Sometimes referred to as the "fourth utility," compressed air plays a vital role in many manufacturing and process industries. Yet as energy costs rise, the price for this resource increases accordingly. That's why compressor maker Curtis Toledo has begun offering variable speed drives on its line of screw compressors in the 50 to 150 hp range.
According to Curtis Toledo sales manger Jerry Elsen, the new ABB ACS800 drives allow the compressor speeds to match demand. A compressor that doesn't use a drive constantly loads and unloads as it runs continuously, keeping pressure in an accumulator within high and low limits. By precisely matching compressor speed to compressed air demand, the variable speed design avoids any wasteful cycling.
A touch screen displays energy savings "right where people can see it," says ABB application engineer, Steve Boren. The interface also makes it easier for operators—in this case, maintenance personnel—to control the compressor, he adds. In many cases, they haven't seen a high-end drive before. The touch screen lessens any chance for intimidation.
Another benefit of the variable speed compressor drive is the gains it makes in keeping pressure constant. For some manufacturing processes like rotary blow molding, a source of constant air pressure is very important, Boren says. In some cases, secondary bypass valves are used to keep load/unload cycles to a minimum. Swings of 15 psi can be quite detrimental to some processes, he says.
Monitoring outlet pressure of the compressor and using that data to control pump speed can keep pressure within a single psi under normal plant conditions, Boren says. The drive also monitors pressure drop across the separator to detect clogging there. It monitors oil temperature, too, as a safety measure.
With some utilities offering incentives for variable speed equipment and with energy costs soaring, especially on the coasts, the payback on an investment in a variable speed compressor can be very short indeed, Elsen says.