Two-phase expansion system and method for energy recovery

A power generation system comprising:

• a gas turbine;
• a closed loop expansion system for energy recovery comprising:
• a heat exchanger for using heat from the gas turbine to heat a working fluid of the closed loop expansion system to a temperature below the vaporization point of the working fluid;
• a radial inflow expander for receiving the working fluid from the heat exchanger and for expanding and partially vaporizing the working fluid;
• a screw expander for receiving the working fluid from the radial inflow expander and for further expanding and vaporizing the working fluid;
• a condenser for receiving the working fluid from the screw expander and for liquefying the working fluid.

An energy recovery method comprising repeating the following sequence of steps while pumping working fluid through a closed loop expansion system:

• using heat from a heat source to heat a working fluid of the closed loop expansion system to a temperature below the vaporization point of the working fluid;
• expanding and partially vaporizing the heated working fluid in a first expander and then further expanding and vaporizing the partially vaporized working fluid in a second expander;
• converting mechanical work from the first expander, the second expander, or the first and second expanders into electrical power;
• and
• condensing the further expanded and vaporized working fluid.