Organic Rankine Cycle: concept
Cycle it is a thermodynamic cycle. Rankine it is theoretically given by 2 isobar and 2 adiabatic thermodynamic transformations. Organic it exploits an organic working fluid.
The principle is based on a turbogenerator working as a normal steam turbine to transform thermal energy into mechanical energy and finally into electric energy through an electric generator. Instead of the water steam, the ORC system vaporizes an organic fluid, characterized by a molecular mass higher than water, which leads to a slower rotation of the turbine and to lower pressure and erosion of the metallic parts and blades.
Efficiency: The incoming thermal power is transformed into electric power (up to 25-26%) and heat (up to 80%), with extremely limited thermal leaks, only 2% due to thermal isolation, radiance and losses in the generator. The electric efficiency obtained in non-cogeneration cases is much higher (more than 24% of the thermal input).
ORC provides significant advantages as compared to steam
Water vs High Molecular Mass - Working Fluid
Waste heat to power ORC plant
- Heat-carrying loop may be filled with verse media e.g. thermal oil, saturated steam, pressurized water or it can be replaced by a direct exchange between the exhaust and the organic fluid
- Possibility to exploit multiple thermal sources
- Cooling tower, water cooled condenser, air cooled condenser, other.
ORC finds many applications in the Oil&Gas sector
- Gas turbines exhaust gas
Gas compressor stations, natural gas liquefaction, oil pumping stations, etc.
- Hot water from exhausted/unused oil wells
- Associated Petroleum Gas (APG)
- Refinery hot streams
Distillation columns, Oil/Gasoline/Kerosene production, etc.
A. Gas turbines exhaust gas
Natural Gas Compressor Stations: a big opportunity for Heat Recovery
- World natural gas yearly consumption: about 3,000 billion m3
- Compressor stations usually placed at 40 to 100 kilometers intervals along the pipelines
- Dozens of GW of compression capacity to move natural gas from production sites to users
- Most compressor stations are operating on an open cycle (efficiency about 30-35%)