SE1930144A1

SE1930144A1 - An attemperator for a steam-based plant and a method for assembly of such an attemperator

Info

Publication number: SE1930144A1
Application number: SE1930144A
Authority: SE
Inventors: Pontus Rååd
Original assignee: Bvt Sweden Ab
Priority date: 2019-05-01
Filing date: 2019-05-01
Publication date: 2020-11-02
Also published as: WO2020222691A1

Abstract

The invention relates to an attemperator (10) for a steam-based plant. The attemperator (10) comprises a pipe section (12) and a tubular liner (14). A first opening (20) is arranged in the pipe section and a second opening (22) is arranged in the liner. At least one water nozzle (24) extends through the openings. A circumferentially extending projection (25) is arranged on the pipe section (12), said projection (25) having a circumferentially extending groove (27). A radially extending projection (26) is arranged on the liner (14). A corresponding recess (28) is arranged in the projection (25) such that, when the liner (14) is being inserted into the pipe section (12), the projection (26) passes through the recess (28) and enters the circumferentially extending groove (27). The invention further relates to a method (50) for assembly of an attemperator for a steam-based plant.

Description

Case P201_SE AN ATTEMPERATOR FOR A STEAM-BASED PLANT AND AMETH D F R A EMBLY F H AN ATTEMPERAT R FIELD OF THE INVENTION On a general level, the invention concerns an attemperator for a steam-based plant and a method for assembly of such an attemperator.

BA K R ND FTHE INVENTI N Attemperators are devices enabling reduction of the steamtemperature. Desired temperature reduction is achieved through acontrolled injection of water into the steam flow. Attemperation is the primarytechnique used for controlling the steam temperature in a boiler or a heatrecovery steam generator (HRSG). When employed in steam-based powerplants, attemperators are typically located upstream of the turbine. Workingmedium of such plants is typically superheated steam, i.e. a high-temperature vapor generated by further heating of the steam obtained byboiling water.

When in operation, the attemperator introduces precise amounts ofwater into the superheated steam flow. Water, intended to cool off thesuperheated steam, is injected into the steam supply pipe at a pipe sectionthat typically is lined. The purpose of the internally provided tubular liner isto protect the pipe section from thermal degradation.

Superheated steam flowing through the pipe work has a temperaturein the range of 600 °C. ln order to withstand these extreme temperatures,suitable materials have been developed. Accordingly, pipes carrying the superheated steam are typically made in highly resistant steel alloys, such as Grade 91 steel. ln addition to steel, Grade 91 steel alloys includechromium and molybdenum. ln a related context, the temperature in the attemperator itselffrequently exceeds 600 °C. As is known in the art, the previously discussedsteel alloys are not sufficiently resistant at temperatures exceeding 600 °C.Accordingly, the liner of the attemperator is normally made in more resistantGrade 22 steel alloy.

Traditionally, the liner in Grade 22 steel is joined to the correspondingpipe section in Grade 91 steel by means of welding. Such welding processis disclosed in WO2018117957A1. As is known in the art, this weldingprocess presents numerous challenges, especially when thick pipes are tobe joined. Moreover, heat generated during the welding process couldstructurally damage either steel alloy and entail reduced mechanical stabilityand/or degraded heat resistance of the attemperator. ln a related context, welding of these advanced materials is subject torigorous standards, for instance subject to a standard developed by ASME(American Society of Mechanical Engineers) - the ASME Boiler andPressure Vessel Code (BPVC). The compliance with welding procedureaccording to BPVC entails a more complex production process and resultsin a reduced production rate.

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 QF THE INVENTIQN The above stated objective is achieved by means of the attemperatorfor a steam-based plant, which includes the features defined in theindependent claim 1. Particular embodiments of the attemperator are defined in the dependent claims 2 to 8.

The invention also concerns a method for assembly of the attemperator, which includes the method steps defined in claim 9.

The present invention obviates the need for welding when installingan attemperator in a steam-driven power plant or a steam generating unit.As discussed above, this entails significant benefits, e.g. faster attemperatorinstallation as well as preserved structural and thermal properties of the used steel alloys. ln the same context, the present solution enables radial expansion/contraction of the tubular liner. This is very desirable since materialdeformation in the attemperator is substantial in consequence of steam temperatures exceeding 600°C and pressures of over 200 bars.

Moreover, the water-spraying nozzles are here provided with dualfunctionality. ln addition to its primary function - to inject water into thesteam flow, they are used to contribute in immobilization of the liner withrespect to the pipe section. ln addition and contrary to the cited prior art, the present designmakes it possible to position fastening means, in particular the radiallyextending projections, in proximity of the water-spraying nozzle. As aconsequence, the axial expansion of the liner is easier to predict and theopenings that accommodate the nozzle may be made relatively small. This improves structural properties of the liner and the pipe section.

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 shows a perspective view of an attemperator according to oneembodiment of the present invention. A portion of a pipe section is removed so that a liner can appear in greater detail.

Fig. 2 is a radial cross-sectional view of the attemperator and its water supply according to one embodiment of the present invention.

Figs. 3 and 4 are longitudinal cross-sectional views of the attemperator shown in Fig. 2.

Fig. 5 shows a flow chart of a method for assembly of an attemperator.

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 of the pipesection/liner. The pipe section and the tubular liner typically have circularshape, i.e. their respective cross-section is a circle. Notwithstanding this,other cross-sectional shapes such as elliptic are conceivable.

Fig. 1 shows a perspective view of an attemperator 10 according toone embodiment of the present invention. The shown attemperator 10 issubstantially assembled. A portion of a pipe section 12 is removed so that aliner 14 can appear in greater detail. An inlet 13, 15 of the pipe section 12and the liner 14 can be seen. The inlet, 13, 15 is used for connection to asteam supply (not shown). The pipe section 12 encloses the liner 14 so thata gap (shown in Fig. 3) is created between an inner surface of the pipe section 12 and an outer surface of the liner 14.

Two first openings 20 are arranged opposite each other in the pipesection 12. Analogously, two second openings 22 are arranged oppositeeach other in the liner 14. Each first opening is coincident with one of thesecond openings.

A nozzle 24 extends through the first 20 and the second 22 openings.When the attemperator 10 is fully assembled, the nozzle 24 is fixediyattached, for instance welded, to the outer surface of the pipe section 12.When the attemperator 10 is in operation, the nozzle 24 injects water into aregion delimited by an inner surface of the liner 14 with the purpose to cooloff the superheat that passes through the liner 14. Typically, there is a plurality of coincident first and second openings that are uniformly circumferentially distributed. ln the shown embodiment, there are two pairsof oppositely positioned openings. When the attemperator 10 is fullyassembled and the liner 14 is immobilized in the axial direction with respectto the pipe section 12, a nozzle 24 extends through each pair of the first andthe second openings. Accordingly, the water-spraying nozzles are providedwith dual functionality. ln addition to its primary function - to inject water intothe steam flow, they are used to contribute in axial immobilization of the linerwith respect to the pipe section.

The attemperator 10 further comprises substantially radiallyextending projections 26 arranged on the outer surface of the liner 14 at theliner inlet 15. Preferably, all corners and edges of the projections 26 arerounded. ln addition, there is a circumferentially extending projection 25arranged on the inner surface of the pipe section 12 close to the pipesection inlet 15. This projection 25 is provided with a circumferentiallyextending groove 27. A recess 28 is arranged in the circumferentiallyextending projection 25 such that, when the liner 14 is being inserted intothe pipe section 12, each projection 26 may pass through the correspondingrecess 28 and enter the circumferentially extending groove 27. Subsequentrotating of the liner 14 relative the pipe section 12 axially affixes the liner 14 with respect to the pipe section 12. The liner 14 is rotated relative the pipe section 12 around an axially extending axis (visualized in Fig. 2; said axispasses through the intersection of A-A-line and B-B-line and continues intothe plane of the paper). The proposed solution obviates the need forwelding when assembling an attemperator. This entails significant benefits,e.g. faster attemperator installation as well as preserved structural andthermal properties of the used steel alloys. Further, the radial expansion/contraction of the tubular liner is not prevented. This is very desirable sincematerial deformation in the attemperator is substantial.

Frequently, the attemperator includes a plurality of projections 26 andcorresponding recesses 28 and the projections and the recesses areuniformly circumferentially distributed. ln the embodiment shown in Fig. 1,there are four projections and four corresponding recesses.

As seen in Fig. 1, the projections 26 and the corresponding recesses28, are positioned in proximity of the water-spraying nozzle 24. As aconsequence, the axial expansion of the liner 14 is easier to predict and thefirst 20 and the second 22 openings that accommodate the nozzle 24 maybe made relatively small. This improves structural properties of the attemperator 10 as a whole, and in particular those of the liner 14.

Fig. 2 is a radial cross-sectional view of the attemperator 10 and itswater supply according to one embodiment of the present invention. Thetwo water supply conduits 29 convey water to the nozzles 24. The nozzles24 project into a region 21 delimited by the inner surface of the liner 14. Asdiscussed in connection with Fig. 1, the purpose of the nozzles 24 is toinject water into the region 21 delimited by the inner surface of the liner 14in order to cool off the superheated steam that is conveyed through the liner14. An axially extending axis of rotation passes through the intersection ofA-A-line and B-B-line and continues perpendicularly into the plane of the paper Typically, the shown attemperator 10 is installed in a heat recovery steamgenerator (HRSG), an energy recovery unit that recovers heat from a hotgas stream. ln addition to protecting the pipe section 12 from thermalstresses, the liner 14 also acts as a flow profiler, increasing the relativesteam velocity near the nozzles 24.

At least one further recess (not shown) is arranged on the innersurface of the liner 14 and positioned downstream with respect to thecircumferentially extending projection 25. This further recess is configured toenable fluid communication between the region 21 delimited by the innersurface of the liner 14 and a gap (shown in Fig. 3). Accordingly, a portion ofthe inflowing steam will exit the tubular liner 14 via the further recess andenter the gap 16. Subsequently, this steam will come into contact with theinner surface of the pipe section 12. ln consequence, the temperature of thepipe section 12 will increase, and the temperature gradient with respect tothe liner 14 will decrease. Mounting of attemperator components hereby isfacilitated. Moreover, the further recess will allow for water and condensate to be drained from the gap. ln one embodiment, center points of the recess 28, the further recess and the first opening 20 are aligned along an axially extending line.

Fig. 3 is a longitudinal cross-sectional view of the attemperator 10shown in Fig. 2 along the A-A-line. A pipe section 12 and a liner 14 arevisible. The pipe section 12 encloses the liner 14 so that a gap 16 is createdbetween an inner surface of the pipe section 12 and an outer surface of theliner 14. A portion of a water conduit 29 for the nozzle 24 may also be seen.A circumferentially extending projection 25 is arranged on the inner surfaceof the pipe section 12 close to the pipe section inlet. The projection 25 has acircumferentially extending groove (not visible in Fig. 3). Substantiallyradially extending projections 26 of the liner 14 are positioned in the groove.A steam outlet 17, 19 for each of the pipe section 12 and the liner 14 arealso shown. ln certain, non-limiting embodiments, the inner surface of the pipesection 12 may be provided with axially extending groove(s) (not shown) atthe pipe section inlet. Hereby, superheated steam may enter the gap 16.This solution will even allow for water and condensate to be drained out ofthe gap 16.

Fig. 4 is a Iongitudinal cross-sectional view of the attemperator 10shown in Fig. 2 along the B-B-line. ln addition to what is disclosed inconnection with Fig. 3, the nozzle 24 is inserted in the first and the secondopenings. Also, an annular guide 31 normally having axially extendinggrooves (not shown) is arranged close to outlet end of the pipe section and the liner.

Fig. 5 shows a flow chart of a method 50 for assembly of anattemperator. ln a first method step, a pipe section having acircumferentially extending projection arranged on the inner surface of thepipe section, said projection being provided with a circumferentiallyextending groove, at least one first opening arranged in the pipe section andat least one recess arranged in the circumferentially extending projection, isprovided 60. Subsequently, a tubular liner comprising at least onesubstantially radially extending projection arranged on the outer surface ofthe liner at the liner inlet and at least one second opening arranged in theliner is provided 70. Thereafter, the liner is inserted 80 into the pipe sectionso that at least one projection passes through the recess and enters thecircumferentially extending groove. ln a next step, the liner is rotated 90 withrespect to the pipe section so that the projection moves in the groove andthe liner becomes substantially axially immobilized with respect to the pipesection and the first and the second openings coincide, Finally, at least one water-injecting nozzle is inserted 100 into the first and the second openings.

For a detailed discussion of effects, advantages and benefitsattributable to the method for assembly of the attemperator, a reference ismade to the suitable section of the description related to Fig. 1. 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

1. An attemperator (10) for a steam-based plant, said attemperator (10) comprising: - a pipe section (12) and a tubular liner (14), wherein the pipe section(12) encloses the liner (14) so that a gap (16) is created between an innersurface of the pipe section (12) and an outer surface of the liner (14),wherein each of the pipe section (12) and the liner (14) has an inlet (13, 15) for connection to a steam supply and a steam outlet (17, 19), - at least one first opening (20) arranged in the pipe section (12) and atleast one second opening (22) arranged in the liner (14), the first opening being coincident with the second opening, - at least one nozzle (24) extending through the first and the secondopenings (20, 22) for injecting water into a region (21) delimited by an innersurface of the liner (14), - a circumferentially extending projection (25) arranged on the innersurface of the pipe section (12) close to the pipe section inlet (15), saidprojection (25) being provided with a circumferentially extending groove(27), - at least one substantially radially extending projection (26) arrangedon the outer surface of the liner (14) at the liner inlet (15) and at least onecorresponding recess (28) arranged in the circumferentially extendingprotection (25) such that, when the liner (14) is being inserted into the pipesection (12), the at least one projection (26) passes through the recess (28)and enters the circumferentially extending groove (27), and wherein ll - whentheatleastoneprojection (26) h as entered thecircumferentially extending groove (27), the liner (14) is rotated relative the pipe section (12) around an axially extending axis.

2. An attemperator (10) according to claim 1, wherein theattemperator (10) comprises a plurality of projections (26) andcorresponding recesses (28) and wherein the projections (26) and the recesses (28) are uniformly circumferentially distributed.

3. An attemperator (10) according to claim 2, wherein theattemperator (10) comprises four projections (26) and four correspondingrecesses (28).

4. An attemperator (10) according to any of the preceding claims,wherein the attemperator comprises a plurality of coincident first and secondopenings (20, 22), wherein the first and the second openings (20, 22) areuniformly circumferentially distributed, and wherein a plurality of nozzies(24) extends through the first and the second openings (20, 22).

5. An attemperator (10) according to any of the preceding claims,wherein all corners and edges of the at least one projection (26) are rounded.

6. An attemperator (10) according to any of the preceding claims,wherein the attemperator (10) is installed in a heat recovery steamgenerator (HRSG).

7. An attemperator (10) according to any of the preceding claims,wherein at least one further recess (32) is arranged on the inner surface ofthe liner (14) and positioned downstream with respect to thecircumferentially extending projection (25), said further recess (32) beingconfigured to enable fluid communication between the region (21) delimited by the inner surface of the liner (14) and the gap (16). 12

8. An attemperator (10) according to claim 7, wherein center points ofthe recess (28), the further recess (32) and the first opening (20) are aligned along an axially extending line.

9. A method (50) for assembly of an attemperator for a steam-basedplant, said method comprising following steps: - providing (60) a pipe section having a circumferentially extendingprojection arranged on the inner surface of the pipe section, said projectionbeing provided with a circumferentially extending groove, at least one firstopening arranged in the pipe section and at least one recess arranged in the circumferentially extending protection, - providing (70) a tubular liner comprising at least one substantiallyradially extending projection arranged on the outer surface of the liner at theliner inlet and at least one second opening arranged in the liner, - inserting (80) the liner into the pipe section so that the at least oneprojection passes through the recess and enters the circumferentiallyextending groove, - rotating (90) the liner with respect to the pipe section so that theprojection moves in the groove and the liner becomes substantially axiallyimmobilized with respect to the pipe section, and the first and the second openings coincide, - inserting (100) at least one water-injecting nozzle into the first and thesecond openings.