Cooling Tower

Abstract

A cooling tower, especially for condensing of vaporous media and for cooling liquid media, which is provided with air inlet means in the lower zone of the cooling tower mantle and is also provided with air discharge means in the upper portion of the cooling tower mantle. The cooling tower comprises a plurality of heat exchanging components arranged radially over the cross section of the cooling tower above the air inlet means to form circular rings of components. The height of the rings decreases in the radial direction from the outer periphery of the cooling to the center thereof, and the heat exchanging components are respectively in the form of roof-type structures having a gas impermeable guide wall for the cooling air and a heat exchange wall to be contacted by the cooling air.

Description

This invention relates to a natural or forced draft cooling tower of circular design, in which the elements for the heat exchange are arranged in the lower zone of the mantle wall just above the air inlet apertures, while being distrubuted over the cross-section of the cooling tower.

As a rule the heat exchange elements or components of such cooling towers consist of fin equipped or plain tubes through which flows the medium to be cooled, which medium conveys the heat to be discharged to the cooling air flowing around the outer surfaces of the tubes. This air enters radially through the air inlet apertures, and, after being heated up on the heat exchange surfaces, is with ventilator cooling towers discharged through the diffuser mouth, or with towers cooled by natural draft is through the upper outlet opening of the cooling tower mantle discharged into the environment.

It is well known that in such cooling towers, with simultaneous distribution of the flow resistance of the heat exchange components over the cross-section of the cooling tower, a flow profile is established with rates of flow which rise towards the middle of the cooling tower. This flow profile is brought about by the fact that the diversion losses of the cooling air towards the middle of the cooling tower decrease in relation to the losses on the periphery of the mantle or shell, since the currents of air rising at the edge of the cooling tower are diverted by about 90.degree.. As a result of the different supply of cooling air for the heat exchange components on the individual cooling tower radii, there is automatically produced a differential cooling effect, which fact is detrimental with regard to the optimum heat exchange of the installation as a whole.

Designs have been proposed for making the flow profile of the cooling air more uniform. Where guiding surfaces with low flow resistance have been used to equalize the flow profile of the cooling air over the cross-section of the cooling tower, the outlay with regard to the design has not been found economially feasible. Another proposal aims at reducing the level of supply of the cooling air to the components in the middle of the cooling tower. In this connection the heat exchange components are arranged deeper towards the middle of the cooling tower than on the edge of the latter, either continuously or in a stepped manner. Another arrangement provides for reducing the height of draft of a dry cooling tower, which height of draft in addition to heating up has a definite influence on the buoyancy of the cooling air in natural draft cooling towers. To this end the heat exchange components are arranged higher in the middle of the cooling tower than at the edge.

Although through both methods improvements in the flow profile are obtained to a certain extent, the very mutual contrast of the constructional proposals permits of concluding that oppositely directed results to those desired must be obtained, and this is in fact the case. If the heat exchange components are arranged in the middle of the cooling tower lower than at the outside, the conditions of flow to the cooling components are impaired, but at the same time the draft level is increased, which fact must in its turn result in an increase in the rate of flow. If the heat exchange components are arranged, as in the case of the second proposal, higher in the middle of the cooling tower than at the edge of the tower, the draft level is indeed reduced, but at the same time the conditions of flow of the cooling air to the components are improved so that the intended effect, viz. the reduction in the rate of flow in the middle of the cooling tower, cannot be fully attained.

Further drawbacks of the heretofore known cooling towers in which the heat exchange components are arranged lower in the middle than at the edge, arise through the greater liability to wind action, which is to be attributed to the fact that the components in the middle of the cooling tower lie in the zone of the air inlet orifices, so that the components arranged on the weather side, in the event of wind, receive a greater impact of air than the components on the lee side. Furthermore, the existing cross-sections of flow are poorly utilized in the case of the heretofore known cooling towers because the heat exchange components, which have a rectangular area of projection, are arranged in a circular cross-section, so that if the components are rather long, wedges or gussets are formed which have to be covered and are useless as flow and heat exchange surfaces.

In the case of the wellknown form of construction, in which the exchange components in the middle of the cooling tower are arranged higher than at the edge, it will be appreciated that in the central region of the tower, height of draft is lost, which, with otherwise the same conditions of heat exchange and air-flow, make it necessary to increase the height of the cooling tower. Moreover, the outlay for supporting the heat exchange components is greater.

Another problem underlying the present invention consists in equalising the differing supplies of cooling air for the heat exchange components distributed over the surface of the cooling tower in such a way as to obtain a possibly uniform cooling action over the cross-section of the tower. Whereas according to the proposals heretofore knowh the attempt is made to equalise the flow profile of the cooling air by reducing the level of the supply to the components, or the height of draft, the invention adopts a fundamentally different way according to which the different flow profiles in the cooling tower are equalised over the radius of the cooling tower by adapting the specific heat exchange surface to the flow profile of the cooling air. The specific exchange surface is defined as the ratio between the heat exchange surface and the inflow surface, the latter being deemed to be the horizontal cross section of the cooling tower on a level with the heat exchange components.

With a cooling tower of circular design, especially for condensing vaporous media or for cooling liquid media, with intake openings for the cooling air in the lower region of the mantle wall and with an upper outlet opening provided with heat exchange elements distributed over the cross section of the cooling tower in radial arrangement and located above the air discharge openings, while the exchange elements which consist of finned tubes or plain tubes and which are located in roof-shaped structures and on circular rings the diameter of which decreases in the direction from the outside toward the inside, the invention is seen in the following features. The height of exchange elements decreases in radial direction from the outer edge of the cooling tower to the center thereof. Furthermore, a surface of the roof-shaped design is designed as air guiding wall inasmuch as the upper edge of each element located on a circular ring is connected to the foot of the respective adjacent element by a non-air-permeable partition, whereas the other surface forms the exchange surface.

Preferably, the heat exchange wall comprises plain tubes and tubes with fins through which a heat exchange medium may pass. It is also preferred that the guide wall of each component forms the upper edge of the heat exchange wall to the base of the neighboring component in the same ring.

The invention furthermore provides that the height of the heat exchange components decreases continuously on a gradient from the outer edge of the cooling tower towards the center. According to a preferred embodiment of the invention, the height of the heat exchange components decreases in steps from the edge to the middle of the cooling tower, the group of heat exchange components resting on the same circular ring always having the same height, which height decreases from group to group from the outer area to the inner area.

It has surprisingly been found that by such a design, the heat exchange surface can for all practical purposes under optimal conditions be adapted to the existing flow profile of the cooling air, which results in equal heat exchange conditions throughout the whole cross section of the cooling tower. The width and length of the individual components are optional and are derived from the heat exchange conditions and the data of the medium to be cooled. Accordingly, the number of groups of components arranged over the radius of the cooling tower, and their dimensions, as well as the number of components arranged within a group, can vary.

It is, furthermore, provided according to the invention that the heat exchange surface of the roof-type structure, which surface is provided with heat exchanging elements, may be arranged perpendicularly, i.e. at right angles to the inflow surface, and the pertaining air guiding wall is arranged obliquely, or that the surface equipped with the exchange elements is at an air incline, in which instance the air guiding wall will then extend approximately vertically. The air guiding walls may consist of sheet metal, asbestos, cement, or plastics material, or the like.

Ideally, the specific heat exchange surface rises over the length of a component with constant width or height in inverse proportion to the square of the cooling tower radius. Inasmuch as the rise in the rate of flow towards the middle of the cooling tower is generally less intense, a preferred form of the invention makes provision for the specific heat exchange surface to be adapted continuously or step by step to the flow profile of the cooling air, or to be superimposed thereon. This can be done by reducing the height of the components, in the case of a central arrangement, towards the middle of the cooling tower, or else with an inclined arrangement of the components, the angle of incidence of the components with the inflow surface is reduced continuously or in steps, with a simultaneous reduction in the width of the component. The arrangement of the components over the radius of the cooling tower is, as a rule, horizontal if liquid media are to be cooled. Merely for the sake of better emptying, the components may be given a slight slant. A similar arrangement can be provided in the case of condensation processes for the better discharge of the condensate.

The air guiding walls arranged between the upper edge of a component and the base of a neighboring component act at the same time as wind interception walls. Additional wind breaks, such as are arranged in known structures to avoid the blowing through of individual components, below or between the individual components, may not therefore be necessary.

To compensate for the possible influence of wind, the invention provides that the heat exchange surfaces and the partitions may be arranged on alternate sides over the radius of the cooling tower, while the heat exchange surfaces and the partitions are on opposite sides in the individual groups.

The individual groups can either be operated separately or else be interconnected. Accordingly, the medium to be cooled may be supplied either through an external circular pipe, or through several circular pipes over the radius of the cooling tower. The medium being cooled, or the condensate, is then discharged through circular pipes which are arranged either in the middle of the cooling tower only, or approximately on the inner radius of circles in which the groups of components are located.

A further advantage is obtained due to the fact that the whole of the cross section of the cooling tower is utilized in an optimum manner; only in the middle of the cooling tower is there a dead space which can be utilized for the arrangement of pipes and as a transport lock.

If the cooling tower is to be used as a pure dry cooling tower, according to the invention, the entire cross-sectional surface of the tower may be covered with the heat exchange components. It is, however, also possible to design the cooling tower in the well-known manner as a combined wet-dry cooling tower in order to derive the advantages arising therefrom, namely the prevention of vapor emerging from wet cooling towers and the improvement of the steep characteristic of dry cooling towers, and to reduce the additional water requirement of wet cooling towers by the basic load being taken over by the dry cooling part and the peak load by the wet cooling part. To this end, the cooling tower may be so constructed that components for wet cooling, such as trickle units, are distributed over the cross section of the cooling tower between one or more rows of heat exchange components extending in the radial direction, so that sector-shaped portions of dry cooling components and wet cooling components follow one another alternately.

The invention is illustrated by way of example in the accompanying drawings, in which:

FIGS. 1 and 1a show a partly cut-away side view through the lower part of a natural draft circular cooling tower in the form of a dry cooling tower only.

FIGS. 2 and 2a respectively represent two diagrammatic representations seen from above the heat exchange components, which are shown arranged in a semi-cross-section of the cooling tower.

FIG. 3 is an isometric representation of heat exchange components arranged one after the other in a radial direction.

FIG. 4 shows an enlarged isometric representation of a heat exchange component with an inclined arrangement.

FIG. 5 shows four heat exchange components placed one behind the other in a radial direction, while being arranged vertically.

FIG. 6 is an isometric illustration similar to FIG. 4, of a heat exchange component in a vertical arrangement.

FIG. 7 is a top view of the exchange components and trickle devices shown arranged in semi-cross section in a combined wet-dry cooling tower.

FIG. 8 is a cross section taken along the line VIII--VIII of FIG. 7.

The circular cooling tower of FIG. 1 comprises a shell or mantle 1, which has passage means 1a in the lower zone to form air inlets, through which air enters radially in the direction of the arrows 2. Above the intake orifices 1a there are arranged the heat exchange components 3, which occupy almost the whole cross section of the cooling tower except for a central free area, so that the cooling tower acts solely as a dry cooling tower. The air entering radially, flows, as denoted by the arrows 4, through the individual components 3 and emerges through an upper discharge orifice from the cooling tower.

FIG. 2 is a top view of the heat exchange elements, which are arranged in the cooling tower; these heat exchange components are combined to form the groups I, II, III and IV which are located along circles. Struts 5 act as the supporting means for the heat exchange elements. In FIG. 1, the height of the components 3 decreases from group to group in steps and is constant within each group, while in FIG. 1a a form of embodiment of the invention is represented in which the height of the components of a group, and from group to group, decreases continuously from outside to inside.

FIG. 3 shows several groups of heat exchange components 3, one behind the other in a radial direction, those of each group being placed side by side. The illustrated components or heat exchange elements form a sector-shaped portion of the whole installation. The heat exchange components are accommodated in a roof-type structure, one surface 6 of which contains heat exchange tubes 7, which run horizontally in the illustrated example while the other surface 8 is an airtight partition serving as air guiding wall. As is apparent in particular from FIG. 4, the roof-type structure is open at the bottom, so that air entering in the direction of the arrows 9 is able to pass through the individual heat exchange components. The front and rear ends of the roof-type structure are likewise closed by sealing walls in order to compel the cooling air to pass through the heat exchange components.

In the case of the embodiments shown in FIGS. 3 and 4, the exchange surface 6 of the roof-type structure is arranged obliquely, while the respective air guiding wall 8 is vertical, or approximately vertical. The air guiding wall 8 runs from the upper edge of the roof-type structure to the base of the adjoining component and thus compensates for the widening of the cooling tower towards the outer edge, produced by the radial arrangement in the circular base area.

Whereas in FIGS. 2, 3 and 4, the heat exchange surface is oblique and the partition mainly vertical, in the embodiment represented in FIGS. 2a, 5 and 6 the exchange surface 6 is vertical or substantially vertical, and the air guide wall 8 is arranged obliquely.

In all the embodiments, the height of the exchange components varies in steps from group to group, the components of group 1 having the least height and the components of the group on the outer edge of the cooling tower having the greatest height.

In a preferred practical form of the invention, provision is made for the heat exchange surfaces and the partitions in the individual groups to be arranged on alternate sides, as is shown in FIG. 3, the air guide walls of groups I and III being on the opposide side, as compared with those of groups II and IV. The same holds good for the groups in the embodiment of FIG. 5.

It is apparent from FIG. 1 that the components are arranged substantially horizontally. For condensation processes and for cooling liquids they are given a slight gradient towards the center of the cooling tower, in order to improve the drainage conditions for the condensate, or to make complete emptying feasible.

FIGS. 7 and 8 show a so-called wet-dry cooling tower also of circular design, which not only contains the roof-type exchange components 3 for dry heat exchange, the medium to be cooled flowing through the exchange tubes and being cooled by the cooling air flowing past, but also is fitted with a wet cooling part as well, which contains trickle plates 10. The water being cooled trickles down said plates 10 from top to bottom, while it is cooled by the rising cooling air. As is apparent in particular from FIG. 7, in this embodiment, rows of exchange components 3 and parallel trickle plates 10 suspended one behind the other are with the pertaining water distributing system and drip collectors arranged alternately side by side, so that sector-shaped wet and dry lanes or ducts are created which fill up the cross section of the tower. The exchange components 3 are formed and arranged in the same way as has been explained in conjunction with FIGS. 1 to 6.

It is, of course, to be understood that the present invention is, by no means, limited to the specific showing in the drawings, but also comprises any modifications within the scope of the appended claims.

Claims

What we claim is:

1. A cooling tower, especially for condensing vaporous media and for cooling liquid media, which includes: a mantle having a lower section provided with intake passage means for admitting a gaseous cooling medium into the interior of said mantle, said mantle also having an upper section provided with discharge means for discharging the heated up gaseous cooling medium after it has performed its cooling action, and a plurality of heat-exchanging elements distributed over the cross section of said cooling tower and located in radial arrangement at a level higher than the level of said intake passages and considerably closer to the latter than to said discharge means, said heat exchanging elements including roof-shaped bodies arranged along concentric circles and including tubes adapted to be connected to and to convey the medium to be cooled, the height of said heat exchanging elements decreasing in radial direction from the outer periphery of said cooling tower to the central axis thereof, said roof-shaped bodies having a gas-impermeable guide wall forming one surface and having a heat exchange wall of said tubes forming the other surface.

2. A cooling tower according to claim 1, in which the heat exchange wall comprises tubes provided with cooling fins between which a heat exchange medium may pass.

3. A cooling tower according to claim 1, in which the heat exchange wall comprises tubes having an outer smooth surface.

4. A cooling tower according to claim 1, in which said guide wall of each heat exchanging element forms the upper edge of the heat exchange wall to the base of the neighboring heat exchange element along the same circle.

5. A cooling tower according to claim 1, in which the height of the heat exchanging elements decreases in a continuous manner on a gradient from the outer periphery of the cooling tower towards the center.

6. A cooling tower according to claim 1, in which the height of the heat exchanging elements decreases in steps from the outer periphery of the cooling tower to the center thereof, the group of heat exchanging elements arranged along one and the same circle having the same height.

7. A cooling tower according to claim 1, in which the guide wall of said roof-shaped bodies is substantially vertical, and in which the heat exchange wall of said roof-shaped bodies is arranged at an angle with regard to the pertaining guide wall.

8. A cooling tower according to claim 1, in which the heat exchange wall of said roof-shaped bodies is arranged vertically, and in which the guide wall of said roof-shaped bodies is arranged at an incline with regard to the respective pertaining heat exchange wall.

9. A cooling tower according to claim 1, in which the guide wall of said roof-shaped bodies consists of any of the materials of the group consisting of sheet metal, asbestos, cement and plastic material.

10. A cooling tower according to claim 1, in which the heat exchange walls and the guide walls are along the radii of the cooling tower arranged on alternating sides so that the heat exchange walls and guide walls of the roof-shaped bodies arranged along the same circle are located on opposite sides.

11. A cooling tower according to claim 1, which includes supporting means for supporting said roof-shaped bodies, said supporting means respectively being arranged so as to support adjacent ends of roof-shaped bodies located along the respective radii of the cooling tower.

12. A cooling tower according to claim 1, according to which the heat exchanging elements extend over the entire cross-sectional area of the tower.

13. A cooling tower according to claim 1, which includes trickle units for wet cooling which are distributed over the cross section of the cooling tower and are arranged between at least one radially extending row of heat exchange elements so that sector-shaped portions of dry cooling heat exchange elements and trickle units alternately follow each other.