Page 609 - Air and Gas Drilling Manual

Chapter 11: Specialized Drilling Equipment 11-47
through the circulation system. This injection pressure is the pressure the
compressor output must match.
Compressor Unit Prime Mover Capability
Knowing the injection pressure, it is necessary to ascertain whether the prime
mover of this primary compressor unit has the power to operate at the 4,000 ft
surface elevation. The prime mover for this compressor is a diesel fueled,
turbocharged, Caterpillar Model D398 with a peak output of 760 horsepower at 900
rpm (at API standard conditions) (see Section 4.7 in Chapter 4). The theoretical
˙
shaft horsepower, W , required by each of the two compressors is obtained from
s
Equation 4-35a. Equation 4-35a becomes
, 2 400
04
(.685 ) (. )
12
4
() ( . ) 4 2 553 .4 ()( . )
1
4
41
W ˙ s 1
04
(.) 229 .17 12 .685
W ˙ s 287 .9
The mechanical efficiency, m , is
090
.
m
This is a four-stage reciprocating piston compressor. Therefore,
n s 4
The first stage compressor ratio is
1
553 4 . 4
r s
.
12 685
.
r s 257
The volumetric efficiency (only for the reciprocating piston compressor), v , is
determined from Equation 4-38. The compressor clearance volume ratio, c, is
assumed to be 0.06. Equation 4-38 becomes
1
.
.
.
096 1 006 257 14 . 1
v
0 905
.
v
˙
From Equation 4-39, the actual shaft horsepower, W , required by each compressor
as
is