow of fuel from the burner element, which would otherwise exist between the innermost ring and the :rim over that quadrant.

Under one condition of operation of the burner element, secondary air entering the air register is given a swirling motion about the pipe 43 by .the curved vanes 51, while coal and primary air pass through the central pipe 43 and are spread bythe rim 65 and by the rings 66, 67, and 68 on the dellector 58, which split up the Stream and assist in obtaining an intimate mixture of the pulverized fuel, primary air and secondary air.

Since, however, one quadrant of the dellector 58 is blocked by the closure piece 70, substantially all the pulverized fuel and primary air is forced to flow through `the other three quadrants of the deflector. The secondary air is supplied to the burner element about the Whole periphery of the deflector 58, and as a result the sector of the fuel-air discharge from the quadrant of the burner element adjacent the blocked quadrant of the deflectcr is more rich in air than other sectors of the discharge.

In the arrangement of burners shown in Figs. 3 to 6, the four burners are placed relatively close to one another .with their fuel discharge axes parallel to one another and at the four corners of a rectangular part of the furnace wall, and the burners produce a common flame. When the blocked quadrants of the deflectors of the four burners are positioned as indicated in Fig. 5, there tends to be an insufficiency of air in the region of the furnace space between the .axes of the discharges from the four burners 1 and in the central part or inner region of the resultant common llame. As a result, the flame is of greater length than if the fuel and primary air flowing into the furnace chamber were evenly distributed around the axes of the burner elements. On the other hand, when the four deflectors are rotated to bring their blocked quadrants into the positions indicated in Fig. 6, there is `an excess of combustion air in the region of the furnace space between the axes of the discharges, and as a result, the flame is shorter than when the quadrants were in the positions indicated in Fig. 5.

By varying the length of the llame in this manner, the temperature of the hot products of combustion when they pass through the gas outlet from the furnace chamber may be controlled within limits, and as a result an improved regulation of the final temperature of superheated vapor leaving the boiler may be obtained.

By varying the length of the flame in this manner7 the temperature of the hot products of combustion when they pass into thc lateral gas pass may be controlled within limits, and as a result an improved regulation of the nal temperature of superhcated vapor leaving the unit may be obtained.

I claim:

l. Fuel burning apparatus comprising walls dening a furnace chamber, fuel burning meansfor firing said furnace chamber comprising a plurality of burner elements arranged to discharge streams of fluid fuel through a Wall of said furnace chamber with the fuel discharge axes of said burner elements substantially parallel to one another to'produce a common flame, means for supplying combustion air to said furnace chamber around each of said fuel streams, a rotatable deliector arranged to effect a mixing of each of said fuel streams with the surrounding air stream, each of said deflcctors having a sector substantially ineffective for said mixing action and producing a corresponding air-rich sector in said ame, and means for rotating said dellectors to vary the relative positions of said ineffective sectors and of the corresponding air-rich sectors in said flame.

2. Fuel burning apparatus comprising walls defining a furnace chamber, pulverized fuel burning means for tiring said furnace chamber comprising a plurality of burner elements arranged vto discharge pulverized fuel and primary combustion air through a wall of said furnace chamber with the fuel discharge axes of said burner elements substantially parallel to one another to produce a common llame, means for supplying secondary combustion air to said furnace chamber around each of said pulverized fuel-primary air streams, a rotatable deector arranged to eect a mixing of each of said pulverized fuel-primary air streams with the surrounding secondary air stream, each of said deflectors having a quadrant substantially inefective for said mixing action and producing a` corresponding air-rich sector in said flame, and means for varying the length of said llame in said furnace chamber comprising means for simultaneously rotating said deflectors to vary the relative positions of said ineective sectors and of the corresponding air-rich sectors in said flame.

3. Fuel burning apparatus as claimed in claim 2 in which each deector includes several coaxial frusta-conical rings defining passages inclined outwardly in the direction of lovv of fuel from the associated burner, the passages being blocked over one quadrant of the deector.

References Cited in the le of this patent UNITED STATES PATENTS Re. 16,984 Leach June 5, 1928 1,581,351 Kreisinger et al. Apr. 20, 1926 1,966,054 Wheeler luly 10, 1934 2,293,736 Heller Aug. 25, 1942 2,293,737 Hardgrove Aug. 25, 1942 2,363,875 Kreisinger et al Nov. 28, 1944 2,380,463 Poole July 31, 1945 2,395,276 Jordan Feb. 19, 1946 2,559,589 Brierly July 10, 1951 FOREIGN PATENTS 331,555 Great Britain Iuly 4, 1930

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