One of the Machining centres has installed 2 No’s of 270 cfm compressors for pneumatic operation and also for cleaning operation of components after machining. The compressors are operated at 7 kg/cm2(g) and are on-load for 80 % of the time. The load Power and the un-load Power of each 270 cfm compressor is, 40 kW and 15 kW respectively. The energy audit estimated that cleaning air requirement is 60% of the air generated.
Calculate the daily energy consumption for cleaning air alone, assuming continuous operation of the compressor.
CALCULATION:
Compressor capacity = 270 cfm
% Loading = 80 %
Air Delivered by 2 compressors = (270 X 0.80 x 2)
= 432 cfm
Loading Power drawn by the compressors = (40 + 40)
= 80 kW
Un-Loading power drawn by the compressors = (15 + 15)
= 30 kW
Average kW drawn by the compressors = [(80 x (0.8 x24))+ (30x (0.2 x 24))]/(24)
= 70 kW
SEC of compressor = (70/432)
= 0.162 kW/cfm
Cleaning air consumption at 7 Kg/cm2 = (60 % of generation)
= (0.60 x 432)
= 259 cfm
Energy requirement for Cleaning air per day = (259 x 0.162 x 24)
= 1007 kWh/day
(or) Alternate Solution
= (Load Power x load time) + (Unload Power x Unload time)
= (40 x 0.8) + (15 x 0.2)
= 32+3
= 35 KW
Average KW drawn by the compressors = 35 x 2 = 70 KW
Energy requirement for Cleaning air per day = (70 kW x 0.6) x 24
=1008 kWh/day
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