Page 204 - Air and Gas Drilling Manual

5-46 Air and Gas Drilling Manual
.
 148 3 .
r =
s
 12 685
r = 342 .   05
.
s
The volumetric efficiency (only for the reciprocating piston compressor), ε , is
v
determined from Equation 4-38. The compressor clearance volume ratio, c, is
assumed to be 0.06. Equation 4-38 becomes
  1 
ε = 096 1 − (006 . − 1

.
.

v ) (342 )14 .  
  
ε = 0 879
.
v
˙
From Equation 4-39, the actual shaft horsepower, W , required by each compressor
as
is
W ˙ as = 114 .1
09
(. ) (. 0879 )
W ˙ as = 144 .3
The above determined 144.3 horsepower is the actual shaft power needed by
each of the two compressor to produce the 148.3 psia pressure output at the surface
location elevation of 4,000 ft above sea level. At this surface location, the input
horsepower available from each of the prime mover of the compressor units is a
derated value (derated from the rated 270 horsepower available at 1,000 rpm). In
order for the compressor units 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 surface elevation the input power of each of the
turbocharged prime movers must be derated by approximately 10 percent. The
˙
derated input horsepower, W , available from each prime mover of each of the
i
compressor units is
.
W = 270 1( − 0 10)
i
˙
W = 243 .0
i
For this example, the prime mover of each of the two compressor units derated
input power is greater than the actual shaft horsepower needed. This shows that the
compressor units have sufficient power to operate at a surface elevation of 4,000 ft
above sea level.