EP0202967A1 - Feed water heater for a steam generator - Google Patents

Abstract

A steam generator feed water heater comprises a pressurized enclosure inside which is a heat exchanger through which the feed water is caused to flow. There is at least one horizontal condensate inlet tube, as well as at least one condensate outlet tube at a low point on the enclosure. A double screen device associated with the condensate inlet tube comprises an inner screen with a cylindrical side wall and, surrounding this inner screen, an outer screen having one end linked to the inner screen. A bottom wall common to both screens constitutes an impact wall facing the inner screen. Passage areas are provided by perforations in the screens not facing each other over most of the perimeter of their transverse cross-sections.

Description

The present invention relates to food water heaters for steam generators, in particular for power plants where the steam produced serves as the working fluid in one or more turbines.

To improve energy efficiency, the feed water from the steam generator is preheated in a heat exchanger called the heater, using draw-off steam as well as condensate collected at the outlet of various devices in the system such as dryers and condensers. .

The use of condensates to supply the heaters is favorable for the energy balance of the installation; in fact, the sensible heat recovered in this way can represent a significant fraction (15 to 25%) of the heat involved.

Generally, a heater has an elongated pressure enclosure, comprising in the vicinity of one of its ends, at least one condensate intake manifold. Experience shows that due to the turbulence of the flow of the incoming flow which generally undergoes expansion inside the heater, the adjacent parts of the internal wall are subjected to a violent erosion action. resulting in a relatively rapid decrease in their thickness.

To overcome this defect, it has been proposed to have, inside the enclosure, facing the condensate inlet pipe, an impact wall intended to dissipate part of the kinetic energy of the condensate jet from said tubing. However, in practice, the condensate flow velocities at the level of the walls remain high and the erosion phenomena persist.

In another solution of the known art, the walls of the enclosure are made of a steel resistant to erosion phenomena. However, this solution results in a high production cost, the alloy used being costly and its implementation complex.

The object of the invention is to overcome these drawbacks by fitting the condensate intake into the enclosure of the heater.

The present invention provides for this purpose a condensate intake device for food water heater of steam generators in particular for energy production, of the type comprising, in association with a pressurized enclosure an exchanger through which the water passes. food, at least one condensate inlet pipe arranged horizontally and at least one condensate outlet pipe at a low point of the enclosure, characterized in that it comprises, in association with at least one inlet pipe of condensates, a dual strainer intake device comprising an inner strainer with cylindrical side wall and around it an outer strainer with one end closed on the previous one, while a bottom common to the two said strainers forms impact wall opposite the interior strainer, passage zones being provided by perforations made in the two strainers not facing each other on a major by tie around their cross sections. Thus, the flow escaping radially outward from the passage area of the first strainer undergoes an axial deflection in order to be able to escape through the passage area of the second strainer.

This arrangement allows good separation of the two-phase water-steam mixture that constitutes the condensates; advantageously favors the escape of the steam upwards and the flow of the liquid phase downwards, which has the consequence of reducing the volume flow rate of the condensate flow and therefore the speed thereof along the walls internal speakers. The chicane arrangement of the passage areas also helps dissipate the kinetic energy of the incoming condensate flow. Ultimately, it makes it possible to considerably improve the flow conditions along the walls and to obtain a distribution of speeds compatible with the nature of the materials which constitute these walls, thus removing the risks of erosion-corrosion.

According to a preferred embodiment of the invention, the cuff constituting the internal strainer comprises an axial passage zone in the axial direction, while the envelope forming the external strainer comprises a ferrule made of sheet metal entirely perforated, but covered in its median part, of a mask or baffle a full sheet, extending, in cross section, on an arc of a circle greater than 180 °.

This design allows the experimentation of masks of different geometries with a view to finding an optimal regime according to the particular circumstances of each type of installation.

• -la figure 1 illustre une représentation - schématique simplifiée d'un circuit d'alimentation en vapeur d'une turbine;
• -la figure 2 représente une vue en élévation d'un réchauffeur d'eau alimentaire pour générateur de vapeur;
• -les figures 3 et 4 représentent une vue en coupe longitudinale et une vue en coupe transversale du dispositif de l'invention;
• -les figures 5 et 6 représentent respectivement, une vue en coupe longitudinale selon le plan V-V de la figure 6 et une vue en coupe transversale d'une variante du dispositif de l'invention.

The characteristics and advantages of the invention will become apparent from the description which follows, by way of example, with reference to the appended drawings in which:

• FIG. 1 illustrates a representation - simplified schematic of a steam supply circuit of a turbine;
• FIG. 2 represents an elevation view of a food water heater for a steam generator;
• FIGS. 3 and 4 represent a view in longitudinal section and a view in cross section of the device of the invention;
• FIGS. 5 and 6 respectively represent a view in longitudinal section along the plane VV of FIG. 6 and a view in cross section of a variant of the device of the invention.

According to the very simplified diagram of FIG. 1, a steam supply circuit of a turbine comprises a steam generator 1 supplied, by means of a pump 2, with water coming from a water reserve or food tank 3 after passing through an economizer or heater 4. At the outlet of generator 1, the steam is sent to a high pressure turbine 5; - The steam escaping from this high pressure turbine 5 feeds a low pressure turbine 6 after treatment in a dryer 7; however, a certain flow rate of withdrawal steam from this high pressure turbine 5 is sent along 5 'to the heater 4. On the other hand, a condensate outlet from the dryer 7 is connected along 7' to an inlet of the heater 4, one of which outlet 4 'is connected to the food cover 3.

The steam from the low pressure turbine 6 is condensed in a condenser 8, the outlet of which is connected to the food cover 3.

The draw-off steam from the high-pressure turbine 5 on the one hand, and the condensates leaving the dryer 7 on the other hand, leave part of their heat available in the feed water of the steam generator 1 in the heater 4.

Such a heater thus improves the energy efficiency of the system.

In practice, the installation can comprise several rackings and several dryers.

According to the general diagram of Figure 2, the heater 4 comprises a closed enclosure 10, of cylindrical shape, arranged horizontally. A first end 11 of this enclosure 10 forms an elliptical bottom into which open a condensate inlet pipe 12 near the center of the bottom 11, and a second condensate inlet pipe 13 arranged at a lower level.

A second end 14 of the enclosure 10 has an inlet 15 and an outlet 16 for drinking water connected to a bundle of pinned tubes 17 conveying the drinking water to be heated.

On the body of the enclosure are formed, in the upper part, two inlets 18 of withdrawal steam and, in the lower part, a pipe 19 for the departure of condensates.

A condensate intake zone is formed near the end 11, this intake zone being generally delimited in an axial direction by a weir or water guard, downstream of which a volume of water is retained on an appropriate height, in particular to prevent any escape of vapor by the outlet 19 of condensate.

According to the embodiment chosen and shown in Figures 3 and 4, the invention is applied to a heater comprising two condensate inlet pipes, a so-called main pipe 12 disposed at a level slightly raised relative to the horizontal axis of the enclosure and a so-called secondary tubing 13 disposed at a lower level. The invention essentially consists in associating with each of these pipes a double strainer device intended to optimize the condensate flow conditions.

• -une manchette 20 ayant une paroi latérale de forme cylindrique, raccordée en 21 par une de ses extrémités à la tubulure 12, et présentant, à l'intérieur de l'enceinte 10, des perforations dans une zone de passage médiane 22 délimitée en sens axial;
• - une enveloppe 23, dont la paroi latérale 25 est de forme cylindrique de plus grand diamètre que celui de la manchette 20, et qui est disposée concentriquement à celle-ci, une de ses extrémités 26 étant refermée sur cette manchette 20; cette paroi latérale ou virole 25 est en tôle entièrement perforée et partiellement enveloppée d'un masque 24 constitué d'une plaque en tôle pleine, de forme rectangulaire, qui a été recourbée pour s'étendre, en coupe transversale, sur un arc d'angle supérieur ou égal à 180°.

We thus find, in association with the main tubing 12:

• a cuff 20 having a cylindrical shape side wall, connected at 21 by one of its ends to the tube 12, and having, inside the enclosure 10, perforations in a median passage zone 22 delimited in direction axial;
• - A casing 23, whose side wall 25 is of cylindrical shape of larger diameter than that of the cuff 20, and which is arranged concentrically thereto, one of its ends 26 being closed on this cuff 20; this side wall or ferrule 25 is made of entirely perforated sheet metal and partially wrapped in a mask 24 consisting of a sheet of solid sheet metal, of rectangular shape, which has been curved to extend, in cross section, over an arc of angle greater than or equal to 180 °.

In the axial direction, this mask 24 extends over a length less than the length of the ferrule 25 and equal to or greater than the length of the perforated middle part 22, of the cuff 20.

An impact wall 27 formed of a flat plate perpendicular to the axis of the condensate inlet pipe forms a bottom common to this cuff 20 and this casing 23 at their second ends 28 and 29.

In a manner known per se, this structure is held in place by means of fixing cheeks 30 between which is placed a bar 31 connected to the walls of the enclosure 10.

A similar double strainer device comprising a cuff 32, a casing 33 and an impact plate 34 is associated with the second inlet pipe 13 for condensates coming from a purge of a so-called high-speed type dryer by example, the envelope 33 having its upper half alone provided with perforations, while the cuff is perforated over its entire length located inside the envelope.

This structure is held in place by means of a fixing element 35 upstream of the weir or water guard 36.

In operation, in a manner known per se, the food water which circulates in the bundle of hairpin tubes 17 is heated by means of the withdrawal vapors which cool and condense on the walls of these tubes 17, and condensates from the inlet pipes 12 and 13 which penetrate into the enclosure 10 at high speeds, generally undergoing expansion therein causing their partial vaporization.

The arrangement of the mask 24 on the ferrule 23, facing the perforated median zone 22 of the cuff imposes on the incoming flow which comes to strike the impact wall 27 for its upward and lateral flow, a baffled course which favors, on the one hand, the separation of vapor, which tends to rise, from water, which tends to descend by gravity; the whole has the effect, on the other hand, of dissipating part of the kinetic energy of the incoming condensate flow.

In FIG. 4, the radial planes delimiting the peripheral zone of the external strainer 23 which is covered by the mask 24 over two thirds, for example of the circumference opposite the passage zone 22 of the internal strainer, have been indicated in A and B . It follows that the part of the liquid phase of the incident condensate which can tend to escape directly from the internal strainer is confined in a solid angle delimited by the two planes A and B: this part of the liquid phase will therefore necessarily meet, before being able to reach the wall of the enclosure, the liquid mass already formed in it with an average level such as CC determined by the weir 36. For its part, the remaining part of the liquid phase escaping by the remainder of the passage area of the external strainer will necessarily have undergone at least one change of direction in the axial direction and therefore a significant reduction in its kinetic energy. This explains the considerable reduction that can be seen in the erosion-corrosion effects of the walls of the enclosure.

As for the device associated with the secondary tubing 13, it can be simplified, on the one hand, because the flow of condensates arriving through this inlet is normally lower and, on the other hand, because this device is normally immersed in the liquid mass accumulating upstream of the weir 36. So we have been content to limit the passage area of the external strainer to the upper half thereof: this avoids any direct escape of the liquid phase towards the area immediately adjacent to the wall of the enclosure which is below the device.

The hydrohynamic studies carried out with the intake devices thus constituted have made it possible to show that one obtains in the vicinity of the walls a distribution of speeds favorable to a good resistance in time of these walls made of steels of covering quality.

The embodiment illustrated in Figures 5 and 6 differs from the previous one by the juxtaposed arrangement on either side of a vertical diametral plane of the enclosure of two intake pipes between which is distributed in two substantially equal parts the main incident condensate flow. Furthermore, a different geometry of the mask covering the external strainer of the device associated with each of these two pipes has been adopted here.

To designate the various elements of these two devices, the references already used in the description of the embodiment of FIGS. 3 and 4 have been requested, by assigning them, respectively, suffixes a and b.

Around the passage zone 22 axially delimited to a median zone of the interior strainers 20a and 20b, the mask 24a, 24b is again found on the exterior strainers still extending over about two thirds of the circumference: however, as it is visible on the FIG. 5, in this case, the mask comprising on the side adjacent to the wall a stop zone devoid of perforations extending on either side of this median zone, up to the ends of the external strainer, this zone stop extending over approximately 90 ° so as to protect the adjacent wall from the enclosure 10 while maintaining upwards and on the side opposite to the side wall two passage zones 41, 42 situated opposite the non-perforated parts of the internal strainer 20a (or 20b).

Furthermore, on the lower side (FIG. 6), the downward passage zones are angularly offset towards the center of the device: thus, the planes Aa and Ba for example, which delimit the downward passage zone of the strainer 23a, are offset by a certain angle in the counterclockwise direction, while the planes Ab and Bb of the other device are in the opposite direction. Consequently, the average directions of exhaust of the condensate flows downwards, as indicated by arrows Da and Db are oriented towards the lowest central part E, therefore the most distant from the wall of the enclosure.

The laterally adjacent parts of the wall of the enclosure are thus sheltered from a direct impact from the flows of condensate liable to escape from the two devices.

The invention is of course not limited to the details of the embodiments which have just been considered by way of example. Thus, in particular, instead of being constituted by a fully perforated ferrule and equipped with a mask, the external strainer could of course also be constituted by a perforated ferrule in the only passage areas that we have decided to take care of it. Furthermore, an installation may include several heaters, possibly in series: a heater of the type illustrated in FIGS. 5 and 6 may be mounted for example downstream of a heater of the type of FIGS. 3 and 4 to receive the condensate from the latter .

Claims (8)

1. Food water heater for steam generators, in particular for energy production, of the type comprising, in association with a pressure vessel (10) an exchanger (17) through which the food water passes, at least one tube - (12) condensate inlet arranged horizontally and at least one condensate outlet pipe (19) at a low point of the enclosure, characterized in that it comprises, in association with at least one inlet pipe condensate, a dual strainer intake device comprising an internal strainer (20) with cylindrical side wall and around it an outer strainer (23) with one end (26) closed over the previous one, while a bottom common (27) to the two strainers forming an impact wall opposite the interior strainer (20), passage zones being provided by perforations made in the two strainers not facing each other over a major part of the around their tr sections ansversales. 2. Heater according to claim 1, characterized in that the internal strainer (20) has an axially delimited passage zone in a middle part. 3. Heater according to claim 1 or 2, characterized in that the external strainer (23) comprises a ferrule (25) perforated except on a stop zone extending over a major part of its periphery, facing the zone passage of the interior strainer. 4. Heater according to claim 3, characterized in that the stop zone has an axial extension opposite the non-perforated zones of the internal strainer on the side facing the adjacent wall of the enclosure. 5. Heater according to any one of claims 3 to 5, characterized in that the passage zones are formed on the external strainer by means of a mask (24) adapted to partially cover a ferrule (25) fully perforated. 6. Heater according to any one of the preceding claims, characterized in that the downward passage region of the external strainer is confined between two radial planes (A, B) forming between them an angle less than 180 °. 7. Heater according to any one of claims 1 to 5, characterized by the juxtaposition on either side of a diametral vertical plane of the enclosure of two condensate inlet pipes each equipped with a device admission to double straining, the downward passage zones having their mean directions (Da, DD) directed towards a line (E) defined on the wall of the enclosure by said vertical plane. 8. A heater according to any one of claims 1 to 7, also comprising a secondary tube (13) for condensate inlet disposed opposite a normally submerged part of said heater, characterized by the association with this tube of a double strainer device comprising an interior strainer (32) fully perforated and an outer strainer (33) perforated in its only upper half.

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