Aftercooling Systems

Compressed air systems typically incorporate air aftercooling to improve efficiency. When the air is compressed, it gains heat and includes moisture. The air is cooled to assist with moisture removal, as well as provide a lower temperature gas to the process system.

Compressed air aftercooling is performed with drying systems and heat exchanger systems. Drying systems are typically used for smaller volume plant air and instrument air systems. Larger capacity air systems, such as in snowmaking systems, typically use heat exchangers in conjunction with moisture separators.

Compressed air aftercoolers (heat exchangers) for larger capacity are available in two configurations;

• Water cooled shell and tube type
• Air to air radiator type

Selection is typically dictated by the availability (or lack of) cooling water. When a good source of cold cooling water is available, water cooling shell and tube units are typically utilized due to their simplicity and cost. More commonly cooling water is not available, and air to air units are selected. The air to air aftercoolers are a high efficiency radiator type unit, with a cooling fan to provide ambient airflow across the unit. VFD (variable speed) temperature controls are utilized in conjunction with air cooled units to maintain outlet air temperature in varying ambient conditions and to prevent overcooling and coil freeze up.

In either case (water cooled or air cooled), a high efficiency moisture separator is recommended. When the air is cooled, its ability to hold suspended moisture vapor is reduced. The air flows through a moisture separator unit, and the moisture vapor is collected as a liquid. The liquid (condensate) can then be vented off for disposal. A vane type moisture separator is typically selected for its large operating flow range and high moisture removal efficiency.