STRUCTURE

TECHNICAL FIELD

The invention relates to an air cooling tower to serve heat dissipation from thermal power plants or industrial processes.

BACKGROUND ART

A number of air cooled towers exist including natural draft and different mechanical draft variants.

The natural draft towers need low auxiliary power and favorably small maintenance care. However, natural draft towers have relatively large footprint and a tall superstructure which is not only expensive (thus to be used mainly for larger capacities) but its construction may be restricted at sites with strict height limit.

Air cooled towers with mechanical draft can be either with forced or with induced draft fans. Most of these towers have rectangular arrangement what is advantageous for smaller or medium sized projects, whereas for larger capacities these arrangements have some drawbacks, too. One of these is warm air recirculation due to the limited level difference between the cooling air inlet and outlet. It can be especially harmful for towers with forced draft fans, where even the inlet air velocity enhances the warm air recirculation (i.e. higher inlet velocity paired with lower outlet velocity). In addition, forced draft fans are rather sensitive to wind from point of view of their performance as well as structurally.

DISCLOSURE OF THE INVENTION

It is an object of the invention to provide an air cooling tower which is free of disadvantages of prior art solutions to the greatest possible extent. It is a further object of the invention to provide a cooling tower characterized by efficient cooling, simple structure, easy maintenance, as well as reduced negative wind effect, auxiliary power requirement and noise emission.

The objects of the invention have been achieved by means of the cooling tower according to claim 1. Preferred embodiments of the invention are defined in the dependent claims.

BRIEF DESCRIPTION OF THE DRAWINGS

Fig. 1 is a partly sectional view of a circular air cooling tower with dual draft, where the diameter of the tower is smaller than that of the circle around which the cooling deltas are arranged;

Fig. 2 is a top view of a circular air cooling tower with dual draft, where the tower structure and the circle of cooling deltas (cooling delta frame structure) have the same diameter;

Fig. 3 is a sectional view along plane B-B of Fig. 2;

Fig. 4 is a schematic view of an arrangement of cooling deltas and fans; and

Fig. 5 is a diagram showing a sectional arrangement of cooling deltas, louvers and an electric preheater net.

MODES FOR CARRYING OUT THE INVENTION

A joint mechanical and natural draft air cooled tower having a circular or polygonal shape tower structure is suggested, i.e. its footprint is circular or polygonal (preferably close to the circular). Air coolers are located vertically around a lower circumferential part of the tower structure, preferably along the basic circumference of the cooling tower.

The erection units of the air coolers are the so-called cooling deltas. A cooling delta comprises of two cooling panels put into a rigid steel framework with an angle. The triangular shape (i.e. delta shape) cross section of the frame ensures an angle (about 60°-50°) between the two air cooler panels and the third side is open for cooling air inlet, or equipped with louvers.

To provide the mechanical draft (in summer it is the major part), induced draft fans are applied arranged in the vertical plane, i.e. with horizontal axes. That is, fans suction ambient air through the air cooler panels and blow the warmed-up air into the inside of the tower shell. Depending on the vertical length of the cooling deltas the fans can be arranged only in a single row or in several rows above each other. A further opportunity is not to cover with fan draft the whole lengths of the cooling deltas especially in areas without extreme warm ambient air temperatures as well as if the tower structure is tall enough boosting air draft. In such a case if at cooling water side 2-pass air coolers are applied (i.e. cross counter-flow connection), e.g. instead of two rows of fans only one row can be applied for the lower half of the cooling deltas. Then for the upper half of the air coolers cooling air flow is induced solely by natural draft.

Fans and their casing are also supported by the steel frame structure of the cooling deltas. Cooling deltas are supported - via their steel frame structure - by delta legs at three points, in line with the triangular shape of the delta. Up to the level where the air cooler surface starts the delta legs have a cover to avoid cooling air bypassing the heat exchanger surface.

The basically circular shape tower structure may be either of reinforced concrete or of structural steel with covering. Since it is only for boosting cooling air flow in addition to mechanical draft, its height is preferably only 2-4 times of the cooling delta length, thus remaining well behind the height of usual natural draft towers. At least 2 times of the cooling delta height is necessary for the tower structure to be able to produce considerable natural draft. The diameter of the circle around which the vertical cooling deltas are arranged is usually larger than that of the tower structure above the top of cooling deltas. Then the tower structure has its own separate legs and supports and there is a widening cover between the tower structure and the top of cooling deltas. However, in case of structural steel towers an especially advantageous arrangement can be realized if the tower structure diameter and that of the circle around which the cooling deltas located are identical or correspond to each other. It gives an opportunity to use cooling deltas steel frames, i.e. the cooling delta frame structure and its supporting legs to be applied at the same time to support the whole tower structure, which results in a major reduction in both the required material and the construction costs.

As it has been mentioned for areas of freezing danger, the air inlet side of the cooling deltas may have outside louvers. For very cold winter areas, in addition to the cooling delta inlet side further louvers may be applied between the inward edges of neighboring cooling deltas (i.e. inside louvers at the warm air outlet sides). At extreme cold sites to avoid freezing danger, there may be an electric heater, preferably a heater net, between the inlet louvers and the cooling deltas. The heater is operative only during start-up at such extreme climates.

A potential advantageous embodiment of the invention is shown in Fig. 1 . Cooling deltas 1 - each comprising two air cooler panels - are arranged vertically around a basically circular shape tower structure 2 of the cooling tower 3. The tower structure 2 is made of concrete or steel structure with a surface covering 6. A widening cover 13 is applied between the tower structure and the cooling deltas 1. The height of the tower structure 2 is at least 2 times, preferably about 2-4 times that of the cooling deltas 1. Since the natural draft induced by such tower height is not enough for efficient air cooling, also mechanical draft shall be used. Fans 4 are located in the vertical plane, suctioning cooling air 5 through the cooling deltas 1 and blowing it inside the air cooling tower 3.

Fig. 2 and its section B-B shown in Fig. 3 show a similar though even more advantageous embodiment of the invention. The tower structure 2 is a near cylindrical shape steel frame with a surface covering 6 at ambient air side. The specialty of the arrangement in Fig. 2 and Fig. 3 is that the cooling deltas 1 , thus also their frames are arranged practically on the same diameter as of the tower structure 2. Therefore, the cooling delta frame structure 7 acts in addition as the support and elongation of the tower structure 2. Accordingly, cooling delta legs 8 also serve as supporting legs for the complete cooling tower 3.

Fig. 4 shows the relative arrangement of the cooling deltas 1 and the fans 4. Elements of the cooling delta frame structure 7 (known per se) are also schematically depicted. Independently of the type of tower structure, the relative positon and arrangement of the cooling deltas 1 and the induced draft fans 4 are similar for both towers shown in Fig. 1 and Fig. 2. However in Fig. 2 relatively long cooling deltas 1 are applied which may justify the application of fans 4 in three rows positioned in the vertical plane above each other.

In both cases of Fig. 1 and Fig. 2, if the tower structure is relatively high, there is an opportunity to cover only the lower part of the whole length of cooling deltas 1 with fan draft, thus applying only a single row of them instead of two (as in Fig.1 ) or three (as in Fig. 2 and Fig. 3). In these cases the cooling air 5 flow streaming through the remaining cooling delta surface is induced only by natural draft.

In most of the cases - as it is a usual solution - inlet, i.e. outside louvers 9 are equipped for controlling (modulating, closing or opening) the stream of the cooling air 5. The exception is if at the cooling tower 3 site there is no freezing danger. However, in areas of extreme cold winter, to avoid possible freezing especially during start-up, as shown by Fig. 5 not only outside louvers 9 may be applied but additional inside louvers 10 as well. In addition to applying duplicated louvers, between the outside louvers 9 and the air cooler surface - i.e. the cooling panels 11 - an electrical heater 12, preferably electrical heater nets are located, which are activated during the start-up procedure in the coldest period.

Hereunder some of the advantageous features of the inventive arrangement of structures and equipment are highlighted again.

- Besides using fans, applying a moderately tall tower structure reduces the auxiliary power requirement (in cold weather the fans even can be stopped) and warm air exhausted at the elevated level of tower height makes avoidable the warm air recirculation to the air coolers.

- The duplicated source of draft improves availability and reliability.

- Location of fans within the tower and relative to air coolers:

- reduces negative wind effect on cooling tower performance originating from fan static pressure head loss; - protects fans and their driving from wind and wind gusts induced dynamic forces (what is the most frequent cause of mechanical failures);

- reduces noise emission: at air inlet side due to the sound absorbing effect of air cooler panels and their delta from arrangement, and at air outlet due to the elevated exhaust level.

- When the tower structure has the same diameter as on which the cooling deltas are arranged, it can be supported by the delta frames - resulting in a measurable reduction of the structural costs.

The invention also relates to embodiments comprising any combination of the introduced solutions and features. It shall be mentioned that the embodiments of the suggested inventive arrangement are not limited to those described herein. Thus the invention is not limited to the preferred embodiments described in details above, but further variants, combinations, modifications and developments are possible within the scope determined by the claims.