US3202139A

US3202139A - Method and apparatus for operating furnace

Info

Publication number: US3202139A
Application number: US173204A
Authority: US
Inventors: William L Livingston; Mathew P Stengel; Larry D Mcnair
Original assignee: Combustion Engineering Inc
Current assignee: Combustion Engineering Inc
Priority date: 1962-02-14
Filing date: 1962-02-14
Publication date: 1965-08-24
Anticipated expiration: 1982-08-24
Also published as: SE327250B; GB967420A

Description

1965 w. 1.. LIVINGSTON ETAL 3,202,139

METHOD AND APPARATUS FOR OPERATING FURNACE Filed Feb. 14, 1962 2 Sheets-Sheet l F'ICBJ INVENTORS WILLIAM L.. LIVINGSTCiN MATHEW P- STENGEL. -L.ARRY D- McNAIR [jun 013% ATTORNEY w. L. LIVINGSTON ETAL 3,202,139

METHOD AND APPARATUS FOR OPERATING FURNACE 2 Sheets-Sheet 2 Aug. 24, 1965 Filed Feb. 14, 1962 INVENTORS WILLIAM L. L'VINGSTON MATHEW P 'STENGEL. LARRY D- MNA|R ATTORNEY United States Patent 3,202,139 METHUD AND APrAuATUs FOR orEnAriNo FURNACE William L. Livingston, Bloomfield, Mathew P. Stengel,

This invention relates generally to an improved method of and apparatus for operating a furnace, such as that of a steam generator, and has particular relation to such a method and apparatus for preventing the build up of a flammable fuel-air atmosphere in the furnace incident to a furnace flame-out.

It is the present practice in furnace firing techniques to monitor the burning of the fuel in the furnace by means of a flame detector and in response to a flame-out as d tected by this device to trip the fuel supply or in other words stop the introduction of fuel to the furnace. The

supply of air is generally continued in an effort to purge flawless procedure when the flame-out is due to, or there exists in the furnace, an air rich mixture of fuel and air. However if the cause of the flame-out is an excess of fuel or if there exists in the furnace at the time of flame-out a fuel rich mixture of fuel and air then the procedure of stopping the fuel supply while continuing the air supply is extremely dangerous in that an explosive atmosphere in the furnace will be produced as a result of operating in this manner. Flame detectors are unable to determine the cause of a flame-out in the furnace. They are merely able to determine that the fire has been extinguished with the cause of the extinguishment thereof being undetermined. As a result of this limitation with regard to flame detectors, there is a grave risk involved in tripping the fuel While maintaining the air supply in response to the flame detector signaling that the flame has been extinguished. In accordance with the present invention there is provided a completely safe method and system for operating the furnace incident to a flame-out with the method and system preventing the development in the furnace of an atmosphere which is in the flammable zone and accordingly explosive. In accordance with the method and sys tern of the invention the fuel supply is terminated and the air supply is terminated or at least greatly reduced immediately upon the detection of the loss of flame in the furnace and along with thus manipulating the fuel and air supply an inert gas is introduced into the furnace with the introduction of the gas being suflicient in quantity and time to insure that the atmosphere in the furnace will be nonflamrnable regardless of the fuel-air ratio in this atmosphere. It is essential that the introduction into the furnace. of fuel be terminated and of air be greatly re- 'duced or terminated quickly, preferably in about one second after fiameout. Since it is difiicult to stop or greatly reduce the supply or air to the furnace in such a short time, it is preferred to introduce the inerting gas, which is at a relatively high pressure into the air supply duct with this introduction having the effect of completely or substantially blocking the supply of air and having the further effect of introducing the inert gas into the furnace through the air supply ports or passages of the burner or burners. By introducing the inert gases in 3,2h2,l39 Patented Aug. 24, 1965 2 this fashion this gas will follow the same path as the air which was supplied to the furnace having a similar mixing with the atmosphere in the furnace and the same sweeping action of the furnace so as to prevent the formation or build-up of isolated pockets of fuel and air undiluted by this inert gas.

The invention has particular application to the furnaces of steam generators since in a steam generator there is readily available a high pressure steam source which may be utilized as a source of inerting gas to inert the furnace in the event of a loss of the flame in the furnace, such an arrangement is extremely economical and convenient and is a very effective way to inert the furnace atmosphere.

- Accordingly,- it is an object of the invention to provide an improved method and system for operating a furnace wherein the furnace is inerted by an inert gas incident to flame-out thereby preventing the formation of an explosive atmosphere in the furnace.

Other and further objects of the invention will become apparent to those skilled in the art as the description proceeds.

With the aforementioned objects in view, the inven tion comprises an arrangement, construction and combination of the elements of the inventive organization in such a manner as to attain the results desired as hereinafter more particularly set forth in the following detailed description of an illustrative embodiment, said embodiment being shown by the accompanying drawings wherein:

FIG. 1.is a view of a steam generator employing the present invention and being in the nature of a vertical section with this view being diagrammatic in nature;

FIG. 2 is a ectional view taken generally along line 2-2 of FIG. 1 and showing the firing arrangement of the furnace;

FIG. 3 is a detailed sectional view showing the burner and air duct disposition in one corner of the furnace and the position of theinerting distribution pipe in the air duct; and

FIG. 4 is a graphic representation showing the resulting fuel-air mixture produced in the furnace incident to various procedures of operation after a flame-out.

Referring now to the drawings, wherein like reference characters are used throughout'to designate like elements, the illustrative and preferred embodiment of the inven tion as depicted therein includes a steam generator having a furnace fit into which fuel and air are introduced through the burners or burner assemblies 12 located in each corner of the furnace in the burner zone, with the fuel being burned in the furnace and the combustion gases produced by burning of the fuel passing upwardly therethrough and then down through the gas pass 14 and the air heater 16 which may be of the rotary regenerative or other suitable type. From the air heater the gases pass through the induced draft fan 52 to a final point of discharge such as a stack.

The steam generating circuit of the steam generatorineludes the economizer 13 through which feedwater is forced by means of pump 2i) with the effluent from the economizer being conveyed to the chamber 22 by conduit 24. From chamber 22 the working fluid of the steam generator passes down through conduit 26 and then up through the tubes 27 which line theinner surface of the walls of the furnace. From these tubes the Workmg fluid is conveyed to the chamber 22 through conduit 28. Steam is conveyed through conduit 30 to the superheater section 32 and then to the superheater section 34 with this steam after being superheated to its desired temperature being conveyed through conduit 36 to a desired point of use such as a turbine.

Although the invention may be used with a variety of firing arrangements such as front wall, cyclone and others,

v for the purpose of illustrating the invention the tangential firing system has been chosen. In this system a plurality of burners or burner assemblies, identified as 12 in the drawing, are disposed at symmetrical locations about the furnace, such as at the corners, with the burners directing streams of fuel and air tangent to an imaginary centrally located vertical cylinder 37 in the furnace thereby creating a whirling action and a rapidly rotating burning mass within the furnace.

In the illustrated tangential firing system each of the burners or burner assemblies 12 (which may be similar to the burner assemblies disclosed in US. Patent 2,697,- 422 of December 21, 1954) include fuel nozzles 38, there being a plurality of such nozzles in each assembly 12, which nozzles receive a supply of pulverized coal from the pulverizing mill 4%). This coal is conveyed from the mill through distribution duct 42 which delivers it to the various nozzles in the burner assemblies 12.

Also provided in the burner assemblies are the air directing nozzles 44 which direct the streams of air into the furnace as previously mentioned. These nozzles receive their air supply from a suitable duct or windbox 4.6 and heated air is supplied to this duct from the air heater 1d through connecting duct work 50. In the illustrative arrangement a forced draft fan 48 is employed to force the air through the air heater 16 and connecting duct work Stl to the duct or windbox 46. However, in lieu of the forced draft fan and the forced draft system disclosed, a suction firing system may be utilized which does not require a forced draft fan but rather requires only the induced draft fan 52. An induced draft fan is generally employed in a forced draft system, although, if desired, it may be eliminated.

The supply of pulverized coal to the burners 12 may be controlled by means of the conventional regulatable feeder 53 that feeds the mill. Quick termination of the delivery of fuel to the burners may be assisted by means of the damper 54 positioned in the duct 42 and/or by means of the drive motor 56 for the pulverizer with the damper being moved to the closed position and/ or motor 56 being deactivated when it is desired to terminate the fuel supply.

In an effort to control the supply of air to the burners the motor operated damper 58 may be positioned in the duct 50 and additionally the motor for the forced draft fan 48 may be controlled.

In order to determine whether or not a flame is present in the furnace there is provided a flame detector 60 which may take a variety of forms with there being a number of types of detectors currently utilized to detect the presence or absence of flame in the furnace some of which operate on the principle of sensing the light emitted from the flame while others respond to the conductivity of the flame and still others respond to the ultra violet radiation emitted by the flame. These flame detectors provide a signal which indicates when a flame-out occurs with this signal being received by the controller 62. When such a signal is received, the supply of fuel to the furnace is immediately terminated and the supply of air is immediately terminated or greatly reduced and steam is introduced into the furnace through the nozzles that were previously utilized to direct the air into the furnace. To accomplish this result conduit 64 is connected with the steam pipe or conduit and with the distributors 66. These distributors are elongated hollow tubes or cylinders which extend down into and across the width of the air ducts or windbox 46 adjacent each of the burner assemblies 12 and have openings distributed throughout their length. When high pressure steam of pounds per sq. in. or higher is supplied to these distributors it effectively blocks or substantially completely blocks the flow of air even without the de-energization of forced draft fan 48 or the closing of the damper 58 thereby providing a very rapid termination or substantial reduction of the air supply to the furnace which is essential and otherwise difi'icult to achieve because of the inertia of fan 58 and the time required to operate the large damper S3 and because of the leakage past damper 58. The steam is supplied in such quantity and at such pressure that it effects this result with the steam filling the windbox and being directed into the furnace through the nozzles 44. The supply of steam to the distributors 66 is controlled by means of the valve 68 in the conduit 64. Upon receipt of a flame-out signal from the flame detector 6% the controller 62 quickly causes the valve 68 to open through the actuator '76 with this valve being normally closed but having a quick opening action. Also incident to receipt of this signal the controller 62 causes the supply of fuel to the furnace to be terminated through shutting down of feeder 53 and also, if desired, closing of damper 54- by motor '72 and/ or deactivation of drive motor 56 for the pulverizer. In addition the controller will cause damper 58 to be moved to a closed position by motor '74 and/ or cause the drive motor '76 of the forced draft fan 48 to be deactivated. The induced draft fan 52 is maintained in operation after fiame-out and while the inert gas is supplied to the furnace.

With this method and system of operation, upon detecting a flame-out in the furnace regardless of the cause f the flame-out, i.e., whether due to a fuel rich mixture, an air rich mixture or other causes, the supply of fuel will be immediately terminated and the supply of air terminated or greatly reduced and the furnace will be inerted by introducing inert gas thereinto through the previously employed air introduction nozzles or means. Even though there may be some air introduced into the furnace with the inert gas the oxygen concentration of the mixture will be well below the lower limit required for flammability of the fuel fired. The introduction of the inert gas through the air nozzles tends to prevent the formation of isolated fuel-air pockets in the furnace since the inert gas then follows the same path as the fuel and air that were introduced into the furnace and accordingly has the same mixing and sweeping action on the furnace atmosphere as was had by the fuel and air. The intro duction of inert gas into the furnace is maintained for a sufficient time and suflicient gas is introduced to insure that an explosive furnace atmosphere cannot be developed regardless of the ratio of fuel to air in this atmosphere. It is preferable that there be suflicient inert gas introduced so that 12 to 15 changes of furnace atmosphere are provided after the fuel and air feed has been stopped.

The arrangement with regard to a steam generator wherein steam is utilized as the inerting gas provides an ideal system and method since the steam supply at substantial pressure is readily available and is very well suited for inerting the furnace. This particular system or combination is accordingly both reliable in operation and economic to install or set up with it being a relatively simple task to modify an existing steam generator unit in a manner to utilize this inerting method and system with it being unnecessary to provide a special and extensive storage facility for storing the gas to be used for inerting.

Considering now the graphical representations of FIG. 4, this figure illustrates how explosive atmospheres may be formed in the furnace after a fiameout when following certain procedures. From this illustration it is evident that with the inerting method and system of the invention an explosive atmosphere is prevented from forming regardless of the cause of the flame-out while such is not the case with other procedures under various operating conditions. The abscissa of the FIG. 4 curve is graduated to represent both theoretical air and excess air. The percent of theoretical air ranges from zero at the extreme left of the abscissa (where the percent of fuel-air mixture is infinity) to infinity at the extreme right end (where the percent of fuel-air mixture is zero The percentage of excess air ranges from zero at the location of percent theoretical air to 100 at the location of 200 percent theoretical air. The ordinate of this graph or curve represents percentages of inerts in the furnace atmosphere. The curve as identified concerns a methaneair mixture.

Assuming a flame-out at the point '73 resulting from an excess of fuel, in one second the characteristic of the furnace atmosphere will descend along the line 78a to the point 78. If the flame detector has in this time detected the flame-out, tripped the fuel and air supply, and activated the inerting system, the characteristics of the furnace atmosphere will then be represented by the line 785, with each of the points on this curve 78b (as will all the curves) being approximately one second apart with regard to time. This curve 78b extends upwardly from the point 73 into the increasingly inert zone so that no flammable methane-air mixture is formed in the furnace atmosphere. If, instead of tripping the fuel and air and activating the inert system, the procedure that is followed is to trip the fuel but leave the air supply on and provide no inert gas, then the characteristics of the furnace atmosphere will follow the curve 78c which extends through the flammable zone and accordingly produces an explosive atmosphere in the furnace. If the air is tripped but the fuel is left on and no inert gas is provided the furnace atmosphere characteristics will be those represented by the curve 78d. If both the fuel and air are left on and the inerting system is not activated the furnace atmosphere would have the characteristic represented by the curve 782. If the fuel is tripped, the air left on and the inerting system activated the furnace atmosphere will have the characteristic represented by the curve 781. If the air is tripped, the fuel left on and the inerting system activated, the furnace atmosphere will have the characteristic represented by the curve 78g.

Assuming a flame-out at the point 8t) where there is an excess of air, the furnace atmosphere will have the characteristic represented by the curve 8% and in one second Will be at the point 80'. From this point, as in the previously explained set of curves the furnace atmosphere will have the characteristics represented by the curve 30b if the fuel and air are tripped and the inerting system is activated; curve 8th: indicates the furnace atmosphere characteristics after fuel is tripped but the air left on and inerting system is not activated; 89d is the curve provided when the air is tripped but the fuel is left on and the inerting system is not activated with an explosive atmosphere resulting; curve dtie represents the furnace atmosphere characteristics when the fuel and air are left on and the inerting system is not activated; curve 8%)) represents the furnace atmosphere when the fuel is tripped, the air is left on and the inerting system is activated; and curve titlg indicates the atmosphere characteristics when the air is tripped, the fuel is left on and the inerting system activated.

Assuming that a flame-out occurs at point 82, again because of an excess of air, in one second the furnace atmosphere will have the characteristic represented by the point 82' and if the various procedures mentioned in describing the previous two sets of curves are followed the furnace atmosphere characteristics will fall along the various curves extending from this point 82 with the legend on the FIG. 4 curve sheet indicating the procedure followed to produce the various atmosphere characteristics.

Although only three flame-out points have been represented on the FIG. 4 curve sheet, the initial flame-out can occur throughout a range of inert concentrations of the furnace atmosphere so that position of the initial flame-out composition along the ordinate of the curve or plot of FIG. 4 is a factor that may vary.

It is thus evident that with the invention assurance is provided that an inflammable atmosphere will not be produced in the furnace after flame-out which might otherwise not be the case.

While we have illustrated and described a preferred 6 embodiment of our invention it is to be understood that such is merely illustrative and not restrictive and that variations and modifications may be made therein without departing from the spirit and scope of the invention. We therefore do not wishto be limited to the precise details set forth but desire to avail ourselves of such changes as fall within the purview of our invention.

What we claim is:

1. In the operation of a furnace into which fuel and air are introduced and the fuel burned the method comprising continuously monitoring the burning of fuel in the furnace and in response to and directly after a flameout terminating the'fuel supply and substantially reducing the air supply to the furnace and introducing an inert gas thereinto in sufiicient quantity and for a suflicient time to insure nonflammability of the furnace contents. 2. The process comprising providing a stream of air,- introducing this air along with fuel into a confined volume and burning the fuel therein with the air supporting combustion thereof, continuously determining whether or not the fuel is burning and in response to the burning ceasing, discontinuing the introduction of said fuel, introducing an inert gas into the air stream to effectively block said stream and introducing the inertgas into said confined volume to insure that the contents thereof is nonflammable.

3. In the operation of a furnace into which fuel is introduced and also into which combustion supporting an is introduced with the fuel being burned therewithin the process comprising continuously determining whether or not the fuel introduced into the furnace is being burned therewithin and providing a signal indicative of a failure of burning, in response to this signal terminating the introduction of fuel and at least substantially reducing the air introduction into the furnace and introducing inert gas thereinto in sufficient quantity to insure that the contents in the furnace are nonflammable.

4. In a steam generator including a furnace into which fuel and combustion supporting air are introduced with the fuel being b u rned therewithin and with the heat evolved being utilized to generate high pressure steam, the process comprising continuously determining whether or not the fuel introduced into the furnace is burning therewithin and upon and in response to cessation of burning of the fuel terminating the fuel supply and at least substantially reducing the air supply and introducing sufficient of the high pressure steam into the furnace to insure that the contents of the furnace are nonflammable.

5. The process comprising creating a mass of burning fuel by supplying fuel and combustion supporting air to a burning zone, utilizing a portion of the heat evolved from this burning fuel to generate high pressure steam, monitoring the burning of the fuel in said combustion zone and in response to and directly after a flame-out terminating the supply of fuel and at least substantially reducing the supply of air to the zone and introducing the high pressure steam into the zone trough the location at which air was supplied to the zone.

6. The process comprising forming a stream of air and introducing this air along with fuel into a confined volume and burning the fuel therewithin with the air supporting combustion thereof, generating high pressure steam by imparting a portion of the heat thus evolved to water to vaporize the same, continuously determining the presence of flame in the confined volume and in response to and directly after a flame-out discontinuing the introduction of fuel into said volume, introducing the high pressure steam into the air stream to substantially block said air stream and introducing said steam into the confined volume to insure that the contents thereof with there being a steam generating circuit associated With the furnace to produce high pressure steam, the method of operation comprising continuously determining whether or not the fuel introduced into the furnace is burning therewithin and in response to and in the event of a flame-out terminating the introduction of the fuel and introducing high pressure steam into the air supply duct in such a manner as to substantially block the introduction of air into the furnace and introduce the steam into the furnace at the location of the previous air introduction.

In the operation of a furnace of a steam generator Where fuel and combustion supporting air are introduced into the furnace and a portion of the heat evolved used to generate high pressure steam, the improvement characterized by continuously detecting the presence or absence of'iiarne in the furnace during the supply of fuel and air thereto, in response to a flame-out providing a signal indicative of said flame-out, in response to said signal simultaneously terminating the introduction of fuel and at least substantially reducing the introduction of air into the furnace and introducing the high pressure steam produced by the steam generator into the furnace so as to insure that the contents in the furnace are not flammable.

9. The combination comprising a furnace, means for introducing fuel into the furnace, means for introducing into the furnace air to support combustion of said fuel, flame detector means, a supply of inert gas, means for introducing said gas into the furnace and means responsive to said flame detector means effective to control the supply of fuel and air to the furnace and the introduction of inert gas thereinto to terminate said fuel and at least substantially reduce the air supply and introduce said inert gas into the furnace in the event of a flame-out in the furnace. I

10. A steam generator comprising in combination a furnace, steam generating means associated with the furnace and etfective to generate high pressure steam, means for introducing fuel into the furnace, means for introducing combustion supporting air into the furnace, flame 40 detector means, means for conveying high pressure steam generated in the steam generating means to and introduce the same into the furnace, and means operative effectively controlled by the fiame detector means to prevent the introduction of high pressure steam thereinto during the presence of flame in the furnace but prevent the introduc-' tion of fuel into the furnace and initiate the introduction of high pressure steam thereinto in response to a flameout in the furnace.

11. In combination a steam generator including a furnace, a steam generating circuit disposed to absorb heat evolved by the burning of fuel in the furnace and produce high pressure steam, an air supply system including duct means to supply combustion supporting air to the furnace, means for introducing fuel into the furnace, flame detecting means, an inerting system for inerting the furnace atmosphere in the event of a flame-out and including means to introduce high pressure steam from the steam generator into said duct, and means regulated by the flame detector means operative to maintain the furnace inerting system inactive while a flame is present in the furnace but to render said system active and to terminate the fuel supply in the event of a fiameout.

References (Cited by the Examiner UNITED STATES PATENTS 1,746,123 2/30 Lopez 1'22504.3 2,533,339 12/50 Vt illenborg 158123 2,587,700 3/52 Cowan 15836 2,601,041 7/52 Logan 1584 X 2,916,022 12/59 Arant 122-504 2,949,958 8/60 \Volters 153-424 2,975,771 3/61 Cunningham 122504 3,043,366 7/62 V-lentworth 158-36 3,049,169 8/62 Bredesen et al. 15828 FOREIGN PATENTS 839,430 6/60 Great Britain.

PERCY L. PATRLCK, Primary Examiner.

FREDERICK L. MATTESON, JR., Examiner.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3,202,139 August 24, 1965 William L Livingston et 211,

It is hereby certified that error appears in the above numbered patent requiring correction and that the said Letters Patent should read as corrected below.

Column 1, line 64, for "supply or air""read supply of air column 6, line 58, for "trough" read through column 8, line 2, strike out "operative", and insert the same after "means" in line 3, same column 8.

Signed and sealed this 24th day of May 1966 (SEAL) Attest:

ERNEST W. SWIDER Attesting Officer EDWARD J. BRENNER Commissioner of Patents

Claims

1. IN THE OPERATION OF A FURNACE INTO WHICH FUEL AND AIR ARE INTRODUCED AND THE FUEL BURNED THE METHOD COMPRISING CONTINUOUSLY MONITORING THE BURNING OF FUEL IN THE FURNACE AND IN RESPONSE TO AND DIRECTLY AFTER FLAMEOUT TERMINATING THE FUEL SUPPLY AND SUBSTANTIALLY REDUCING THE AIR SUPPLY TO THE FURNACE AND INTRODUCING AN INERT GAS THEREINTO IN SUFFICIENT QUANTITY AND FOR A SUFFICIENT TIME TO INSURE NONFLAMMABILITY OF THE FURNACE CONTENTS.