US2302931A - Feedwater control method and apparatus - Google Patents

Description

Nov. 24, 1942. C B. ARNOLD 2,302,931

FEEDWATER CONTROL METHOD AND APPARATUS Filed 'April e. 1940 "22 .SUPER/WAUW@ o 45 OLER DRUM g y 46/ 5 /0 T0 STEAM M10/N v ATTORN Patented Nov. 24, 1942 r OFFICE FEEDWATER CONTROL METHOD AND 'APPARATUS l Charles B. Arnold, Hempstead, N. Y.

1940, serial No. 328,218y

Application April 6,

9 Claims.

This 'invention relates to feedwater control method and apparatus and more particularly to a boiler feedwater control system which will compensate for the eiects of varying boiler rating to maintain thedesired water level in the boiler.

-In the operation of steam boilers the water in l,

the boiler vappears to lswell or shrink during changes inthe rate of steam output. This apparent or shrinking is due to changes of steam bubble'volume in the boiler Water during load changes. In consequence, the Water level rises f momentarily during an increase in load and falls momentarily during-a decrease in load. Where the feedwater to the boiler is regulated solely upon'changes of waterv level in the boiler, the swelling or shrinking of the water increases or decreases the weight of water above the lower tap, which is generally above the bottom of the boiler, and produces the same eiTect on the regulating apparatus as anfactual increaseor de- Avcrease in the quantity Aof 'water in the boiler, thereby causing'unsatisfactor'y regulation.

With straight water levelcontrol, the flow of water to the boiler can be decreased only by a rise of water level, and increased only by a fall of Water level. This requires that the water level be maintained higher at low loads than at high loads, which is an undesirable characteristic when the boiler is required to operate under variable load conditions. Assume that the boiler is steaming aty a low rate with a relatively high .I

water level and the load is suddenly increased. Thesudden swell of the water due to the ncreased steam ebullition, will raise the already high level even higher and may, under extreme conditions, cause slugs of Water to be carried outofv'the` boiler with the steam. On the other hand, if the boiler load is suddenly decreased the water in the boiler will shrink to a lower level 4and may, under some conditions, force the level dangerously low.

Further, with straight level control, the rise 'and fallo'f water level due to swell or shrinkage of boiler water during load changes causes erratic feedwater regulation. Upon an increase of load the feedwater valve is rst momentarily closed due to the rise of water level, and is not opened until the water level lowers due to a deciency of Water supply. Conversely, the fall of water level Which momentarily follows a decrease in load opens the feedwater valve when it should close down. These momentary reverse actions of the regulator during load changes produce 'a hunting condition wherein either too a considerable `period of time is required before an equilibrium condition of input and output is established.jv H i. Y f y The fpre'sent 'invention overcomes the aforementioned `disadvantages` by providinga device whichwill regulate the ow of water to the boiler in'close'r accord with boiler output at all times. It-'isone of the'obJ'ects of the present invention. to-provide'a feedwater control method and apparatus by which the supply of water to the boiler vis controlled by factors responsive to load on'the boilery as Well as to water level so that the water supply isnot decreased momentarily upon an increase of load nor increased momentarily upona decrease lof load due to swelling orshrink ingof waterin the boiler. I

' Another object' ofthe invention is to provide a feedwater' control method and apparatus which will enable? ahigher water level 4to be maintained in the boiler at `high loads than at low loads which is in accord with rather than contrary to the normal swelling orxshrinking yof'the boiler water during load changes and `thus permit the water level: to be maintained within 'closer limf its...

Still another'object of the invention is to provide a feedwater control apparatus which is relativelyv simpleA and inexpensive to'v construct and which is readily adaptable for installation on existing'boilers 'I-he above and other objects, advantages and novel 'features of the invention will be apparent from the:following description of the embodiment shown Vin the accompanyingdrawing,y in which: f

Figure l is adiagrammaticview illustrating a boiler feedwater control system embodying the invention; and

' Figure 2 is an enlarged section of the heat eX- change unit of Figure 1.-

In Figure 1 the boiler drum is indicated generally at IU and is provided with a ysight glass I2 for indicating the level of Water in the boiler. A Vsecond sight glass I4 is connected to the boiler atI above the Water level therein 'and atV I8 below the water level in the boiler. 'Asuperheater indicated at 20 is provided in connection with the boiler and `discharges intoy a header 22 from which steam may be withdrawn to 'any ldesired point of use. Water is supplied to the vboiler through a'pipe 24 by a feedwater pump 26, a valve 28 being provided to control the rate of water supply.

According to the present invention an extermuch Aortoo ,little water is fed to the boiler and 55 nal circulating system Vis provided shownv as being formed of a plurality of conduit sections 30, 32, 34 and 36. The conduit 30 is connected to the water connection I8 and a valve 38 is provided to regulate the flow therethrough. If desired, a drain valve 40 may be connected to the lower part of the circulating system to drain water therefrom.

The sight glass I4 is connected at its lower end to the conduit 30 and at its upper end to a conduit 42 leading from the connection I6. If desired, a conduit 44 in parallel with the sight glass may be provided.

Circulation through the secondary circuit is established by leading a pipe 46 from the superheated steam header 22 through a vertical leg 36 of the circulating system. A valve 48 is provided in the pipe 46 and temperature gauges 50 may be connected to the pipe above and below the conduit section 36. At its lower end the pipe 46 may lead to the steam main from the boiler.

The valve 28 is controlled by a water'level responsive regulator which may be of the type shown in the patent to Smoot, No. 1,904,554 including a wobble pot 52 including interconnected mercury chambers mounted on a weigh-beam 54 and having its opposite sides connected to the conduits 30 and 42. The weigh-beam 54 controls a power unit 56 which moves an arm 58 vertically to open and close the Valve 28 through a connection 60. The power unit may be a uid motor as shown in Smoot Patent No. 1,904,554 controlled through the weigh beam by a pilot valve to move the outer end of the arm 58 vertically thereby to control the valve 28. In operation, the pressure kon the left side of the wobble pot normally exceeds that on the right side tending to tilt the weigh beam counterclockwise to move the arm 58 downwardly thereby to close the valve 28 to compensate for an increase in water level in the boiler.

With a device of this character the regulator will control the valve 28 so as to maintain a constant differential across the wobble pot thereby resulting in a higher water level in the boiler at high ratings than at low ratings. In order to compensate for this effect a characteristic spring is provided at 62 connected under tension to the arm 58 and the weigh beam 54. The spring normally urges the weigh beam to turn in a. clockwise direction partially to balance the tilting force of the wobble pot and as the arm 58 is moved up or down by the power unit, the spring will exert a varying tension on the weigh beam providing a variable characteristic dependent upon the position of the arm 58 and the valve. Thus in different positions of the valve a different differential on the wobble pot will rebalance the weigh beam so that the water level in the boiler will be maintained more nearly constant at all times.

The conduit section 36 is illustrated in somewhat more detail in Figure 2 as including an elongated tubular casing having an inlet connection 64 at its lower end for connection with the pipe 34 and an outlet connection 66 at its upper end for connection with the pipe 38. The opposite ends of the tube are closed by plugs 68 welded or otherwise permanently secured in place,

and each of which is formed with a relatively f small central opening 10. A coiled pipe 12 extends longitudinally through the casing 36 with its ends projecting through the openings 1I) and terminating in connectors 14 for connection to the pipe 46. One method of securing the parts illustrated, is to connect the ends of the coil 12 and the connectors 14 to plates 16, which may be bolted to the end closures 68 as shown. The coil 12 is preferably so formed that it may be threaded through one of the openings 10 somewhat in the manner of a corkscrew so that it may be removed or replaced without disturbing the end closures 68.

In operation of the system the valve 48 should be adjusted so that the temperature of steam leaving the pipe 46 at the lower end of the casing 36 is slightly, for example about 5 F., above the temperature of water in the boiler at approximately maximum load. With the boiler operating at about its maximum capacity the valve 38 should then be adjusted until the level in the sight glass I4 is below that in the sight glass I2, an amount equal to the desired compensation; for example, 6". The characteristic spring 62 on the regulator should then be adjusted to apply force on the weigh-beam which will substantially balance out the amount of compensation.

After these adjustments have been made the system is ready for operation and will operate as follows. Superheated steam from the header 22 will flow through the coil 12 in the casing 36 and will heat water and generate steam therein to establish a thermal circulation through the conduits 38, 32 and 34. Heating of the water in the casing 315 and the consequent steaming will reduce the density of the water column in the casing 36 causing some of the water therein to enter the boiler through the connectionV I8 and this will cause a pressure in the pipe 30 less than that which would normally exist therein due to the circulating flow through the restriction of the valve 38. This, in eiect, will lower the water level in the sight glass I4 so that it is less than the actual Water level in the boiler as indicated by the sight glass I2'. by an amount proportional to the reduction of pressure caused by circulation in the circulating system. Since the regulator is connected, in effect, across the sight glass I4 it regulates the supply of water to the-boiler in accordance with this compensated level.

If the load on the boiler should be increased, an increased quantity of steam will flow through the conduit 46 to increase circulation in the external conduit system. This will effect a. greater reduction of pressure in the conduit 30 and Will compensate for the eiect of swelling of the water in the boiler so that the feedwater valve 28 will not be closed. Conversely, if the load should be decreased the flow of steam through conduit 46 will decrease so that less compensation will be provided, thereby to neutralize the effect of shrinking .of the water.

The system has the further effect of controlling the valve 28 to provide a higher water level at high loads than at low loads. This may be due partially to the compensating action of the external circulating system and partially to the effect of the characteristic spring 26 on the regulator.

While one embodiment of the invention has been shown and described in detail it will be understood that this is illustrative only and is not intended as a definition of the scope of the invention, reference being had for this purpose to the appended claims.

What is claimed is:

l. The method of controlling the supply of water to a steam boiler which comprises creating a differential pressure proportional to the head in place, as

of water in the boiler, creating an external circulation of fluid in a circuit closed except for communication with the boiler proportional to a function of the flow of steam from the boiler, reducing said differential by an amount proportional to a function of the rate of said circulation, and controlling the supply of water to the boiler in accordance with the reduced differential.

2. The method of controlling the supply of water to a steam boiler which comprises creating a differential pressure proportional to the head of water in the boiler, heating water external to the boiler by flow of steam from the boiler, causing said water to circulate in response to the rate of heating, reducing the differential by an amount proportional to a function of the rate of water circulation, and controlling the supply of water to the boiler by the reduced differential.

3. Feedwater control apparatus for steam boilers comprising connections to the boiler above and below the normal water level therein, means forming a complete water circuit external to the boiler, a steam connection from the boiler through a vertical part of said circuit to heat the water and generate steam therein to set up a thermal circulation in said circuit, a connection from said circuit to one of said boiler connections to modify the water level effect, means to supply water to the boiler, and control means connected to the boiler connections to vary said water supply in accordance with changes in the modified water level.

4. Feedwater control apparatus for steam boilers comprising connections to the boiler above and below the normal water level therein, means to supply water to the boiler, control means for the water supply connected to the boiler connections, means forming a complete water circuit external to the boiler, a superheater associated with the boiler to superheat steam therefrom, means to circulate steam from the superheater through a vertical part of said circuit to heat the water and generate steam therein, and a connection from said circuit to one of the boiler connections between the boiler and the control means to modify the water level effect in pro'- portion to a function of the rate of circulation in the circuit.

5. Feedwater control apparatus for steam boilers comprising connections to the boiler above and below the normal water level therein, means forming a complete water circuit external to the boiler, a superheater associated with the boiler to superheat steam therefrom, means to circulate steam from the superheater through a vertical paril of said circuit to heat the water and generate steam therein, a connection from said circuit to one of the boiler connections to modify the Water level effect in proportion to a function of the rate of circulation in the circuit, means to supply water to the boiler, control means for the supply means, a regulator controlling said control means, and connections from the regulator to the boiler connections beyond the connection from said circuit to one of the boiler connections, the regulator including a characteristic spring to oppose the tendency of the regulator to provide a higher water level at high boiler ratings than at low boiler ratings.

6. Feedwater control apparatus for steam boilers comprising connections to the boiler above and below the normal water level therein, means forming a complete water circuit external to the to one of the boiler connections to modify the water level effect in accordance with the rate boiler, a connection from said circuit to the boiler below the water level therein, means in a vertical part in said circuit to circulate steam from the boiler therethrough to cause a thermal circulation in the circuit, a connection from the circuit to one of the boiler connections to modify the water level effect in accordance with the rate of circulation in the circuit, means to supply water to the boiler, and control means for the supply means connected to the boiler connections beyond the connection from said Acircuit to one of the boiler connections and responsive to the pressures therein.

7. Feedwater control apparatus for steam boilers comprising connections to the boiler above and below the normal water level therein, means forming a complete water circuit external to the boiler, a connection from said circuit to the boiler below the water level therein, a superheater con nected to the boiler, means in a vertical part of said circuit to circulate steam from the superheater therethrough to cause a thermal circulation in the circuit, a connection from the circuit or rcirculation in the circuit, means to supply water to the boiler, and control means for the supply means connected to the boiler connections beyond the connection from said circuit to one of the boiler connections and responsive to the pressures therein.

8. Feedwater control apparatus for steam boilers comprising connections to the boiler above and below the normal water level therein, a series of conduits forming a complete circulating system external to the boiler, one of said conduits being formed by an enlarged casing extending vertically and formed with inlet and outlet connections at its lower and upper ends, a coil extending vertically through the casing, steam connections from the boiler to said coil, a connection from the circuit to one of the boiler connections to modify the water level effect in accordance with the rate of circulation in the circuit, means to supply water to the boiler, and control means for the supply means connected to the boiler connections beyond the connection from said circuit to one of the boiler connections and responsive to the pressures therein.

9. Feedwater control apparatus for steam boilers comprising connections to the boiler above and below the normal water level therein, a series of conduits forming a complete circulating system external to the boiler, one of said conduits being formed by an enlarged casing extending vertically and formed with inlet and outlet connections at its lower and upper ends, the ends of said casing having relatively small openings therein, a coil extending vertically through the casing with its ends projecting 'through said openings, said coil being so formed that it may be threaded through one of said openings without removing the end of the casing, steam connections from the boiler to said coil, a connection from the circuit to one of the boiler connections to modify the water level effect in accordance with the rate of circulation in the circuit, means to supply water tothe boiler, and control means for the supply means connected to the boiler connections beyond the ,connections from said circuit to one of the boiler connections and responsive to the pressures therein.

CHARLES B. ARNOLD.

CERTIFICATE vOF CORRECTION Patent No.` 2,502,951. November 2li, 1914.2.

' CHARLES B. ARNOLD.

It is hereby certifiedthat error appears in the printed specification of the above nwnberedv patent requiring eorreotion as follows: Page lyfirst ,column-, line before "or" insert "swellingpage 5, second column, line 5, claim 6, for in said read of said; f and line TO, Claim 9, for "the connections read --the oonneotion; and that the said Letters Patent should be read with this correction therein that the same may conf l fom to. the record of the case in the Patent Offige. l

signed and sealed this 13th day of January, A. D. 19u?.

Y Henry Van Arsdalie, (Seal) Acting Commissioner of Patents

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