US2784912A

US2784912A - Control system for vapor generators

Info

Publication number: US2784912A
Application number: US393815A
Authority: US
Inventors: Edwin D Scutt
Original assignee: Leeds and Northrup Co
Current assignee: Leeds and Northrup Co
Priority date: 1953-11-23
Filing date: 1953-11-23
Publication date: 1957-03-12
Anticipated expiration: 1974-03-12

Description

March 12, 1957 E. D. scuTT CONTROL SYSTEM FOR VAPOR GENERATORS Filed Nov. 23, 1953 5 Sheets-Sheet l March 12, 1957 E. D. SCUTT CONTROL SYSTEM FOR VAPOR GENERATORS 5 Sheets-Sheet 2 Filed NOV. 23, 1953 March 12, 1957 E. D. scuTT CONTROL SYSTEM FOR VAPOR GENERATORS 5 Sheets-Sheet 3 Filed Nov. 23, 1953 E. D. SCUTT CONTROL SYSTEM FOR VAPOR GENERATORS March 12, 1957 5 Sheets-Sheet 4 Filed NOV. 23, 1953 March 12, 1957 E. D. scuTT CONTROL SYSTEM FOR VAPOR GENERATORS 5 Sheets-Sheet 5 Filed Nov. 25, 1955 United States Patent 2,784,912 CONTROL SYSTEM non vAPon GENERATORS Edwin D. Scott, Willow Grove, Pa., assignor to Leeds and Northrup Company, Philadelphia, Fa, a corporation of Pennsylvania Application November 23, 1953, Serial No. 393,815 Claims. (Cl. 236- 44 This invention relates to control systemsjfonvapor generators of the type delivering vapor to a common line and including two independent furnacesandhas for an object the provision of means for varying the fuel supplied to each furnace to maintain optimum conditions of combustion of fuel with any selected ratio of heat generation within the respective furnaces.

Though the present invention is applicable to vapor generating units of widely differing design, it has particular usefulness in applications where the vapor or steam requirements are quite high. For example, some present-day turbine generators have capacities of 200,000 kilowatts and above. As the boiler capacities have been increased to meet such heavy loads, furnaces for them have been subdivided into severalfcombustion chambers as a means of overcoming constructional, combustion, and heat transfer problems encountered in connection with the larger units.

In one type of boiler, known as a split-furnace boiler, the paths for combustion. gases come together beyond the two combustion chambers. Another type,known as a twin-furnace boiler, has, in effect, two separate furnaces in that fuel supplies thereto and passages for combustion gases therefrom are entirely separate. This type is particularly advantageous when steam returned from ahigh pressure turbine is tohe reheated and again ,fed to a turbine. With completely separate gas passages for the two furnaces, and with location of the reheater section in one furnace only, that furnace may be independently brought up to temperature, but only after steam is availableto pass through the reheater, thus avoiding overheating of the reheater section.

Twin-furnace boilers present unusual control problems, since while the furnaces are separate, there is only one steam pressure and one steam flow which can be measured for purposes of control. New methods are therefore required toassure that each furnace is operated with high efficiency while supplying its proper share of the heat.

The present invention is particularly useful when furnaces of the foregoing type utilize coal as fuel. .As is well understood by those skilled in the art, pulverizers are in general located adjacent the furnace with delivery of pulverized coal directly to the tire chamber. While there is a more orless regulated flow of coal to the fire chamber, as by adjustment of the speeds of the coal feeders which deliver the fuel to the pulverizers, nevertheless, a number of factors contribute to substantial irregularity in the amount of coal delivered per unit of time at a given speed of operation. Whenthere is superimposed on such. variables a varying B. t. u. contentof the coal, the heat content of the fuel delivered in unit-time may represent a variable of substantial magnitude and may give rise to unequal heating conditions inthe several furnaces and to undesirable conditions of combustion andheat distribution.

In carrying out the present invention in one form thereof, advantage is taken of the fact that combustion 2,784,912 Patented Mar. 12, 1957 efiiciency is related to the oxygen content of the products of combustion from each furnace. Accordingly, with the oxygen content at a predetermined value, .it will be known that the conditions of combustion for the fuel are maintained at optimum values. There is provided a sensitive means exposed to the combustion products from each furnace for developing an outputwhich varies with the efficiency of combustion of fuel within each furnace.

.While oxygen may be preferred as a component. of products of combustion selected to vary the output of such an element, it is to be understood that another component or a product of the combustion may be utilized to produce a variable output which is indicative of efficiency of fuel combustion within the furnace. While variation in such output can be utilized to vary the relationship between fuel delivery and combustion air, it is preferred to predetermine the flow of combustion air inaccordance with the steam flow in the delivery line to adjust the total fuel to the two furnaces to maintain the steam, pressure, and relatively to adjust the rate of fuel delivery to each furnace to equalize the combustion conditions between the furnaces through maintaining the difference between the outputs of said sensitive elements at a predetermined value, generally zero.

For further objects and advantages of the invention and for a more detailed description thereof, reference is to be had to the following description taken in conjunction with the accompanyingidrawings, in which:

Fig. l illustrates, partly by block diagram and partly diagrammatically, one embodiment of the invention;

Fig. .2. diagrammatically illustrates a control system for regulating the supply of combustion air to the furnaces;

Fig. 3 diagrammatically illustrates the control system for maintaining predetermined pressure conditions within thefurnaces;

Fig. 4 diagrammatically illustrates a preferred form of an oxygen detecting system for the several furnaces; and

Fig. 5 diagrammatically illustrates a modified form of the. invention.

Referring to. Fig. l the invention has been shown in one form as applied to a vapor generator or steam boiler 10 of the multiple furnace type. One furnace 11 has its own steam heating sections schematically represented by the coils 12a and 1211, its own means for regulating the flow of combustion air therethrough, as by the dampers 13,.and its own fuel burners 14a and 1412. A second furnace 15 has its own steam heating sections represented schematically by the coils 16a and 16b, its own means for regulating the flow of combustion air therethrough comprising the dampers 17 and its own burners 18a and 18b. The burners 14a and 14]) are' supplied with powdered coal from pulverizers 20, while the burners 18a and 18b are supplied from pulverizers 21.

Mention has already been made of the fact that the steam coils 12 and 16 are but diagrammatic representations of conventional arrangements of steam heating sections which may, and will, be provided in each of furnaces 1 1 and 15. For example, in furnace 11 there may be included a steam generating section, a primary superheatersection 12a and a secondary superheater section 12b, while the other. furnace 15 maybe provided with a steam generating section, a primary superheater section 16a and a reheater section 16b, these being supported in conventional locations within each furnace. As shown in Fig. 1, however, the gases and products of combustion flow from each furnace through

ducts

22 and 23 leading to a stack 24. In the passageway to the stack there is included a fan 25 for applying an induced draft to both of the

ducts

22 and 23 and thence to the

furnaces

11 and 15. i

end of the arm 60a.

A source of vapor for coils 12 and 16 is represented by a steam drum 27, the superheated steam from coils 12a, 12b and 16a being delivered by way of a common line 28 to a steam header 29 for the supply of steam to the turbine-generator units, only one of which, the unit 30, being shown.

In order to equalize and to maintain at optimum conditions the combustion of fuel, powdered coal, for each furnace, there is provided in each of them a sensing device'for producing an output which varies with efficiency of the combustion of the fuel. More specifically, for furnace 11 such a device 31 having a gassampling line 31a produces an output varying with the amount of oxygen present as a component of the products of combustion. Similarly, for furnace 15a device 32 having a gas-sampling line 32a produces an output which varies with oxygen as a component of the products 'of combustion.

The manner in which each of the

devices

31 and 32 functions will be later explained in connection with more detailed showings of one suitable type of equipment, it being sufficient for the purposes of Fig. 1 to say that the device 32 serves relatively to adjust the position of a slidewire contact 33a relative to its slidewire 33, similar relative adjustment occurring as between slidewire 34 and its associated contact 34a as a result of operation of device 31.

Slidewires 33 and 34 are connected in an electrical bridge or network 35 developing an output applied to a control system represented by a block 36 for applying control signals to

conductors

37 and 38 depending upon whether the oxygen content in furnace 11 is greater or less than the oxygen content in furnace 15 as indicated by

devices

31 and 32.

If the oxygen content in furnace 11 exceeds that in furnace 15, current flows under the control of system 36 as from a supply line 39 by way of conductor 38 to a motor 40 and to the other supply line 39a. The motor 40 is thereupon energized for rotation in a direction which through associated apparatus increases the speed of coal feeders 20a and decreases the speed of coal feeders 21a.

If the oxygen content in furnace 15, as detected by device 32, rises above that in furnace 11, it will be understood that the control system 36 will apply through conductor 37 a control signal for reverse operation of motor 40 again to equalize the oxygen content in the two furnaces by relatively changing the rate of fuel delivery to them.

The speeds of operation of coal feeders 20a and 21a are adjusted by the operation of motor 40 by any suitable means, the one illustrated including speed adjusters similar to the type known as Reeves drives. More particularly, a pair of motors 41 drives coal feeders 20a through a pair of Reeves drives 42, while a pair of motors 43 drives coal feeders 21a through Reeves drives 44. Motors 46 respectively serve to adjust the Reeves drives 42, the motors being connected in parallel to

control conductors

47 and 48. Similarly, motors 49 connected in parallel to

control conductors

50 and 51 serve to adjust the Reeves drives 44.

The coal feeder speed-adjusting motors 46 are energized under the control of a Kelvin balance 60 having coils 61-64, the energization of which positions a control arm 60a to complete a circuit from a supply line 65 through a movable contact and one or the other of stationary contacts to one or the other of

control conductors

47 and 48. The position of the control arm 60a of the Kelvin balance 60 likewise depends upon the pressure applied to it by a diaphragm of a pressure-responsive'device 66 as through an element bearing against an As will later be explained in detail, the force applied to arm 60a by device 66 varies in response to changes of pressure within steam header ,29. If the steam pressure in header 29 decreases, the

arm 60a is moved to close a circuit through conductor 47 to energize motors 46 in directions to increase the speed of operation of coal feeders 20a. The circuit ex-' tends from supply line 65 by way of the movable contact, the left-hand stationary contact, conductor 47 and through the respective motors 46 and thence to the other supply line 67. As shown, the

coils

61 and 62 produce opposing magnetic fluxes, while the coils 63 and 64 produce fluxes which develop attractive forces. Thus, the respective pairs of coils 61-62 and 6364 tend to rotate arm 60a in a clockwise direction about pivot 68, the movement being opposed by the thrust developed by pressure-responsive device 66.

By including in the energizing circuit of coils 61-64 an autotransformer 70, several purposes are served. First, upon energization of motors 46, and through mechanical connections 46a and 46b, autotransformers 71 and 72 are adjusted to produce an increased output voltage with increasing speed of operation of the coal feeders; and a decreasing output for a decreasing speed of operation of the coal feeders.

The outputs from transformers 71 and 72 are applied to the primary windings of insulating transformers 73 and 74. They have their secondary windings connected in series-aiding relationship in a series-circuit formed by

conductors

76 and 77 leading to the autotransformer 70.

An increase in pressure on device 66 causes arm 60a to move in a counterclockwise direction. The resultant operation of autotransformers 71 and 72 increases the energization of autotransformer 70. The increased energization of the coils of the Kelvin balance increases the clockwise torque applied to arm 60a to bring about a new balance with the movable contact in open-circuit position and with the coal feeders operating at the newly established increased speed.

The second function performed by the autotransformer 70 and its counterpart 70a, associated with a Kelvin balance 80, is produced by the operation of the motor 40 in one direction or the other under the control of the oxygen-responsive system including network 35. As already explained, when the oxygen content in furnace 11 differs from that in furnace 15, the motor 40 is energized in a direction which changes the output of autotransformers 70 and 70a for operation of the respective Kelvin balances 60 and 80 to vary the speeds of operation of the coal feeders until the oxygen contents in

furnaces

11 and 15 are equalized. It is to be understood, of course, that motor 40 moves adjustable contact of autotransformer 70 to increase its output at the same time it moves the adjustable contact of transformer 70a to decrease its output, and vice versa.

The pressure-

responsive devices

66 and 81 associated with the respective Kelvin balances 60 and 80 directly affect the position of the control arms 60a and 80a. Thus the primary response of the control system is to steam pressure in header 29. The adjustment of arms 60a and 80a with change of setting of autotransformers 70 and 70a represents a secondary adjustment. The described operation under the control of the oxygen-responsive bridge 35 has been termed a secondary eifect for the reason that in normal operation only a small adjustment of autotransformers 70 and 70:: will be required to equalize the oxygen contents in the

respective furnaces

11 and 15 to maintain optimum conditions of combustion.

Though more extensive changes in the speeds of operation of the coal feeders may be obtained in accordance with the invention, other provisions for the control of combustion conditions result ordinarily in the need for only limited adjustment of autotransformers 70 and 70a.

There will now be explained some of the other provisions for procuring optimum conditions of combustion offuel. To large extent, the combustion air supplied to each furnace is determined in accordance with steam fl w through the common steam line 28 extending to heade 2 s. he am un o ombu ist ir or th ,ratejat which it flows is related to the load to be carried in Fig. 2, will be later described.

In the vapor or steam generator 10 of Fig. 1, a number of desirable conditions of operation are met in addition to those which havejust been outlined. As is well understood, the fan applies an induced draft to

furnaces

11 and 15. The magnitude of the induced draft is under the control of dampers 8 4 adjustable as by a control device 85. Device 85 adjusts dampers 84 to predetermine the ratio of total air flow to both furnaces with respect to the steam flow in the common line 28.

Dampers

13 and 17 respectively in

furnaces

11 and 15 are adjusted to maintain equality or predetermined bias or difference in flow of combustion air as between the two furnaces.

A fan 83 is provided for applyingforced draft to the

furnaces

11 and 15. The magnitude of that draft is regulated by dampers 88, adjusted by device 89 to maintain a desired average pressure within the two furnaces as compared to the external pressure. In; general, aslight negative pressure within the furnace relative to ambient pressure represents a desirable condition.

When one or the other of

dampers

13 and 17 is moved toward a closed position to decrease the flow of combustion air, there will be a corresponding adjustment of be moved toward closed position for equalization of furnace pressure,

dampers

13 and 86 under the assumed conditions remaining in their open positions.

There will now be described the manner in which the pressures applied by

devices

66 and 81 to the Kelvin balances and are varied in response to steam pressure in header 29. The pressure in header 29 is applied by a pipe 91 to a pressure-responsive element, as a Bourdon tube 92, forming a part of a master controller93.

The master controller 93 may be constructed in the manner fully described in McLeod Patent No. 2,507,606 to which reference may be made for a more detailed description, or it may be similar to the schematic illustration thereof as appearing in Fig. 1.

An increase in pressure in header 29 causes the Bourdon tube 92, through a push rod 94, to move a control lever in a clockwise direction about a spring-pivot 96. A

decrease in pressure causes Bourdon tube 92 to move to the left, as by spring 97, the push rod 94 and the control lever 95 also moving to the left by reason of the spring bias produced by the spring-hinge 96. The movement of a baffle 98 toward and ,away from a nozzle 99 varies the pressurein an output line 100 under the control of a pneumatic relay 101 supplied with air pressure from a suitable source of supply as indicated by the air supply line 102.

With an increase in steam pressure on Bourdon tube 92 baffle 98 is moved away from nozzle 99, thus reducing the pressure on the pneumatic relay or booster 101 and likewise reducing the air output pressure in line 100. The effect upon the Kelvin balances 60 and 80 has already been described, the reduction in pressure in line 100 resulting in clockwise rotation of control arms 60a and 3011 with resultant completion of motor .circuits to the right-hand stationary contacts to reduce the rate of supply of fuel to the

respective furnaces

11 and 15. Though not essential, there has been shown proportional bellows 105 and reset bellows 106 associated with an auxiliary control arm 107, spring-pivoted at 108 and having its opposite end spring-centered as by a pair of springs 109. The proportional bellows 105 is connected to output line 110 through a rate adjustment valve111 which introduces a rate action in the operation of the device. The reset bellows 106 is connectedto output line 110 by way of a reset adjustment valve 112 and introduces reset action into the operation.

The booster or pneumatic relay represented by the block 101 corresponds with the booster 560i said McLeod patent, and in that patent there will also be founda description of how the proportional b and may be'adjusted as desired, the manner in which the reset bellows 106 corrects for droop and the manner in which the rate valve 111 provides the rate action already mentioned.

With the fuel delivery determined by the master controller 93, it will now be seen that if the fuel delivery to the furnace 11 differs from that to the furnace 15, there will be excess air or excess fuelin the one as againsfthe other. 1 Accordingly, the oxygen content of the products of combustion will differ, and in response to

sensing devices

31 and 32 an output signal will be applied to pile of

conductors

37 and 38 for energization of motor 40 in a direction to increase the energization of the coils of oneKelvin balance and to decrease the energization of the coils in the other Kelvin balance. Thus, there is provided the further control action varying the operation of the coal feeders. The rates of fuel delivery to the two furnaoes are changedeone being increased and the other decreased, untilthe oxygen content of the products of combustionare equalized or brought to values maintaining a predetermined difference between them. That predetermined diiference may be readily adjusted by. operation of a knob 115 for relatively adjusting

slidewires

116 and 117 in the bridge 35 for balance of the bridge with relativelydifiering outputs from the

devices

31 and 32.

Referring now to Fig. 2, there will be described the system which automatically establishes a predetermined flow of combustion air to the two

furnaces

11 and 15 in response to the rate of flow of steam from the two furnaces, as for example, through the header 29. The system automatically varies the combustion air with change of flow of steam and in direction to increase the combustion air and, hence, to increase the combustion rate with increased steam flow and to decrease the combustion rate on decreased steam flow. As greater loads are imposed upon the turbine-generator, it will beunderstood by those skilled in the art that the amount of steam flowing from header 29 to the turbine will be increased, and as the load on the turbine-generator is reduced, the steam flow to the turbine will be decreased.

As shown in Fig. 2, an indication or measurement of steam flow in header 29 is obtained by means of the pressure differential across a restriction shown as a venturi 29a. A high-pressure line 120 applies the high pressure to the left-hand side of a tilting manometer 121, and a low-pressure line 122 from venturi 29a is connected to the right-hand side of the manometer 121. With varying differential pressure, the manometer 121 will rotate or tilt to the right or to the left about a fulcrum 123 to move a contact 12410 the right or to the left for energization from

supply lines

125 and 126 of the device or motor 85 for rotation in a direction to adjust dampers 84 to vary the total flow of combustion air through the

furnaces

11 and 15 in accordance with changes in steam flow.

As shown in Fig. 2 the level of liquid in the tilting manometer 121 is much higher on the right-hand leg and, hence, the resultant diiferential-pressure torque tends to rotate the manometer in a clockwise direction. This torque is opposed by a torque applied through a link 127, connected at its upper end to a nut or threaded carriage on a threaded rod 123, and at its lower end connected to a diaphragm 129. As later explained, a pilot air flow in line 134 containing restriction 133 is maintained proportional to total combustion air flow. The differential pressure across restriction 133 is applied to diaphragm 7 129 in the direction to produce a downward pull on link 1 27 and thereby exert a counterclockwise torque on manometer 121. The two torques are automatically balanced through the operation of motor in adjusting dampers 84, as earlier described.

If it be desired to change the ratio of flow as between steam flow in header 29 and air flow in line 134, it is only necessary to move the connection of link 127 toward or away from the fulcrum 123 of the tilting manometer. As shownflthis is accomplished by energization of a motor to rotate the threaded rod 128 to move the end of link 127 to the right or to the left. Though the motor may be controlled automatically, a single-pole, doublethrow switch 13511 is shown as operated to the right or to the left to energize the motor for forward or reverse operation.

The flow of pilot air from a supply regulator 130 by way of pipe 134 is made proportional to the total flow of air through the

furnaces

11 and 15 in the manner now to be described.

The flow of air through the furnace 11 is determined from the drop of pressure across a flow restriction within the furnace. This restriction, which is represented by a baffle 11a, will ordinarily be the restriction introduced by a bank of tubes or other furnace structure.

Lines

137 and 138 respectively extending from the high and low pressure sides of baflle 11a are connected to a tilting manometer 139 which, as a result thereof, has applied to it a torque tending to rotate it in a clockwise direction. That torque is opposed by the air pressure applied to the upper side of a diaphragm 140, being the air pressure in a line 141. Line 141 is terminated by a flow restriction 142, flow of air therethrough being under the control of a pressure regulator 143 interposed between line 134 and line 141. The regulator 143 includes a valve element connected to a diaphragm 143a exposed on its upper side to the pressure in line 141 and on its lower side to the pressure applied by way of a line 144. Thus, the valve is moved between open and closed positions in accordance with the differential of pressure across diaphragm 143a. As shown, the valve element is biased toward open position by a spring, though it may be omitted if desired.

The pressure in line 144 is determined by the position of a valve 145 of the throttling or leak-port type. from a suitable source is applied at constant pressure by way of regulator 146 to the valve 145 which produces in line 144 and against diaphragm 143a a pressure varying with the position of the valve stem 145a. That valve stem is positioned by the control element 13% of tilting manometer 139. Thus, as the flow of air through furnace 11 increases, the differential pressure applied to manometer .139 increases and the manometer rotates in a clockwise direction to reduce leakage at valve 145 and to increase the pressure against the lower side of the diaphragm 143a. This moves the valve element of the regular 143 toward open position and increases the pres sure in line 141. The resultant increase of pressure applied to diaphragm 141i restores balance of the manometer 139 in its new position. The flow of air through the restriction or orifice 142 is then proportional to the flow of air through the furnace 11. It follows then that the pressure above atmosphere within line 141 is proportional to the differential of pressure across bafllc 110.

A tilting manometer 149 is connected by lines 151i and 151 across a baffle 15a of furnace 15. By means of a pressure regulator 152, a valve 153 and a diaphragm 154 there is maintained in line 155, a pressure above atmospheric, proportional to the ditferential of pressure across baffle 15a and a flow of air through orifice 1.56 porportional to the flow of combustion air through furnace 15.

Inasmuch as the air flow through restriction 142 is proportional to the flow of combustion air through furnace 11 and the flow of air through restriction 156 is proportional to combustion air through furnace 15, it follows til arsenic.

at once that'the flow of air through line 134 is proportional to the sum, i. e., to the total flow of combustion air to the two

furnaces

11 and 15. It is in this manner that the manometer 121 responds to deviations from a predetermined ratio between steam-flow in header ,29 and flow of total combustion air to the two furnaces.

In order to maintain a predetermined division of combustion air as between

furnaces

11 and 15, provision is made relatively to adjust

dampers

13 and 17. As shown, a motor 160 operates an actuating member 161 to move dampers 17 toward closed'position with dampers 13in fully opened position or to move dampers 13 toward closed. position with dampers 17 in fully open position. This is accomplished by rotation of member 161 against one or the other of

push rods

162 and 163 respectively connected to move

dampers

13 and 17 between open and closed positions, each push rod being provided with a spring normally biasing the associated dampers in the open position. The motor 160 is rotated in one direction or the other under the control of a tilting manometer 164, one side of which is connected by a line 165 to the line 155, and thus the pressure applied to the manometer through line 165 is proportional to the differential of pressure across bafile 15a and, hence, is representative of the flow of combustion air through furnace 15. If the other connecting line 166 of manometer 164 be directly connected to line- 141, the manometer 164 will respond to any differences between pressure differentials across baffie 15a in furnace 15 and battle 11a in furnace 11.

With any change of such pressure drops, manometer 164 through movable contact 164a will energize motor 160 for rotation in one direction or the other to change the relative positions of

dampers

13 and 17 to equalize said differentials of pressure. Such an operation is contemplated, but in order to provide greater flexibility and to make it easy to maintain any desired division of flow of combustion air and any desired rate of combustion in the two furnaces, a pressure regulating valve 167 and a pneumatic booster or relay 168 are provided between

lines

141 and 166. Pressure from line 141 is applied by way of a line 169 to the lower side of a diaphragm 168a of large diameter as compared with a second diaphragm 1681;. A valve element 1680 is normally biased to open position for flow of air from a source including a regulator 170 to a line 171 and thence through valve 167 to line 166. The pressure in line 171 is applied to the upper side of diaphragm 16Sb connected to the valve stem, and thus opposes the pressure applied to the lower side of the larger diaphragm 163a. Accordingly, the position of the valve will depend upon the balance between these two pressures, neglecting a light spring which may be included to bias the valve element 1680 to the open position. Since the diaphragm 168a is of larger diameter, a higher pressure must exist in line 171 for application to the smaller diaphragm 1623b in order to balance the forces on the valve stem. Thus the pressure in line 171 will be proportional to that in line 169, but higher in the ratio of the relative areas of the two diaphragms. The ratio of pressures may be of the order of 1.6. The valve 167 is preferably of the throttling type with a leak-port so that upon movement as by knob 172 of its stem in one direction, the pressure in line 166 may be reduced to any desired degree, to a value lower than or equalling the pressure in line 171. When in a position to produce equalityas between pressures in

lines

141 and 166, the

operation will be as described above where the assump tion was made of a direct connection from line 166 to line 141.

When the pressure in line 166 is higher than in line 141, the tilting manometer 164 will energize motor 160 for rotation of element 161 in a direction to open damper 17. This will increase the flow of air through furnace 15 relative to the flow of air through furnace 11. There will then be an increased pressure drop across bafile 15a which will result in an increased pressure in line 165 which is the diagrammatic system of Fig. 3.

applied to the: tilting manometer 164., the change. being in a direction to restore balance. If it be insufficient to restore balance, the motor lo'o'will continue to: rotate in the same direction until dampers 17 have. beenmoved to the fully opened position and dampers 1'3 moved toward the closed position. The change in the differential of pressure across bafile 11a in furnace 11 and in a decreasing direction will, of course, result in reduced pressure in line 141, as appliedby line 169 upon diaphragm 168a to reduce the pressure in line 166, a change which is also in the direction to restore balance of the manometer 164 and to deenergize motor 160.

Any changes in total flow of combustion air through

furnaces

11 and 15. produced by relative adjustments of

dampers

13 and 17 is detected by tilting manometer 121; and motor 85 is energized in the direction to maintain the total flow of air to both furnaces at a predetermined value relative to the steam flow in head er 29.

The control of combustion air in the manner which has now been explained has been demonstrated to be effectively related to the steam flow from the associated vapor generator or steam boiler. The manner in which the rate of fuel delivery has been made dependent upon the pressure within steam header 29 and upon the oxygen content of the products of combustion in the two furnaces has been explained in connection with Fig. 1. The requirements of maintaining steam generation to meet variable loading of the turbine-generator 30 to maintain optimum conditions of combustion are met by the functioning of the two systems which, for convenience, sepa-' rately appear in Figs. 1 and 2.

The operation. of

dampers

8d, 87 and 88, though described in connection with Fig. 1, was not mentioned in the description of the system of Fig. 2. The manner in which they are operated to maintain a predetermined pressure within furnaces 11 and will now be described in The air pressure within each of

furnaces

11 and 15 is applied, respectively, by way of

lines

175 and 176 to

manometers

177 and 178. Since in most cases it will be desired to maintain the pressures within the furnaces in the neighborhood of atmospheric pressure, the manometer 177 may be provided with a counterbalance weight 177a on the tilting arm thereof on one side of the fulcrum, while on the opposite side thereof the pressure from furnace 11 is applied by way of

lines

175 and 179 to a liquid-sealed chamber 180., while the pressure from furnace 15 is applied by way of

lines

176 and 181 to a liquid-sealed chamber 182. Thus, the tilting arm of manometer 177 has a torque applied to it tending to rotate it in a counterclockwise direction with pressures in

chambers

180 and 182 below atmospheric and in a clockwise direction with pressures above atmospheric.

As shown, the pressures within the

furnaces

11 and 15 are slightly below atmospheric and the manometer arm is shown exactly balanced by the counterweight 177a. With a rise in pressure within either or both of

furnaces

11 and 15, the manometer 1'77 closes a circuit for motor 89 for operation of dampers 38 toward closed position to reduce the furnace pressures to values such that their sum as represented by torques on the arm of manometer 177 is equal to the torque applied to it by the counterweight 177a. In order that not only the sum of the pressures shall be maintained at a predetermined value, but also so that the pressures within the two furnaces may be at all times equalized,

lines

175 and 176 are connected to a differential tilting manometer 178 which responds to any difference between them to energize a motor 183 in a direction to move dampers 86 toward closed position with dampers 87 in their fully opened position or, as shown, to move dampers 87 toward closed position with dampers 86 in the fully open position. Schematically, an actuating element 184 and associated push rods function in the same manner as described for the actuatins elemen lfil. f? g. 2 and. he e, ne d no asainb described in detail. I

Mention has already been made of the fact that variables other than oxygen content of the products of combustion may be utilized to maintain optimum conditions of combustion within the furnaces 11 and .15, such for example, as carbon dioxide. However, the oxygen-content detecting system has been illustrated in Fig. 4 where there is .shown in detail the apparatus included in each of the

blocks

31 and 32 of Fig. 1. In Fig. 4 sampling elements 31a and 32aare illustrated as pipe lines through which products of combustion are withdrawn. from the

respective furnaces

11 and 15 as by applying suction to the flow lines. In each of

lines

31a and, 32a there are provided filters and 191 to prevent transfer of solid products into flow lines 1 92 and 193.

The apparatus illustrated within the

blocks

31 and 32 is fully described in Foley et a1 Patent. No. 2,603,964 and, hence, need not here be described in detail. For convenience, the applicable reference characters used in the Foley et al. patent, Fig. 9, have been applied to the present Fig. 4, but in the 200 series.

Filtered products of combustion flowing through line 192 are passed through

gas cells

215 and 214 and exit from the .outlet of an aspirator 195 having a fluid inlet pipe 196 for producing reduced pressure on

lines

192 and 31a. The

cells

214 and 215 are provided with

resistor elements

216 and 217. Associated with the cell 214 is a. magnet 223 which exerts a strong magnetic field extend-- ing in a direction transversely of the longitudinal axis and which is preferably shaped to provide a steep magnetic gradient in a direction perpendicular to the longitudinal axis of element 216..

Resistor elements

216 and 217 are heated by flow of current therethrough to set up convection currents within each cell. In cell 214 the cooling effect of the convection currents is increased due to the accelerating effect of the magnetic field from. the permanent magnet 223.

The mass susceptibility of a paramagnetic gas, such as oxygen, varies inversely as its temperature. Therefore, the cooler paramagnetic gases adjacent the walls of the cell 214 are directed downwardly toward the zone of maximum magnetic force and into the vicinity of the heated resistor 216. The magnetic component of flow thusproduced is a function of the concentration of oxygen in the products of combustion, and since this flow component is in a direction to augment the cooling effect on resistor 216, its temperature will be lowered below that of corresponding resistor 217 in cell 215. The resistances will differ by an amount directly related to the concentration of the oxygen content of the gas.

The above brief explanation applies, of course, to the other cells shown in Fig. 4. To measure the oxygen content, the

resistor elements

216 and 217 are connected in two arms of a Wheatstone bridge 250,

additional resistor elements

227 and 228 forming the other two arms of the bridge. The bridge is energized from alternatingcurrent supply lines, and the unbalanced output is applied to an amplifier 230 in opposition to the output of a bridge 254 provided with elements functioning in manner similar to those described in the bridge 250 but exposed to a paramagnetic gas of known concentration of oxygen, such for example, as the oxygen-containing atmosphere. The flow path includes filter 190a, cells 215a and 214a and the aspirator 195a.

The output from bridge 250 is derived across the resistor 263a and the output from bridge 254 is derived across a slidewire resistor 263. The movable contact 263b is adjustable by motor 197 in response to a difference between the output of bridge 250 and that of a bridge 254 in a direction to bring the fractional part of the output voltage of bridge 254 to a value equal to the output of bridge 250. Thus, the ratio of the unbalances of the two

bridge circuits

250 and 254 provides a relative measure of the oxygen content of the gases from furuacell. The motor 197 may be used to operate a pen-index 198 of a recorder 199 and also relatively to adjust contact 34a relative to its slidewire 34.

' The apparatus in block 32 functions for the furnace in exactly the manner described for furnace 11, and the parts of the two

bridges

350 and 354 have been given like reference characters with those of said patent, except they are in the 300 series.

The oxygen content of the gases from furnace 15 is measured and recorded by a recorder 199a driven by a motor 197a and that motor also relatively adjusts contact 33:: relative to its slidewire 33. The Wheatstone bridge 35 energized from an alternating-current source of supply has an output proportional to the difference between the oxygen content of the gases in furnace 11 and those in furnace 15. The operation of the bridge 35 has already been described in connection with Fig. 1 and will not here be repeated.

The control system shown by block 36 within bridge.

35 of Fig. 1 may comprise the amplifier shown in Fig. 1 of Davis Patent No. 2,530,326. In Fig. 4 of the present case, the output of bridge 35 is applied to an amplifier 36a corresponding with the amplifier 28 of said Davis patent, the output thereof serving to energize the operat ing coil of a relay 36b of the single-pole, double-throw type for operation in one direction upon unbalance of the bridge in one direction and for operation in the opposite direction upon reverse of said unbalance. While the relay may be of the polarized type, it may be also of the type diagrammatically illustrated in said Davis patent, i. e., one responsive to change in lever of energization, which level occurs upon change of direction of unbalance of the bridge. Where carbon dioxide is to be used as the component of the combustion gases to maintain optimum conditions of combustion, it will, of course, be understood that a different type of detecting system should be used, one, such for example, as disclosed in Peters Patent No. 1,504,707.

It is to be further understood that only one of the systems within

rectangles

31 and 32 need be used, suitable provisions being made for simultaneous transfer, first for the measurement of the oxygen content Within furnace 11 and then for the measurement of the oxygen content within furnace 15, the transfer mechanism in each case serving first to adjust contact 3411 and then to adjust the contact 33a in the bridge 35. The advantages of eliminating any need for identical response as between and that certain features may be used with other features omitted, and that other types of control systems may be utilized in conjunction with the system of maintaining the magnitude of a selected product of combustion at a predetermined value. For example, in the modification of the invention illustrated in Fig. 5 it will be shown that the flow of the combustion air to the respective furnaces need not depend upon steam flow in the header 29. Combustion air may be controlled in response to a different type of steam-responsive means, namely, one responding to changes in steam pressure. For the most part, Fig.

5 corresponds with the air control system of Fig. 2, and

the same parts have, of course, been given the same reference characters. However, there has been added to Fig. 5 the master controller 93 of Fig. 1 which through line 91 is connected to the header 29 to produce an air pressure in line 100 which varies inversely with change of steam pressure in line 29. Because of the proportional and reset bellows 105 and 106, the air pressure in line 100 varies with change in the vapor load upon the vapor generator. With other than steady-state conditions, the rate function introduced by rate valve 111 modifies the air pressure in line 100 and, of course, at least another component of control action is introduced by the proportional bellows 105. After change in steam pressure, following a change in load and subsequent return of steam pressure in line 29 to its predetermined value, the pressure in line 100 will be established at a new steady value related to the new load.

The master controller 93 continues to function in connection with the Kelvin balances and of Fig. 1 directly to regulate the rate of fuel delivery to the

respective furnaces

11 and 15. However, the total flow of air to those two furnaces depends upon the setting of dampers 84 by motor 85. In Fig. 5 motor is energized under the control of a single-pole, double-throw switch 124a operable by a tilting manometer 360 having applied to the lefthand chamber by way of line 361 the pressure on the high side of the restriction 133 and having applied to its righthand chamber the pressure on the low pressure side of said restriction by way of line 362. The tendency of the tilting manometer 360 to rotate about its pivot in a clockwise direction is opposed by the air pressure applied to a diaphragm 368 having a value determined by the output air pressure in line and the setting of a leak-port valve 364 which is of the same construction as similar leak valves and 153 of this same figure.

It will be recalled that the total air flow through restriction 133 is related to the total air flow through

furnaces

11 and 15 and is made to vary with any change in that air flow. The tilting manometer 360 functions in response to any change in air flow through the furnaces as reflected by a change in air flow through restriction 133 to return the total air flow to a predetermined value as by energizetion of motor 85 in one direction or the other. Similarly, any change in steam pressure reflected by a change in air pressure in line 100 changes the bias exerted on the tilting manometer 360 by diaphragm 368 and causes the single-pole double-throw switch 124a to move in a direction to energize motor 85 to open dampers 84 to increase the total air flow whenever the steam pressure falls and to decrease the total air flow whenever the steam pressure in header 29 rises. The modification of Fig. 5 will, in some cases, be preferred to that shown in Fig. 2, and is a modification to be considered when oil burners or types of fuel other than powdered coal are to be utilized.

What is claimed is:

1. In combination, a vapor generator having independent furnaces, each with its own fuel burner and its own vapor heating sections, said sections being connected to a common line for delivery of vapor to a load, means responsive to an operating condition of said vapor generator representative of its vapor load for establishing a predetermined total air flow to said furnaces, means responsive to an operating condition of said vapor generator representative of the vapor load for increasing the total rate of fuel supply to said furnaces with increase in vapor load and for decreasing said total rate of fuel supply to said furnaces with decrease in said vapor load, a

sensitive element for each furnace exposed to combustion products generated therein for developing an output which varies with effieiency of combustion of fuel within said furnace, and means responsive to the outputs of said sensitive elements for increasing the rate of fuel supply to one furnace while decreasing the rate of fuel supply to the other furnace until the outputs of said sensitive elements bear a predetermined relation one to the other.

2. In combination, a vapor generator having independent furnaces, each with its own fuel burner and its own 1 vapor heating sections, said sections being connected to a common line for delivery of vapor to a load, means responsive to an operating condition of said vapor generator representative of its vapor load for establishing a predetermined total air flow to said furnaces, means responsive to an operating condition of said vapor generator representative of the vapor load for increasing the total rate of fuel supply to said furnaces with increase in vapor load and for decreasing said total rate of fuel supply to said furnaces with decrease in said vapor load, a sensitive element for each furnace exposed to combustion products generated therein for developing an output which varies with the oxygen content of said combustion products, and means responsive to the outputs of said sensitive elements for increasing the rate of fuel supply to one furnace while decreasing the rate of fuel supply to the other furnace until the outputs of said sensitive elements bear that predetermined relation one to the other indicative of oxygen contents representative of optimum conditions of combustion of fuel in said furnaces.

3. In combination, a vapor generator having independent furnaces, each with its own fuel burner and its own vapor heating sections, said sections being connected to a common line for delivery of vapor to a load, means responsive to the rate of flow of vapor in said common line for establishing a predetermined total air flow to said furnaces, means responsive to the vapor pressure of said vapor generator for decreasing the total rate of fuel supply to said furnaces with increase in vapor pressure and for increasing said total rate of fuel supply to said furnaces with decrease in said vapor pressure, a sensitive element for each furnace exposed to combustion products generated therein for developing an output which varies with efiiciency of combustion of fuel within said furnace, and means responsive to the outputs of said sensitive elements for increasing the rate of fuel supply to one furnace while decreasing the rate of fuel supply to the other furnace until the outputs of said sensitive elements bear a predetermined relation one to the other.

4. In combination, a vapor generator having independent furnaces, each with its own fuel burner and its own vapor heating sections, said sections being connected to a common line for delivery of vapor to a load, means responsive to the vapor pressure of said vapor generator for establishing a predetermined total air flow to said furnaces, means responsive to the vapor pressure of said vapor generator for decreasing the total rate of fuel supply to said furnaces with increase in vapor pressure and for increasing said total rate of fuel supply to said furnaces with decrease in said vapor pressure, a sensitive element for each furnace exposed to combustion products generated therein for developing an output which varies with efficiency of combustion of fuel within said furnace, and means responsive to the outputs of said sensitive elements for increasing the rate of fuel supply to one furnace while decreasing the rate of fuel supply. to the other furnace until the outputs of said sensitive elements bear a predetermined relation one to the other.

5. In combination, a vapor generator having independent furnaces, each with its own fuel burner and its own vapor heating sections, said sections being connected to a common line for delivery of vapor to a load, means responsive to an operating condition of said vapor generator representative of its vapor load for establishing a predeter mined total air flow to said furnaces, means responsive to an operating condition of said vapor generator representative of the vapor load for increasing the total rate of fuel supply to said furnaces with increase in vapor load and for decreasing said total rate of fuel supply to said furnaces with decrease in said vapor load, a sensitive element for each furnace exposed to combustion products generated therein for developing an electrical output which varies with efficiency of combustion of fuel within said furnace, means including a network for producing an output related to the difference between said electrical outputs from said elements, and means responsive to said output of said network for modifying the fuel supply to the burners of one of said furnaces relative to the fuel i4 supply to the other of said furnaces without changing said total rate of fuel supply to said furnaces until said electrical outputs of each of said sensitive elements bears a predetermined relation one to the other.

6. in combination, a vapor generator having independent furnaces, each with its own fuel burner and its own vapor heating sections, said sections being connected to a common line for delivery of vapor to a load, means responsive to an operating condition of said Vapor generator representative of its vapor load for es= tablishing a predetermined total air flow to said fur naces, means responsive to an operating condition of said vapor generator representative of the vapor load for increasing the total rate of fuel supply to said furnaces with increase in vapor load and for decreasing said total rate of fuel supply to said furnaces with decrease in said vapor load, a sensitive element for each furnace exposed to combustion products generated therein for developing an electrical output which varies with the oxygen content of said combustion products, means including a network for producing an output related to the difference between said electrical outputs from said elements, and means responsive to said output of said network for modifying the fuel supply to the burners of one of said furnaces relative to the fuel supply to the other of said furnaces without changing said total rate of fuel supply to said furnaces until said electrical outputs of each of said sensitive elements bears a predetermined relation one to the other.

7. In combination, a vapor generator having independent furnaces each with its own fuel burner, its own vapor heating sections and its own means for regulating the flow of combustion air thereto, said vapor heating sections being connected to a common line for delivery of vapor to a load, means responsive to vapor flow in said line for regulating the total amount of combustion air flowing into said furnaces and in amount related to the vapor flow in said common line, means responsive to the pressure of vapor within said line for decreasing the total rate of fuel supply to the burners of said furnaces with increase of pressure within said line and for increasing said fuel supply with decrease of pressure within said line, a sensitive element for each furnace exposed to combustion products generated therein for developing an output which varies with oxygen content of the combustion gases within its said furnace, means for comparing the outputs of said sensitive elements, and means for relatively varying the fuel supply by said burners to each of said furnaces Without changing said total fuel supply until the outputs of said sensitive elements bear a predetermined relation one to the other for producing like conditions of combustion of fuel within each of said furnaces as reflected by equal oxygen content of the gases therein.

8. In combination, a fluid heater having independent furnaces each with its own fuel burners, its own heating sections and its own means for regulating the flow of combustion air thereto, said fluid heating sections being connected to a common line for flow of fluid to a load, means responsive to the fiuid load upon said heater for producing a force varying with change in said load, means responsive to the sum of the flows of combustion air through said furnaces for developing an opposing force varying in magnitude with change in the sum of said flows of combustion air, means for increasing the flow of combustion air with increase in flow of fluid in said line and for decreasing the flow of combustion air with decrease of flow of fluid in said line, means responsive to decrease in pressure within said line for simultaneously increasing the rate of fuel supply to said burners of said furnaces and for decreasing said fuel supply upon increase of pressure in said line, a sensitive element for each furnace exposed to combustion products generated therein for developing an output which varies with efficiency of combustion of fuel within its said furnace, means including a network for producing an output related to the difierence between the outputs from said elements, and means responsive to the output of said network for modifying the fuel supply to the burners of one of said furnaces relative to the fuel supplied to the other of said furnaces until the outputs of each of said sensitive elements bears a predetermined relation one to the other.

9. The combustion set forth in claim 8 in which said sensitive elements comprise paramagnetic detectors for producing outputs representative of the magnitude of the paramagnetic gases contained in said combustion products.

10. The combination set forth in claim 8 in which said means for controlling the rate of supply of fuel to 15 2,328,499

for varying the energization of said Kelvin balances in response to change in the relative outputs of said sensitive devices.

References Cited in the file of this patent UNITED STATES PATENTS 382,489 Pratt May 8, 1888 935,763 Mailloux Oct. 5, 1909 1,166,758 Gibson Jan. 4, 1916 1,931,948 Armacost Oct. 24, 1933 2,052,375 Wunsch Aug. 25, 1936 2,259,417 Gorrie Oct. 14, 1941 '1943 Saathofi Aug. 31,