Patent Application
20140091485
Not Applicable
Not Applicable
1. Field of the Invention
The present invention pertains generally to steam desuperheaters or attemperators and, more particularly, to a uniquely configured spray nozzle assembly for a steam desuperheating or attemperator device. The nozzle assembly is specifically adapted to, among other things, prevent thermal shock to prescribed internal structural components thereof, to prevent “sticking” of a valve stem thereof, and to create a substantially uniformly distributed spray of cooling water for spraying into a flow of superheated steam in order to reduce the temperature of the steam.
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. Along these lines, the precise control of final steam temperature is often critical for the safe and efficient operation of steam generation cycles.
A steam desuperheater or attemperator can lower the temperature of superheated steam by spraying cooling water into a flow of superheated steam that is passing through a steam pipe. By way of example, attemperators are often utilized in heat recovery steam generators between the primary and secondary superheaters on the high pressure and the reheat lines. In some designs, attemperators are also added after the final stage of superheating. 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.
A popular, currently known attemperator design is a probe style attemperator which includes one or more nozzles or nozzle assemblies positioned so as to spray cooling water into the steam flow in a direction generally along the axis of the steam pipe. In many applications, the steam pipe is outfitted with an internal thermal liner which is positioned downstream of the spray nozzle attemperator. The liner is intended to protect the high temperature steam pipe from the thermal shock that would result from any impinging water droplets striking the hot inner surface of the steam pipe itself.
One of the most commonly encountered problems in those systems integrating an attemperator is the addition of unwanted water to the steam line or pipe as a result of the improper operation of the attemperator, or the inability of the nozzle assembly of the attemperator to remain leak tight. The failure of the attemperator to control the water flow injected into the steam pipe often results in damaged hardware and piping from thermal shock, and in severe cases has been known to erode piping elbows and other system components downstream of the attemperator. Along these lines, water buildup can further cause erosion, thermal stresses, and/or stress corrosion cracking in the liner of the steam pipe that may lead to its structural failure.
In addition, the service requirements in many applications are extremely demanding on the attemperator itself, and often result in its failure. More particularly, in many applications, various structural features of the attemperator, including the nozzle assembly thereof, will remain at elevated steam temperatures for extended periods without spray water flowing through it, and thus will be subjected to thermal shock when quenched by the relatively cool spray water. Along these lines, typical failures include spring breakage in the nozzle assembly, and the sticking of the valve stem thereof. Further, in probe style attemperators wherein the spray nozzle(s) reside in the steam flow, such cycling often results in fatigue and thermal cracks in critical components such as the nozzle holder and the nozzle itself. Thermal cycling, as well as the high velocity head of the steam passing the attemperator, can also potentially lead to the loosening of the nozzle assembly which may result in an undesirable change in the orientation of its spray angle.
With regard to the functionality of any nozzle assembly of an attemperator, 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 typically pass through the superheated steam flow and impact the interior wall or liner of the steam pipe, resulting in water buildup which is undesirable for the reasons set forth above. 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. Further, 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 Applicant's U.S. Pat. No. 6,746,001 (entitled Desuperheater Nozzle), U.S. Pat. No. 7,028,994 (entitled Pressure Blast Pre-Filming Spray Nozzle), U.S. Pat. No. 7,654,509 (entitled Desuperheater Nozzle), and U.S. Pat. No. 7,850,149 (entitled Pressure Blast Pre-Filming Spray Nozzle), the disclosures of which are incorporated herein by reference. The present invention represents an improvement over these and other prior art solutions, and provides a nozzle assembly for spraying cooling water into a flow of superheated steam that is of simple construction with relatively few components, requires a minimal amount of maintenance, and is specifically adapted to, among other things, prevent thermal shock to prescribed internal structural components thereof, to prevent “sticking” of a valve stem thereof, and to create a substantially uniformly distributed spray of cooling water for spraying into a flow of superheated steam in order to reduce the temperature of the 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 spray nozzle assembly for an attemperator which is operative to spray cooling water into a flow of superheated steam in a generally uniformly distributed spray pattern. The nozzle assembly comprises 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 movable between a closed position and an open (flow) position. The nozzle housing defines a generally annular flow passage. The flow passage itself comprises three identically configured, arcuate flow passage sections, each of which spans an interval of approximately 120°. One end of each of the flow passage sections extends to a first (top) end of the nozzle housing. The opposite end of each of the flow passage sections fluidly communicates with a fluid chamber which is also defined by the nozzle housing and extends to a second (bottom) end of the nozzle housing which is disposed in opposed relation to the first end thereof. A portion of the second end of the nozzle housing which circumvents the fluid chamber defines a seating surface of the nozzle assembly. The nozzle housing further defines a central bore which extends axially from the first end thereof, and is circumvented by the annular flow passage collectively defined by the separate flow passage sections, i.e., the central bore is concentrically positioned within the flow passage sections. That end of the central bore opposite the end extending to the first end of the nozzle housing terminates at the fluid chamber.
The valve element comprises a valve body or nozzle cone, and an elongate valve stem which is integrally connected to the nozzle cone and extends axially therefrom. The nozzle cone has a tapered outer surface, with the junction between the nozzle cone and the valve stem being defined by a continuous, annular groove or channel formed within the valve element. The valve stem is advanced through the central bore of the nozzle housing. Disposed within the central bore of the nozzle housing is a biasing spring which circumvents a portion of the valve stem, and normally biases the valve element to its closed position.
In the nozzle assembly, cooling water is introduced into each of the flow passage sections at the first end of the nozzle housing, and thereafter flows therethrough into the fluid chamber. When the valve element is in its closed position, a portion of the outer surface of the nozzle cone thereof is seated against the seating surface defined by the nozzle housing, thereby blocking the flow of fluid out of the fluid chamber and hence the nozzle assembly. An increase of the pressure of the fluid beyond a prescribed threshold effectively overcomes the biasing force exerted by the biasing spring, thus facilitating the actuation of the valve element from its closed position to its open position. When the valve element is in its open position, the nozzle cone thereof and the that portion of the nozzle housing defining the seating surface collectively define an annular outflow opening between the fluid chamber and the exterior of the nozzle assembly. The shape of the outflow opening, coupled with the shape of the nozzle cone of the valve element, effectively imparts a conical spray pattern of small droplet size to the fluid flowing from the nozzle assembly. Importantly, fluid flow through the nozzle assembly normally bypasses the central bore, and thus does not directly impinge the biasing spring therein. In one embodiment of the present invention, prescribed portions of the valve stem of the valve element may include grooves formed therein in a prescribed pattern, such grooves being sized, configured and arranged to prevent debris accumulation in the central bore which could otherwise result in the sticking of the valve element during the reciprocal movement thereof between its closed and open positions.
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:
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 a preferred embodiment of the present invention only, and not for purposes of limiting the same,
The nozzle assembly 10 of the present invention comprises a nozzle housing 12 which is shown with particularity in
As is most easily seen in
As further seen in
The nozzle assembly 10 further comprises a valve element 36 which is moveably interfaced to the nozzle housing 12, and is reciprocally moveable in an axial direction relative thereto between a closed position and an open or flow position. The valve element 36 comprises a valve body or nozzle cone 38, and an elongate valve stem 40 which is integrally connected to the nozzle cone 38 and extends axially therefrom. The nozzle cone 38 defines a tapered outer surface 42, with the junction between the nozzle cone 38 and the valve stem 40 being defined by a continuous, annular groove or channel 44 formed in the valve element 36. As is best seen in
In the nozzle assembly 10, the valve stem 40 of the valve element 36 is advanced through the central bore 30 such that the nozzle cone 38 predominately resides within the fluid chamber 20. The nozzle assembly 10 further comprises a helical biasing spring 50 which is disposed within the central bore 30 and circumvents a portion of the valve stem 40 extending therethrough. More particularly, as seen in
The nozzle assembly 10 further comprises a nozzle guide nut 52 which is cooperatively engaged to the valve stem 40 of the valve element 36. When viewed from the perspective shown in
The nozzle guide nut 52 further includes a bore which extends axially therethrough, and is sized to accommodate the advancement of a portion of the valve stem 40 through the nozzle guide nut 52. More particularly, as seen in
In the nozzle assembly 10, the nozzle guide nut 52 is maintained in cooperative engagement to the valve stem 40 through the use of a locking nut 62 and a complimentary pair of lock washers 64. As seen in
As indicated above, the valve element 36 of the nozzle assembly 10 is selectively moveable between a closed position (shown in
When the valve element 36 is in its closed position, a portion of the outer surface 42 of the nozzle cone 38 is firmly seated against the complimentary seating surface 22 defined by the nozzle housing 12, and in particular the outer wall 24 thereof. At the same time, a substantial portion of the bottom flange portion 48 of the valve stem 40 resides within the bottom section of the central bore 30, as does approximately half of the width of the channel 44 between the valve stem 40 and nozzle cone 38. Still further, while the bottom portion 56 of the nozzle guide nut 52 resides within the top section of the central bore 30, the channel 58 between the top and bottom sections 54, 56 of the nozzle guide nut 52 does not reside within the central bore 30, and thus is located exteriorly of the nozzle housing 12. As previously explained, the biasing spring 50 captured within the top section of the central bore 30 and extending between the rim 60 of the nozzle guide nut 52 and the shoulder 32 of the nozzle housing 12 acts against the nozzle guide nut 52 (and hence the valve element 36) in a manner which normally biases the valve element 36 to its closed position.
In the nozzle assembly 10, cooling water is introduced into each of the flow passage sections 18a, 18b, 18c at the top end 14 of the nozzle housing 12, and thereafter flows therethrough into the fluid chamber 20. When the valve element 36 is in its closed position, the seating of the outer surface 42 of the nozzle cone 36 against the seating surface 22 blocks the flow of fluid out of the fluid chamber 20 and hence the nozzle assembly 10. An increase of the pressure of the fluid beyond a prescribed threshold effectively overcomes the biasing force exerted by the biasing spring 50, thus facilitating the actuation of the valve element 36 from its closed position to its open position. More particularly, when viewed from the perspective shown in
When the valve element 36 is in its open position, the nozzle cone 38 thereof and that portion of the nozzle housing 12 defining the seating surface 22 collectively define an annular outflow opening between the fluid chamber 20 and the exterior of the nozzle assembly 12. The shape of such outflow opening, coupled with the shape of the nozzle cone 38, effectively imparts a conical spray pattern of small droplet size to the fluid flowing from the nozzle assembly 12. When the valve element 36 is in its open position, the bottom flange portion 48 of the valve stem 40 still resides within the bottom section of the central bore 30, though the channel 44 resides predominantly within the fluid chamber 20. Further, both the bottom portion 56 and channel 58 of the nozzle guide nut 52 reside within the top section of the central bore 30. As will be recognized, a reduction in the fluid pressure flowing through the nozzle assembly 10 below a threshold which is needed to overcome the biasing force exerted by the biasing spring 50 effectively facilitates the resilient return of the valve element 36 from its open position shown in
Importantly, fluid flow through the nozzle assembly 10, and in particular the flow passage sections 18a, 18b, 18c and fluid chamber 20 thereof, normally bypasses the central bore 30. As previously explained, the top section of the central bore 30 is effectively cut off from fluid flow by the advancement of the bottom portion 56 of the nozzle guide nut 52 into the top section of the central bore 30 proximate the rim 66 of the inner wall 26 irrespective of whether the valve element 36 is in its closed or open positions, and the positioning of the bottom flange portion 48 of the valve stem 40 within the bottom section of the central bore 30 irrespective of whether the valve element 36 is in its open or closed positions. As a result, fluid flowing through the nozzle assembly 10 does not directly impinge the biasing spring 50 residing within the top section of the central bore 30. Thus, even when the nozzle assembly 10 heats up to full steam temperature when no water is flowing and is shocked when impinged with cold water, the level of thermal shocking of the biasing spring 50 will be significantly reduced, thereby lengthening the life thereof and minimizing occurrences of spring breakage. Further, as is most apparent from
In addition, in the nozzle assembly 10, the travel of the valve element 36 from its closed position to its open position is limited mechanically by the abutment of the shoulder 68 of the nozzle guide nut 52 against the rim 66 of the inner wall 26 of the nozzle housing 12 in the above-described manner. This mechanical limiting of the travel of the valve element 36 eliminates the risk of compressing the biasing spring 50 solid, and further allows for the implementation of precise limitations to the maximum stress level exerted on the biasing spring 50, thereby allowing for more accurate calculations of the life cycle thereof. Still further, the aforementioned mechanical limiting of the travel of the valve element 36 substantially increases the pressure limit of the nozzle assembly 10 since it is not limited by the compression of the biasing spring 50. This also provides the potential to fabricate the nozzle assembly 10 in a smaller size to function at higher pressure drops, and to further provide better primary atomization with higher pressure drops. The mechanical limiting of the travel of the valve element 36 also allows for the tailoring of the flow characteristics of the nozzle assembly 10, with the cracking pressure being controlled through the selection of the biasing spring 50.
Referring now to
Similarly, the bottom portion 56 of the nozzle guide nut 52 may include a series of debris grooves 72 within the peripheral outer surface thereof, preferably in prescribed, equidistantly spaced intervals. The debris grooves 72 circumvent the entire periphery of the bottom portion 56, and each extend in spaced, generally parallel relation to the axis of the bore of the nozzle guide nut 52, and hence the axis of the valve stem 40 of the valve element 32.
When the valve element 32 is in either its closed position (as shown in
Referring now to
When used in conjunction with the nozzle assembly 10, the tab washer 76, in its originally unbent state, is advanced over a portion of the nozzle housing 12 and rested upon an annular shoulder 80 which is defined thereby and extends in generally perpendicular relation to the above-described flats 34. Thereafter, upon the advancement of the nozzle assembly 10 into the nozzle holder 74, the enlarged tabs 78 of the tab washer 76 are bent in the manner 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.
