EP0131670B2 - Feed-water preheater with a desuperheater, in particular for a thermal power plant - Google Patents

Abstract

1. A feed-water heater comprising a chest (13) for de-superheating the steam and through which extends longitudinally a nest of tubes (21) through which the feed water flows, characterized in that the chest comprises a steam inlet extending substantially throughout the length of the de-superheating chest (13) and a steam outlet extending along the lateral side opposed to the steam inlet and along an equivalent length.

Description

The present invention relates to a food water heater comprising a desuperheating zone, in particular for a thermal electric power station.

In a thermal power plant, the water supplying the boiler passes through a series of heaters generally consisting of a tube bundle, an outer casing and water boxes or collectors.

The heating steam enters the envelope around the tube bundle where it eventually condenses, giving up its heat to the food water passing through the tubes.

When the steam is overheated, the heat transfer coefficient of the steam to the tubes remains very poor up to the point where the condensation of the steam begins.

To overcome this poor heat transmission, it is known to increase the speed of the vapor by circulating it through a desuperheating zone contained in a box also crossed by the tubes of the heater and comprising baffles also serving to support tubes (for example GB-A-931698).

This is achieved, however, at the cost of an increase in the pressure drop which deteriorates the performance of the heater and which is all the more important as the number of baffles is high. This pressure drop determines the pressure difference that the box must be able to support.

The entry and exit of steam into the desuperheating zone are particularly delicate places because they are very localized and have a reduced section, which results in an impact by steam which can be dangerous for the tubes which are subjected to it ( vibrations, erosion).

Furthermore, EP-A-0 123 986, which represents a state of the art according to article 54 (3) EPC, describes a water heater comprising a box traversed by a bundle of tubes traversed by drinking water. However, in this heater, the box has a central inlet which extends only over a small part of the length.

The present invention aims to provide a food water heater comprising a desuperheating zone which does not have the drawbacks of the prior art.

To this end, the subject of the present invention is a food water heater comprising a steam desuperheating box traversed longitudinally by a bundle of tubes traversed by the food water, characterized in that the box comprises a steam inlet s '' extending practically over the entire length of the box and, the steam outlet extending on the lateral side opposite the steam inlet and over an equivalent length, so as to allow a circulation of steam orthogonally to the tubes passing through the box .

Steam guidance in parallel currents can also be ensured by integral plates supporting the tubes, arranged orthogonally to these tubes and occupying substantially the entire cross section of the box, without this causing pressure losses additional. Moreover, the support plates can be brought together without increasing the speed of the vapor, this being conditioned by the total length of the box.

It is also advantageous for the heater to be free of condensation tubes in the zone for the outlet of the vapor from the box, thus avoiding any obstacle when entering the condensation zone of the heater.

Thanks to the present invention, the effects of impact of the vapor on the tubes and consequently the phenomena of vibration and erosion are avoided.

• la Fig. 1 est une vue schématique partielle en coupe longitudinale d'un réchauffeur classique;
• la Fig. 2 est une vue de dessus de la Fig. 1 représentant les chicanes;
• la Fig. 3 est une vue partielle en coupe transversale d'un réchauffeur selon l'invention; et
• la Fig. 4 est une vue en perspective du caisson de surchauffe présent dans le réchauffeur représenté sur la Fig. 3.

The invention will be explained below in more detail with reference to the accompanying drawings, in which:

• Fig. 1 is a partial schematic view in longitudinal section of a conventional heater;
• Fig. 2 is a top view of FIG. 1 representing the baffles;
• Fig. 3 is a partial view in cross section of a heater according to the invention; and
• Fig. 4 is a perspective view of the overheating chamber present in the heater shown in FIG. 3.

The heater 1 shown in Figs. 1 and 2 is a conventional heater. At the upper part of the heater 1 is an inlet 2 for superheated steam. This input is connected to a horizontal desuperheating chamber 3 via a distribution box 4. The box is traversed longitudinally by tubes such as 5. Vertical baffles are arranged inside the box 3. These baffles partly used to support the tubes 5.

In such a box the steam undergoes a series of changes of direction which contribute to increasing the pressure drop.

In addition, the entry of steam into the box as well as its exit take place in very localized locations causing harmful impacts by the steam.

The heater 10 according to the invention shown in FIG. 3 comprises a cylindrical envelope 11.

At the upper part of the heater 10 is disposed a vertical inlet 12 of superheated steam. This inlet 12 is connected to a desuperheating box 13 arranged horizontally by means of a distribution box 14 arranged horizontally.

The boxes 13 and 14 have the lengths substantially equal to each other and are separated by a horizontal wall 15.

The distribution box further comprises an upper horizontal wall 16, a vertical side wall 17 and a flat inclined side wall 18 close to the wall of the casing 11 of the heater and connecting to the horizontal lower wall 19 of the box 13 by l 'through a vertical wall 20.

A space is provided between the partition wall 15 and the inclined wall 18 on all of their lengths to allow the entry of steam into the desuperheating box 13 from the distribution box 14.

The vapor is thus introduced into the box 13 along the inclined wall 18, then passes between the horizontal walls 15 and 19 where there is arranged a beam of tubes 21, horizontal and parallel to the axis of cylindrical envelope 11.

These tubes 21 are supported by a series of plates 22 orthogonal to the tubes. These plates are in one piece and are shaped like a rectangle with cut upper corners. These plates occupy the entire cross section of the box 13 with the exception of an area in the vicinity of the walls 18 and 20.

These plates serve not only to support the tubes 21, but also to guide the vapor which thus circulates in parallel currents between the plates 22.

The vapor leaves the box 13 in the vicinity of the wall of the cylindrical envelope 11 in an area where the heater is devoid of condensation tubes, all the condensation tubes such as 23 being disposed at a level below the level of the bottom wall 19 of box 13.

It appears, both at the level of the entry of steam into the desuperheating box 13 and at the level of the outlet of the steam from this box, that there is no localization of the passage of steam. The problems associated with such localization are thus avoided.

On the other hand, it also avoids with the present invention the large pressure drops that were in the prior art.

Descriptions of the heater shown in Figs. 3 and 4 are given only as an example (with a vertical steam inlet and horizontal tubes).

Any other orientation of the heaters is possible. In particular, the steam inlet can be horizontal and the tubes vertical.

In addition, the distribution box may include, instead of the inclined wall 18 and the vertical wall 20, a single curved wall connecting to the walls 16 and 19 and close to the wall of the envelope 11.

Claims (4)

1. A feed-water heater comprising a chest (13) for de-superheating the steam and through which extends longitudinally a nest of tubes (21) through which the feed water flows, characterised in that the chest comprises a steam inlet extending substantially throughout the length of the de-superheating chest (13) and a steam outlet extending along the lateral side opposed to the steam inlet and along an equivalent length, so as to permit circulation of steam in a direction perpendicular to the tubes extending through the chest (13).

2. A heater according to claim 1, characterised in that it comprises a distribution chest (14) extending along the de-superheating chest (14) and distributing the steam throughout the inlet of this chest (13).

3. A heater according to any one of the claims 1 and 2, characterised in that it is devoid of condensation tubes (23) in front of the zone in which the steam leaves the de-superheating chest (13).

4. A heater according to any one of the claims 1 to 3, characterised in that the tubes (23) which extend through the chest (13) are supported by plates which are in a single piece (22) and orthogonal to said tubes (21).

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