Page 143 - Air and Gas Drilling Manual

a) Surface location at sea level.
The total fixed ratio across all three stages that is needed. The atmospheric
pressure at sea level (i.e., assuming API Mechanical Equipment Standard
atmospheric pressure) is Chapter 4: Compressors 4-29
p = 14 696. psia
i
Thus, the output pressure is
.
p o = 240 + 14 696 = 254 696 psia
.
The total fixed compression ratio across all three stages of the compressor, r st, is
.
.
r st = 254 696 = 17 33
14 696
.
This is the fixed mechanical ratio designed into the compressor and must be
determined at the standard conditions of the compressor specifications. The above
total fixed ratio will be needed to determine the maximum pressure available from
the compressor when the compressor system is operated at surface elevations above
sea level (part b of this example).
The specific heat ratio for air is
k = 14
.
3
The rated volumetric flow rate into the compressor is 900 ft /min. For this
example the compressor is located at sea level, thus,
q = 900 scfm
i
The number of stages are

n = 3
s
With the above terms the theoretical shaft horsepower required to compress the
air moving through the machine is given by Equation 4-35a. Thus, the theoretical
shaft horsepower is
. ( ) (14
() 31 4 .696 ) (900 )    254 .696  ()( . (04 )  
˙
W = 31 . ) 4 −1
s
. (04 ) 229 .17   14 .696  
   
˙
W = 189 .1
s