Civil Engineering Reference
In-Depth Information
The energy balance already introduced for the compression process can be used
for end user processes.
End user requirements are generally expressed in m
3
/min if only the
constant-pressure work is considered Power (W) can be calculated
approximately as follows:
air flow m
3
=
s
end user pressure Pa
ðÞ
Higher values can be obtained if the expansion work (the opposite of the
compression work) is added.
11.7
Energy-Saving Investments
As discussed in Sect.
11.2
, energy can be saved by improving the overall efficiency
of the system.
Typical suggestions are:
• Discharge pressure must be kept as low as possible, depending on the real end
user needs. Reduction of pressure by throttling valves must be avoided;
• Compressed-air temperature must be lowered in order to reduce the volume
flowing through the compressor;
• Leaks along the pipeline must be carefully avoided by proper maintenance;
• The no-load operating hours must be kept as low as possible by using variable
speed drives;
• Heat recovery from cooling systems, particularly for high-power systems, is
always advisable;
• Proper sizing of the compressors, fixed and variable speed drive, and its related
equipment allows operation at high efficiency.
11.8
Practical Examples
Example 1
Reduction of the compressor discharge pressure to the real end user
needs.
A factory has an air-compressor plant which works at a discharge pressure of
0.9 MPa (130.5 psi). Most equipment may correctly operate at 0.6-0.65 MPa (87-
94.3 psi), except one which needs 0.8-0.85 MPa (116-123.2 psi) with a small air
flow requirement (roughly 10 % of the total air flow). Throttling valves are used to
reduce the pressure to the end user requirements.
Evaluate the energy saved if the air-compressor plant operates at lower pressure,
0.7 MPa (101.5 psi), to supply the main equipment. The user at 0.8-0.85 MPa (116-
123.2 psi) will be supplied with a separate air compressor.
