AN ATTEM P ERATQR FOR A STEAM-BASE D P LANT AN D A

M ETHOD FOR ASSEM BLY OF S UCH AN ATT EM P ERATQR

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.

BACKGROUND OF THE INVENTION

Attemperators are devices enabling reduction of the steam temperature. Desired temperature reduction is achieved through a controlled injection of water into the steam flow. Attemperation is the primary technique used for controlling the steam temperature in a boiler or a heat recovery steam generator (HRSG). When employed in steam-based power plants, attemperators are typically located upstream of the turbine. Working medium of such plants is typically superheated steam, i.e. a high- temperature vapor generated by further heating of the steam obtained by boiling water.

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

Superheated steam flowing through the pipe work has a temperature in the range of 600 °C. In 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. In addition to steel, Grade 91 steel alloys include chromium and molybdenum.

In a related context, the temperature in the attemperator itself frequently exceeds 600 °C. As is known in the art, the previously discussed steel alloys are not sufficiently resistant at temperatures exceeding 600 °C. Accordingly, the liner of the attemperator is normally made in more resistant Grade 22 steel alloy.

Traditionally, the liner in Grade 22 steel is joined to the corresponding pipe section in Grade 91 steel by means of welding. Such welding process is disclosed in WO2018117957A1. As is known in the art, this welding process presents numerous challenges, especially when thick pipes are to be joined. Moreover, heat generated during the welding process could structurally damage either steel alloy and entail reduced mechanical stability and/or degraded heat resistance of the attemperator.

In a related context, welding of these advanced materials is subject to rigorous standards, for instance subject to a standard developed by ASME (American Society of Mechanical Engineers) - the ASME Boiler and Pressure Vessel Code (BPVC). The compliance with welding procedure according to BPVC entails a more complex production process and results in a reduced production rate.

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 the attemperator for a steam-based plant, which includes the features defined in the independent 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 installing an attemperator in a steam-driven power plant or a steam generating unit. As discussed above, this entails significant benefits, e.g. faster attemperator installation as well as preserved structural and thermal properties of the used steel alloys.

In the same context, the present solution enables radial expansion/ contraction of the tubular liner. This is very desirable since material deformation 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 dual functionality. In addition to its primary function - to inject water into the steam flow, they are used to contribute in immobilization of the liner with respect to the pipe section.

In addition and contrary to the cited prior art, the present design makes it possible to position fastening means, in particular the radially extending projections, in proximity of the water-spraying nozzle. As a consequence, the axial expansion of the liner is easier to predict and the openings 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 appear more 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 one embodiment 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 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 of the pipe section/liner. The pipe section and the tubular liner typically have circular shape, 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 to one embodiment of the present invention. The shown attemperator 10 is substantially assembled. A portion of a pipe section 12 is removed so that a liner 14 can appear in greater detail. An inlet 13, 15 of the pipe section 12 and the liner 14 can be seen. The inlet, 13, 15 is used for connection to a steam supply (not shown). The pipe section 12 encloses the liner 14 so that a 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 pipe section 12. Analogously, two second openings 22 are arranged opposite each other in the liner 14. Each first opening is coincident with one of the second 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 fixedly attached, 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 a region delimited by an inner surface of the liner 14 with the purpose to cool off the superheat that passes through the liner 14. Typically, there is a plurality of coincident first and second openings that are uniformly circumferentially distributed. In the shown embodiment, there are two pairs of oppositely positioned openings. When the attemperator 10 is fully assembled and the liner 14 is immobilized in the axial direction with respect to the pipe section 12, a nozzle 24 extends through each pair of the first and the second openings. Accordingly, the water-spraying nozzles are provided with dual functionality. In addition to its primary function - to inject water into the steam flow, they are used to contribute in axial immobilization of the liner with respect to the pipe section.

The attemperator 10 further comprises substantially radially extending projections 26 arranged on the outer surface of the liner 14 at the liner inlet 15. Preferably, all corners and edges of the projections 26 are rounded. In addition, there is a circumferentially extending projection 25 arranged on the inner surface of the pipe section 12 close to the pipe section inlet 15. This projection 25 is provided with a circumferentially extending groove 27. A recess 28 is arranged in the circumferentially extending projection 25 such that, when the liner 14 is being inserted into the pipe section 12, each projection 26 may pass through the corresponding recess 28 and enter the circumferentially extending groove 27. Subsequent rotating 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 axis passes through the intersection of A-A-line and B-B-line and continues into the plane of the paper). The proposed solution obviates the need for welding when assembling an attemperator. This entails significant benefits, e.g. faster attemperator installation as well as preserved structural and thermal properties of the used steel alloys. Further, the radial expansion/ contraction of the tubular liner is not prevented. This is very desirable since material deformation in the attemperator is substantial.

Frequently, the attemperator includes a plurality of projections 26 and corresponding recesses 28 and the projections and the recesses are uniformly circumferentially distributed. In 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 recesses 28, are positioned in proximity of the water-spraying nozzle 24. As a consequence, the axial expansion of the liner 14 is easier to predict and the first 20 and the second 22 openings that accommodate the nozzle 24 may be 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 its water supply according to one embodiment of the present invention. The two water supply conduits 29 convey water to the nozzles 24. The nozzles 24 project into a region 21 delimited by the inner surface of the liner 14. As discussed in connection with Fig. 1 , the purpose of the nozzles 24 is to inject water into the region 21 delimited by the inner surface of the liner 14 in order to cool off the superheated steam that is conveyed through the liner 14. An axially extending axis of rotation passes through the intersection of A-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 steam generator (HRSG), an energy recovery unit that recovers heat from a hot gas stream. In addition to protecting the pipe section 12 from thermal stresses, the liner 14 also acts as a flow profiler, increasing the relative steam velocity near the nozzles 24.

At least one further recess (not shown) is arranged on the inner surface of the liner 14 and positioned downstream with respect to the circumferentially extending projection 25. This further recess is configured to enable fluid communication between the region 21 delimited by the inner surface of the liner 14 and a gap (shown in Fig. 3). Accordingly, a portion of the inflowing steam will exit the tubular liner 14 via the further recess and enter the gap 16. Subsequently, this steam will come into contact with the inner surface of the pipe section 12. In consequence, the temperature of the pipe section 12 will increase, and the temperature gradient with respect to the liner 14 will decrease. Mounting of attemperator components hereby is facilitated. Moreover, the further recess will allow for water and condensate to be drained from the gap.

In 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 10 shown in Fig. 2 along the A-A-line. A pipe section 12 and a liner 14 are visible. The pipe section 12 encloses the liner 14 so that a gap 16 is created between an inner surface of the pipe section 12 and an outer surface of the liner 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 surface of the pipe section 12 close to the pipe section inlet. The projection 25 has a circumferentially extending groove (not visible in Fig. 3). Substantially radially 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 are also shown. In certain, non-limiting embodiments, the inner surface of the pipe section 12 may be provided with axially extending groove(s) (not shown) at the pipe section inlet. Hereby, superheated steam may enter the gap 16. This solution will even allow for water and condensate to be drained out of the gap 16.

Fig. 4 is a longitudinal cross-sectional view of the attemperator 10 shown in Fig. 2 along the B-B-line. In addition to what is disclosed in connection with Fig. 3, the nozzle 24 is inserted in the first and the second openings. Also, an annular guide 31 normally having axially extending grooves (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 an attemperator. In a first method step, a pipe section having a circumferentially extending projection arranged on the inner surface of the pipe section, said projection being provided with a circumferentially extending groove, at least one first opening arranged in the pipe section and at least one recess arranged in the circumferentially extending projection, is provided 60. Subsequently, a tubular liner comprising at least one substantially radially extending projection arranged on the outer surface of the liner at the liner inlet and at least one second opening arranged in the liner is provided 70. Thereafter, the liner is inserted 80 into the pipe section so that at least one projection passes through the recess and enters the circumferentially extending groove. In a next step, the liner is rotated 90 with respect to the pipe section so that the projection moves in the groove and the liner becomes substantially axially immobilized with respect to the pipe section 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 benefits attributable to the method for assembly of the attemperator, a reference is made to the suitable section of the description related to Fig. 1. 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