On a general level, the invention concerns a water flow control valve. More specifically, the valve has a plurality of flow controlling units arranged in line. This configuration ensures reliable and precise control of the water flow through the valve.

In a modern, industrial-scale energy-generating process, it is often required to reduce pressure of the water flowing through the pipework.

By way of example, gas turbines of a thermal power plant require air cooling of the turbine blades. The cooling air is typically produced in an OTC-unit (OTC - Once Through Cooler). Structurally, an OTC is a heat exchanger that cools hot air originating from the gas turbine. More specifically, the OTC uses process water, also called feed water, as a refrigerant in order to cool down the incoming hot air that subsequently is reused in order to cool down blades of the turbine. As sufficient cooling of the turbine blades is extremely important for the operation of the gas turbine of the power plant, it is of the utmost importance that the temperature of the cooled air is controlled within a narrow 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 the heat balance in the OTC, an advanced control valve for feed water pressure is required. Its main purpose is to sufficiently reduce flow rate and pressure of the incoming feed water. I n this context, such a water pressure reducing valve is typically expected to have a turndown ratio, i.e. a quotient of the maximum feed water flow rate at the control valve inlet and the minimum feed water flow rate at the control valve outlet, of 100: 1 or more. I n addition, risk of cavitation, i.e. emergence of vapor bubbles in the water flow followed by their subsequent collapse resulting in generation of shock waves in the water needs to be handled by the trim design of such a valve. I n the related context, the geometry of the trim of the control valve needs to allow for passage of foreign particles in suspension in the feed water flow such that particulate accumulation and/or clogging cannot take place. Further, the feed water control valve needs to be designed such that zones of flashing, i.e. regions where 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 control valve design is to provide a lengthy and tortuous water path with water passages typically having rather small size. This is often achieved by providing a control valve having a plurality of stacked discs with perforations. Every disc typically has individual water flow channels and the water flow is controlled by a vertically reciprocating valve plug.

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

W097/15772 attempts to overcome above-identified disadvantages. It discloses a control valve for reducing pressure of a fluid. The valve is provided with a fixed cage member. A movable valve plug is slidably mounted within the cage member. A fluid flow path is provided through the plug and through the interior of the cage member so that three successive stages of pressure reduction are obtained. The proposed solution is inherently limited with regard to a number of possible, successive pressure reducing stages. More specifically, the inherent design constraints when assembling the valve entail that a lower part of the cage member needs to have larger inner dimensions than a cage member part arranged immediately above. Consequently, only a small number of pressure reducing stages may be achieved. I n consequence, the valve’s total pressure reducing capacity is also limited. Furthermore, the disclosed valve solution is prohibitively voluminous and calls for a valve seat having a large diameter. A valve seat that exceeds 30 mm in diameter is normally required.

US3715098 discloses a valve that controls flow by means of a so-called cascade trim featuring labyrinth-type restrictions providing a cascading effect. As is known in the art, this particular valve design is susceptible to cavitation and flashing. In addition, labyrinth-type restrictions, typically grooves, are easily plugged by the particulate being carried by the process water.

CN 104455469 is structurally similar to US3715098 as it features a single flow controlling unit and a valve trim that enables fluid throttling. Accordingly, CN 104455469 is ridden with the same drawbacks as US3715098.

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

The above stated objective is achieved by means of the water flow control valve which includes the features defined in the independent claim 1 . Particular embodiments of the water flow control valve are defined in the dependent claims 2 to 10.

The valve seat is positioned upstream with respect to an array of flow controlling units. Accordingly, flow control doesn’t occur over the valve seat. Instead it takes place at a later stage, further away from the valve seat. This keeps water stream velocities across the valve seat at a minimum. I n consequence, risks of flashing and cavitation over the sealing surfaces of the valve 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 when compared with the flow controlling unit arranged further away from the valve seat, i.e. the second unit. Consequently, more water pressure reduction occurs over the first unit than the subsequent, second unit. Advantageously, the risk of cavitation is further reduced. The general design of the flow controlling units as well as their serial arrangement improves debris management in the valve. Moreover, the total size of the openings is such that any solid state debris entrained in the feed water that cascades towards the valve outlet will pass through the valve without plugging up the flow passages. This enables the valve to be self-flushing.

In addition, each opening of the flow controlling units comprises at least two sections, wherein a section facing the water outlet of the water flow control valve has a tapering shape. This renders the operation of the water valve 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 units entails that rather large travel of the valve stem and the thereto attached plug assembly results in minor opening of the valve and small amounts of feed water at the valve outlet. This valve property is particularly useful during valve start-up when feed water conditions, such as flow temperature and pressure, are continuously changing.

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

BRI EF DESCRI PTION OF TH E DRAWI NGS

The objects, advantages and features of the invention will appear more clearly in the following description made with reference to the non-limiting embodiments, illustrated by the drawings, in which:

Fig. 1 shows a perspective view of a water flow control valve according to one embodiment of the present invention. A portion 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 flow control valve when in operation, showing the feed water cascading between a water inlet and a water outlet.

Fig. 5 is a schematic view of the valve of Figs. 1 -4 with half of the valve trim shown in the closed position and the other half of the valve trim shown in the open position.

The present invention will now be described more fully hereinafter with reference to the accompanying drawings, in which preferred embodiments are shown. This invention may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein; rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the invention to those skilled in the art. In 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 control valve 10 according to one embodiment of the present invention. The shown valve 10 is substantially assembled. A portion of the valve body is removed so that interior of the valve 10 can appear in greater detail. As shown, a feed water inlet 12 is arranged 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. I n the shown embodiment, said array 37 has seven flow controlling units, but other configurations are possible, depending on the process requirements. The water flow control valve 10 and its various parts will be described in greater 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 also handle other liquids having similar physical properties, but is not suitable for handling streaming gases and/or steam.

As it may be inferred from Fig. 1 , the water flow control valve 10 is of the flow-to-close type. Accordingly, if an actuator is 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 is particularly suitable for applications characterized by low water flows at valve inlet 12 as well as high pressure drops. I n one embodiment, the valve 10 has a turndown ratio of about 250. Fig. 2 is a radial cross-sectional view of the water flow control valve 10 for reducing water pressure according to one embodiment of the present invention. The control valve 10 comprises a previously disclosed water inlet 12 and a water outlet 14. Further, a substantially axially extending valve body 16 is shown. The valve body 16 encloses a first, axially extending cavity 18 that is cylindrically shaped. A bonnet 20 that is attached to the valve body 16 by means of bonnet bolts 21 has a second, axially extending cavity 22 that is cylindrically shaped. The two cavities 18, 22 are aligned so that a valve stem 24 and a plug assembly including a plug 28 and an elongate plug 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 the plug 28. The valve stem 24 is guided by a stem guide 25. The elongated member 32 may be provided with irregularly arranged and oriented grooves, so-called labyrinth grooves, so as to prevent leakage. A gland 27 that prevents feed water leakage is kept in compression by means of a gland yoke 29 and gland bolts 31 . A valve cage 33 positioned inside the valve body 16 surrounds the plug 28. One of its purposes is to hold the reciprocating plug 28 in place. The valve 10 further comprises a valve seat 34. The valve 10 is closed when the plug 28 abuts against the valve seat 34. The valve body 16, the plug assembly and the valve seat 34 are typically manufactured in hardened stainless steel.

In the first, axially extending cavity 18, an array 37 of water flow controlling units is arranged. These units are positioned in line, i.e. one after another. They substantially occupy the space between the valve seat 34 and the water outlet 14. Each flow controlling unit may have externally arranged labyrinth grooves (not shown) so as to prevent water leakage between uni itself and the valve seat 34. Each flow controlling unit comprises a plurality of openings (discussed in connection with Figs. 3a and 3b). The total area of the openings associated with a proximal flow controlling unit 36 is smaller than the total area of the openings associated with a distal flow controlling unit 38. Here, terms proximal and distal are to be construed with reference to the valve seat 34. Consequently, more water pressure reduction occurs over the proximal unit. As a consequence, the risk of cavitation is reduced. I n a related context, 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 debris entrained in the feed water will pass through the valve 10 without plugging up the flow passages. This enables the valve to be self-flushing and effectively prevents accumulation of debris in the interior of the valve 10.

Furthermore, the flow characteristics of a water flow controlling unit 36, 38 could be of the equal percentage type or of the linear type. The flow controlling units 36, 38 and their properties will be discussed more thoroughly in conjunction with Figs. 3a and 3b.

In one embodiment, the valve 10 comprises a detachable seat cartridge that includes the seat 34, a seat holder 41 , an inner seat gasket 39 and the array 37 of water flow controlling units. Accordingly, the seat cartridge is fully replaceable which means that valve trim may be quickly and readily replaced in case 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 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. Each opening of the flow controlling units comprises at least two sections, wherein a section facing the water outlet of the water flow control valve has a tapering shape. This renders the operation of the water valve very accurate, especially for low water flows subject to high pressures. Such design of the flow controlling units 36, 38 entails that rather large travel of the valve stem and the thereto attached plug assembly entails only a minor opening of the valve and results in small amounts of feed water at the valve outlet.

Turning to openings 40 shown in Figs. 3a and 3b, a section facing the water outlet of the water flow control valve has a substantially triangular shape and two sections facing away from said water outlet have a substantially rectangular shape. In the non-limiting embodiment of Figs. 3a and 3b, each water flow controlling unit 36, 38 has four openings 40, wherein said openings 40 are uniformly circumferentially distributed. However, other flow controlling units having even number of uniformly distributed openings. In another, thereto related embodiment, all openings 40 associated with a water flow controlling unit 36, 38 are identical.

In another embodiment (not shown) a water flow control valve comprises at least three water flow controlling units and the total area of the openings associated with the penultimate water flow controlling unit is two times larger than the total area of the openings associated with the first water flow controlling unit and the total area of the openings associated with the ultimate water flow controlling unit is at least 4 times larger than the total area of the openings associated with the first water flow controlling unit. I n a related embodiment, said valve comprises a plurality of water flow controlling units having the total area of the openings equal to the total area of the openings associated with the first water flow controlling unit.

Fig. 4 is a radial cross-sectional view of a water flow control valve 10 when in operation, showing the feed water cascading from a water inlet 12 towards a water outlet 14. The direction of the feed water flow is indicated by arrows. For the sake of brevity, valve components thoroughly described in conjunction with Fig. 2 are not further discussed. As easily seen, the feed water upon flowing past a valve seat 34, flows in an axial direction through a first flow controlling unit until it encounters an obstacle. Subsequently, the water exits through the openings in the flow controlling unit and continues flowing outwardly in a radial direction. Thereafter the water flows in the axial direction outside of the flow controlling unit. Finally, feed water encounters another obstacle and begins to flow in a radial direction inwardly and enters a subsequent flow controlling unit via its opening. This process is repeated for each flow controlling unit (seven in total in the embodiment of Fig. 4)and the water pressure is successively reduced across each flow controlling unit.

In one embodiment, the feed water having a sufficiently low pressure, typically about 1 bar, exits the valve 10 via the water outlet 14 and is supplied to an OTC-unit (not shown). I n connection herewith, the valve 10 is normally welded to the pipe works, 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. In related context and as described in the ’’Background of the l nvention”-section, the supplied feed water is used in the OTC-unit (Once Through Cooler) to cool down the hot air. Normally, feed water is then fed back into a heat recovery steam generator (H RSG), a device that recovers heat from a hot gas stream.

Since the valve seat is positioned upstream with respect to the array of flow controlling units, flow control doesn’t occur over the valve seat. This keeps water stream velocities across the valve seat at a minimum. I n consequence, risks of flashing and cavitation over the sealing surfaces of the valve seat are significantly reduced.

In one embodiment, the water flow control valve is provided with a deadband. Accordingly, for certain stroke lengths, although the valve stem travels and the plug no longer abuts the valve seat, the feed water doesn’t propagate through the flow controlling units. In 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 with half of the valve trim shown in the closed position and the other half of the valve trim shown in the open position.

In the drawings and specification, there have been disclosed 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 limitation, the scope of the invention being set forth in the following claims.