The Challenge
We were approached about gas compression for a gathering system compression location where our customer was considering an oil flooded twin screw for the first stage of a two stage operation.
The Solution
Original Design:
Oil-flooded screw compressor package with a single 1500 HP (4000V) electric motor driven twin screw (direct driven – no gear)
Capacity (design): 6.9 MMSCFD @ 13 PSIA inlet and 110 PSIA discharge pressures, requiring 1262 BHP.
SCFM Design:
Oil-flooded screw compressor package with a three 400 HP (480V) electric motors, each driving single screws (direct driven – no gear)
Capacity (design): 7.0 MMSCFD @ 13 PSIA inlet and 110 PSIA discharge pressures, requiring 1098 BHP (total for all screws).
The single screws are more efficient fully loaded than any twin screw and even more efficient partly loaded than any twin screw. The single screws are also lower maintenance $ in both labor and parts than any twin screw.
The Results
Hp/MM was lowered from 183 to 157 a reduction of 14%. Fuel cost savings at $0.05 per kwh total $153,000 per year based on 18 MMSCFD total flowrate. It was not considered for the purposes of this calculation that three twin screws would have to operate at less than 100% capacity to meet the design flowrate of 18 MMSCFD. This would cause this fuel cost savings to be greatly increased.
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