US2905236A - Pilot burner and igniter - Google Patents

Description

Sept- 22, 1959 R. C; wmGH-r 2,905,236

' PILOT BURNER AND IGNITER Filed sept. 22, 1953 United States PILOT BURNER AND IGNITER Richard C. Wright, Bay Village, Ohio, assignor to Iron Fireman Manufacturing Company, Portland, Oreg.

This invention relates generally to large industrial oil or gas fueled burners but more particularly to gas fueled pilot burners for such large burners and specifically to such pilot burners which are electrically ignited.

For many years large oil and gas fueled burners have commonly been equipped with gas pilot flame devices which have been more or less crude but reasonably satisfactory because the requirements of nicety of operation have not been high. Usually in the past the main burner installations have been of the naturally induced draft type and the pilot burners have also been simple natural draft torches of either the non-aerated or pre-mix types.

Where electric ignition of these prior art gas pilot torches has been used the electric igniting arc or spark equipment has been located in the main combustion chamber at the base of the pilot flame and thus located are difficult to inspect, adjust, and service as well as subject to the impact of radiant heat from the high temperature llame of the main burner and subject to severe carbon deposition if not enough primary air is used at all times.

With the advent of more modern burners and furnace techniques, using more elegant control techniques and forced draft, leading to much greater ratios of heat release to furnace volume than previously used the old type pilot torches have proven undependable and expensive to service and maintain.

Specifically the non-aerated type of pilot torch has been found diillcult to ignite electrically since the spark location was critical and the spark subject to failure from carbon deposited by thermal decomposition of gas. Also this type flame was unstable and easily blown away from the burner tip. And finally the newer flame conductivity type electronic flame sensing devices do not work well in raw gas flames.

The pre-mix type of pilot torch had the disadvantages of having too small a flame in proportion to the burning rate of the torch and of providing a flame to which the photocell and lead sulphide flicker cell type sensing devices do not well respond. These llames also have the same difficulties as do non-aerated flames if slightly air starved.

To be satisfactory in modern practice the automatic ignition means for the pilot burner must be dependable and located outside the furnace free from high temperatures and carbon deposits and easy to inspect and adjust.

The pilot llame itself must be relatively large to ensure ignition of the main flame under adverse conditions such as excessive draft or defective main burner pattern. The pilot flame must have a low ratio of B.t.u. input to flame size because usually pilot flame gas fuel is much more expensive than main burner fuel, especially when the pilot fuel is liquid petroleum gas and the main burner fuel is crude oil. Again low B.t.u. input is important from the safety standpoint because with most automatic control systems the pilot operates for a certain period of time without supervision and it would be possible for an excessive amount of gas to accumulate in the rebox with a arent 'ice high B.t.u. pilot which did not ignite properly. The pilot flame must also be stable and not readily extinguished by adverse reboX conditions such as high velocity drafts and the llame must provide good response to flame sensing elements of automatic control systems.

It is therefore a primary object of my invention to provide a gas fueled pilot burner with electric ignition which will satisfy all the above requirements.

It is a second object to provide such a pilot burner which is simple and low in cost, easy to inspect and ad-v just and dependable in operation.

It is a third object to provide such a pilot burner which has a low B.t.u. input, large luminous llame for good' main burner ignition and ready detection by the flame sensing elements of the control systems commonly used.

It is a fourth object to provide such a pilot burner which has an inherently stable flame, easy to adjust and inherently trouble free.

It is a fifth object to provide such a pilot burner adapted for use at any furnace pressure either above or below or at atmospheric pressure.

lt is a sixth object to provide such a pilot burner with dependable electric ignition from without the furnace.-

How these and other objects are attained will be explained in the following description referring to the at pilot burner and igniter Fig. 3 is a partial sectional elevation along the line 3 3 of Fig. 2.

Fig. 4 is a partial sectional elevation along the line 4 4 of Fig. 2.

Fig. 5 is an enlarged part View of the structure of Fig. 4.

Like numerals of reference refer to like parts in the several figures of the drawing.

Referring now to the drawing my pilot light and igniter 10 is shown generally as installed in connection with a combination rotary cup atomizing oil burner and industrial gas burner adapted to generate heat in a combustion chamber having a front wall 11 intercepted by a burner mounting antechamber defined by a front wall 12 and a cylindrical outer wall 13. Spaced outside wall 13 is a second cylindrical wall 14 defining with walls 13, 12 and boiler front 11, a secondary air plenum chamber 15 from which secondary combustion air passes through multiple secondary air passages 16 to the annular secondary air passage 17 formed by the refractory lining 18 of the antechamber and the heavy refractory protection block 19 for the oil burner nozzle 20 and the fuel gas plenum ring main fuel, the fuel gas is injected into secondary air passage 17 by multiple gas jets 22.

Pilot burner and igniter 10 as shown is inserted from outside the antechamber through a hole in front wall 12 to extend well into the secondary air passage 17. The pilot burner and igniter is supported on front wall 12 by a bracket (not shown) secured to body 23 and bolted to front wall 12.

As clearly shown in the several figures of the drawing my pilot burner and igniter comprises a hollow metal body 23 into which is secured a pilot gas fuel tube 24 spaced from and enclosing a pilot burner ignition tube 25 also secured into body 23.

Pilot burner fue] gas is supplied to tube 24 from gas pipe 26 secured to body Z3 by typical fitting 27 threaded into cavity 28 and passageway 29 formed in body 23.

Patented Sept. 22, 1959L box 21 from which, when gas is used for the The vgas to tube 24 is metered by orice'plug 30 pressed into passageway 29.

Air under pressure and regulated by a manually set valve (not shown) in air line 31 is introduced into main cavity 32 of body 23 through fitting 33 and passageway 34 formed in body 23. Inspection opening 35 formed in body `23 is normally closed with a threaded plug 48. Ignition tube 25 communicating with cavity 32 receives air under pressure at a preset rate from air line 31 through cavity 32 as shown.

`For construction purposes ignition `gas passageway 36 is formed in body 23 as shown in Figs. 4 and 5 but in use the lower end is closed with blind plug 37. Gas passageway 38 connects cavity 28 with passageway 36 whereby ignition gas at a controlled rate is passed from cavity 28 through orice plug 39 in passageway 38, passageway v36 and 34 to main body cavity 32 where it is mixed with air and passed on to ignition tube 25.

Spark plug 40 includes a shouldered porcelain tube 41 adapted to seat on shoulder 42 formed in main cavity 32 of body 23 and to be secured in position by plug nut 43 threaded into body 23. Electrode 44 is electrically and mechanically secured to terminal stud 45 extending out the upper end of tube 41 and adapted to carry insulating spool 46 secured thereon by nuts 49 threaded onto terminal stud 45. Insulated terminal nut 47 with al kmetallic threaded insert cast therein is adapted threadedly to engage the upper end of stud 45 and secure a high voltage electrical conductor (not shown) to stud 45. The position of the lower or spark end of electrode 44 with respect to the inner surface of body 23 in cavity 32 can be observed and adjusted through inspection opening 35 and the spark gap adjusted to the most ecient sparking length for the voltage used.

In practice pilot burner gas under pressure is introduced at a rate controlled by the normal gas line pressure 'and the size of the orifice in plug 30 into gas tube 24 from gas line 26.

.Air under pressure from air line 31 is allowed to ow into body cavity 32 and from there into ignition tube 25. At the same time gas from cavity 28 at a rate metered by the orice in plug 39 enters cavity 32 through passageways 38 and 36 and mixes with air in cavity 32 to form a combustible mixture.

Then when a high voltage from a source not shown is impressed on stud 45 a spark occurs from the lower end of electrode 44 to the inner surface of grounded body 23 thus igniting the air gas mixture in cavity 32 `from where the burning mixture advances to the free end of tube 25 and ignites the pilot gas emerging from the free end of tube 24.

When the gas emerging from tube 24 is properly ignited and the pilot ame stabilized as indicated by a flame sensing means applied to the pilot llame in any of the ways well known in the art, the flame sensing vmeans signals this condition to other control mechanism which then is free to remove the high voltage from stud 45 and to start the main burner (either oil or gas) supplying fuel and air to the combustion chamber.

It should be noted rthat the fuel-air ratio of the gases introduced into cavity 32 is adjusted to be such that a stable ame will carry through tube 25 out its free end, and ignite the gas emerging from tube 24, but that the mixture is so proportioned that with the spark cut off the rate of ame propagation in the -gas mixture will not be suiicient to cause flame from the free end of tube 25 to advance backward alongtube 25 against the incoming stream of fuel-air mixture to ignite the mixture in cavity 32. It is thus'seen that the interior of'body 23, the lower endsof porcelain 41 and electrode 44 andthe interior of tube V25 are only subject to the products of combustion for the short time required for ignition and that the ignition mixture `is proportioned -for complete combustion of the gas. Therefore there is no fouling of the ignition parts which ordinarily would lead to faulty operation.

It should again be particularly noted that the pilot flame from the raw gas emerging from tube 24 tends to give me the bushy large ame characteristic of the non aerated burner but that the continuous introduction of the stream of pre-mix gas from tube 25 continuously provides a burning core to the otherwise non aerated flame character of the burner. The result is a stable bushy pilot flame with no tendency to wander away from the burner tip, a ame large enough to light any main burner, stable enough to ignite even an unbalanced fuel mixture from the main burner, and a flame which works well with any of the present day pilot ame sensing control means.

Additionally it should be noted that neither the supply `of air or fuel to my pilot burner and igniter can be influenced by the draft conditions within the combustion chamber.

Having thus Vset forth some of the objects of my invention, illustrated and described a preferred form of my invention, and explained its operation, I claim:

`A pilot burner and igniter for furnaces including an elongate tube, an elongate sleeve substantially co-extensive with the tube and surrounding the latter throughout substantially its entire length to form a burner and igniter assembly adapted to be positioned with one end adjacent the main burner of a furnace, a fitting receiving the opposite end of the assembly remote from the burner end thereof, said fitting having a passage communicating with the `space inside the tube and a passage communicating with the space between the sleeve and the tube, means supplying fuel gas to each passage, means supplying air under pressure to the passage communicating with the tube and electrical ignition means within said last mentioned .passage within said fitting.

References Cited in the le of this patent UNITED STATES PATENTS 1,938,851 McKee Dec. l2, 1933 2,285,704 Frank June 19, 1942 2,596,729 See May 13, 1952 2,643,709 Haverland June 30, 1953

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