Compressor - Thumb rules

• Every 40 C rise in inlet air temperature results in a higher energy consumption by 1% to achieve equivalent output. Hence cool air intake leads to a more efficient compression.
• For every 250 mmWC pressure drop rise across at the suction path due to choked filters etc, the compressor power consumption increases by about 2% for the same output.
• Compressors located at higher altitudes consume more power to achieve a particular delivery pressure than those at sea level, as the compression ratio is higher.
• In a reciprocating compressor an increase in 5.50 C in inlet air to the second stage results in a 2% increase in specific energy consumption (use of water at lower temperatures decreases specific power consumption), very low temperature may lead to condensation.
• A reduction in the delivery pressure by 1 bar in a compressor would reduce power consumption by 6-10%
• Typical acceptable pressure drop in industrial practice is 0.3 bar in main header at the farthest point and 0.5 bar in distribution system .
• Fittings are also sources of pressure losses.
• Capacity of centrifugal compressors can be controlled using variable inlet guide vanes, another efficient way to match compressor output to meet varying load requirements is by speed control. For loads more than 40 % speed control is recommended.
• If air demand is less than 50 % of compressor capacity, consider change over to smaller compressors or reduce compressor speed appropriately.
• Worn out valves of compressor can reduce its efficiency by as much as 50 %, so keep them in good condition.
• If pressure required for processes are widely different, it is advisable to have two separate compressed air systems .
• Reduce compressor delivery pressure where ever possible to save energy.
• Provide extra air receivers at points of high cyclic air demand which permits operation without extra compressor capacity.
• Highest possibility of energy savings is by reducing compressed air use
• On account of high pressure drop, ball or plug or gate valves are preferable over globe valves in compressed air lines.
• In compressed air systems leaks frequently occur at air receivers, relief valves, pipes and hose joints, shut off valves, quick release coupling tools & equipments.
• Regenerative air dryers – uses the heat of compressed air to remove moisture.

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