US3007084A

US3007084A - Ignition means

Info

Publication number: US3007084A
Application number: US783650A
Authority: US
Inventors: Harvey A Thomasian; Roy E Baharian
Original assignee: Individual
Current assignee: Individual
Priority date: 1958-12-24
Filing date: 1958-12-24
Publication date: 1961-10-31
Anticipated expiration: 1978-10-31

Description

Original Filed June 8, 1954 Oct. 31, 1961 H. A. THOMASIAN ETAL 3,007,084

IGNITION MEANS 3 Sheets-Sheet 1 INVENTORJ HARVEY H. 771'OM/4S/fiN For E. BAHn/Pm/v Mm V ATTORNEY Oct. 31, 1961 H. A. THOMASIAN ETAL 3,007,084

IGNITION MEANS Original Filed June 8, 1954 3 Sheets-Sheet 2 Fig.7

- INVENTORS HARVEY 4. THOMAS/AN Roy E. BnHAR/mv ATTORNEY Oct. 31, 1961 H. A. THOMASIAN ETAL 3,007,084

IGNITION MEANS Original Filed June 8, 1954 3 Sheets-Sheet 3 I'll/ll 1111/1 11 INVENTORS HARVEY H. 77-IOMfl5/19N Roy E. BAHHR/fl/V 'BYMWIJQBZJ ATTORNEY United States Patent Riley This invention relates to ignition means and more particularly to apparatus for igniting fuels electrically. This application is a continuation of patent application Serial Number 435,142, filed June 8, 1954, now abandoned.

In the burning of fuel and particularly of pulverized coal, it is common practice to provide a smaller flame or pilot which burns continuously and which uses a fuel which is less likely to blow out. It is necessary to provide some means for igniting the pilot in turn and for maintaining it in lighted condition at all times. At the present time it is usual practice to use an ignitable gas as pilot fuel and to use an electric spark asan ignition means. However, in the past it has been found that when a sufiicient voltage is used to produce a sizable spark, the electrodes soon wear out. This is particularly true when, as is usually the case, it is desirable to initiate the spark at frequent intervals to make certain that the pilot is always lighted. The burning of the electrodes brings about a period of unstable ignition until the condition of the electrodes is discovered and then it means a shutdown of the burner until replacement of the electrodes can be made. This is a very undesirable condition and it is the purpose of the present invention to obviate these difficulties of the prior art.

It is therefore an outstanding object of the present invention to provide an ignition means having extremely long electrode life.

It is still another object of this invention to provide an ignition means providing a spark which apparently moves or travels from one part of the electrode to another.

Another object of the instant invention is the provision of an ignition means having a novel electrode construction in which localized burning is obviated.

A further object of the invention is the provision of an ignition means or such a construction that a longer and more positive spark at more frequent intervals is permitted.

With these and other objects in view as will be ap parent to those skilled in the art, the invention resides in the combination of parts set forth in the specification and covered by the claims appended hereto.

The character of the invention, however, may be best understood with reference to certain of its structural forms as illustrated by the accompanying drawings in which:

FIG. 1 is a vertical sectional view of a burner making use of the principles of the present invention,

FIG. 2 is a perspective view of a portion of an ignition means used in the apparatus shown in FIG. 1,

FIG. 3 is a vertical sectional view of a portion of the invention taken on the line III-III of FIG. 4,

FIG. 4 is an end view of the invention,

FIG. 5 is a view taken on the line V-C of FIG. 4,

. FIG. 6 is an end view of another embodiment of the invention,

FIG. 7 is a sectional view of the invention taken on the line VIIVII of FIG. 6,

FIG. 8 is a sectional View of still another embodiment of the invention taken on the line VIII--VIII of FIG. 10,

FIG. 9 is an external View of the invention taken on the line IX--IX of FIG. 10, and

3,007,084 Patented Oct. 31, 1961 FIG. 10 is a sectional view of the invention taken on the line X--X of FIG. 9.

Like reference characters denote similar parts in the several figures of the drawings.

Referring first to FIG. 1, wherein are best shown the general features of the invention, the ignition means of the invention, indicated generally by the reference numeral 10, is shown in use with a pilot burner 11 and a pulverized coal burner 12. The ignition means, the pilot, and the burner are mounted in generally coaxial relationship before the opening 13 in a refractory furnace wall 14. This furnace wall may be a part of a steam generating unit. The burner 12 is provided with a secondary air chamber 15, the flow of air to which is controlled by means of vanes 16. A main burner tube 17 is located coaxially of the opening 13. Secondary air vanes 18 are mounted around the burner tube 17. At the outer end of the burner tube 17 is mounted a coal receiving housing adapted to be attached to a source of pulverized coal and primary air. Coal distributing vanes 20 are provided surrounding the pilot 11 which extends through the burner tube and through the coal receiving housing 19. The pilot burner 11 is mounted within a tubular housing 21 whose forward end is threaded into a sleeve integral with a coal spreader 22 mounted in the forward portion of the burner tube 17. The pilot burner 11 is held ooaxially within the tube 21 by means of set screws 23 at the forward end and a collar 24 at the rearward end. The pilot 11 consists of an elongated tube 25 which extends through the burner and is coaxial therewith and is attached at its rear end through a coupling 26 to a T fitting 27 and a spark plug 28. The fitting 27 is connected through a conduit 29 to a source of ignitable gas, not shown. The tube 25 is connected to one side of the secondary 30 of a transformer 31. The other side of the secondary is connected to the spark plug 28. The primary 32 of the transformer is connected to a source of alternating current 33. In general practice the source 33 will give electrical current having a voltage of volts at a frequency of 60 cycles per second. The transformer 31 is so constructed that the voltage across the secondary will be in the order of 10,000 volts.

Referring next to FIG. 2 wherein is shown the forward end of the tubular portion 25 of the pilot 11, it can be seen that it is provided with a coaxial cylindrical electrode 34 which in turn is surrounded at the inner extremity of the tube by rectangular fin-line electrodes 35. In FIG. 3 it can be seen that the electrode 34 is held fixed in its coaxial position within the tube 25 by means of mounting elements 36 of insulating material. In the preferred embodiment they are ceramic disks having a circular aperture in the center for holding electrode 34. These disks are also provided with apertures arranged in a circle around the center aperture, these apertures functioning to control the flow of the gas-air mixture and to promote thorough mixing. In this event it can be seen also that the electrodes 35 have inner edges 37 which are exactly parallel with the centerline of the electrode 34 and that the electrodes 35 are coextensive with the electrode 34 for a considerable distance. In FIG. 4 it can be seen that the electrodes 35 are four in number and that they are spaced equidistantly around the electrode 34. In FIGS. 2 and 5 are particularly shown slots 38. The slots 38 are two in number and are located directly opposite each other in the tube 25. They extend back from the forward edge of the tube 25 a distance slightly greater than the length of the electrodes 35.

The operation of the apparatus will now be understood in view of the above description. Pulverized coal carried in suspension by primary air enters the coal receiving housing 19 and the coal air mixture is giving a circular motion within the housing by means of the vanes 20. It then enters the burner tube 17 while revolving about the axis of the pilot 11. Since this motion tends to cause the coal stream to travel in a Zone adjacent to the inner surface of the tube 17, the vanes 20 are also arranged to divert the stream toward the center" and evenly distribute it through the pipe. Coal and primary air then passes through the coal spreader 22 which breaks the coal stream into alternate layers of rich and lean mixtures. The rich mixtures ignite practically instantaneously and act as kindling to the remainder of the mixture. The vanes of the coal spreader 22 also divert the air coal mixture into a conical shape or flare. Secondary air supplied under pressure passes through the dampers 16 which control the quantity of air and in passing between the vanes 18 is giving a whirling motion. The intensity of whirl is determined by the angularity of the vanes. In most cases the direction of rotation of the secondary air is the same as that of the primary air and coal, but the design is such as to permit opposite rotation if this is desirable. Mixing of secondary air and primary air and coal occurs beyond the burner tube 17 and after ignition has taken place. The coal stream issuing from the burner in the form of a flare is violently whipped by the stream of secondary air assuring intimate mixturing of the air and coal. The angularity or flare of the flame is adjusted by advancing or retarding the coal spreader 22 with relation to the burner tube 17 and by the angularity of the secondary vanes 18. Now it is difficult to maintain this coal and air mixture in its burning condition. Various transient factors and unexpected happenings may cause the flame to go out suddenly. In order to maintain the flame, gas is introduced through the conduit 29, the fitting 27, and the tubular portion 25 of the ignition means 11. The gas passes through the tube 25, through the apertures in the mounting elements 36, between the

electrodes

34 and 35, and outwardly into the opening 13 in the furnace wall 14. As long as this gas remains lighted, the coal and air mixture will also remain lighted. For that purpose it is desirable to maintain a spark in the flow of gas to insure that this gas continues to burn. As. has been described above, the secondary of the transformer 31 is connected on one side through the spark plug 28 to the electrode 34, while the other side is connected through the wall of the tubular portion 25- to the electrodes 35. A short circuit from the electrodes 35 to the electrode 34 is prevented by the mounting elements 36. Since the frequency of the alternating current on the secondary 30 of the transformer 31 is approximately 60 cycles per second, a spark will attempt to pass from the electrode 34 to the electrodes 35 once every one hundredand-twentieth of a second. The voltage tending to make this spark take place is 10,000 volts. It is the characteristic of the present invention that the spark may take place between the electrode 34 and any one of the four electrodes 35. Furthermore it is characteristic that the spark may take place at any point on these electrodes, although, of necessity, the spark will pass between points on the electrode 34 and on the electrode 35 which are a minimum distance apart. The particular points between which the spark will take place is determined by many factors. It is the feeling of the present applicant that the selection of this point is not merely related to probability, but that he condition of the electrode surfaces and the condition of the gas passing therebetween determine to a great extent the position of the spark. In practice the successive sparks which pass between the electrodes take place in successive positions so that the spark appears to move or travel lengthwise of the axis of the pilot 11. Although the theory of this movement is not clearly understood, there is reason to believe that the initial spark ionizes the gas existing between the electrode surfaces at that particular time and that as this small body of ionized gas moves between the electrodes, the ignition takes place always through this body of gas, since it provides a path of least resistance for the spark. Since the gas is moving due to the velocity of flow through the tube 25, it might be supposed that this small body of ionized gas is blown along between the electrode surfaces until it reaches a point at which it is projected out into the air outside of the electrodes at which time the spark will seek another spot at which to take place. At any rate, due to the continuous moving or traveling of the spark, a given point on an electrode will be used as a sparking point at very infrequent intervals and, therefore, the electrodes do not have a tendency to pit, burn, or corrode. The result is that the electrodes may be left in operation at high voltages with high frequency of sparking and continuous operation without difliculty with maintenance or breakdown. Furthermore, the gas and air are thoroughly mixed by passage through the apertures in the mounting elements 36, so that the likelihood of the pilot flame going out is considerably decreased.

Referring next to FIG. 6 wherein is shown another pilot burner 51 making use of the philosophy of the present invention, one electrode is provided by the tube 52 of the burner, while the other electrode 53 is dish-shaped with the concave side facing inwardly of the tube 52. The electrode 53 is held on the end of a shaft 54 which in turn is mounted in a tube 55 held coaxially of the tube 52 by means of perforated disks 56. The operation of this version of the invention is very similar to that de scribed above. Ignitable gas and air pass along the tube through the perforations in the disks 56 where they are thoroughly mixed and pass outwardly through the gap between the disk 53 and the end of the tube 52. The tube 52 is connected to one side of the secondary of a transformer, while the disk 53 is connected through the shaft 54 to the other side ofthe secondary of a transformer and the spark appears between the two

electrodes

52 and 53. As in the preferred embodiment of the invention, the spark may take place between any two points around the electrodes, although the apparent effeet is that the spark travels around the periphery of the electrode 53..

FIG. 8 shows still another version of the invention in which the pilot flame has directional properties at right angles to the axis of the burner. The pilot burner 61 consists of a tubular electrode 62, the outer end of which is closed by an end member 63. A slot 64 is provided in the surface of the tube 62 and extends part way around the periphery thereof at a right angle to the axis thereof. In this slot resides an electrode 65 of plate-like configuration having a shape best shown in FIG. 10. The electrode 65 has an edge 66 which is coextensive with the surface of the tube 62. The electrode fans inwardly from the edge 66 to a central portion 67 through which is fastened a shaft 68. The shaft 68 is mounted centrally ofa supporting tube 69 which is held in turn by set screws 70 and ceramic disks 71. Each disk is apertured or notched to regulate the flow of gas and air and to promote through mixing thereof. The tube 69 is made of ceramic material and is formed in sections which are joined by intermediate sleeves 72 in a well-known manner. The shaft 68 is held centrally of the tube 69 by means of a conical washer 73 and a nut 74 which is mounted on the threaded outer end of the shaft 68. The operation of this embodiment of the invention is very similar to that of the other versions. The gas and air pass along the tube 62 through notches in the mounting disks 71 and outwardly through the slot 64 between the edges of the slot and the electrode 65, the disks causing through mixing of the gas and air. The electrode 65 is connected through the shaft 68 to one side of the secondary of a transformer, while the tube 62 is connected to the other side of that secondary. Successive sparks passing between the edge of the slot 64 and the electrode 65 take place in various positions and the appearance of the action is that of a continuously moving spark between the two electrodes. It can be seen that in this case the flame will be projected to one side only of the burner and this particular construction may be used when it is desirable that the flame should not impinge on certain parts of the main puiverized-coal burner.

It can be seen then that the above-described ignition means is such that electrical current of high voltage and high frequency may be maintained continuously in the pilot burner associated with a pulverized coal burner without deterioration of the electrode surfaces and without interruption of service. Furthermore, the use of apertured mounting disks combines a novel means of mounting the electrode with a beneficial regulation and mixing of the gas and air.

it is obvious that minor changes may be made in the form and construction of the invention without departing from the material spirit thereof. It is not, however, desired to confine the invention to the exact form herein shown and described, but it is desired to include all such as properly come within the scope claimed.

The above invention having been thus described, what is claimed as new and desired to secure by Letters Patent is:

1. An ignition means for use with an ignitable gas comprising a tubular portion, a first electrode having an elongated, thin edge, a second electrode having a broad surface coextensive with the edge of the first electrode, the edge of the first electrode being fixed in a position parallel to the surface of the second electrode, the two electrodes being situated so that the ignitable gas passes therebetween, the electrodes being connected across a high-voltage, alternating electrical source, one of the electrodes consisting at least partly of a long rod, mounting disks formed of insulating material arranged along the tubular portion and holding the said rod coaxially thereof, each disk having apertures passing therethrough.

2. An ignition means for use with an ignitable gas comprising an elongated tube having integral therewith a series of elongated plates extending radially inwardly thereof and having thin edges consituting first electrodes, a second electrode having a cylindrical surface coextensive with the edges of the first electrodes and coaxial of the tube, the edges of the first electrodes being fixed in positions parallel to the axis of the second electrode and slightly spaced from the surface thereof, the ignitable gas passing through the tube and between the two electrodes, the electrodes being connected across a highvoltage, alternating electrical source, the second electrode 'being mounted in insulating mounting members fitted into the tube, each mounting member consisting of an apertured ceramic disk.

3. An ignition means for use with an ignitable gas comprising an elongated tube having a thin end edge constituting a first electrode, a second electrode in the form of a circular spherical segment having a portion of its surface coextensive with the edge of the first electrode, the edge of the first electrode being fixed in a position slightly spaced from the surface of the second electrode, the ignitable gas passing through the tube and between the two electrodes, the electrodes being connected across a high-voltage, alternating electrical source, the second electrode being mounted at the end of an elongated shaft which is mounted coaxially of the tube and is insulated therefrom, mounting disks formed of insulating material arranged along the tube and supporting the said shaft, each dish having apertures extending therethrough.

4. An ignition means for use with an ignitable gas comprising an elongated tube having a slot therein presenting a thin edge constituting a first electrode, a second electrode in the form of a circular segmental plate having a portion of its surface coextensive with the edge of the first electrode, the edge of the first electrode being fixed in a position slightly spaced from the surface of the second electrode, the ignitable gas passing through the tube and between the two electrodes, the electrodes be ing connected across a high-voltage, alternating electrical source, the second electrode being mounted at the end of an elongated shaft which is mounted coaxially of the tube and is insulated therefrom, mounting disks formed of insulating material arranged along the tube and supporting the said shaft, each disk having apertures extending therethrough.

References Cited in the file of this patent UNiTED STATES PATENTS 1,614,692 Schroeder Ian. 18, 1927 1 ,724,400 Fogarty Aug. 13, 1929 2,013,979 Bray Sept. 10, 1935 2,129,472 Lysholm Sept. 6, 1938 2,395,614 Csepely Feb. 26, 1946 2,412,655 Shannon Dec. 17, 1946 2,655,209 Newton Oct. 13, 1953 2,725,718 Sheets Dec. 6, 1955