US2458992A

US2458992A - Pulverized fuel burner

Info

Publication number: US2458992A
Application number: US674734A
Authority: US
Inventors: Floyd T Hague
Original assignee: Westinghouse Electric Corp
Current assignee: CBS Corp
Priority date: 1946-06-06
Filing date: 1946-06-06
Publication date: 1949-01-11
Anticipated expiration: 1966-01-11

Description

Jan. 11, 1949. F. T. HAGUE PULVERIZED FUEL BURNER Filed June 6, 1946 INVENTOR FL. ova T. Haqu:

BY. W M

WITNESSES! 5 TH 1M5 7?}6'777: e o-17 ATTORNEY rv y nsjrznnmt st m 1* Floyd T.-Hague, llr'exel Hill, Pa asslgnor to Welt-R lnghou'se Electric Corporation, East Pittsburgh,

Pa... a corporation of Pennsylvania Application June 6,1948, Serial No. 574,134

3 Claims. (01. 110-28) This invention relates to combustion apparatus, more particularly to combustion apparatus for pulverized fuel, and has for an object to provide improved apparatus of this character.

In studies of pulverized fuel firing, it has been found that when using a medium volatile coking coal the incoming fuel particles, under the influence of furnace temperature, are blown'up into cenospheres by escaping volatile matter. A cenosphere is defined as an empty orv hollow sphere, ball or-globe. Consequently, it has been concluded that the temperature and rate of tem perature rise in the region just ahead of the zone of ignition should be maintained as high as possible. Contrary to previous assumptions, the fuel particles in the form of cenospheres burn essentially at constant diameter, leaving a very fragile, highly-perforated, lacy structure, which is usually broken into fragments in the flnal stage of combustion. The more rapid the rate of temperature rise in'the region just ahead of the zone of ignition, the more violent is the break-up of the cenospheres into small sized particles and the finer is the resultant fly ash.

To obtain this desired high temperature and high rate of temperature rise in the region just ahead of the zone of ignition, the present invention provides for strong axial counterflow, bringing the hottest furnace gases back to the center of the burner to heat up the incoming fuel and air streams. This counterfiow of the hottest furnace gases insures burner stability and early ignition of the mixing fuel and air streams as well as effectiveproduction of the smallest possible fly ash particle'slze, as explained in the first part of the preceding paragraph.

The strong axial ccunterflow discussed above is, in turn, dependent upon high swirl velocity of the fuel and/or air streams, and to obtain swirl velocities of suitable values, the present invention provides for introduction of the "fuel and air to the combustion chamber in a novel manner. Conventional burners usually introduce the airborne fuel in the center of a swirling secondary air supply core, and thefuel'is gradually dispersed or diffused throughout this secondary air stream. This gradual diffusion of the fuel into the secondary air stream takes a measurable time,

and the observation of a burner of this type shows The present invention, on the other hand, provides an annular series of nozzle vanes, through 'alimited number of which the airborne fuel is admitted, the secondary air entering through the remaining nozzle vanes of this annular series.

.Various ratios of fuel nozzle vanes to secondary air nozzle vanes may be used, and a ratio of approximately nine secondary air nozzle vanes for eachfuel nozzle vane has been found to be satisfactory for general purposes. For example, with a half ton per hour burner, sixty nozzle vanes may be employed; six of these admitting airborne fuel and the remaining fifty-four admitting secondary air. The limited number of fuel nozzle vanes will be uniformly spaced in the annular series of nozzle vanes, and in the example mentioned, each of the six fuel vanes will be spaced sixty degrees apart, with nine Secondary there is little radial component of flow of fuel and secondary air from the vanes to the inner wall of the combustion chamber, which wall confines the swirling cylinder of fuel and air. Consequently, little of the swirl velocity is dissipated in radial expansion and the .axial component of flow of the swirling stream is thereby maintained at a maximum. Likewise, the swirl turbulence is maintainable for the maximum axial-distance, usually for the full length of the combustio chamber. I

Therefore, another object of the invention is to provide early .mixing of fuel and air streams in pulverized fuel combustion apparatus.

Yet another object of the inventionis to provide high swirl velocity in the fuel and air streams of pulverized fuel combustion apparatus.

A further object of the invention is to provide a high degree of fuel and air swirl turbulence in pulverized fuel combustion apparatus.

Another object of the invention is to provide maintenance of high swirl turbulence throughout the length of the combustion chamber of pulverized fuel combustion apparatus.

An additional object of the invention is to proinvention as will be apparent from the following description and claims taken in connection with the accompanying drawings, forming a part of this application, in which:

Fig. 1 is a longitudinal sectional view of combustion apparatus embodying the principles of the present invention;

Fig. 2 is an elevational view of the downstream or discharge end of the fuel nozzle or burner of Fig. 1, and showing the disposition of the nozzle fuel vanes relative to the nozzle secondary air vanes; and

Fig. 3 is a sectional view, taken along the lines III-III of Fig. 1, looking in. the direction indicated by the arrows.

Referring now to the drawings more in detail, the reference character I indicates, in its entirety, combustion apparatus comprising a furnace ll having front and rear end walls l2 and I3, respectively, joined by aside wall II which may be of circular or non-circular cross section.

These walls are herein illustrated as of brick, but

it will be apparent that any suitable material may be utilized, for example, cast iron or steel. The walls l2, l2 and I4 define a combustion chamber It to which both fuel and air are supplied by the burner l1, located centrally of the front wall l2,-and whose novel construction and operation are now to be described.

The burner l'l comprises a cylindrical inner casing is to which finely-pulverized fuel (for example, coal) is borne through the conduit II by a stream of primary air. An outer casing 2|, of materially greater diameter than the inner casing l8, surrounds the latter in concentric relation, secondary air being introduced to the annular space 22 between said inner and outer casings by the conduit 22.

In order to distribute the flow of secondary air uniformly through the various sections of the annular space 22, the latter is provided with numerous partitions 2l,extending radially between the inner and outer casings l8 and 2! preferably in uniformly spaced relation circumferentially of said annular space, and defining, with the inner and outer casings l8 and 2|, segmental nozzle passages 26 (Fig. 2) through which the secondary air from duct 23 passes to enter the combustion chamber l8. 7

To obtain uniform mixing of the pulverized fuel and secondary air immediately upon entry thereof to the combustion chamber, the airborne fuel is diverted radially from the, downstream end of the inner casing 18 into a limited number of segmental fuel nozzle passages 21, ilnterspersecl among the remaining air nozzle passages 26, and preferably being uniformly spaced circumferentially of the annular series of nozzle passages.

In the arrangement illustrated in Figs. 1 and 2, four fuelnozzle's 21 are uniformly dispersed among twenty-four secondary air nozzles 2|, communication' between the interior of the inner casing II and the fuel nozzles 21 being effected by openings 28 provided in the inner casing it at locations aligned with the fuel nozzle segments 21 (Fig. 1). All of the airborne fuel delivered to the inner casing I8 is forced to flow through the openings 28 into the communicating fuel nozzle segments 21, since the downtream end of casing It is blocked by the end wall 29-.

The fuel nozzle segments 21 pass only airborne fuel from the inner casing l8, entry of secondary air thereto from the conduit 23 being prevented by closure walls 3| extending diagonally of the fuel nozzle segments 21 (Figs. 1 and An annular series of inclined vanes 32 is provided adjacent the outlet or downstream end of the annular series of fuel and

air nozzle passages

21 and 26, the vanes extending radially and all being inclined in the same direction to impart swirling action to the air and fuel streams entering the combustion chamber I6. Preferably, these vanes 32 are secured to, or formed integral witht'the exit edges of the partitions 24 separating the nozzle passages 26-21 (Figs. 1 and 3).

Preferably, these vanes are of the type used in steam turbine diaphragms, which are recognized to be about 98 per cent eflloient. It is believed that nozzles of this type have never before been used in apparatus of the character concemed with here.

In operation, airborne pulverized fuel is supplied through the conduit l9 to the burner I! where it enters the fuel nozzle passages 21 through the openings 28 in the inner casing l8. Simultaneously, secondary air, supplied through the conduit 23, enters the alrnozzle passages 26, and both air and fuel, emerging from the'nozzle passages 26-21, enter the combustion chamber IS with a swirling motion imparted thereto by the inclined vanes 22, this swirling action continuing throughout the length of the combustion chamber. This high swirl velocity of the fuel and air stream within the chamber sets up a strong axial counterflow of hot gases from the rear end of the chamber, which flow occurs from the rear towards the front of the chamber along the axial center thereof, as indicated by the arrows A of Fig. 1.

' This strong axial counterflow brings'hot gases to the inlet end of the chamber where they produce' both high temperatures and high rate of temperature rise in the entering stream of fuel and air. These high temperatures and high rates of temperature rise provide both early ignition of the swirling fuel-air stream and maximum size reduction of the fuel particles incident to their transformation to cenospheres, as previously discussed.

No attempt has been made to illustrate any particular type of heat-utilizing means in association with the heat-producing apparatus herein disclosed, as it will be apparent that the novel combustion apparatus will have utility with numerous types of heat-utilizing apparatus. If the combustion apparatus of the present invention were to be utilized in connection with a steam boiler, the tubes of such boiler might well be positioned in the downstream or rear portion of the combustion chamber IS, the products of combustion passing through the outlet openbe conducted through the outlet opening 36 to a gas turbine, or other heat-utilizing apparatus.

While the invention has been shown in one form, it will be obvious to those skilled in the art that it is not so limited but is susceptible of various changes and modifications without departing from the spirit thereof.

What is claimed is:

1. In a pulverized fuel burner, inner and outer concentrically-disposed annular casings defining therebetween an annular nozzle chamber, radial partitionsseparating said annular nozzle chamber into a plurality of nozzles, means for supplying airborne fuel to the space within the inner casing, means for supplying secondary air to certain of the nozzles, means for admitting airborne fuel from the interior of the inner casing to the other of the nozzles, and means preventing entry of secondary air to said other nozzles.

2. Structure as specified in claim 1, including means for imparting swirling motion to the fuel and air leaving said nozzles.

3. In a pulverized fuel burner, wall structure said nozzles, means for supplying air to the remainder of said nozzles, and means for converting r the pressure energy of the fuelianduairwithin defining an annular nozzle ring, means dividing said ring into a plurality of nozzles, means for supplying pulverized fuel to alimited number of the nozzles into velocity energy adjacent and before the nozzle exits and for imparting a swirling motion to the fuel and air, said last-mentioned 9 means comprising an annular row of steam turbine diaphragm type vanes.

FLOYD T. HAGUE.

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