US3260511A - Water cooling towers - Google Patents

Description

July 12, 1966 K. R. GREER 3,250,511

WATER COOLING TOWERS Filed July 20, 1962 4 Sheets$heet 1 Kan/r PEA/wry 6e55,?

July 12, 1966 Filed July 20, 1962 K. R. GREER 3,260,511

WATER COOLING TOWERS 4 Sheets-Sheet 2 FIG. 2a.

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July 12, 1966 K. R. GREER 3,260,511

WATER COOLING TOWERS Filed July 20, 1962 4 Sheets-Sheet 5 July 12, 1966 K. R. GREER 3,260,511

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//VI/E/l/7 0A A/E/VT FEAA EY GREE United States Patent 3,260,511 WATER COOLING TGWERS Kent Reaney Greer, Marple Bridge, England, assignor to Imperial Chemical Industries Limited, London, England, a corporation of Great Britain Filed July 20, 1962, Ser. No. 211,377 4 Claims. (Cl. 261-412) This invention relates to improvements in cooling towers and more particularly to improved film-flow packings within the towers.

There are many different types of cooling tower but they can be divided broadly into two main types; the atmospheric open type in which the water is sprayed over a structure open to the atmosphere and the chimney type in which the cooling is carried out within an enclosed space, the cooling medium being supplied by induced or forced draught. The draught may be horizontal or vertical. Cooling hot water is normally carried out by allowing the water to pass downwards in such a manner as to present a large surface area to contact with a counteror crosscurrent of a cold fluid, usually air. The air may enter at the bottom of the tower for counter-current cooling or may be caused to enter the side of the tower when cross-current cooling is preferred.

It is apparent that the greater the surface area of a given body of water presented to the cold air, the more efficient will be the cooling of the water, and the attainment of large surface area-to-volume ratios for the water has been achieved in different ways. In early forms the water was sprayed on to a system of closely spaced laths and slats inclined to the vertical and placed below the point of distribution of the water and within an uprising current or cross-current of cold air; the water ran down the inclined surfaces of one set of laths and dripped on to another set which was placed in spaced relationship below the first set and this process was repeated down the tower. The system is known as droplet cooling. Recently larger surface areas per unit volume of Water have been attained by causing the water to flow downwards as a film over continuous supporting surfaces thus presenting a very large surface area to the current of cooling air.

For this second and improved method of water cooling known as film-flow cooling it is clear that the greater the surface area available to act as a support for the water film within a given space, the more eflicient will be the cooling. Hitherto, conventional film-flow packings have been constructed from wood, from asbestos or, more recently, from expanded plastic materials. Other film-flow packings have been constructed from plastic materials which have been extrusion or injection moulded in the form of grids. The packings fabricated from wood, expanded plastic material and to a certain extent asbestos are made normally from rather thick materials in order to maintain, rigidity, and thicknesses of the order of 0.375 inch are generally used. The thickness of the material necessarily places a limit on the maximum film supporting area obtainable in any given space.

It is an object of the present invention to provide a film flow packing which presents a large surface area per unit space occupied by the packing.

According to one object of the present invention, we provide packings for cooling towers which are formed from at least one unit having a structure which comprises a stack of alternate flat and corrugated sheets of rigid thermoplastic organic polymeric material held together and arranged such that the points or lines of contact of a corrugated sheet with one side of a flat sheet are curvilinear and coincident with the points or lines of contact with the flat sheet of the corrugated sheet on the other side of that same flat sheet.

Patented July 12, 1966 ice By rigid thermopastic organic polymeric material, we mean any thermoplastic organic polymeric material having a Youngs modulus of the order of 10 lbs./ sq. in. or

more.

In order that the invention may be more clearly understood a preferred embodiment will now be described with the aid of the accompanying drawings in which FIG- URE 1 represents a typical structural unit according to our invention, FIGURES 2a, 2b, 3a and 3b show various means of connecting the separate-units of the structure and FIGURE 4 represents a structural unit according to a modification of the invention.

In our specified structure, there are two basic construction units, the flat sheet and the corrugated sheet and in FIGURE 1, illustrating our preferred embodiment in which the sheets are formed from a vinyl chloride polymer, preferably a copolymer of vinyl chloride and vinyl acetate, it can be seen that we prefer the corrugated sheets (la, 1b and 10) to have a V-shaped cross section with an angle of corrugation of since then our structure has the cross-sectional form of an isosceles triangle, which section gives the structure good rigidity combined with a high surface area for the space occupied.

In our preferred embodiment, the isosceles triangle has a side length of 1.5" but this is by no means critical. The thickness of the Hat and corrugated sheets may be chosen within a wide range of limits which depends mainly on the type of thermoplastic material being used and the service conditions. On the whole, we have found that in our preferred construction using sheet formed from the copolymer of vinyl chloride and vinyl acetate, the use of a sheet thickness of the order of from 0.01" to 0.03" gives rigid structures capable of spanning the distances likely to be encountered in the common run of water cooling towers.

The corrugated sheets and the flat sheets may be held together by any usual means such as for example pinning, cementing or high-frequency welding. They may also be held together by clamps or other similar devices. FIG- URE 3a shows how the structure may be held together by a press stud 2 moulded or otherwise formed on the peak of one corrugated sheet engaging with a corresponding hole 4 formed in a peak of an adjacent corrugated sheet, intermediately passing through a hole 3 punched or otherwise formed in the intermediate fiat sheet. In order that the studs may be held firmly, we prefer that at least part of the stud towards the extremity thereof should have a larger diameter than the remainder of the stud. This can be achieved for example by making the studs frusto-conical in shape with the larger diameter at their butt ends or else as shown in FIGURE 3a with the butt end 5 having alarger diameter than the stud itself. The holes may have some means of allowing them to distend partially when accepting the butt ends of the studs such as for example one or more slits 6 extending radially outwards from the circumference of the holes, as shown in the diagram in FIGURE 3b. We prefer the holes to have two diametrically opposed slits extending radially outwards from the circumference of the holes. Thus the sheets may be rigidly held together by a series of these press studs mounted at convenient intervals along the peaks of the corrugated sheets. The intervals should be sufficient- 1y short to maintain dimensional rigidity in the structure.

FIGURE 20 shows another method of building the structure whereby a stud 7 formed on the peak of one corrugated sheet is threaded through a corresponding hole 8 in the flat sheet and is cemented to a recessed butt 9 formed on the peak of adjacent corrugated sheet facing the said flat sheet. Any suitable adhesive may be used but the final choice will depend on the thermoplastic material being used for the structure.

In our preferred example sheets measuring 72 inches by 18 inches were used to build up a structure with final dimensions of approximately 72 inches by 18 inches by 18 inches. A structure of about this size is preferred because it is of convenient size and will not be too heavy to be handled by one man. However, other considerations such as for example distances between supports for the structure may well lead to the use of structures of much larger or smaller size.

Examples of rigid thermoplastic organic polymeric materials which may 'be used include polyvinyl chloride, polymethyl methacrylate, polypropylene, polythene, polyvinylidene chloride, copolymers of vinyl chloride and vinyl acetate, polystyrene, oxymethylene polymers, rubber/resin compositions (e.g. mixtures of butadiene/acrylonitrile copolymer rubbers and styrene/acrylonitrile resins) and polyesters such as polyethylene terephthalate.

The fiat and corrugated sheets may be fabricated from a single thickness of one of these materials or they may be formed from a plurality of layers of these materials which may be of different thicknesses, if desired.

Although in our preferred embodiment we prefer to use corrugated material of which the corrugations are V shaped in cross-section, our invention includes equally the use of corrugations of any cross-section whether it be straight sided or in the form of a continuous curve or in any intermediate form. However, when corrugations with a substantially curved cross-section are used, there is a likelihood of loss of rigidity in the structure. Similarly, the angle of 60 for the angle of corrugation mentioned in our preferred embodiment is not exclusive. Any corrugation angle may equally well be used in our invention, but the use of an angle of 60 combined with a V shaped cross-section provides a structure with the optimum combination of rigidity and available surface area for the space occupied and the use of other angles will result either in loss of rigidity or in loss of available surface area.

The distance between adjacent peaks on the corrugated sheet is not critical and any distance may be chosen However, it is apparent that as this distance is increased, the available surface area of the resultant structure for any given space occupied will be reduced and as the distance is decreased, more material per unit space will be required with consequent increase in cost and weight of the structure. We have found that our preferred dimension of 1.5" results in a most useful combination of these variables. However, in many cases a larger dimension is preferred, for example for reasons of economy or weight or in order to reduce the surface area to volume ratio. In such cases there is a danger that, when our specified packings are used in counter-flow cooling towers (where they will normally be stood with the corrugations vertical and where the liquid is normally distributed from above), drops of liquid may descend freely some considerable dis tance without touching the surfaces of the structure which will substantially all be in the vertical plane. In order to obviate this, it is desirable to present the packings so that at least some of the surfaces are not entirely in the vertical plane and may therefore interrupt the downward path of the liquid drops. This may be accomplished simply by canting the packings at a small angle from the vertical (for example, up to about 30) but this may entail difficult or expensive structural modifications to the supporting skeleton in the cooling tower. Another way is to so form our packings that while the packings as a whole may stand squarely on the supporting structure the corrugations of the corrugated sheets within the packings are at an angle (e.g. of up to about 30) from the vertical in the plane of the packings, and thus present inclined surfaces intercepting the paths of the liquid droplets distributed from above. Yet a further modification which achieves the desired object is to use modified packings according to the invention in which the corrugated sheets used in the packing are so formed that the corrugations describe a non-linear, preferably curvilinear and, more preferably, sinusoidal or substantially sinusoidal, path in the plane of the sheet.

We prefer to use curvilinear corrugations as they are relatively easy to manufacture and of these those with sinusoidal or substantially sinusoidal corrugations are most preferred because of their ease of manufacture.

A representation of a packing according to this modification of the invention is shown in FIGURE 4 of the drawings.

In many types of cooling tower, a cross-draught is used as the cooling means. In these forms, the liquid to be cooled is normally distributed on the top of the structure through which a horizontal or substantially horizontal draught of cooling fluid is blown. Where our structures are to be used in this form of cooling tower, it is preferred that they are stacked with the corrugations horizontal so that the draught passes through the tubes of the elongated honeycomb structure so formed. The flat sheets of the structure sould of course still be kept vertical in this case.

When this horizontal arrangement of the corrugations is used, the corrugated and flat sheets in the structure should be spaced laterally one from the other in order that water distributed upon the top of the structure may be able to penetrate to the bottom. Where the structures are built up by use of the system of studs and recessed butts as shown in FIGURE 2a for example, the spacing may be caused by forming collars on the studs and extensions 10 to the recessed butts of the corrugated sheets (as shown in FIGURE 2b) so that in effect when the structure is assembled using this means of attachment, there is a spacing of the fiat sheets from the peaks of the adjacent corrugated sheets. Other means of forming the gap (such as the use of spacers) will be apparent and the gap so formed should be of a width sufficient to allow a film of water to flow freely down both sides of both the corrugated and flat sheets. A spacing of the order of 0.0625 inch is appropriate. Spacings of less than about this size are likely to be insufficient to allow the free flow of the liquid to be cooled while larger gaps merely create a wastage of space. 7

When the flow of cooling fluid, normally air, is across the direction of flow of the water, there Will be a tendency for the water flow to be deflected from the perpendicular path and in the direction of the air flow. This would render the part of the structure nearest to the source of air inoperative and also cause an unwanted concentration of water at the side remote from the source of air, and in order to obviate this some means of counteracting this effect is preferably incorporated in the structure. For example, baffles in the shape of small ribs may be formed on the corrugated portions and/or the flat portions, of the structure at a slight angle to the vertical so that in effect the water flow would normally be deflected by them in the direction opposite to that imposed by the cross draught. By adjusting the frequency of these deflectors and their angle, it may be possible to substantially counteract this undesired effect of the cross draught.

Again, when using this packing with the corrugations horizontal it is advisable to remove half of the Width of the topmost face of the top corrugated section of each corrugated sheet so that the water being distributed from above may be distributed on to'both sides of the corrugations equally; and it is a further advantage to fit a tray across the top of the structure having outlets formed in its base to coincide with the desired water receiving areas on the top of the structure. This Will ensure efficient distribution of the water and at the same time will obviate the necessity of using :a complicated spray distribution system. The trays may also be of plastic material if desired or may be Qf WQQCL metal or other suitable material.

Our specified structures may be used'as individual units or stacked in nests and may be held in a skeletal supporting framework within the walls of the tower. They may be sawn to shape to fit in angles or to coincide with curved shapes such as for example the inside surface of the wall of a conventional hyperboloidally shaped counter-draught cooling tower of circular or substantially circular cross-section. Our structures may also be used in the construction of spray eliminators at the top of counter-draught type cooling towers.

Since our structures are built from rigid thermoplastic materials as hereinbefore defined, they still maintain their rigidity when the thickness of the material used is much less than when wood or asbestos is the construction material and in consequence our structures provide a film-flow packing with an available surface area per space occupied considerably greater than a similar packing made from such materials. Also, the structure itself is considerably lighter than the said counterparts of similar size while still maintaining rigidity and strength and, since the packing can be built up from individual unts, the upkeep and maintenance of the packing is considerably facilitated as the individual units may be replaced with ease. The packing is very corrosion-resistant and does not rot as in the case of timber. In addition, due to its corrosion-resistant properties, packings of this type may be used for cooling corrosive liquors.

I claim:

1. A packing uni-t for the treatment of liquids which are allowed to flow as a film over the surfaces in the packing comprising: a stack of alternate flat and corrugated sheets of rigid thermoplastic organic polymeric material, the corrugated sheet on one side of a given flat sheet having studs integrally molded on the peaks of the corrugations closest to said given flat sheet and the corrugated sheet on the other side of said given flat sheet having recessed butts integrally molded on the peaks closest to said given fiat sheet, said given fiat sheet having apertures permitting passage therethrough of said studs, all said sheets in said unit being arranged in overlying relationship with said studs passing through said apertures and beng connected to said recessed butts.

2. A packing unit according to claim 1 in which said studs are cemented in said recessed butts.

3. A packing unit according to claim 1 in which the alternate flat and corrugated sheets are spaced laterally from one another and in which the flat sheets are in vertical planes and the peaks of adjacent corrugated sheets are in horizontal planes.

4. A packing unit according to claim 3 in which the spacing between the flat sheets and the peaks of the adjacent corrugated sheets is of the order of 0.0625 inch.

References Cited by the Examiner UNITED STATES PATENTS 77,859 5/1868 Allerton 16154 1,324,982 12/1919 Rogers. 2,471,612 5/1949 Freeman 161114 X 2,485,849 10/ 1949 Simmons. 2,538,396 1/1951 Sutin 24216 X 2,709,290 5/1955 Rosenthal 24216 X 2,837,788 6/1958 Mazzocco 16153 X 2,986,379 5/1961 Kramig 261l12 3,013,781 12/1961 Haselden 261-112 3,084,918 4/ 1963 Kohl et a1. 3,160,131 12/1964 George et a1.

FOREIGN PATENTS 776,649 11/ 1934 France. 160,228 3/ 1921 Great Britain.

HARRY B. THORNTON, Primary Examiner.

RONALD R. WEAVER, Examiner.

D. M. RIESS, Assistant Examiner.

Claims (1)

1. A PACKING UNIT FOR THE TREATMENT OF LIQUIDS WHICH ARE ALLOWED TO FLOW AS A FILM OVER THE SURFACES IN THE PACKING COMPRISING: A STACK OF ALTERNATE FLAT AND CORRUGATED SHEETS OF RIGID THERMOPLASTIC ORGANIC POLYMERIC MATERIAL, THE CORRUGATED SHEET ON ONE SIDE OF A GIVEN FLAT SHEET HAVING STUDS INTEGRALLY MOLDED ON THE PEAKS OF THE CORRUGATIONS CLOSEST TO SAID GIVEN FLAT SHEET AND THE CORRUGATED SHEET ON THE OTHER SIDE OF SAID GIVEN FLAT SHEET HAVING RECESSED BUTTS INTEGRALLY MOLDED ON THE PEAKS CLOSEST TO SAID GIVEN FLAT SHEET, SAID GIVEN FLAT SHEET HAVING APERTURES PERMITTING PASSAGE THERETHROUGH OF SAID STUDS, ALL SAID SHEETS IN SAID UNIT BEING ARRANGED IN OVERLYING RELATIONSHIP WITH SAID STUDS PASSING THROUGH SAID APERTURES AND BEING CONNECTED TO SAID RECESSED BUTTS.

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