US1869372A - Fuel-air ratio control system - Google Patents

Description

Aug. 2, 1932, J. M. HoPwooD FUEL-AIR RATIO CONTROL SYSTEM Filed May '7. 1930 4 Sheets-Sheet l lNvENT'oR 171 @MWWGAM @f @www Aug. 2, 1932. J. M. HoPwooD 1,869,372

FUEL-AIR RATIO CONTRQL SYSTEM Filed May '7. 1930 4 Sheets-Sheet 2 A11g- 2, 1932. I J. M. HoPwQoDk 1,869,372

FUEL-AIR RATIO CONTROL SYSTEM Filed May 7. 1930 4 Sheets-Sheet 5 Wm @MW Allg. 2, 1932. J, M, HQPWOD 1,869,372

FUEL-AIR RATIO CONTROL SYSTEM Filed May '7, 1930 4 Sheets-Sheet 4 45- g 44 DtcrMS@ Increase i Patented Aug. 2, 1932 UNITED STATES JOHN M. HOPWOOD, OF PITTSBURGH, PENNSYLVANTA FUEL-AIR RATIO Application filed. May 7,

This invention relates to a fuel-air ratio control system for furnaces, and more particularly to a system wherein the admission of air into a furnace burning powdered coal s is controlled in accordance with the variations in the'carbon dioxide content of the products of combustion or gases escaping from said furnace.

This invention is particularly adapted to i be used on furnaces in which theoutlet damper and the feeding of fuel thereto are controlled byvariations in the steam pressure. Tn such a control system when the steam pressure demands morey fuel the regulator controlling the fuel feeder is opened and `more fuel is admitted.A As the same time the outlet damper on the furnace is automatically opened and the draft through the furnace is increased. also automatically opened increasing the air supply.

This arrangement, however, cannot be depended on to maintain the proper fuel-air ratio as there is nothing in the system that is responsive to a change in heating value of the coal, or to its physical condition, that might affect the amount of coal which would be handled for a given speed of the feeder.

If the fuel-air ratio is incorrect for proper combustion, a change in the carbon dioxide content of the gases produced by the combustion takes place. This change in the carbon dioxide content of the gases causes the furnace to operate at a decreased efficiency,

"-1 that is, the furnace operates under other than the most favorable conditions for which it was designed.

One object of this invention is to provide means for making a final adjustment of the fuel-air ratio in a furnace burning powdered coal in accordance with and by means of the carbon dioxide content of the escaping gases.

This and other objects which will be apparent to those skilled in this particular art The furnace draft damper is CONTROL SYSTEM 1930. seriai No. 450,404.

are obtained by means of this invention, one embodiment of which is set forth in the following specificationand illustrated inthe accompanying drawings forming a part hereof and in which: u n

Figure 1 is a schematic nillustration of a boiler furnacey and a control system therefor embodying the'k invention; l

Fig. 2 is a view in front elevation of an auxiliary regulator for Ymodifying the air delivered to the furnace in accordance with variations in the carbon dioxide content of the products ofcombustion. 'l

Fig. 3 is a view in side elevation regulator shown in Figure `2. I Y

Fig. 4 is anenlarged fragmentary view, partially in section,of the device illustrated in Figs. 2 and 3; i

Fig. 5 is atop plan View of a portion of the device illustrated in Fig. 4; and

Fig. 6 is a diagrammatic illustration of circuits and apparatus embodied in the sys# tem shown in Fig. l. Y

Similar referencecharacters refer to similar parts throughout the several views.

In the drawings a master regulator or relay 1 is shown of the type describedV in Letters Patent No. 1,7 87,407, granted December 30, 1930 to Thomas A. Peebles, and in application, Serial No. 361,657, filed May Z5 9, 1929 by Thomas A. Peebles for combustion control svstem.

This regulator is suitably connected by va pipe 2 with the steam header 3 of the furnace. When variations in the steam pres- S0 sure occur, the regulator l sends out impulses to the receiving regulators l and 5 of the type described in said Letters Patent No. 1,787 ,407 and which regulate the fuel and air admitted to the furnace. If thev plant S5 load hasl been increased, for example, there will be Yadecrease of pressure in the steam header on account of an increased resistance to the flowof steam through the super heaters, non-return valves, etc. VInresponserto 90 of l the this decrease in steam pressure, the master regulator 1 will operate and modify the pressure impulses transmitted to said receiving regulators to rebuild the steam pressure.

The regulator 4 controlling a rheostat 6 on a feeding motor 6, operates to increase the speed of said motor, whereby more powdered coal is fed to the furnace. At the same time the receiving regulator 5 opens the damper 7 in the stack. The opening of the damper in the stack increases the suction in a furnace and the controller 16, such vas shown in Letters Patent No. 1,800,400, granted April 14, 1931 to Thomas A. Peebles which is balanced to maintain a furnace combusf tion chamber pressure is put out of balance. To maintain the predetermined furnace chamber pressure the controller 16 operates to open the air control damper 15 thereby increasing the air delivered to the furnace Vuntil the furnace chamber pressure has been 'brought backto standard. On an increase 1n steam pressure the reverse operation takes place, the fuel and air supply to the furnace being decreased.

he powdered coal feeder 10 for the fur- -nace is supplied with air vfrom the forced draft fan 11 through a pipe 12. A secondary air pipe 13 leads from the fan 11 to a burner 14; via duct 13 from whichV air is admitted to the furnace and in vwhich the damper 15 is disposed.

In order to maintain a constant air'pressure in the duct 13, and to insure a steady supply of airvfor the furnace, a balanced controller 8, such as illustrated in said Patent No. 1,800,400 is provided. When the Vpressure of the air in the duct 13 varies beyond predetermined limits the controller becomes unbalanced. To regain its equilibrium, the controller through its associated mechanism either opens or closes the damper 9, depending on whether the pressure is below or above' the determined minimum or maximum, increasing or decreasing the secondary air.V going into the duct until the pressure between the two dampers has been brought back to the predetermined standard. This regulator 8 may be attached as described or it may be used to control the speed of the forced draft fan 11 directly and thus to maintain the pressure in said duct by varying the speed of the fan. Y

This arrangement is forthe purpose of maintaining a constant steam pressure in the boiler and while it makes a primary adjustment in the fuel-air ratio as described it cannot be depended on tovmaintain a registers the carbon dioxide content of the gases escaping from the furnace.

lf the carbon dioxide content of the gases of combustion is too high, that indicates that the furnace is not receiving` sufficient air, therefore, regulator 16 should open damper 15 wider than is necessary to maintain the furnace chamber pressureY at that value which would otherwise be maintained therein by the regulator. When the carbon dioxide content is too low, that indicates thatthe furnace is receiving too much air, hence regulator 15 should close the damper more or less until the proper fuel air ratio-is attained. v

The carbon dioxide recorder 17, a circuit controlling` device 17 (see Fig. 6) operated thereby, auxiliary regulator 19 and al bellows 40 are arranged to so modify the operation of regulator 16, that, as the carbon dioxide content of the gases of combustion varies, either too high or too low, more or less air is admitted to the furnace until the carbon dloXide centen is of the proper value.

Regulator 16 comprises a fluid motor 0, and a pressure responsive device b for controlling the operation of the motor. Y

Motor a com rises a c linder c havin(r `a reciprocating piston thereinv andapiston rod d to whichis attached a frame e. The frame is connected to damper 15, so that as the frame moves up or down with thepiston rod, damper 15 will be either closed or opened. rreversing valve V is mounted on the cylinder and'controls the admission of pressure thereto. Thus, when the valve is moved to one position, the piston moves up wardly, and when moved to another the pis ton moves downwardly.

`Valve V is controlled by device 'Thus when the pressure in the furnace'chamber rises, the valve is shifted to effect upward movement of the regulator; or if the furnace chamber pressure falls, the valve is reversed to cause the frame to move downwardly.

' Pressure responsive device Z) comprises a beam f fulcrumed at 7L, having inverted bells i and attached to the opposite ends thereof. The bells are partially immersed in a` liquid held in a tank 76. The interior of bell z' is subjected to atmospheric pressure by means of an. open. ended pipe Z that extends upwardly through the bottom of the tank and into the interior of the iioat.l

The interior of bell j is subjected to the furnace chamber'pressure which is communicatedv thereto by a pipe 46. 1

Beam /f is operatively connected to valve V by suitable linkage, indicated generally at m; the arrangement of the linkage isfully described in a copending application for Letters Patent, Serial No.y 520,949, filed March fused-fem lin response vto a decrease in furnace chamber pressure, the valve is reversed to effect a downward movement of the regulator frame.

`In order to cause regulator 16 to operate damper 15 in accordance with the carbon dioxide content of the regulator, a-bellows 40 is provided. Bellows 40 operates upon anextension 40 of beam upon which a weight w is disposed.

If the carbon-dioxide content of the gases of combustion is vtoo low, recorder 17 andthe circuit controlling device 17 ltherof causes auxiliary regulator 19 to;transmit a pressure tothe bellows 40, thereby causing it to expand. As it expands the beam is rocked lcounter clockwise, (that is inthe same direction as an increase in pressure 'within bell would rock it) thereby causing the regulator vto shift damper 15 towards its closed position to reduce the amount of air delivered to the furnace.

When the carbon dioxide content is V too high, auxiliary regulator operates to Yreduce ythe pressure in Vbellows 40, so that `weight w becom-es effective to rock beam 4f'clockwise (that is, in the same 4direction as it :would be rocked by bell if the furnace 4chamber' ff pressure were reduced), thereby to reverse valve V and cause ythe regulator frame to move downwardly to open damper 15 rto y1n- -crease the amount of air delivered to the furnace.

Auxiliary regulator 19 comprisesfa sending relay 19 which is operated by a solenoidoperatedcam device N. Sending relay 19 is illustrated and fully described in Letters Patent No. 1,7 87,407 previously referred to herein.

Solenoid operated cam device N comprises a friction wheel mounted on and secured to the shaft S and a cam26 mounted on and secured to the shaft in spacedrelation to the 'I friction wheel. The particular form of cam illustrated is that of a circular disc mounted eccentrically on the shaft. Since the cam .and wheel are secured to the shaft, the cam may be turned inone direction or the other by turning the friction wheel.

In order to rovide for turnino the friction wheelfand the camin a clockwise direction, a pawl or dog 22 -is provided. vPawl or dog 22 is pivotally mounted between the outer end of two arms 25, the inner ends of which are loosely mounted on shaft S. Pawl 22 provided with a gripping'member 22 which is arranged to grip the friction wheel when the pawl lis turned clockwise. Pawl 22 is operated by a solenoid 20 which is provided with a movable armature conneotedby a .link 22 to the pawl. Thus, when solenoid `2O -isenergized, the armature will be attractedftherebyandmove link 22 upwardly.

vAs link -22 lmoves upwardly, the pawl is actuated into .gripping relation with the friction wheel. The gripping actionbetween the pawl and the `friction wheel takes vplace during the initial upward movement of link 22.v As'the'link continues to Amove upwardly, arms 25 willmove upwardly with the pawl as friction wheel 25 turns. Vhen solenoid 20 is deenergized, arms 25 are released thereby breaking the gripping relation between the pawl and the friction wheel. If the solenoid is again energized, vthe friction wheel will be turned or advanced a Vprede- :termined distance vin a clockwise direction.

Thus it will be apparent that by alternately Venergizing and deenergizing solenoid 20, friction wheel 25 and cam A26 may be advanced step-by-step in a clockwise direction.

YVhen solenoid 20 is deenergized, arms25 rest on an adjustment screw 31, andthe outer end of :pawl or dog 22 rests on a support 2.4. By adjusting set screws 81, `the travel of cam 26 each time one or the other of the solenoids is energized may be increased or .decreased as desired.

ynately energizing and deenergizing solenoid A21, cam 26 and friction wheel 25 maybe advanced in a counter-clockwise direction step-by-step.

'Movements of cam 26 are utilized-to op- `crate sending relay 19'.. The sending relay includesa floating lever 26, a multi-way valve 3,4, apressure responsive bellows that operates against a spring 36, and a push rod 37 which is mounted on the bellows. The upperend ofpush rod 37 is pivotally connected to floating lever 26.

One end of floating lever 26 is pivotally connectedv at 32 to linkage 33 that operates valve 84. The opposite end of floating lever 26'has apin 27 attached thereto which rests on cam 26. -Pin 27 is yieldingly held in engagement with the surface ofthe cam by means'of a spring 28, one end of which is attache'd to lever 26 and the other end of which is anchored at 29 to :the Vhousing 30 of sending'relay 19.

`Valve 34 has an inlet port which is connccted :to -a pipe line 47 Ehaving therein a Jury..

medium under pressure, such as air. vThe valve also is provided with an outlet port 48 that is connected to the interior of bellows and to the interior of pipe 38 leading to indicator 39, and to the interior'of a pipe line 49 that leads to the interior of bellows 40. Valve 34 also has an exhaust port 50.

When valve linkage 33 is moved downwardly, communication vis established throughY valve 34 with pressure supply .pipe 47 and the interior of bellows 35, pipe 38 and pipe line 49. Thus a pressure impulse is transmitted to bellows 40, which as stated hereinbefore, causes damper 15 to movey towards its closed position. `When pressure is applied to the interior of bellows 35 it expands and moves push rod 37 upwardly, thereby causing floating lever 26 to pivot about pin 27. Thus, valve linkage 33 is moved upwardly thereby closing off communication between the pressure line 47, the interior of bellows 35, pipe 38 and pipe line 49.

Tf valve linkage 33 is moved upwardly and above its neutral position, communication will be established between the interior of bellows 35, pipe 38 and pipe line 49v and the atmosphere through exhaust port 50.V Thus the pressure within the bellows, pipe 38 and pipe line 49 will be reduced. Wh-en the pressure is reduced, bellows 35 contracts, thereby moving valve linkage 33 downwardly and returning the valve to its neutral position.

As stated previously herein a reduction in pressure in bellows 40, which occurs Awhen the pressure in pipe line 49 is reduced, causes regulator 15 to open damper 15 to admit more air tothe furnace.

When cam 26 is turning clockwise, valve 34 is operated to reduce the pressure in pipe line 39 and'bellows 40 in the manner aforesaid. As stated previously herein the pres,- sure in bellows 40 should be reduced when the carbon dioxide content of the gases of combustion is too high.

. Counter-clockwise turning ot cam 26 causes valve 34 to operate to` increase the pressure in pipe line 49 and bellows 40 thereby to effect a closing of damper-15 and a reduction in the amount of air delivered to the Jfurnace, when the carbon'dioxide content is Vtoo low. y

From the above it will be seen that solenoid 2O of auxiliary regulator- 19 Vfunctions when the carbon dioxide content, of the gases of combustion, is too'hi'gh, and that solenoid 21 operates to etect a closing of damper 15 and a reduction-in th-e amount of air delivered to the furnace when the carbon dioxide content is too low. Y r

' In F ig. 6 of the drawings, the circuit. connections between circuit controlling device ,'17, which is operated by the carbon dioxide analyzer 17, and solenoids 20 and 21, are schematically illustrated. VThe current for energizing the solenoids is derived from power lines L1 vand L2, a switch 51y being provided to either connect or disconnect the solenoids and the circuit controlling device 17 toor from the power lines. f

Circuit controlling device 17 has a movable contact member 52 which when the carbon dioxide content of the gases of combustion are too high, engages a stationary contact member 53 whereby solenoid 20is connected across power lines L1 and L2. Circuit control device 17 as stated previously herein, is of the type in Awhich the movable Contact member 52 is depressed at frequent intervals by a movable depressor bar (not shown) into engagement with contact member 53. Thus the circuit to solenoid 20 is alternately energized and deenergized to effeet the step-by-step movement of cam 26 in a clockwise direction. Y

When the carbon dioxide content of the gases of combustion is too high, movable contact member 52 engages a stationary contact member 54, and when in the region or" contact member 54 the depressor bar actuates contact member 52 into engagement with Contact member 54, at' predetermined intervals, whereby solenoid 21 is alternately energized and deenergized to effect step-by-step vmovement of cam 26 in a lcounter-clockwise direction. y v

If it is desired to manually control the en- `Vergization oi solenoids .20 and 21 push button switches 44 and 45`may be employed.

To manually increase theamount Aof air suppliedto the urnace,fwhen the carbon dioxide content is too high, push button switch may be manually closed to thereby Venergize solenoid 20. Thus by alternately opening and closing switch 45 thevstep-bystep turning ot cam 26 in a clockwise direction may be eiiected.

It it is desired to decrease the amount of ir delivered to the furnace in case the carbon dioxide content 'of the gases of combustion Yare too low, push button switch 44 is alternately closed and opened to thereby alternately energize and deenergize solenoid 21, whereby the step-by-step turning of cam 26 in a counterclockwise direction is effected.

`When the system is operating on automatic control, the switch operated by push rbuttons 42 and 43 is closed whereby movable contact member 52 of circuit controlling device 17 is connected to power line L2. Even dioxide'content of the gases of combustion,

slightly less.

sistance to the flow from the furnace to the outlet of the boiler. This resistance is termed the draft loss across the boiler and must in each case be equal to the difference between the furnace draft and the outlet un` der the boiler damper. Therefore, when the furnace draft is changed, as is the case in controlling from carbon dioxide` content as described, and the outlet damper remainsconstant, it follows that there must be a change in the weight of the gases passing through the boiler.

If the carbon dioxide of the gases escaping from the furnace goes above the value for which the recorder has been set, it will energize one of the solenoids which sends the impulse as described to the bellows 40 increasing the pressure therein. For the controller to remain in equilibrium the furnace suction must be decreased which is accomplished by the opening of the damper l5 increasing the amount of air passing into the furnace. Since the suction in the 'furnace has been decreased and the outlet draft remains constant the draft loss across the boiler has increased, increasing the amount of air passing into the boiler and making the proper fuel-air ratio correction by adjustment of said damper l5.

On the other hand if the carbon dioxide content becomes too low the reverse action of the carbon dioxide sender acts to increase the draft in the combustion chamber and to decrease the pressure in the bellows 40. To maintain the equilibrium of the controller the furnace suction must be increased. This can only be done by reducing the secondary air admitted to the furnace and the damper l5 is so adjusted. In this way the carbon dioxide content of the gases is again brought back to the correct value.

The carbon dioxide recorder is adjusted so that an analysis of the carbon dioxide content is made about every two minutes or If one analysis proves tobe either too high or too low an impulse is sent out from the sender and a definite pressure change in the bellows 40 results. This effects a slight adjustment in the fuel-air ratio but no continuing adjustment is made until there is another analysis made by the recorder. If this analysis shows the fuel-air ratio to be still incorrect another adjustment is made and so on until the correct fuel-air ratio is secured; otherwise no further ad- -solenoids may be energized by actuating one or the other of the push buttons 44 or 45 on the panel. This permits the CO2V contentof the gases to be regulated to the proper value without Waiting for the automatic sending device to operate. y f

While I have described the preferred embodiment of my invention, it is obvious that certain additions, substitutions, variations or omissions may be made without departing from the spirit of myl invention or the scope of the appended claims. wherever I refer to a recorder registering the variations in CO2 content I do not limit myself to a device which makes an actual record of the analyses although itis clear that I may' use such a device. The recorder may, however, be merely a suitable indicating device either visual or sounding' and operating in any suitable or preferred manner.

In addition, while I may utilize the CO2 yconi tent as the cont-rollin factor, it is clear that I may-in similar fas o ion utilize some other constituent of the gen, or the like.

What I claim as new by Letters Patent is: Y e i l. The combination in a fuel-air control system for` a boiler furnace of means responsive to variations in steam pressure for regulating the supply of fuel to said furnace, means responsive to saidl steam pressure for controlling the outlet damper of said furnace, means responsive to the furnace cham-v ber pressure for regulating the inlet damper and means for making a further adjustment in the inlet damper in accordance, with theV CO2 content of gases escaping from the furnace.

2. The combination in a fuel-air control vand desire to secure system for a boiler furnace of a regulator responsive Vto variations in steamv pressure and adapted to transmit impulses ltherefrom in accordance with said variations, a plurality of regulators actuated by said impulses for controlling the admission of fuel to said furnace and operating the outlet damper of said furnace, a controllerfor maintaining a constant air pressure in a duct leading to said furnace, a recorder for registering CO2 content in gases escaping from the furnace, a sending device energized by the variations in CO2 registeredA by said recorder, having mechanism associated therewith for admitting air fromsaid duct into the furnace.

8. The combination in a fuel-air control system for a boiler furnace of a regulator responsive to variationsin steam pressure and adapted to transmit impulses therefrom ,in accordance with said variations, a plurality of regulators actuated by said impulses for controlling the admission of Vfuel to said. furnace and operating the outlet damper of said furnace,` a controller for maintaining a constant air pressure in a duct leadingto said furnace and means for admitting air from gas, such as oxygennitro- F or example,

said duct into the furnace to maintain the proper fuel-air ratio in said furnace, said means comprising a recorder registering the variations in the carbon dioxide content of 'the gases escaping from said furnace, a plutrolling the admission of air to said furnace.

4. A device for admitting air into a boiler furnace in accordance with the carbon dioxide content of gases escaping therefrom comprising a recorder registering the content of carbon dioxide in said gases, a plurality of solenoids, means associated therewith to energize one of said solenoids when the carbon dioxidek content varies beyond predetermined limits, an eccentric cam controlled by said ysolenoids and having connected therewith mechanism controlling the rate of delivery of air to said furnace.

5. A device for controlling the air supply in a boiler furna-ce in accordance with the CO2 content in the gases escaping from said furnace, comprising a recorder for registering the CO2 content of said gases, means connected into said recorder for making an electric circuit, when said CO2 content varies from predetermined limits, a plurality of solenoids connected with the circuit controlling means, one of Which is adapted to be energized when an electric circuit is made, an eccentric cam operated by said energized solenoid through an articulated linkage, a lever actuated by said cam, in turn actuating a pilot valve adapted to build up pressure in a bellows connected therewith, and means for transmitting the pressure to mechanism for controlling a damper regulating the furnace draft.

6. The combination in a fuel-air control system for a boiler furnacer of means responsive to variations in steam pressure for regulating the supply of fuel to said furnace, means responsive to said steam pressure for controlling the outlet damper to said furnace, means responsive to furnace chamber pressure to control the inlet damper,l

and means for making a further adjustment in the inlet damper in accordance with the content of a selected'constituent of the gases escaping from the furnace.

7 In combination, a valve mechanism having pressure increase, decrease andneutral positions, adapted to transmit variable pressure impulses to an actuating device, a cam for operating said valve mechanism, means including a solenoid for operating said cam in one direction thereby to actuate said valve mechanism to eHec't the transmission of increasing impulses to said actuating device, means including a solenoid for actuating said cam in the opposite direction thereby to actu'- ate said valve mechanism vto effect the transmission of decreasing pressure impulses to said actuating device, means responsive to the-pressure impulses delivered to said actut

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