ORC turbogenerators (Organic Rankine Cycle) work similarly to steam turbines, where precisely the steam generated by a boiler that heats water expands inside suitably shaped ducts, acquires kinetic energy and pushes the blades of an impeller.
But a ORC turbogenerator use a closed-cycle organic fluid to make the impeller move.
The organic fluid is evaporated using the heat coming from a boiler, using a diathermic oil exchanger; the vaporized organic fluid then actuate the turbine that produces electricity. After passing through the turbine, the vaporized fluid is cooled and condensed, thus transferring heat to the district heating network (or other uses of the heat), to be sent back to the evaporator. This closes the thermodynamic cycle.
How to generate the heat needed to vaporize the working fluid?
The ORC technology makes it possible to produce electricity from thermal waste in a cost-effective and environmentally sustainable manner, contributing to energy supply without increasing CO2 emissions. Thanks to the exploitation of waste heat from industrial processes or to the biomass combustion otherwise difficult (and onerously) disposable, it is possible to obtain an extra gain from the electricity produced and sold online.
As process products we have, in addition to electrical energy, heat (from the condenser) which can be reused, for example, to power supply small utilities.
How does the system work?
Hot side
Is a closed-circuit piping system containing a liquid that allows to extract heat through a special heat exchanger installed on the thermal energy source (boiler flue or engine exhaust). The heat is carried through a pump to the evaporator which transmit the energy to the working fluid
ORC circuit
It’s a closed circuit containing the working fluid. This particular fluid, through the Rankine cycle, evaporates, passes through the turbogenerator and finally condensed to then start the cycle from the beginning.
Cold side
It is an open circuit (cooling tower) or closed circuit (dry cooler) piping system that allows, through a special exchanger, to extract heat from the working fluid, condensing it. In many cases it’s also possible to size a direct condensation system, which therefore does not require a separate circuit to extract heat.
Electric circuit
The generator, set in motion by the action of the fluid on the turbine wheel, produces electrical energy which is then regulated by an inverter and put into the electricity grid.
Some advantages of the Organic Rankine Cycle
Organic Rankine Cycle (ORC) plants have the following advantages compared to steam plants:
High thermodynamic efficiency
Reduced rotor wear;
The dry working fluid eliminates the problem of turbine blades
erosion;
High efficiency of Organic Rankine Cycle (ORC) plants even under partial load;
For the operation of ORC plants no specialized personnel or authorizations / certifications are required;
Organic Rankine Cycle plants do not pollute (there are no emissions of any kind).
