US1995237A - Boiler feed water regulating apparatus - Google Patents

Description

March 19; 1935. J. M. BARRETT 1,995,237

BOILER FEED WATER REGULATING APPARATUS Filed 6, 1930 2 Sheets-Sheet l FIG.1

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INVENTOR Jo eph M Barrett,

4am M A TORNEY March 19, 1935.

STEAM FLOW WATER FLOW J. M. BARRETT BOILER FEED WATER REGULATING APPARATUS Filed Aug. 6, 1930 FIGS PRESSURE DROP THROUGH SUPERH EATER DIFFERENTIAL PRESSURE PRESSURE DROP THROUGH SUPERHEATER STEAM FLOW ACROSS REGULATOR H DIFFERENTIAL PRESSURE ACROSS REGULATOR H WATER FLOW POSITION 2 Sheets-Sheet 2 VALVE STEM PASSAGE AREA WATER FLOW PASSAGE AREA VALVE STEM POSITION WATER FLOW INVENTOR' I JOSeph M B arrect.

ATTORNEY Patented Mar. 19, 1935 UNITED STATES a g tnszii BOILER FEED WATER REGULATING I APPARATUS Joseph M. Barrett, Cleveland Heights, Ohio, as-

signor to Bailey Meter Company, a corporation of Delaware Application August 6, 1930, seem No. 473,459

6 Claims. (01. 122 -4512) This invention relates to: regulating apparatus for. the feeding of water to steam generating boilers, and in particular to provide an arrangement whereby water will be fed to the boiler at thepropei rate for efficient and safe operation.

Such boilers commonly have one or more drums in an upper partof the assembly, for water storage. One or more of. these drums are usually only partly filled with water, thus providing a steam liberating surface. To the steam space so formed, the steam outlet pipe is connected, and it is important that the level of water be so maintained that with steam leaving the boiler at high velocities, water is not car I ried out in slugs or otherwise with thesteam.

It is equally important that the level be not lowered to a point where burning of the parts would occur due to being exposed to high tcmperatures without heat conducting liquid on the other side of the metal.

For a definite weight of water in the boiler the location in elevation of the steam liberating surface, commonly termed the drum level, will vary widely with changes in rating due to swell. or the efiect of the percentage of'steam bubbles below the surface of the water. Immediately upon an increase in rate of steam generation the Water in the boiler will swell up, raising the drum level appreciably, and it has been almost universally the operation of feed water regulators to immediately pinch down on the rate of feed until the increased rate of evaporation in the boiler has-used water from, the storage total to an extent that the level'within the drum drops from its. swelled position not only to its ori inal level but to a lower level corresponding to the new rate of steam generation, sufficient to open up the feed water regu-i lator an amount whereby water will be supplied at a rate corresponding to the new rate of output.

By so allowing the water in the boiler drum to evaporate down to a minimum level before the feed water regulator opens further and admits water at a rate commensuratewith the new rate of steam generation, a lag in water inflow compared to steam outflow is introduced which is ofttimes serious considering the small storage available for water. High pressure design dictates from a cost standpoint the use of small water storage drums containing possimy only if) to 20% of the total water of the boil er. Such conditions mean that at a high rate of steam generation the water stored in the boiler drum is sui'ficient to last onlyfa minute or a fraction thereof, so that if the feed of wa-I ter to the boiler'is interrupted or not in step with changes in steam output, the water stored in the drum will be used up and serious damage might result. j v

, The primary object of my invention is to provide an improved construction and arrangement for controlling the supply of feed water. to a boiler whereby the supply is controlled from factors indicative of the usage and of the total weight or mass of water in the boiler, rather than from factors indicative of. drum level, which as pointed out above, is affected not only by usage but also by swell. I

A "further object of my invention is to maintain the level ofwater in the boiler drum within safe limits while allowing it to vary with varying rates of operation.

Another object is to provide means for feeding water to the boiler inaccordancewith the usage," to keep a definite weight of water inthe boilen Other objects of the invention-are ob- J vious and in part will appearmore in detail from the descriptionv hereinafter. In .the drawings Fig; 1 represents {diagrammatically one arrangement offee'd water regulating apparatus embodying the invention:""

Fig. 2 is a sectional'view of part ofa regulat= ingvalva- 3 Figs. 3m 9 inclusive represent graphically, re-

lations between various wfactorsin my invention."

.Referring to the drawings, 1 indicates conventionally a steam boiler. comprising-upper andlower drums connected by ,boiler tubesda.. Con nected to an upper drumis-a conduit which leads through a superheatert to a discharge conduit 4, and connected 'to an'upper drum is a feed. water supply conduit "2. Conduit 2 is shown in part on a large scale in order to illustrate better the con; struction of certain parts; The structure so far described is to 'be taken as typical of any suitable boiler structure. r

' In the embodiment being described, is-illustrated a valve means located in the conduit'2 controlling the admission of water to the boiler varying with rate of steam generation in the boiler, which for a constant opening of the flow regulating valve, results in an admission of water to the boiler directly proportional to the rate of steam generation. However, due to leakage or other causes, the weight of water in the boiler may gradually increase or decrease, and I readjust the amount of opening of the flow regulating valve to compensate for the change in weight of water in the boiler.

As an indication of variation in the total weight of water in the boiler, I have found that the level in a cold water leg of a U-tube, of which the boiler proper forms the hot water or other leg, is the most satisfactory. Referring to Fig. 1, the pipe 6, external to the boiler, is connected to the lowest chamber of the boiler and by the joining pipe '7, to the steam space of an upper drum. A U-tube joined at the upper ends on account of the pressure in the boiler, is thus formed. The level of water within the boiler, indicated at A, is subject to swell, ebullition and entirely different temperature-density conditions than is the level indicated at B, in the communicating pipes 6 and '7 external to the boiler. Normally the water level B is lower than the level A, except when the boiler is cold, at which time the temperatures'being uniform throughout the system, levels A and B will be the same. Water level B is unafiected by swell, varies only with usage, and is therefore indicative of'the weight of water in the boiler as a whole.

As a means of operating the flow regulating valve 11, responsive to variations in the. .water level B, indicative of weight of water in the boiler,

I employ a trapped vapor-generating system, comprising a generator indicated generally at 5, connected by a pipe 1'7 to an expansible metal bellows 16 mounted on the valve 11, in a manner to position thevalve parts and regulatethe passage area for flow through the valve-. The generator comprises a pipe 8 joined to and in communication withthe piped, lying across or spanning inclinably thenormal water level B in the pipe 6, and surrounded by J a trapped annular chamber 9a'as enclosed by av pipe 9 provided with fins for heat radiation. and closed at the ends by flanges 10. The trapped chamber 9a contains a vaporableliquid such as water in contact or suit- ,able heat-conducting relation with pipe 8 which has normally awater level B corresponding with the water level in pipe 6.

- Steam in the pipe 8 above the water level B, by heat transfercauses a vaporizing of someof the liquid in the chamber. 911-, creating a pressure effective upon the remainder of the liquid in the chamber 9a acting upon the expansiblemetal bellows 16 through the connecting pipe 17. A state of equilibrium is reached in the trapped generating system when the level of liquid within the annular chamber 9a corresponds to the level in'the pipe 8, through vaporization, and the resulting pressure having transferred some of the trapped liquid to the expansible metal bellows 16, causes a movement of its abutment 15, which movement is resisted by a spring 14.

To the movable abutment 15 of the motive bellows 16 is connected the'valve stem 13- and movement of the abutment results in movement of the valve stem 13 to vary the passage opening through the valve 11. The passage area for flow through the valve 11 is thus varied in accordance with variations in a water level existing in the pipe 6, indicativeof the weight of water in theboiler.

To control the pressure of the water entering the flow regulating valve 11, I provide a valve means 12 located in the conduit 2 at the inlet to the valve 11. The pressure of the water entering the valve 11 is controlled through the throttling action of valve discs fastened to a stem 18 and positioned relative to their seats in the valve 12. The stem 18 is fastened to and operated by a piston 20 movable in a suitable cylinder part of the valve 12, the piston 20 being subjected to the pressure of the water at the inlet to valve 11 on its upper side and the pressure existing in the boiler 1 on its lower side. To transmit to the piston 20 a pressure representative of that in the boiler 1, is shown a pipe 21 connected by the pipe 7 to an upper drum of the boiler, and having a condensation chamber 22 located at the highest point of connection so as to provide a definite static water head.

It is necessary that the pressure of the water entering the valve 11 be greater than the pressure in the boiler, otherwise water would not enter the boiler. Furthermore, some frictional loss of pressure will occur in the passage of'the water through the passage-area of the valve 11.

' To control the pressure of the water entering the valve 11, a spring 19 is provided, acting against a lever support 27 at the one. end and effective on the stem 18 at the other end to urge the stem and valve discs away from the valve seats, in the same direction of force as-the boiler pressiu'e acts on the piston 20. For a fixed position of the lever support 2'7, the valve discs are urged away from their seats by the effect of the spring 19 plus the force of the boiler pressure on the piston 20, and are urged toward their seats by the force of the water pressure at the outlet of the valve, acting on the other side of the piston 20. The spring 19 then forms a .calibrating measure of the pressure differential which will exist between the pressure in the boiler and the pressure of the water entering valve 11, the tendency being toalways supply water at a constant excess over boiler pressure.

In order that the feedof water to the boiler shall be directly proportional to the rate of steam generation or boiler output I provide in connection with the valve means 12, a further arrangement of parts, responsive to a function of boiler output, for varying the efiect of the spring 19 and correspondingly Varying the excess of pressure of the water entering the valve 11 over the pressure in the boiler.

To vary the effect'of the spring 19 is provided a means for moving its support, namely the lever 27, so that for any given position of the valve stem 18, the spring will be moreor less compressed and exert a greater or lesser force tending to move the valve stem. The lever 27 is pivoted between its ends and at'the end opposite that supporting the spring 19, is connected to a rod .26, having an adjustment, illustrated as a turnbuckle 29, for length. To the lower end of the rod. 26 is fastened themovable abutment 25 of an expansible metal bellows 24 which is sub.-

jected to a pressure differential varying in a known manner with rate of steam generation.

The pressure which is eifective on the outside of the bellows 24 is that of theboiler 1 transmitted through the pipes '7 and 21, while that effective on the inside of the bellows 24 is that of the steam outlet conduit 4, transmitted through the pipe 23. The difference between these two pressures is that lost by the steam in its passage from the boiler drums, through the superheater' 3 to the outlet conduit 4 and thispressure loss or differential varies in a known manner with rate of steam flow. The pressure difierentialefiective upon the bellows 24 and upon the loading of the spring 19 bears, then, a definite relation to boiler output. s j

For the valve means 12 I have provided various adjustments to take care of changes in operating orother conditions. At 28 is indicated a stop threaded through the casing, providing an adjustable limit to the travel of the piston and through the stem 18 of the valve discs relative to their seats. By adjustment of the screw 28 upwardly toward the piston 20 the travel of the piston will be so limited in the one direction that the valve may have any desired minimum opening to protect against completely shutting 01f the flow of water supplying the valvell. Adjustable means indicated at 29as aturnbuckle may be used to vary thelength of the rod 26 and change the initial loading of the spring 19 and correspondingly the effect of the function of boiler output upon the loading. of the-spring 19. At 30 I have indicated a stop threaded through the casing, adjustable to limit the travel of lever 27 whereby the minimum loading of the spring 19 may be varied. v

The movable abutment of the bellows 24 is mechanically limited in its travel in an upward direction by the casing of the pressure differential valve 12 and in a downward direction by a stop 31. The hand adjustment illustrated at 29 as a turn buckle then serves to shorten or lengthen the connecting link 26, thereby increasing or decreasing the compression of the spring 19 and correspondingly loading or unloading the differential pressure valve 12. By this means a limit may be set to the lowest excess pressure which can exist across the two sides of regulating valve 11.

The adjustable stop 28 not only provides for limiting the travel of the valve stem 18 in a manner such that the valve can never be closed below a predetermined amount as controlled by the position of thestop28,but also provides a hand means of opening the valve to any desired position regardless of pressure conditions throughout the system. The valves on stem 18 are permittedto seat and close off, if the adjustable stop 28 is Y backed downwardly out of the way. The adjust able stop acting against the lever 2'? provides a means for limiting the unloading effect on the spring 19 and providing hand adjustment below the limit encountered when the movable abut-i ment 25 ofthe bellows24-comes against the cas ing'of the pressure valve 12.

I have described in detail the component parts and mechanisms illustrated in Fig. 1 and in accordance with the present embodiment of myinvention they are preferably located indefinite re-' lation to each other and the boiler. For instance, I prefer to locate the pressure control valve 12 in the conduit 2 at the inlet side of the flow regulating valve .11. I have shown anddescribed the spring 19 of the valve means'12 as being located 1 in accordance with a pressure differential which is obtained across the superheater 3 but I might equally as well insert an orifice or other pressure differential producing device in the conduit 4. Likewise, the generator 5 is. shown at a certain inclination across the water level 13 in the pipe 6 whereas it might under certain conditions be desirable to incline it more or less or move it up or down relative to the pipe 6. I

The relation (due to swell) between the water level Aandi the rate of steam generation, assuming a constant weight of water in the boiler, is approximately'parabolic in function. The actual location in elevation and inclination ofthe generator 5 across the level B isdetermined by the limitations of drum size and allowable or desirable change in the level 'A with variations in rat of steam generation. I

It may be desirable to allow a relatively low level A to exist at low rates of steam output'so that upon a sudden or appreciable increase in the rate of output the level will not go to a dangerous height and conversely, to have a high level A at high rates of steam output so that upon a sudden and appreciable decrease, in rate of output, the level will not fall to a dangerous low point.

The feed water regulators now common in which the valve is positioned from level A affected by swell, are in effect geared to level. That is, there is a definite level A and a definite valve position for each rate of steam generation,

and not only will these levels vary with a dif-.-

ferent excesspressure across the valve opening, but for equal increments of rate of steam. generation, there will be unequal increments of change in level'A due to the characteristic of the swell relation. Further, equal increments of valve stem travel may not result in equal increments of flow of water through the valve.

With my invention I provide for the feeding of water to the boiler in accordance with the usage, and tending to keep a definite weight of water in the boiler. My invention is responsive to variations in a level which is unaffected by swell, and to a factor indicative'of rate of usage.

In operation, assumea definite rate of steam generation in which, for example, level A exists approximately at the center line of the drum as shown, and level 13 at the centerline of" the in clined generator 5. The flow regulating'valve l1 and the pressure controlling valve 12 have a certain assumed open position, and water is being fed to the boiler. I will now describe the effect of an increase'in the rate of steam generation or.

however, unaffected by swell and varies only as r the total weightof water in the boiler changes from discrepancy between inputand output, or

from losses such as blowdown, blowing of the safety valves, leakage, etc.

I have in the flow regulating valve 11 two variables responsible for changes in the rate of feed of Water to the boiler, first the passage-area, and second the differential pressure impressed across the valve, resulting in flow through the passagearea." I

The first is controlled or varied-by movement of the valve stem 13 in-accordance with changes in level B indicative of weight of water-in the boiler, or discrepancy between input and output.

An important. feature of my'invention is that I different sizes or designs of valves. I may if desired so shape the ports or passages that the rela tion between equal increments of valve stem motion and increments of flow may be direct, verse, or as any desired function.

Cal

In Fig. 9 I have plotted a straight line "relation between valve'stem position and water flow, the relation which exists in the preferred form of my invention wherein-equal increments of movement of the stem 13 of the regulating valve 11 result in equal increments of water flow for a given excess pressure across thevalve 11. This is accomplished by so shaping the ports or passages 11a that a relation asshown in Fig. 7 between valve stem position and passage-area will result in the relation shown in Fig. 8 between water flow and passage-area, in turn giving the straight line relation of Fig. 9. The curves Fig. 7 and Fig. 8 are drawn of arbitrary shape and are preferably obtained by experiment. The curve of Fig. 9 results from those of Fig. '7 and Fig. 8 as Figs. 7 and 8 are of the same shape and incremental value.

The second variable, the excess pressure, I control to give a flow of water directly proportional to the rate of steamgeneration or boiler output. For a given passage-area the water flow will vary directly as the square root of the excess pressure across the regulating valve 11. The excess pressure is controlled directly by the loading of the spring 19 through the action of the expansible metal bellows 24 acted upon by the differential pressure or drop in pressure of the steam flowing through the superheater 3. This differential pressure varies as the square of the rate of steam flow so that water flow (for any givenpassage-area in the regulating valve 11) will be directly proportional to the rate of steam output.

In Fig. 3 I have plotted the relation existing 1 between flow and pressure drop, in which the rate of flow of steam through the superheater varies as the square root of the pressure drop. Fig. 4 is a similar curve of the relation existing across the regulating valve ll for a given passage-area in which the rate of flow of water through the given passage-area varies as the square root of the excess pressure across said passage-area.

Inasmuch as the pressure drop through the superheater is applied through the bellows 2 4, the movable abutment 25, link 26 and lever 27 to load the spring 19 which is coactingiwith the piston 20 in positioning the valve discs relative to v their seats in the pressure'controlling valve 12 to control the pressure of water at the inlet to the regulating valve 11 relative to boiler pressure atthe outlet side of the regulating valve 11, and

thus control the differential pressure across the given passage-area in-regulating valve 11, then the relationexisting;v between pressure drop through the superheater and the differential pressure across the regulating valve as plotted in Fig.5 as a straight line holds true.

With the differential pressure across the regulating valve 11 directly proportional to the pressure drop, through the superheater, which in turn varies as the square of the rate of steam flow and itself varies as the square of the rate of water flow, then the relation between steam flow and water flow as plotted in Fig. 6 is astraight line.

I have then a regulating valve 11 through which the flow of water will vary directly in accordance with changes in weight of water in the boiler as well as directly with the rate of steam genera tion.

If then the rate of steam output is increased there will be an immediate change in the rate of feed of Water to the boiler through a change in excess pressure. The increased flow of steam through superheater 3 will result inv a change in the pressure drop, and this will be reflected through conduits '7 and 21 to one side of the bellows 24 and through conduit 23 to the other side of the bellows 24, causing a change in the positionv of the movable abutment 25 which through the intermediary of the rod 26 and the fulcrumed' lever 27 varies the loading on .the spring 19 resulting in a change in the pressure of the water at the inlet to the regulating valve 11 relative to the pressure in the boiler 1 on the outlet side of the regulating valve 11. As explained before, the flow through the fixed passage-area of the regulating valve 11 will vary directly with the change in the rate of steam generation.

Now assuming that leakage or discrepancy be tween the input and outflow results in a change in the weight of Water in the boiler, this will be reflected by a change in the level B in the intercommunicating conduit system comprising conduits 7, 8 and 6. With the level B in conduit 8 gradually sinking, for, example, through the using up of stored water, a greater steam zone comes in contact with the liquid trapped in chamber 9a, additional liquid is vaporized and the increase in pressure so generated acting through the connecting conduit 17 on the bellows 16 operates to open the regulating valve 11 somewhat or change its passage-area. Inasmuch as the valve ports or openings are in this embodiment so designed that equal increments of valve stem travel will result inequal increments of flow, then for a constant differential pressure across the passage-area an increased flow of water will result, directly proportional to variations in. the level B which is indicative of changes in the weight of water in the boiler as a whole.

I have then to all intents and purposes a regulating apparatus which-is responsive to a level unaffected by swell for obtainingzthe valve opening, and at said valve opening has impressed upon it a pressure differential varying as a function of the rate of steam generation or boiler output, controlling to maintain a definite weightof water in the boiler system.

I have illustrated and described one embodiment of my invention, but it is expressly understood that by so doing I have not limited my invention other than, as stated in the claims in view of prior art.

'WhatI claim as new and desire tosecure by Letters Patent of the United States, is:-

1. In combination, .a boiler, a conduit for supplying liquid to the boiler, a conduit through which vapor is discharged from the boiler, a valve in the supply conduit, means responsive to variations in an indication of the weight. of water in the boiler for positioning said valve, a second valve in said conduit in advance of said first-named valve, and means responsive to the rate of flow of vapor from. the boiler for positioning. said second-named valve, said second-named valve controlling the pressure at the inlet to the firstnamed valve'proportional to a function of the saidrate of flow of vapor.

2. A boiler, a feed water regulator, a generator controller therefor comprising a conduit connected to and. spanning in elevation the entire boiler and a trapped'generator chamber containing a vaporable liquid located to be responsive to variations in an indication of the weight of water. in the boiler, and means responsive to a function of boiler output to vary the pressure diiferential across said regulator. 3. 'In combination, a boiler, a feed water regulator therefor, controlmeans for said regulator responsive to variations in an indication of the weight of water in the boiler, and means responsive to the rate of flow of steam from said boiler to vary the pressure of the water supplied to said regulator. r

4. A boiler, a feed water regulator, a controller therefor responsive to variations in the weight of water in the boiler, and means responsive to a function of boiler output to vary the pressure differential across said regulator.

5. In a boiler feed water regulator, means responsive to Variations in the weight of water in the boiler for varying the passage-area of the regulator, and means responsive to a function of steam outflow to vary the pressure differential across said regulator.

6. A boiler, a feed water regulator therefor having means for varying the area of the flow passages therethrough, said means responsive to variations in the weight of water in the boiler, the flow passages so proportioned as to result in a definite relation between increments of'regulat JOSEPH M. BARRETT.

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