Patent Application
20090278266
Not Applicable
Not Applicable
1. Field of the Invention
The present invention pertains generally to steam desuperheaters and, more particularly, to a uniquely configured valve element for use in a spray nozzle assembly for a steam desuperheating device. The nozzle assembly is specifically adapted for creating a substantially uniformly distributed spray of cooling water for spraying into a flow of superheated steam in order to reduce the temperature thereof.
2. Description of the Related Art
Many industrial facilities operate with superheated steam that has a higher temperature than its saturation temperature at a given pressure. Because superheated steam can damage turbines or other downstream components, it is necessary to control the temperature of the steam. Desuperheating refers to the process of reducing the temperature of the superheated steam to a lower temperature, permitting operation of the system as intended, ensuring system protection, and correcting for unintentional deviations from a prescribed operating temperature set point.
A steam desuperheater can lower the temperature of superheated steam by spraying cooling water into a flow of superheated steam that is passing through a steam pipe. Once the cooling water is sprayed into the flow of superheated steam, the cooling water mixes with the superheated steam and evaporates, drawing thermal energy from the steam and lowering its temperature. If the cooling water is sprayed into the superheated steam pipe as very fine water droplets or mist, then the mixing of the cooling water with the superheated steam is more uniform through the steam flow.
On the other hand, if the cooling water is sprayed into the superheated steam pipe in a streaming pattern, then the evaporation of the cooling water is greatly diminished. In addition, a streaming spray of cooling water will pass through the superheated steam flow and impact the opposite side of the steam pipe, resulting in water buildup. This water buildup can cause erosion and thermal stresses in the steam pipe that may lead to structural failure. However, if the surface area of the cooling water spray that is exposed to the superheated steam is large, which is an intended consequence of very fine droplet size, the effectiveness of the evaporation is greatly increased.
In addition, the mixing of the cooling water with the superheated steam can be enhanced by spraying the cooling water into the steam pipe in a uniform geometrical flow pattern such that the effects of the cooling water are uniformly distributed throughout the steam flow. Conversely, a non-uniform spray pattern of cooling water will result in an uneven and poorly controlled temperature reduction throughout the flow of the superheated steam. Along these lines, the inability of the cooling water spray to efficiently evaporate in the superheated steam flow may also result in an accumulation of cooling water within the steam pipe. The accumulation of this cooling water will eventually evaporate in a non-uniform heat exchange between the water and the superheated steam, resulting in a poorly controlled temperature reduction.
Various desuperheater devices have been developed in the prior art in an attempt to address the aforementioned needs. Such prior art devices include those which are disclosed in U.S. Pat. Nos. 6,746,001 (entitled Desuperheater Nozzle) and 7,028,994 (entitled Pressure Blast Pre-Filming Spray Nozzle), and U.S. Patent Publication No. 2006/0125126 (entitled Pressure Blast Pre-Filming Spray Nozzle), the disclosures of which are incorporated herein by reference. The present inventions represent an improvement over these and other prior art solutions, and provides a desuperheater device for spraying cooling water into a flow of superheated steam that is of simple construction with relatively few components and that requires a minimal amount of maintenance, is capable of spraying cooling water in a fine mist with very small droplets for more effective evaporation within the flow of superheated steam, and is capable of spraying cooling water in a geometrically uniform flow pattern for more even mixing throughout the flow of superheated steam. Various novel features of the present invention will be discussed in more detail below.
In accordance with the present invention, there is provided an improved valve element for a spray nozzle assembly of a steam desuperheating device that is configured to spray cooling water into a flow of superheated steam in a generally uniformly distributed spray pattern.
The nozzle assembly is comprised of a nozzle housing and a valve element which is movably interfaced to the nozzle housing. The valve element, also commonly referred to as a valve pintle or a valve plug, extends through the nozzle housing and is axially slidable between a closed position and an open (flow) position. The nozzle housing has a housing inlet and a housing outlet. The housing inlet is located at an upper portion of the nozzle housing. The housing outlet is located at a lower portion of the nozzle housing. The upper portion of the nozzle housing defines a housing chamber for receiving cooling water from the housing inlet. The lower portion of the nozzle housing defines a pre-valve gallery that is separated from the housing chamber by an intermediate portion of the nozzle housing. A valve stem bore is axially formed through the intermediate portion.
A plurality of housing passages are formed in the intermediate portion to fluidly interconnect the housing chamber (i.e. the housing inlet) with the pre-valve gallery (i.e. the housing outlet) such that cooling water may enter the housing inlet, flow into the housing chamber, through the housing passages, and into the pre-valve gallery before exiting the housing assembly at the housing outlet when the valve element is displaced or actuated to the open position.
The valve element comprises a valve body and an elongate valve stem that is integrally attached to the valve body and extends axially therefrom. The valve stem extends axially from the valve body and is advanced through the valve stem bore of the nozzle housing and is sized and configured to provide an axially sliding fit within the valve stem bore such that the valve element may be reciprocated between the open and closed positions. The lower portion of the nozzle housing includes a valve seat formed thereabout for sealing engagement with the valve body. The valve seat is preferably configured to be complementary to the valve body.
In one embodiment of the present invention, the valve body itself comprises a nozzle cone which is integrally connected to the valve stem, and defines an outer surface which is specifically shaped to have a curved, elliptical profile. Integrally formed on a bottom surface of the nozzle cone is a generally quadrangular hub having four ribs protruding from respective ones of four corner regions defined thereby. Integrally connected to each of the ribs is a generally circular fracture ring. The outer ends of the ribs are continuous with both the outer surface of the nozzle cone and the outer surface of the fracture ring, with the outer surfaces of the nozzle cone, the ribs and the fracture ring collectively defining a tapered profile for the valve body.
In the valve body, the fracture ring is disposed in spaced relation to the lower edge of the nozzle cone which circumvents the bottom surface thereof. In this regard, a series of windows are formed in the valve body, with each window being framed by a segment of the lower edge of the nozzle cone, an adjacent pair of the ribs, and a segment of the top edge of the fracture ring. The edges of the windows are sharp to cut the sheet flow leaving the outer surface of the nozzle cone, with the sharp edges being important to reducing droplet sizes from the valve element and hence the nozzle assembly.
The fracture ring of the valve body has a delta wedge cross-sectional configuration, with the apex of such wedge preferably intersecting the tangent line from the lower edge of the nozzle cone. Similarly, each of the ribs preferably has a delta wedge cross-sectional configuration, with the apex of the ribs continuing inwardly toward the axis of the valve element until the ribs are ultimately connected to the hub formed on the bottom surface of the nozzle cone. The integral connection of the ribs to the hub and thus the nozzle cone significantly improves the mechanical strength of the ribs and the fracture ring integrally connected to the ribs. The internal surfaces of the valve body defined by the ribs, fracture ring, hub and nozzle cone have no square corners or intersections, the elimination of which prevents the formation of streaks in the sheet flow leaving the valve element. Those of ordinary skill in the art will appreciate that the generation of such streaks in turn creates undesirable large droplets at lower nozzle flow rates.
In accordance with another embodiment of the valve element of the present invention, the outer end surface of each of the ribs may be stepped relative to the lower edge of the nozzle cone. This is in contrast to the aforementioned embodiment which is an in-line profile wherein the outer surface of the fracture ring, the outer surfaces of the ribs, and the outer surface of the nozzle cone are substantially flush or continuous with each other as indicated above. With the stepped profile, the outer surfaces of the fracture ring and ribs, while being substantially flush or continuous with each other, are at a slightly acute angle relative to the outer surface of the nozzle cone, and thus intersect the nozzle cone at a step beneath the same. The purpose of the stepped profile is to generate a detached sheet flow at lower flow rates. The sheet flow is split at the fracture ring, with the differential angle diverting a portion of the flow outward radially, thus increasing the cone area of the spray. In contrast, with the in-line profile, the tangent or continuous outer surfaces of the fracture ring, ribs and nozzle cone minimize disruption to the sheet flow, especially at low nozzle flow rates.
In accordance with yet another embodiment of the valve element of the present invention, the fracture ring is separated from the nozzle cone by a continuous gap or channel. In this particular embodiment, the ribs are integrally connected to a generally circular hub portion which is integrally connected to the bottom surface of the nozzle cone.
Despite the somewhat complex geometries of the valve elements constructed in accordance with the present invention, such valve elements can be manufactured quite simply. The internal tapered profiles and curved elliptical paths of the profiles are generated by machining the valve body with a simple tapered profile tool on a CNC machine. This represents a significant improvement over prior art valve element designs which are often too difficult to manufacture without compromising performance and strength.
In each embodiment of the valve element of the present invention, a portion of the outer surface of the nozzle cone is configured to be complimentary to the valve seat of the nozzle assembly such that the engagement of the outer surface of the nozzle cone to valve seat defined by the lower portion of the nozzle housing effectively blocks the flow of cooling water out of the nozzle assembly when the valve element is in the closed position. Conversely, when the valve element is axially moved from the closed position to the open position, cooling water is able to flow downwardly through an annular gap collectively defined by the outer surface of the nozzle cone and the valve seat. The combination of the conical valve seat and conical outer surface is effective to induce a conical spray pattern for the cooling water that is exiting the annular gap when the valve element is in the open position. As the film of cooling water flows downwardly over the outer surface of the nozzle cone of the valve body, a portion of the cooling water sheet impinges the fracture ring, with all of the cooling water eventually entering into the flow of super heated steam passing through the steam pipe.
As a result of the structural and functional attributes of the valve elements constructed in accordance with each embodiment of the present invention, cooling water droplet size is kept to a minimum, thus improving the absorption and evaporation efficiency of the cooling water within the flow of superheated steam, in addition to improving the spatial distribution of the cooling water. In this regard, the structural and functional attributes of the valve elements constructed in accordance with the present invention are operative to induce a conical spray pattern for the coolant water that is generated from the spray nozzle assembly when the valve element is in the open position, with the passage of a portion of the cooling water sheet over the fracture ring providing the desirable lower droplet size attributes describes above.
The present invention is best understood by reference to the following detailed description when read in conjunction with the accompanying drawings.
These, as well as other features of the present invention, will become more apparent upon reference to the drawings wherein:
a is a longitudinal cross-sectional view of the nozzle assembly of
b is a longitudinal cross-sectional view of the nozzle assembly of
Common reference numerals are used throughout the drawings and detailed description to indicate like elements.
Referring now to the drawings wherein the showings are for purposes of illustrating preferred embodiments of the present invention only, and not for purposes of limiting the same,
The cooling water feed line 16 is connected to a cooling water control valve 14. The cooling water control valve 14 may be fluidly connected to a high pressure water supply (not shown). The control valve 14 is operative to control the flow of cooling water into the cooling water feedline 16 in response to a temperature sensor (not shown) mounted in the steam pipe 12 downstream of the nozzle assembly 20. The control valve 14 may vary the flow through the cooling water feedline 16 in order to produce varying water pressure in the nozzle assembly 20.
When the cooling water pressure in the nozzle assembly 20 is greater than the elevated pressure of the superheated steam in the steam pipe 12, the nozzle assembly 20 provides a spray of cooling water into the steam pipe 12. Although
Turning now to
Alternatively, the nozzle housing 22 may be fabricated as two separate components comprising the upper portion 24 and the lower portion 26 as is shown in
Referring still to
As seen in
In addition, the housing passages 36 may be configured as a plurality of generally arcuately-shaped slots extending axially through the intermediate portion 76 in equidistantly spaced relation to each other. The housing passages 36 are spaced about the valve stem bore 42 in order to eliminate the tendency for the cooling water to exit the nozzle assembly 20 in a streaming spray pattern. In this regard, the combination of the housing passages 36 and the geometry of the valve element 78 are configured to cooperate in order to provide a geometrically uniform spray pattern of the cooling water into the steam pipe 12. Regardless of their specific geometric arrangement, size and shape, the housing passages 36 are configured to provide a flow of cooling water from the housing inlet 28 to the housing outlet 30 when the valve element 78 is moved to the open position, as will be described in greater detail below.
Having thus described the structural and functional attributes of the nozzle assembly 20, the specific functional and structural attributes of the valve element 78 thereof will now be discussed with specific reference to
The valve body 80 of the valve element 78 itself comprises a nozzle cone 86 which is integrally connected to the valve stem 82 and defines a conical outer surface 88 which is specifically shaped to have a curved, elliptical profile as it extends along the axis of the valve element 78. In addition to the outer surface 88, the nozzle cone 86 defines a bottom surface 90 circumvented by a generally circular, peripheral lower edge 92. Integrally formed on the bottom surface 90 of the nozzle cone 86 is a generally quadrangular hub 94. Integrally connected to the hub 94 is a plurality of (e.g., four) ribs 96 which protrude from respective ones of the four corner regions defined by the hub 94. As seen in
In the valve element 78, the fracture ring 98 of the valve body 80 is disposed in spaced relation to the peripheral lower edge 92 of the nozzle cone 86 which, as indicated above, circumvents the bottom surface 90 thereof. The fracture ring 98 also preferably has a delta wedge cross-sectional configuration as shown in
As indicated above, in the valve body 80, the fracture ring 98 is disposed in spaced relation to the lower edge 92 of the nozzle cone 86. As a result, a plurality of (e.g., four) windows 100 are formed in the valve body 80, with each window 100 being framed by a segment of the lower edge 92 of the nozzle cone 86, an adjacent pair of the ribs 96, and a segment of the top edge 102 of the fracture ring 98. The edges of the windows 100, and in particular the top edge 102 of the fracture ring 98, are sharp to cut the sheet flow leaving the outer surface 88 of the nozzle cone 86, with the sharp edges being important to reducing droplet sizes from the valve element 78 and hence the nozzle assembly 20.
In the valve element 78, the integral connection of the ribs 96 to the hub 94 and the nozzle cone 86 significantly improves the mechanical strength of the ribs 96 and the fracture ring 98 integrally connected to the ribs 96. Additionally, the internal surfaces of the valve body 80 defined by the ribs 96, fracture ring 98, hub 94 and nozzle cone 86 are each preferably formed such that cooling water flowing over the valve element 78 is not exposed to any square corners or intersections, the elimination of which prevents the formation of streaks in the sheet flow leaving the valve element 78. In this regard, as seen in
As indicated above, the valve stem 82 is slidably advanced through the valve stem bore 42 and operatively coupled to the nozzle housing 22 so as to allow the valve element 78 to be reciprocally moveable between its open and closed positions. In the nozzle assembly 20, the lower portion 26 of the nozzle housing 22 at the housing outlet 30 defines an annular valve seat 44 which is adapted for sealing engagement with the valve body 80, and in particular a portion of the outer surface 88 of the nozzle cone 86 thereof. The valve seat 44 is typically angled into a generally conical configuration, as is shown in
Preferably, the outer surface 88 of the nozzle cone 86 of the valve body 80 is configured such that its half angle differs from a half angle of the valve seat 44. More specifically, the half angle of the outer surface 88 is preferably configured to be less than or greater than the half angle of the valve seat 44. Additionally, the half angle of the outer surface 88 and the half angle of the valve seat 44 are preferably between about 20 degrees and about 60 degrees. Further, as seen in
When the valve element 78 is actuated to its open position as shown in
Referring back to
Also included in the nozzle assembly 20 is a valve stop 62 mounted on the valve stem 82 of the valve element 78. The valve stop 62 may be configured to extend beyond the diameter of the spacer 60 for configurations of the nozzle housing 22 that include a spring bore (not shown) formed therethrough. In such configurations including a spring bore, the valve stop 62 may limit the axial movement of the valve element 78. In
As further shown in
In operation, a flow of superheated steam and elevated pressure passes through the steam pipe 12, to which the nozzle housing 22 is attached, as is shown in
As indicated above, the adjustment of the load nut 64 compresses the valve spring 58 to apply a compressive force to the valve body 80 against the valve seat 44. In this regard, the spring preload serves to initially hold the valve element 78 in the closed position, as shown in
When the pressure of the cooling water against the valve body 80 overcomes the combined pressure of the spring preload and the elevated pressure of the superheated steam, the valve body 80 moves axially away from the valve seat 44, opening the annular gap 56 as shown in
As explained above, as a result of the structural and functional attributes of the valve element 78, cooling water droplet sizes from the of the conical sheet passing over the valve element 78 are minimized, thus improving the absorption and evaporation efficiency of cooling water within the flow of superheated steam, in addition to improving the spatial distribution of the cooling water. In this regard, the cooling water enters the steam pipe 12 in a cone-shape pattern of a generally uniform fine mist spray pattern consisting of very small water droplets. The uniform mist spray pattern ensures a thorough and uniform mixing of the cooling water with the superheated steam flow. The uniform spray pattern also maximizes the surface area of the cooling water spray and thus enhances the evaporation rate of cooling water.
Referring now to
The sole distinction between the valve elements 78, 78a lies in the outer end surface of each of the ribs 96a in the valve element 78a being stepped relative to the lower edge 92a of he nozzle cone 86a thereof. This is in contrast to the valve element 78 which is an in-line profile wherein the outer surface of the fracture ring 98, the outer end surfaces of the ribs 96, and the outer surface 88 of the nozzle cone 86 are substantially flush or continuous with each other as indicated above. With the stepped profile, the outer surfaces of the fracture ring 98a and ribs 96a, while being substantially flush or continuous with each other, are at a slightly acute angle relative to the outer surface 88a of the nozzle cone 88 and thus intersect the nozzle cone 86a at a step 99a beneath the same as best shown in
Referring now to
The valve body 108 of the valve element 106 itself comprises a nozzle cone 114 which is integrally connected to the valve stem 110 and defines an outer surface 116 which is specifically shaped to have a curved, elliptical profile as it extends along the axis of the valve element 106. In addition to the outer surface 116, the nozzle cone 114 defines a bottom surface 118 circumvented by a generally circular, peripheral lower edge 120. Integrally formed on the bottom surface 118 of the nozzle cone 114 is a circular, generally cylindrical hub 122. Integrally connected to the hub 122 is a plurality of (e.g., four) ribs 124. The ribs 124 protrude radially outward from the hub 122 at equidistantly spaced intervals of approximately 90°. Integrally connected to the distal end of each of the ribs 124 is a generally circular or annular fracture ring 126.
In the valve element 106, the fracture ring 126 of the valve body 108 is disposed in spaced relation to the peripheral lower edge 120 of the nozzle cone 114 which, as indicated above, circumvents the bottom surface 118 thereof. The fracture ring 126 also preferably has a delta wedge cross-sectional configuration as shown in
In the valve body 108 of the valve element 106, the fracture ring 126 is disposed in spaced relation to the nozzle cone 114, and in particular the lower edge 120 thereof. As a result, a continuous channel or gap 132 is defined between the nozzle cone 114 and the fracture ring 126, and more particularly between the lower edge 120 of the nozzle cone 114 and the top edge 128 of the fracture ring 126. The top edge 128 of the fracture ring 126 is sharp to cut the sheet flow leaving the outer surface 116 of the nozzle cone 114, with such sharp edge being important to reducing droplet sizes from the valve element 106 if integrated into the nozzle assembly 20.
In the valve element 106, the integral connection of the ribs 124 to the hub 122 significantly improves the mechanical strength of the ribs 124 and the fracture ring 126 integrally connected to the ribs 124. Additionally, the internal surfaces of the valve body 108 defined by the ribs 124, fracture ring 126, hub 122 and nozzle cone 114 are each preferably formed such that cooling water flowing over the valve element 106 is not exposed to any square corners or intersections, the elimination of which assists in preventing the formation of streaks in the sheet flow leaving the valve element 106.
The operative attachment of the valve element 106 to the remainder of the nozzle assembly 20 occurs in the same manner described above in relation to the interface of the valve element 78 into the remainder of the nozzle assembly 20. The outer surface 116 of the nozzle cone 114 is further configured such that its half angle differs from the half angle of the valve seat 44 as needed to facilitate the prescribed sealed engagement between the valve element 106 and the nozzle housing 22 when the valve element 106 is in the closed position. If the valve element 106 is substituted for the valve element 78 and actuated to the open position similar to that shown in
This disclosure provides exemplary embodiments of the present invention. The scope of the present invention is not limited by these exemplary embodiments. Numerous variations, whether explicitly provided for by the specification or implied by the specification, such as variations in structure, dimension, type of material and manufacturing process may be implemented by one of skill in the art in view of this disclosure.
