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Special Feature | November 2013

Cooling Towers: Dissipating heat

Industrial cooling towers are considered critical for many industries where cooling forms an important part of industrial process, yet availability of water remains a key challenge for cooling towers.

Cooling towers became popular during the beginning of the industrial revolution. The huge industries that were built required a method to remove heat successfully from the cooling process. This led to the invention of cooling towers. In the modern world, cooling towers find wide application in various industries such as power plants, petrochemical plants, food processing plants, semiconductor plants and so on.

In some cases, cooling may be a part of the product manufacture process or for maintaining ambient temperature. A cooling tower dissipates heat into the atmosphere and this is spread over a large area. Adequate care must be taken while designing a cooling tower to prevent any ecological or environmental damage.

Global overview
The global market for cooling towers is set to reach $1.8 billion by 2015. The US and Europe dominate this market currently. On the global front, this is quite a mature market with little scope for growth for new market participants. The market will tend to veer towards repairs and innovations, which will be based on various environmental regulations imposed by governments across the world.

This is a highly technology sensitive market and newer technology can tilt the balance in favour of growth. Competition in this segment has heated up with the presence of low cost Asian manufacturers including Indian and China.

Vibrant growth for the cooling tower industry in India
India is quite a warm country almost all the year through, so cooling towers are quite essential in industrial applications. The country has become a major hub for their manufacture.

Initially, cooling towers in India were manufactured from wood but this has since evolved into more durable material like fiberglass reinforced plastic (, FRP) as well as roller compacted concrete (RCC).

The favoured shape for cooling towers was cylindrical during the initial phase. As their popularity and function grew, so did the size. This necessitated a change in shape and today the most favoured shape is the hyperbolic as it offers superior structural strength and resistance to ambient wind loadings. However, there is no hard and fast rule and depending on client needs cuboid, bottle-shaped and even rectangular ones are available.

Growth drivers
Growth in the Indian market is driven by factors like the increasing need for tightening legislation, energy efficiency, replacement demand, rising greenfield projects and capacity expansion. With energy being a scarce resource, there is a tendency towards energy savings and this will drive the cooling tower industry strongly. Replacement of old cooling towers and innovation in new product designs with value added functional features and benefits will propel the market forward.

Challenges
The major challenge that companies need to overcome is the necessity for water, a scarce resource in India. Thermal power plants for instance consume large quantities of water for cooling and there needs to be a constant source. A majority of industries use 'once-through cooling systems', which means water once used for cooling is discharged. Shortage of labour is another major issue that manufacturers have to contend with.

Heat transfer methods
The primary classification is into dry towers or wet towers, and some hybrid wet-dry combinations exist. Wet cooling towers rely on the latent heat of water evaporation to exchange heat between the process and the air passing through the cooling tower. In dry cooling towers, this process is carried out through a surface, which separates the working fluid from ambient air but does not use evaporation. Fluid coolers or closed circuit cooling towers are hybrids, here the working fluid moves through a tube bundle where clean water is sprayed and a fan-induced draft applied. The future for cooling towers in India is quite bright with the growth in industries and infrastructure.

At the top
Paharpur Cooling Towers are the clear leaders in the cooling tower industry in India. Their product range consists of small factory assembled units to large concrete towers which require construction on site. Gactel, Towertech, Cooltech, ABR, Artech, Matrix Solutions and North Street are some of the other top companies in the segment.

Types of cooling towers
Cooling towers fall into two major categories natural draft cooling tower and mechanical draft cooling tower. Each of these has further sub-categories.

Natural draft cooling tower
This is also known as a hyperbolic cooling tower and works on the technique of using the difference in temperature between the ambient air and the hotter air inside the tower. Hot air always rises up and moves upwards through the tower and fresh cool air is drawn into the tower through an air inlet at the bottom. This consists of two kinds: Cross flow tower and Counter flow tower. Cross flow tower: Here air is drawn across the falling water and the fill is located outside the tower. Counter flow tower: Here, air is drawn up through the falling water and the fill is located inside the tower.

Mechanical draft cooling tower
Here large fans force or draw air through circulated water. Since the water falls downwards over fill surfaces, this helps increase the contact time between the water and the air and cools it optimally. These are of three types Forced draft cooling tower, induced draft cross flow cooling tower and induced draft counter flow cooling tower.

Forced draft cooling tower
In this type, the air is blown through the tower by a fan located in the air inlet. The fan is relatively quiet and works well in cases of high air resistance

Induced draft cross flow cooling tower
In this case, water enters the tower from the top and passes over fill air entering on one side (single-flow tower) or opposite sides (double-flow tower). Then an induced draft fan draws this air across the fill to the exit.

Induced draft counter flow cooling tower
Here hot water enters the tower from the top whereas air enters from the bottom and exits at the top after being pushed out by draft fans.

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