US3304988A

US3304988A - Ignitor

Info

Publication number: US3304988A
Application number: US493477A
Authority: US
Inventors: John M Rackley
Original assignee: Babcock and Wilcox Co
Current assignee: Babcock and Wilcox Co
Priority date: 1965-10-06
Filing date: 1965-10-06
Publication date: 1967-02-21
Anticipated expiration: 1984-02-21

Description

Feb. 21, 1967 J- M. RACKLEY IGNITOR Filed Oct. 6, 1965 FIG.4

INVENTOR. John M. Rackley ATTORNEY United States Patent IGNITOR John M. Rackley, Alliance, Ohio, assignor to The Babcock & Wilcox Company, New York, N.Y., a corpora This invention relates generally to ignitors for fuel burners and more particularly to an improved electricallyignited, gas-fired ignitor.

It is common practice in the design of fuel burning equipment to provide ignitors for initiating combustion of the fuel discharged from main fuel burners. Generally, these ignitors are used only intermittently for short periods, i.e. during start up, and for stabilizing flame conditions during low load and upset conditions. They are not needed and hence do not function during normal operation. Nevertheless, it is essential for safe operation that the ignitors operate effectively when needed, since it is during thse periods of abnormality that most serious explosions occur. Thus it can be appreciated that an ignitor must be capable of reliable performance under extremely adverse and variable conditions to insure safe operation.

- US. Patent 2,806,518 discloses a gas-fired ignitor which has been proven to be reliable at capacitiesup to 3 million B.t.u.s per hour under actual commercial operating conditions. Moreover, the compact arrangement of this ignitor has been recognized as being advantageous in alleviating the crowded burner front conditions which normally characterize common windbox, multiple burner installations. With the evolution of larger burners and fuel burning systems wherein space conditions make desirable the use of a single ignitor to ignite two adjacent burners, it has been found that higher ignitor capacity is required Furthermore, it is desirable from the standpoint of accessibility and ease ,of servicing that the high capacity ignitor be as small as possible to avoid crowding of equipment at the burner front.

It is therefore an object of the present invention to tions. It is a further object that this ignitor have a fuel firing capacity greater than has heretofore been commonly used. It is a still further object that this improved ignitor be compact so that it requires substantially no more installation space than lower capacity ignitors heretofore known in the art.

These and other objects are attained according to the present invention in a gas-fired ignitor constructed and arranged for mounting in flame propogating relation to an associated main fuel burner. The ignitor includes a tubular ignitor head divided by a longitudinally extending partition into a pilot ignition chamber and a by-pass passage. A pair of electrodes, one of which is connected with a suitable high voltage transformer, are arranged within the pilot chamber to form a spark gap across which a high energy electrical discharge is created to initiate combustion. A fuel gas supply conduit having an open discharge end is rigidly connected with the ignitor head. The leading edge of the partition is arranged relative to the discharge end of the gas supply conduit so as to divide the incoming gas stream into predetermined fixed proportions for parallel flow into the pilot chamber and through the by-pass passage. The leading edge of the partition has a curved portion arranged to splay incoming gaseous fuel throughout the pilot ignition chamber.

For a better understanding of the invention, its operating advantages and specific objects attained by its use, reference should be had to the accompanying drawings ice in which FIG. 1 is a partially sectioned longitudinal side view of an ignitor according to the present invention; FIG. 2 is an end view of the ignitor taken along line 22 of FIG. 1; FIG. 3 is an end view of the ignitor taken along line 33 of FIG. 1; and FIG. 4 is an enlarged section view of a portion of the ignitor head.

Referring to the drawings, the ignitor 10 is mounted within an elongated aperture tube 11 which extends through a circular opening formed in a furnace casing 12. It should be recognized that the casing 12 may delimit, for example, a pressurized windbox or furnace chamber; moreover, it should be recognized that the ignitor 10 is arranged in flame propagating relationship to one or more main fuel burners (not shown).

An ignitor housing 15 fits within the outer end of the aperture tube 11 andincludes an outer rectangular flange portion 15A which extends beyond the periphery of the tube 11. A gasket 16 is interposed between the flange portion 15A and the end of the tube 11, a seal between these members being effected by drawing the flange portion 15A toward the casing 12 by means of four bolt attachments 17.

. ward end of the electrode tube 22 connects with a mounting plate 23 which is formed with a handle 24. A guard member 27, formed of electrically non-conductive material is attached to the mounting plate 23, both the plate 23 and guard 27 being held in place by a pair of wing nuts 25 which engage a pair of studs extending rearwardly from the housing 15. A high voltage lead 31 (connected with a suitable high voltage source such as a transformer) is electrically connected with a spring 26 on the inside of the guard member 27. The spring 26 is arranged to connect the end of an electrode rod 28A that extends axially along the length of the access tube 21 and terminates within the ignitor head 50. The rod 28A is suitably positioned by means of a pair of

insulators

29A and 29B. Attached to the inner end of the electrode tube 22 is a second (ground) electrode rod 28B which extends into the ignitor head parallel to the electrode rod 28A and has formed on its end a right angle bend which terminates adjacent the end of the electrode 28A to form a spark gap.

The above-described electrode assembly is substantially similar to that shown in FIG. 7 of the aforementioned US. Patent 2,806,518, and reference should be made to that patent for details concerning assembly and operation. It should be recognized, however, that an electrical discharge can be created across the spark gap, which discharge has suflicient energy to ignite a mixture of gaseous fuel and air.

Formed as a part of the housing 15 is a threaded connection 38 to which may be attached a suitable supply of high pressure fluid, such as compressed air. The connection 38 communicates with a chamber 37 which extends around the electrode access tube 21. A plurality of apertures 39 are formed in.the access tube 21 and arranged to direct streams of air forwardlyand toward in detail in the aforementioned US. Patent 2,806,518, thecompressed air supplied to the connection 38 may also be used to cool and clean the

insulators

29A and 29B, and then blow soot accumulations from the electrodes 3 28A and 28B by means of dust blower nozzle 40, the end of which is arranged to discharge jets of air into the ignitor head 50 (see FIG. 2).

A gas supply pipe or conduit 35 is secured to and extends through the housing 15. Threadably connected with the outer end of the gas pipe 35 is a valve member 36 of the type employing an adjustable orifice whereby the gas flow to the gas pipe 35 may be preset. It should be understood that the valve member 36 is suitably connected with a source of pressurized gaseous fuel (not shown). The inner or discharge end of the gas pipe 35 is welded to the ignitor head 50.

Since the gas pipe 35 is cooled by the fluid flowing therethrough, while the ignitor access tube 21 is relatively uncooled, only the gas pipe is rigidly connected with the head 50, the tube 21 being arranged to move relative to the head 50 so as to accommodate differential thermal expansion. A spacer block 41, welded only to the access tube 21, is used to maintain the proper alignment between the gas pipe 35 and access tube 21.

The ignitor head 50 is an alloy casting of generally oval outer cross-section. A longitudinally extending curved partition 51 integrally cast with the tubular outer wall, divides the head into an upper pilot ignition chamber 52 and a relatively small lower gas by-pass passage 53. The discharge end of the pilot ignition zone is open except for the three inwardly projecting flame retainer studs 54 which serve to disrupt the flow of gases to thereby create eddy currents wherein ignition can be readily stabilized. An integrally cast backplate 55 (see FIG. 2) partially closes the rearward end of the head 50, the outline of the backplate opening being shaped to partially embrace the circular ends of the ignitor access tube 21, the gas supply pipe 35 and the dust blower 40. An additional contoured portion 56 is provided in the opening, through which a flame rod detector element (not shown) may be extended if desired.

It should be noted that the leading edge of the partition 51 is arranged immediately adjacent the open discharge end of the gas supply pipe 35. Thus it can be seen that the partition 51 serves to split the fuel gas stream issuing from the pipe 35 so that a major portion by-passes the pilot chamber 52 via passage 53, while a minor portion passes into the pilot ignition chamber 52. Particularly referring to FIG. 4, the leading edge of the partition 51 is formed with a sharp lower corner 51A and a rounded upper surface 51B. The rounded surface 51B causes the gas impinging thereon to be splayed upwardly into the pilot ignition chamber 52 while the sharp lower corner 51A allows the gas flowing under the partition 51 to pass relatively undisturbed into and through the by-pass passage 53. The laterally arcuate form of the partition 51 (see FIG. 2) further tends to distribute the gas throughout the pilot chamber 52.

In operation, the valve member 36 is preadjusted to admit a quantity of gas equal to the desired total capacity of the ignitor into the supply pipe 35. Simultaneously, with the admission of gas, a spark is created in the pilot ignition chamber 52. A minor portion of the gas is splayed throughout the pilot ignition chamber 52 and mingles with the air admitted through the opening in the backplate 55 to form a readily ignitable mixture. The major unignited portion of the gas by-passes the pilot chamber 52 via passage 53 and is burned at the discharge from the head 50 as it contacts and mixes with the burning eflluent from the pilot chamber 52.

What is claimed is:

1. A gas-fired ignitor including a tubular ignitor head enclosing a longitudinally extending pilot ignition chamber having an open discharge end, means for effecting an electrical spark within said pilot ignition chamber, a gas supply conduit having an open discharge end communicating with said pilot ignition chamber and having its axis offset to one side of the axis of said ignition chamber, means for by-passing a portion of the fuel issuing from said conduits around said pilot ignition chamber, and means for splaying the remaining portion of the gaseous fuel issuing from said conduit throughout said pilot ignition chamber including a distribution element having a deflecting surface positioned at said one side of the pilot ignition chamber directly in the path of gas outflow from said conduit.

2. A gas-fired ignitor including a tubular ignitor head having an inlet end and an open distal end, a longitudinally extending partition having its edges connected with the inner wall of said tubular ignitor head and dividing the interior of said head into a pilot ignition chamber and a gas by-pass passage, means for effecting an electrical spark in said pilot ignition chamber, and a gas supply conduit having an open discharge end communicating with the interior of said ignitor head, said partition having a leading edge extending transversely of and arranged immediately adjacent the discharge end of said supply conduit to divide the gas stream issuing therefrom for parallel flow through the pilot ignition chamber and the gas by-pass passage.

3. An ignitor according to claim 2 wherein the leading edge of the partition is formed with a deflecting surface arranged directly in the path of gas outflow from said conduit to spray only a portion of the gaseous fuel issuing from the gas supply conduit throughout the pilot ignition chamber.

4. An ignitor according to claim 2 wherein the tubular head and partition are an integrally cast structure.

5. An ignitor according to claim 2 wherein the gas supply conduit is rigidly connected to the inlet end of the ignitor head, and the means for effecting an electrical spark includes a pair of electrodes extending through the inlet end of the ignitor head and terminating within the pilot ignition chamber, and a tubular shield enclosing said electrodes, said tubular shield having an end thereof in sliding engagement with the inlet end of the ignitor head.

6. An ignitor according to claim 5 wherein the inlet end of the ignitor head is formed with limited opening means for admitting air into the pilot ignition chamber.

7. An ignitor according to claim 1 wherein said deflecting surface is curved.

8. A gas-fired ignitor including a tubular ignitor head having an inlet end and an open distal end, a longitudinally extending partition having its edges connected with the inner wall of said tubular ignitor head and dividing the interior of said head into a pilot ignition chamber disposed on one side of said head and a gas by-pass passage disposed on the other ide of said head, means for effecting an electrical spark in said pilot ignition chamber, and a gas supply conduit having an open discharge end commmunicating with the interior of said ignitor head, said partition having a leading edge extending transversely of and arranged adjacent the discharge end of said supply conduit to divide the gas stream issuing therefrom for parallel flow through the pilot ignition chamber and the gas by-pass passage.

9. An ignitor according to claim 8 wherein the leading edge of the partition is formed with a deflecting surface arranged directly in the path of gas outflow from said conduit to splay only a portion of the gaseous fuel issuing from the gas supply conduit throughout the pilot ignition chamber, and wherein the tubular head and partition are an integrally cast structure.

References Cited by the Examiner UNITED STATES PATENTS 2,715,200 8/1955 Flynn. 2,777,512 1/1957 Johnson et al 15828 X 2,806,518 9/1957 Poole et al. 15828 3,117,619 l/1964 Lange et al. 158ll5 3,168,133 2/1965 Zoschak 15828 JAMES W.- WESTHAVER, Primary Examiner.