US3202200A - Method and apparatus for igniting and burning gaseous fuel - Google Patents

Description

1965 D. M. MARSHALL ETAL 3,202,200

METHOD AND APPARATUS FOR IGNITING AND BURNING GASEOUS FUEL Filed Oct. 27. 1960 2 Sheets-Sheet 1 FIG.1

15 INVENTORS David M. Marshall BY Andrew B. Sreever ATTORNEY 24, 1965 D. M. MARSHALL ETAL 3,202,200

METHOD AND APPARATUS FOR IGNITING AND BURNING GASEOUS FUEL Filed Oct. 27. 1960 2 Sheets-Sheet 2 IIIII a A U IIIIII IIHIII IN V EN TORS David M. Marshall Andrew B. Sfeever AT TORNEY- United States Patent 3,202,200 METHGD AND APPARATUS FGR IGNITING AND BURNENG GASIEQUS FUEL David M. Marshall, Akron, Ghio, and Andrew B. Stecver, Old Greenwich, Conn., assignors to The Bab'cock & Wilcox Company, New York, N.Y., a corporation of New Jersey 1 Filed Get. 27, 1960, Ser. No. 65,447

8 Claims. (Cl. 158-109) The present invention relates to the combustion of fuel, and more particularly to a liquid cooled burner for high temperature and high pressure service, and to a method of igniting and burning the fuel delivered by such aburner.

The use of liquid cooling in fuel burners has heretofore been known and various designs of such burners have proven reasonably satisfactory in low pressure combustion service. However, when the space served by the burner has been operated at high pressures, such as 1000 p.s.i.a. and above, the burner fluid cooling provisions have become unwieldy, complicated, and entirely unsatisfactory.

In the present invention, we provide a burner assembly suitable for high pressure and high temperature furnace operation. In such a burner, a novel method is provided for igniting the fuel supplied to the burner and for maintaining stable combustion conditions within the furnace or combustion space. The burner assembly includes an elongated nozzle constructed from a plurality of small diameter pipes arranged in side-by-side spaced relation. The pipes are connected for the flow of a cooling fluid therethrough and the nozzle assembly is provided with elongated slot-like openings between adjacent pipes for the discharge of the fuel from the burner nozzle. In a preferred form of the invention, space confining walls define an annular flow passageway for combustion air, for example around the nozzle. The combustion air is preferably introduced into the flow passageway with a tangential component of motion so that it will whirl in a generally helical flow path around a plurality of outlet slots adjacent the end of the nozzle.

When the burner is serving a furnace operated at super atmospheric pressures, of the order of 1000 p.s.i. and above, it is advantageous to reduce the number of openings in the furnace as much as possible so as to avoid unnecessary weakening of the furnace wall structure. In accordance with another aspect of our present invention, We provide means for igniting the fuel delivered through the burner nozzle by means of a spark ignition electrode positioned in the fluid flow path leading to the burner nozzle. With such an arrangement, a low fuel pressure pilot flame is ignited and moves along the interior of the burner nozzle to discharge from the slotted nozzle outlet. The movement of the ignited fuel is accomplished by the admission of additional fuel which pushes the flame through the nozzle slots and into the furnace. The additional fuel may be from either a high or low pressure source, and preferably the former. As the flame leaves the nozzle outlets, it ignites the high pressure fuel stream discharging into the combustion air or high oxygen content gases which are whirling through the combustion air passageway. This novel means for igniting and burning either high or low pressure fuel in the same burner assembly minimizes the number of openings in the walls of the furnace and has moreover, proven entirely reliable for igniting and maintaining the combustion of fuel under pressurized high temperature combustion conditions.

The various features of novelty which characterize our invention are pointed out with particularity in the claims annexed to and forming a part of this specification. For a better understanding of the invention, its operating advantages and specific objects attained by its 3,202,200 Patented Aug. 24, 1965 use, reference should be had to the accompanying drawings and descriptive matter in which we have illustrated and described a preferred embodiment of the invention.

Of the drawings:

FIG. 1 illustrates a high pressure, high temperature regenerative heater provided with the burner of the present invention;

FIG. 2 is an enlarged elevation, in section, of the burner assembly; and

FIG. 3 is a further enlarged section of the burner nozzle taken on line 3-3 of FIG. 2.

The fuel burner of the present invention is illustrated as applied in supplying fuel to a high pressure, high ternperature regenerative heater 10 where the hot gases produced by combustion in the upper portion of the heater give up heat to a bed of heat exchange pellets or pebbles maintained in the lower and intermediate portions of the heater. The flow of the hot combustion gases is down wardly from the upper portion to a gas discharge at the lower end portion of the heater. After the heat exchange bed has been heated to a desired value, the admission of fuel and air ceases and a high pressure relatively cool gas is introduced into the lower portion of the heater body for upward movement through and discharge into a side outlet from the upper portion of the heater. In passing through the heater, the high pressure, relatively cool gases are heated to a desired value for subsequent use.

In the heater illustrated, the heating and cooling of the heat exchange bed is cyclic, and in this particular embodiment of the invention, the relatively cool high pressure air is heated in the regenerative heater for discharge at a temperature of the order of 4000 F. and at a pressure of approximately 2000 p.s.i. To attain this heating effect, the burner first must be operated in order to bring the heat exchange bed to the comparable 4000 F. temperature and the fuel must be burned at a pressure high enough to insure passage of the heating gases through the heat exchange bed.

The regenerative heater 10 illustrated in the drawing forms the subject matter of a copending application Serial No. 831,994, filed August 6, 1959, now Patent No. 3,120,380, in which a co-inventor is also a co-inventor of the present application. As disclosed and claimed in the said copending application, and shown generally in FIG. 1 of the present application, the regenerative heater 10 includes an upright heavy walled pressure vessel 11 having integral upper and lower nozzles 12 and 13 respectively, of reduced horizontal cross-sectional dimensions. The upper nozzle 12 provides a confined space for the admission of combustion air and fuel, which is burned in that portion of the pressure vessel 11 above the upper surface of the bed of heat transfer pebbles disposed therein. In a similar manner, the lower nozzle 13 is provided with an outlet fitting 14 for the discharge of spent heating gases and an inlet fitting 15 for the introduction of the high pressure gas or air to be heated which is discharged through an outlet 19.

As shown in FIGS. 1 and 2, the upper nozzle 12 is cylindrical with its axis coaxial with that of the pressure vessel. The upper end of the nozzle is flanged as at 16 and is provided with a cover plate 17 which is attached thereto. The plate is formed with a central opening 18 through which the burner nozzle 20 of the burner assembly'extends. A collar 21 mounted on the plate 17 sup ports a cap plate 22 to which is welded (for example) a fuel inlet pipe 23 and cooling fluid inlet and outlet chambers 24 and 25, respectively. The cap plate 22 is removably attached to the collar 21 and the cover plate 17 by circumferential series of bolts 28, so that the assembly, including the burner nozzle 20, may be removed for maintenance or replacement, as necessary.

The burner nozzle is formed from a plurality of U- shaped tubes 26, as hereinafter described in detail, with the opposite ends of each tube opening to the inlet and outlet chambers 24 and 25, respectively, for the flow of a cooling fluid, is. water, therethrough. The inlet and outlet chambers are defined by a dome shaped hollow member 27 of circular horizontal cross-section in cooperation with the fuel inlet pipe 23. The cylindrical wall portion of member 27 is welded to the upper surface of the plate 2 2. Suitable diaphragms (not shown) extend within the annular space between the member 27 and the exterior surface of the pipe 1-3 to separate the inlet and outlet chambers 24 and 25, respectively. The chambers are provided with flanged pipe connections 39 and 31 for the admission and discharge, respectively, of the cooling fluid.

The burner nozzle 20 is constructed of a plurality of steel tubes 26 arranged in spaced side-by-side relationship, as shown in FIGS. 2 and 3, to define a burner nozzle of generally circular cross-section. Each tube of the nozzle assembly forms a complete flow circuit from the water inlet chamber 24, through a return bend 32 at the lower extremity of the nozzle, to open into the fluid outlet chamber 25. The tubes 26, adjacent the return bend portions 32, are swaged over a portion of their height to form a plurality of axially elongated slots 33 between adjacent tubes.

In order to provide a gas-tight burner nozzle, the space between the tubes 26 is continuously welded, as at 26', with reinforcing and sealing wires 2-6 incorporated in the weldment as shown in FIG. 3. This construction prevails throughout the lengths of the extending nozzle tubes 26 except in that region where the tubes are swaged to provide the slots 33 between adjacent tubes. Additionally, to effect a seal at the upper ends of the nozzle tubes, adjacent the lower annular plate of the housing 29, the housing is welded to the plate 22 and the tubes 26 are welded to the lower plate where they project through the housing 29. Thus, fuel gas passing downwardly through the fuel inlet pipe 23 into the nozzle 20 is discharged from the nozzle in a plurality of horizontally directed jets.

In the embodiment shown, the slots 33 are each approximately 2% inches long and 4 inch wide and the internal diameter of the nozzle 20 is 3 inches. In the illustrated example, the exterior of the nozzle 20, with the exception of the vertically elongated slotted openings,

is coated with a protective coating of Nichrome which is flame sprayed thereon. A refractory material 34 supported on the tubes 26 of the nozzle 20 by stainless steel rings 35, for example, is provided to reduce the heat absorption of the tubes 26.

With the described construction, the tubes 26 are each /3 inch 0D. with a wall thickness of .120", and advantageously have sufficient strength to withstand an external pressure of 2000 p.s.i.a. without crushing. As shown, the burner nozzle 2%) is covered in part by the refractory material 34, such as zirconia, to reduce the heat absorption of the water cooled tubes of the nozzle.

As disclosed in said copending application and shown in FIGS. 1 and 2, combustion air is introduced into the annular space 36 between the inner wall of nozzle 12 and the burner nozzle 29, entering through four circumferentially equally spaced tangential inlets 37. Thus, a whirl ing or rotary motion is imparted to the combustion air in its passing downwardly through the nozzle 12 to enter the upper end portion of the pressure vessel 11. The

turbulence resulting from the whirling motion of the bustion air. As shown schematically in FIG. 1, the air is supplied at 12 p.s.i.g., for example, from an air compressor 49, with the air passing through a connecting pipe 41 leading to the four tangentially arranged air inlet openings 37 in the wall of the nozzle 12. Oxygen may be admitted to the pipe 41 through a valved pipe connection 48. A separate low pressure air source, provided from a fan 42, is connected by a pipe 43 with the pipe 41 from the high pressure air compressor 40. The low pressure air system is also connected through a separate pipe 44- with the natural gas supply pipe 45 whch leads to the nozzle 29, as hereinafter described. Both the high pressure air line 41 and the low pressure air line 43, 44 are suitably provided with check valves, flow regulating and closure valves generally indicated at 46.

Natural gas is provided at 15 p.s.i.g., for example, through a pipe 50 which directly connects via line 45 with the gas inlet pipe 23 of the burner nozzle 29 In addition, a separate low pressure gas line 51 connects with the pipe 50 for the delivery of 3 p.s.i.g., for example, gas to the burner nozzle 20, when required. The low pressure gas line is provided with a flow regulating valve 52 which is actuated by a pressure switch 53 actuated by the pressure in the gas line 45. The pressure switch may be adjusted to close the low pressure valve 52 at an increase in pipe pressure to, for example, 4 p.s.i.g. Between the low pressure gas pipe 51 connection with the pipe 45, and the burner nozzle 26, is positioned a gas bypass pipe 54 where the pipe 45 and the bypass pipe 54 are provided with a pressure control valve 55 and a flow control valve 56, respectively.

In accordance with the present invention, a spark plug 57 is inserted in the gas pipe 45 ahead of the burner nozzle 20 and after the connection between the bypass pipe 54 and pipe 45. The arrangement is such that either low pressure gas with low pressure air or high pressure gas may be delivered to the burner nozzle 29 While either low pressure air or high pressure air, enriched with oxygen, as desired, may be delivered to the combustion air space 36 surrounding the burner nozzle 20.

When starting up the burner, it is customary to introduce low pressure air through the connecting pipe 44 and pipes 45 and 23, thence into the burner nozzle 2%, so as to purge the system. To operate the burner, the low pressure gas is passed sequentially through pipes 51, 45, 54 and 45 and simultaneously the spark plug 57 is actuated. When the gas reaches the spark plug, it is mixed with low pressure air present as a result of the purging operation and low pressure air which is introduced simultaneously with the low pressure gas, where the mixture is ignited. The flame progresses through the burner pipe 23 then enters into and is discharged from the burner nozzle 20 through the slots 33. Immediately thereafter the high pressure gas valves are opened while simultaneously both the low pressure air flow and the low pressure gas flow are discontinued. The high pressure gas, in passing through the pipe 45, closes the valve 52 and continuing its flow pushes the burning mixture of air and low pressure gas through the nozzle 20 with the flame initiated by the low pressure gas igniting the high pressure gas as the latter leaves the nozzle 26 through the slots 33 to establish normal high pressure fuel combustion conditions. It is, of course, understood that opening the high pressure gas line necessitates the use of high pressure air so that the flame may then be stabilized with the proper quantities of gas and oxygen. It has been found possible to initiate flow of high pressure air through the ports 37 before the high pressure gas is introduced, without aflecting the ignition of the low pressure gas and air.

In the normal cyclic operation of the heat transfer apparatus illustrated, the combustion of the gaseous fuel occurs for a limited period of time, usually some fraction of an hour. Thereafter, with fuel combustion stopped, the air or gas to be heated is introduced into J the heat transfer apparatus through inlet 15, passing upward through the bed for another fraction of an hour, with the firing cycle thereafter repeated.

It will be noted the present invention provides a fuel burner adapted foruse as an igniter as well as a main burner, and constructed and arranged for cyclic operation where the fuel burning portion of the cycle is conducted at relatively low pressures and the burner is capable of withstanding extremely high pressures and temperatures during its off period. During the high pressure portion of the cycle, the high pressure medium enters the burner nozzle so that both the exterior and interior portions of the burner nozzle are exposed to the pressure and temperature effects of the medium, and thus equalizes the effect of pressure on the nozzle. Advantageously, the burner nozzle is fluid cooled so as to minimize the adverse influence of the high temperature medium on the burner nozzle.

While in accordance with the provisions of the statutes we have illustrated and described herein the best form and mode of operation of the invention now known to us, those skilled in the art will understand that changes may be made in the form of the apparatus disclosed without departing from the spirit of the invention covered by our claims, and that certain features of our invention may sometimes be used to advantage without a corresponding use of other features.

What is claimed is:

1. A burner nozzle comprising an elongated tube having a closed end and a plurality of discharge openings spaced around the periphery of and adjacent said closed end, said elongated tube being defined by a plurality of spaced hollow tubular members positioned with their axes substantially parallel to the longitudinal axis of said elongated tube, the intertube spaces being closed on opposite ends of said discharge openings, each of said tubular members being directly and solely flow connected at the closed end of said elongated tube with another said tubular member to cool the closed end of said burner nozzle, and means for passing a fiuent cooling medium through said tubular members.

2. A fuel burner comprising an elongated tube having a closed end and a plurality of elongated discharge openings spaced around the periphery of and adjacent said closed end, means for cooling said elongated tube including a plurality of return bend tubes connected in gas tight relationship to define the wall and closed end of said elongated tube, means for passing a fuel constituent through said elongated tube for discharge through said discharge openings in an outward direction from the closed end portion of said tube, wall means spaced from the wall of said elongated tube and defining a combustion air flow passageway surrounding said elongated tube, and means for passing combustion air through said passageway in mixing relationship with the fuel constituent discharged through the openings of said elongated tubev 3. A fuel burner comprising an elongated nozzle of circular crosssection having a closed end, a plurality of tubular members defining the wall and closed end of said nozzle, each of said tubular members being bent across the closed end of said nozzle, means for passing a cooling medium through said members, means for passing fluent fuel through said nozzle, means adjacent an end of said nozzle for directing the fuel discharged therefrom transversely of the longitudinal axis of said nozzle, wall means spaced from and substantially parallel to the exterior surface of said nozzle to define a combustion air passageway therebetween, said wall means diverging away from said nozzle in the vicinity of the fuel discharge position of the nozzle, means for introducing combustion air into said passageway upstream of the fuel discharged from said nozzle, said combustion air moving axially of said nozzle with a transverse direction of swirling motion imparted thereto for intimate mixing of said fuel and combustion air leaving said fuel burner.

4. A fuel burner comprising an elongated nozzle of circular cross-section having a closed end, a plurality of U tubes arranged in circumferentially spaced side-byside relationship to define the walls and end of said nozzle, means for passing a cooling medium through said U tubes, means for passing fluent fuel through said nozzle, means adjacent the closed end of said nozzle for directing the fuel discharged therefrom transversely of the longitudinal axis of said nozzle, wall means spaced from andsubstantially parallel to the exterior surface of said nozzle to define a combustion air pa-ssageawy therebetween, said wall means diverging away from said nozzle in the vicinity of the fuel discharge position of the nozzle, means for introducing combustion air into said passageway upstream of the fuel discharged from said nozzle, said combustion air moving axially of said nozzle with a transverse direction of swirling motion imparted there-to for intimate mixing of said fuel and combustion air leaving said fuel burner.

5. In a fuel burner the combination comprising an elongated nozzle having an opening in an end thereof, means for directing a flow of high pressure combustion air externally past said nozzle, a gaseous fuel supply pipe connected to and discharging fuel into said nozzle, an ignilter positioned in said supply pipe upstream of said nozzle, a source of high pressure gaseous fuel and a source of relatively low pressure gaseous fuel, valved means separately connecting said sources of fuel with said fuel supply pipe, and valved means for connecting a superatmospheric low pressure source of air with said supply pipe for introduction of air to said elongated nozzle.

6. In a fuel burner having an elongated nozzle with a plurality of discharge openings in an end thereof for discharge of fuel substantially transverse to the axis of said nozzle, means for directing a flow of high pressure combustion air externally past the discharge openings of said nozzle, a gaseous fuel supply pipe connected .to and discharging fuel into said nozzle, an igniter positioned in said supply pipe upstream of said nozzle, a source of high pressure gaseous fuel and a source of relatively low pressure gaseous fuel, valved means sepa rately connecting said sources of fuel with said supply pipe, and valved means for connecting a low positive pressure source of air with said supply pipe for selective introduction of air to said elongated nozzle.

7. -In a fuel burner having an elongated fluid cooled nozzle with a plurality of discharge openings in an end thereof for discharge of fuel in directions substantially transverse .to the axis of said nozzle, means for directmg a whirling flow of high pressure combustion air externally past the discharge opening of said nozzle, a gaseous fuel supply pipe connected to and discharging fuel into said nozzle, an igniter positioned in said supply pipe upstream of said nozzle, a source of high pressure gaseous fuel and a source of relatively low pressure gaseous fuel, valved means separately connecting said sources of fuel with said supply pipe for selected flow of gaseous fuel to said supply pipe, and valved means for connecting a low positive pressure source of air with said supply pipe for introduction of air to said elongated nozzle.

8. In a fuel burner having an elongated fluid cooled nozzle surrounded by a confined combustion air flow passageway, the method of operating said burner which comprises the steps of passing a stream of low pressure air through said nozzle, introducing a flow of low pressure gaseous fuel into said nozzle, igniting the mixture of air and gaseous fuel in said nozzle and passing the burning mixture from said nozzle into said confined combustion air flow passageway, introducing a separate stream of high pressure gaseous fuel into said nozzle while simultaneously stoping flow of said air and said low pressure gaseous fuel to said nozzle, and passing a whirling stream of high pressure combustion air through said confined combustion air flow passageway to sustain the combustion :of the high pressure gaseous fuel discharging from said nozzle and ignited by the low pressure burning mixture ignited in said nozzle.

References Cited by the Examiner UNITED STATES PATENTS Reiohhelrn 158-99 Fischer 158-119 X Danforth 158-1175 Lilge 158-109 Forster 158-118 Alfery 236-1 Witzke 122-235 Nagel 158-1175 Patterson 158-99 Furczyk v 158-7 X Peters 158-115 OCathey et a1. 158-109 Wright 158-115 FOREIGN PATENTS Great Britain.

JAMES W. WESTHAVER, Primary Examiner.

FREDERICK KETTERER, FREDERICK L.

MATTESON, JR., Examiners.

Claims (1)

1. 2. A FUEL BURNER COMPRISING AN ELONGATED TUBE HAVING A CLOSED END AND A PLURALITY OF ELONGATED DISCHARGE OPENINGS SPACED AROUND THE PERIPHERY OF AND ADJACENT SAID CLOSED END, MEANS FOR COOLING SAID ELONGATED TUBE INCLUDING A PLURALITY OF RETURN BEND TUBES CONNECTED IN GAS TIGHT R ELATIONSHIP TO DEFINE THE WALL AND CLOSED END OF SAID ELONGATED TUBE, MEANS FOR PASSING A FUEL CONSTITUENT THROUGH SAID ELONGATED TUBE FOR DISCHARGE THROUGH SAID DISCHARGE OPENINGS IN AN OUTWARD DIRECTION FROM THE CLOSED END PORTION OF SAID TUBE, WALL MEANS SPACED FROM THE WALL OF SAID ELONGATED TUBE AND DEFINING A COMBUS-

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