Abstract
A consolidated and widely diffused biomass-based CHP (combined heat and power) technology consists of boilers fed with solid (lignocellulosic) biomass coupled with ORC (Organic Rankine Cycle) generators. A different technology – particularly promising for the small scale generation – although often not completely commercially mature, consists of downdraft gasifiers coupled with ICE (Internal Combustion Engine). In northern Italy, more than 20 power plants – small scale CHP systems – have been set thanks to a very convenient feed-in tariff on the generated electricity. In this work, the monitoring of two CHP systems based on wood chips (i.e., boiler-ORC and gasifier-ICE) is reported; mass and energy balance are given. The main outcome highlight the very competitive electrical efficiency of gasifierICE complexes versus other bioenergy systems. Gasification plants are designed to operate at nominal conditions, which is the actual case when the entire generated energy which is sold to the grid a fixed price. Boiler-ORC systems instead generally have a lower electrical efficiency, but this is not particularly penalised at partial load. The Italian support scheme for bioenergy has been discussed, since it promotes the electrical production rather than the primary energy saving. In addition, a review about the potential of the lignocellulosic agricultural residues has been carried out at European level. The results highlight that different approaches by the authors lead to dissimilar estimation of the agriculture potential.