1) Transformation into energy

Heat of the type that normally occurs in a kitchen kettle comes from the combustion of vegetal material in our case and is transferred into water thereby transforming it into steam.

The steam is then superheated to high pressures and temperatures [(p) and (T)] and then released into the turbine where expansion takes place.

In this way, part of the thermal energy generated is converted into mechanical rotational energy to turn the turbine and the rest into electrical energy via a 15kV generator connected to the turbine.

The spent low temperature steam [(T) and (p)] still has an appreciable energy content (latent heat) that it surrenders in an air or water heat exchanger thereby transferring heat to the potential thermal utility downstream (district heating) or dissipated in the environment.

2) Steam generation parameters

The steam generation process operates according to the Rankine thermodynamic cycle with pressurized superheating of the steam (Hirn cycle) with superheating of the steam (Hirn cycle) at pressures (p) and temperatures (T) that are notably above the temperatures of traditional biomass installations:

• p = 90 bar
• T = 540 °C

On the basis of these dimensions, the electricity output (n) therefore results in being:
• n = 35%
in comparison with standard reference values of approximately 25-28%.

3) Electricity output

The electricity output n is the parameter that permits the definition of how much thermal energy (heat) generated by the combustion transforms into electrical energy.

To make things easy, we can identify 3 distinct installation classes characterized by different n values:

• Fossil fuelled power stations: n = 40% (Italian national average)

• High-efficiency straw fuelled power stations: n = 35% [high (p) and (T)]

• Conventional biomass fuelled power stations: n = 25-28% [medium (p) and (T)]

Biomass installations with high-efficiency technology have an energy performance not far away from fossil fuelled installations thereby generating profitability with minimum environmental impact.