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Two Drivers - Better Than One 

02-28-2019 16:13


Dual drives provide fuel and operational flexibility, system redundancy and improved economics. Describes how to automate dual drivers and compares capital and operational economics to the alternatives of single drivers or two single driver trains in CHP, combined cycle, district cooling systems, and compressed air and liquid air energy storage systems. Improved utilization of steam in combined cycle heating and chilling systems during shoulder months is also discussed.

Case Studies

1. University of Iowa, Iowa City, Iowa. This unique CHP system to be installed in 2019 includes two different size back pressure steam turbines driving a common 11 MW generator. The automated selection of which turbine operates, or both, optimizes turbine efficiency providing maximum power over the wide range of system heat demand from mid-winter to fall, spring and summer operation.

2. Compressed Air Energy Storage System, McIntosh, Alabama. This large energy storage system (115MW) is scalable for campus size requirements. At night a motor/generator is used as a motor to drive a compressor using off-peak power to store high pressure air. At peak times the motor/generator is used as a generator and driven by a fired hot air expansion turbine using the compressed air to produce low cost peak power, with the compressor disconnected from the train. The study explains how the dual use of the motor/generator is accomplished and the savings compared to using a separate motor and generator.

3. Liquid Air Power and Storage System. The innovative Pintail Power liquid air power and storage system dual drives a generator with a high pressure air turbine and an organic Rankine cycle expansion turbine. The cold from the liquid air (produced at off peak times with inexpensive power) after it is pumped to high pressure for the air expansion process, is used as a heat sink fluid for the Rankine cycle condenser resulting in a higher expansion ratio and increased power compared to an ambient cooled condenser. The improved economics of the dual drive are discussed.


James Berry, SSS Clutch Company
Richard Garrett McKay, SSS Clutch Company


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Uploaded - 02-28-2019