US2829277A - Vapor power plant with novel auxiliary flame igniter - Google Patents

Description

F. COWAN ET AL VAPOR POWER PLANT WITH NOVEL AUXILIARY FLAME IGNITER I Filed Feb. 26, 1954 April 1, 1958 Frederick Cowun Joseph A. Locerenzn Harvey C. Miflendorf flT'I'O Y5) w QM. V Q m E N 5 a I H w L 6 mm mm wn w t E mm mm vm E Y vw 8 N% W. Db M. wm mm I w mm w 9v 1 vm mm I Q N m m v .5 it E. U 4% l m vb u \\\\\.\\\-\\\\\\\Q n m9 mm mm Q mm e9 mm nited State VAPOR POWER PLANT WITH NOVEL AUXILIARY FLAME IGNITER Application February 26, 1954, Serial No. 412,769

Claims. (Cl. 290-2) This invention relates to power plants employing vapor generators fired with a suitable fuel and methods of operating such power plants and has particular relation to such a power plant and method wherein insurance is provided against an unstable flame condition in the generator thereby eliminating the dangers and disadvantages which accompany such a condition.

in the operation of present day large steam generators, it is the practice to use an auxiliary flame igniter to initially ignite the fuel supplied to the furnaces of these generators through the rather large main burners. Once this fuel has been lit these igniters are extinguished with the combustion of the fuel than being self-sustaining. The supply of fuel is controlled in accordance with the demand placed upon the power plant and as this demand decreases the rate of firing is likewise decreased. It has been found that when this firing rate is decreased to a predetermined value or point the resulting flame in the furnace begins to surge and becomes unstable resulting in poor combustion efficiency and establishing a potentially extremely dangerous condition since such an unstable flame may be extinguished completely causing the furnace to fill with unburned fuel which if ignited will result in an explosion.

With the present invention this inefficient and potentially dangerous condition is eliminated by lighting the auxiliary flame igniter before the rate of fuel flow is decreased to the point where an unstable flame is produced with these igniters when activated having the effect of stabilizing this flame throughout the entire lower end of the firing range of the burners. The igniters are activated and deactivated by a control system which is effectively responsive to the load on the power plant and this control system is arranged to automatically activate the igniters prior to the rate of firing of the boiler reaching the point where the flame becomes unstable.

-t is an object of this invention to provide an improved power plant employing vapor generators fired with suitable fuel and an improved method of operating the same wherein unstable flame conditions in the generator are eliminated.

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 invention comprises an arrangement, construction and combination of the elements of the power plant 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:

Figure 1 is a diagrammatic view of a power plant having a pulverized coal fired steam generator and embodying the igniter control system of the present invention;

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Figures 2, 3 and 4 show various detailed modifications I of the igniter control system.

While the present invention is shown and described in connection with a pulverized fuel fired installation it is to be understood that it is equally applicable Where other fuels are employed which produce an unstable flame at the low end of the range of the burner as for example gas or oil.

Referring now to the drawing wherein like reference characters are used throughout to designate like elements the power plant diagrammatically illustrated in Figure 1 comprises a steam generator 10 having a furnace 12 which is lined with steam generating tubes 14 and which is firs-d through a suitable burner 16. The steam and water mixture in tubes 14 is conveyed from the upper end thereof into steam and water drum 38 with the water being conveyed from this drum through downcorner 2t? to circulating pump 22 which pumps it into orifice drum 24 from which it is distributed to tubes 14. Steam is conveyed from the top of drum 18 through superheater 26 to turbine throttle valve 28 with the steam that is delivered to this valve being maintained at a predetermined constant temperature and pressure through suitable control means forming a part of the steam generator.

The fuel system for supplying burner 16 with pulverized fuel, such as coal, includes pulverizing mill 3% connected to burner 16 by duct 32 and driven by electric motor 34. Control of the rate of raw fuel delivered to mill 36 is maintained by feeder 36 located at the bottom of storage hopper 38 and connected to the mill by duct 34?. This feeder may be of any well known type and is operative to adjustably regulate the rate of feed from hopper 38 to mill 30. As diagrammatically illustrated this rate of feed is adjusted by lever 2 with the rate being decreased as the lever moves in a clockwise direction as indicated by arrow 44.

The pressure of the steam delivered to throttle valve 2% is maintained constant or substantially constant by regulating the rate of fuel fired to furnace 12 and for so regulating this fuel firing, control mechanism 46 is subjected to this steam pressure through conduit 48 and is effective to regulate the operation of motor 51 to adjust lever 42 to the desired setting, resulting in a fuel delivery rate which will produce the desired steam pressure. Thus, as the steam pressure deviates from the desired value lever 42 will be adjusted to correct the rate of the fuel supply to bring the pressure back to its desired value.

The amperage drawn by motor 34 varies in accordance with the rate of fuel supplied to mill 30 with this amperage increasing as the rate of fuel supplied is increased.

Adjacent the burner 16 is auxiliary flame igniter 50 which is supplied with fuel (preferably oil) and air through conduits 52 and 54 respectively, and which, as diagrammatically disclosed, is provided with an electric spark igniter element 56. The flow through conduits 52 and 54 is controlled by valves 58 and en respectively, these valves being normally biased closed and being opened by electromagnet 62 upon energization of this electromagnet. The electric circuit for this electromagnet, designated generally 63, comprises a pair of conductors 64 and 66 connected across a potential 68. The electric spark igniter element 56 is electrically connected into this circuit in parallel with electromagnet 62 so that upon energization of the circuit valves 53 and 6h will be moved to an open position simultaneously with the energization of igniting element 56 thereby resulting in activation of auxiliary flame igniter 50. The flame igniter 50 is so positioned relative to burner 16 that when the flame igniter is activated the flame it produces extends into the mass of fuel which burner 16 projects into the furnace.

As embodied in the Fig. 1 organization, in series with conductor 64 is the manual control switch 70 for effecting manual control of flame igniter 563 as desired. Also in series with this conductor are the contacts of relay 72 which are biased to the closed position by spring 7d. Energization of coil '76 of this relay 72 is controlled by transformer '78 which has its primary winding in the circuit of motor 34 and its secondary winding in the circuit of the coil. Thus, as the amperage drawn by motor 3d increases the current flow through the coil will likewise increase thereby increasing the magnetic attraction produced by this coil so that at a prede :rmined current flow the magnetic force created by the coil will be sufficient to overcome the bias of spring 74 causing the contacts of the relay to open while for all current flows below this predetermined value the bias of spring M will be greater than this mag etic force and the contacts of the relay will remain closed. By adjusting the tension of spring 7 or the relation between the primary and secondary coils of transformer 78 the amperage drawn by motor 34 which is effective to actuate relay '72 may be selected as desired.

In order that auxiliary flame igniter .ill will be activated and in operation before the rate of fuel supply through burner 16 becomes so low that an unstable flame is produced the operation of relay '72 is regulated so that the contacts of the relay will close when the rate of fuel supply to mill 30 reaches a predetermined value which is above that which will result in an unstable flame, this predetermined value being evidenced by a predetermined current flow through the circuit of motor 34. Thus when the rate of fuel supplied to mill 3i) decreases to this predetermined value the contacts of relay 72 will close resulting in energization of electromagnet 62 and igniting element 56 and consequent activation of auxiliary flame igniter 50. With this rate of fuel supply the flame is still stable, but as the rate is further decreased the flame would ordinarily become unstable if flame igniter 56 were not in operation. However, with flame igniter 50 in operation the rate of fuel supplied may be lowered to the lowest range of the burner with the flame remaining stable and there being no danger of it being extinguished and causing an explosion.

The superheated steam produced by superheater 26 is supplied through throttle valve 28 to turbine 80 with the exhaust from this turbine being condensed and returned to the steam generator in a well known and conventional manner. The turbine 88 is connected with and drives the electric generator 82 which supplies electric energy to a variable load through transmission lines 84 with this variable load being what is known as the load on the power plant or the load supplied or met by the power plant. Since the frequency of the alternating current produced by generator 82 must be maintained constant the generator must be driven at a constant rotational speed as for example 1800 R. P. M. For this purpose the speed of the turbine and accordingly the speed of the generator is controlled by a suitable governor connected with valve 28 and operative to regulate this valve to control the steam flow to turbine 80 to maintain the speed of the turbine constant. While there are numerous conventional governing mechanisms for accomplishing this control, for the purposes of illustration, there is shown in the drawing the well known fly ball type of governor which includes pivoted arms 36 connected with vertically movable sleeve 88 and effective to move the sleeve up and down as the turbine speed increases or decreases respectively. The operating stem of throttle valve is interconnected with sleeve 8-3 by linkage 90 and is moved in the direction to close valve 23 when the sleeve moves upwardly in response to an increase in turbine speed thereby reducing the speed of the turbine and conversely is moved to open valve in response to a downward movement of sleeve 88 resulting from a decrease in turbine speed. Thus the fly ball governor adjusts valve a 28 in a manner to maintain the speed of turbine substantially constant.

The load on the power plant, i. e., the load supplied over transmission lines 84, is measured by watt meter 52 operatively connected with these transmission lines.

Eince the load on the power plant determines the posi tion at which throttle valve 28 is placed, the greater the load the further this valve is moved to its open position, and since variations in the positioning of throttle valve 23 affect the adjustment of the feeder 36, due to the control of this feeder being responsive to the steam pressure delivered to the throttle valve, causing the feeder to feed fuel to mill 34) at an increased rate as the opening of this valve is increased in order to maintain this pressure constant and finally since the current drawn by motor 34 is responsive to the rate of feed to mill 39 it will be seen that the control of the rate of fuel firing through burner 16 and the control of the activation of flame igniter fill is ultimately responsive to the load on the power plant and that so long as the activation of flame igniter Ell is responsive to a condition reflecting a decrease in this load to a value above that at which the flame in furnace 12 becomes unstable, which condition is manifest before the flame becomes unstable, the broad aspect of this invention will be realized. It is thus apparent that several modified forms of control circuits may be used in lieu of the particular arrangement of Fig. 1. Fig. 2, 3 and 4 show three such modifications.

In the circuit of Fig. 2 conductors 64 and 66 are connected across potential 63. In series with conductor 66 is switch 94 operated by lever 42 and arranged to be closed by this lever when it is at a position representing a predetermined rate of fuel supply to mill 3:; and accordingly burner to below which rate the flame in furnace 12 becomes unstable with the switch remaining closed for all rates below this predetermined rate. As pointed out hereinbefore upward or clockwise movement of lever 42 decreases the rate of feed of feeder 36. The closing of switch fi iactivates flame igniter 50 thereby preventing the flame from becoming unstable due to a low rate of fuel firing.

In Fig. 3 the energization of electric circuit 93 is controlled by switch 96. This switch is connected to and operated by linkage which forms a part of the governor operating mechanism and interconnects valve 28 with the governor. The switch 96 is arranged so that it is closed and flame igniter 56 is energized when valve 28 is moved to a position which corresponds with a predetermined fuel flow through burner 16 below which the flame in furnace 12 is unstable with the switch remaining closed for all positions of valve 28 corresponding to fuel flows below said predetermined flow.

In Fig. 4 energization of the electric circuit is controlled by switch 98 having contacts 100 and 102. This switch is operated in accordance with movements of the indicator of the watt meter 92 and is arranged so that contacts 100 and 102 are closed and flame igniter St) is energized when the indicator of this meter is in a position which corresponds with a predetermined rate of fuel firing through burner 16 below which the flame in furnace 12 becomes unstable with the contacts remaining in engagement for all positions of this indicator representing a rate of fuel firing below this predetermined rate.

It will thus be seen that this invention provides a control for the auxiliary flame igniter which is effective to activate the igniter before a dangerous condition arises in the furnace thereby eliminating the possibility of an explosion.

While we have illustrated and described a preferred embodiment of our novel organization 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 wish to 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. A power plant comprising in combination a vapor generator, a prime mover generator unit driven by vapor from said vapor enerator, said vapor generator including a furnace, burn-er means for projecting fuel into said furnace with said fuel being burned within said furnace, said burner being operable over a given range of rates of firing, adjustable means for controlling said rate of firing of said burner, means effectively regulated in accordance with the load on the power plant and operative to control the last named means in such a manner that the output of the power plant reflects the adjustment thereof, said furnace being of such a size and said burner being of such a construction and so related to the furnace that the flame produced by the burning fuel within the furnace is unstable for a given portion of the lower end of said range of operation of the burner, an auxiliary flame igniter that is of small capacity with relation to said burner and disposed adjacent to said burner and in such relation thereto that when it is activated it is effective to stabilize said unstable flame, and means responsive to a condition manifest prior to the reduction of the rate of fuel supply to the vapor generator below the value whereat said flame becomes unstable and reflecting a decrease in load on said power plant to a predetermined value for activating said auxiliary flame igniter before said flame becomes unstable thereby preventing such instability and the ineflicient combustion and dangerous condition incident thereto.

2. The organization of claim 1 wherein the means that controls activation of the auxiliary flame igniter includes electrical means operative to directly measure the load on the prime mover generator unit and means responsive to said electrical means for activating said auxiliary flame igniter when the load decreases to said predetermined value.

3. In combination, a boiler having a furnace fired by pulverized fuel through a suitable burner, means for supplying said fuel to said burner including a pulverizer and a fuel feeder operative to regulate the rate of fuel supply to said pulverizer and including adjustable means for varying said rate, means effectively controlled in accordance with the load on the boiler operative to control said adjustable means to regulate the rate of fuel supply so that the output of the boiler will meet said load, the burner being operable and the fuel rate being regulated over a given range of rates of firing, the burner being of such a construction and so related to the furnace that the flame produced by the burning fuel within the furnace is unstable for a given portion of the lower end of said range of regulation, an auxiliary flame igniter that is of small capacity with relation to said burner and disposed adjacent said burner and in such relation thereto that when it is activated it is efiective to stabilize said unstable flame, and means controlled in accordance with the control of said adjustable means and operative to activate said auxiliary flame igniter immediately prior to the rate of fuel supply being lowered to the point I where the flame becomes unstable.

4. In combination, a boiler for generating steam, said boiler having a pulverized fuel system including a burner for projecting the pulverized fuel into the furnace of the boiler with the fuel being burned within the furnace, a pulverizer connected to supply said burners with pulverized fuel and a regulatable feeder operative to reg- Cit ulate the rate of feed of fuel to the pulverizer, means effectively controlled in accordance with the load on the boiler and operative to control said feeder to regulate the rate of feed so the output of the boiler will meet the load imposed thereon, the burner being operable and he fuel rate being regulated over a given range of rates of firing, the furnace being of such a size and the burner being of such a construction and so related to the furnace that the flame produced by the burning fuel within the furnace is unstable for a given portion of the lower end of said range of regulation, electric motor means for driving said pulverizer, the electric current required by said motor means decreasing with a decrease in the rate of fuel supply, an auxiliary flame igniter that is of small capacity with relation to said burner and disposed adjacent said burner and in such relation thereto that when it is activated it is effective to stabilize said unstable flame, and means effectively responsive to the amperage drawn by said motor means effective to activate said auxiliary flame igniter when said amperage falls to a predetermined value reflecting a rate of feed at least somewhat higher than the rate at which said flame becomes unstable.

5. A power plant comprising a steam generator and a turbine generator unit driven by steam from said steam generator, said steam generator including a furnace, a. fuel firing system including a main burner through which fuel is projected into said furnace and burned therewithin, said burner being operable over a given range of rates of firing, said furnace being of such asize and said burner being of such a construction and so related to the furnace that the flame produced by the burning fuel within the furnace is unstable for a given portion of the lower end of said range of operation of the burner, adjustable means operative to control the rate of firing of said burner, means effectively regulated in accordance with the load on the power plant to control said last named means so as to maintain the steam supplied to the turbine at a substantially constant pressure, valve means for controlling the amount of steam supplied to the turbine, a governor responsive to the speed of the turbine and operative to regulate said valve to maintain the turbine speed substantially constant, an auxiliary flame igniter that is of small capacity with relation to said main burner and in such relation thereto that when it is activated it is effective to stabilize said unstable flame, and means to activate and deactivate said igniter, said means being responsive to the regulating action of the governor and regulated thereby to activate said auxiliary flame igniter prior to the reduction of the rate of fuel supply to the point where the flame becomes unstable.

References Cited in the file of this patent UNITED STATES PATENTS 656,165 Bickford Aug. 21, 1900 1,160,371 Brown Nov. 16, 1915 1,459,072 Peebles June 19, 1923 1,657,436 Munro Jan. 24, 1928 1,994,447 Bailey et al. Mar. 12, 1935 2,053,061 Bristol Sept. 11, 1936 2,137,754 Francis Nov. 22, 1938 2,184,224 Lucke Dec. 19, 1939 2,354,999 Ladd Aug. 1, 1944 2,361,117 Millett Oct. 24, 1944 2,670,725 Cummins Mar. 2, 1954 2,681,418 Bristol June 15, 1954

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