US2468535A - Control system for steam boiler - Google Patents

Description

Ap 1949- G. R. ANDERSON CONTROL SYSTEI FOR STEAM BOILER FURNACES 2 Sheets-Sheet l Huh-ATTORNEY Filed Oct. 31, 1944 April 26, 1949.

Filed Oct. 31, 1944 G. R. ANDERSON CONTROL SYSTEM FOR STEAM BOILER FURNACES 2 Sheets-Sheet 2 INVENTOR BY $144k i #44 ATTORNEY Patented Apr. 26, 1949 CONTROL SYSTEM FOR STEAM BOILER FURNACES George R. Anderson, Mount Lebanon, Pa., assignor. by mesne assignments, to Hagan Corporation, Pittsburgh, Pa., a corporation of Pennsylvania Application October 31, 1944, Serial No. 561,299

6 Claims.

This invention relates to control systems for steam boiler furnaces in which either gaseous, liquid, or powdered solid fuels either alone or in admixture, are burned and more particularly to systems for maintaining a predetermined relationship between the rates of steam flow and the rate at which air is supplied to the combustion chamber or space of the boiler furnace.

An object of this invention is to provide an automatic control system for boiler furnaces which embodies means for measuring the rate of steam flow from a boiler and developing a force whose magnitude is a function of such steam flow rate, means for measuring the rate of flow of combustion air to the furnace and developing a second force whose magnitude is a function of such air flow rate, and means responsive jointly to said steam flow and air flow forces for so regulating the air supply that said control forces are maintained in balance with each other for all ratings at which the boiler is operated on automatic control.

A further object of the invention is to provide means for regulating the supply of fuel to the furnace in accordance with variations in steam pressure. Thus, the control system above set forth is designed and arranged to match the rate at which combustion air is supplied to the furnace with the rate of steam flow, and to cause fuel to be supplied to the furnace at a rate which will maintain the steam pressure at some predetermined desired value.

A still further object of the invention is to provide a control system that shall be simple, rugged, and yet sensitive and accurate in operation.

Other objects of the invention will, in part, be apparent and will, in part, be obvious from the following description taken in conjunction with the accompanying drawings in which Fig. 1 is a more or less diagrammatic view of a steam boiler furnace provided with a control system embodying what now appears to be a preferred form of the invention;

Fig. 2 is a view in section of a steam flow measuring device embodied in the control system;

Fig. 2a is a cross sectional view of a sending valve; and

Fig. 3 is a more or less diagrammatic view in longitudinal section of a totalizer embodied in the control system. i

Throughout the drawings and specification like reference characters designate like parts.

In Fig, 1 of the drawings, reference character I indicates a steam boiler furnace having a steam drum 2 and superheater 3 through which steam from drum 2 flows to a distribution header 4. The furnace is provided with a forced draft fan 5, an induced draft fan 6, and means 1, such as a pulverizer mill, for supplying fuel to burners 8.

The fuel supply means 1 may, for purposes of illustration, be considered as a coal pulverizer having a supply pipe 9 through which carrier air is supplied to the pulverizer for conveying pulverized coal through a pipe ID to burners 8.

The forced draft air supply from fan 5 is controlled by means of a louvre type damper I I which is operated by a positioning power cylinder l2. The forced draft air supply passes through a preheater l3 and a duct M to burners 8.

The induced draft fan 6 carries exhaust gases out of the furnace to a stack, not shown. The exhaust gases of the furnace pass out of the furnace through a conduit I5 into preheater l3 and discharge from the preheater through a pipe 16 into the suction or inlet of fan 6.

A damper I! in the exhaust pipe I6 is provided to regulate the suction of the furnace so that the pressure within the combustion chamber of the furnace may be maintained at a predetermined substantially constant value, say at atmospheric pressureor at a value slightly below or slightly above atmospheric pressure, as desired. Damper H is operated by a power cylinder [9. Power cylinder I9 is caused to position damper I! by means of a regulator 20 which responds to deviations in pressure in the combustion chamber of the furnace from the value desired to be maintained therein. Regulator 20 is designed, as stated above, to respond to changes in pressure within the combustion chamber of the furnace from that value which it is desired to be maintained therein and causes a control force to be sent from its control valve 2| through a sending line 22 to a diaphragm chamber 23 of a mechanism which operates a pilot valve 24 of power cylinder IS. The value of the control force delivered by valve 2| of regulator 20 to the diaphragm chamber 23 of power cylinder 19 is such as will cause cylinder Hi to so move damper ll towards open or'closed position that the pressure within the combustion chamber of the furnace will be maintained substantially constant at the desired value.

Power cylinders or operators l2 and I9 are, for convenience, illustrated as being of the same type and may be of the type shown in United States Patent 2,044,936. Regulator 20 may be of any type suitable for maintaining a balanced draft such, for example, as the regulator shown in Fig. 4 of United States Patent 2,243,944.

. 3 V The rate at which carrier air is delivered to pulverizer'1 is controlled by a positionin power cylinder or operator 21 of the same type, for example, as power operators 12 and I9. Power cylinder 21 is controlled from a steam pressure responsive master regulator 28, which is of the type shown at 8 in United States Patent 2,220,837. This master regulator is responsive to the steam pressure of the boiler either as measured at the steam header 4 or, if desired, at drum 2. Master regulator 23 is designed to send out a control force from its valve 29 through a pipe 30 to a fuel cutback totalizer 3|, which, in turn, transmits or repeats the control impulse of line 36 in and through line 32 to the diaphragm chamber 33 of the operator for pilot valve 34 of power cylinder 21. As the steam pressure in steam header 4 decreases, master regulator 28 responds causing the control force delivered to line 30, and as repeated in line 32, to decrease proportionately, and if the steam pressure rises, the'control forces in pipes 30 and 32 are caused to increase proportionately. As the steam pressure in header 4 decreases and the control force delivered to the diaphragm chamber 33 of power cylinder 21 decreases, operator 21 causes more fuel to be delivered to the furnace. When the steam pressure in header 4' increases, the control forces delivered through pipes 30 and 32 increase, whereby operator 21 causes fuelto be delivered to the furnace at a decreased rate.

In order that a predetermined relationship may be maintained between the rate at which steam flows from the boiler drum 2 through steam superheater 3 to the steam header 4 and thence to the point where the steam is consumed, and the rate at which air is supplied for combustion to furnace l, a steam flow measuring device 35, an airflow measuring device 36, and a totalizing regulator 31 are provided. Totalizing regulator 31 responds to a control force developed by the steam flow measurin device 35 and a control force developed by the air flow measuring device 36, and sends out a control force through pipe 38 to power cylinder |2 wherebypower cylinder l2 so positions damper II that the air flow impulse developed by device 36 is caused to balance the control force developed by the steam flow measuring device 35.

The steam flow measuring device 35 and the totalizing regulator 31 are shown more or less in detail in Figs. 2 and 3, respectively, and will be described more particularly hereinafter.

Inorder to make provisions for the circumstance where, for some reason or other, the forced draft air supply to the furnace should fail or should become inadequate and fall behind the rate of steam fiow from the boiler, means are provided for decreasing the rate at which fuel is delivered to the furnace in order that proper .i'uel-air ratio may be maintained. The means for reducing the fuel input Or cutting back on the fuel input in case the air supply'rate falls behind or below the rate at which steam flows from the boiler, consists of a totalizing device 40 which responds to the control forces developed by devices 35 and 36, respectively, and sends out a loading force to the cutback totalizer 3| thereby to so modify its operation that the impulse delivered through pipe 32 to the diaphragm 33 for the operator of pilot valve 34, reduces the fuel to a value corresponding to the rate at which air is supplied to the furnace. Devices 31, 40 and 3|, respectively, are similar in construction, hence the detailed illustration of Fig. 3 hereinafter described will suffice for each of the devices.

The steam flow responsive device 35, as shown more particularly in Fig. 2, comprises a, twopart housing 4| and M11 in which is disposed a flexible bellows 42 and the end of a beam 43 having a knife-edge 45 that bears against a knife edge bearing 46 rigidly supported in a bearing housing 41 secured to housing Ma. The inner end of beam 43 projects into the chamber of housing 4|a but the opening through which the beam extends is sealed by means of a sealing bellows 48. The inner end of beam 43 is provided with a knife-edge bearing 49 which accomodates a knife-edge 50 carried at the lower end of a push rod 5| bellows 42.

It will be seen by inspection of Fig. 2 that bellows 42 divides the interior of housing 4| into two separated chambers 52 and 53. Chamber 52 is connected, see Fig. l, by a pipe 54 at 54a to when the steam flow from the boiler is zero the pressures in chambers 52 and 53 will be equal, but as the steam flow increases from zero to higher and higher values the pressure in chamber 53 will be less than that in chamber 52 because of the pressure drop through superheater 3. This pressure drop will cause bellows 42 to be compressed in accordance with the steam flow and will have maximum compression at maximum steam flow and minimum compression at zero steam flow.

As the bellows 42 is flexed in accordance with the rate at which steam flows from the boiler to the distribution header 4, beam 43 is caused to rock on its knife edge 45 and to so actuate an escapement sending valve 56 that the pressure transmitted by this valve to its sending line 56a will be proportional to the pressure drop across superheater 3. Since the pressure drop across superheater 3 is proportional to the square of the flow of the steam through it, the value of pressure established in sending line 56a will therefore be proportional to the square of the.

bellows 6| is connected by line 64 to the sending port of valve 56 to balance the torque appliedto the knife edge bearing 49.

Beam 43 is provided with an adjustable tension spring 66, the upper end of which is connected to a knife edge 61 bearing on the upper face of the beam near its free end, and the other end of which is connected to an adjustin screw 63 supported in a spring barrel 69. The tension in spring 66 is adjusted to compensate for the weight of the moving parts and the resistance of the sealing bellows 48.

Valve 56, Fig. 2a, comprises a body 10 having an inlet 1| connected to a supply of fluid, such as compressed air at constant pressure, an inlet seat 12, an exhaust seat 13, and a sending port 14 located between the inlet and exhaust seats. A valve member 15 having conical surfaces 16 and 11, respectively, is mounted within the body to coact with the inlet and exhaust ports 12 and secured to the upper end of I3. Valve I5 is urged towards its exhaust port I3 by means of a spring I8. Each end of valve I5 is provided with guides 80 and 8|, respectively. Guide 8| coacts with a link 82, the upper end of which coacts with an adjustable screw 83 carried by beam 43 at its free end. As beam 43 rocks, the inlet ports 12 and 13 are opened or restricted,' as the case may be, in such manner that the pressure of the compressed air issuin from port 14 will vary from a maximum; when the exhaust port I3 is closed, to a minimum when the inlet port I2 is closed, the values of pressures between the minimum and maximum varying with the position of valve 15 as determined by the position of beam 43, which, in turn, is determined by the pressure differential acting on bellows 42.

The totalizers 3|, 31 and are similar in construction and are represented by the showing of Fig. 3. This device comprises a housing 85 having a dividing partition 86 therein and flexible diaphragms 81 and 88 disposed on each side of the partition. The diaphragms are connected together by means of a rigid spacer post 89, the opposite ends of which carry clamping plates 90 and 9|. A clampin plate 92 coacts with clamping plate 9|, being secured thereto in any suitable manner, whereby the diaphragm 88 is held firmly between plates 9I and 92. A clamping plate 93 coacts with plate 90 to rigidly clamp the diaphragm 81 between plates 90 and has a valve seat 94 that communicates with a passage 95 which extends through plate 9| and post 89 and terminates in a lateral passage 96. Bellows 91 and 98, respectively, are sealed to clamping plates 90 and partition 86 and plate SI and partition 86 so as to provide a sealed space 99 about post 89. Partition 86 is formed with an exhaust passage I00- that communicates with passage 95 and lateral passage 96. These passages provide an exhaust for valve seat 94. A valve IOI is disposed to coact with valve seat 94 and an inlet valve seat I02. Valve seat I02 is disposed within a body I03 having an inlet I04 connected to a source of fluid pressure, such as compressed air at constant pressure. A light spring I06 tends to urge diaphragm 88 towards its neutral position, in which position the exhaust valve seat 94 and inlet port seat I02 are closed.

An adjustable compression spring I0! is disposed in a chamber I08 formed as part of body 85. As shown, this is a compression spring, the tension of which may be adjusted by means of a screw adjustment I09. The initial tension set up in spring I0? is determined by the values of the actuating pressures which may be supplied to act on diaphragms. 81 and 88 when connected through the respective ports I 09, H0 and III.

If actuating pressures are connected to ports I 09 and H0, these pressures will act in opposition to each other on diaphragms 8! and 88 and cause a pressure to be established in chamber I I2 of the device which will cause the unbalance between the pressures acting in opposition to each other on these diaphragms to be balanced out.

When in balance, the valve seats 94 and I02 will be closed. If a pressure is also introduced through port I I I as well as through ports I 09 and II 0, the pressure established in chamber II2 will be proportional to the alegbraic sum of the pressures acting on diaphragms 81 and 88 through ports I09 to I inclusive.

As shown in Fig. 1, sending line 56a is connected to port I09 of totalizer 31. Chamber H2 is connected to pipe 38, and pipe 38 is also con- 93. Plate 92 nected through a needle valve I I3 and suitable piping to port I, so that the pressures acting in chamber I I2 on diaphragm 88 and in chamber I I4 on diaphragm 81 will balance out after a length of time as determined by the setting of the needle valve II 3. A volume chamber I I5 is connected to the piping leading from needle valve II3 to port II I to give stability to the device.

I The port I I0 of totalizer 31 is connected to pipe 68 in which a variable pressure is established by device 36, the value or magnitude of this pressure being a function of the rate of air flow to the combustion chamber of the furnace.

The steam flow measuring device 35 will maintain a pressure as delivered through port I09 and acting on diaphragm 81 that is a function of the rate of steam flow, being proportional to the pressure drop across superheater 3. This pressure tends to move diaphragms 81 and 88 to the left as viewed in Fig. 3, whereby the inlet port I02 is closed and the exhaust port 94 uncovered, thereby decreasing the pressurein chamber II2 which is delivered to the forced draft damper power operator I2. In response to this decreased sending pressure sent to the pilot valve operator of power cylinder I2, damper II will be moved towards a Wider and wider open position until the sending pressure delivered by device 36 through p pe 68 and port I I8 is sufficient, when acting on the opposite face of diaphragm 88, to balance the force of the pressure in pipe 56a acting on diaphragm 81. Vfhen this balance is achieved the setting of damper II will be the setting required -to cause the air flow to the combustion space of the boiler to match the steam flow out of the boiler. In other words, for any value of pressure introduced through port I09 by the steam fiow device 35, the sending pressure from chamber II2 to operator I2 will continue to vary until the air flow impulse developed by device 36 and transmitted through pipe 66 is sufficient to balance the steam flow impulse and the initial bias imposed by spring I01. Thus the air flow will always be caused to bear a definite relationship to steam flow.

The effect of the needle valve I I 3 is to allow the pressures in chambers I I2 and I I4 to be equalized after a predetermined length of time, so that the only operative forces after such time period are those developedby the pressures connected to ports I09 and H0. For example, if it be assumed that the device is in balance and there is a decrease in steam flow resulting in a decreased pressure acting through port I09, then the pressure acting on diaphragm 88 through port I I0 will tend to uncover the inlet valve seat I02, thereby increasing the pressure in chamber II2 which acts on diaphragm 88 in opposition to the pressure acting on the other side of this diaphragm to delay or resist a wide opening of the valve I02 thereby allowing power operator I2 to move towards its required position without overtravel. The needle valve II3, however, allows the increase in pressure in chamber II2 over the pressure existing in chamber II4 to be gradually equalized so that the resisting force of the pressure in chamber H2 is gradually wiped out, or balanced out.

Devices 3| and 40 coact to reduce the fuel supply delivered from the pulverizer 'I to the furnace when, for some reason or other, the supply of forced draft fails or is incapable of matching the steam flow from the boiler. Device 40 is connected like device 31 is connected, except that the steam flow impulse from line 56a is connected to port H and line 66 is connected to port I00, that is, the opposite of the connections for device 31. Thus so long as the air flow impulses in lines 56a. and 66 are equal or within predetermined limits of difference in value, the sending impulse from device 40 through line II8 to port IIO of device 3I will remain at a predetermined value which may range from zero gauge pressure to any high value, depending upon the minimum amount of fuel that is to be delivered to the boiler at some predetermined rating less than full rat- Device 3! acts as a repeater of the pressure impulse in line 30, which pressure is proportional to the value of the steam pressure in header 4. Line 30 is connected to port III of device 3| so that the pressures acting through this port and the pressure acting through port 0 are. in the same direction. Thus if the pressure in pipe II8 does not vary, the pressure in pipe 32 will mere ly be a repeat of the pressure in pipe 30, so that the amount of fuel delivered to the furnace will be proportional to the steam pressure in header 4. However, if the air flow for some reason or other falls behind the steam flow, then the pressure in pipe II8 will be increased, whereby the repeated impulse in line 32 will be increased, thereby causing power operator 21 to decrease the rate at which fuel is supplied to the furnace, whereby the ratio of fuel to air delivered to the furnace is maintained at that value required for eflicient combustion. I

Device 36 comprises a housing H9 in which a diaphragm I20 is disposed. The outer edges of this diaphragm are clamped between flanges I2I of the diaphragm housing. The diaphragm housing has an opening I22 which is closed by a fulcrum diaphragm I23 which acts as a fulcrum for beams I24 and I25, respectively. Beam I24 is connected by means of a clamping plate I21 to the middle portion of diaphragm I20 and beam I25 is disposed to actuate an escapement valve I28 which is similar in construction and operation to valve 56. Thus valve I28 will be positioned to control its inlet and exhaust ports I29 and I30, respectively, so that the pressure issuing from its outlet or sending port I3I will be a function of the position of diaphragm I20 as determined by the pressure drop across the forced draft air preheater. In order that the pressure transmitted from sending port I3I to line 65 may be caused to bear a definite relationship to the pressure drop across the air preheater, a loading device I33 is provided. This loading device comprises a diaphragm chamber I34 having therein a flexible diaphragm I35 that acts against a gradient spring I36 which resists the pressure in chamber I34. The diaphragm I35 is connected by a push rod I31 to a cam I38. Cam I38 coacts with a roller I39 on a bell crank I40, one arm of which is connected to a spring I4I. Spring MI is connected to a junction I42 between links I43 and I44 operatively connected to beam I25. Link I43 is connected at its outer end by a pin I46 to a gear wheel I41. The gear wheel coacts with a worm wheel I48 disposed to 'be actuated by a hand wheel I49 to vary the angle between links I43 and I44 to thereby vary the ratio between the pressure difference acting on diaphragm I20 and the pressure sent out by valve I 28. If the pressure diflerence acting on diaphragm I20 changes so as to cause valve I28 to be moved,

8 the pressure sent out by its sending port I3I will continue changing until the force of this pressure acting on diaphragm I35 is sufflcient to position the cam I48 at a point where the force of spring I4I, acting through links I43 and I44, balances the force of the pressure differential acting on diaphragm I20. Thus for every value of pressure differential acting on diaphragm I20 there will be-a definite sending pressure in line 56 and acting in chamber I34.

It will be evident from the foregoing description that steam flow measuring device 35 and the air flow measuring device 36 each develop control forces that act on totalizer 31 in such a manner that the totalizer so controls the air flow regulator as to cause the air flow rate control force developed by device 36 to be in balance with the-l steam flow rate control force developed by device 35. Thus the rate at which air is supplied for combustion is caused to immediately follow and match the rate of steam flow from the boiler.

The control forces developed by devices 35 and 36 also act on totalizer 40 in such a manner that when a certain predetermined condition prevails in the air supply with respect to steam flow, it transmits a control force through line II8 to totalizer 3I which under these conditions modifies the. rate of supply of fuel to the furnace to a value required by the available air supply.

' Although one embodiment of the invention has been herein illustrated and described, it will be evident to those skilled in the art that various modifications may be made in the details of construction without departing from the principles herein set forth.

I claim:

1. A control system for'steam boilers provided with regulatable supplies of combusion air and fuel and means responsive to steam pressure for regulating the fuel supply, said system comprising means responsive to the rate of steam flow from the boiler for developing a control pressure whose magnitude is a function of such steam flow rate, means responsive to rate of flow of combustion air for developing a control pressure whose magnitude is a function of such air flow rate, a regulator for controlling the rate of flow of air, and means responsive to the difference between said control pressures for transmitting a control pressure to said air flow regulator and causing the same to so regulate the rate of flow of combustion air that said air flow rate and steam flow rate control pressures are in equilibrium with each other.

2. A control system for steam boilers provided with regulatable supplies of combusion air and fuel and means responsive to steam pressure for regulating the fuel supply, said system comprising means for measuring the rate of steam flow from the boiler and developing a fluid pressure that is a function of the value of steam flow rate measurement, means for measuring the rate of flow of combusion air to the boiler furnace and developing a fluid pressure that is a function of the value of said air flow rate measurement, and pressure actuated means responsive to the difference between steam flow rate and air flow rate fluid pressures for so regulating the air supply that the air flow rate fluid pressure balances the steam flow rate fluid pressure.

3. A control system for steam boiler furnaces provided with regulatable'supplies of fuel and combustion air, a fuel supply regulator and a regulator for adjusting the rate of supply of combustion air, comprising a rate of steam flow assaaac responsive device having means for establishing a fluid pressure whose magnitude varies with and is a function of the steam flow rate, a device responsive to the rate of flow of combusion air to the furnace having means for establishing a fluid pressure whose magnitude varies with and is a function of the air flow rate, and pressure actuated means responsive differentially to said fluid pressure for so controlling the operation of said air flow regulator that the air flow rate fluid pressure is directly proportional in value to said steam flow rate fluid pressure.

4. A control system for steam boiler furnaces provided with regulatable supplies of fuel and combustion air, a, fuel supply regulator and a regulator for adjusting the rate of supply of combustion air, comprising a rate of steam flow responsive device having means for establishing a fluid pressure whose magnitude varies with and is a function of the steam flow rate, a device responsive to the rate of flow of combustion air to the furnace having means for establishing a fluid pressure whose magnitude varies with and is a function of the air flow rate, pressure actuated means responsive differentially to said fluid pressures for so controlling the operation of said air flow regulator that the air flow rate fluid pressure is directly proportional in value to said steam flow rate fluid pressure, means responsive to steam pressure having means for establishing a control pressure adapted to so actuate the fuel supply regulator that the rate of combustion is adjusted to maintain said steam pressure at a substantially constant value, and means responsive to a predetermined difference between the steam flow rate fluid pressure and said air flow fluid pressure for modifying the operation of said fuel supply regulator to effect a reduction in the rate of supply of fuel to the boiler.

In a control system for steam boiler furnaces including fuel and air supply means, said system comprising means for measuring the rate of steam flow from the boiler of said furnace and developing a fluid pressure whose magnitude is a function of such steam flow rate, means for measuring the rate of flow of combustion air to the furnace and developing a second fluid pressure whose magnitude is a function of such air flow rate, and means responsive to the difference between said steam flow rate and air flow rate fluid pressures or so regulating the air supply that the magnitude of said air flow rate fluid pressure is maintained in balance with the magnitude of said steam flow rate fluid pressure.

6. In a control system for steam boiler furnaces provided with regulatable supplies of combustion air and fuel, said system comprising means responsive to steam pressure for regulating the rate of supply of fuel so as to increase the rate when the steam pressure decreases and to decrease the rate when the steam pressure increases, means traversed by steam flowing from a boiler producing a pressure drop varying in magnitude with the rate of flow of said steam, a pressure differential responsive device responsive to said steam flow pressure drop, said steam pressure differential responsive device having an escapement valve disposed to be positioned by. said device in accordance with the magnitude of said steam flow'pressure 'drop and to transmit a fluid pressure corresponding to said valve position, means traversed by the combustion air supplied to said boiler producing a pressure drop varying in magnitude with the rate of flow of said combustion air, a pressure differential responsive device connected to respond to said air flow pressure drop, said air flow responsive device being provided with an escapement valve disposed to be positioned thereby and to transmit a fluid pressure whose magnitude varies with the position of said valve, 2, pressure actuated relay having a valve for transmitting a fluid pressure of varying magnitude, said relay having diaphragm means responsive differentially to the fluid pressures transmitted by said steam flow and air flow pressure drop responsive devices and acting in opposition to each other so that. the valve is actuated to vary the magnitude of the transmitted pressure in response to an unbalance between the transmitted pressures of. said steam flow and air flow pressure-drop-responsive devices, and means responsive to said relay-transmitted pressure for so regulating the rate of flow of air that the said steam flow and airflow pressure drops are maintained in balance, whereby the rate of flow of air to the boiler is caused to correspond in magnitude to the rate of flow of steam from the boiler.

v GEO. R. ANDERSON. REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Great Britain June 5, 1930

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