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Friday, March 25, 2011

Eliminate Inappropriate Uses of Compressed Air

Compressed air generation is one of the most expensive utilities in an industrial facility. When used wisely, compressed air can provide a safe and reliable source of power to key industrial processes. Users should always consider other cost-effective forms of power to accomplish the required tasks and eliminate unproductive demands. Inappropriate uses of compressed air include any application that can be done more effectively or more efficiently by a method other than compressed air. The table below provides some uses of compressed air that may be inappropriate and suggests alternative ways to perform these tasks.

Potentially Inappropriate Uses could be replaced by following suggested alternatives:
  • Clean-up, Drying, Process cooling: Low-pressure blowers, electric fans, brooms, nozzles
  • Sparging: Low-pressure blowers and mixers
  • Aspirating, Atomizing: Low-pressure blowers
  • Padding: Low to medium-pressure blowers
  • Vacuum generator: Dedicated vacuum pump or central vacuum system
  • Personnel cooling: Electric fans
  • Open-tube, compressed air-operated vortex coolers without thermostats: Air-to-air heat exchanger or air conditioner, add thermostats to vortex cooler
  • Air motor-driven mixer: Electric motor-driven mixer
  • Air-operated diaphragm pumps: Proper regulator and speed control; electric pump
  • Idle equipment (Equipment that is temporarily not in use during the production cycle.): Put an air-stop valve at the compressed air inlet
  • Abandoned equipment (Equipment that is no longer in use either due to a process change or malfunction.): Disconnect air supply to equipment
The table below shows inappropriate uses of compressed air in an automobile assembly plant. The plant took several action steps identified in the table to eliminate or reduce these inappropriate uses. Peak flow is identified in cubic feet per minute (cfm).

The plant audit showed that the energy used to generate the compressed air averages 18 kW/100 cfm. The aggregate electric rate at the plant is $0.05 per kWh.

Annual savings = [kW per cfm] x [cfm savings] x [# of hours] x [$ per kWh]

= 18/100 x [(150 x 6,500) + (1,000 x 5,000) + (800 x 3,500)
+ (750 x 3,500)] x $0.05
= $102,600

Net savings:
Calculate electric energy costs for the motor-driven vacuum pump, fans, and actuators, and subtract these costs from the annual savings calculated to determine the net savings. Note that there will be a one-time cost of installation for the added equipment.


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