How to save energy — compressed air systems?

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This post was last edited by 955559 on 2018-8-3 at 16:38. According to the U.S. Department of Energy, air compressors are among the devices that consume the most electricity in industry in the United States. Although the U.S. Department of Energy once considered electric motors to be the devices that consume the most electricity, the energy savings achieved by improving the design and operation of compressed air systems **exceed those resulting from improved motor efficiency. Energy savings of 20-50% can be achieved by improving the design and operation of compressed air systems. Many companies regard compressed air as a utility equivalent to coal, electricity, and water. Unlike other utilities, few people know the cost of compressed air per cubic meter per minute. The cost of compressed air at 1 cubic meter per minute can be calculated as follows:
· Assumptions: Motor service factor = 110%, Power factor = 0.9
· A typical air compressor produces 4 CFM per 1 HP.
· 1 HP = 110% × 0.746 kW / 0.9 = 0.912 kW
· Therefore, 0.228 kW is required to produce 1 CFM of compressed air.
· If the cost per unit of electricity is 0.65 yuan, then 1 CFM costs 0.1482 yuan per hour.
· 1 cubic meter per minute equals 35.315 CFM; thus, the cost per cubic meter per minute is 5.23 yuan per hour.
· Hence, an air compressor with a capacity of 10 cubic meters per minute will consume 10 × 8,000 × 5.23 = 418,694 yuan in electricity over 8,000 hours of operation.

Where can you save on electricity costs? In a typical factory, compressed air leaks account for 20% of the total demand. Assuming that a factory’s compressed air system operates for 8,000 hours per year, with an electricity cost of 0.65 yuan per unit, and a pipeline pressure of 7.0 kgf/cm2, the factory’s demand for compressed air is 10 cubic meters per minute. With 20% leakage, the actual amount of air lost is 2 cubic meters per minute; thus, the total demand remains at 12 cubic meters per minute.

The cost of electricity for compressed air is as follows:
10 × 8,000 hours × 5.23 yuan = 418,694 yuan
2 × 8,000 hours × 5.23 yuan = 83,738 yuan
Total: 502,433 yuan

Leaks also create enough additional load that requires two air compressors to operate simultaneously. Without a backup compressor, it’s not possible to perform maintenance on either compressor. To achieve a leakage rate of 2 cubic meters per minute at a pressure of 7.0 kgf/cm2, either:
· 3 leak points of 3 mm each, resulting in 2.2 cubic meters per minute, or
· 1 leak point of 6 mm, resulting in 2.832 cubic meters per minute