GB2031139A

GB2031139A - Process and apparatus for correcting the draught in natural draught dry-process cooling towers

Info

Publication number: GB2031139A
Application number: GB7839116A
Authority: GB
Original assignee: Renault Techniques Nouvelles Appliquees
Current assignee: Renault Techniques Nouvelles Appliquees
Priority date: 1978-10-03
Filing date: 1978-10-03
Publication date: 1980-04-16

Abstract

In a natural draught dry cooling tower comprising a plurality of heat exchangers 4 disposed in a generally horizontal plane above the ground, baffle means are provided at or adjacent the base of the tower for maintaining an adequate vertical air flow through the tower when adverse ambient conditions prevail, namely strong horizontally directed minds. The baffle means may be in the form of radially disposed screens 7 of rectangular, triangular or trapezoidal shape, or comprise a continuous (Fig. 4) or part circular screen (Figs. 5a, 5b) surrounding and spaced from the base of the tower, the part circular screen being movable on a rail. Alternatively fixed or movable defector blades (Figs. 6a, 6b) may be used. <IMAGE>

Description

SPECIFICATION Process and apparatus for correcting the draught in natural draught dry-process cooling towers The present invention relates to a process and an apparatus for correcting the draught in natural-draught cooling towers.

Air coolers of this kind are primarily used for dissipating the excess heat which is not converted into electricity in generating stations such as steam and nuclear generating stations.

A cooling tower, for example of the socalled dry type, essentially comprises a shell of round section which forms a stack of substantial height, which is supported at its base by a ring of posts (set at an inclined angle) upon which a circular lintel is mounted. The heat exchangers in which the fluid or fluids to be cooled circulate in closed circuits may be in the form of batteries or may be provided by simple pipes or pipes provided with vanes.

In the case which is of interest to the present applicants, the batteries of heat exchangers are disposed on a right section of the shell in the vicinity of the base, that is to say, in a general horizontal plane at a certain height relative to the ground.

The heat exchangers rest on a metal latticelike frame which is supported by vertical posts set out on the base surface of the tower.

With this arrangement, the cold air or external wind current passes into the tower by way of the base of the tower, between the various support posts, and passes vertically through the heat exchangers to be discharged towards the top of the tower, dissipating the heat to atmosphere.

The tower is so calculated and structured as to provide for dissipation of the nominal heat flow, as is the case in particular for the process and the tower which are developed by the present applicants, in Patent Application No. 30605/78 (Serial No. 2001423).

When strong and very strong winds are blowing, the winds pass through the base of the tower horizontally at a speed such that the vertical flow of air through the battery of heat exchangers becomes insufficient. This phenomenon corresponds to a rapid virtual increase in the total of pressure drops in the tower, which should be reduced as greatly as possible in order to re-establish the nominal air flow and to provide for dissipation of the nominal heat flow.

To increase the rising force necessary for extraction of the hot air, one solution would be substantially to increase the height of the tower, but this solution cannot be reasonably employed, for economic reasons.

According to one aspect of the present invention there is provided a process for correcting the draught in a natural draught, dryprocess cooling tower, which is provided with a battery of heat exchangers arranged on a right section of the tower at a certain height from the ground, in which the dynamic pressure of the air surrounding the base of the tower is broken and the wind is directed towards the heat exchangers by suitable means in order to ensure dissipation of the nominal heat flow of the tower.

For carrying out the process, the invention provides several apparatuses which provide for the installation of a series of fixed or movable deflector screens, director blades and orientation correction flaps, which are used separately or in combination.

For a better understanding of the present invention, and to show how the same may be carried into effect, reference will now be made, by way of example, to the accompanying drawings in which: Figures la and ib diagrammatically show respecively a view in elevation and a plan view from above, of the base of a tower provided with deflector screens according to one embodiment of the invention, of rectangular or triangular shape, which are distributed in a star configuration, Figures 2 and 3 show deflector screens according to another embodiment of the invention, of trapezoidal configuration, which are respectively truncated vertically and horizontally, Figure 4 shows a continuous circular screen according to a further embodiment of the invention, outside the perimeter of the tower, Figures 5a and 5b show an elevational view and a plan view from above of a screen according to yet another embodiment of the invention in the form of a movable sector, and Figures 6a and 6b show an elevational view and a view in section of half of director blades or adjustable flaps according to an embodiment of the invention, which are respectively installed either between inclined support posts which support a shell of the tower or between vertical posts which support heat exchangers or along a ring of posts external to the tower.

Referring to Fig. 1, there is shown the base of a natural draught dry-process cooling tower which has a shell 1 which is supported at its base by a ring of inclined posts 2 upon which a circular lintel 3 is mounted.

A battery of heat exchangers 4 are installed on a right section of the tower in a general horizontal plane at a given distance from the ground 5 and supported by a series of vertical posts 6 which can be seen in Fig. 6b.

In accordance with a first series of embodiments of the invention, wind which arrives horizontally as indicated by arrow F1 is broken up, in the dynamic pressure of the air is broken, and deflected through the exchangers (F2) by means of a plurality of radial screens 7 which are disposed vertically at the base of the tower, to ensure dissipation of the nominal heat flow of the tower. The screens 7 converge on the axis of symmetry 8, and are arranged in a surface which substantially cor responds to the projection 9 on to the ground of the heat exchange surface.

Each arm of the star configuration which is thus formed (see Fig. 1 b) may be in various shapes, in particular rectangular shapes (see Fig. 1a), triangular shapes (broken lines 1 7 in Fig. la), or preferably trapezoidal shapes which are truncated either vertically (see Fig.

2) or horizontally (see Fig. 3), or again may comprise a combination of the shapes set out above, with a variable height which may reach the lower surface 10 of the heat exchanger battery.

The star configuration shown has eight arms but it will be appreciated that there may be any number of arms, preferably from four to twelve, and the arms may or may not be symmetrical.

In any case, the deflector screens may be solid or apertured to provide variable permeability in regard to the winds. Thus, the deflector screens may be made of concrete, sheet metal or by means of tensioned structures. A spreadable net having large meshes makes it possible in particular to facilitate access to the heat exchangers, for example for maintenance purposes.

The satisfactory results achieved with this arrangement of the screens may be illustrated by the following numerical example, which applies in particular for triangular or trapezoidal screens: for operation when the wind is fairly strong, that is to say, when there is a ratio of 4.5 between the speed of the wind at the bottom of the tower (horizontal, of the order of 75 kilometres/hour), and the speed of the air at the discharge from the tower (vertical), the correction assembly according to the invention makes it possible to reduce the increase in the pressure drop due to the wind, relative to operation without wind, in an approximate proportion of 4.7 to 2.

Similar results can be achieved by other alternative forms of structure.

The structure shown in Fig. 4 represents a continuous circular screen which is installed at the external periphery of the tower, the height of the screen being sufficient to break the wind, in relation to the distance D of the screen from the base of the tower.

The screen 11 may be economically formed by one or more rows of trees or by a metal or concrete wall, to give non-limiting examples.

Figs. 5a and 5b show a screen 1 2 which is in the form of a sector, which is permeable to the winds to a greater or lesser extent, according to the material used. The screen is movable on a rail 1 3 and is positioned according to the direction of the wind blowing on the tower. The screen may comprise one or more motorised members, preferably at the immediate periphery of the tower, and of sufficient height.

Figs. 6a and 6b show various alternative forms using fixed director blades 14 to guide and channel the wind towards the heat exchangers 4. The blades may be distributed either between the inclined posts 2 which support the shell 1 of the tower (see Fig. 6a), or between the vertical posts 6 which support the exchangers along an internal ring (Fig.

6b), or again along a ring 1 5 which is external to the base of the tower, it being understood that the latter case requires a caisson structure 1 6 for connection to the lintel 3 of the shell (see Fig. 6b). Various combinations of the above-described alternative forms are possible.

Referring again to the arrangements shown in Figs. 6a and 6b, it is also possible to replace the direct blades 1 4 by movable flaps for correcting the direction of the wind, the flaps being actuated manually or automatically.

The invention is not limited to the embodiments described above but also covers all technical equivalents which achieve the desired aim.

Claims

1. A process for correcting the draught in a natural draught, dry-process cooling tower, which is provided with a battery of heat exchangers arranged on a right section of the tower at a certain height from the ground, in which the dynamic pressure of the air surrounding the base of the tower is broken and the wind is directed towards the heat exchangers by suitable means in order to ensure dissipation of the nominal heat flow of the tower.

2. Apparatus for carrying out the process according to claim 1 including radial screens locatable vertically at the base of a natural draught dry-process cooling tower between the ground and a battery of heat exchangers arranged above the ground on a right section of the tower so that the screens converge on the axis of symmetry of the tower in the manner of a star.

3. Apparatus according to claim 2, wherein the screens are of a vertically and/or horizontally truncated trapezoidal form.

4. Apparatus according to claim 2 or claim 3, wherein the screens are solid or apertured, having a degree of permeability with respect to air.

5. Apparatus according to claim 4, wherein the screens are made of concrete, sheet metal, or a tensioned structure such as a net.

6. Apparatus for carrying out the process according to claim 1, including a circular screen of sufficient height, locatable at a distance from the external periphery of a natural draught dry-process cooling tower having a battery of heat exchangers arranged above the ground on a right section of the tower, the screen being in the form of at least one row of trees or a metal or concrete wall.

7. Apparatus for carrying out the process according to claim 1, including an at least part circular screen having at least one sector which is movable on rails, the screen being locatable at the immediate periphery of a natural draught dry-process cooling tower having a battery of heat exchangers arranged above the ground on a right section of the tower.

8. Apparatus for carrying out the process according to claim 1, including a series of fixed director blades which are locatable between support posts of a natural draught dryprocess cooling tower or in the vicinity of the ring formed by said posts, the tower having a battery of heat exchangers arranged above the ground on a right section of the tower.

9. Apparatus according to claim 8, wherein the blades are locatable vertically either along an inner ring between the support posts for the heat exchangers or along a ring external to the base of the tower.

10. Apparatus for carrying out the process according to claim 1, including movable flaps for correcting the direction of the wind, the flaps being locatable between support posts of a natural draught dry-process cooling tower or in the vicinity of the ring formed by said posts, the tower having a battery of heat exchangers arranged above the ground on a right section of the tower.

11. Apparatus according to claim 10, wherein the movable flaps are locatable vertically either along an inner ring between the support posts of the heat exchangers or along a ring which is external to the base of the tower.

1 2. A process for correcting the draught in a natural draught dry-process cooling tower according to claim 1, substantially as hereinbefore described with reference to the accompanying drawings.

1 3. Apparatus for carrying out the process according to claim 1, substantially as hereinbefore described with reference to the accompanying drawings.

14. A natural draught dry-process cooling tower having apparatus according to any one of claims 2 to 11 and 13.