Page 554 - Air and Gas Drilling Manual

(
.
090
m
The first stage compressor ratio is
1 Chapter 10: Stable Foam drilling 10-79
275 0 . 3
r s
12 685
.
.
r 279
s
The volumetric efficiency (only for the reciprocating piston compressor), ( , is
v
determined from Equation 4-37. The compressor clearance volume ratio, c, is
assumed to be 0.06. Equation 4-37 becomes
1 !
( 096 1 006 . 1 ∀
.
.
v 279 14 .
#
( v 0 899
.
˙
From Equation 4-38, the actual shaft horsepower, W , required by each compressor
as
is
296 .8
W ˙
as
(. 0 90 ) (. 0 899 )
W ˙ as 367 .3
The above determined 367.3 horsepower is the actual shaft power needed by
each of the primary compressors to produce the 275 psia pressure output at the
surface location elevation of 4,000 ft above sea level (while drilling at a depth of
7,000 ft). At this surface location, the input horsepower available from the
Caterpillar Model 3508 prime mover is a derated value (derated from the rated 644
horsepower available at 1,000 rpm). In order for the compressor unit to operate at
this 4,000 ft surface location elevation, the derated input power available must be
greater than the actual shaft power needed. Figure 4-15 shows that for 4,000 ft
elevation the input power of a turbocharged prime mover must be derated by
˙
approximately 10 percent. The derated input horsepower, W , available from the
i
prime mover is
W ˙ i 644 (1 . 0 10 )

W ˙ i 579 .6