Organic Rankine, Kalina and sCO2 cycles
Cycles using special fluids to make power from lower-temperature heat.
Recovery and reuse · Heat to power and cogeneration · No. 126
- Recovery and reuse
- Heat grade: Low to medium
Swap water for a fluid that boils far lower, and heat too cool for steam can still spin a turbine.
Chart: Illustration: Organic Rankine, Kalina and sCO2 cycles
Where it comes from
Chart: Map of where it comes from
An organic Rankine cycle works like a steam plant but uses a fluid that boils at lower temperature, taking heat from about 95-260 C. Most units sit behind a thermal-oil loop that keeps out dust and acid.
Three things to know
- Low-temperature ORCs convert only 8-9% of heat to power, yet that is about 35-40% of what thermodynamics allows at 120 C.
- ORC turbines run efficiently down to about 10% of rated power, so they cope with fluctuating kiln gas better than steam.
- A supercritical CO2 pilot turbine spins at 27,000 rpm and cost USD 169 million for a 10 MW test facility.
The journey
- 1 Warm sourceKiln air, engine water, geothermal brine
- 2 Oil loopThermal oil carries heat, protecting the turbine
- 3 EvaporatorOrganic fluid boils at low temperature
- 4 TurbineVapour spins a generator, often air-cooled
- 5 ElectricityFuel-free, water-free power for the site