EP1918532B1

EP1918532B1 - Desuperheater apparatus for steam lines

Info

Publication number: EP1918532B1
Application number: EP06425745.4A
Authority: EP
Inventors: Salvatore Ruggeri
Original assignee: Valvitalia SpA
Current assignee: Valvitalia SpA
Priority date: 2006-10-30
Filing date: 2006-10-30
Publication date: 2016-04-20
Anticipated expiration: 2026-10-30
Also published as: ES2574011T3; EP1918532A1

Description

The present invention relates to a desuperheater apparatus for steam lines according to the preamble of claim 1, particularly to an apparatus for use in a steam bypass line of a steam turbine or cogeneration system.
As is known, steam pressure is reduced in these apparatus through multiple chambers, typically:

a first chamber having an upstream end closed by a throttling section for steam pressure reduction in which steam pressure reduction depends on the position of the closing member of a valve;
a second static steam pressure reducing chamber, generally defined by a perforated basket filter and
a final chamber, which is equipped with water spray nozzles having the purpose of cooling steam.

Referring to the above desuperheater apparatus and to the steam cooling process implemented thereby, efficiency problems arise, due to the difficulty of mixing the water sprayed by nozzles with steam flow. Particularly, the presence of residual water droplets in the steam flow downstream from the desuperheater apparatus is undesired as it can cause erosion in the steam pipeline. Particularly, a higher degree of erosion is found at the extrados of a pipe bend, i.e. where the radius of curvature is larger.
It shall be further noted that, water droplets in steam tend to gather at the intrados of a pipe bend, i.e. where the radius of curvature of the pipe is smaller.
In order to avoid these drawbacks, a long section of straight pipe has to be provided immediately downstream from the desuperheating apparatus, to increase contact time between the two phases before a bend. This adds a constraint to the design of the steam line, which is not always optimally compatible with the remaining requirements of the system.
Document DE 3720918 discloses a known steam reducing valve.
This invention is based on the issue of providing a desuperheater apparatus which has such structural and functional characteristics as to fulfill the need of reducing the undesired presence of residual water droplets in the steam flow at the outlet of the desuperheater apparatus, while obviating the above prior art drawbacks.
This issue is addressed by a desuperheater apparatus according to the features of claim 1.
Further features and advantages of the desuperheater apparatus of this invention, will be apparent upon reading the following description of one preferred embodiment thereof, which is given by way of illustration and without limitation with reference to the accompanying figures, in which:

Figure 1 is a plan diagrammatic view of a steam line section in which a desuperheater apparatus of the invention is located;
Figure 2 is a schematic sectional view of a desuperheater apparatus of the invention and
Figures 3 and 4 are two plan sectional views of a detail of the desuperheater apparatus of Figure 2 as taken from two different points of view.

Referring to the annexed figures, numeral 1 generally designates a desuperheater apparatus of the invention, which is adapted to be integrated in a steam bypass line of a turbine or a cogeneration system.
Particularly, Figure 1 shows the desuperheater apparatus 1 interposed between two sections T of the steam pipeline.
The apparatus 1 comprises a plurality of chambers placed in series and separated by suitable steam pressure reducing sections. These chambers and steam pressure reducing sections define a fluid path for a steam flow within the apparatus 1. As steam flows through the steam pressure reducing sections, it is subjected to pressure reduction.
Particularly referring to the preferred embodiment of Figure 1, the desuperheater apparatus 1 comprises the following three chambers:

a first chamber 2 having a throttling section for steam pressure reduction in which steam pressure reduction depends on the position of a closing member 6 of valve means 5;
an intermediate expansion chamber 3 having an inlet with static means 8 located thereat for providing a steam pressure reduction and
a final chamber 4.

The first chamber 2 has its inlet connected to the steam supply pipe and its outlet connected to the inlet of the next intermediate chamber 3. The throttling steam pressure reducing section of the first chamber 2 comprises valve means 5 with a perforated cage-like valve seat defining a steam pressure reducing section, which receives a slideable closing member 6, whose position relative to the valve seat can be adjusted from the outside. It will be appreciated that, by adjusting the position of the closing member from a completely closed to a completely open position, various valve capacity control values may be obtained, which are caused by changes of the throttling section, and steam flow rates through the desuperheater apparatus 1.
The intermediate chamber 3 is shaped in such a manner as to provide expansion of the steam flowing out of the above mentioned valve means 5. Particularly, this effect is achieved because the intermediate chamber 3 defines an expansion chamber.
It should be noted that the intermediate expansion chamber 3 has its upstream end closed by the above mentioned static means 8 which form a section adapted to reduce the pressure of steam flowing into the intermediate chamber 3.
Preferably, these static steam pressure reducing means 8 include a perforated basket filter, through which steam must flow to enter the intermediate expansion chamber 3. The perforated basket 8 allows to reduce both the velocity of steam at the outlet of the first chamber 2 and the noise generated by the flowing steam.
Once steam has flown through the perforated basket 10, which defines a steam pressure reducing section, it can enter the intermediate expansion chamber 3, where it is expanded before entering the next final chamber 4.
The final chamber 4 comprises a tubular body 10 extending along a predetermined longitudinal axis X-X.
The upstream end of such tubular body 10, with reference to the steam flowing direction along the longitudinal axis X-X, is closed by a steam diffuser 11, which defines a steam reducing section, having a plurality of holes 12 for the passage of steam.
The final chamber 4 has at least two spray nozzles 9, which are associated to the tubular body 10 to generate respective steam cooling spray cones C in such tubular body 10. At each spray nozzle 9, the tubular body 10 has through holes for the ends of such spray nozzles 9 to extend therethrough.
According to an advantageous embodiment, the spray nozzles 9 are placed in the proximity of the steam diffuser 11. It should be noted that the holes 12 of the steam diffuser 11 are located in greater number near each spray nozzle 9, where they define corresponding perforated portions.
Advantageously, these perforated portions of the steam diffuser 11 are inclined to form a predetermined angle A with the above mentioned longitudinal axis X-along which the tubular body 10 of the final chamber 4 extends, so that the perforated portions are substantially parallel to the lateral surface of the spray cones C generated by their corresponding spray nozzles 9.
Preferably, the steam diffuser 11 is tapered and has a frusto-conical shape in the illustrated example, having a diverging taper with respect to the longitudinal axis X-X, as seen in the steam flowing direction within the tubular body 10.
Preferably, the spray cone C generated by each spray nozzle 9 tangentially flows over the corresponding perforated portion of the steam diffuser 11. This effect is simply obtained, with the spray nozzles 9 oriented perpendicular to the longitudinal axis X-X (like in the illustrated embodiment), by the following provisions:

the inclination angle A of the perforated portions to the longitudinal axis X-X shall be substantially one half of the width of the spray cone C generated by the spray nozzles 9 and
the holes 12 shall be substantially perpendicular to the lateral surface of the spray cone C generated by the corresponding spray nozzle, which condition occurs when the holes 12 are perpendicular to the conical surface of the perforated portions.

According to a further preferred aspect, in the proximity of the inner wall of the tubular body 10, the steam diffuser 11 is conformed in such a manner as to define a limited annular portion 13, which is substantially perpendicular to the wall of the tubular body and is joined to the conical portion. It should be noted that, at each spray nozzle 9, such annular portion 13 also has a plurality of holes 12 for the passage of steam.
According to the illustrated preferred embodiment, this annular portion 13 of the steam diffuser 11 is integrally joined to an inner tubular element 14, which is coaxially inserted in such tubular chamber 10 that defines the final chamber 4 to be in contact therewith all along its surface. At each spray nozzle 9, the inner tubular element 14 has respective through holes which are substantially aligned with the holes of the tubular body 10 to allow the passage of the spray nozzles 9.
Referring to the above structure, and particularly regarding the structural and/or operational characteristics of the final chamber, the desuperheater apparatus of the invention fulfills the above mentioned need and also obviates prior art drawbacks as set out in the introduction to this disclosure. That is, the desuperheater apparatus of the invention considerably improves the efficiency of the steam desuperheating process thanks to the provision of the frusto-conical diffuser and to the manner in which the steam flowing therethrough impinges the spray cone C of each spray nozzle 9. Particularly, the desuperheater apparatus of the invention provides the following advantages:

the steam diffuser 11 is closer to the delivery nozzle 9, thence to the point in which the spray cone C is generated, where water droplets are larger;
the steam to water contact area at the outlet of the spray nozzles 9 is reduced and
the steam flow out of the steam diffuser 11 impinges upon the outer surface of the spray cone C generated by the spray nozzles 9 as orthogonally as possible.

Advantageously, in addition to being closer to the outlet of the spray nozzles 9, the steam diffuser a higher density and localization of holes at the spray nozzles 9, so that steam passage is concentrated where it is actually more useful.
As a whole, the desuperheater apparatus of the invention improves the overall steam desuperheating efficiency when compared with prior art apparatus, thereby providing apparent advantages to the steam plant in which such desuperheater apparatus is designed to be used.
The conformation and particular arrangement of the final chamber of the desuperheater apparatus afford a considerable reduction of the noise deriving from water supply to the spray nozzles.
The desuperheater apparatus allows to reduce the length of the section of straight steam pipeline to be provided downstream from the desuperheater apparatus.
A further advantage of the desuperheater apparatus of the invention is its structural simplicity.

Claims

A desuperheater apparatus for steam lines, wherein a plurality of chambers (2, 3, 4) separated by steam flow pressure reducing sections define a steam path for said steam flow, wherein:
- at least one chamber (4) comprises a tubular body (10) extending along a predetermined longitudinal axis (X-X),

- said tubular body (10) has its upstream end, with reference to the steam flowing direction along said path, closed by a steam diffuser (11), having a plurality of holes (12) for the passage of steam,

- said at least one chamber has at least two spray nozzles (9) for generating respective spray cones (C) in said tubular body (10), said spray nozzles (9) being placed in the proximity of said steam diffuser (11), characterized in that

- said spray nozzles (9) are associated to said tubular body (10),

- close to said spray nozzles (9), said steam diffuser (11) has perforated portions, which are inclined with respect to said predetermined longitudinal axis (X-X) in such a manner as to be substantially parallel to the lateral surface of the spray cones (C) generated by their respective spray nozzles.
A desuperheater apparatus as claimed in claim 1, wherein the spray cone (C) generated by each spray nozzle (9) tangentially flows over the corresponding perforated portion of said steam diffuser (11).
A desuperheater apparatus as claimed in claim 1 or 2, wherein said perforated portions of the steam diffuser (11) are inclined with respect to said predetermined longitudinal axis (X-X) to form an angle (A) that is substantially equal to one half of the width of the spray cones (C) generated by said spray nozzles (9), said perforated portions being divergent with respect to the longitudinal axis (X-X) with reference to the steam flowing direction within the tubular element.
A desuperheater apparatus as claimed in any one of claims 1 to 3, wherein the holes (12) of said perforated portions are oriented substantially perpendicular to the lateral surface of the spray cone (C) generated by the corresponding spray nozzle (9).
A desuperheater apparatus as claimed in any one of claims 1 to 4, wherein said steam diffuser (11) has a conical shape, with a diverging taper as seen in the steam flowing direction within the tubular body along the longitudinal axis (X-X).
A desuperheater apparatus as claimed in any one of claims 1 to 4, wherein said steam diffuser (11) has a frusto-conical shape, with a diverging taper as seen in the steam flowing direction within the tubular body along the longitudinal axis (X-X).
A desuperheater apparatus as claimed in claim 5 or 6, wherein in the proximity of the inner wall of said tubular element, said steam diffuser (11) has an annular portion (13), which is substantially perpendicular to the tubular wall and is joined to the conical portion.
A desuperheater apparatus as claimed in claim 7, wherein said annular portion (13) has a plurality of holes (12) for steam passage, at said spray nozzles (9).
A desuperheater apparatus as claimed in claim 8, wherein said annular portion (13) is joined to an inner tubular element (14), which is coaxially inserted in the tubular chamber (10) to be in contact therewith all along its surface, said inner tubular element (14) having a through hole at each of said spray nozzles (9).
A desuperheater apparatus as claimed in any one of claims 1 to 9, wherein said spray nozzles (9) are perpendicular to the longitudinal axis (X-X) of the tubular body (10).
A desuperheater apparatus as claimed in any one of claims 1 to 10, wherein said at least one chamber is preceded by a first chamber (2) which is delimited upstream therefrom by a throttling section for steam pressure reduction in which steam pressure reduction depends on the position of the closing member (6) of valve means (5).
A desuperheater apparatus as claimed in claim 11, wherein a second expansion chamber (3) is interposed between said first chamber (2) and said at least one chamber (4), and has an inlet with static means (8) located thereat for reducing pressure of the steam flowing therethrough.
A desuperheater apparatus as claimed in claim 12, wherein said static steam pressure reducing means (8) of said second chamber (3) include a perforated basket filter.