US2858779A - Powdered coal burner for pressurized combustors - Google Patents

Description

Nov. 4, 1958 PQWDERED COAL BURNER FOR PREssuRIzRD coMBUsToRs Filed Nov. 19 1951 s sheets-sheet 1 NOV.v 4, 1958 7 P KM, RQTZLER 2,858,779

vPOWDERED COAL BURNER FOR PRESSURIZED COMBUSTORS Filed Nov. 19, 1951 3 Sheets;Sheet 2 `\O) v "N,

AQ R4 f lINVENTOR PaulMJiozler.

BY MM/ ATTORNEY NOV- 4, 1958 P. M. ROTZLER POWDERED COAL. BURNER FOR PRESSURIZED coMBUsToRs 3 Sheets-Sheet 3 Filed NOV. 19 1951 .WHR

' Y INVENTOR.

Paul MROi'zLer.

l BY WL/l 2.720151 POWDERED COAL BURNER FR PRESSURIZED COMBUSTORS Paul M. Rotzler, Dunkirk, N. Y., assignor to vBituminous Coal Research, Inc., Washington, D. C., a corporation of Delaware This invention relates to powdered coal burners forv use with pressurized combustors of the type used for generating and supplying motive fluid to direct-fired,open cycle gas turbines. More particularly, the invention relates to duplex or universal burners which can handle any fluent fuel, alone, or in any desired combination, and in high pressure installations of restricted size, such as are required in the power plants of generating electric locomotives whose generators are energized by gas turbine power plants using powdered coal as a primary fuel, and in mobile power plants generally.

The space and operative requirements of power plants for locomotives are rigidly restricted. This means that all necessary equipment must be as small as possible,

consonant with the power required.v More power in less' space is possible with gas turbines, and it is interesting to note the following comparison of horsepower per cubic foot of essential space among several typical power plants:

In coal burning installations, the space requirements can be greatly reduced by burning powdered coal, (in.

pressurized combustive air streams, in combustors of the cold wall type having burner domes` and flame tube sections comprised of overlapping rings or bands, with the burners mounted axially in the dome sections. Additionally, the special conditions of locomotive service rel quire that an auxiliary oil burner must be used with each combustor for starting and emergency operation when the coal burner is out of service. Multi-jet type burners I United States Patent O have been found to be unsuitable for use in powdered coal-burning combustors for' gas turbine motive uid' generators of generating electric locomotives." The conguration of the pressurized, open-cycle gas turbine combustion system is such that the coal-air stream must enter through the pressure shell (of the combustor). at right angles to the burner axis. The resulting 90 bend normally causes irregular distribution of the coal, with a few of the jets receiving most of the powdered fuel.

Also, with a multi-jet burner, there is no easy way to ized combustor, as shown in the drawings. A wide range oil burner is spacedly mounted and centered in the hollow core of the annular burner. The pressurized air-borne coal stream spins out of the annular burner, with a reduction in pressure and concomitant increase in velocity, into the llame tube of the combustor. An inner stream of air swirls out, with an opposite spin, from the annulus between the oil burner and the innervwall of the annular coal burner, and is enveloped by and mixes with the flame from the annular burner. The dome of the combustor, in which the burner is mounted, forms a third annulus through which the remainder of the pressurized secondaryA air enters the flame tube of the combustor and envelops the flame of the burning annular air-coal stream from the burner, as well as the burner itself. By proper selection of the gap width of the various passages, the air quantities supplied yto the combustor become adequate for efficient combustion and the burner elements remain cool.

Ignition of a combustive air-borne pulverized coal stream is normally accomplished by the use of a small arne of burning oil or gas. The system herein contemplates the use of an igniter comprising a simple shielded oil-jet, equipped with a spark plug and mounted on the combustor shell. The spark is needed only when the igniter is lit olf; the air supply Vis so proportioned that the igniter can be lit at anytime regardless of the air velocity in the combustor. The novel annular burner of the present invention can also be used as an igniter by introducing an insulated electrode through the inner annulus and striking a spark otf the axially disposed oil burner tip.

The operative requirements of a burner can be evaluated best by considering the fundamental requirements for the combustion of pulverized coal under gas turbine conditions, which is, essentially, a three-stage process. First, the coal must be conveyed into the system byy a primary stream of compressed air. The air-coal ratio must be` kept near one pound of air per poundv of coal, and the velocity must be above 50 F. P. S., to prevent the ame from flashing back. Second, the air-coalmixture must be introduced into the flame tube by a burner which adds the secondary air necessary to support combustion. Third, after combustion is complete, the remaining excess air is added to bring the air temperature down to a usable level. This three-stage process is further complicated by the fact that the walls of the flame tube must be swept by air to 4keep the metal below 1500 F., but the cooling air must not be allowed to dilute the ilame prematurely. l v 4 The novel duplex or composite burner of the present invention enables the gas turbine, in locomotive service, and in mobile, self-powered equipment generally, to burn diesel fuel as well as coal. This is permitted by the wide range oil burner which is axially disposed in the annular coal burner, and which can be used for ignition, run-up and ystandby full-load operation.

The critical function of the burner in combustors for use with gas turbine installations is intimately related to the major problem4 of the maximum reduction in weight and space requirements of the elements comprising such installations. With pressurized operation there is a higher throughput possible with units of reduced size. Concomitantly, however, there must be a maximum of etticiency in the delivery and combustion of the combustive air-borne powdered fuel, and this is now rendered possible, for the first time, by the improved annular burner of the present invention in combination with the novel cold wall combustor structures to be adverted to more in detail hereinafter.

It is therefore among the features of novelty and advantage of the present invention to provide novel powdered coal burners for pressurized combustors generally, and for such combustors when specifically incorporated in coal burning, open-cycle gas turbine power plants of self-powered, mobile equipment generally, and, inter erating Electric Locomotive With Coal Fired Gas Turbine. It is also amongthe'features of noveltyl and'advantage ofi this invention to provide a duplex burner for burning powdered coal and incorporating an oil burnervfor ignition, run-up, and standby full-load operation, and includ-L ing, where desired, electric ignition means for the oil burner. a I

Further features of novelty andadvantage of the present invention includeV the provision of cylindrical combustors for the generation of motivefluid for open-cycle gas turbines, which combustor's incorporate non-spraying, axially mounted, elongatedhollowl duplex' air-co'al'and oil burners bathed in the ambient pressurized secondary air stream.

With'theseand other desirable featuresof novelty and advantage, which may be incident to the improvements herein, the inventionconsists in the partsV and combinations to'be hereinafter se'tV forth and claimed, with the understanding that theV several necessary elements comprising the invention,- may be varied in construction, proportions and arrangements, without departing from the spirit andascope of' the'appended claims.

In order to make 'the invention more clearly understood, there is shown in the accompanying drawings means `for carrying the same into practical effect, without limiting thek improvements in their useful application tothe particular constructions, which, for the purposeV of explanation, have" been made the subject of illustration.

In the drawings, like numerals refer to similar parts throughout the several views, of which:

Figure 1- is a' schematic showing of a coal-burning, open cycl'egasA turbine-powered generating electric locomotive power plant incorporating special pressurized cmbusto'rs utilizing the' novel powdered coal and oil burner of the' present invention;

Fig; 2 is an elevation, partly in broken section, of a special combustor, showing the mounting of the duplex burner herein;

Fig. 3 is a detail elevation, partly in broken section, of the burner section vof the Vcombustor of Fig. 2;

Fig. 4 is a longitudinal section of the burner herein with the coal-air inlet shown in elevation;

Fig. 5 is a partial vertical section through the coal-air inlet of the burner of Fig; 4'

Fig. 6 is a front view of the burner showing the air Y flow in the various sections'thereof, and e Fig. 7 is a view similarto Fig. 4, showing the incorporation of electric ignition. means 'for the oil burner.

Turning now to the drawings, and more particularly to Fig. 1, there is shown a coal-burning, open-cycle gas turbine-powered, generating electric power plant particularly adapted for use in restricted' spaces, such as obtain in generating electric and other locomotives, and-in selfpowered mobile power units generally. The system, as shown, comprises generally a source of combustive airborne uidized coal 1, a coal' splitter 2, a plurality of combustors, designated generally by the' numeral 3, and feed lines 4 from the splitter to the combustors. Motive uid is delivered from the combust'ors to ash. separator 5 through ducts 6. Cleaned motive fluid is delivered to the turbine 7 through expansionA ducts S, and the expanded gas from the turbine vents to the exhaust stack. 9, which mounts a regenerator 10 in heat-exchanging relation withy the stack gases. A main air compressor 11 is driven by the turbine, and delivers secondary and cooling air through duct 12 to the regenerator, whence the heated air is fed to the combustors 3 through expansion ducts 13. The turbine shaft is coupled, in any suitable manner, to the power unit comprising D. C. traction generators 14, and auxiliary generators 15. 4 The novel burner of the present invention, as previously indicated, is especially adapted Vfor use with pressurized combustion systems using cold Wall combustors, and such use is illustrated in the copending application of Frederick D. Buckley, Ser. No. 257,i65, filed November 19, 1951, now Patent No. 2,823,627, for Cold Nall Combustor for Pressurized Combustion of Pulverized Fuel and Flexibly Mounted Flame Tube Therefor. This form of cold wall combustor, as shown and claimed in the said Buckley'- applica'tion, comprises a iiame tube of overlapping concentric rings or bands, supported at their upstream edges only by radial supports slidably mounted in spaced hoops or bands which are xedly secured to longitudinal bars. The longitudinal bars or rods are severally secured at their ends to the burner dome and mixing chamber, respectively, whereby the flame tube elements are restrained from any substantial axial movement, while remaining capable of radial movement. The outer surface of the flame tube is bathed by cooling air, which ows into the ame tube through the spaces between the flame tube elements, whereby the supported, upstream ends of said elements are cooled, and any axial expansion and contraction therein is restricted to the unsupported, downstream edges thereof. Another form of cold wall combustor with which the novel burner herein can be used is illustrated in Figs. 2 and 3 of the drawings of the present case, which combustor will now be described:

The flame tube, designated generally by the numeral 20, comprises a dome section, a combustion section, and a mixing section. The dome section, which mounts the burner 50, is comprised of a dished dome 21 and overlapping ring 22. The burner 5t) is axially mounted in member 21, while an auxiliary ignition burner 23 is mounted in ring 22. The combustion section is comprised of a series of overlapping rings or bands, designated generally by the numeraly 24, which are mutually spaced to provide for the controlled `flow of secondary combustion and cooling air therethrough and into the combustion chamber proper. The mixing chamber 25 overlaps the downstream end of the combustion section, and' is provided with an annular series of diagonally disposed, overlapping slots 26 at its downstream end. The downstream end of the mixing chamber 25 is provided with an integral outer ange 27 conformed to and receiving one end of the fluted radiation shield 30 in gastight relation. The other end of the radiation shield extends to the dome section of the arne tube. A plurality of longitudinal spacing and stiening members 28 are t'ted in the utes of the radiation shield, and are provided with integral feet sections 29 which are severally conformed and xedly secured to the overlapping rings ofthe dome and combustor sections of the flame tube, whereby the latter are fxedly secured in place. The flame tube and its radiation shield are xedly mounted in and coaxial with the combustor casing in any suitable manner, and this mounting will not be described further, as it forms no part of the invention herein.

The novel duplex burner herein comprises an elongated, hollow annular coa'l-air burner, mounted in the longitudinal axis of the combustor, and designated generally by the numeral S0, and an oil burner 60, axially and spacedly mounted therein, as shown more particularly in Figs. 4 and 5. The annular burner 50 will be seen t-o comprise a hollow tubular casing 51 having a a'red mouth 52, and a necked-in collar 53 at the other end. The collar 53 terminates in a lbell-mouthed secondary air inlet 54. The bell mouth 54 serves as a scoop to receive and introduce a maximum volume of the rectilinearly inflowing ambient secondary air, as a pressurized core stream, into the hollow core of the elongated annular burner. At the base or root of the ared mouth 52, the casing is provided with a projecting annular shoulder 55, whose function will be adverted to more in detail hereinafter. A tangential coalair delivery duct 56 is formed integral with the casing and is disposed at the rear end thereof, immediately in advance of the collar 53. The duct 56 is provided: with suitable cou i plin'gnlean's, such as the screw threads 56. The inner wall of the collar 53 is recessed to receive one end of tube 57 which is concentric with casing 51 and forms an annular chamber 58 therewith. The annular chamber 58 is in free iiuid communication with duct 56 at its inlet end, and is restricted at its mouth or discharge end by the internal collar or restrictor 55, previously described. A subjacent lug 59, suitably apertured as shown in Fig. 4, is formed integral with the casing 51, and serves to support the burner when mounted in place in cooperative associationwith the combustor 20.

The operation `of the burner 50 is simple and substantially fool-proof. Additionally, it is especially suited for the handling of combustive air-borne powdered co-al, because the pressurized stream of air-borne powdered coal delivered through duct 56 is introduced into the annular chamber 58 of the burner in a relatively iiat spiral which advances to the mouth 52, scouring the walls of the annular chamber, whereby'deposition or silting out of the entrained coal particles is prevented. Because of the restrictor 55, an appreciable back-pressure is built up and maintained in the burner chamber 58, and this pressure is suddenly released as the coal-air stream passes through the throat formed by and between the restrictor 55 and the adjacent outer surface of inner tube 57 of the burner. Because of the drop in pressure at this point, the coalair stream issuing from the mouth 52 of the burner Will have an increased velocity, and will be projected forwardly as a swirling spray into the combustion section of the circumjacent iiame tube of the combustor, where i it will be ignited by the iiame from the pilot burner 23 (Fig. 3).

It has been found that it is imperative to maintain the walls of the combustors substantially ash-free for economical operation, and particularly to avoid fouling of the combustor, with necessary overhaul and replacement of parts, let alone the time lost when a power plant unit is kept out of service from such cause. ,The novel coalair burner herein substantially eliminates the diliiculties due to fouling of the ame tube wall and its sections.

This is due tothe fact that the high velocity, spinning coal-air stream, as it issues from the mouth of the burner, is ignited and simultaneously subjected to the yaction of an outer envelope of high pressure secondary combustion air and an inner core of the same air, but desirably at a lower pressure than that of the envelope or sheath air, whereby a pressure gradient is established in the flame, from the outside inwardly, so that the normal spray pattern of the ame is converted in a constricted, axial cone, and the solid combustion residues are axially asported in the combustion gases, and are prevented from being centri'ugally cast on to the walls of the combustor. The discharge of a low-pressure, high-velocity core stream of secondary air axially into the hollow mantle of the coal ame is made possible by providing any suitable flow restrictor in the hollow center of the annular burner. This can be effected most simply by providing the burner tip of the axially disposed oil burner 60 with an annular protuberance, whereby a restricted annular air passage is formed between it yand the adjacent wall of the inner tube 57 of the annular burner, and the pressurized core stream of secondary air is reduced in pressure and increased in velocity by passage therethrough.

The annular burner herein uses a wide-range oil burner 6i)v as its central element. The primary air-coal stream enters tangentially into the burner, and spins out of the mouth thereof into the iame tube. An inner stream of air swirls out with an opposite spin (Fig. 6) from the. annulus between the o-il Iburner and the inner wall of casing l of annular burner 50. The dome 21 of the ycombustor forms a third annulus through which the remainder of the secondary air enters. By properly select- Aing the width of the various passages, the air quantities becomeadequate for eiiicient combustion, and the burner' elements remain cool.

The oil burner is of the positive pressure type, and comprises a tubular body 61, with a spray nozzle tip 62 which has a lateral bulge or swelling 63. This bulge forms a restrictor in conjunction with the adjacent section of the inner wall of annular burner element 57. The casing 61 is provided with a threaded oil inlet 64, at right angles thereto, and this stub pipe is secured in a suitable aperture in the bell mouth 54 of the annular burner by nuts 65. By suitably adjusting the nuts 65 on the member 64, the burner 60 can be axially centered in the hollow center of the elongated, annular burner 50. An oil return tap 66 is secured to the end of casing 61 by a lock nut 67. The oil supply is connected to the burner 6i) in any suitable manner, and a positive flow is maintained by a circulating pump. The details of the oil supply form no part of the present invention, except in the combination shown, and will not be described further.

As noted hereinabove, and with particular reference to Fig. 3, the coal-air and oil sprays of the burner are ignited by a pilot light, designated generally by the numeral 23. The combination burner herein, as illustrated in Fig. 7, can function as a self-contained pilot unit, where necessary, by providing a spark electrode 68 juxtaposed to the burner tip 62. The electrode is connected to a suitable high tension source, not shown, through insulated lead 69, the return lead being throughground, as shown.

There has been described and illustrated a device capable of performing all of the specifically mentioned objects of this invention as well as others which are apparent to those skilled in the art. Various uses of the present invention may be made employing the described structure. Accordingly, it is apparent that variations 4as to operation, size and shape, and rearrangement of the elements may be made without departing from'the spirit of the invention. Accordingly, limitation is sought only in accordance with the scope of the following claims.

I claim:

1. A powdered coal burner specially adapted for use pressurized combustion chambers of open-cycle, direct red, gas turbine power plants, comprising, in combination, an elongated, hollow, double-walled tubular member closed at one end to form an openended annular chamber; tangential inlet means at the closed end of the said annular chamber, whereby a combustive air-borne stream of particulate combustible material is delivered to said `chamber in a relatively flat helix; restrictor means incorporated in the annular chamber, intermediate .the ends thereof, whereby the air-borne particulate material stream is discharged therefrom, at reduced pressure, and increased Velocity, as a whirling spray; pressurized secondary air supply means coaxial with the burner; means for delivering said pressurized secondary air rectilinearly as a core stream through the burner and as a sheath stream about said burner; and restrictor means for the core stream, whereby the sheath stream envelops the combustive air-borne combustible material and the coiiowing core stream of secondary air, and the flame of the burner is constricted to an axial cone.

2. Combustor according to claim l, characterized by the fact that the annular burner mounts the insulated lead of a spark electrode which is juxtaposed to the head of the second, axially disposed fluid burner, and the latter is electrically grounded, whereby when an are is struck between the electrode and the fluid burner head, the secondary air issuing from the secondary air duct of the burner blows the arc into the path of the fluid jet issuing from the burner and the jet is ignited. I

3. A non-fouling cold wall combustor particularly adapted for the combustion of residue-forming fuels as streaming entrainments of discrete particles in pressurized primary combustive air streams, comprising, in combination, a combustor casing; a radiation shield in and c0- extensive with the casing; a segmented combustion chamber of overlapping rings axially disposed in the casing and spacedly supported in the radiation shield; a domed cornbustion head at one end of the combustion chamber; a whirling spray annular burner in the combustion head; combustive air-borne, particulate, residue-forming fuel supply means feeding through the casing wall and the radiation shield, thence through the combustion head and the combustion chamber wall into the combustion charnber; and means at the mouth of the burner effective to reduce the pressure of the issuing, primary air-borne particulate spray below the pressure of the ambient secondary air, whereby the normal spray pattern of the burner is converted to a restricted, convergent cone pattern, and combustion residues are asported in and by an axial stream of combustion products and out of contact with the wall of the combustion chamber, characterized by the fact that the secondary air inlets in the combustion chamber or dame tube wall are adapted and arranged to introduce charges lof cooling air, seriatim, into the stream of combustion products, whereby the asported iluent combustion residues are at least supercially chilled and frozen, characterized by the fact that the burner incorporates a second, axial secondary air duct, and the primary and secondary air ducts of the burner severally incorporate flow restrictors, and characterized by the fact that a second, Huid burner is axially mounted in the secondary air duct of the annular burner and its head cooperates with the circumjacent wall of the annular burner to form a ow restrictor.

4. A lduplex powdered coal and oil burner specially adapted for use in combustion -chambers of pressurized motive iluid generators of open-cycle, direct-fired gas turbine power plants, comprising, in combination, an elongated, hollow annular burner for powdered coal and an axially disposed oil burner in the annular burner and -spaced therefrom; said annular lburner comprising a double-walled tube closed at one end to form an openended annular chamber; combustive air-borne powdered coal supply means; pressurized oil supply means; taugen tial inlet means for powdered coal at the closed end of the annular burner, whereby a combustive air-borne stream of powdered coal is 4delivered to said annular chamber in a relatively flat helix; ow restrictor means in the said annular chamber, intermediate the ends thereof, whereby the vorticose combustive air-borne powdered coal stream is discharged, at reduced pressure, as a whirling spray about an axial oil llame; pressurized secondary air supply means coaxial with the burner; means for Adelivering said secondary air recti'linearly as a core stream through the burner an about the oil llame, and as a separate sheath stream about the whirling coal ame, whereby the sheath stream of secondary air envelopes the powde-red coal llame, and the coal flame is constricted to an axial cone.

References Cited in the le of this patent UNIT STATES PATENTS 1,369,602 Amsler Feb. 22, 1921 1,393,654 Wales Oct. 11, 1921 1,468,008 Dyson Sept. 18, 1923 1,535,886 Zulver Apr. 28, 1925 1,702,298 Hetsch Feb. 19, l929 1,708,496 Clendon Apr. 9, 1929 1,726,870 Trent Sept. 3, 1929 1,738,176 Dyer Dec. 3, 1929 1,738,199 Peabody Dec. 3, 1929 1,852,531- Kreutzberg Apr. 5, 1932 1,971,328 Byrne et al Aug. 28, 1934 v2,325,442 Vroom July 27, 1943 2,382,483 Holden Aug. 14, 1945 2,500,925 Bonvillian et al Mar. 21, 1950 2,601,390 Hague June 24, 1952 FOREIGN PATENTS 305,437 Great Britain Feb. 7, 1929 312,254 Great Britain May 23, 1929 323,578 Great Britain Jan. 9, 1930 OTHER REFERENCES Comparative Performance of Coals of Different Rank in a Film Cooled Gas-Turbine Combustor, T. E. Warren et al., Paper No. 52-SA-4, A. S. M. E.

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