Page 140 - Air and Gas Drilling Manual

4-26 Air and Gas Drilling Manual
The rated volumetric flow rate into the compressor is 900 ft /min. For this
example the compressor is located at sea level, thus,
q = 900 scfm 3
i
With the above terms the theoretical shaft horsepower required to compress the
air moving through the machine is given by Equation 4-35a. Thus, the theoretical
shaft horsepower is
 (. ) 
04
() ( . ) (.696 ) (900 )   164 .696  () ( . ) 
14
31 4
W = − 1
4
3
1
˙
s
04
(.) 229 .17   14 .696  
 
˙
W = 156 .8
s
˙
The actual shaft power, W , is actual power needed to compress the air to a
as
pressure of 150 psig. Actual shaft power is given by
W ˙ s
W ˙ as = εε (4-39)
m v
For this example
ε m = 090
.
and Equation 4-39 becomes
W ˙ as = 156 .8 = 190 .4
. (0 90 ) . (0 915 )
The above determined 190.4 horsepower is the actual shaft power needed by the
compressor to match the back-pressure of 150 psig. This power level is less than the
prime mover’s rated input power of 300 horsepower, thus, this compressor system is
capable of operating at a sea level surface location.
b) Surface location at 6,000 ft above sea level.
The volumetric efficiency, ε , can be determined using Equation 4-39.
v
n = 3
s
p = 11 769. psia
i
.
p o = 150 + 11 769 = 161 769 psia
.
Equation 4-37 becomes