FIELD OF THE INVENTION

On a general level, the invention concerns a steam conditioning valve for use in a steam-based power plant, said valve being adapted to simultaneously reduce pressure and temperature of the incoming steam. BACKGROUND OF THE INVENTION

Steam conditioning valves that simultaneously control pressure and temperature are well-known in the art. One such valve is disclosed in US4718456.

While these valves perform satisfactorily in many situations, it has been established that for small openings of the valve plug, for instance in start-up situations, an adequate cooling of the process steam is very difficult to achieve.

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

WO94/04255 discloses a steam conditioning valve for reducing pressure and temperature of the incoming steam. WO94/04255 focuses on providing sufficient cooling for small valve openings. The coolant is introduced into the valve via a plurality of circumferentially extending, equisized calibrating holes. Inherently, a flow characteristic associated with said plurality of calibrating holes in circumferential arrangement is strictly linear. On the other hand and as is known in the art, a flow characteristic associated with a standard steam conduit of the steam conditioning valve is non-linear. In the above-described setup, it becomes rather tedious to determine a value of valve opening required in order to optimize the cooling process.

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.

SUMMARY OF THE INVENTION

The above stated objective is achieved by means of a steam conditioning valve which includes the features defined in the independent claim 1. Particular embodiments of the steam conditioning valve are defined in the dependent claims 2 to 7.

Improvements conferred by the invention are based on the insight that process regulation is greatly facilitated if both flows, steam and cooling water, have the same flow characteristic. A further necessary insight is provision of arrays having orifices of different sizes, specifically diameter of the orifices of the outermost, circumferentially extending array needs to be inferior to diameter of the holes of the thereto neighboring, circumferentially extending array. As a result, improved mixing of the cooling water and the steam in the mixing chamber is obtained. Accordingly, the mixing of the steam with the cooling water is better controlled, which results in a faster and more reliable steam cooling process. Further benefits attributable to the invention are reduced consumption of the cooling water and/or steam. The solution is particularly applicable for small valve openings and/or limited fluid flows, e.g. during system start-up.

BRIEF DESCRIPTION OF THE DRAWINGS

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 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 orifice provided 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 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 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 10 according to one embodiment of the present invention. The valve 10 is used in order to simultaneously reduce pressure and temperature of steam. In Fig. 1, a sealing surface of a valve plug 22 abuts an annular valve seat 18 and 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 are typically manufactured in hardened stainless steel. The valve 10 has a first inlet port 12 for the introduction of cooling water into an interior of the valve 10 and a second inlet port 14 for the introduction of high-pressure, superheated steam into the interior of the valve 10. Here, the pressure of the cooling water is about 30 bars and its temperature is around 90 °C whereas the process steam typically has a pressure of around 60 bars and the temperature of approximately 450 °C. It is also shown an outlet port 16 for evacuating the steam created by the mixing of the cooling water and the process 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 for connecting to an actuator (not shown), the previously-mentioned valve plug (its sealing surface resting against the valve seat as the valve is shown in closed position in Fig. 1) and two axially extending pipes, a water carrying pipe 24 and a steam carrying pipe 26. The water carrying pipe 24 is at least in part enclosed by the steam carrying pipe 26. The valve stem 20, the valve plug 22 and the two axially extending pipes 24, 26 are immobilized with respect to one another so that they make up an axially reciprocable unit. This unit is normally made in hardened stainless steel. The movement of the valve stem 20 is controlled by the actuator that may be either hydraulic, pneumatic or electric. Here, stroke length is the distance the valve plug 22 (and the other parts of the axially reciprocable unit) travels in the valve interior between the valve being fully open 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 plug

22. 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 with a plurality of radially extending channels for allowing steam passage into the mixing chamber 17.

In the embodiment shown in Fig. 1 , the water carrying pipe 24 is rather long such that the water outlet 25 of the water carrying pipe 24 is arranged in vicinity of the steam outlet 27. Other alternatives are possible, for instance, the water carrying pipe 24 being significantly shorter. The length of the water carrying pipe 24 is typically determined by the pressure and temperature of the incoming steam/water as well as the specified pressure and the temperature at the valve outlet 16.

Fig. 2a is a cross-sectional view of a section of the steam conditioning valve 10 of Fig. 1. As disclosed in connection with Fig. 1 , a sealing surface of a valve plug 22 rests against a valve seat 18 as the valve 10 is shown in closed position. Accordingly, neither steam nor cooling water may enter the valve trim and the valve is closed.

Fig. 2b is a cross-sectional view of a section of the steam conditioning 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) that is 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, 26 are immobilized with respect to one another so that they make up an axially reciprocable unit. In Fig. 2b, this axially reciprocable unit is moved slightly upwards with respect to Fig. 2a such that a certain amount of the cooling water and the steam may enter the valve trim.

Still with reference to Fig. 2b, the water carrying pipe 24 is, at a first end, provided with provided with at least two arrays 41 , 43 of circumferentially extending orifices, for receiving cooling water from a first inlet port 12. The water carrying pipe 24 is, at a second end, provided with at least one water outlet (shown in Fig. 1) for injecting received water into a mixing chamber. Diameter of the orifices of the outermost, circumferentially extending array 41 is inferior to diameter of the orifices of the thereto neighboring, circumferentially extending array 43. The arrays of orifices 41 , 43 are associated with a first flow characteristic. As also seen in Fig. 2b, at least one steam channel 21 is arranged in the valve plug 22. The steam channel 21 transports the steam from a second inlet port 14 to the steam carrying pipe 26 for subsequent steam injection into the mixing chamber via a steam outlet of the steam carrying pipe (shown in Fig. 1). The steam channel 21 is associated with a second flow characteristic. Accordingly, for small valve openings only fluid flows through the valve are the cooling water passing through the water carrying pipe 24 and the steam flow passing via the steam channel 21 into the steam carrying pipe 26. These fluids are brought in contact in the mixing chamber (shown in Fig. 1).

In this context, improvements conferred by the invention are based on the insight that process regulation is greatly facilitated if both flows, steam and cooling water, have the same flow characteristic. A further necessary insight is provision of arrays having orifices of different sizes, specifically diameter of the orifices of the outermost, circumferentially extending array needs to be inferior to diameter of the holes of the thereto neighboring, circumferentially extending array. As a result, improved mixing of the cooling water and the steam in the mixing chamber is obtained. Accordingly, the mixing of the steam with the cooling water is better controlled, which results in a faster and more reliable steam cooling process. Further benefits attributable to the invention are reduced consumption of the cooling water and/or steam. The solution is particularly applicable for small valve openings and/or limited fluid flows, e.g. during system start-up.

The two flow characteristics will be discussed in greater detail in connection with Fig. 4.

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

Figs. 3a and 3b show different embodiments of a water carrying pipe 24 having different orifice distribution patterns. More specifically, in Fig. 3a there are two arrays 41 , 43 of circumferentially and equidistantly arranged orifices, wherein at least orifices of the first array 41 have a first diameter and orifices of the second array 43 have a second diameter, smaller than the first diameter. In another embodiment (not shown), the first array has fewer orifices than the second array. In yet another embodiment (shown in Fig. 3b) a third array 45 of circumferentially extending orifices is provided and the distance between the first 41 and the second 43 arrays is different than the distance between the second 43 and the third 45 arrays.

Fig. 4 visualizes a first flow characteristic associated with at least two arrays (shown and discussed in connection with Figs. 3a-3b) of circumferentially extending orifices of the water carrying pipe 24 and a second flow characteristic associated with the steam channel. In the shown embodiment, flow characteristic is represented by means of a fluid flow, or mass flow, as a function of a stroke length, said stroke length, as explained above in connection with Fig. 1 , being associated with the valve plug. As seen in Fig. 4, a flow characteristic associated with a standard steam conduit of the steam conditioning valve is non-linear. This knowledge belongs to the state of the art. Thanks to the inventive features of claim 1 , a flow characteristic associated with said arrays of circumferentially extending orifices of the water carrying pipe 24 is also non-linear and resembling the flow characteristic of the standard steam conduit. In consequence and as easily seen in Fig. 4, the kink of the respective curve occurs for substantially the same stroke length. For a more detailed discussion of hereby conferred advantages and benefits a reference is made to the suitable section of the description related to Figs. 2a-2c.

Still with reference to Fig. 4, any one of the first and the second flow characteristics comprises at least a first straight line having a first gradient and a second straight line having a second, larger gradient.

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