US1874878A - Method of and apparatus for combustion control - Google Patents

Description

E. S. BRISTOL Aug. 30, 1932.

METHOD OF AND APPARATUS FOR COMBUSTION CONTROL Filed April 16, 1950 R W W N Clan, @Awd' ATTORNEY.

Patented Aug 30, 1932 UNITED STATES PATENT OFFICE,

EDWARD S. BRISTOL, OF PHILADELPHIA, 'PENNSYLVANIA, ASSIGNOB TO LEEDS d: NOBTHRUP COMPANY, OF PHILADELPHIA, PENNSYLVANIA, A CORPORATION OF PENNSYLVANIA 7 METHOD OF AND APPARATUS FOR COMBUSTION CONTROL My invention relates to a method of and apparatus for combustion control in a steam generator, furnace, or the like.

In accordance with my invention, there is maintained a given relation between load demand on the generator or furnace and the speed of operation of suitable means for supplying the same with fuel, the arrangement or manner of operation being such that such speed has a predetermined andsubstantially constant value when the load demand is zero.

Further in accordance with my invention, an electromotive force is developed and varied in accordance with variations in load demand on the generator or furnace, a second and substantially constant electromotive force developed independently of such load demand, and the joint effect of these forces utilized to control rate of supply of an agent or agents contributing to combustion.

Further in accordance with my invention, an electromotive force is developed and varied in accordance with variations in required rate of supply of an agent or agents contributing to combustion, a second electromotive force developed and varied in accordance wlth variations in the actual rate of supply of such agent or age ts, a third electromotive force developed independently of said required and actual rates of supply, and the joint effect of these forces utilized to control the actual rate of supply of such agent or agents.

More particularly in accordance with my invention, an electromotive force is developed and varied in accordance with variations in required rate of supply of an agent or agents contributing to combustion, a second electromotive force developed and varied in accordance with variations in the actual rate of supply of such agent or agents, a third and su stantially constant electromotive force developed independently of said required and actual rates of supply and caused to act with the first force, the first and third forces balanced against the second force, and the actual rate of supply of such agent or agents varied in accordance with conditions of unbalance between such forces.

My invention resides in the method and a paratus hereinafter disclosed and claimed.

- For the purpose of illustrating my invention, one embodiment thereof is shown in the drawing in which Fig. 1 is a schematic showing of a. system for combustion control and Fig. 2 is an enlarged, elevational, d tail view.

In Fig. 1 is shown a combustion control system of the same general character as the system disclosed in my copending application Serial No. 440,597, filed March 31, 1930, and the various parts and connections have been designated by the same reference characters designating corresponding parts and connections in saidapplication.

That part of the construction and operation of the system which is well known in the art and to which no claim is made per so, will first be described, after which the various parts and the method of operation pro vided thereby, which, in combination with the former constitutes my present invention, will be described.

The steam generator or fuel burning apparatus G is connected by a pipe line 2 to the steam header 2a, the rate of combustion in such apparatus controlled by variations in current in an electric control circuit comprising a master control rheostat 14 connected to the voltage supply line 16, connection 15, and resistance R2 connected to the voltage supply line 17 A suitable fluid-pressure motor 6 is connected to header 2a and operates to change the position of the master control contact 13 in accordance with variations in the header pressure occurring upon variations in load demand or boiler pressure, the arrangement being such that upon mcrease in load'demand or decrease in boiler pressure contact 13 is moved downwardly the proper amount to increase the current in the control circuit, this contact moved upwardly to decrease the control current upon decrease in load demand or increase in boiler pressure and in amount corresponding to such variations.

The combustion rate in generator G 1s controlled by the stack damper 4 actuated by the dam er drive unit B which may be of any suita hle construction and comprises the usual reversible driving motor connected across lines 16 and 17 by an air-flow controller A comprising coils wand I) connected in series .with respect to each other, such series having terminals 7 and 9 whereby the same is connected as shown in series with connection 15 forming part of the control circuit. The coil 6 controls movement of a contact 61 and is pivotally supported for movement between coils a which are fixed, contact 61 engaging with either of the fixed contacts al to eflect proper connection of the damper drive unit B across the voltage supply lines to eflect operation thereof in one direction or the other as the case may be, and corresponding adjustment of damper'4. The movable coil 6 is urged in a clockwise direction by a force proportional to the current in the-control circuit and which is representative of the required combustion rate in generator G, and is urged in a counter-clockwise direction-by a second force balancing the first force and which is representative of the rate of flow of the gaseous products of combustion through the generator. The second force is equal to the pressure differential between the points 72. and i to which controller A is connected by pipe lines 28 and 30. When the control current varies in one sense or the other, controller A is out of balance and movable coil 6 moved in the corresponding direction to effect adjustment of damper 4 in such wise that the draft through generator G is changed and the pressure differential between points 71. and z varied in such sense that the second force referred to again' balances the first force to cause return movement of coil 1) to its central or neutral position with respect to fixed coils a. whereat contact 121 is out of engaging relation with the fixed contact all it had just engaged.

The construction and manner of operation of the air-flow controller A is described in detail in my co-pending application 234,410, filed November 19, 1927.

Coming now to descriptionof the various parts and connections which, in combination with those just described, provide for my present improved method of and system for combustion control, the fuel feeding mechanism comprises the units F for delivering pulverized fuel to a furnace, eachunit comprising a suitable fuel pulverizer or mill 34 fed from a hopper 33 under control of a valve 32 or other adjustment means. The pulverized fuel is transferred or drawn from the pulverizer-by a blower 36 driven by a variable speed motor 41, the mixture of fuel and air entering the associated furnace at considerable velocity by way of the burner duct 37.

For varying the speed of motors 41, their fields are connected, respectively, by conductors 42 and 43 with the field rheo-stats 44, each comprising, in the example shown, a suitable resistance element 45 connected to conductor 42 and a conductive strip 46 connected to conductor 43. A contact point on the electrically conductive arm 47 co-acts with element 45, and another contact thereon c0- acts with the conductive strip 46, said arm comprising a portion 48 of suitable insulating material carried by the collar 49 mounted on the shaft 50-, To the end that arm 47 may be adjusted circumferentially of shaft 50, collar 49 may be providedwith a slot 51, as more clearly shown in Fig. 2, into which extends a pin 52 carried by the shaft, said collar being .maintained in a desiredadjusted position by a set screw 53 or the like, threaded into said collar and co-acting with the shaft 50. Each rheostat 44 may be provided with the contact strips 54 forming continuations of the ends of resistance element 45. In the event of overtraveling movement of arm 47 in one direction or the other, the end thereof rides upon and is supported by one of said strips.

As indicated, shaft 50 is common to the .collars 49 and, accordingly, rotation of said shaft effects simultaneous adjustment of each rheostat.

Forming a part of each unit F is a suitable device, as the commutating magneto M, for

generating a uni-directional Voltage proportional to the speed of motor 41. To this end, the rotatable element of the magneto is driven at a speed proportional to the motor speed in any suitable manner, as by the endless band or chain 54 encircling pulleys carried,

respectively, by the motor and magneto shafts.

The pulverizers are driven by motors 410 connected to bus lines 32a and operating at constant speed. Tachometers M0 are driven at constant speed by motors 410, as shown. Resistances 59 having adjustable contacts 60 are connected across the commutators of the variable speed tachometers M, while resistances 61 having adjustable contacts 62 are connected across the commutators of the constant speed tachometers Me, as indicated.

Those sections of resistances 59 and 61 between the upper ends thereof and the respective associated contacts 60 and 61 at any positions of adjustment of the latter, are connected in series relation with respect to each other and such series is connected through conductors 55 and 56 in series with the galvanometer 78 and that section 02 of resistance R2 between the lower end thereof and the associated adjustable contact 123 in any position of adjustment of the latter. This arrangement or connection provides a balanced control circuit in which the section 12 of resistance R2 also forms part of the con-- 14, connection 15, the coils a and b of controller A, and resistance R2. The connections are such that the constant electromotive forces developed across the effective sections of resistances 61 are additive with respect to forces balanced against and acting in oppositlon to the electromotive forces developed across the effective sections of resistances 59 which are additive with respect to each other.

The galvanometer 78 is part of a controller or control mechanism indicated generally by reference character A1 and which is shown as being of the general type described in detail in Patent 1,332,182 of February 24, 1920 to Leeds. Controller A1 comprises the fixed contact 89 connected to supply line 17 by connection 94, and the fixedv contacts 90 connected as shown through suitable limit switches 96 and-102 to the field coils 99 and 105 of the reversible motor 100 for rotating shaft 50 in either direction. As is well known, when galvanometer 78 of controller A1 is connected in a circuit of the character shown and balanced conditions exist, the needle 77 is at rest in a neutral position whereat the controller is non-effective with respect to the various parts controlled thereby, but upon unbalancing of the circuit in one sense or the other, the needle deflects in the corresponding direction to effect controlling action of the controller inthe proper sense such that electrical connection is made between contact 89 and one of the contacts 90, and motor 100 accordingly connected across lines 16 and 17 for operation in the proper direction. In the present system, upon increase in load demand and operation of master controller 14 in the usual manner to effect corresponding increase in the control current, the drop across resistance section 12 increases in amount directly proportional to the requiredrate of fuel supply, whereby the galvanometer circuit is out of balance and needle 77 deflected to cause operation of motor 100 in such direction that rheostats 44 are adjusted to vary the speed of motor 41 and the actual rate of fuel supply until the simultaneously occurring variation in the electromotive forces developed across the effective sections of resistances 59 are again of suflicient value to rebalance the galvanometer circuit. zero load demand, whereat the drop across resistance section 12 will be zero or at least such value as would otherwise call for complete shut down of the fuel supply units, the constant electromotive forces across the effective sections of resistances 61 and'which are developed independently of load demand, call for operation of the blowers 36 at a predetermined and constant rate whereat the electromotiveforces then developed across the effective sections of resistances 59 balance such constant electromotive forces.

The valves 32 for controlling rate of supply of fuel from the hoppers to the pulverizers are connected by sprocket wheels 64 and 65 and chains 66 to shaft 50 for simultaneous adjustment with rheostats 44, the arrangement being such that upon decrease in the speed of motors 41 corresponding closing movement is imparted to valves 32, and vice versa.

The adjustable contact 123 permits variation in the amount by which actual rate of fuel supply is changed for a given variation of steam demand. The voltage drop or electromotive force developed across resistance section 12 is proportional to the required rate of fuel supply. 1

The adjustable contacts 60 provide for vaactual speed of the blowers and steam demand or required rate of fuel supply.

The adjustable contacts 62 provide for variation of the initial required blower speed at zero steam or load demand.

The voltage drop across connections 55 and 56 is proportional to the actual speed of the blowers 36.

The air-flow controller A functions in the well known manner to maintain a constant balance between electric control current and metered air-flow by regulating damper 4.

The constant speed tachometers M0 constitute means operating independently of load demand to provide a bias controlfor operation of the blower 36 or other fuel supply means. That is, tachometers M0 operate in dependently of load demand to induce operation of the fuel supply means at a predetermined and substantially constant speed. At

zero load demand, therefore, the blowers 36 are driven at a predetermined, constant speed which may be varied at will by adjusting contacts'62, this speed being just below that at which the blowers are effective to feed the ulverized fuel into the boilers. When there is any load demand the blowers are therefore immediately effective to feed fuel at the proper rate, the rate of fuel supply increasmg, as explained, under control of the master controller 6 as the load demand increases. The adjustment of valves 32 may be such that the same are closed at zero load demand. In lieu of tachometers M0, batteries or any other suitable constant voltage source may be employed.

What I claim is: ""1. In the art of combustion control'in a system of the character described, the method 1 which comprises developing an electromotive force whose magnitude is continuously substantially proportional to the load demand on the system, developing a second and sub- 'supply of said agent approaches. a limit greater than zero.

2. In the art of combustion control in a system of the character described, the method which comprises developing an electromotive riation of the maintained relation between J force whose magnitude is continuously substantially proportional to the required rate of supply to said system of an agent contributing to combustion therein, developing a second electromotive force which is a function of the actual rate of supplyto said system of such agent, developing a third. electromotive force independently of said required and actual rates of supply, and utilizing the joint efiects of said forces to control the actual rate of supply of such agent to said system in order as the load demand approaches zero the rate of supply of said agent approaches a limit greater than zero.

3. In the art of combustion control in a system of the character described, the method which comprises developing an electromotive force which is a function of the required rate of supply to said system of an agent contributing to combustion therein, developing a second electromotive force which is a function of the actual rate of supply to said system of such agent, developing a third electromotive force independently of said required and actual rates of supply, balancing said first and third forces against said second force, and controlling the actual rate of supply of such agent to said system in accordance with conditions. of unbalance between said forces.

4. In a system of the character described, apparatus for burning fuel, an' electrical circuit, means developing in said circuit an electromotive force which is a function of the required rate of supply to said apparatus of an agent contributing to combustion therein, means developing in said circuit a second electromotive force which is a function of the actual rate of supply to said apparatus of such agent, means developing in said circuit a third electromotive force independently of said required and actual rates of supply, sa' first and third forces bal anced agains said second force, and means controlling the actual rate of supply of such agent to said apparatus in accordance with current conditions in said circuit.

5. In a system of the character described, apparatus for burning fuel, an electrical control circuit, means operable to control current conditions in said circuit in accordance with required rate of fuel supply to said apparatus, means responsive to current conditions in said circuit and operating in accordance with variations in such conditions to control rate of air supply to support fuel combustion in said apparatus, a balanced electrical circuit, a resistance common to and forming part of said circuits and developing an electromotive force in said balanced circuit, mechanism for feeding fuel to said apparatus, means developing in said balanced circuit a second electromotive force which is a function of the rate of operation of said mechanism, means developing in said balanced circuit a third and substantially eration of said mechanism and including means driven by said driving means.

7. In a system of the character described,

apparatus for burning fuel, and means for controlling rate of combustion in said apparatus, said control means including an electrical circuit, tachometers connected in said circuit, means driving certain of said ta-' chometers at a rate varying in accordance with variations in required rate of combustion in said apparatus, and means driving certain other of said tachometers ata substantially constant rate and independently of such variations.

8. In a system of the character describer, apparatus for burning fuel, and means for controlling rate of combustion in said apparatus, saidcontrol means including an electrical circuit, tachometers connected in said circuit, means driving certain of said tachometers at a rate varying in accordance with variations in required rate of combustion in said apparatus, and means driving certain other of said tachometers at a substantially constant rate and independently of such variations, said tachometers connected in said circuit in electrical opposition with respect to each other.

9. A control system for a vapor generator comprising fuel supply means, means for producing a force which is a function of the required rate of supply of fuel, means for producing a force which is a function of the actual rate of supply of fuel, means for pro- I ducing a substantially constant force, and means responsive to unbalance between said second force and the sum 'of said first andv third forces controlling the speed of said fuel supply means.

10. A control system for a vapor generator comprising fuel supply means, air supply means, means for producing a force which is a function of the load demand, means for producing a force which is a function of the rate of air supply, means for producing a force which is a function of the rate of fuel supply, means for producing a substantially constant force, means responsive to unbalance of said first and second forces for controlling said air supply means, and means responsive to unbalance between said third force and the sum of said first and fourth forces for controlling the speed of said fuel supply means.

11. A control System for a vapor generator comprising fuel supply means, means for producing a force which is a function of the required rate of supply of fuel, means for producing a force which is a function of the actual rate of supply of fuel, means for producing a substantially constant force, means responsive to unbalance between, said second force and the sum of said first and third forces controlling the speed of said fuel supply means, and means manually adjustable to vary the relation between the required and actual rate of supply of fuel for which said forces are balanced.

12. A control system for a vapor generator, fuel. supply means, air supply means, means for producing a force which is a function of the load demand, means for producing a force which is a function of the rate of air supply, means for producing a force which is a function of the rate of fuel supply, means for producing a substantially constant force, means responsive to unbalance of said first and second forces for controlling said air supply means, means responsive to unbalance between said third force and the sum of said first and fourth forces for controlling the speed of said fuel supply means, and means manually adjustable to vary the relations between load demand, the rate of supply of air, and rate of supply of fuel for which said forces are balanced.

13. A system comprising a vapor generator, means for supplying an agent contributing to combustionto said generator,means responsive to changes in the demand upon said generator for varying a control force in accordance with demand, means producing a force of constant magnitude, and means for controlling the speed of said supply means in accordance with the joint magnitude of said forces whereby the speed varies with vapor demand but approaches a predetermined speed above zero as the vapor demand approaches zero.

14. In a system of the character described, apparatus for burning fuel, a source of current, means associated therewith for obtaining a voltage whose magnitude is continuously substantially proportional to the required rate of supply of fuel, a second source ofcurrent, means associated therewith for "obtaining a second voltage whose magnitude is substantially proportional to the rate of supply of fuel, a source of substantially constant voltage, and means responsive to unbalance between said first variable voltage and the sum of said second variable voltage and'said constant voltage for varying the rate of supply of fuel.

15. A system comprising a vapor generator, a variable speed blower for producing a jet conveying fuel to said vapor generator, means responsive to changes in demand upon said generator for producing a control force, means driven by said blower for producing a control force, means producing a control force of constant magnitude, and means for varying the speed of said blower in accordance with unbalance between said first con EDWARD S. BRISTOL.

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