Page 140 - Air and gas Drilling Field Guide 3rd Edition

5.6 Prime Mover Input Power Requirements 131

2
compressor to match the back pressure of 103.4 N/cm gauge is 131.0 kW. Thus,
the percent load on the prime mover, or power ratio PR is
131:0
PR ¼ ð100Þ¼ 59:0:
221:9
Entering the abscissa of Figure 5-16 with the power ratio percent, the approxi-
mate fuel consumption rate can be read on the ordinate using the diesel fuel
curve. The approximate fuel consumption rate at this power level is 3.460
N/kW-hr. The total weight of diesel fuel consumption per hour is
_ w f ¼ 3:460ð131:0Þ¼ 453:3N=hr:

The specific gravity of diesel fuel is 0.8156, thus the total volume (in U.S. gallons)
of diesel fuel consumption per hour is

453:3
q f ¼ ¼ 56:7 liters=hr:
ð0:8156Þð9:81Þ
Illustrative Example 5.4 Determine the diesel fuel consumption rate (in gallons
per hour) for the helical lobe (screw) air compressor system and conditions given
in Illustrative Example 5.2 for (a) a surface location at sea level and (b) a surface
location elevation of 6000 ft (1829 m).
(a) Surface location at sea level (USCS units)
The prime mover has a maximum 350 hp available at 1800 rpm at sea level con-
ditions. The actual shaft power needed by the two-stage helical lobe (screw) com-
pressor to produce the fixed design pressure of 300 psig is 246.6 hp. Thus, the
percent load on the prime mover, or power ratio PR is
246:6
PR ¼ ð100Þ¼ 70:5:
350
Entering the abscissa of Figure 5-16 with the power ratio percent, the approxi-
mate fuel consumption rate can be read on the ordinate using the diesel fuel
curve. The approximate fuel consumption rate at this power level is 0.535 lb/
hp-hr. The total weight of diesel fuel consumption per hour _ w f is
_ w f ¼ 0:535ð246:6Þ¼ 129:5lb=hr:

The specific gravity of diesel fuel is 0.8156 at 60 F [5]. The total volume (in U.S.
gallons) of diesel fuel consumption per hour q f is
129:5
q f ¼ ¼ 19:1 gal=hr;
ð0:8156Þð8:33Þ
where the specific weight of fresh water is 8.33 lb/gal.

(a) Surface location at sea level (SI units)
The prime mover has a maximum 261 hp available at 1800 rpm at sea level
conditions. The actual shaft power needed by the two-stage helical lobe (screw)