Capstone WHG125 Waste Heat Recovery Generator
Organic Rankine Cycle (ORC)
Operating Principle of Various Turbines
Energy from a fluid flow converts in useful work (rotor shaft rotation).
Depending on the type of working fluid there are several types of turbines:
- Gas turbines: Working fluid – hydrocarbons and air mixture combustion products
- Hydro turbines: Working fluid – water
- Steam turbines: Working fluid – steam (Rankine cycle implies evaporating water into steam).
Organic Rankine Cycle (ORC) Working Fluid
To utilize low-temperature waste heat it is required to use liquid with boiling temperature lower than that of water. Initially, hydrocarbons were used in the process giving the name "organic" to the cycle. Nowadays the most common working fluids include propane, pentane, toluene and HFC-R245fa. Low boiling temperature is the main criterion for using these fluids in ORC-cycle.
|Pressure / Working Fluid||Water||HFC-R245fa|
|1 bar||100 °С||15,6 °С|
|19.6 bar||212 °С||121 °С|
Waste Heat Sources:
- Microturbine exhaust gas
- Flue and process gases (drying, heating)
- Organic wastes: biomass or biogas – direct combustion or indirect heating
- Heat from onsite fuel sources: peat, coal, coal-bed methane, associated gas
Capstone WHG125 ORC System Diagram
How It Works
The working fluid is stored as a liquid in the receiver at condensation temperature and pressure. The pump is used to transfer the R245fa into the evaporator increasing the fluid's pressure. The working fluid flows through economizer and is heated by the steam from the power generating module. After that the fluid enters the evaporator where it is vaporized being heated by an external heat source. Then the vapor enters the turbine unit where it expands setting the rotor with electric generator into motion. At the discharge of the turbine the fluid still has significant amount of thermal energy. This heat is partially used in the economizer increasing the overall efficiency of the system. The vapors of working fluid flow in the cooler where they are condensed into liquid state for the next cycle.
WHG 125 ORC Turbine Applications
Low-temperature heat is not useful for other types of power generation and usually is dissipated in the atmosphere. ORC turbines are an efficient solution for the utilization of microturbine exhaust gas and the thermal wastes of chemical industry, furnaces, dryers and boilers.