A press operation used a pulse of compressed air for cleaning operations for 10 seconds, once every 10 minutes. The compressed air flow to the press during the cleaning was 400 cfm, a quite significant flow, and data logger measurements of the air compressors found that each time the blow happened, a 150-hp compressor would load for 10 seconds and remain unloaded for the remainder of the time.
The press already had a 660-gallon storage tank installed in an attempt to hold pressure at the press. However, it was installed with no restriction, so each time the blow fired the air compressors would see the full 400 cfm peak demand, loading the 150 hp compressor. The compressor had an unload timer set for 15 minutes, so the unit never stopped on automatic. The compressor consumed 45 kW continuously when unloaded, which wasted $40,000 worth of electricity per year and caused additional unnecessary maintenance costs.
A compressed air auditor suggested using the tank as “dedicated storage with metered recovery.” A restriction was installed at the inlet of the tank which was set to limit the flow to about 10 cfm. With the restriction, when the blow operated, the 400 cfm for 10 seconds (67 cubic feet) came from the storage receiver (660 gallons stores 6 cubic feet of compressed air in every 1 psi pressure differential), reducing the receiver pressure by about 10 psi. The air consumed by the blow was replenished over 10 minutes through the restriction at a flow of 10 cfm. Since the compressors did not now see the 400 cfm flow, the 150 hp compressor timed out and shut off.
This is an example of some good savings gained when using dedicated storage and a few hundred dollars of parts to save $40k per year!