Operational Analysis of a Small Size CHP Plant for Energy Production from Residual Wood Biomass

The aim of this work is the operation analysis of a CHP system based on the combustion of wood biomass residues. A superheated­water boiler, which is fired with biomass residuals from pruning activities, supplies heat to two Organic Rankine Cycle (ORC) units and to a small district heating system. Operation data of the two units have been analyzed over more than two years with an hourly time­step, in order to analyze the system performance with respect to design conditions. The results show a good availability of the biomass system, but the average gross power output of the two ORC units is lower than the nominal power. The main cause is related to the temperature of the water supplied to the evaporator of the ORC units, which is often lower than the required value: the poor quality of the biomass and the high moisture result in low combustion conditions. The results of this study point out the importance of considering real operation conditions during the design phase of the system: the variability of the input biomass can lead to off­design conditions, with lower performance than expected.