SE1930246A1 - A water flow control valve - Google Patents

Abstract

The invention relates to a water flow control valve (10) for reducing water pressure. The valve (10) comprises at least a first (36) and the second (38), serially arranged water flow controlling units positioned in the valve body cavity (18). The controlling units (36, 38) comprise a plurality of openings (40) and the total area of the openings (40) associated with the first water flow controlling unit (36) is smaller than the total area of the openings associated with the second water flow controlling unit (38). The flow characteristics of the each feed water flow controlling unit (36, 38) is either of the equal percentage type or of the linear type.

Description

Case P202_SE A WATER FLOW CONTROL VALVE FIELD OF THE INVENTION On a general level, the invention concerns a water flowcontrol valve. More specifically, the valve has a plurality of flowcontrolling units arranged in line. This configuration ensures reliable and precise control of the water flow through the valve.

BACKGROUND OF THE INVENTION ln a modern, industrial-scale energy-generating process, itis often required to reduce pressure of the water flowing through the pipework.

By way of example, gas turbines of a thermal power plantrequire air cooling of the turbine blades. The cooling air istypically produced in an OTC-unit (OTC - Once Through Cooler).Structurally, an OTC is a heat exchanger that cools hot airoriginating from the gas turbine. More specifically, the OTC usesprocess water, also called feed water, as a refrigerant in orderto cool down the incoming hot air that subsequently is reused inorder to cool down blades of the turbine. As sufficient cooling ofthe turbine blades is extremely important for the operation ofthe gas turbine of the power plant, it is of the utmost importancethat the temperature of the cooled air is controlled within anarrow range. Consequently, the temperature and, more importantly, the pressure of the feed water to be used as a refrigerant need to be precisely controlled, in particular during system start-up.

Accordingly, in order to ensure adequate control of theheat balance in the OTC, an advanced control valve for feedwater pressure is required. lts main purpose is to sufficientlyreduce flow rate and pressure of the incoming feed water. ln thiscontext, such a water pressure reducing valve is typicallyexpected to have a turndown ratio, i.e. a quotient of themaximum feed water flow rate at the control valve inlet and theminimum feed water flow rate at the control valve outlet, of100:1 or more. ln addition, risk of cavitation, i.e. emergence ofvapor bubbles in the water flow followed by their subsequentcollapse resulting in generation of shock waves in the waterneeds to be handled by the trim design of such a valve. ln therelated context, the geometry of the trim of the control valveneeds to allow for passage of foreign particles in suspension inthe feed water flow such that particulate accumulation and/orclogging cannot take place. Further, the feed water control valveneeds to be designed such that zones of flashing, i.e. regionswhere vapor builds up in the feed water stream, are located towards the outlet of the valve trim.

One way to deal with inherent challenges of water controlvalve design is to provide a lengthy and tortuous water path withwater passages typically having rather small size. This is oftenachieved by providing a control valve having a plurality ofstacked discs with perforations. Every disc typically hasindividual water flow channels and the water flow is controlled by a vertically reciprocating valve plug.

Above-described design performs satisfactorily insituations where the feed water is free from dirt. However, in certain scenarios the feed water is not clean and it might alsocontain particulate of relatively large sizes. This could result inthe narrow flow passages associated with the stacked discdesign becoming plugged by the particulate material present inthe water stream. Obviously, this would significantly reduceefficiency of the valve and could also lead to permanent damage to the valve trim.

WO97/15772 attempts to overcome above-identifieddisadvantages. lt discloses a control valve for reducing pressureof a fluid. The valve is provided with a fixed cage member. Amovable valve plug is slidably mounted within the cage member.A fluid flow path is provided through the plug and through theinterior of the cage member so that three successive stages ofpressure reduction are obtained. The proposed solution isinherently limited with regard to a number of possible,successive pressure reducing stages. More specifically, theinherent design constraints when assembling the valve entailthat a lower part of the cage member needs to have larger innerdimensions than a cage member part arranged immediatelyabove. Consequently, only a small number of pressure reducingstages may be achieved. ln consequence, the valve's totalpressure reducing capacity is also limited. Furthermore, thedisclosed valve solution is prohibitively voluminous and calls fora valve seat having a large diameter. A valve seat that exceeds mm in diameter is normally required.

On the above background, one objective of the inventionat hand is to at least alleviate above-identified and other drawbacks associated with the current art.

SUMMARY OF THE INVENTION The above stated objective is achieved by means of thewater flow control valve which includes the features defined inthe independent claim 1. Particular embodiments of the waterflow control valve are defined in the dependent claims 2 to 10.

The valve seat is positioned upstream with respect to anarray of flow controlling units. Accordingly, flow control doesn'toccur over the valve seat. lnstead it takes place at a later stage,further away from the valve seat. This keeps water streamvelocities across the valve seat at a minimum. ln consequence,risks of flashing and cavitation over the sealing surfaces of thevalve seat are significantly reduced.

The flow controlling unit arranged closer to the valve seat,i.e. the first unit, has smaller total area of the openings whencompared with the flow controlling unit arranged further awayfrom the valve seat, i.e. the second unit. Consequently, morewater pressure reduction occurs over the first unit than thesubsequent, second unit. Advantageously, the risk of cavitationis further reduced.

The general design of the flow controlling units as well astheir serial arrangement improves debris management in thevalve. Moreover, the total size of the openings is such that anysolid state debris entrained in the feed water that cascadestowards the valve outlet will pass through the valve withoutplugging up the flow passages. This enables the valve to be self-flushing. ln addition, the inherent flow characteristics of the eachwater flow controlling unit is either of the equal percentage typeor of the linear type. This renders the operation of the watervalve very accurate, especially for low water flows subject to high pressures, frequently exceeding 200 bars at the valve inlet.More specifically, the configuration of the controlling unitsentails that rather large travel of the valve stem and the theretoattached plug assembly results in minor opening of the valveand small amounts of feed water at the valve outlet. This valveproperty is particularly useful during valve start-up when feedwater conditions, such as flow temperature and pressure, are continuously changing.

Finally, the inventive design of the water control valveenables reduced valve footprint without negative impact on theperformance. Accordingly and by virtue of the valve design athand, a valve seat having diameter of 10 mm is achievable. Thisentails that dimensions of other components, such as a valve body and flow controlling units, may also be reduced.

BRIEF DESCRIPTION OF THE DRAWINGS The objects, advantages and features of the invention willappear more clearly in the following description made withreference to the non-limiting embodiments, illustrated by thedrawings, in which: Fig. 1 shows a perspective view of a water flow controlvalve according to one embodiment of the present invention. Aportion of the valve body is removed so that interior of the valve can appear in greater detail.

Fig. 2 is a radial cross-sectional view of the water flow control valve shown in Fig. 1.

Fig. 3a is perspective view of the water flow controlling units being part of the water flow control valve shown in Figs. 1 and 2. The units of Fig. 3a are shown in cross-section in Fig.3b.

Fig. 4 is a radial cross-sectional view of a water flowcontrol valve when in operation, showing the feed watercascading between a water in|et and a water outlet.

Fig. 5 is a schematic view of the valve of Figs. 1-4 withhalf of the valve trim shown in the closed position and the other half of the valve trim shown in the open position.DETAILED DE RlPTl N F THE lNVENTl N The present invention will now be described more fullyhereinafter with reference to the accompanying drawings, inwhich preferred embodiments are shown. This invention may,however, be embodied in many different forms and should notbe construed as limited to the embodiments set forth herein;rather, these embodiments are provided so that this disclosurewill be thorough and complete, and will fully convey the scope ofthe invention to those skilled in the art. ln the drawings, like reference signs refer to like elements.

For the purposes of this application, terms like ”axial”,”radial” and "circumferential" are in reference to the different directions of the interior cavities of the valve.

Fig. 1 shows a perspective view of a water flow controlvalve 10 according to one embodiment of the present invention.The shown valve 10 is substantially assembled. A portion of thevalve body is removed so that interior of the valve 10 canappear in greater detail. As shown, a feed water in|et 12 isarranged perpendicularly with respect to a feed water outlet 14.An axially extending array 37 of water flow controlling units is arranged in a first, axially extending cavity 18 that is cylindrically shaped. ln the shown embodiment, said array 37has seven flow controlling units, but other configurations arepossible, depending on the process requirements. The waterflow control valve 10 and its various parts will be described ingreater detail in conjunction with Fig. 2 and its operation will be explained in conjunction with Fig. 4.

The shown valve 10 is adapted for controlling water flow,either clean or containing particles. Obviously, it could alsohandle other liquids having similar physical properties, but isnot suitable for handling streaming gases and/or steam.

As it may be inferred from Fig. 1, the water flow controlvalve 10 is of the flow-to-close type. Accordingly, if an actuatoris not applied on the valve 10, the water flowing towards the water inlet 12 will effectively close the valve trim.

As previously mentioned, the valve solution at hand isparticularly suitable for applications characterized by low waterflows at valve inlet 12 as well as high pressure drops. ln one embodiment, the valve 10 has a turndown ratio of about 250.

Fig. 2 is a radial cross-sectional view of the water flowcontrol valve 10 for reducing water pressure according to oneembodiment of the present invention. The control valve 10comprises a previously disclosed water inlet 12 and a wateroutlet 14. Further, a substantially axially extending valve body16 is shown. The valve body 16 encloses a first, axiallyextending cavity 18 that is cylindrically shaped. A bonnet 20 thatis attached to the valve body 16 by means of bonnet bolts 21has a second, axially extending cavity 22 that is cylindricallyshaped. The two cavities 18, 22 are aligned so that a valve stem24 and a plug assembly including a plug 28 and an elongateplug member 32 are reciprocally movable within said cavities 18, 22. The valve stem 24 and the elongated member 32,respectively, are attached to opposite surfaces 26a, 26b of theplug 28. The valve stem 24 is guided by a stem guide 25. Theelongated member 32 may be provided with irregularly arrangedand oriented grooves, so-called labyrinth grooves, so as toprevent leakage. A gland 27 that prevents feed water leakage iskept in compression by means of a gland yoke 29 and glandbolts 31. A valve cage 33 positioned inside the valve body 16surrounds the plug 28. One of its purposes is to hold thereciprocating plug 28 in place. The valve 10 further comprises avalve seat 34. The valve 10 is closed when the plug 28 abutsagainst the valve seat 34. The valve body 16, the plug assemblyand the valve seat 34 are typically manufactured in hardened stainless steel. ln the first, axially extending cavity 18, an array 37 ofwater flow controlling units is arranged. These units arepositioned in line, i.e. one after another. They substantiallyoccupy the space between the valve seat 34 and the wateroutlet 14. Each flow controlling unit may have externallyarranged labyrinth grooves (not shown) so as to prevent waterleakage between uni itself and the valve seat 34. Each flowcontrolling unit comprises a plurality of openings (discussed inconnection with Figs. 3a and 3b). The total area of the openingsassociated with a proximal flow controlling unit 36 is smallerthan the total area of the openings associated with a distal flowcontrolling unit 38. Here, terms proximal and distal are to beconstrued with reference to the valve seat 34. Consequently,more water pressure reduction occurs over the proximal unit. Asa consequence, the risk of cavitation is reduced. ln a relatedcontext, the general design of the flow controlling units 36, 38 as well as their serial arrangement improves debris management in the valve 10. Hence, any solid state debrisentrained in the feed water will pass through the valve 10without plugging up the flow passages. This enables the valve tobe self-flushing and effectively prevents accumulation of debrisin the interior of the valve 10.

Furthermore, the inherent flow characteristics of at leastone water flow controlling unit 36, 38 is either of the equalpercentage type or of the linear type. The flow controlling units36,38 and their properties will be discussed more thoroughly inconjunction with Figs. 3a and 3b. ln one embodiment, the valve 10 comprises a detachableseat cartridge that includes the seat 34, a seat holder 41, aninner seat gasket 39 and the array 37 of water flow controllingunits. Accordingly, the seat cartridge is fully replaceable whichmeans that valve trim may be quickly and readily replaced incase of wear-out due to extended use and/or damage. This reduces down time of the valve 10.

Fig. 3a is perspective view of the water flow controllingunits being part of the water flow control valve shown in Figs. 1and 2. The units of Fig. 3a are shown in cross-section in Fig.3b. The inherent flow characteristics of the shown water flowcontrolling units, determined inter alia by various properties ofopenings 40, is either of the equal percentage type or of thelinear type. This renders the operation of the water valve veryaccurate, especially for low water flows subject to highpressures. Such design of the flow controlling units 36,38entails that rather large travel of the valve stem and the theretoattached plug assembly entails only a minor opening of thevalve and results in small amounts of feed water at the valveoutlet. Openings 40 shown in Figs. 3a and 3b have a generally tapering shape. ln the non-limiting embodiment of Figs. 3a and3b, each water flow controlling unit 36, 38 has four openings 40,four, wherein said openings 40 are uniformly circumferentiallydistributed. However, other flow controlling units having evennumber of uniformly distributed openings. ln another, theretorelated embodiment, all openings 40 associated with a waterflow controlling unit 36, 38 are identical. With respect to theshape of the openings 40 and in non-limiting embodiments, they may be also embodied as circular and/or triangular.

Fig. 4 is a radial cross-sectional view of a water flowcontrol valve 10 when in operation, showing the feed watercascading from a water inlet 12 towards a water outlet 14. Thedirection of the feed water flow is indicated by arrows. For thesake of brevity, valve components thoroughly described inconjunction with Fig. 2 are not further discussed. As easilyseen, the feed water upon flowing past a valve seat 34, flows inan axial direction through a first flow controlling unit until itencounters an obstacle. Subsequently, the water exits throughthe openings in the flow controlling unit and continues flowingoutwardly in a radial direction. Thereafter the water flows in theaxial direction outside of the flow controlling unit. Finally, feedwater encounters another obstacle and begins to flow in a radialdirection inwardly and enters a subsequent flow controlling unitvia its opening. This process is repeated for each flowcontrolling unit (seven in total in the embodiment of Fig. 4)andthe water pressure is successively reduced across each flow controlling unit. ln one embodiment, the feed water having a sufficientlylow pressure, typically about 1 bar, exits the valve 10 via thewater outlet 14 and is supplied to an OTC-unit (not shown). ln ll connection herewith, the valve 10 is normally welded to the pipeworks, but it could also be connected by means of a flange.Further, the preferred orientation for the valve is vertical, but horizontal installation is also possible. ln related context and as described in the ”Background ofthe lnvention”-section, the supplied feed water is used in theOTC-unit (Once Through Cooler) to cool down the hot air.Normally, feed water is then fed back into a heat recovery steamgenerator (HRSG), a device that recovers heat from a hot gas stream.

Since the valve seat is positioned upstream with respect tothe array of flow controlling units, flow control doesn't occurover the valve seat. This keeps water stream velocities acrossthe valve seat at a minimum. ln consequence, risks of flashingand cavitation over the sealing surfaces of the valve seat are significantly reduced. ln one embodiment, the water flow control valve isprovided with a deadband. Accordingly, for certain strokelengths, although the valve stem travels and the plug no longerabuts the valve seat, the feed water doesn't propagate throughthe flow controlling units. ln a preferred embodiment, the deadband is about 10 % of the total stroke length.

Fig. 5 is a schematic view of the valve of Figs. 1-4 withhalf of the valve trim shown in the closed position and the otherhalf of the valve trim shown in the open position. ln the drawings and specification, there have beendisclosed typical preferred embodiments of the invention and,although specific terms are employed, they are used in a generic and descriptive sense only and not for purposes of 12 Iimitation, the scope of the invention being set forth in the following claims.

Claims (10)

1. A water flow control valve (10) for reducing water pressure, said water flow control valve (10) comprising: - a water inlet (12),- a water outlet (14), - a substantially axially extending valve body (16) having a first, axially extending cavity (18), - a bonnet (20) attached to the valve body (18), the bonnet (20) having a second, axially extending cavity (22), - a valve stem (24) attached to a first surface (26a) of aplug (28) belonging to a plug assembly, wherein the plugassembly further comprises an elongate plug member (32)attached to a second surface (26b) of the plug (28), said secondsurface (26b) being arranged opposite with respect to said firstsurface (26a), wherein the valve stem (24) and the plugassembly are reciprocally movable within the first (18) and the second (22) cavities, - a valve seat (34), wherein the water flow across the valveseat (34) is prevented when the plug (28) abuts against the valve seat (34), - at least a first (36) and a second (38) water flowcontrolling units, wherein the units are positioned in series inthe first, axially extending cavity (18) between the valve seat(34) and the water outlet (14) and the first water flow controlling unit (36) is adjacent to the valve seat (34), 14 - wherein the first (36) and the second (38) flow controllingunits comprise a plurality of openings (40) and the total area ofthe openings (40) associated with the first water flow controllingunit (36) is smaller than the total area of the openings associated with the second water flow controlling unit (38), and - wherein the flow characteristics of the at least one waterflow controlling unit (36, 38) is either of the equal percentage type or of the linear type.

2. A water flow control valve (10) according to claim 1,wherein the water flow control valve (10) is of the flow-to-close type.

3. A water flow control valve (10) according to any of thepreceding claims, wherein the water flow control valve (10) is provided with a deadband.

4. A water flow control valve (10) according to any of thepreceding claims, wherein at least one of the water flowcontrolling units (36, 38) has an even number of openings (40),wherein said openings (40) are uniformly circumferentiallydistributed.

5. A water flow control valve (10) according to any of thepreceding claims, wherein all openings (40) associated with a water controlling unit (36, 38) are identical.

6. A water flow control valve (10) according to any of thepreceding claims, wherein the openings (40) are circular and/ortriangular and/or of generally tapering shape.

7. A water flow control valve (10) according to any of thepreceding claims, wherein the water flow control valve (10) supplies water to an OTC-unit.

8. A water flow control valve (10) according to any of thepreceding claims, wherein the water flow control valve (10) has a turndown ratio of about 250.

9. A water flow control valve (10) according to any of thepreceding claims, the valve (10) comprising a detachable valveseat cartridge that includes the valve seat (34), a seat holder(41), an inner seat gasket (39) and the feed water controllingunits (36, 38).

10. A water flow control valve (10) according to any of thepreceding claims, wherein the water flow control valve (10)comprises a plurality of flow controlling units (36, 38),preferably between three and eight flow controlling units, andeach flow controlling unit comprises a plurality of openings (40)and the total area of the openings (40) associated with the firstwater flow controlling unit (36) is smaller than the total area ofthe openings (40) associated with any one of the remaining feed water flow controlling units.