US2335471A

US2335471A - Fluid fuel burner control system

Info

Publication number: US2335471A
Application number: US338938A
Authority: US
Inventors: Joseph P Asheraft
Original assignee: Honeywell Inc
Current assignee: Honeywell Inc
Priority date: 1940-06-05
Filing date: 1940-06-05
Publication date: 1943-11-30
Anticipated expiration: 1960-11-30

Description

Nov. 30, 1943. J. P. AsHcRAFT 2,335,471

FLUID FUEL BURNER* CONTROL SYSTEM Filed June 5, 1940 23 QoL fg (7 43 22 q. gli@ I f I I I 24 I I /20 I 26 ,76 2g z8: 21

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(le LH 57 25 65 |16 'I'l"; )));""""`Jllill'lllllllllllllllllvlllll? F15@ '6* -INVENTOR 'Joseph P. Ashcraf- ATTORNEY Patented Nov. V30, 1943 FLUID FUEL BURNER CONTROL SYSTEM .vloseph P. Ashcraft, Dallas, Tex., assignor to Minneapolis-Honeywell Regulator Company, Minneapolis, Minn., a. corporation of Delaware Application June 5, 1940, Serial No. 338,938

'z claims. (c1. 15s-115) This invention relates to a uid fuel burner control system, and more particularly to one employing a pilot burner, wherein means is provided toishut down the main burner uponfailure of the pilot flame.

In fluid fuel burner control systems employing a pilot burner, it has been proposed to place the hot junction of a thermocouple in the pilot flame, and to provide means responsive to a drop in the thermocouple E. M. F. such as occurs upon llame failure, to shut down the burner. Such systems which have been built in the past have been slow to respond to failure of the pilot flame, because of the relatively long time necessary for the hot thermocouple junction to cool down enough to produce the required drop in E. M. F. The thermocouple response has been particularly slow in those cases wherein the hot junction was exposed to radiation from the main burner flame, and pilot failure has occurred while the burner was in operation. Radiation from hot furnace wa-lls has likewise sometimes delayed the thermocouple response when the pilot failed immediately after the burner was shut down. Radiation from the main burner flame, and from hot furnace walls, are particularly apt to be troublesome in large burners employing a forced draft, which usually operate at a higher temperature than natural draft burners. Furthermore, forced draft burners are especially liable to have their pilot burner extinguished, because of the rapid air movements near the burner.

Another difficulty with the devices proposed in the past has been that the copper conductors leading to the thermocouple have tended to oxidize in the intense heat to which they are exposed.

An object of the present invention is to construct a pilot burner and thermocouple arrangement, wherein means are provided to accelerate the cooling of the hot junction of the thermocouple upon extinguishment of the flame.

Another object of the invention is to construct a pilot burner and thermocouple arrangement wherein the gas iiowing through the burner is utilized to increase the difference in temperature of the hot and cold junctions during normal flame conditions, and to reduce the difference in temperature when the flame becomes extinguished.

A further object of the invention is to construct a pilot burner and thermocouple device wherein the thermocouple is so situated relative to the gas burner that the gas flowing toward the burner conducts heat away from the cold junction of the thermocouple, and the gas flowing from the burner after flame failure conducts heat away from the hot junction.

A still further object of the present invention is to provide a pilot burner and thermocouple device wherein the electrical leads to the thermocouple are protected against the heat of the burner. It is also an object of this invention to utilize the gases flowing to the pilot burner to cool the thermocouple leads.

Other objects of the present invention will be apparent from a consideration of the specifica` tion, claims, and drawing, of which:

Figure 1 is a diagrammatic sketch of a fluid fuel burner control system embodying my invention,

Figure 2 is an enlarged view, partly in cross section, showing my invention as applied to a commercial type of pilot burner,

Figure 3 is an exploded view of the packing washers used in calrying the thermocouple leads of my invention t rough the wall of the pilot burner fuel supply conduit, in their assembled relation, and

Figure 4 is a vertical sectional view of the thermocouple on a considerably larger scale than in Figure 2. i

In the drawing the Wall of a gas burning furnace is indicated at I0. A main burner II is mounted adjacent an opening in this wall and is connected by pipe I2 with a motor driven mixer and blower I3. Gas is supplied to the mixer through the pipe I4 and air through another pipe I5. An electrically operated valve I6 of any suitable type is connected in the pipe I4. A `smaller pipe I1, connected to the pipe I4 on the inlet side of the valve I6, conveys fuel to a pilot burner generally indicated at I8.

The energization of the motor of the mixer and blower I3 is controlled by a thermostat 20 which is located in the room or space being heated by the furnace. This thermostat comprises a bimetallic element 2I to which is secured a contact arm 22 for cooperation with the stationary contact 23. A magnet 24 is located adja cent the contact arm 22 and serves to impart a snap action thereto.

A thermocouple indicated schematically at 25 located within the pilot burner I8 is electrically connected to a solenoid 26 of a safety switch 21 which may be of any suitable type, such as that disclosed in Patent No. 2,165,801, issued to Carl G. Kronmiller on July 11, 1939. The switch 2'I comprises in addition to the solenoid 26 a switch arm 28 and a stationary contact 29. Under normal' ame conditions, solenoid 26 is energized sufficiently by thermocouple 25 so that it will hold switch arm 28 which serves as an armature, ln its attracted position, where lt engages contact 29. The energization of solenoid 26 provided by thermocouple 25 is not enough, however, to

` tact 29, and has to be reset manually before the circuit therethrough can be completed. I! depicks up its armature automatically when the pilot is relighted, ,may be used.

A pressure responsive switchgenerallyvindicated at cooperates with the thermostatr 26 to control the energizationV of the valve I6. The

switch 30 comprises a mercury switch 3l which.

is mounted on a pivoted support 3.2 against which a bellows element 33 bears. The bellows element is connected by means of a pipe 34 to thepipe I2 at the outlet side of the blower I3. u Power is supplied to the control system fromvv l lines 4.0 and 4I through a step down transformer 42 having a primary winding 43 and a secondary 44.

The thermocouple 25, which is of the concentric type, is provided withthe

usual members

45 and 46 of different thermoelectric charac-r` teristics which are jointed at 64 to provide the hot junction of the thermocouple. The inner member 45 is secured tov a conductor 41 which is insulated as at 48. The outer member 46 is connected at 65 to a copper reducing sleeve 49 which in turn is connected to a copper tubing 51. The connection 65 between member 46 and sleeve 49 forms the cold junction of the thermocouple. The'tubing 51 is electrically connected to one end of the solenoid 26, while the conductor 41 is connected to the other end.

The pilot I8 consists of a nozzle mounted on the end of a pipe 5I. This nozzle has an exterior opening 52 located centrally of its outer end and bounded by a flange 52a. Within the body of the nozzle is a partition 53 of a generally conical shape which is provided with' a large central opening 54 and a plurality of small openings 55 spaced radially from the central opening. A second wall 56 is located at the back of the nozzle and serves to support substantially centrally thereof the thermocouple 25. The wall 56 is provided with suitable openings which permit the flow of gas therethrough. The

conductors

41 and 51 pass along the center of the pipe 5I and out through a packing gland 58. Gas is supplied to the pilot burner I8 through the pipe I1 :in which is inserted an air intake 59 of any suitable design. The pipe I1 is connected to the pipe 5I through a T connection 60. The pipe 5| is connected to one of the arms of the T connection and the othenarm, while the pipe I1 is connected to the upright of the T. This construction enables the

conductors

41 and 51 to pass out through the opening located centrally of the packing gland 58 without the tubing 51 touching the sides of the pipe 5I at any point. The conductors 41 are supported in the gland 58 by a fiber'washer 6I. In order to provide a pressure tight seal, metal washers 62 are provided in the packing gland, each of which has a slot extending from one edge thereof beyond the center. Two of these washers with their slots oppositely disposed are placed on each side of the fiber washer 6I, as' shown in Figure 3. The washers are clamped into the gland 58 by a packing nut 63. A f

As previously noted, an air intake 59 is pro- .Videdso that a mixture of gas and air' is supplied to the pilot burner I8. Because of this, combustion occurs immediately beyond the wall 53 which acts as ascreen to prevent combustion on the upstream side of this wall. The outer portion of the nozzle 50 thus acts as a housing to confine the flame. This confining action is aided by the ange 52a. The result of this is 50 which is snede 'sensitive safety switch of the type which. that the pilot name, despite th turbulent conditions surrounding it, remains ln igniting relation to the main burner. Furthermore, the conflning action of the housing 5I) results in the llameA being more effectively directed against the hot junction 64 of the thermocouple. Thus. it is possible to use a fuel mixture of gas and air in the pilot burner in association with a forced draft gas burner and still obtain proper heating of the hot. junction of the thermocouple.

l The thermocouple 25 may be mounted so as to extend slightly eccentrically from the mouth 62 of the nozzle 50, if the nozzle 50 ls of such a construction'that it provides a symmetrical vflow of gas through the opening thereof. It has been found that in such cases,` if the thermocouple 25 is located in the exact center of the nozzle, a cone of unburned gas may form around the end of the thermocouple, and prevent it fromv The various elements are shown in the positions they have when there is no demand for operation of the burner by the thermostatic dewice 20. It is presumed that the pilot I8 is lit and that the safety switch 21 has not opened. When the 'temperature of the room or space to be controlled falls below the value which the thermostat 20 is set to maintain, the switch arm 22 will be moved into engagement with the contact 23 thereby completing a circuit which will result in energization of the motor of the blower I3. This `circuit may be traced from the upper terminal of secondary winding 44, as it appears in the drawing, through a conductor 10, contact 23, switch arm 22, bimetallic element 2|, a conductor 1I, contact 29., switch arm 28,

conductors

12 and 13, a starting relay 14 for the motor of blower I3,

conductors

15 and 16 to the lower terminal of secondary winding 44. Energization of the relay 14 will result in the connection of the blower motor to the line wires 40 and 4I.

As soon as the blower has started the pressure in the outlet pipe I2 thereof will increase. The increased pressure will be carried through the pipe 34 to the bellows element 33. The expansion of this bellows will lift the support 32 so as to move the mercury switch 3I to close its contacts, which will result in the completion of an energizing circuit for the valve I6. This circuit may be traced from the upper terminal .of secondary winding 44 through conductor 10,

contact 23, switch arm 22, bimetallic element 2l, conductor 1l, contact 29, -switch arm 28, conductor 12, a conductor 11, switch 3l, conductor 18, valve I6, and conductor 16 back to the lower terminal of secondary winding 44. This will result in the opening of the valve I6 to supply fuel to the blower and mixer I3. A combustible mixture rof fuel and air will then be blown from the mixer out through the nozzle of burner Il'and ignited by the pilot. The resulting combustion in the Afurnace I0 will raise the temperature of the room or space under control, and, as soon as it has reached the desired value, the thermostat 20 will operate to separate the

contacts

22 and 23, thereby deenergizing the system. It should be noted that, because of the When the pilot burner is mounted ver-M pressure-responsive switch 30, fuel is not supplied to the burner until after a flow of air therethrough has been started. This scavenges the furnace of any .accumulated gas, and also serves to prevent flash-back.

If the llame at the pilot burner should become extinguished at any time, the flow of gas through the nozzle thereof will operate to cool the hot junctionof thermocouple 25 which has been in the pilot flame. As the temperature of the hot junctions falls, the electromotive force produced by the thermocouple soon becomes insuillcient to maintain the energization of solenoid 26 with the result that switch arm 28 moves away from contact 29, and the system cannot then operate until the switch 21 is manually reset. It will be seen that by placing the `thermocouple in the center of the pilot burner nozzle advantage is taken of the flow of gas through this nozzle to cool the cold junction of the thermocouple under normal conditions and to cool both junctions upon failure of the pilot flame. By-reason of this construction the thermocouple is made much more sensitive to failure of the flame than any of the previously existing devices, and amore rapid response of the switch 21 to failure of the pilot flame is obtained.

It will be further apparent that the thermocouple lead 51 is protected by the pipe 5| from the heat of the burner. Furthermore, the flow of the gas and air mixture around the lead 51 keeps it well below the temperature (approximately 600 degrees F.) at which copper starts to oxidize.

While I have shown a speciflc embodiment of my invention for the purpose of illustration it is to be understood that my invention is limited only by the appended claims.

I claim as my invention:

1. A safety pilot for a uid fuel burner control system, comprising a pilot burner having a plurality of apertures in the tip thereof, one of which is located centrally of said tip, and a thermocouple mounted so as to extend asymmetrically through said central aperture, with one junction on the outer side of said aperture and exposed to a flame resulting from fuel issuing through another of said apertures, and the other junction exposed to the unignited fuel flowing to said burner.

2. A safety pilot for a fluid fuel burner control system, comprising a pilot burner having a substantially cylindrical body, a supply pipe for saidl burner, one end of said body engaging said pipe, said body having a transverse wall near -2 said one end, and a substantially conical wall intermediate its ends, said conical wall being coaxial with said cylindrical body, the other end of said cylinder being substantially open, each said wall having a plurality of apertures therethrough, one of said apertures being located substantially centrally of each said wall, and a thermocouple mounted in the central aperture of said transverse wall, and extending through the central aperture of said conical wall, with its hot junction exposed to the pilot burner flame, and its cold junction exposed to the fuel flowing from the supply pipe to the burner.

3. A safety pilot for a fluid fuel burner control system, comprising a pilot burner having a substantially cylindrical body and a substantially conical wall intermediate the ends of said the supply pipe.

4. In combination, a pilot burner having a substantially cylindrical body and a substantially conical Wall intermediate the ends of said body and coaxial therewith, said wall having a flowing through the supply pipe.

5. In combination, a pilot burner comprising a tubular body having an apertured partition therein, means for supplying a fuel mixture of to said tubular body so that when ignited a flame projects from said tubular body starting from said apertured partition, a thermocouple mounted so as to extend through said one junction within said flame and the other junction within said tubular body in the direct path of the unignited fuel flowing through said body, and means projecting from l beyond said apertured partitlon and partially confining the flame so as to direct it against said one junction. i

6. In combination, a pilot burner comprising a tubular body having an apertured partition therein, means for supplying a fuel mixture of gas and air to said tubular body so that when ignited a flame projects from said tubular body starting from said apertured partition, a thermocouple mounted so as to extend through said partition with one junction within said flame and the other junction within said tubular body 1n the direct path `of the unignited fuel flowing through said body, and an open ended housing projecting from said tubular body beyond said apertured partition so as to confine the flame and direct it against said one junction.

7. In combination, a pilot burner comprising a tubular body having an apertured partition therein, means for supplying a fuel mixture of gas and air to said tubular body so that when ignited a flame projects from said tubular body starting from said apertured partition, a thermocouple mounted so as to extend through said partition with one junction within said flame and the other junction within said tubular body in the direct path of the unignited fuel ilowing through said body, and a housing projecting from said tubular body beyond said apertured partition so as to confine the flame and direct it against said one junction, said housing terminating at its outer end in an opening surrounded by an inwardly extending flange which aids in confining said flame.

JOSEPH P. ASHCRAF'I'.