GB2157818A

GB2157818A - Drift eliminator for cooling tower

Info

Publication number: GB2157818A
Application number: GB08429149A
Authority: GB
Inventors: Paul Albert Frohwerk
Original assignee: Ceramic Cooling Tower Co
Current assignee: Ceramic Cooling Tower Co
Priority date: 1984-04-23
Filing date: 1984-11-19
Publication date: 1985-10-30
Also published as: GB8429149D0; IT8448780A0; IT8448780A1; GB2157818B; ZA845466B; AU3134684A; DE3429086A1; IT1179419B; FR2563330A1; NZ209149A

Abstract

A drift eliminator for a cooling tower comprises a plurality of spaced-apart parallel vanes (22). Each vane has a generally vertically extending lower portion (26), an inclined intermediate impact portion (27), and a generally vertically extending upper portion (28). In one specific embodiment the lower portion of each vane extends vertically, the intermediate portion forms an included angle (A) of 135 DEG with the lower portion, the upper portion forms an included angle (B) of 127.5 DEG with the intermediate portion and the lower portions of adjacent vanes are spaced from about 1 inch (25.4 mm) to about 1.5 inches (38.1 mm) apart. <IMAGE>

Description

SPECIFICATION Drift eliminator for cooling tower This invention relates to drift eliminators for cooling towers.

Examples of cooling towers are described in US Patent Nos. 4,422,983 and 4,382,046.

Cooling towers are used to cool liquid by contact with air. The liquid is allowed to flow downwardly through a heat and mass transfer section in the tower, and a countercurrent flow of air is drawn through the falling liquid by various means. A common application of liquid cooling towers is for cooling water (dissipating waste heat) used in electrical generating and process plant and industrial and institutional air conditioning systems.

The water is broken up into droplets in the heat and mass transfer section, and some of the water becomes entrained in the air. Accordingly, cooling towers conventionally include a drift eliminator through which the air passes before it leaves the tower in order to remove the droplets from the air.

Most drift eliminators for cooling towers are inertial impact separators. Such drift eliminators provide obstructions to the flow of air, and water which is carried by the air is carried by its inertia into contact with the obstructions.

Two conflicting considerations must be kept in mind when designing a drift eliminator-the amount of water loss or drift, and air resistance. Increasing the obstruction to air flow in order to increase water separation also increases the air resistance of the drift eliminator. The efficiency of a cooling tower is a function of the air resistance or pressure drop of the tower. Although the air flow through a tower with high air resistance could be increased by using a more powerful fan, this would result in increased equipment and energy cost. On the other hand, if the air resistance of the drift eliminator is reduced, the water loss will generally increase.

Many types of prior art drift eliminators have been used in cooling towers. Such drift eliminators commonly have a zig-zag or air foil configuration in which the air is forced to follow a zig-zag or curved path. In prior art drift eliminators the first portion of the air passage is generally inclined from the vertical or provides some resistance to upward air flow. It is believed that this resistance directs some of the air away from the air passage and increases the air resistance of the eliminator.

Also, it is believed that in some of the designs the streamlined flow of air forms eddies under high air speed in the vicinity of obstructions in the eliminator which interfere with the inertial impact of the water on the obstruction.

The invention provides a drift eliminator with improved drift efficiency and lower air resistance. The drift eliminator includes a plu rality of spaced-apart parallel vanes, each vane having a vertical lower portion, an intermediate or impact portion which extends at an angle of about 45 to the vertical, and an upper portion which extends substantially vertically. The vertical lower portions of the vanes channel the upwardly flowing air toward the impact portions, and the inclined impact portions provide a substantial impact area for the water. The upper portion provides another impact area and redirects the air so that it flows substantially vertically when it leaves the eliminator.

The invention will now be explained, by way of example, in conjunction with an illustrative embodiment with reference to the accompanying diagrammatic drawings, in which.

Figure 1 is a perspective view, partially broken away, of a cooling tower equipped with a drift eliminator in accordance with the invention.

Figure 2 is a perspective view, partially broken away, of a portion of the drift eliminator; Figure 3 is a side elevational view of a portion of the drift eliminator; Figure 4 is an enlarged side elevational view of one of the vanes of the drift eliminator, and Figure 5 is a fragmentary perspective view of one of the vane holders of the drift eliminator.

Fig. 1 illustrates a cooling tower 10 of the type described in US Patent No. 4,422,983.

The cooling tower includes a basin 11, a rectangular side wall 12, and a top 13. A heat and mass transfer section 14 is supported above the basin 11, and a water distribution assembly 1 5 is supported above the heat and mass transfer section 1 4. The water distribution assembly 1 5 includes a header pipe 1 6 and a plurality of lateral pipes 1 7 which extend from opposite sides of the header pipe 1 6. The lateral pipes 1 7 are equipped with spray nozzles or orifices for distributing the water over the heat and mass transfer section.

As described in US Patent Nos. 4,422,983 and 4,382,046, the preferred embodiment of heat and mass transfer section comprises layers of extruded clay tiles. As water flows downwardly through the tiles, air is drawn upwardly through the tiles by a fan 1 9 which is mounted in a fan opening in the roof.

A drift eliminator 20 is supported between the water distribution assembly 1 5 and the fan 1 9 to remove the water droplets and vapour from the air before the air leaves the cooling tower 10. In the embodiment illustrated, the drift eliminator is supported on top of the lateral pipes 17, but a separate support can be used if desired. The portion of the drift eliminator in the lower right portion of Fig. 1 has been removed to show the water distribu tion pipes and the heat and mass transfer section.

The drift eliminator 20 includes a plurality of vanes or blades 22 (Fig. 2) which are held in a fixed relationship by retainer rails 23 (Figs. 1 and 5) which extend transversely with respect to the vanes 22. Referring to Fig. 5, each retainer rail 23 is provided with slots 24 which have the same general shape as the vanes 22, and the vanes 22 are inserted into the slots 24 in the rails 23. The retainer rails 23 may be spaced about 2 feet (610 mm) apart.

Each of the vanes includes a vertically extending lower portion 26, an inclined impact portion 27, and an upper portion 28. In the preferred embodiment the impact portion 27 extends at an angle of 45 to the vertical, and the upper portion 28 extends at an angle of 7.5 to the vertical. The included angle A (Figs. 3 and 4) between the lower portion 26 and the impact portion 27 is therefore 135 , and the included angle B between the impact portion and the upper portion 28 is 127.5 .

The angle C between the upper portion and the vertical is 7.5 .

The spacing between adjacent vanes 22 and the dimensions of the vanes are such that the drift eliminator provides high drift efficiency and embodiment, the spacing D (Fig. 3) between the vertical lower portions of adjacent vanes is from about 1 to 1.5 inches (25.4 to 38.1 mm). The height E (Fig. 4) of each lower portion is 0.5 inch (1 2.7 mm), the horizontal component F of the length of the impact portion is 3 inches (76.2 mm), and the height G of the upper portion is 1 to 2 inches (25.4 to 50.8 mm). The length of the impact portion is F/cos (A-90"C) or 4.24 inches (107.8 mm). The maximum thickness T of each vane 22 should be no more than 0.05 inch (1.3 mm). The preferred material of the vanes is polyvinylchloride.

The retaining rails 23 hold the vanes in fixed positions so that the respective portions 26-28 of the vanes extend parallel to each other. As the air is drawn upwardly by the fan 1 9 and approaches the drift eliminator 20, the air flows into the vertical channels provided by the parallel lower portions 26 without any significant turbulence. The air is thendirected by the vertical channels toward the impact portions 27. The horizontal component F of each impact portion extends substantially beyond the width of the vertical channel and provides a substantial impact area for the water which is entrained in the air.

As the air flows upwardly between adjacent impact portions 27, the angled upper portions 28 provide additional impact areas. The upper portions 28 also serve the redirect the air so that the air is flowing substantially vertically and in the direction of the fan 1 9 when it leaves the drift eliminator 20. Although in the preferred embodiment the upper portions 28 are angled slightly beyond the vertical, i.e.

7.5 , the upper portions could also extend vertically without a significant decrease in drift efficiency.

The 1 to 1.5 inch (25.4 to 38.1 mm) spacing between the lower portions 26 of the vanes 22 optimizes the competing considerations of component economics, drift efficiency, and air resistance. If the spacing is increased to over 2 inches (50.8 mm), the drift becomes unacceptable but the air resistance remains about the same as for the 1 inch (25.4 mm) spacing. If the spacing is decreased below 1 inch (25.4 mm), the air resistance becomes unacceptably high.

While in the foregoing specification a detailed description of a specific embodiment of the invention has been set forth for the purpose of illustration, it will be understood that many of the details herein given may be varied considerably by those skilled in the art without departing from the scope of the

Claims

claims. CLAIMS

1. A drift eliminator for a cooling tower comprising a plurality of spaced-apart parallel vanes, each vane having a substantially vertical lower portion and an inclined portion extending angularly from the lower portion.

2. A drift eliminator according to Claim 1 in which each vane includes an upper portion which extends angularly from the inclined portion, the included angle between the upper portion and the inclined portion being less than the included angle between the lower portion and the inclined portion.

3. A drift eliminator according to Claim 1 or 2 in which each vane includes an upper portion which extends substantially vertically upwardly from the inclined portion.

4. A drift eliminator according to any one of Claims 1 to 3 in which the inclined portion of each vane extends at an angle of about 135 from the lower portion.

5. A drift eliminator according to any one of Claims 1 to 4, in which each vane includes an upper portion which extends at an angle of about 127.5 from the inclined portion.

6. A drift eliminator according to any one of Claims 1 to 5 in which the lower portions of adjacent vanes are spaced about 1 to 1.5 inches (25.4 to 38.1 mm) apart.

7. A drift eliminator according to any one of Claims 1 to 6, in which the lower portion of each vane has a height of about 1.5 inch (38.1 mm).

8. A drift eliminator according to any one of Claims 1 to 7 in which the length of the inclined portion of each vane is about 4.2 inches (106.7 mm).

9. A drift eliminator according to any one of Claims 1 to 8 in which the upper portion of each vane has a length of about 2 inches (50.8 mm).

10. A drift eliminator for a cooling tower constructed, arranged and adapted to operate substantially as herein described with reference to, and as shown in, the accompanying drawings.