Drift Eliminators For Atmospheric Cooling Tower

Abstract

To reduce or eliminate droplet formation in the plume issuing from a cooling tower, a layer of finned tubes is provided to heat the moist air prior to its issuance from the tower. The fins have a shape similar to conventional drift eliminator blades and thus the blades, at the same time, function to eliminate droplets from the gas stream. In addition, the above-mentioned tubes can be fitted with vertical outlet tubes or nozzles such that the finned tubes fulfill the following functions: Collect the water droplets contained in the air leaving the cooling tower; Warm up the air leaving the tower; and Distribute the water to be cooled in the cooling tower, over the heat transfer section.

Description

This invention relates to drift eliminators for cooling towers. In general, a cooling tower is a device wherein an exchange of heat takes place between a liquid such as water from a power plant installation and atmospheric air. This liquid is allowed to play or drip down from a plurality of nozzles or other outlet means through a heat exchange grid within the cooling tower. The cooling towers may be of a considerable vertical extent and are defined by criss-crossed, for example, wooden boards, slats, or the like, which define a plurality of contact surfaces to interrupt and deflect the falling liquid and to bring about intimate contact between the liquid and the cooling gas stream, generally air. The cooling tower may be of the natural or of the induced draft type. In an induced draft type, the hot water generally enters from the top of the cooling tower and by the time it reaches the bottom has experienced an appreciable temperature drop. The air as it exits from the cooling tower will be at a higher temperature than the air which enters the cooling tower because of the heat exchange with the warm liquid.

The atmospheric natural draft or mechanical draft cooling towers offer the drawback of giving generally a vapor plume at the outlet of the hot air, which causes drizzle precipitation of droplets in the neighborhood of the tower. Such precipitation is not desirable for a variety of reasons; for example, droplets of water may freeze on nearby roads in the winter thus creating a safety hazard. Further, atmospheric pollution due to the precipitating droplets collecting smoke and other impurities may take place.

Conventional drift eliminators normally provided in atmospheric cooling towers above the heat transfer packing in the tower only partially avoid the above-mentioned drawbacks. The failure of conventional drift eliminators is primarily due to the fact that the air issuing from the tower is saturated or close to its saturation point and mixing of the warm saturated gas with the cooler ambient atmosphere induces condensation and super-saturation of the air in the vicinity of the gas distributed from the cooling tower.

Conventional drift eliminators are generally constructed of metal, plastic or asbestos cement and the blades or fins thereof are shaped to cause a baffling of the air passing therebetween. The baffling of the air often results in the failure of the fins or blades to remove the smallest airborne droplets constituting the fog or mist leaving the tower.

The present invention is directed to drift eliminators generally consisting of one or more layers of metallic finned tubes, with the fins being arranged similarly to the arrangement of fins in conventional drift eliminators. The tubes associated with the fins are fed by heated water directed to the cooling tower. The heated fluid directed to the finned tubes is afterwards distributed by the conventional hot water distribution system for the tower. Heat transmitted by the finned tubes from the heated water to the air passing through the tower increases the air's temperature without increasing its actual vapor content. The forgoing results in a decrease in the relative humidity of the air issuing from the tower and consequently a substantial reduction or the complete elimination of condensation of vapor at the outlet of the tower or in the vicinity thereof. These favorable conditions are also brought about by the fact that droplets of liquid which may not be eliminated by the shaped fins of the drift eliminator are evaporated by the warmed air in which the relative humidity has been reduced by the heated water. Condensation nucluii formed by liquid droplets which would normally issue from conventional atmospheric cooling towers are thus eliminated or substantially reduced.

In general, all of the heated water to be cooled is fed to the finned tubes of the invention and after passing through the tubes the water is directed to the normal water distribution system of the cooling tower.

It is contemplated, however, that only a part of the hot water flow to the tower may be directed to the finned tubes and after flowing therethrough the water may be combined with the hot water being directed to the normal distribution system of the cooling tower.

A third situation may comprise passing a heated liquid, which is at a temperature higher than the normal temperature of the air passing from the tower, to the drift eliminator tubes in order to heat the air and cool the liquid without direct contact between the liquid and the atmosphere.

Further, the fluid directed to the finned tubes may comprise a vapor which is condensed in the drift eliminator tubes.

The heated liquid or the vapor referred to above may be entirely independent of the water to be cooled in the cooling tower.

The present invention may also comprise at least one layer of horizontal finned tubes with each of the tubes being provided with a series of downwardly directed bores or holes within which are secured liquid distribution nozzles. With this form of construction the system accomplishes the following:

removal of liquid droplets suspended in the air leaving the cooling tower;

the distrbution of water to be cooled over the packing of the cooling tower; and distribution

the reduction of the relative humidity of the air leaving the cooling tower .

The invention will be more particularly described in reference to the accompanying drawing wherein:

FIG. 1 is an elevational cross-section of a typical forced draft cooling tower containing apparatus constructed in accordance with the present invention.

FIG. 2 is a view of a typical prior art drift eliminator blade construction.

FIG. 3 is a view of such a device modified to include the vapor plume reducer according to the practice of this invention.

FIG. 4 is a perspective view of a portion of the vapor plume reducing means illustrated in FIG. 3.

FIGS. 5, 6, 7 and 8 are cross-sectional views of embodiments similar to that shown in FIG. 3.

FIG. 9 is a perspective view of a further modification of the present invention.

Referring now to FIG. 1 of the drawing, 10 generally denotes a cooling tower of the type often employed in conjunction with air-conditioning systems and includes vertical walls 12 which rise above the base 13. A plurality of apertures 14 are provided in the lower portion of the walls 12 for the intake of atmospheric air. At the upper end of the tower 10 is a warm, moist air exit shroud 16, which ideally is of a Venturii type construction and adjacent the throat of the Venturii is mounted an air moving fan means 18 connected to a suitable electric motor 20 via shaft 22 and speed reducing gear means 24, which gear means is supported from a spider 26 mounted in the upper end of the tower.

Below the spider 26 and adjacent the exit orifice 16 is mounted the improved vapor plume reducer 28 constructed in accordance with the present invention as to be more fully described in reference to FIGS. 3 through 8 of the drawing.

Below the vapor plume eliminator 28 are a plurality of headers 30, each of which is provided with nozzled outlets 32 whereby the liquid to be cooled is uniformly distributed downwardly onto an array of vertically stacked, lathed, frame elements generally designated 34, which in turn are supported by cross-beam members 36, as more fully described in U.S. Pat. application, Ser. No. 771,513, filed Oct. 29, 1968 for "Cooling Tower," A.A.A. Lemmens.

Adjacent the bottom of the tower means 31 are provided to remove the cooled liquid such as water from the tower.

FIG. 2 shows one of the more frequent realizations of conventional drift eliminators. These drift eliminators 50 are made of a series of blades 52 parallel-arranged at a short distance one from the other and having such a shape that most of the droplets contained in the air are collected because of its sinuous flow pattern between those blades. The elements 54 are used to join the blades together by maintaining them parallel and at a short distance one from the other.

Referring to FIGS. 3 and 4, one form of the system of the present invention is illustrated, which system consists of a plurality of metallic blades 58 through which pass the tubes 56. The tubes 56 are fed by water entering the cooling tower or by an independent hot water flow via, for example, header tube 60, illustrated in FIG. 1 of the drawing. The fins 58 are intimately joined to the tubes 56 and the assembly may be constructed, as is well known in the art, by, for example, welding or force fitting the fins to the tubes.

The specific shape of the fins is not critical and the fins and tubes may be shaped as illustrated at 56 and 58' of FIG. 5; 56 and 58" of FIG. 6; 56 and 59 of FIG. 7; or 56 and 59' of FIG. 8.

Referring specifically to FIG. 8, this form of the invention offers the advantage of a substantially better heat transfer between the water flowing through the tubes 56 and the air passing about the fins as the upper portion of the fins remains free or substantially free of water droplets.

Referring specifically to FIG. 9, there is shown one of the possible arrangements wherein the system fulfills simultaneously all of the preferred functions, heretofore set forth; that is, the retention of droplets contained in the air leaving the tower, the reduction of the relative humidity of air, and finally, the distribution of water to be cooled over the filling of the tower.

Referring now to this FIG. 9 of the drawing, the numeral 70 denotes generally a bank of parallel heat transfer finned tubes wherein each individual fin element is denoted by the numeral 72 and each tube is designated 74. Each tube or tube segment 74 is in turn provided with downwardly depending tubes 76. The arrows coming in from the right of the drawing illustrate hot water which is fed to the cooling tower for treatment, which water heats the fins 72 as described above and, in the present embodiment, the water is then released from the tubes 74 through the outlet tubes 76 and falls or flows downwardly onto the packing of the cooling tower for conventional treatment.

Where desired a plurality of layers of finned tubes constructed in accordance with the present invention may be arranged one above the other adjacent the exit of a cooling tower. The tubes of each of the layers may be connected to the same source or to different sources of heating fluid and the flow circuit for the fluid may be arranged in parallel, in series, or series parallel flow.

It is also contemplated that the finned tubes or mist eliminator of the invention may be employed in conjunction with conventional mist eliminators in stacked arrangement or the finned tube mist eliminator of the invention may cover only a portion of the cross-sectional area of the tower with the remaining area being fitted with conventional mist eliminators.

It will also be apparent that when a plurality of stacked eliminators are employed only the lowermost layer would be provided with outlet tubes such as illustrated in FIG. 9 and further that where outlet tubes or nozzles are employed, as illustrated in FIG. 9, the nozzles or outlets of the tubes have a length such that the liquid issuing therefrom does not impinge on the fins or eliminator blades.

Claims

I claim:

1. An atmospheric cooling tower comprising side walls provided with an air inlet means for atmospheric air and having a top outlet means for the exit of heated outlet air, gas liquid contact means within the tower intermediate the air inlet means and the air outlet means, a plurality of heat exchange tubes arranged in a generally horizontal layer transversely within the tower above said contact means, a plurality of metallic fins mounted on the tubes in heat exchange relation therewith, said fins being in generally parallel relation and being nonplanar and defining a series of tortuous vertical flow paths for the heat exchange flow of the outlet air over the tubes, means provided at the ends of the tubes for passing through said tubes a heated liquid with the outlet air passing from the contact means through the flow paths so as to reduce liquid droplets suspended in the outlet air existing through the outlet means and to reduce the relative humidity of said outlet air, and said tubes having depending outlet nozzles for directing the heated liquid therein onto the contact means within the cooling tower.

2. The invention of claim 1 wherein the fins are spaced apart and define zig-zag air flow passages.

3. The invention of claim 1 wherein the fins have upper end portions through which the tubes pass so that the major portions of the fins depend from the tubes.

4. The invention of claim 1 wherein the means at one of the ends of the tubes is an outlet header means and is in fluid communication with the water supply system for the tower.

5. The invention of claim 1 wherein the means at one of the ends of the tubes is an inlet header means and is in communication with a source of heated liquid.