SE1930345A1 - A Steam Conditioning Valve - Google Patents

Abstract

The invention relates to a steam conditioning valve (10) for simultaneously reducing pressure and temperature of steam and comprising a first inlet port (12) for the introduction of cooling water, a second inlet port (14) for the introduction of steam and an outlet port (16) for evacuating the fluid created by mixing of the cooling water and the steam. The valve (10) comprises a valve stem (20), a valve plug (22) and two axially extending pipes (24, 26), all immobilized with respect to one another so that they make up an axially reciprocable unit. A water pipe (24) has an orifice (23) for receiving cooling water and means for injecting received water into a mixing chamber (17). The orifice (23) is associated with a first flow characteristic. A steam channel (21) transports steam into the steam pipe (26) for subsequent injection into the chamber (17). The steam channel (21) is associated with a second flow characteristic. The first and the second flow characteristics have the same general shape.

Description

Case P204_SE A STEAM CONDITIONING VALVE FIELD OF THE INVENTION On a general level, the invention concerns a steam Conditioning valvefor use in a steam-based power plant, said valve being adapted to simultaneously reduce pressure and temperature of the incoming steam.

BA K R ND FTHE INVENTI N Steam conditioning valves that simultaneously control pressure andtemperature are well-known in the art. One such valve is disclosed inUS4718456.

While these valves perform satisfactorily in many situations, it hasbeen established that for small openings of the valve plug, for instance instart-up situations, an adequate cooling of the process steam is very difficultto achieve.

US5380470 attempts to solve the above-identified problem byproviding a dedicated steam duct as well as a separate cooling waterconduit. These are so arranged that the steam impinges on the jets ofcooling water flowing from the outlets of the cooling water conduit. Hereby,steam cooling process is improved. However, extensive use of these valvesin real-life conditions has shown that the solution proposed in US5380470still is ridden with considerable drawbacks such as insufficient cooling of theincoming steam and/or cooling water occasionally being prevented to flowout of the outlets.

On the above background, one objective of the invention at hand is toat 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 a steamConditioning valve which includes the features defined in the independentclaim 1. Particuiar embodiments of the steam conditioning valve are definedin the dependent claims 2 to 8.

By characterizing the orifice of the water carrying pipe with the firstflow characteristic and the steam channel supplying steam to the steamcarrying pipe with the second flow characteristic, it is possible to quantifyflow of the respective fluid through the valve, upstream of the mixingchamber. As a result, the respective flow characteristic may be representedby means of a curve. This method is particularly applicable for limited fluidflows, e.g. during system start-up. Thus obtained process information maybe used to compare and, by suitably configuring the orifice distributionpattern, match the two curves so that the two flow characteristics have thesame general shape. Advantageously, this entails improved mixing of thecooling water and the steam in the mixing chamber, especially for smallvalve openings. Accordingly, the mixing of the steam with the cooling wateris better controlled, which results in a faster and more reliable steam coolingprocess. Further benefits attributable to the invention are reducedconsumption of the cooling water and/or steam.

BRIEF DESCRIPTION OF THE DRAWINGS The objects, advantages and features of the invention will appearmore clearly in the following description made with reference to the non- limiting embodiments, illustrated by the drawings, in which: Fig. 1 is a perspective view showing cross-section of a steam conditioning valve according to one embodiment of the present invention.

Fig. 2a is a cross-sectional view of a section of the steam Conditioning valve of Fig. 1, where a valve plug is closed.

Fig. 2b is a cross-sectional view of a section of the steam conditioning valve of Fig. 1, where a valve plug is slightly open.

Fig. 2c is a cross-sectional view of a section of the steam conditioning valve of Fig. 1, where a valve plug is fully open.

Figs. 3a and 3b show different embodiments of a water carrying pipe having different orifice distribution patterns.

Fig. 4 visualizes a first flow characteristic associated with the orificeprovided in a water carrying pipe and a second flow characteristic associated with the steam channel provided in a valve plug.

DETAILED DESCRIPTION OF THE INVENTION The present invention will now be described more fully hereinafterwith reference to the accompanying drawings, in which preferredembodiments are shown. This invention may, however, be embodied inmany different forms and should not be construed as limited to theembodiments set forth herein; rather, these embodiments are provided sothat this disclosure will be thorough and complete, and will fully convey thescope of the invention to those skilled in the art. ln the drawings, likereference signs refer to like elements.

For the purposes of this application, terms like ”axial”, ”radial”, and”circumferential” are in reference to the different directions as defined by the valve body. Here, the cross-section of the valve body is essentially a circle.

Fig. 1 is a cross-sectional view of a steam conditioning valve 10according to one embodiment of the present invention. The valve 10 is usedin order to simultaneously reduce pressure and temperature of steam. lnFig. 1, a sealing surface of a valve plug 22 abuts an annular valve seat 18and the valve 10 is in closed position. Main components of the valve 10, such as valve body 15, i.e outer shell of the valve, and the valve seat 18 aretypically manufactured in hardened stainless steel. The valve 10 has a firstinlet port 12 for the introduction of cooling water into an interior of the valve10 and a second inlet port 14 for the introduction of high-pressure,superheated steam into the interior of the valve 10. Here, the pressure ofthe cooling water is about 30 bars and its temperature is around 90 °Cwhereas the process steam typically has a pressure of around 60 bars andthe temperature of approximately 450 °C. lt is also shown an outlet port 16for evacuating the steam created by the mixing of the cooling water and theprocess steam in a mixing chamber 17. By way of example, said steam has the pressure of 12 bars and the temperature of about 200 °C.

Still with reference to Fig. 1, it is further shown a valve stem 20 forconnecting to an actuator (not shown), the previously-mentioned valve plug(its sealing surface resting against the valve seat as the valve is shown inclosed position in Fig. 1) and two axially extending pipes, a water carryingpipe 24 and a steam carrying pipe 26. The water carrying pipe 24 has atleast one orifice 23 and is at least in part enclosed by the steam carryingpipe 26. The valve stem 20, the valve plug 22 and the two axially extendingpipes 24, 26 are immobilized with respect to one another so that they makeup an axially reciprocable unit. This unit is normally made in hardenedstainless steel. The movement of the valve stem 20 is controlled by theactuator that may be either hydraulic, pneumatic or electric. Here, strokelength is the distance the valve plug 22 (and the other parts of the axiallyreciprocable unit) travels in the valve interior between the valve being fullyopen and being fully closed. Operation of the steam conditioning valve 10 will be discussed in greater detail in connection with Figs. 2a - 2c.

As seen in Fig. 1, a steam channel 21 is provided in the valve plug22. The valve plug 22 also comprises a cylindrically shaped structure 31,frequently denominated cage, with perforations to allow steam passage,where the structure 31 extends in axial direction. Further, attached to the valve body 15 there is a cylindrically shaped pressure pipe 33 provided witha plurality of radially extending channels for allowing steam passage into the mixing chamber 17. ln the embodiment shown in Fig. 1, the water carrying pipe 24 israther long such that the water outlet 25 of the water carrying pipe 24 isarranged in vicinity of the steam outlet 27. Other alternatives are possible,for instance, the water carrying pipe 24 being significantly shorter. Thelength of the water carrying pipe 24 is typically determined by the pressureand temperature of the incoming steam/water as well as the specifiedpressure and the temperature at the valve outlet 16.

Fig. 2a is a cross-sectional view of a section of the steamconditioning valve 10 of Fig. 1. As disclosed in connection wth Fig. 1, asealing surface of a valve plug 22 rests against a valve seat 18 as the valve10 is shown in closed position. Accordingly, neither steam nor cooling watermay enter the valve trim and the valve is closed.

Fig. 2b is a cross-sectional view of a section of the steamconditioning valve 10 of Fig. 1 with a valve plug 22 being slightly open, i.e.the sealing surface of the valve plug 22 is not in contact with the valve seat 18. The opening is effected by a movement of an actuator (not shown) thatis connected to a valve stem 20. As discussed in connection with Fig. 1, the valve stem 20, the valve plug 22 and the two axially extending pipes 24, 26are immobilized with respect to one another so that they make up an axiallyreciprocable unit. ln Fig. 2b, this axially reciprocable unit is moved slightlyupwards with respect to Fig. 2a such that a certain amount of the coolingwater and the steam may enter the valve trim.

Still with reference to Fig. 2b, the water carrying pipe 24 is, at a firstend, provided with at least one orifice 23 for receiving cooling water from afirst inlet port 12. The water carrying pipe 24 is, at a second end, providedwith at least one water outlet (shown in Fig. 1) for injecting received water into a mixing chamber. The orifice is associated with a first flow characteristic. As also seen in Fig. 2b, at least one steam channel 21 isarranged in the valve plug 22. The steam channel 21 transports the steamfrom a second inlet port 14 to the steam carrying pipe 26 for subsequentsteam injection into the mixing chamber via a steam outlet of the steamcarrying pipe (shown in Fig. 1). The steam channel 21 is associated with asecond flow characteristic. Accordingly, for small valve openings only fluidflows through the valve are the cooling water passing through the watercarrying pipe 24 and the steam flow passing via the steam channel 21 intothe steam carrying pipe 26. These fluids are brought in contact in the mixingchamber (shown in Fig. 1).

By characterizing the orifice 23 with the first flow characteristic andthe steam channel 21 with the second flow characteristic, it is possible toquantify and parametrize flow of the respective fluid through the valve 10,typically representing each flow characteristic by means of a curve. The twoflow characteristics will be discussed in greater detail in connection with Fig.4. The proposed characterization is particularly applicable during systemstart-up. Furthermore, the information obtained in this manner may be usedto compare and, by suitably configuring the orifice distribution pattern,match the two curves so that the first and the second flow characteristicshave the same general shape. Advantageously, this entails improved mixingof the cooling water and the steam in the mixing chamber, especially forsmall valve openings. Accordingly, the mixing of the steam with the coolingwater is better controlled, which results in a faster and more reliable steamcooling process. Further benefits attributable to the invention are reducedconsumption of the cooling water and/or steam.

Fig. 2c is a cross-sectional view of section of the steam conditioningvalve 10 of Fig. 1 with a valve plug 22 being fully open. Accordingly, in Fig.2c, the previously-defined axially reciprocable unit is moved completelyupwards with respect to Figs. 2a and 2b such that, in addition to the coolingwater and the steam flowing through the respective pipe 24, 26, incoming steam also passes across a cylindrically shaped structure 31 withperforations. A significant steam pressure reduction takes place across theperforations of the structure 31. This steam then reaches a pressure pipe(not shown in Fig. 2c) provided with a plurality of radially extending channelsso that the steam passes into a mixing chamber (not shown in Fig. 2c) forsubsequent mixing with the cooling water. ln this context, the flow of thecooling water is maximal as all orifices of the water carrying pipe 24 are influid communication with a water inlet 12 discussed in connection with Fig.1.

Figs. 3a and 3b show different embodiments of a water carrying pipe24 having different orifice distribution patterns. More specifically, in Fig. 3athe orifice 23 is embodied as two arrays 41, 43 of circumferentially andequidistantly arranged orifices, wherein at least one orifice 23 of the firstarray 41 has a first diameter and at least one orifice 23 of the second array43 has a second diameter, different than the first diameter. ln anotherembodiment (not shown), the first array has fewer orifices than the secondarray. ln yet another embodiment (shown in Fig. 3b) a third array 45 ofcircumferentially extending orifices is provided and the distance between thefirst 41 and the second 43 arrays is different than the distance between thesecond 43 and the third 45 arrays.

Fig. 4 visualizes a first flow characteristic associated with the orificeprovided in a water carrying pipe and a second flow characteristicassociated with the steam channel. ln the shown embodiment, flowcharacteristic is represented by means of a fluid flow, or mass flow, as afunction of a stroke length, said stroke length, as explained above inconnection with Fig. 1, being associated with the valve plug. As seen in Fig.4, any one of the first and the second flow characteristics comprises at leasta first straight line having a first gradient and a second straight line having asecond, larger gradient. Further, for both the first flow characteristic and thesecond flow characteristic the kink, i.e. the transition between the first straight line and the second straight line, occurs for substantially the samestroke length. ln Fig. 4, the orifice distribution pattern of the water carryingpipe has been suitably configured, such that the kink of the respective curveoccurs for the same stroke length. For a more detailed discussion of herebyconferred advantages and benefits a reference is made to the suitable section of the description related to Figs. 2a-2c. ln the drawings and specification, there have been disclosed typicalpreferred embodiments of the invention and, although specific terms areemployed, they are used in a generic and descriptive sense only and not forpurposes of limitation, the scope of the invention being set forth in the following claims

Claims (8)

1. A steam Conditioning valve (10) for simultaneously reducing pressure and temperature of steam, wherein the valve (10) comprises - a first in|et port (12) for the introduction of cooling water into aninterior of the valve, - a second in|et port (14) for the introduction of high-pressure,superheated steam into the interior of the valve, - an outlet port (16) for evacuating the fluid created by the mixing of the cooling water and the steam in a mixing chamber (17), an annular valve seat (18) arranged in the valve interior, a valve stem (20) for connecting to an actuator, a valve plug (22) resting against the valve seat (18) when the valve(10) is in closed position, two axially extending pipes, a water carrying pipe (24) and a steamcarrying pipe (26), wherein the water carrying pipe (24) at least inpart is enclosed by the steam carrying pipe (26), wherein - the valve stem (20), the valve plug (22) and the two axially extendingpipes (24, 26) are immobilized with respect to one another so thatthey make up an axially reciprocable unit, wherein - the water carrying pipe (24) is, at a first end, provided with atleast one orifice (23) for receiving cooling water from the firstin|et port (12), wherein said orifice (23) is associated with a firstflow characteristic, - the water carrying pipe (24) further is, at a second end,provided with at least one water outlet (25) for injectingreceived water into the mixing chamber (17), - at least one steam channel (21) is arranged in the valve plug(22), wherein said steam channel (21) is associated with a second flow characteristic, wherein the steam channel (21) transports the steam from the second inlet port (14) to thesteam carrying pipe (26) for subsequent steam injection intothe mixing chamber (17) via a steam outlet (27) of the steamcarrying pipe (26), and - the first flow characteristic and the second flow characteristic have the same general shape.

2. A steam conditioning valve (10) according to claim 1, wherein anyone of the first and the second flow characteristics is represented by means of a fluid flow as a function of a stroke length associated with the valve pug(22).

3. A steam conditioning valve (10) according to claim 2, wherein anyone of the first and the second flow characteristics comprises at least a first,substantially straight line having a first gradient and a second, substantially straight line having a second, larger gradient.

4. A steam conditioning valve (10) according to claim 3, wherein akink associated with the first flow characteristic and a kink associated with a second flow characteristic occur for the same stroke length.

5. A steam conditioning valve (10) according to any of the precedingclaims, wherein the at least one water outlet (25) of the water carrying pipe(24) is arranged in vicinity of the steam outlet (27).

6. A steam conditioning valve (10) according to any of the precedingclaims, wherein the at least one orifice (23) comprises at least two arrays(41, 43) of circumferentially and equidistantly arranged orifices (23), whereinat least one orifice (23) of the first array (41) has a first diameter and at leastone orifice (23) of the second array (43) has a second diameter, differentthan the first diameter.

7. A steam conditioning valve (10) according to any one of the claims 1-5, wherein the at least one orifice (23) comprises at least two arrays (41, ll 43) of circumferentiaiiy arranged orifices, wherein the first array (41) has fewer orifices (23) than the second array (43).

8. A steam Conditioning valve (10) according to ciaim 7, wherein athird array (45) of circumferentiaiiy extending orifices is provided and thedistance between the first (41) and the second (43) arrays is different thanthe distance between the second (43) and the third (45) arrays.