US1906244A

US1906244A - Combustion contboi

Info

Publication number: US1906244A
Authority: US
Publication date: 1933-05-02
Anticipated expiration: 1950-05-02

Description

Mayz, 1933- G. BENJAMIN 1,906,244

COMBUSTI ON CONTROL Original Filed Oct. 29, 1929 2 Sheets-Sheet l INVENTOR M. G. BENJAMIN COMBUSTION CONTROL Original Filed Oct. 29, 1929 2 Sheets-Sheet INVENTOR Patented May 2, "1933' UNITED srArasrA E T OFFICE MERRILL G. BENJAMIN, OI LAKEWOOD, OHIO A consumer con'rnon Application filed October 29, 1988 Serial No. ,Beneviedv September 12, 1882.

,My invention relates to systems for automatically controlling the supply of fuel and air to a boiler furnace in order to produce the most efiicient operation thereof.

Systems of this character have been pre viously proposed based on the principle that the magnitude of steam flow from a boiler is an accurate index of the conditions thereof. Other systems have utilizedvariations the supply of fuel and air to the furnace. Both of these types of systems, however, are subject to the disadvantage that they are inherently somewhat inaccurate and are charcontrol impulse, whether it variation in steam flow or steam pressure.

-I propose to overcome certain difiiculties 2o characteristic of known systems of this type the supply of fuel and air. I have discovere that the color of the flame in the furnace afthereof. My invention also contemplates the use of the principles of spectrum analysis as applied to the gases in the combustion chamber of the furnace.

. spond immediately to changes in furnace conditions and bring corrective forcesinto play with a minimum loss of time so that any de parture from normal conditions is swiftly arrested.

A further feature of my invention is in the control of the thickness of the fuel bed on a furnace grate in accordance Withthe, rate at which the boiler and furnace are beingoperated.

An additional element which I propose to employ in' connection with the control sys teln mentioned above is an automatic device for controlling the operation of clinker grinding rolls in the furnace ashpit.

In my copending application, Serial No. 323.145. filed December 1. 1928, I have disclosed and claimed a complete system of combustion control utilizing certain novel apparatus and principles; It is myintention, in the present application. to disclose and claim certain improvements of the system in the boiler steam pressure for controlling acterized by a low speed of response to the by the use of means responsive to the actual conditionswithin the furnace for controlling I Such devices re-' the furnace chamber for controlling the various devices for supplying fuel and air to the furnace. The electric currents generated by these devices are amplified by means of known types of amplifiers, such as vacuum tube devices, and the controlling equipment is actuated by the amplified currents. For a complete description of my invention, reference is made to the accompanying draw-- ings in which,

Figure 1 is a diagrammatic illustration of a present preferred embodiment of; the invention;

Figure 2 is a modification of the system shown in Figure 1;

Figure 3 is a further modification; and Figure 4 is a similar illustration of the means I- have invented for controlling the thickness of the fuel bed on the furnace grate. fords an accurate index as to the operation Referring in detail to the drawings and with especial reference to Fig. 1, the illustrated embodiment includes a boiler and fur- -nace 10 having steam drums 11, water tubes 12,.and baffles 13 in the combustion chamber 14 thereof. Fuel is supplied to the combustion chamber by means of an automatic stoker 15 driven by an electric motor 16. Aforced I draft of air is supplied to the grate 17 by means of a fan 18 driven by an electric motor 19. An uptake 20 provides an" exit for the flue gas' and may be connected to a stack (not shown). i I

for the removal of the clinkers after they have been ground.

I control thesupply of fuel and air to-the' combustion chamber 14 of the furnace 10 by varying the speed of the

motors

16 and 19, which drive the stoker 15 and fan 18, re spectively. The current is supplied to the motors from the supply buses 25 and 25', and the speed of the motors may be controlled by shiftingthe setting of the shunt field rheostats 26 and 27 thereof: The au- The furnace 10 has an ashpit 21 provided with clinker grinders 22 which are driven by a motor 23. A conveyor 24 is employed tomatic control system which I provide includes

pilot motors

28 and 29 for operating the

rheostats

26 and 27. The

motors

28 and 29 are of the two-winding reversible type and have forward field windings 287 and 29f and reverse field windings 281' and 291-.

The operation of the

rheostat motors

28 and 29 is controlled by the selective energization of

control buses

30 and 31. One terminal of the armatures of the motors is permanently connected to the negative bus and by selectively connecting the

control buses

30 and 31 to the positive supply bus, I am able to control the direction of rotation of the

motors

28 and 29.

I provide a steam pressure responsive control device for effecting a primary control of the motors which drive the furnace auxiliaries such as the stoker and forced-draft fan. One form of the pressure-responslve means includes a-Bourdon tube 32 which is connected to the steam drum 11 by a pipe te h d 34 is also connect- 33 A mam S am ea er and 49, one of the windings of the motor 47 1s ed to the drum 11 for supplying steam to the load supplied by the boiler such as a turbine (not shown). nism 35 includes a pair of relatively fixed contacts 36 and 37, which are mounted on a movable support 38. Cooperating with the contacts36 and 37 is a movable contact arm 39 which is pivotally connected to the Bourdon tube 32 by means of a linkAO. The contacts 36 and 37 are connected to the

buses

30 and 31 and the contact arm 39 is connected to the positive supply bus. When the arm 39 engages one or the other of the contacts 36 and 37, the

buses

30 and 31 are selec tively energized to cause operation of the

rheostat motors

28 and 29. The resulting addisclosed herein may be of use in connection witha number of master regulators.

Iii-order to restore the contacts 36 and 37 to the out of contact position with respect to the arm 39 after an engagement of the latter with one of the contacts has been effected. I employ a follow-up motor 41. having forward and reverse field windings 41f and 411'.

The motor 41 is effective to shift the support 38 for the contacts 36 and '37 up or down through a worm 42 and worm wheel 43 and a rack 44 on the support 38. The motor field windings are connected to the

buses

30 and 31 so that the motor opera es in the same di- A contact-making mecha negative bus.

rection and at the same time as the

rheostatoperating motor

28 and 29.

As disclosed in my copending application hereinbefore referred to, it is desirable that supplemental contral means he provided for the fuel and air supplying means, in addition to the primary control means which is responsive to steam pressure variations. The improved form of supplemental control means which I provide for the forced-draft fan 18 45 is actuated so that its moving contact 50 engages one or the other of the contacts 48 connected to the positive supply bus and the circuit is completed through the motor to the The motor is thus operated to effect the desired adjustment of the supplemental control rheostat 46. By the use of.

the means disclosed in my copending application, I- may dispense with the supplemental control rheostat 46 and cause the supplemental control to be effected by a further operation of the rheostat 27. The present system is disclosed in order to eliminate the illustration and description of the mechanical details of the apparatus disclosed in the co pending application, but a practical. em-

bodiment would preferably employ the latter.

The relay 45 is operated by a pair of opposed solenoids 51 and 52. The solenoid 51 is controlled by a photo electric cell 53 mounted in the furnace wall and focused so as to be responsive to color of the flame in the combustion" chamber. Suitable focusing means such as lenses may be utilized if found desirable. As is generally known, the photo electric cell 53 produces an electric current proportionate to the intensity of the light impinging thereon. The output of the cell 53 is amplified by means of a standard vacuum tube amplifier which is indicated sche matically at 54. The amplified current is then conducted to the solenoid 51.

Similar control means are provided for th solenoid 52. A photo electric cell 55 is mounted in a suitable housing so as to be affected by a portion of the spectral band of colors which is produced from the light emitted from the combustion chamber 14 by a spectroscope indicated'schematically at 56.

-An amplifier 57 similar to that shown at 54,

serves to magnify the output of the photo electric cell 55 for energizing the solenoid 52. The use of the spectroscope in analyzing tain composition as regards content and the like, a characteristic spectral band will be brightly illuminated. When the composition of the furnace gas-differs, this band will be less brightly illuminated since the portion of the band which is most strongly illuminated depends upon the composition of the substance being analyzed. By means of the photo electric cell 55, I produce an electric current, the magnitudeof which is controlled by the composition of the furnace gas as described above.

U The balance relay affords means for '85 plied for combustiomthe flame will have its comparing the effectof the spectrum analysis of the furnace gas and color of the flame in the furnace. By combining these two characteristics electrically in the relay 45, it is possible to obtain a close and accurate regulation of the supply of air to the furnace. If the spectrum analysis of the furnace gas shows that the CO content is excessive, the relay 45 will operate the motor 47 to cause a reduction of the speed of the forced-draft fan 18. The color of the flame in the combustion chamber 14 simultaneously influences the operation of the relay 45. It is known that, when the proper amount of air.is supmaximum brilliance. If excessive or-insuflicient air is supplied, the brilliance of the flame will tend to diminish. This variation is suflicient to control the solenoid 51 of the relay 45 through the photo electric cell 53 so as to correct t e air supply in accordance with conditions as indicated by the color of the flame.

If the spectrum analysis of-the furnace gas shows CO content to be deficient, the photo electric cell 53 is influenced thereby and the relay-45 tends to causean increase in the speed of the fan 18 to supply additional air to the furnace. v

In addition to using photo electric cells for controlling the operationof the boiler and furnace auxiliaries, I employ the same device for controlling the operation of the clinker grinders 22. To this end, I mount a photo electric cell 58 in the wall of the ashpit 21. An amplifier 59 receives the output of the photocell 58 and energizes a relay 60 in accordance therewith. The relay 60, being sufficiently energized, opens the circuit from Jv thepositive bus to the motor 23, which drives the'clinker grinder rolls. In the operation of-the furnace, the incandescent mass of clinkers, formedion the grate 17 as the coal 1 .is. burned,'flows into the ashpit 21'. As the clinkers descend into the pit 21, they are cooled so that they can be readily ground by the grinder rolls 22 without injury to the latter. The photocell 58 is placed at such a distance above the grinder rolls 22 that the relay 60 will be operatively energized when the mass of clinkers opposite the cell 58 is incandescent. The operation of the grinder rolls will thus be intermittent. As the hot clinkers descend into the ashpit, the photocell 58 causes the relay 60 to be energized to stop the motor 23. After the clinkers have cooled, the photocell 58 no longer energizes the relay 60 and the motor 23 is started again. When the cooled clinkers have been ground, and the hot clinkers have descended to the level of the photocell 58, the latter causes the relay 60 to be energized to stop the motor 23 again.

In Fig. 2, I have illustrated a modified form of my control system utilizing photo electric cells. According to this modification, aphotocell 61 is focused so as to be influenced solely by the color of the' flame in the combustion chamber 14 of the furnace 10. In order to eliminate the effect of the heated refractory lining of the furnace, I provide a water-cooled wall portion 62 therein, having a blackened surface to prevent the reflection of light from other portions of the furnace. The connections for cooling water are shown at 63. A second photo electric cell 64 is focused 'on the fuel bed and the grate refractories, which are heated to incandescence. The incandescent refractories afford a standard with which the color of the flame may be compared. Variations of the rate of the operation of the furnace having some effect upon the intensity of the light emitted by the fuel bed and grate refractories. The color of the flame in the combustion chamber, however, varies in the same proportion if the gas analysis remains the same. Any variation in flue gas composition alters the intensity of the brilliance of the flame as comparedwith that of the fuel bed and grate refractories.

.In order to compare the effect of the flame color with that of the fuel bed brilliance, I

provide

solenoids

65 and 66 energized, re-

spectively, by

amplifiers

67 and 68. The

amplifiers

67 and 68 magnify the currents pro-- duced by the photo electric cells 61 and. 64. The

solenoids

65 and 66 comprise one element of a balance relav- 69 similar to that shown. .at 45 in Fig. 1. The other element of the relay 69 is a solenoid 70, the energizationof which is controlled by a rheostat 71 operatively connected to the shaft of the motor 29 which serves to control the rheostat 26, as shown in connection with Fig. 1. The relay 69, by means of

contacts

48 and 49, similar to those shown at 48 and 49 on relay 50, con trols the forward and reverse fieldwindings of the motor 47 to shift the rheostat 46 to supplementally control the speed of the forced-draft fan 18. Although all the ele ments of Fig. 1 are not duplicated in Fig. 2, it is to be understood that in an operative embodiment of the modification shown in Fig. 2, all the boiler and furnace auxiliaries customarily employed with an associated control apparatus will be made use of.

The modification shown in Fig. 3 is similar to that shown in Fig. 2, except that the color of the flame in the furnace chamber 14, as indicated by the photocell 61, is compared with the power input to the motor 19 instead of with a standard such as that afforded by the photocell 64 focused on the incandescent grate refractories. Corresponding elements of Figs. 2 and 3 are indicated by similar reference numerals. The relay 69 in Fig. 3 comprises the

solenoids

65 and 70 and a solenoid 72 which is adapted to be energized in accordance with the power input to the motor 19. As an example of the means by which this control of the solenoid 72 may be effected, I have shown a shunt 73 in the lead from the positive bus 25 to the motor 19, although any means for energizing the solenoid 72 in proportion to the power supplied to the motor 19 may be employed.

The modification of Fig. 3 is found to exert a close control on the operation of the forced-draft fan 18 and is especially advantageous because it takes account of the thickness of the fuel bed on the grate. When the fuel bed is thick, the weight of air supplied thereto by the fan is less for a given fan speed than that supplied when the fuel bed is thin, although the pressure under a thick fuel bed is greater. The power in ut to the motor 19, of course, varies with t e weight of air moved by the fan 18, regardless of the pressure built up by the fan.

Fig. 4 illustrates schematically a device for varying the thickness of the fuel bed in accordance with the rate of furnace operation. The desirability of this device will be readily apparent from a consideration of the fact that, when the boiler is operated at a high rate, the velocity of the forced-draft fan is greater and the tendency for the draft to blow holes in the fuel bed is increased. When the furnace is operated at a comparatively low rate, the fuel bed thickness may be decreased so that less air pressure will be necessary to force the desired weight of air therethrough. The device which I have invented to control fuel-bed thickness in accordance with the rate of furnace operation comprises a rheostat 74. The rheostat 74 includes a fixed resistor 75 and a movable support 76 carrying

contact fingers

77, 78, and 79 cooperating with the resistor 75. Relays 80 and 81 are mounted on the support 76. These relays control

armatures

82 and 83 which cooperate with the contact fingers 77 7 8, and 79. The

armatures

82 and 83 are normally retracted by suitable springs 84.

' When both of the relays 80 and 81 are deenergfied, the armature 82 en ages the contact ger 78 and the contact ngers 77 and 79 are ineffective, although their engagement with the resistor 75 is not broken. Under these conditions, the excitation of the field winding 16' of the motor 16 is controlled by the position of the'contact finger 78. The position of this finger may be changed by moving the support 76 on which it is mounted. This movement is effected by means of a motor 28' corresponding to that shown at 28 in Fig. 1. The rotation of the motor 28' is determined by the energization of the

buses

30 and 31, as previously explained. A worm 85 is driven by the motor 28 and cooperates with a worm wheel 86 to shift the

contact fingers

77, 78 and 79 of the rheostat 74 by means of a rack 87 on the support 76.

When the bus 31 is energized to cause the motor 28 to rotate in a forward direction, relay 81, which is connected in arallel with the field winding 28' is likewlse energized and attracts its armature 83. When 'attracted, the armature 83 engages the contact finger 79. The

armatures

82 and 83 are connected to the positive bus 25 and when the armature 83 engages the finger 79, the finger 78 is no longer effective and the field winding circuit extends. from the bus 25, through the armature 83 contact finger 79, a portion of the resistor 75 to the field winding 16, and the negative bus 25'. Although the armature 82 remains in engagement with the contact finger 78, the portion of the resistor between the

fingers

78 and 79 is shunted.

As the motor 28' continues to operate, the position of the three fingers, 77 78, and 79, is simultaneously altered. When the adjustment has proceeded to the desired extent,

the motor 28, its forward field winding 28'f and the relay 81 are de-energized. The armature 83 is retracted and contact finger 78 again becomes effective to control the speed of the motor 16. It will be observed, however, that during the period in which the adjustment of the contact fingers of the rheostat is being completed, an excess adjustment of the motor speed 16 is effected by the operation of the relay 81. In the case under discussion, the operation of the motor 28 was in such direction as to effect a decrease in the speed of the motor 16. The relay 81 caused a temporary excessive reduction in the speed of the motor 16 to reduce the amount of fuel being supplied to the grate final thus to reduce the thickness of the fuel When the reverse field winding 281' of the motor 28' is energized by the connection of the bus 30 to the positive bus 25, the relay 80 is energized to render the contact finger 78 of the rheostat 74 ineffective and to make the contact finger 77 effective in its place. In this case, the movement of the support 76 is in such direction as to shift the

fingers

77, 78 and 79 to increase the s eed of the motor 16. The operation of t e relay 80 renders the finger 7 temporarily effective to produce an excessive increase in the speed.

of the motor 16. This excessive increase in the motor speed causes an additional amount of fuel to be supplied to the grate to build up the required thickness of fuel bed. After the required adjustment has been made, the motor 28 stops, the relay 80 is de-energized and the finger 78 again becomes effective at a higher speed setting than it originally occupied but at a lower speed setting than that of the finger 77.

It will be apparent that, as long as the to control the. fuel bed thickness in accordance with the rate of furnace operation.

Although Fig. 4 shows only aportion of the apparatus and control equipment illustrated in Fig. 1, it is my intention to utilize. the devices of Fig. 4 in connection with a system, as that shown in complete detail in Fig. 1.

The systems which I have described for the automatic control of combustion in a boil er furnace makes possible more accurate control of the fuel and air supplying auxiliaries and the motor rigid maintenance of a fixed pressure in the boi ers. Economical operation is another result which follows from the automatic control of the fuel so that only the amount necessary to maintain the normal steam pressure will be consumed. The control devices which I utilize are immediately responsive to changing furnace conditions and no time lag in the operation of the control equipment hinders the prompt adjustment of the auxiliaries to remedy any abnor-' mal condition of the steam pressure.

Although I have shown the system applied to a single boiler, it is obvious that it may be readily utilized in connection with a battery of boilers supplying steam to a common header. In this case, the master control equipment, comprising the steam pressure responsive means 32 and the contact making mechanism 35, would be connected to the steam header 34, instead of the drum 11 and would serve to control simultaneously the rheostat operating motors for the auxiliaries of all boilers in the battery. Each furnace would be provided, in addition, with supplemental control means, including the light responsive devices for effecting the desired secondary control of the auxillaries of each furnace individually.

, Numerous additional modifications in the embodimentof the invention disclosed'will be apparent. .Instead'of utilizinga variable speedforced-draft fan, a constant speed fan and a motor operated damper may serve to vary the amount of air supplied .to the combustion chamber. Means other than electric motors for driving the various auxiliaries may likewisebe resorted to. These changes, however, and all others thatfall within the spirit of the invention may be madewithout departing from the scope of appendedclaims. I y

I claim:

1. The combination with a boiler and furnace, auxiliaries for supplying the elements of combustion to said furnace, and means responsive to steam pressure for effecting a primary control of'said auxiliaries, of supple- H mental control means for one of said auxiliaries. including a photocell responsive to'the color of the-flame in the, furnace and a photo- .cell responsive to the spectrum analysis ofthe combustion chamber gases. 7 a I y Y 2. In a combustion-control system, a boiler and furnace, means for supplying fuel and air to said furnace, means responsiveto the steam pressure in said boiler for controlling said means, supplemental control means for the air-supplying means including ,lightsensitive devices responsive respectively to the color of flame in the furnace and the spectrum) analysis of combustion-chamber gases for operating the supplemental control means.

3. A combustion-control system for fuel and air suppl ing auxiliaries of a boiler and furnace inclu ing means responsive to boiler pressure for controlling the rate of fuel and air supply and supplemental control means for the air supply responsive to the color of the flame and to the spectrum analysis of the gases in the combustion chamber.

4. In a boiler and furnace, fuel and airsupplying means, control means therefor responslve to the steam pressure in the boiler, supplemental control means for the air-supply means inqluding photocells responsive respectively to the color of the flame in the furnace and the light emitted by the incandescent fuel bed and refractory lining.

5. The'combination with a boiler and furnace, means forsupplying an element of combustion thereto, control mechanism for said means, responsive to the pressure in said boiler, and supplemental control means therefor including means for comparing the color of the flame in the combustion chamber with a standard source of light.

6. Supplemental control means for a boiler and furnace auxiliary including means responsive to the light emitted by the flame in the combustion chamber as compared with the light radiated from the fuel bed or refractories.

7. A control device for a furnace auxiliary 5 including hotocells focused respectively on a cooled, d arkened spot on the furnace wall and on the fuel bed and refractories of the furnace.

,8. Su plemental control means for a boiler and urnace auxiliary including means responsive to the relative mtensities of the light emitted by the flame and the fuel bed in the furnace, and means responsive to the power input to said auxiliary.

9. In a combustion-control system for a boiler and furnace having a fuel feeder, means responsive to the pressure in the boiler for controllingsaid feeder, and means actuated by said pressure-responsive means for rendering effective an abnormal adjustment of the feeder control to make the thickness of the fuel bed correspond to the adjusted rate of feeding fuel.

10. In a control system for a boiler and 25 furnace, an automatic stoker, means for acceleratingor retarding the rate of o ration of said stoker in accordance with t e pressure in the boiler and means rendered effective thereby to cause a temporar excessive acceleration or retardation of t e rate of stoker operation to alter the thickness of the fuel bed in proportion-to the adjusted rate of fuel feed. I

In testimony whereof I have hereunto set 3 my hand.

MERRILL G. BENJAMIN.