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Cooling tower is required in industries to cool the water for its reuse/recirculation. It consists of various components like Fill media, Drift eliminator, and mechanical components like fan motor and gear. Drift eliminator does not directly take part in cooling the water, but has indirect effect due to its pressure drop component. Thus the prime role of drift eliminator, i,e entrapping drift, is not given due importance.
Drift is the loss of water (water treatment chemicals dissolved in it) from the cooling tower along with the velocity of the air. This water is in the form of droplets and these could be trapped by economic methods of impingement separators. The basic purpose of a drift eliminator was to control the undesirable loss of water, to reduce the damage to mechanical components and to reduce the nuisance caused to equipment in surrounding due to spray. A drift loss in the range of 0.05 % of the circulating water flow was considered to sufficient low and acceptable.
In past three decades, number of industries increased multifold and these being localised lead to a situation where availability of resources became limited. One of the most abundant and cheap resources i.e water also got scare is now available limited. Limited availability of water and possibility of making efficient designs of drift eliminator from PVC enabled the industry to reduce the water loss to radically low values of 0.005 to 0.001%.
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Saving in makeup Water requirement |
Commonly available designs of eliminator have drift loss of 0.05% of circulating water. Whereas, improved PVC design with hook on top can meet requirements of 0.001% of drift loss.Thus water saved is 0.05-0.001=0.049% of circulating water
For water flow of 27500CuM/Hr, 0.049*27500= 1347.5 CuM/Hr
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Saving in Fan power |
Modern design of PVC eliminator with wide pitch and profile width offer less pressure drop as compared to Conventional ACB or PVC eliminator with small pitch and profile width.
Reduction in static pressure drop of 0.295mm means increased tower capability of approximately 1.3% or reduced CWT of 0.07 deg C or reduced fan power 1.31 KW
1.31Kw x 24Hrs/Day x 350 days/year = 11004 KW @ Rs 2.5 /KW = Rs 27510 per annum per fan.
Reduced cold water temperature does not appear significant as the water volume per cell is as high as 2000CuM/Hr.
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Drift is a direct cost :
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Cost of arranging water : Water requirement of an industry is made available either drawn through bore well or pumped from a lake or river. |
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Cost of water treatment : All water used in circulation is treated to make sure that it is non-scaling, non-corrosive and also does not contain large suspended solids. Sedimentation, filtration and then chemical treatment are carried out on water before it is used through heat exchangers. All water lost in any form including drift is to be made up. Thus loss of treated water is a direct cost equivalent to the cost of treating equal amount of water. This cost is increasing day by day. |
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Drift is a concern in siting the cooling tower away from plant equipment and thus increases cost of piping and pumping. |
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