Before selecting and installing the centralized regenerative desiccant compressed air dryer, moisture in the compressed air supply was causing a number of problems. Moisture vapor was condensing and causing pipe corrosion. Water and untreated compressor oils were damaging air-operated equipment, such as motors, cylinders, and valves. Even more seriously, the water froze in exposed lines during cold weather, stopping some operations completely (air hoists in the shipping department, for example) until lines could be reopened.

These problems began with air leaving the compressor's after-cooler, which could not drop the dew point temperature sufficiently to prevent the inherent moisture from condensing. "Inadequately sized dryers located in the air mains suppressed the dew point, but not sufficiently," according to the plant's mechanical engineer. Additional drying was required at points of use, with smaller desiccant type dryers performing the function. "However, lack of centralized control resulted in inconsistent dryer performance as well as high maintenance costs," Whitaker said.

The steel producer determined that one centralized compressed air dryer of 10,000 scfm capacity would meet its long-term quality and efficiency objectives better than several individual dryers or temporary nitrogen usage.

Installing a centralized versus end point dryer provides a constant and consistent supply of quality compressed air throughout the plant. This ensures a safe dew point throughout the year, which reduces maintenance, prevents freeze-ups and eliminates moisture related downtime.

A custom-designed Van Air Systems regenerative desiccant air dryer was installed in the plant's power substation. This dryer was specified to provide a -40ºF pressure dew point for both instrument and process air. It was sized for 10,000 scfm with the capability of expanding to a capacity of 12,000 scfm by adding more desiccant.

Wet air flows through the inlet transfer valve and flows upward through the desiccant bed in the drying tower where moisture is attracted to and adsorbed onto the desiccant. Dry process air with a -40ºF pressure dew point exits through the outlet transfer valve. In the regenerating tower, moisture is stripped from the desiccant by atmospheric air drawn in through a blower and passed over a heater. As the hot, dry purge air flows through the bed, it collects moisture and is discharged through the purge exhaust valve.

Since start-up, the cost of individual dryer maintenance and the high cost of supplemental nitrogen have been eliminated. Compressed air line freeze-ups have also been prevented. On-time delivery of mill products has been enhanced. Valves which had been left open to drain condensate are now closed. And, since it is no longer necessary to bleed air into the atmosphere for moisture removal and freeze-up protection, a savings of 2,000 scfm of compressed air (the equivalent of 400 horsepower of compression) has been achieved.

These benefits contribute to and reflect the mission of a steel producer - to offer the highest value products and services; maintain excellence through investments in state-of-the-art technology; and continually improve, emphasizing the fundamental operating principles of quality and investment usage.