US3764254A - Burner unit for carbonaceous gas waste - Google Patents

Abstract

A burner unit is disclosed which is particularly suitable for use with a furnace for burning carbonaceous waste gases. The air and fuel gas mixture for igniting the burner is mixed at the front end of the burner, to prevent ''''flashback'''' into the burner body. Mounted on the front end of the burner is a closure disc, which is connected into an air operator unit. The air operator unit moves the closure disc backward or forward in response to air pressure fluctuation in the mixing chamber. Moving the disc back and forth regulates the velocity of air which passes through an annular opening defined between the disc and the front end of the burner. Regulating the velocity of the air enables precise control of the firing rate of the burner.

Description

United States Patent 1191 Giadney et al.

[ BURNER UNIT FOR CARBONACEOUS GAS WASTE [75] Inventors: Frank L. Gladney, Freeport;

Michael L. Turner, Lake Jackson, both of Tex.

[73] Assignee: The Dow Chemical Company,

Midland, Mich.

[22] Filed: July 24, 1972 [21] Appl. No.: 274,217

1451 Oct. 9, 1973 3,486,834 12/1969 Frey et a1 431/12 Primary Examiner-Edward G. Favors Attorney-William M. Yates et al.

[57] ABSTRACT A burner unit is disclosed which is particularly suitable for use with a furnace for burning carbonaceous waste gases. The air and fuel gas mixture for igniting the burner is mixed at the front end of the burner, to prevent flashback into the burner body. Mounted on the front end of the burner is a closure disc, which 52 U.S. c1. 431/89, 431/181 is connected into an air Operator unit- The air w [51] Int. Cl. F23n 1/02 tor unit moves the closure disc backward or forward 58 Field of Search 431/89, 12, 181 in response to air pressure fluctuation in the mixing chamber. Moving the disc back and forth regulates the 5 References Cited velocity of air which passes through an annular open- UNITED STATES PATENTS ing defined between the disc and the frontend of the 3 135 314 6/1964 Bummer 431,12 burner. Regulating the velocity of the air enables pre- 3,217,779 11/1965 Reed et al... 431/181 use control the finng rate of the burner 3,315,726 4/ 1967 Williams 431/89 3 Claims, 2 Drawing Figures F Fue/ air 10 PATENTEU URI 9 I973 NQ C BURNER UNIT FOR CARBONACEOUS GAS WASTE BACKGROUND OF THE INVENTION Various chemical products, such as chlorinated solvents, are obtained by the chlorination of methane or higher hydrocarbons. One of the waste products left over from the reaction process is a mixture of carbonaceous gases. Since it is undesirable to discharge the chlorinated gas waste into the atmosphere, it is usually disposed of by burning in a furnace with a sealed combustion chamber.

Typical conventional burners which are used to ignite the waste gas mixture are units usually referred to as fixed flow" burners. The fixed flow burners, however, have certain drawbacks when employed in a furnace for burning carbonaceous gas waste. One disadvantage is that the fuel mixture will usually pre-ignite within the body of the burner. This occurrence, which is generally referred to as flashback, frequently results in premature burnout of the burner body. Another drawback is that the burner tip is constructed with a perforated screen inserted therein, which is always open to the furnace combustion chamber. As the waste mixture burns, therefore, it develops an extremely high temperature and the resulting heat will back up through the screen into the burner body.

SUMMARY OF THE INVENTION In the present burner unit, the chamber for mixing the fuel gas and air has an open front end and a closed rear end. In use, the burner is mounted on a furnace with the front end in communication with the combustion chamber of the furnace. A tube sheet is positioned cross-wise in the mixing chamber between the front and rear end. A front compartment is defined in the mixing chamber by the space between the front end and the tube sheet. The space between the tube sheet and the rear end provides a rear compartment.

Positioned in the front compartment of the mixing chamber is a tube bundle, made up of several spaced apart, parallel open end tubes. The rear end of each tube fastens into the tube sheet, so that the open end communicates with the rear compartment. The opposite open end of each tube is in communication with the front compartment. Fuel gas is conducted into the rear compartment through a fuel gas inlet conduit. A similar inlet conduit conducts air into the front compartment.

A pilot tube, open at both ends, is slidably mounted on the tube sheet and rear end of the mixing chamber. This tube, which extends centrally through the rear and front compartments of the mixing chamber, carries a fuel-gas air mixture into the furnace for the pilot flame. Mounted on the front end of the slidable pilot tube is a closure disc with a central opening therein. The closure disc can be moved backward or forward, to close or open the front end of the mixing chamber, in response to air pressure fluctuation in the chamber.

Connected into the rear end of the pilot tube is a pilot fitting, with an inlet conduit for carrying a fuel gas-air mixture into the fitting. An ignitor fitting, which connects into the pilot fitting, includes separate inlets for conducting air and fuel gas into the fitting. The ignitor fitting includes a means for igniting the fuel gas-air mixture. An ignitor tube is provided by a small tube, open at both ends, which extends centrally through the pilot fitting and pilot tube. The rear end of the ignitor tube 2 connects into the ignitor fitting and the front end is flush with the front end of the opening in the closure disc. The purpose of the ignitor tube is to carry the ignited fuel mixture from the ignitor fitting into the furnace combustion chamber.

DESCRIPTION OF THE DRAWINGS FIG. 1 is a top plan view, partly in section, of one embodiment of the burner unit of this invention. In FIG. 1 the burner unit is shown installed in a typical operating position in the combustion chamber of a furnace.

FIG. 2 is a cross-section view, taken on line 22 of FIG. 1, looking toward the front end of the burner unit.

DESCRIPTION OF A PREFERRED EMBODIMENT Referring particularly to FIG. I of the drawing, the burner unit is indicated generally by numeral 10. The main part of burner 10 comprises a fuel mixing chamber 11, which has an open front end 12 and is closed at the rear end by a cover plate 13. In a typical use, the burner 10 is mounted in the combustion chamber of a furnace. As shown in FIG. 1 the burner 10 is mounted on a wall 14 of the furnace combustion chamber, with the open front end 12 being in communication with the combustion chamber of the furnace.

A tube sheet 15 is positioned crosswise in mixing chamber 11 and it is spaced from each end of the chamber. Tube sheet 15 is held in place in mixing chamber 11 by being clamped between opposing flange members 16 and 17 on chamber 11. A rear compartment 18 in mixing chamber 11 is defined by the space between tube sheet 15 and cover plate 13. Also, a front compartment 19 is defined by the space between tube sheet 15 and the front end 12 of chamber 11.

Positioned inside the mixing chamber 11 is a tube bundle. The tube bundle is made up of several open end tubes 20, which are positioned in spaced apart, parallel relation. Each tube 20 is connected at the rear end into tube sheet 15, so that one open end of each tube is in communication with rear compartment 18. From tube sheet 15 the tubes 20 extend lengthwise into the front compartment 19 of mixing chamber 11, so

that the opposite open end of each tube communicates with compartment 19,

An inlet conduit 21 is connected into rear compartment 18 between flange 16 and rear cover plate 13. Conduit 21 provides a means for conducting a fuel gas into rear compartment 18. A second inlet conduit 22 is connected into the front compartment 19 between flange l7 and a mounting flange 23, by which burner 10 is fastened to the furnace wall 14. Conduit 22 provides a means for conducting air into the front compartment 19.

Means for carrying a fuel gas-air mixture into the furnace combustion chamber, to initiate a pilot flame, is provided by a pilot tube 24, which is open at both ends. The pilot tube 24 is slidably mounted on tube sheet 15 and on rear cover plate 13, the tube being carried by the front end opening 12 in mixing chamber 11. Con versely, by moving the pilot tube 24 forward, disc 26 will disengage from the front end opening 12 in chamber 11. The rear end of pilot tube 24 is connected into one branch of a cross fitting 27, which functions as a pilot fitting. A fuel gas-air mixture is directed into pilot fitting 27 through an inlet conduit 28, which is connected into a second branch of fitting 27. Pilot fitting 27 also includes a thermocouple sensor 29, which is connected into a third branch of the fitting directly opposite to inlet conduit 28.

Connected into the fourth branch of pilot fitting 27, which is opposite to the pilot tube connection, is the front end of an ignitor fitting 30. Basically, the ignitor fitting 30 consists of a coupling which is threaded on both ends, with a central lengthwise bore 31 therein, which intersects a crosswire bore 32 near the rear end of the fitting. An inlet conduit 33, which is connected into one end of bore 32, is for directing a fuel gas into the bore 31 in fitting 30. Connected into the opposite end of bore 32 is a second inlet conduit 34, through which air is directed into bore 31 of fitting 30. Means for igniting the fuel gas-air mixture in fitting 30 is provided by a spark plug 35, which is mounted in the fitting with the electrodes seated in bore 31. An electrical lead 36 connects the spark plug 35 into a source of power (not shown).

A small diameter, open end ignitor tube 37 provides means for carrying the ignited fuel gas-air mixture from fitting 30 into the furnace combustion chamber. The rear end of tube 37 is fitted into bore 31 of fitting 30. From fitting 30 the tube 37 extends centrally through the pilot fitting 27 and pilot tube 24, with the front end being flush with the front end of opening 26a in disc 26. The rear end of ignitor fitting 30 is connected to a piston rod 38, which operates a diaphragm plate (not shown) inside an air operator unit 39. Piston rod 38 is slidable within a collar 40, which is mounted at the base of the air operator unit 39.

Fastened to opposite sides of collar 40 are arm members 41 and 42, which are attached to leg members 43 and 44. In the unit illustrated herein each of the leg members 43 and 44 comprises two separate pieces of angle iron which are slidably connected. The leg members are slidably connected to permit back and forth movement of closure disc 26. The end of each leg member which is opposite to collar 40 is fastened to the rear end of mixing chamber 11 adjacent to cover plate 13. The combined structure of arm members 41 and 42 and leg members 43 and 44 defines a yoke member for attaching the air operator unit 39 to mixing chamber 11.

A pneumatic multiplying relay 45 provides means for actuating the air operator unit 39 in response to air pressure fluctuation in the front compartment 19 of mixing chamber 11. The air pressure fluctuation in compartment 19 is monitored by relay 45 through an air line 46, which connects the relay into air inlet conduit 22. The air pressure signal received by relay 45 is multiplied by the relay and sent through a second air line 47 to another pneumatic relay (not shown) in air operator unit 39. Regular instrument air required by the relay 45 is directed into the instrument through a third air line 48.

In one example of the practice of this invention, the burner unit is used to ignite a waste product which comprises a mixture of carbonaceous gases. In carrying out the operation, the waste gas is first directed into a furnace combustion chamber in which the burner unit 10 is installed. To initiate a starter flame, a mixture of fuel gas and air is directed into bore 31 of ignitor fitting 30, through the fuel inlet conduit 33 and air inlet conduit 34. Spark plug 35 is then fired to ignite the fuel mixture and the flame is propagated through ignitor tube 37, so that the flame burns at the front edge of opening 26a and closure disc 26.

In the event the starter flame is not being propagated through ignitor tube 37, the tube will not heat up. If the starter flame should go out, therefore, the thermocouple 29 will immediately sense the drop in temperature, so that corrective action can be taken. With regard to igniting the starter flame, this can be done by ignition means other than spark plug 35. For example, any device suitable for igniting a fuel gas mixture may be used. Also, as an alternative procedure, the starter flame can be ignited by positioning the ignitor device immediately adjacent to the front opening in ignitor tube 37. Once the starter flame is lit, a second fuel gasair mixture is directed into pilot fitting 27 through inlet conduit 28. The resulting fuel mixture travels forward through pilot tube 24, around ignitor tube 37, and is ignited by the starter flame at the front edge of opening 26a. The second flame then functions as a pilot flame.

After the pilot flame is lit, a charge of fuel gas is directed into the rear compartment 18 of mixing chamber 1 1 through the fuel gas inlet conduit 21. From compartment 18 the fuel gas travels through the tubes 20 and spills out into the front compartment 19 of chamber 11 immediately behind the closure disc 26. Simultaneously, a volume of air is directed into compartment 19 through air inlet conduit 22. As the air and fuel gas mix in compartment 19, the mixture is ignited by the pilot flame to initiate the burner flame. The burner flame, in turn, ignites the gaseous mixture in the furnace combustion chamber.

Once the burner flame is lit, the flame is sustained by closely controlling the firing rate of the burner. Specifically, the firing rate is controlled by regulating the velocity of the air which passes through the annular opening between the periphery of closure disc 26 and the inner wall surface of the open front end 12 of mixing chamber 11. For example, if the air velocity pouring through this annular opening should get too high, it will extinguish the burner flame, which is actually burning at the outside face of closure disc 26. In such a situation, the rapidly increasing air velocity will build up a back pressure in compartment 19 of mixing chamber 11. To correct the situation, the air pressure is constantly monitored by multiplier relay 45 through air line 46 into conduit 22. Once the air pressure in conduit 22 exceeds a predetermined level, therefore, which is set in relay 45, the air signal will actuate the relay.

The relay 45, in turn, multiplies the air signal and sends it through the air line 47 into the air operator unit 39. In unit 39 the air signal triggers a second relay, which operates a diaphragm assembly to push piston rod 38 forward. In its forward movement, the piston rod 38 pushes the pilot tube 24 and closure disc 26 forward to increase the size of the annular opening at the front end of mixing chamber 11. Increasing the size of the annular opening, therefore, reduces the air velocity to a level low enough to sustain the burner flame.

If a condition of no air pressure should occur in front compartment 19, during operation of burner 10, the air operator unit 39 will pull the closure disc 26 backward to close off the front opening of the burner from the furnace. Such a condition can occur, for example, if there is a malfunction in the air system, or if the burner is turned off. In practice, for example, the burner opening is usually closed off when the burner is not operating. This is done to protect the inner structure of mixing chamber 11 from the furnace flame, so as to prolong the life of the burner.

One example of a fuel which may be used in the burner unit of this invention, is a mixture of air and methane gas. In general, a satisfactory burner flame is achieved by mixing the fuel and air in approximately stoichiometric proportions. A particular advantage of the present burner over the fixed flow burners is that it can operate over a wide range of heat release and throughput. in practice, the present burner unit was operated at a maximum heat release of about 2.07 million Btu/hr., which corresponds to a throughput of about 2,298 SCFl-l of methane and 21,905 SCFH of air. The minimum of heat release was determined to be about 20,000 Btu/hr., which is equivalent to a throughput of about 22.2 SCFl-l of methane and 211 SCI-H of air.

What is claimed is: I

1. A burner unit for use with a furnace for burning combustible gases, which includes:

a. a fuel gas mixing chamber having an open front end and a closed rear end, the burner unit being adapted for mounting on a furnace with the open front end of the mixing chamber in communication with the combustion chamber of the furnace;

b. a tube sheet positioned crosswise in the mixing chamber and spaced from each end of the chamber;

c. a rear compartment in the mixing chamber defined by the space between the tube sheet and the rear end of the chamber;

d. a front compartment in the mixing chamber defined by the space between the tube sheet and the front end of the chamber;

e. a tube bundle comprising several open end tubes in spaced apart, parallel relation, each tube being connected at one end into the tube sheet, such that one open end of each tube communicates with the rear compartment of the mixing chamber and the opposite open end of each tube communicates with the front compartment of said mixing chamber;

f. a fuel gas inlet conduit connected into the rear compartment of the mixing chamber, which is adapted for conducting a fuel gas into said rear compartment;

g. an air inlet conduit connected into the front compartment of the mixing chamber, which is adapted for conducting air into said front compartment;

h. a pilot tube which has an open front end and an open rear end, which is slidably mounted on the tube sheet and the rear end of the mixing chamber, which extends centrally through the rear compartment and the front compartment of the mixing chamber, and which is adapted for conducting a fuel gas-air mixture into the furnace combustion chamber;

i. a closure disc which is mounted on the front end of the slidable pilot tube, which has a central opening therein that joins into the front end of the pilot tube, which can move backward with the slidable pilot tube to seat into and close the front end opening in the mixing chamber, and which can move forward with the slidable pilot tube to disengage from the front end opening in the mixing chamber;

j. a pilot fitting connected into the rear end of the pilot tube, including an inlet conduit therein for conducting a fuel gas-air mixture into said pilot fitting;

k. an ignitor fitting which is connected into the pilot fitting, which has a fuel gas inlet conduit therein for conducting a fuel gas into the ignitor fitting, which has an air inlet conduit therein for conducting air into said ignitor fitting, and which includes a means mounted in the ignitor fitting for igniting the fuel gas-air mixture directed into said fitting;

1. an ignitor tube which has an open front end and an open rear end, which extends centrally through the pilot fitting and the pilot tube, with the rear end being connected into the ignitor fitting and the front end being flush with the front end of the opening in the closure disc, and which is adapted to carry the ignited fuel mixture from the ignitor fitting into the furnace combustion chamber.

2. The burner assembly of claim 1 including an air operator unit which is operatively connected into the air inlet conduit in the mixing chamber and into the pilot tube, the said air unit providing means for automatically moving the pilot tube and closure disc backward or forward in response to air pressure fluctuation in the front compartment of the mixing chamber.

3. The burner unit of claim 1 which includes a temperature sensor connected into the pilot fitting, the sensor providing means for detecting a temperature change in the ignited fuel mixture in the ignitor tube.

Claims (3)

1. A burner unit for use with a furnace for burning combustible gases, which includes: a. a fuel gas mixing chamber having an open front end and a closed rear end, the burner unit being adapted for mounting on a furnace with the open front end of the mixing chamber in communication with the combustion chamber of the furnace; b. a tube sheet positioned crosswise in the mixing chamber and spaced from each end of the chamber; c. a rear compartment in the mixing chamber defined by the space between the tube sheet and the rear end of the chamber; d. a front compartment in the mixing chamber defined by the space between the tube sheet and the front end of the chamber; e. a tube bundle comprising several open end tubes in spaced apart, parallel relation, each tube being connected at one end into the tube sheet, such that one open end of each tube communicates with the rear compartment of the mixing chamber and the opposite open end of each tube communicates with the front compartment of said mixing chamber; f. a fuel gas inlet conduit connected into the rear compartment of the mixing chamber, which is adapted for conducting a fuel gas into said rear compartment; g. an air inlet conduit connected into the front compartment of the mixing chamber, which is adapted for conducting air into said front compartment; h. a pilot tube which has an open front end and an open rear end, which is slidably mounted on the tube sheet and the rear end of the mixing chamber, which extends centrally through the rear compartment and the front compartment of the mixing chamber, and which is adapted for conducting a fuel gas-air mixture into the furnace combustion chamber; i. a closure disc which is mounted on the front end of the slidable pilot tube, which has a central opening therein that joins into the front end of the pilot tube, which can move backward with the slidable pilot tube to seat into and close the front end opening in the mixing chamber, and which can move forward with the slidable pilot tube to disengage from the front end opening in the mixing chamber; j. a pilot fitting connected into the rear end of the pilot tube, including an inlet conduit therein for conducting a fuel gas-air mixture into said pilot fitting; k. an ignitor fitting which is connected into the pilot fitting, which has a fuel gas inlet conduit therein for conducting a fuel gas into the ignitor fitting, which has an air inlet conduit therein for conducting air into said ignitor fitting, and which includes a means mounted in the ignitor fitting for igniting the fuel gas-air mixture directed into said fitting; l. an ignitor tube which has an open front end and an open rear end, which extends centrally through the pilot fitting and the pilot tube, with the rear end being connected into the ignitor fitting and the front end being flush with the front end of the opening in the closure disc, and which is adapted to carry the ignited fuel mixture from the ignitor fitting into the furnace combustion chamber.

2. The burner assembly of claim 1 including an air operator unit which is operatively connected into the air inlet conduit in the mixing chamber and into the pilot tube, the said air unit providing means for automatically moving the pilot tube and closure disc backward or forward in response to air pressure fluctuation in the front compartment of the mixing chamber.

3. The burner unit of claim 1 which includes a temperature sensor connected into the pilot fitting, the sensor providing means for detecting a temperature chanGe in the ignited fuel mixture in the ignitor tube.

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