AU762513B2

AU762513B2 - Preheater in steam power plants

Info

Publication number: AU762513B2
Application number: AU64518/99A
Authority: AU
Inventors: Mustafa Youssef
Original assignee: Alstom Schweiz AG
Current assignee: General Electric Switzerland GmbH
Priority date: 1998-12-11
Filing date: 1999-12-13
Publication date: 2003-06-26
Anticipated expiration: 2019-12-13
Also published as: EP1008803A1; EP1008803B1; AU6451899A; ID24396A; DE59807987D1

Description

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AUSTRALIA

Patents Act 1990 -ABB ALSTOM UPOWER (Selweiz) AG

ORIGINAL

COMPLETE SPECIFICATION STANDARD PATENT

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Invention Title: Preheater in steam power plants The following statement is a full description of this invention including the best method of performing it known to us:- Technical field The invention relates to a preheater in a steam power plant for heating up water for the water/steam circuit of the power plant by heat exchange between tapped steam from turbines and water flowing in tubes.

The invention is concerned with so-called duplex and multiplex preheaters, in which two or more preheaters of different stages and pressures are accommodated in a casing. The preheaters are in each case connected in 15 series on the water side and in parallel on the tappedsteam side. The invention relates, in particular, to the design of bundle carriers and of a partition which separates the two or more preheaters from one another within the preheater casing.

Prior art A duplex preheater is described, for example, in BWK, Volume 37 (1985) No. 10, October, pages 387- 396. This preheater has, in its casing, two heat exchange spaces, each with a steam inlet connection piece and a tube bundle having an associated water inflow and water outflow. Tapped steam of different temperature and different pressure is conducted into the two heat exchange spaces. The pressure regions of the heat exchange spaces are separated from one another by a partition which closes on itself. The water chamber for the water to be heated up, which is conducted through the tube bundle, is subdivided by two shrouds into four compartments, in which the water inflows and water outflows of the two tube bundles are arranged.

DE 195 11 264 describes a duplex preheater with an elongate cylindrical outer casing. The first heat 2 exchange space is located in an elongate inner casing, whilst the second heat exchange space is formed by the interior of the outer casing and the exterior of the inner casing of the first heat exchange space. The separation between the two pressure regions therefore consists of a complete inner casing. The latter is formed on one side by a semicircular vertical wall and on the other side by a straight vertical wall.

A further duplex preheater is disclosed in DE 195 37 478. The preheater has in its interior a straight vertical partition which separates the two heat exchange spaces or pressure regions from one another.

15 Presentation of the invention The object of the invention is to provide a duplex and multiplex preheater of the type mentioned in the introduction, which has a bundle carrier design and, for separating the heat exchange spaces or pressure regions, one or more partitions which can be produced and mounted cost-effectively and which are also thermally insulating.

This object is achieved by means of a duplex or multiplex preheater having an outer casing or steam jacket accommodating two or more heat exchange modules which are in each case separated from one another by a partition, a heat exchanger tube bundle supported by supporting plates being arranged in each heat exchange module. According to the invention, here, the partition between the heat exchange spaces is designed with a zigzag-shaped cross section. For this purpose, the partition has a high middle part, which extends over the region of the supporting plates, and two short parts, which, bending relative to the middle part, in each case extend from the two ends of the latter towards the steam jacket and are welded to the said steam jacket. The pressure difference between the heat exchange spaces results in a pressure force on the 3 partition. According to the invention, the partition is made zigzag-shaped and is therefore flexible, so that it yields to the pressure force by being displaced and, at the same time, bending only very slightly. Under the action of the pressure force, the zigzag shape of the partition allows a displacement of the wall during which the middle part of the partition is displaced.

As a result of the displacement of the partition, the latter comes into contact with the supporting plates which, in turn, come into contact with the steam jacket. As a result, there is a transmission of pressure force from the partition to the thicker steam jacket which absorbs the force.

By virtue of the transmission of force, it becomes possible, in particular, to manufacture the partition from thinner walls.

In a preferred version, the partition has a doublewalled design, in that two walls run parallel to one another, at least over the region of the high middle S* 20 part of the partition, and between these walls there is an interspace. In an extended version, the supporting S.plates of the tube bundles have inner and outer wings, of which the inner extend to the partition and the outer towards the steam jacket. These wings are 25 arranged with respect to the partition and the steam jacket in such a way that the partition, during its displacement, comes into contact with the inner wings and the outer wings come into contact with the steam jacket. Here too, the pressure force is transmitted to the steam jacket via the wings of the supporting plates.

In order to bring about the transmission of the pressure force from one wall of the double-walled partition to the other, metal plates are arranged in the interspace between the individual walls and, under the action of the pressure force, come into contact with the walls of the partition.

The invention relieves the partition of the pressure force by transmitting the pressure force from the 4 partition to the supporting plates and the jacket of the preheater casing. It thereby becomes possible to make the walls of the double partition thin and manufacture them cost-effectively at a low outlay in terms of material.

The zigzag shape of the partition has the advantage that it allows deformations due to thermal expansions.

The rectilinear displacement of its long middle part acts to only a slight extent on the welds on the steam jacket. The double-walled partition also affords the advantage of thermal insulation. As compared with an individual preheater, additional heat losses occur in a duplex preheater. These are reduced by the thermal *"insulation of the double wall.

5 description of the drawings In the drawings: Figure 1 shows an outer side view of a duplex preheater 20 with water chambers and with an outer casing for two heat exchangers and a cross section through the water chamber of the duplex preheater, Figure 2 shows an axial cross section through a duplex preheater in order to illustrate the design of the supporting plates according to the invention and of the double-walled partition, Figure 3 shows an axial cross section through the same duplex preheater in order to illustrate the use of the partition according to the invention under the action of the pressure force from one pressure region to the other, Figure 4 shows an example of a multiplex preheater, with three heat exchange spaces separated by partitions according to the invention, and a cross section through the water chamber of the multiplex preheater.

5 Embodiment of the invention Figure 1 shows the exterior of a duplex preheater with an outer casing or steam jacket 1.

Attached to the steam jacket 1 are steam inlet connection pieces 3 and 4. Steam, for example from a first tapping stage of a low-pressure turbine, is conducted via the two steam inlet connection pieces 3 into a first preheater space inside the jacket 1, whilst steam from a second tapping stage of a lowpressure turbine is conducted via the steam inlet connection piece 4 into a second preheater space within the jacket 1. Arranged so as to adjoin the steam jacket 1 is a tube plate 15, in which tubes of U-shaped tube ee 15 bundles for the two heat exchangers are anchored.

S* Connected to the tube plate 15 is a water chamber 2 with four part water chambers 11', 12', 13', 14', a water inlet connection piece 7 and a water outlet connection piece 8. The water to be heated up passes S 20 through the water inlet connection piece 7 into a first part water chamber 11', the water inlet zone for the first-stage preheater, and from there through the tube bundles arranged in series. (The direction of flow of the water from the part water chambers into the tube bundles and from these into the part chambers is indicated by crosses and circles.) The tube bundles are connected to one another via a second part water chamber 12', the water outlet zone of the first preheater, and a third part water chamber 13', the water inlet zone of the second preheater. After flowing through the two tube bundles, the water flows into a fourth part water chamber 14', the water outlet zone of the second preheater, and finally emerges from the duplex preheater via the water outlet connection piece 8. The part water chambers 11' and 14' are formed by two shrouds 16 and 17, the part water chambers 12' and 13' being formed by the outer walls of the shrouds 16 and 17 and the inner wall of the water chamber 2 and being connected to one another.

6 Figure 2 shows the interior of the duplex preheater with the partition 20 according to the invention for subdividing and separating the pressure regions of the two heat exchangers and with the supporting plates 19 according to the invention for the tube bundles 11-14 for implementing the transmission of the pressure force to the steam jacket 1.

Shown again on the steam jacket 1 are the steam inlet connection pieces 3 and 4, via which steam at a pressure P1 is conducted into the first heat exchange space SI, or first-stage preheater, and steam at a pressure P2 is conducted into a second heat exchange space S2, or second-stage preheater, in which case P1<P2. Arranged in each of the two regions S1 and S2 is S 15 a U-shaped tube bundle, the legs of which are designated by 11 and 12 in the region S1 and by 13 and 14 in the region S2.

The tapped steam from the low-pressure turbines, which passes via the inlet connection pieces 3 and 4 into the regions S1 and S2, flows through the tubes of the tube bundles. Baffle plates 22 may be mounted opposite the inlet connection pieces 3 and 4 in order to protect the tubes.

Condensate is led into the region S2 from a preheater of higher (here third) stage via a cascade inlet connection piece 6. Condensate forms on the tube surfaces as a result of the condensation of the steam and collects in the lower region of the preheater. The condensate in the region S2 is discharged via the condensate outlet connection piece 10 and can be pumped forwards to the higher stage or be supplied to the region Sl, after throttling via a level-regulating valve, by way of the cascade inlet connection piece The collected condensate in the region S1 is discharged via the condensate outlet connection piece 9 and supplied to the lower preheater stage or to the condenser of the plant.

In order to remove non-condensable gases (air) from the preheater, vent tubes 24, via which the gases are 7 sucked away, are mounted in the bundle lanes inside the tube bundles.

The cover plates 23 serve for preventing steam from flowing directly into the bundle lane and the air suckaway zone having the lowest pressure. In both regions S1 and S2 the tube bundles are in each case supported by supporting plates 19. The supporting plates 19 are themselves clamped together by means of tie rods and sleeves 18 which run through the preheater in the longitudinal direction. Furthermore, the supporting plates 19 lie on angles and rails 21 which are fastened in the lower region of the steam jacket 1.

According. to the invention, the supporting plates 19 have wings 19' and 19". In this version, on each supporting plate 19 two wings 19' extend towards the middle of the preheater and two further wings 19" extend from the outer edge of the supporting plates 19 towards the jacket i.

The heat exchange regions S1 and S2 are formed by the S 20 partition 20 according to the invention and by the surrounding jacket 1. The partition 20 has a basic zigzag shape. The partition 20 consists of three parts: of a high middle part 20', which extends slightly beyond the region of the supporting plates 19, and of two short parts 20", which run in a bend from the high middle part 20' towards the jacket 1 of the preheater; the two short parts 20" may be parallel. They are welded to the jacket 1 at the welds or clamping points 38 and 39.

The partition 20 is designed as a double wall over a large part of the zigzag shape, the first wall, which faces the heat exchange space of higher pressure, serving for maintaining the pressure difference, and the second wall, which faces the heat exchange space of low pressure, serving for thermal insulation. The individual walls of the double wall are manufactured from thin sheet metal which is not intended for absorbing the pressure force. The sheet metal is manufactured, for example, with thicknesses of 2-5 mm, 8 the first wall being preferably designed to be thicker than the second wall. The insulation affords a reduction in the lost-heat flow and a power saving. If, for example, a partition of simple design consists of carbon steel, a heat flow of 1000-2000 kW can be transmitted from the second preheater module into the first preheater module by thermal conduction. For this purpose, a steam flow of approximately 0.5-0.8 kg per second would additionally have to be tapped from the turbine one stage earlier. This would lead to an increase in the thermal consumption of the steam plant of approximately 0.03 to 0.05%. These losses can be reduced by the choice of a rust-proof material for the partition, although this would entail higher costs. By 15 using a partition according to the invention having a *double design, the heat losses mentioned are minimized and even virtually avoided.

At the same time, the individual walls are separated from one another by an interspace having a S 20 width of a few millimetres. Arranged in the interspace are intermediate plates 30 which, together with the wings 19', serve for transmitting the pressure force to the thicker and stronger jacket 1 by coming into contact with the partition during the displacement of 25 the latter.

Figure 3 illustrates the force on the partition which occurs as a result of the pressure difference between the regions S1 and S2. The pressure force is indicated here by arrows. For the sake of simplicity, here its effect is shown only on the left-hand wall of the double wall. By virtue of its zigzag shape, the partition 20 yields to the pressure force by being displaced into the position indicated by the broken line; it bends, at the same time, only slightly. It has essentially the function of transmitting the pressure force to the supporting plates 19 and the jacket 1. In contrast to the prior art, it does not have the function of absorbing the force solely by undergoing a high load. During the transmission of force, the 9 bending points 36 and 37 move virtually on circular lines, the welds or clamping points 38 and 39 being the centres of the circles. The high middle part 20' of the partition is slightly displaced obliquely upwards as a result of the pressure force. During this displacement, the first wall of the double wall comes into contact with the intermediate plates 30 which then come into contact with the second wall of the double wall. This results in a parallel displacement of the middle part 20' of the two walls of the double wall. The double wall then touches the wings 19' and transmits the pressure force to the supporting plates 19. The wings 19" at the outer edge of the supporting plates finally transmit the force to the jacket 1 which absorbs it by 15 virtue of its greater material thickness.

The pressure force is both transmitted to the jacket via the supporting plates 19 and the wings 19', 19" and absorbed by the welds 38, 39. As a result, high bending loads on the partition 20, in particular in the S 20 vicinity of the two welds 38, 39, are avoided.

Moreover, the relief of the partition by its being supported on the supporting plates and wings makes it possible for the partition to have a thin design at a S"low outlay in terms of material.

Figure 4 shows a multiplex preheater by the example of a preheater with three preheater stages in a casing. It has partitions according to the invention for subdividing the pressure regions and also supporting plates for transmitting the pressure forces between the preheater regions to the jacket of the preheater. The multiplex preheater surrounded by the jacket 1 is subdivided into three pressure regions Sl, S2, S3, or first-, second- and third-stage preheaters, in which pressures P1, P2 and P3 prevail, in which case Pl<P2<P3. Tapped steam is conducted via inlet connection pieces 41, 42, 43 into the three preheater regions. In a similar way to the duplex preheater, U-shaped tube bundles, through which the water to be heated up flows, are arranged in each region. The 10 direction of flow through the bundle legs 44-49 is indicated by crosses and circles. The tube bundles, in turn, are supported by supporting plates 19 which lie on angles and supports 21 in the lower region of the preheater casing.

The condensate resulting from the condensation of the steam on the tube surfaces also collects in the lower region. Condensate from a fourth-stage preheater is led via the cascade inlet connection piece 6 into the region S3. The collected condensate in the region S3 is discharged via condensate outlet connection pieces after which it is supplied via a connection piece 51 to the collected condensate in the region S2. The region S2 has a condensate outlet connection piece 52, via 15 which the condensate is discharged from this region and is led via the cascade inlet connection piece 5 into the region Sl. Via a condensate outlet connection piece 53 in the region S1, the condensate from this region is supplied to the condenser of the power plant.

20 The partitions 54 and 55 between the regions S3, S2 and S•S2, S1 are designed in a similar way to the partition in Figure 2, and they have middle parts 54', 55' and short parts 54", 55" of zigzag shape. They are S"displaced in a similar way to that illustrated in Figure 3. The supporting plates 19 in each case have two or three wings on each side, depending on the size of the multiplex preheater. The supporting plates in the middle preheater S2 have, on both sides, wings 19' which face partitions 54 and The water chamber for the multiplex preheater is designed in a similar way to the water chamber for the duplex preheater according to Figure 1. The water chamber is correspondingly subdivided into six part water chambers with the aid of two shrouds and a waterside zigzag-shaped partition, thus ensuring the series connection of the tube bundles. The first shroud surrounds the part chamber for the inlet of water into the bundle leg 44. The water-side zigzag-shaped partition runs from the water-chamber jacket 2 first 11 between bundle-tube zones 45' and 47', then between bundle-tube zones 46' and 47' and finally between bundle-tube zones 46' and 48' to the jacket 2. The second shroud surrounds the part chamber for the outlet of water from the bundle-tube zone 49'.

In an extended version, the duplex and multiplex preheaters have a subcooler in the second or the second and third preheater stages. For the purpose of reducing the pipeline length, in particular the pipelines for tapped steam from the low-pressure turbine, which have a large diameter, the duplex or multiplex preheater is arranged preferably as near as possible to the low-pressure turbine. Arranging the duplex preheater in the condenser neck is an optimum 15 solution in terms of a saving of pipelines, if the pressure losses of the low-pressure turbine steam around the duplex preheater are not high.

o *oooo* o *o 12 List of reference symbols 1 Steam jacket, outer casing 2 Water-chamber casing 3 Steam inlet connection piece (turbine tapped steam) 4 Steam inlet connection piece (turbine tapped steam) Cascade inlet connection piece 6 Cascade inlet connection piece (from higherstage preheater) 7 Water inlet connection piece 8 Water outlet connection piece 9 Condensate outlet connection piece from preheater Sl Condensate outlet connection piece from preheater S2 11-14 Tube-bundle legs 11' Water inlet zone preheater S1 "12' Water outlet zone from preheater Sl 13' Water inlet zone preheater S2 14' Water outlet zone from preheater S2 15 Tube plate 16 Water inlet shroud (part water chamber) in water chamber 17 Water outlet shroud (part water chamber) in water chamber 18 Tie rods and sleeves 19 Bundle supporting plates 19' Wing on supporting plate towards the middle of the preheater 19" Wing on supporting plates towards the jacket of the preheater Partition between heat exchange spaces S1 and S2 Partition between heat exchange spaces S1 and S2, high middle part Partition between heat exchange spaces S1 and S2, short parts 13 21 Angles and supports 22 Baffle plate 23 Cover plate 24 Vent tubes Intermediate plates 36,37 Bending points 38,39 Welds 41-43 Inlet connection pieces to multiplex preheater 44-49 Bundle legs in multiplex preheater Condensate outlet connection piece from S3 51 Condensate inlet connection piece to S2 52 Condensate outlet connection piece from S2 53 Condensate outlet connection piece from Sl 54 Partition between pressure regions S3 and S2 54' Partition between pressure regions S3 and S2, middle part 54" Partition between pressure regions S3 and S2, short parts Partition between pressure regions S2 and S1 •55' Partition between pressure regions S2 and Sl, middle part 55" Partition between pressure regions S2 and Sl, short parts 56 Water-side zigzag-shaped partition

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Claims

1. Preheater in steam power plant, with a steam jacket accommodating at least two preheater stages, each with a heat exchange space, turbine tapped steam of different pressure being conducted via steam inlet connection pieces into each heat exchange space, at least one partition being arranged for subdividing the pressure regions of the heat exchange spaces, and there being arranged in each heat exchange space of the at least two preheater stages tube bundles, through which water to be heated up flows and which are supported by supporting plates, characterized in that the at least one partition is designed with a zigzag-shaped cross section, and it has in each case a high middle part, which extends over the region of the supporting plates, and two short parts, which run in bends to the middle part extend from the ends of the middle part as far as the steam jacket and are welded to the latter, and the at least one partition, by virtue of its zigzag shape, is flexible, in that it yields to the pressure force between a heat exchange space of higher pressure and a heat exchange space of low pressure, is displaced and comes into contact with the supporting plates, the supporting plates coming into contact with the steam jacket and transmitting the pressure force to the latter.

2. Preheater according to claim 1, characterized in that, for the purpose of thermal insulation, the at least one partition is of double-walled design, in that it has in each case two walls which are arranged parallel at least over the region of the high middle part and are separated from one another by an interspace, and the two walls are in each case of thin design.

3. Preheater according to claim 2, characterized in that intermediate plates are arranged between the parallel walls of the at least one partition.

4. Preheater according to claim 3, characterized in that the supporting plates have first wings, which in each case extend towards a partition, and further wings, which in each case extend towards the steam jacket.

5. Preheater according to claim 4, characterized in that the supporting plates are clamped together by means of tie rods with sleeves.

6. Preheater according to claim 5, characterized in that the supporting plates are supported on angles and rails in the lower region of the preheater.

7. Preheater according to claim 6, characterized in that the steam jacket has a first cascade inlet connection piece which leads condensate out of an external higher-stage preheater into the preheater.

8. Preheater according to claim 7, characterized in that the steam jacket has further cascade inlet connection pieces which lead condensate from a heat exchange space of higher pressure into a heat exchange space of lower pressure.

9. Preheater according to one of the preceding claims, characterized in that the preheater has a subcooler in each of the individual heat exchange spaces. Preheater according to one of the preceding claims, characterized in that the preheater has three preheater stages, each with a heat exchange space, in which two partitions for subdividing the pressure regions of the heat exchange spaces are arranged. us Dated this tenth day of December 1999 o -AB ALSTOM P OR (CHWVEIZ Patent Attorneys for the Applicant: F B RICE CO