Biomasses are the starting point of the biomass-energy production chain and of the energy systems planning for the concurrent production of electric and thermal energy (cogeneration) by renewable sources. Unlike fossil fuel, biomass isn’t distributed homogeneously on the territory and hasn’t a continuous and constant availability during the year. A cogenerative system from renewable sources can only start from a thermal demand and a biomass availability.
The transformation process consists in the production of a biofuel (wood chips, biogas, syngas, vegetable oil, biodiesel, bioethanol, etc.). The choice of the transformation process and therefore the energy system at the bottom of the process, depends from the characteristics of the biomass (humidity, composition, size, etc.). The processes can be of different nature: biochemical (i.e. anaerobic digestion), thermochemical (i.e. direct combustion, gasification) and chemical and physical (i.e. mechanical extraction of oils from oleaginous plants).
Finally, as cogenerative energy systems fed with biomass are used the same systems used for cogeneration from non renewable sources: alternative endothermic engines, Stirling with external combustion engines, gas micro turbines and steam cycles or ORC (Organic Rankine Cycle). As said beforehand, the choice of the energy system is dependent by the available biomass and to the chosen transformation process.
Among the different production chains, which can be considered consolidated, can be citied:
- (i) direct solid biomass combustion in boilers fed by water steam cycles or organic fluid,
- (ii) anaerobic digestion of zootechnical waste, agroindustrial residuals or dedicated cultivation with biogas production and combustion in alternative endothermic engines or gas micro turbine.
- (iii) gasification of cultivation residuals or wooden biomasses wit syngas production and combustion in alternative endothermic engines,
- (iv) vegetable oils extraction from dedicated oleaginous cultivations and the oil combustion from alternative endothermic engines.