The subject matter disclosed herein relates to waste heat recovery systems, and more specifically, to waste heat recovery systems that employ nonpolar organic solvents as working fluids.
Waste heat recovery systems may be employed to recover low-grade heat, such as heat with a temperature below approximately 500° C., from industrial and commercial processes and operations. For example, waste heat recovery systems may be employed to recover low-grade heat from hot exhaust gases produced by gas turbines. Waste heat recovery systems that implement an organic Rankine cycle (ORC) by circulating an organic working fluid may be particularly efficient at recovering low-grade heat due to the relatively low phase change enthalpies of organic working fluids.
In general, ORC systems may circulate an organic working fluid in a closed loop through a cycle of expansion and pressurization to convert heat into work. For example, the working fluid may be directed through a heat exchanger where the working fluid may absorb heat from a heat source, such as exhaust gas, to vaporize the working fluid. The vaporized working fluid may then be expanded across a turbine to drive a load, such as a generator, that produces electricity. The expanded working fluid may then be directed to another heat exchanger to condense the working fluid into a liquid. The liquid working fluid may then be pressurized in a pump and returned to the first heat exchanger. Typical ORC systems may employ a refrigerant, such as R143a or R245fa, as the organic working fluid and may operate at temperatures of approximately 80° C. to 100° C. However, it may be desirable to operate at higher cycle temperatures to increase the system efficiency and power output.