US1949408A

US1949408A - Fluid flow regulation

Info

Publication number: US1949408A
Application number: US325730A
Authority: US
Inventors: Edward S Bristol
Original assignee: Leeds and Northrup Co
Current assignee: Leeds and Northrup Co
Priority date: 1928-12-13
Filing date: 1928-12-13
Publication date: 1934-03-06
Anticipated expiration: 1951-03-06

Description

March 6, 1934. E, s sms- 349,408

' FLUID FLOW REGULATION Filed Dec., 15, 1928 Patented Mar. 6, 1934 UNlTED STATES PATENT OFFICE FLUI'D FLOW REGULATION Application December 13, 1928, Serial No. 325,730

11 Claims.

My invention relat'es to a method of and apparatus for controlling the supply of fluid, as of feed water to steam boilers or generators, and particularly to a group or battery thereof supplying a common load, as by their connection to the samo header.

In accordance with my invention, balance is effected, preferably continuously and automatically, between an effect whose magnitude is related to the difference between a reservoir pressure and Supply fluid o'r influent pressure, specifically boiler and feed water pressures, and an effect representative of the magnitude of efliuent, speciflcally. boiler output, for example a pressure difference varying in accordance with change of rate of flow of steam; more speciflcally an effect produced by or in accordance With the pressure of feed water available at each boiler of a group and pressure of the individual boiler to which that water is fed is balanced by an efect produced by or in accordance with the rate of flow of steam from that boiler.

Further in accordance with my invention and more particularly, the Setting of a valve control- 25 ling flow of feed. water to a boiler is varied by or 4 in accordance with change of water 1eve1 of that boiler, and the difierence between the feed Water and boiler pressures is varied with change of boiler output; more specifically, the Setting of a second valve in series relation to the first valve is varied in accordance with change of boiler load to vary the pressure drop across the first valve; preferably, at least one of the valves, and particularly the second valve, is operated by a piv- 35 oted lever, the arms of which are connected to members movable in response to the pressure differences aforesaid and in such manner that the lever and valve are stationary when balance of the pressure diiferences exists For an understanding oi' my invention and some of the arrangements and apparatus for practicing it, reference is to be had to the accompanying drawing, in which the pipe or conduit 1 connected to boiler drums 2 and 3 by-branch pipes 4 and 5 respectively Supplies feed water thereto in amount varled as hereinafter set forth. Boiler drums 2 and 3 supply steam to a common header 6 through outlet pipes '1 and 8 respectively, each of which may include'a superheater 9. A device 10 of any suitable known type responsive to change of the level of water within the boiler drum 2 vai-ies the Setting of a valve 11 to vary the flow of feed water to the boiler drum upon' change of water level within the boiler. In like manner, a similar water level responsive device 12 varies the Setting of a. valve 13 controlling the flow of water to boiler drum 3 through branch feed pipe 5.

A sylphon or collapsible bellows 14, or equivalent, is in communjcation with pipe 4 on the side of the valve 11 remote from the boiler, through a connecting pipe 15, and a similar pressure responsive instrumentalityl is connected to a point in the boiler output system, as to' pipe 7 adjacent boiler drum 2, or more preferably directly to the steam space of the boiler drum by a pipe or conos ductor 17. As shown, the sylphons 14 and 16 are mechanically connected in opposing relation to one end of pivoted lever structure 18. The difference between the pressure of feed water in pipe 4 on the side of valve 11 remote from the boiler. 1o

.and the boiler pressure tends to eflfect rotation of the lever structure 18 about its fixed pivot 19. Another arm of the lever structure is mechani- ,cally connected to the opposed sylphons 20 and 21 connected respectvely to the steam header 6,

or other point in the output system of the boiler and the pressure-communicating pipe 17. Variation in rate of flow of steam from the boiler drum 2 effects a change in the relative magnitudes of pressure within the sylphons 20 and 21, there ao being drop of pressure due to pipe line resistance, including that for example of the superheater, between the points of their connection to the path of steam. It will be understood that the sylphons 20 and 21 may be connected to any 3 points in the output system of boiler drum 2 between which there exists a drop in pressure. due

to flow of steam.

A force related in magnitude to the steain output of the boiler tends to efiect rotation of the go pivoted lever structure 18 in one direction, and the excess of feed water pressure over boiler pressure tends to effect rotation of the structure in an opposite direction. Upon change in load, for example, increase in load, the diiference between the pressures acting upon sylphons 20 and 21 increases, producing in the ararngement shown in Fig. 1 clockwise rotation of pivoted lever structure 18, which rotation is opposed by an unbalanced and lesser force representative of the excess oo of feed water pressure over boiler pressure. Movement of the leverstructure effects engagement between an electrical contact 22 carried thereby and a flxed contact 23 to complete an electrical circuit through a reversible motor M mechanicany connected through suitable speed-reducing mechanism generically indicated by gears 25 and 26 to a valve 27 in the branch feed water Supply pipe 4. The direction of rotation of the motor is in a sense increasing the Opening of valve 27. thereby 11o increasing the pressure of feed water available at the inlet valve 11, that is the point remote from the boiler. The excess of feed water pressure over boiler pressure as applied to sylphons 14 and 16 attains a new, higher Value, efiecting reverse rotation of pivoted lever structure 18 against the opposition of the force due to steam flow, and breaking the energizing circuit of the valve controlling motor M. Conversely upon decrease of load, rotatable lever structure 18 rotates in a counter-clockwise direction completing an electrical circuit through contact 22 and fixed contact 24 to eifect rotation of motor M in reverse direction, decreasing the Opening of valve 27, and decreasing the drop of pressure across the valve 11, that is the pressure difi'erence between the feed water available at the boiler and the boiler pressure. An adjustable counterweight 29 is provided so that a desired minimum excess feed water pressure is maintained at zero steam output.

In like manner, feed Water supplied to the boiler drum 3 through pipe 5 is regulated to maintain a desired excess of feed water pressure over boiler pressure for each given load, the excess of pressure Changing with changes of load upon the individual boiler, or with the boiler output. For any given output, the corresponding predetermined excess of feed water pressure is maintained despite changes in the Setting of valve 11 or of change of pressure of the feed water in supply line 1 or in branches 4 and 5 between valves 2'7, 28 and supply pipe 1. The Setting of valve 28 is varied by a reversible motor M1 connected to the fixed contacts 30 and 31 of a reversing switch, adapted to be alternately engaged by a contact 32 actuated by a pivoted structure 33 movable in A response to unbalance between a force of magnitude related to load, the combined effects of pressure within sylphon 34 connected to header 6, and sylphon 35 connected to boiler drum 3, and a force of magnitude related to the excess of feed water pressure over boiler water pressure, the combined efic'ect of pressures acting on sylphon 36 connected to the boiler drum 3 and sylphon 37 in communication with pipe 5 between valves 28 and 13.

It has been found in practice, that When the rate of supply of feed water to the individual boilers of a 'group having a common load, or connected to the same header was controlled in accordance with the individual water levels, that there was often experienced shifting of load between the individual boilers. For example. because of instantaneous conditions at one boiler of the group, it tends to pick up load, decreasing the actual amount of water within the boiler but setting up a faise high level due to increased bubbling. The level responsive device then functions to temporarily reduce 'the feed water supply, so that more of the heat input to the boiler is available for evaporation and the steam output is further increased. Under these conditions the rate of feed water supply is less than the rate of steam output, so that the water level in the boiler starts to drop. Then the level responsive device increases the rate of supply of relatively cold feed water and the rate of evaporation is reduced with a consequent reduction of bubbling action. The faise high level begins to drop, causing the level responsive device to further increase the rate of feed water supply and causing a further .decrease in rate of evaporation. Rate of steam output thus continues to decrease until it is so overbalanced by feed water input that the water level rises once more and rate of feed water supply is checked by the level responsive device. The cycle may then be repeated. With oscillations of the above character in the rate of feed water supply the load carried by the boiler shifts to another or other boilers of the group and the same effect is there experienced, seriously impairing 'the Operating efliciency of the group.

In the arrangement shown in the drawing, as the load upon the individual boiler is increased, for example, rate of flow of feed water thereto is correspondingiy increased although the setting of the valve controlled by the water level responsive device is not varied, reducing or practically eliminating both the time lag due to the inherent sluggishness of the water level type of control and the undesirable response to false changes of level. It will be understood thatinsofar as certain aspects of my invention are concerned, the level responsive device may be dispensed with although preferably it is retained supplementarily to regulate the supply of feed Water to each boiler. Further it will be understood that the pressure drop across the water level responsive valves When used may be varied by change in speed of individual supply pump in accord with change of boiler output instead of varying the Setting of a valve in the branch feed water supply lines.

It will be understood that in some of its aspects my invention is not limited to control of boiler feed water but is applicable to the regulation of fluid flow in general.

What I claim is:

1. In the art of boiler operation, the method which comprises producing an effect representative of boiler output, producing an eifect representative of the difference between the boiler pressure and the pressure of feed water on the supply side of a Variable orifice in the path of flow of the feed water to the boiler from a source of feed water, and varying the pressure of feed water on the supply side of said orifice, independently of its area, to balance said eifects.

2. In the art of boiler operation, the method which comprises producing an efiect representative of boiler output, producing an eifect representative of the difference between the boiler pressure and the pressure of feed water on the supply side of a variable orifice in the path of 'flow of the feed water and between the boiler and source of feed water, and varylng the pressure of feed water on the supply side of said orifice in acoordance with change of boiler output to balance said efiects independently of the area of the variable orifice.

3. Ina system comprising a plurality of boilers having a common steam main, the method of preventing shifting of load between boilers which comprises producing an eflect representative of the steam flow in the main, produciu: effects each representative of the difierence between the pressure of one of said boilers and the pressure of feed water on the supply sideof a variable orifice in the path of flow of the feed water to that boiler from the: source of feed water, and varying the pressure of feed water on the supply side of each of said orifices to balance the said efiects related to each boiler independently of the area of the orifices.

4. A fluid control system comprising means producing an effect varying with change in rate of flow of emuent from a reservoir, a variable orifice in the path of flow of a fluid to said reservoid from. a source of supply, means for producng an eflect of magnitude related to the difference between the reservoir pressure -and the pressure of fiuid on the supply side of said orifice, and means to balance said eifects independently of the area of said variable orifice thereby to maintain a predetermined relation between the rate of flow of efliuent and said pressure difference comprising means to vary the pressure of the fluid on the supply side of said orifice.

5. A boiler feed water control system comprising means producing an effect varying with change of boiler output, a variable orifice in the path of flow of feed water to said boiler from a feed water supply source, means for producing an effect of magnitude determined by the difference between the boiler pressure and the feed water pressure on the supply side of said orifice, and means to balance said effects independently of the area of said variable orifice thereby to maintain a predetermined relation between the boiler.

output and said pressure difference comprising means to vary the feed water pressure on the supply side of said variable orifice.

6. A boiler feed water control system comprising means producing an efl'ect varying with change of boiler output, a variable orifice in the path of flow of feed water to said boiler from a feed water supply source, means for producing an effect of magnitude determined by the diiference between the boiler pressure and the feed water pressure on the supply side of said orifice, and means responsive to said efiects jointly to vary the feed water pressure on the supply side of said orifice independently of the area thereof.

7. In the art of boiler operation, the method of control which comprises producing a force varying with boiler output, producing a second force representative of feed water pressure on the supply side of a variable orifice in the path of feed water to the boiler, producing a third force representative of boiler pressure, opposing said second and third forces to produce a resultant force, and varying the feed water pressure to balance said resultant force against said first force independently of the areaof said variable orifice.

8. A boiler feed water control system comprising means producing an effect varying with change of boiler output, a variable orifice in the path of flow of feed water to said boiler from a feed water supply source, means responsive to the level of water in said boiler for varying the area of said orifice, means for producing an efiect of magnitude determined by the difi'erence between the boiler pressure and the feed water pressure on the supply side of said orifice, and means to balance said efects independently of the area of said variable orifice thereby to maintain a predetermined relation between the boiler output and said pressure difference comprising means to vary the feed water pressure on the supply side of said orifice. y

9. A boiler feed water control system comprising means producing an effect varying with change of boiler output, a valve having a variable orifice in the path of flow of feed water to said boiler from a feed water supply source, means responsive to the level of water in said boiler for varying the area of said valve orifice, means for producing an eifect of magnitude determined by the difference between the boiler pressure and the feed water pressure on the supply side of said orifice, and means responsive to said efiects to vary the feed water pressure on the supply side of said orifice to maintain, irrespective of the area of said orifice, a predetermined relation between and the water pressure in the valve inlet, and also t directly responsive to the steam pressure in the main, for varying the drop in pressure through the valve.

EDWARD S. BRISTOL.