US2636721A

US2636721A - Steam pressure control for directcontact heaters operating on variable pressure steam

Info

Publication number: US2636721A
Authority: US
Inventors: Spining Warren Pierson
Original assignee: Worthington Corp
Current assignee: Worthington Corp
Priority date: 1950-05-22
Filing date: 1950-05-22
Publication date: 1953-04-28
Anticipated expiration: 1970-04-28

Description

2,636,721 ERS April 8, 1953 w. P. SPINING STEAM PRESSURE CONTROL FOR DIRECT-CONTACT HEAT OPERATING ON VARIABLE PRESSURE STEAM Filed May 22, 1950 AUXILIARY STEAM SUPPLY HEATER STEAM RESERVOIR TRAP FIG.I

HEATER- AUXILIARY STEAM SUPPLY AIR RESERVOIR SUPPLY INVENTOR.

G W W Dr S P N E R R A w Patented Apr. 28, 1953 UNITED STATES PATENT OFFICE Warren Pierson Spining, Livingston, N. J., assignor to Worthington Corporation, a corporation of Delaware Application May 22, 1950, Serial No. 163,442

8 Claims.

This invention relates generally to direct-contact feedwater heaters, deaerators and the like, receiving their heating steam from an uncontrolled extraction source as from a steam turbine, and from which boiler feed pumps or boiler feed booster pumps take their suction, and more particularly to a steam pressure control system for direct-contact heaters to stabilize and maintain a sufficient head of Water therein for pumps taking their suction from these said heaters and deaerators.

In most modern central power stations such as are found in the larger public utility or industrial power plants and in many marine power plants, the boiler feed pumps or boiler feed booster pumps take their suction from direct-contact feedwater heaters or deaerators which in turn,

receive their heating steam from an uncontrolled extraction point on the main turbine driving the generators; therefore, varies directly with the load on the main turbine, and the temperature and pressure of the steam acting on the water stored in the heater will accordingly also vary.

One of the major problems coincident with the operation of direct-contact heaters and deaerators on power plant extraction systems is to insure continuous operation of the boiler feed or boiler feed booster pumps under conditions of rapidly varying loads and steam pressures. For,

whenever there is a reduction in main turbine load, with the accompanying reduction in pressure in theheater, a portion or all of the water stored in the heater and in the suction line connecting the pump to the heater, will flash into steam as a result of the corresponding pressure drop in the direct-contact heater. This condition creates the possibility of vapor binding of the pump severe enough to cause damage thereof.

The violence of this flashing and its eifect on the pump will depend upon many factors, the main ones being, the rate of pressure reduction in the heaters, the quantity of stored water in the heater, the temperature and rate of inflow of condensate entering the heater, the design of the storage compartment and the static elevation of the heater above the pump.

In normal operation, the rate of pressure reduction can be controlled sufficiently to assure a full flow of water to the pumps, undisturbed by flashing provided the heater is located high enough above the pump to provide a liberal margin over the net positive suction head requirements of the pumps. However, even under these j-favorable conditions, there is always the possi- The steam pressure in the heater,

bility that the turbine may suddenly be tripped off the line, in which case, in spite of all practical design precautions, the flashing may be severe enough to cause damage to the pump.

In addition, this type of installation increases building and piping cost, and is not easily adaptable to marine installations where sufficient net positive suction head is seldom available, and turbine load must be varied rapidly when maneuvering.

The present invention contemplates a differential steam pressure control system which solves this problem by providing means for controlling the rate of pressure reduction in the direct contact heater independent of the rate of loadreduction of the source or extraction point from which steam is supplied, which includes a differential pressure valve control device actuated by differential pressure between the steam space of the heater and a steam or air receiver, set at a pressure approximately equal to the instant heater pressure and adapted to be reduced slowly, whereby the. control device will allow make-up steam to be initially added to the steam space in the heater and thereafter allow the pressure to be reduced slowly to prevent undue flashing.

Accordingly, it is an object of the present invention to provide a diiferential pressure control system for direct-contact heaters which will assure a constant head of water on the boiler feed or booster pumps taking their suction therefrom,

undisturbed by violent flashing conditions, re-

gardless of the changes in pressures of the source supplying steam to the direct-contact heater.

It is another object of the present invention to provide a steam pressure control system for direct contact heaters which will permit a substantial reduction in elevation of the heater above the pump without sacrificing operating reliability.

With these and other objects in view, as may appear from the accompanying specification, the invention consists of various features of construction and combination of parts, which will be first described in connection with the accompanying drawings, showing a steam pressure control for direct-contact heaters operating on vari able pressure steam of a preferred form embodying the invention, and the features forming the invention will be specifically pointed out in the claims.

In the drawings- Figure 1 is a diagrammatic sketch showing the invention.

Figure 2 is a diagrammatic sketch of a modified form of the invention.

Figure 3 shows one type of valve which may be used with the invention.

Referring to the drawings, Figure 1 shows a diagrammatic sketch of the control system connected to a direct-contact heater i, which may be any suitable type of feedwater heater, deaerator or the like type of direct-contact heater, of which there are several easily purchasable on the open market.

The direct-contact heater i, has a steam receiving space 22 and a water storage space Inlet means l for water is mounted in the heater to admit said incoming water into the steam receiving space for direct-contact with the steam being supplied through conduit from some uncontrolled and variable pressure steam source such as an extraction outlet on the main turbine (not shown) of a power plant, whereby the steam will act as a heating medium for the incoming water. Conduit provided with a check valve ii O that when steam pressure at thesource is less than the steam pressure in the steam receiving space 2 the steam will be prevented from passing back to the source by the check valve.

A boiler feed pump or boiler feed booster pump i is connected to the water storage space 3 by means of suction line 8, and accordingly will talre itssuction from the water storage space.

In order to maintain a constant head of water on the pump, when sudden reduction in pressure occurs in the steam receivingspace 2, an auxiliary steam supply from some fixed source .Sllh as a main boiler (not shown) is connected to the steam receiving space 2 by means of auxiliary steam supply conduit 9.

The quantity of steam from such abovernentioned auxiliary steam supply delivered to the steam receiving space is determined by the differential pressure between the steam receiving space 2 and a pressure or steam reservoir I0 through the medium of a balanced pressure actuated valve l l interposed in the auxiliarysteam supply conduit 9.

The pressure actuated valve l I in the preferred form is indicated in Figure 3 as a balanced diaphragm type valve, it being understood'however, that while this type of valve is shown that any other suitable type of valve may be utilized .for this purpose.

Thus, referring to Figure 3, the pressure actuated valve is shown in section comprising a valve housing it having the valves l3 positioned therein to control the fiow of steam through the valve housing and consequently through the steam supply pipe 9. Connected to the valves 53 is an elongated valve stem Hi which extends upwardly from the valve housing l2, through the valve guide structures it: and it into a sealed chamber ll mounted on the valve housing where it is fixedly connected for movement with 2. diaphragm member l8 lying substantially in the medial plane of said chamber 18 to divide it into an inner chamber is and an outer chamber 2t.

Suitable packing structures

26 and 22 are provided about the valve stem where it passes out of said valve housing 52 and into said valve chamber 2b to prevent steam from leaking to atmosphere.

The diaphragm member 18 is of the balanced type so that as it is moved inwardly and outwardly responsive to steam pressure as hereinafter described, the valve stem will cause the valves is to open and close to control the flow of steam in the auxiliary steam supply conduit 9 to the steam receiving space.

A resilient member 23, is adjustably mounted about the valve stem and is adapted to abut a stop member M, for normally urging the valves it into a closed position. Thus, the total effect across the diaphragm as to the amount it will open over and above this spring member will depend on the balance of pressure between the inner chamber i9 and outer chamber 25].

The means for actuating the diaphragm i8 and thus controlling the action of the valves, also acts to control the rate of pressure reduction in the direct-contact heater, as shown in Figure 1.

Thus, steam reservoir it, which may be any suitable type of well insulated steam reservoir easily purchasable on the open market, will receive steam therein through a connecting conduit 25 leading from the steam receiving space 2 of the direct-contact heater, whereby steam at substantially the same or slightly lower pressure will be present in the steam reservoir it. .A check valve as is provided in connecting conduit 25 to prevent any flow of steam from the reservoir to the direct-contact heater when the pressure is reduced in the direct-contact heater.

A small orifice or needle valve 2? is provided on the steam reservoir 1 8, to permit the constant escape of a smail predetermined amount of steam to atmosphere causing the steam pressure in the steam reservoir to be maintained slightly lower than the steam pressure in the heater during normal operation, and to allow the steam pressure in the steam reservoir'to fall at a fixed or predetermined rate whenever heater pressure is less than reservoir pressure. kfiheclr valve '26 will close to prevent the steam from passing back along the connecting conduit '25 whenever the pressure in the heater reduces below the pressure in the steam reservoir iii.

A trap 28 is also provided in the steam reservoir to remove any condensate which forms therein, and to provide means for returning it through return conduit'iii to the water storage space 3 of the direct-contact heater 5, all of the above being clearly shown in Figure l of the drawings.

Between the check valve 26, and the steam receiving space 2, an inlet pipe 3&3 joins the connecting conduit 25 and the outer chamber 2t whereby steam at substantially heater pressure will be acting in outer chamber 28 on one side of the diaphragm member l8.

Between check valve 26 and the steamreservoir it, a second inlet pipe 3! joins'the connecting conduit 25 and the inner chamber ii! whereby steam at substantially the same pressure as the steam in the connecting conduit and the steam reservoir will be acting in inner chamber [9 on the other side of the diaphragm member I 8, all of which is clearly shown in Figures 1 and 3 of the drawings.

Under normal operating conditions, steam will be delivered to the heater i from the source point or extraction point on the main turbine (not shown). As long as the load operation of the turbine is constant or the supply of steam is delivered at a constant pressure, the pressure in the heater i will be substantially the same or slightly higher than the pressure in the reservoir Hi. Accordingly, the pressure acting in the outer chamber 29 combined with the pressure exerted by the spring member 23 will keep the valves it closed. No make-up steam is needed and accordingly none is delivered.

However, when the turbine extraction steam pressure is reduced or the supplied steam entering through conduit 5 is reduced, heater pressure will also reduce. Check valve 6 will close to prevent steam flowing back through conduit 5. Check valve 26 will close to prevent any steam from flowing back to the steam receiving space 2 and accordingly the pressure acting in inner chamber l9 will be greater than the pressure acting in outer chamber 20 combined with the pressure, exerted by the spring member 23 and the valves It will be opened to allow make-up steam to pass through the auxiliary steam supply pipe 8 to the steam receiving space 2, until the pressure in the steam receiving space 2 builds up the pressure sufficiently to prevent flashing of the water in the water storage space 3 of the heater I. Since, however, steam will be escaping from the reservoir H1, at a predetermined fixed rate, the pressure in the reservoir ||l will gradually fall, until the pressure in the steam receiving space '2 will be equal to the pressure being supplied from the extraction point of the turbine (not shown) or some other source in which case the pressure differential across valve diminishes and the valve closes. Then check valve 6 will open to allow steam once again to .be supplied at the new reduced pressure to the heater. The total action of valve when a reduction in pressure occurs is to maintain a pressure in the heater equal to that in the reservoir l0. Since, however, the rate of pressure drop in the reservoir Hi can be controlled by adjustment of the needle valve or selection of the orifice size, it follows that the rate of pressure reduction in the direct contact heater is likewise controlled.

In some cases, it may be desirable to utilize an air reservoir in place of the steam reservoir for establishing a fixed rate of pressure drop. This modified type of system is illustrated in Figure 2 of the drawings.

Referring therefor to the drawings, Figure 2 shows a direct-contact heater I having a steam receiving space 2 and a water storage space 3'. Inlet means 4 for incoming water is mounted in the heater to admit said water into the steam receiving space 2' for direct-contact with the steam being supplied to the steam receiving space by conduit 5' connected thereto from some uncontrolled steam source such as an extraction outlet on the main turbine (not shown) of a power plant whereby the steam acts as a heating medium for the incoming raw water. Conduit 5' is provided with a check valve 6. A boiler feed pump or boiler feed booster pump is connected by a suction line 8' similarly as described above.

The quantity of steam delivered to the steam receiving space 2 from the auxiliary steam supply (not shown) by means of auxiliary steam supply conduit 9 is determined by the differential pressure between the steam receiving space 2' and an air reservoir I0 through the medium of a balance pressure actuated valve interposed in the auxiliary steam supply conduit 9', all of which is clearly shown in Figure 2 of the drawings.

The valve II is identical with that above described, and accordingly is identical with valve shown in Figure 3 of the drawings.

The means for actuating the diaphragm in valve H, in the modified form will depend on the differential pressure between pressure in the air reservoir 1' and the steam pressure in the steam receiving space and the means for reducing the pressure will be incorporated in the air reservoir ID in similar fashion as hereinafter described.

Air reservoir I0, is substantially cylindrical in construction and may be any suitable type of air receiver of which there are many well known in the compressor art. It is supplied with air under pressure from some suitable source (not shown) through air supply conduit 4|). A balanced-diaphragm type valve 4| is interposed in the air supply conduit 40 to control the flow of air under pressure to the air reservoir I0.

Valve 4| is substantially identical with valve shown in Figure 3.

Valve 4|, is actuated by steam under heater pressure delivered to one side of the diaphragm by a steam connecting conduit 42 connected between the steam receiving space 2' and valve 4|, and on theother side of the diaphragm by an air conduit 43 connected between the air reservoir H3 and the valve 4| which delivers air under reservoir pressure to said other side of the diaphragm. Air at reservoir pressure will tend to close the valve 4| and steam at heater pressure will tend to open it. The total effect with the spring member maintaining the valve normally closed will be that the relative amount that the valve opens will be a function of the differential pressure between the heater and the reservoir Ill.

Thus, as the pressure in the heater falls below that in the reservoir, the air pressure acting on the diaphragm in valve 4| will act to close it.

Since the pressure in the air reservoir In will actuate valve the differential pressure is also established by the pressure of the steam in the heater and the air under pressure in the air reservoir HIT, as steam under heater pressure will be delivered to valve through inlet pipe 30' connected to conduit 42 to act in outer chamber 2i) on one side of the diaphragm, and air under pressure will be supplied through a second inlet pipe 3| connected between the air reservoir It and inner chamber H! to act on the other side of the diaphragm.

The air reservoir Ill similarly to the above described steam reservoir |0, is also provided with an adjustable needle valve or properly sized orifice 44, to allow the pressure therein to be reduced at a constant rate. Thus, since valve maintains heater pressure approximately equal to reservoir pressure, means is provided to positively control the pressure drop in the direct contact heater where reduction of pressure from the uncontrolled extraction point on the turbine (not shown) or uncontrolled and variable pressure source occurs.

In the operation of the modified form, when the pressure is reduced in the direct-contact heater I, check valve 6 closes. The pressurein the air reservoir I0 acts simultaneously to close valve 4| to stop the supply of air under pressure to the air reservoir, and to open valve H to allow make-up steam to enter through auxiliary steam supply conduit 9' to the steam receiving space.

Since the adjustable needle valve 44 will allow the pressure in the air reservoir Ml to reduce at a predetermined controlled rate, pressure in the steam receiving space 2 will slowly reduce to the new lower pressure at which point equilibrium of pressure across the diaphragm of valve H will allow it to close and similar equilibrium of pressure across the diaphragm of valve 4| will allow it to open so that air under pressure may be supplied to the air reservoirs by a supply conduit 40 once again.

In either form of this invention it appears obvious that when steam is supplied at an increased pressure, the problem of flashing will not arise.

It will be understood that the invention is not to be limitedpto the specific construction or at'- rangement of parts shown but that they may be Widely modified within the invention defined by the-claims.

What is claimed is:

1. In a differential pressure control and reduct-ion system for direct contact heaters receiv ing a main source of steam :atvariable pressure in the steam receiving space thereof, an auxiliary steam supply conduit connected to supply make-up steam thereto-a valve inaintainedncrmaily closedconnected in said steam supply conduit for controlling the flow of make-up steam from said auxiliary steam supply to said steam receiving space, a balanced diaphragm means connected to said valve for open ng said valve responsive to differential pressure across said diaphragm, asteam reservoir, 2, connecting conduit be" seen said reservoir and the steam receiving space to supply steam to the reservoir at substantially the same pressure as the steam supplied to steazn'receiving space, a check valve in said-connecting conduit to prevent back. flow or steam when thepressureinsai-d steam re-- ceiving space is less than in the steam reservoir, conduit-means connecting the steam reservoir and the steam receiving to opposite sides of said diaphragm to actuate said diaphragm by the differential pressure between said steam resetoir and said steam receiving space, and adjustable means on "said steam reservoir positioned'to reduce the pressure in steam reservoir to control the rate of pressure reduction in said steam receiving-space irrespective of the reduction of pressure of the variable pressure steam supplied to the steam recei rig-space.

2. In a differential control and reduction system for direct contact heaters claimed in claim 1 wherein said adjustable means on the steam reservoir includes, an august-able needle valve mounted on thesteanrreservoir set'to allow a predetermined quantity of steam to escape to atmosphere from said steam reservoir.

3. In a dilierential control and reduction sys tem for direct contact heaters as claimed in claim 1 wherein means are provided for returning condoused steam from the steam reservoir to the contact heater including a trap connected to the lower portion of said steam eservoir to receive condensate therein, are n conduit connected between the trap and the .ect contact heater to return the-condensate 'fromthe trap to the heater.

4. 111 a difierential pressure control and reductionsystem for direct contact heaters recei ing main source of steam at variable pressure in thesteam receiving space thereof, an auxiliary steam supply conduit connected to said steam receiving space, a first valve maintained normally closed connected in said steam supply conduit for controlling the flow of make-up steam from said auxiliary steam supply to said steam receiving space, a balanced diaphragm connected to said valve for opening said valve responsive to differential pressure across said diaphragm, a pressure reservoir, means connecting the pressure reservoir and the steam receiving space tosaid balanced diaphragm to actuate said diaphragm by the differential pressure between said pressure reservoir andsaid steam receiving space when the pressure of the main source of steam supplied to the direct contact heater is reduced, means including a line for supplying pressure medium to said pressure reservoir, a second valve in said line maintained normally open to regulate the amount of pressuresupplied to said pressure reservoir, a second balanced diaphragm connected to said second valve for closing said second valve responsive to differential pressure across said second diaphragm, means connectin said pressure reservoir and said steam receiving space to said second balanced diaphragm to actuate said second diaphragm for closing the second valve to maintain the pressure reservoir at a pressure substantially equal to the pressure in said steam receiving space, and adjustable means on said pressure reservoir positioned to reduce the pressure in said pressure reservoir at a predetermined rate to contol the rate of pressure reduction in the steam receiving spaceirrespective of the reduction in-pressure of the steam being suppliedLbY the main source to the steam receivin space.

5. In a differential control and reduction systern for direct contact heaters as claimed in claim l wherein said adjustable means on the pressure reservoir includes, an adjustable needle valve inounted-onthe steam reservoir set-to allow a predetermined quantity of the pressure medium to escape to atmosphere from said pressure eservoir.

in a difierential pressure control and reduction system for dir ct contact heaters receivin a main source of steam 'at'variable pressure steam receiving space thereof, valve means :orniaily closed for controlling a supply of makeo from an auxiliary steam-source to said steam receiving space, a pressure reservoir operatively connected to said steam receiving space, conduitmeans connecting saidvalve means with pressure reservoir and said steam-receivspace for controlling and actuating said valve means by the difierential pressure between said pressure reservoir and said steam receiving space, and bleed -off means on said-pressure reservoir to control the rate of reduction in pressure in said pressure reservoir and in said steam receiving space operatively connected therewith irrespective of the reduction in pressure of the steam supplied'to said steam receiving space from said inainsource.

7. In a differential pressure control and reduction system for direct contact heaters receiving a'main source of steam at variable pressure in the steam receiving space thereof, an auxiliary steam supply connected to said steam receiving space, at least one difierential pressure operated valve means in said auxiliary steam supply maintained normally closed, a reservoir, means to operatively connect said reservoir to the steam receiving space, insane for maintaining the pressure in said. reservoir at a pressure substantially equal to the pressure of the-steam supplied to said steam receiving space during normal operation, conduit means connecting said valve means With said reservoir and said steam receiving space whereby said valve means-is controlled and actuated by the diflierential pressure between said reservoir and said steam receiving space when the pressure of said-main source of steam entering said steam receiving space 'is;reduced, and bleed-off means on said pressure reservoir to control the rate of reduction of pressure in said reservoir and in said steam receiving space operatively connected thereto irrespective of the reduction in pressure of the steam supplied to said steam receiving space from said main source.

8.,In a differential pressure control and reduction system for direct contactheaters receiving a main source of supply at variable pressure in the steam receiving space thereof, an auxiliary steam supply connected to said steam receiving space, at least one differential pressure operated valve means in said auxiliary steam supply maintained normally closed, a pressure reservoir, means for maintaining the pressure in said pressure reservoir at a pressure substantially equal to the pressure of the steam supplied to said steam receiving space, a check valve in said means to prevent back flow of pressure medium from said pressure reservoir to said steam receiving space, conduit means connecting said valve means with said pressure reservoir and said steam receiving space whereby said valve means is controlled and actuated by the differential pressure between said pressure reservoir and said steam receiving space when the pressure of said main source of steam entering the steam receiving space is reduced, and bleed-off means on 0 said pressure reservoir to control the rate of reduction in pressure in said reservoir irrespective of the reduction in pressure of the steam supplied to said steam receiving space from the main source.

WARREN PIERSON SPINING.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 642,088 Deems Jan. 30', 1900 2,029,505 Rawson Feb. 4, 1936 2,085,782 Blanchard July 6, 1937 2,372,087 Karassik Mar. 20, 1945 2,489,345 Welch Nov. 29, 1949 FOREIGN PATENTS Number Country Date 307,266 Germany Aug. 12, 1918 387,584 Germany Jan. 4, 1921