Choosing Gearboxes For Process Cooling

The type of cooling tower or air-cooled condenser selected to cool a process system’s water is determined by the economic and environmental considerations of each particular application.

Cooling towers and air-cooled condensers are used in both utility and industrial applications. Utilities include power, cogeneration, geothermal and waste-to-energy plants. Industrial applications include chemicals, petrochemicals, pulp and paper, iron and steel and pharmaceutical plants. This equipment also is used in buildings requiring large air-conditioning facilities.

Cooling towers

The three types of cooling towers that cover most applications are: wet, dry and hybrids.

Each of these cooling tower systems uses large fans and fan drives, an application which suits the use of parallel shaft and right angle speed reducers for reliable, quiet and trouble-free operation.

Cooling towers are typically classified into two categories: open systems and airtight systems. The common part of the systems is that the warm coolant is cooled down by open air taken in through a ventilator.

The difference in the systems is determined by whether the coolant is in direct contact with open air or not.

Since the interior of cooling towers becomes very humid, the motor is normally installed outside of the tower.

The cooling efficiency of the open type of tower is very high because the coolant is in direct contact with the outside air. This system involves evaporation of some of the coolant. It may be necessary to replace or replenish the coolant after long periods because water in the air allows for impurities and toxic substances to build up in the coolant.

In an airtight system, the coolant is kept in a coil-shaped radiator, so the coolant is not in direct contact with the open air. The cooling efficiency is about half that of the open-system type, however, this system is used frequently when trying to avoid dirty water — such as in computer-and semiconductor- related facilities and also where the outside air is polluted

Air-cooled condensers

An air-cooled condenser is a dry system where air is used as the cooling medium. The process involves pumping the coolant through finned tubes in the roof of the condenser building and forcing the cooled air through the roof.

This system is inefficient compared to the cooling tower system, however it is preferable in cases where large supplies of water are not available. Environmental considerations make this cooling equipment less desirable.

The air-cooled condenser can use either a parallel shaft or right angle shaft gearbox. The difference is determined by where the fan blades will be positioned.

Table A shows a summary of some of the advantages and disadvantages between the cooling tower and the air-cooled condenser.

Different industries require different methods of cooling. When selecting gearmotors for either a cooling tower or an air-cooled condenser, look for designs with high performance for these specific applications and their demanding environments.

Stefanie Burns is with Sumitomo Drive Technologies. For more information, contact SM Cyclo of Canada, Oakville, ON, or e-mail customercare@suminet.com.

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