Page 373 - Air and Gas Drilling Manual

8-56 Air and Gas Drilling Manual
=
p
.
176 6 psia
2
d
˙
The theoretical shaft horsepower, W , required by the primary compressor in each
sp
unit is determined from Equation 4-35a. Equation 4-35a becomes
 , 3 398 
04
(.685 )  (. ) 
12
11
() ( . ) 4  2    204 7 ()( . ) 
. 
4
11
W ˙ sp = − 1
(.) 229 .17   12 .685  
04
 
W ˙ sp = 368 .8
The assumed mechanical efficiency, ε , is
m
ε m = 090
.
Rotary compressors have no volumetric efficiency term, therefore, the actual shaft
horsepower, W ˙ as p, required by each compressor can be obtained from Equation 4-39.
This is
W ˙ = 368 .8
asp
(. 090 )
W ˙ asp = 409 .8
The above determined 409.8 horsepower is the actual shaft power needed by the
rotary screw primary compressor to produce the 176.6 psia pressure output at the
surface location elevation of 4,000 ft above sea level (while drilling at a depth of
10,000 ft).
Booster Compressor
This is a two-stage reciprocating piston booster compressor. Therefore,
n = 2
s
˙
The theoretical shaft horsepower, W , required by this booster compressor in each
sb
unit is determined from Equation 4-35a. Equation 4-35a becomes
 , 3 398 
04
(.685 )  (. ) 
12
() ( . ) 4  2    293 .  9 ()( . ) 
2
1
21
4
W ˙ sb = − 1
. 
04
(.) 229 .17   176 6 
 
W ˙ sb = 49 .6