US2777512A - Gas igniter for pulverized coal burners - Google Patents

Description

Jan. 15, 1957 2 Sheets-Sheet 1 Filed July 14, 1952 Ka li lNvENi'oRs ion e]! E Jb/mson BY George Musaz ATTORNEY Jan. 15, 1957 JOHNSON ETAL 2,777,512

GAS IGNITER FOR PULVERIZED COAL BURNERS Filed July 14. 1952 2 Sheets-Sheet 2 No 8, mm 5 w w R N 2 h R Q Q 0 ATTORNEY United States Patent GAS IGNITER FOR PULVERIZED COAL BURNERS Lowell E. Johnson, Alliance, Ohio, and George Musat, East Elmhurst, N. Y., assignors to The Babcock & Wllcox Company, New York, N. Y., a corporation of New Jersey Application July 14, 1952, Serial No. 298,674

7 Claims. (Cl. 158-115) This invention relates to igniters for fuel burners and,

more particularly, to a reliable, relatively simple, and easily serviced gas igniter particularly useful with pulverized coal burners.

In the burning of pulverized fuel, such as pulverized coal, or a mixture of air and the pulverized fuel is delivered to the furnace where it is admixed with additional, or secondary air, for complete combustion. Reliable means must be provided for insuring immediate ignition and maintenance of ignition of the pulverized fuel and air mixture directly after introduction into the furnace, particularly so that the furnace will not become filled with an unburned combustible and explosive mixture. Supplementary maintenance of ignition is of particular importance when the mixture of pulverized coal and air delivered to the furnace has a relatively high humidity or moisture content, which may make it difficult for the combustible mixture to maintain its own ignition up to the time when the furnace is heated to a relatively high operating temperature.

For this reason, various types of igniters are associated with pulverized fuel burners, utilizing such relative easily ignited fuels as oil and gas. The choice of fuel for the igniter is frequently dependent upon the availability of a particular fuel. Where large supplies of gas are easily available, for example, the igniters are generally of the gas burning type.

There are certain prerequisite characteristics necessary to provide a satisfactory igniter. Among other desirable characteristics, the igniter must be reliable in its ignition function, so that there is assurance of there being an ignition flame each time the igniter is turned on. The igniter flame must be large enough to ignite the stream of airborne pulverized coal or other fuel smoothly and the igniter flame must be completely stable. In addition, it is desirable that the igniter be capable of extended periods of operation, in order to maintain ignition of pulverized fuel and air mixtures of high humidity or moisture content when the furnace has not been heated to a high operating temperature, or when the furnace is operating at low load wherein loss of coal ignition is a distinct possibility. Finally, the igniter must be so constructed that it can be easily maintained and serviced without requiring the employment of specialized personnel.

Some of the foregoing requirements conflict with others, so that it is relatively diflicult to provide an igniter fully meeting all of these requirements. For example, a large flame for lighting the fuel requires a correspondingly high volume of gas supplied to the lighter. In turn, if the gas volume is relatively large compared to the available combustion air at the ignition zone of the lighter, it is diflicult to maintain the igniter flame burning stably. Correspondingly, if only the theoretically correct proportions of gas and air are supplied at the ignition zone of the igniter, then only a relatively small stable flame can be produced.

7 Such igniters are generally started by a spark between two ignition electrodes having their sparking ends adja- 2,777,512 Patented Jan. 15, 1957.

cent the zone where the gas is admixed with air; A high potential is applied to these electrodes, requiring a correspondingly good insulation of the electrodes. Frequently, due to the necessity of maintaining the sparking electrodes adjacent the burning gas flame, the insulation of the electrodes may be seriously deteriorated resulting in shorting of the electrodes. Attempts to avoid these difllculties have produced electrode assemblies so arranged relative to the issuing combustible mixture that it is difficult to remove, inspect, and/or repair the electrode assembly.

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In accordance with the present invention, a gas igniter is provided in which the aforementioned desirable characteristics are obtained while still providing for easy inspection and maintenance of the igniter and particularly the electrode assembly. To this end, the gas supply is introduced through a relatively elongated conduit having a metering orifice therein and arranged to deliver the gas into the outer end of an elongated flame retainer or shield having perforations for admission of combustible air to mix with the gas. The electrode assembly is arranged in parallel spaced relation with the gas supply conduit with the arcing ends of the electrodes thus offset laterally from the axis of the gas conduit. Due to this parallel arrangement of a relatively straight electrode assembly, the latter may be easily withdrawn through the outer end of the igniter assembly for inspection and repair. The electrode. assembly includes supportinginsulator means for the live electrodes which are shielded within a tubular member so that insulators are not only adequately supported but also protected from the gas flame.

A feature of the invention is that the supply of raw gas to the igniter flows through two branches, one branch being the aforementioned gas supply conduit. Upstream from the metering orifice in such conduit, a large diameter raw gas pipe is branched oif and arranged to extend through the flame retainer to the outer end of the latter,

considerably in advance of the end of the electrode assembly where the initial pilot flame is provided. By this arrangement, the relatively small pilot flame is stably maintained in a shielded position where it is protected from the inrush of air for the pulverized fuel burners. This relatively small pilot flame furnishes a continual source of ignition for the raw gas delivered from the furnace or inner end of the flame retainer. The combustion air adjacent the furnace end of the igniter supports combustion of the igniter raw gas to provide a long soft flame for maintaining ignition of the pulverized fuel. Should this long flame go out, it is immediately relighted from the constantly burning shielded pilot flame.

For an understanding of the invention principles, reference is made to the following description of a typical embodimentthereof as illustrated in the accompanying drawings. In the drawings:

Fig. l is a partial sectional view of a pulverized fuel fired furnace showing the invention igniter as arranged to extend between roof tubes of the furnace into igniting relation with a combustible mixture of pulverized fuel and air delivered between such roof tubes;

Fig. 2 is the longitudinal section View through a gas igniter embodying the invention;

Figs. 3 and 4 are elevation views, respectively of th outer and furnace ends of the igniter;

Fig. 5 is an axial sectional view through the gas conduit and its metering orifice, taken on the line 5-5 of Fig. 2; and

Fig. 6 is a diametric sectional view on the line 6-6 of Fig. 5, illustrating an interchangeable metering orifice member.

Referring first to Fig. 1 of the drawings, the igniter 10 of the invention is shown as arranged in operative relation in a pulverized fuel fired combustion chamber 11 having roof tubes 12. Igniter 10 is suitablysuppgrtedin the front casing 13 of the windbox 14.

Furnace or combustion chamber 11 is supplied with pulverized fuel and primary air by a burner arrangement comprising, in the usual case, a plurality of primary air and coal delivery nozzles extending through windbox .14 and between the roof tubes 12 lining the refractory roof 16 of chamber 11, secondary air being introduced into the furnace from Windbox 14 which is supplied with air under pressure in the usual manner. A typical pulverized fuel burner arrangement of this type is shown and described in U. S. Patent No. 2,397,793, issued to-L. L. Leach on April 2, 1946.

To simplify the present disclosure, only a single primary air and coal. delivery nozzle 15 is shown extending through windbox 14 and between the roof tubes 12 and into furnace 11,it being understood that more than one coal delivery nozzle 15 may be operatively associated with igniter 10.

In the particular arrangement shown, igniter 10 extends downwardly and inwardly into furnace 11 so that the flame delivered axially from the igniter will intersect the axis of nozzle 15. The igniter is in a separate compartment in the windbox provided by shielding housing members 17 and 18 which divide the igniter compartment 20 from the main part of windbox 14. Refractory bricks 19 close the space between nozzle 15 and member 18 to prevent direct impingement of the secondary air under pressure, from windbox 14, onto the ignition flame directed from the outer end of igniter 10 across the primary air and coal streams from nozzle 15. Housing member 17 has an aperture 21 therein by means of which the secondary air under pressure in windbox 14 flows into and through compartment 20 and thence into furnace or chamber 11, entering the latter between roof tubes 12. The secondary air flowing through compartment 20 supports combustion in the igniter. The usual studs are removed from roof tubes 12, throughout the portions thereof at the open end of compartment 20, to provide space for igniter 10 and for flow of secondary air into chamber 11.

Igniter 10 has its elements generally supported from a relatively large flat plate 24 bolted or otherwise secured to casing 13 and forming a sealing closure for an aperture 26 in the casing section, and through which the igniter is inserted into the compartment 20. A second plate 27 is secured to extend perpendicularly to plate 24 near the lower edge of the latter, this plate being very substantially narrower than plate 24, as best seen in Fig. 3. A third, or face, plate for the igniter is arranged to extend at an angle to both plates 24 and 27, being welded to the latter at its upper and lower edges. Triangular gussetsi28, welded to all three plates, enclose the space between plate 25 and plates 24 and 27. Face plate 25 has an upper relatively small circular aperture 31 therein through which is tightly fitted the main gas conduit 30. A substantially larger aperture 32, below aperture 31, serves for insertion and removal of the ignition electrode assembly generally indicated at 35.

The operating or outer end of the igniter is normally covered by a tightly-fltting enclosing housing 33 which slips over plate 27 and has a fairly close fit withgussets 28. The latter are tapped to receive studs 34 by means of which housing 33 is removably held in place. Theside walls of housing '33 have slots 36 fitting over. an elbow portion 37 of conduit-.30 and slots 39 receiving the studs 34. Access to the outer end of the electrode assembly 35 is attained by merely loosening studs 34 and then sliding cover 33 rearwardly.

Conduit extends substantially at right angles to plate25 into igniter compartment 20, and the inner-end of conduit 30 has a flange 38 welded thereto. Flange 138 is apcrtured to receive bolt and nut assemblies. 41, 41 by means of which flange 38 is secured to, a similar flange 42 on; aninner gas conduitsection 40. : Disposedbetween flanges 38 and 42, and each engaging a flange, are suitable h a resistantssslset .4 cash, ha in a Per p a s us with those of collars 38 and 42. Gaskets 43 serve to efiect a tight seal with a metering orifice member 45 arranged between the gaskets and having a peripheral contour identical with those of the collars and gaskets, as best seen in Figs. 5 and 6. Metering orifice member 45 is one of severalzinterchangeable metering plates, each having a different sized orifice46 therein by means of which therateof gas flow through conduits 30 and may be set at any desired value. To afford easy interchangeability of the meteringorifice members, each one thereof has a pair of open ended slots 47, 47 which slip over bolts 41. Thereby, the metering orifice members may be easily changed merely-'by loosening the bolt and nut assemblies and removing one member and replacing it with another member.

The inner end of conduit section 40 is threaded into a pipe coupling 48 having its other end closed by a threaded plug 51. drilled axially to provide a gas discharge passage 52. Coupling 48 fits within an aperture in a rectangular plate 50 serving as the outer wall of a flame retainer generally indicated at 55. In the particular embodiment shown in the. drawings, flame retainer is rectangular in cross section, being relatively narrow and high, as seen in Fig. 4, so asto fit readily between roof tubes 12. If necessary, the latter may be spread slightly to receive the flame retainer. The inner end of the flame retainer is beveled, as at 56, so that the plane of this end extends at only a slight angle to the axes of tubes 12 (Fig. l).

A second plate 57 is spaced somewhat inwardly from plate 50 and has an aperture 58 coaxial with a nozzle 60, secured to plate 57 and extending inwardly therefrom in axial alignment with gas conduit section 40. Between plates 50 and 57,.the sidewalls or retainer 55 are formed with relatively large apertures 61. Plate 57 is Welded at its lower edge to the bottom wall of retainer 55 and its upper edge is welded to an elongated plate 62 forming, with the upper wall and side walls of the retainer, a raw gas passage extending completely throughout the length of the retainer 55. Apertures 61 provide for air to flow into the mixing compartment 65 formed by plates 50, 57, 62 and the lower and side walls of flame retainer 55.

Intermediate the ends of conduit section 30, a raw gas conduit is joined thereto, as by welding, and has its inner end threaded into a reducer 71 having its smaller end welded into an aperture in plate 50. By this means, raw gas flows, without the restriction of a metering orifice, from conduit section 30 into the raw gas passage 72, branching from section 30, for discharge from the outer end of igniter 10.

Electrode assembly 35 includes a pipe section 74 having its outer end seated in an aperture in a flange 75 disengageably secured in air tight relation to plate 25 by wing nuts 73. The inner end of pipe 74 is threaded into a coupling 76 into which is threaded a second pipe section 77 threaded, at its inner end, into a coupling 78. A third pipesection 81 is threaded into the inner end of coupling 78, and the innermost end of pipe section 81 is cut away on a taper, as indicated at 82, to provide a projecting strip 83. Grounded electrode is in the form of a stud threaded into the outer end of section 83 and held in place by a lock nut 84. Pipe section 81 extends into the 'flame retainer 55 through an aperture 86 in plate 50.

The live electrode is substantially a rectilinear rod having its inner extremity disposed in adjacent spaced relation to electrode 80. Electrode 85 is mounted through a pair of insulators 87, 88 which are supported in rings 91 mounted respectively in the inner end of pipe section 74, both ends of, pipe section 77, and the outer end of pipe section 81. Between each pair of supporting rings, packt ing 92 is disposed around the insulators 87 and 88. Where electrode 85 emerges from, insulator 88,.apair-of short pieces of steel 93," 93 are welded to theelectrode and act as a locating means for the electrode in the insulators. The outer end of electrode 85 is threaded to receive nuts 94 positioning a washer 96 engaging a spring 97 coiled about the electrode and seated against a washer 98 on the outer end of insulator 87. High tension current is supplied to electrode 85 by a conductor 95 having a terminal secured to the electrode by a nut 99. The spring 97 permits relative expansionot electrode 85 without injury to insulators 87 and 88, while still maintaining the electrode assembly in its operating relationship.

Aperture 32 in plate 25 is somewhat larger than couplings 75 and 78. Thereby, the electrode assembly may be readily withdrawn for inspection and repair by removing nuts '73, after cover 33-has been removed, and simply drawing assembly 35 outwardly through aperture 32. The use of the rectilinear electrode 85 enables relatively easy and simple seating of the spark gap between the inner end of this electrode and electrode 80 without the complications involved where bent electrodes are used. It will be noted that the electrode assembly is in parallel spaced relation with the gas supply conduits 30 and 40, and discharge nozzle 60, the spark gap being located somewhat in advance of the discharge nozzle and at the optimum location for ignition of the gas mixture.

In operation, the size of orifice 46 is so selected that the gas-air mixture discharged from nozzle 60 is at the proper ratio for ready ignition by the spark from the electrodes. This relatively small, or pilot flame, is readily ignited and readily maintained, being protected from the rush of air through compartment 20 by the perforated flame retainer 55. The pilot flame is sufiiciently long, however, to maintain ignition of the relatively larger vol ume of raw gas discharged from raw gas nozzle 72 at the outer end of flame retainer 55. The burning raw gas, which is kept constantly ignited by the pilot flame within the fiame retainer, forms a long flame which is fully adequate to reliably ignite the pulverized fuel and primary air mixture discharged from nozzles 15, and to maintain this ignition even though the fuel-air mixture may have a relatively high humidity or moisture content, or the pulverized fuel burners may be operating at a greatly reduced load.

Due to the setting of the sparking end of the electrode assembly intermediate the length of flame retainer 55, the hot gases of combustion of the flame issuing from nozzle 60 recirculate around the end of the electrode assembly. This heated gas at the ignition point makes it relatively easy to maintain ignition. However, the inner end of the electrode assembly is set far enough back from the exit end of the flame retainer that the electrodes are protected from any slag being deposited thereon from the burning fuel in the combustion chamber or furnace 11.

While a specific embodiment of the invention has been shown and described in detail to illustrate the application of the invention principles, it will be understood that the invention may be embodied otherwise without departing from such principles.

What is claimedis:

l. A gas igniter constructed and arranged for mounting in operative relation to furnace main fuel burners, said igniter comprising a tubular flame retainer having an outer end and a discharge end; means, including walls of said retainer and an elongated partition therein, forming a raw gas passage extending longitudinally through said retainer; a gas supply conduit extending into said retainer through the outer end thereof in juxtaposition with said passage, with its gas discharge axis in spaced substantially parallel relation to that of said passage; mixing means communicating with the discharge end of said conduit and arranged to admix air with the gas discharged therefrom, and including a nozzle having its discharge axis in spaced substantially parallel relation to that of said passage and its discharge end substantially upstream of the discharge end of said retainer; tubular shielding means extending through the outer end of said retainer in substantially parallel juxtaposed relation to said supply conduit; a spark-creating electrode assembly including a relatively elongated substantially rectilinear electrode removably supported in insulated relation through said shielding means to extend in substantially parallel spaced relation to said supply conduit, said shielding means constituting a cooperating electrode; the sparking end of said electrode assembly being longitudinally intermediate the discharge ends of said nozzle and said retainer; and a raw gas conduit connected to said raw gas passage.

2. A gas igniter constructed and arranged for mounting in operative relation to furnace main fuel burners, said igniter comprising a tubular flame retainer having an outer end and a discharge end; means, including walls of said retainer and an elongated partition therein, forming a raw gas passage extending longitudinally through said retainer; a gas supply conduit extending into said retainer through the outer end thereof in juxtaposition with said passage, with its gas discharge axis in spaced substantially parallel relation to that of said passage; 'mixing means communicating with the discharge end of said conduit and arranged to admix air with the gas discharged therefrom, and including a nozzle having its discharge axis in spaced substantially parallel relation to that of said passage and its discharge end substantially upstream of the discharge end of said retainer; tubular shielding means extending through the outer end of said retainer in substantially parallel juxtaposed relation to said supply conduit; a spark-creating electrode assembly including a relatively elongated substantially rectilinear electrode removably supported in insulated relation through said shielding means to extend in substantially parallel spaced relation to said supply conduit, said shielding means constituting a cooperating electrode; the sparking end of said electrode assembly being longitudinally intermediate the discharge ends of said nozzle and said retainer; and a raw gas conduit branching from said supply conduit upstream of the discharge end thereof and connected to said raw gas passage.

3. A gas igniter constructed and arranged for mounting in operative relation to furnace main fuel burners, said igniter comprising a tubular flame retainer having an outer end and a discharge end; means, including walls of said retainer and an elongated partition therein, forming a raw gas passage extending longitudinally through said retainer; a gas supply conduit extending into said retainer through the outer end thereof in juxtaposition with said passage, with its gas discharge axis in spaced substantially parallel relation to that of said passage; mixing means communicating the discharge end of said conduit and arranged to admix air with the gas discharged therefrom, and including a nozzle having its discharge axis in spaced substantially parallel relation to that of said passage and its discharge end substantially upstream of the discharge end of said retainer; tubular shielding means extending through the outer end of said retainer in substantially parallel juxtaposed relation to said supply conduit; a spark-creating electrode assembly including a relatively elongated substantially rectilinear electrode removably supported in insulated relation through said shielding means to extend in substantially parallel spaced relation to said supply conduit, said shielding means constituting a cooperating electrode; the sparking end of said electrode assembly being longitudinally intermediate the discharge ends of said nozzle and said retainer; flow restricting orifice means in said supply conduit upstream of said mixing means; and a raw gas conduit branching from said supply conduit upstream of said flow restricting orifice means and connected to said raw gas passage.

4. A gas igniter as claimed in claim 1 in which said flow restricting orifice means comprises an orifice plate interchangeably mounted between disengageably coupled sections of said supply conduit.

5. A gas igniter as claimed in claim 1 in which the walls of said flame retainer are formed with air admitting apertures including at least one relatively large aperture Substantially adjacent said mixing means.

6. A gas igniter constructed and arranged for mounting in operative relation to furnace main fuel burners, said igniter comprising raw gasconduit means, a supply conduit, and tubular shielding means mounted in substantially parallel juxtaposed relation; a relatively elongated tubular flame retainer assembled with and embracing said conduit means, conduit, and shielding means; mixing means mounted Within said flame retainer downstream of the discharge end of said conduit to admix air with gas discharged from said conduit, and including a discharge nozzle mounted laterallyadjacent said raw gas conduit means and with its axis substantially parallel to the axis thereof, the discharge end of said nozzle being upstream of the discharge end of said conduit means to discharge the mixture in substantially parallel spaced relation to said raw gas conduit means and upstream of the discharge end of the latter; and a sparkcreating electrode assembly including a relatively elongated substantially rectilinear electrode removably supported in'insulated relation through said shielding means to extend in substantially parallel spaced relation to said supply conduit, said shielding means constituting a cooperating 'electrode; thesparking end of said electrode assembly being longitudinally intermediate the discharge ends of said nozzle and said raw gas conduit means.

7. A gas igniter constructed and arranged for mounting in operative relation to furnace main fuel burners, said igniter comprising raw gas conduit means, a supply conduit, and tubular shielding means mounted in substantially parallel juxtaposed relation with said conduit laterally intermediate said conduit means and said shielding means; a tubular flame retainer assembled with and embracing said conduit means, conduit, and shielding means, the discharge end of said conduit being within said flame retainer; mixing means mounted Within said flame retainer downstream of the discharge end of said conduit toadmix air with'gas discharged from said conduit, and including a discharge nozzle mounted laterally adjacent said ravv gas conduit means and with its axis substantially parallel to theaxis thereof, the discharge end of said no'zzle'being upstream of the discharge end of said conduitmdns to discharge the mixture in substantially parallel spaced relation to said raw gas conduit means and upstream Qfthedischarge end of the latter; and a sparkcreatingelectrode assembly including a relatively elongated substantially rectilinear electrode removably supported in insulated relation through said shielding means to extend in substantially parallel spaced relation to said supply conduit, said shielding means constituting a cooperating electrode; the sparking end of said electrode assembly being longitudinally intermediate the discharge ends of said nozzle and said raw gas conduit means.

References Cited in the file of this patent UNITED STATES PATENTS 1,735,629 Braden Nov. 12, 1929 1,841,463 Barber et a1. Jan. 19, 1932 1,948,663 Irwin Feb. 27, 1934 2,102,588 Francis Dec. 21, 1937 2,263,170 Haedike Nov. 18, 1941 2,319,351 Shipley et a1. May 18, 1943 2,332,210 Frank Oct. 19, 1943 2,397,793 Leach Apr. 2, 1946 2,402,763 Longini June 25 1946 2,417,981 Graham Mar. 25, 1947 2,480,230 Elster Aug. 30, 1949 FOREIGN PATENTS 526,349 France Oct. 6, 1921 869,141 France Oct. 29, 1941 610,672 GreatBritain Oct. 19, 1948

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