Civil Engineering Reference
In-Depth Information
Table 11.7
Energy saving associated with heat recovery from a screw compressor
Inlet air flow in standard atmospheric conditions 9.3 Sm
3
/min (328.4 Sft
3
/min)
Discharge pressure 0.7 MPa (101.5 psi)
a
Mechanical input power
kW
55
Electric input power
a
b
¼
a
/0.9
kW
61.1
Heat recovery
b
c
¼
0.65
a
kW
35.75
d ¼ c
3,600/1.055
Btu/h
121,990.5
Equivalent fuel
c
e ¼ c
/0.85
kW
42.1
f
¼
e
3,600/1.055
Btu/h
143,518.2
g
¼
e
3,600/41,860
kgoil/h
3.6
h
Working hours
h/year
5,000
i ¼g h
/1,000
Energy saving
TOE/year
18.1
LHV of oil 41,860 kJ/kg
a
Electric motor efficiency equal to 0.9
b
Heat recovery assumed equal to 65 % of mechanical input power
c
Boiler efficiency 0.85 (Lower Heating Value as reference)
Recovery system
• Heat exchanger oil/water
• Inlet oil temperature 95
C (203
F)
• Water volume flow rate 1.6 m
3
/h
• Water inlet temperature 60
C (140
F)
• Water outlet temperature 80
C (176
F)
• Working hours 5,000 h/year.
Table
11.7
lists basic data for the evaluation of the energy saved when water is used
for space heating and other services inside the factory.
The energy saved is equal 18.1 TOE/year.
Notice that the results of this example can easily be extended to other similar
compressors with oil injection or to compressors cooled by means of air/water or
air/air heat exchangers.
