Valutazione tecnico-economica di un impianto a biomasse mediante analisi di rischio

In this paper three solutions for small scale energy conversion of solid biomass are compared from a technical and economical perspective. A real case study is examined, for which the reference technology selected by designers is biomass gasification in a direct downdraft gasifier. Produced syngas is then used in an internal combustion engine to generate biopower. Alternative technologies applicable within the power generation capacity range of this case study are a Rankine cycle steam turbine or an organic fluid Rankine cycle turbine (ORC). Profitability and risk analysis for the reference and alternative technologies are performed for the examined case study with a quantitative risk analysis approach based on Monte Carlo simulation by using the commercial software @RISK®. A spreadsheet model was built to calculate economic performance indicators. A commercial and literature review was performed to gather data on input variables (biomass price, low heating value, capital costs, maintenance costs, systems availability). For most variables, enough data were collected to fit probability distributions as input of the Monte Carlo model. Subjective estimates or deterministic values were used where opportune or where not enough data for objective estimation could be retrieved. Probability distribution of outcome variables (biomass quantities, NPV, power costs) were thus obtained from Monte Carlo simulation. The probabilistic model thus obtained is used to compare profitability and risk performance for the examined alternatives and to assess the examined technologies, especially as to dependence on biomass demand and uncertainty in market prices and as to dependence on systems availability and maintenance, highlighting that a traditional, deterministic analysis sometimes leads to less realistic (and more optimistic) results.