Page 127 - Air and gas Drilling Field Guide 3rd Edition

118 CHAPTER 5 Compressors and Nitrogen Generators

(a) Surface location at sea level (USCS units)
This is a reciprocating piston compressor and, thus, has a volumetric efficiency
term. The volumetric efficiency e v can be determined using Equation (5-38).
n s ¼ 2
p i ¼ 14:696 psia
p o ¼ 150 þ 14:696 ¼ 164:696 psia:

Equation (5-31) becomes
1

164:696 2
r s ¼ ¼ 3:348:
14:696
The specific heat ratio for air is
k ¼ 1:4:

The clearance volume ratio for this compressor is
c ¼ 0:02
With these values, Equation (5-38) becomes
1
8 2 39
< =
e v ¼ 0:96 1 0:02 ð3:348Þ1:4 1 5
4
: ;
e v ¼ 0:934:
3
The rated volumetric flow rate into the compressor is 950 ft /min. For this exam-
ple, the compressor is located at mean sea level (API Standard conditions), thus
q i ¼ 950 scfm:
With these terms, the theoretical shaft horsepower required to compress the
air moving through the machine is given by Equation (5-35a). Thus, the theoreti-
cal shaft horsepower is
2 3
ð0:4Þ

ð2Þð1:4Þ ð14:696Þð950Þ 6 164:696 ð2Þð1:4Þ 7
_ W s ¼ 6 1 7
ð0:4Þ 229:17 4 14:696 5
_ W s ¼ 175:9 hp:

The actual shaft power _ W as is actual power needed to compress the air to a
pressure of 150 psig. Actual shaft power is given by

_ W s
_ W as ¼ : (5-39)
e m e v
For this example,
e m ¼ 0:95