Patent ID: 8046999

Claim:
A Dual-source Organic Rankine Cycle (DORC) for converting thermal power from the combination of a low-grade thermal source and a mid-grade thermal source to electrical power, said method characterized by: condensing a working fluid from a low-pressure cool vapor at total pressure p 1 to a low-pressure condensed working fluid at temperature T 1 in a condenser, where p 1 is greater than 100 kPa but less than 1 MPa, and where T 1 is greater than 260 K but less than 340 K, producing pressurized working liquid by pumping said low-pressure condensed working fluid to pressure p 2 , where p 2 is greater than 1.3 p 1 but less than 5 MPa, heating and boiling at least a portion of said pressurized condensed working fluid in a boiler using thermal power that originates from said low-grade source to create pressurized vapor at temperature T 5 , using a high-temperature (HT) recuperator to produce preheated vapor at temperature T 6 , greater than T 5 , utilizing heat from an expander exhaust vapor flow, using thermal power that originates from said mid-grade source to produce final superheated vapor at temperature T 7 , greater than T 6 , expanding said super-heated vapor at temperature T 7 through a turbine to low-pressure hot vapor of temperature T 8 and pressure near p 1 to produce shaft power for subsequent conversion to electrical power, cooling hot vapor through said HT recuperator to warm vapor at temperature T 9 , greater than T 5 , further cooling said warm vapor to at least its condensing temperature and repeating the above cycle, said method further characterized as including means for separating a portion of the heavy hydrocarbons (HHCs) from said working fluid, where HHCs are defined as having molecular mass greater than 79 and normal boiling point greater than 354 K.