Wood biomass CHP in district heating systems: simulation and operation analysis

This research work is focused on the development of a simulation model for the operational analysis of wood biomass CHP (combined heat and power) units supplying district heating systems. The integrated approach that has been adopted offers the possibility of considering the effect of each system component during the different operation conditions that can occur during the year. The aim of the model is to provide a support for different situations: the design of the components of the system, the analysis of real operation to match the requested performance and the local energy planning considering the effects of the actual behaviour of those systems throughout the year. The model has been improved thanks to an analysis of real operation data, both on demand side and on supply side. The heat demand from different district heating systems has been investigated, by analysing the main differences and analogies with respect to size and climate conditions. Considering the supply side, two different ORC systems have been analysed over some years of operation with an hourly time step. These data analysis has pointed out the significant variations that can occur in DH systems when the actual operation conditions are different than the ones forecast in the system design. The model has been used for a case study analysis to assess the optimum size of a CHP unit coupled to a heat storage system in an existing district heating network. An economic analysis has been performed in order to evaluate the current Italian incentive framework for RES (renewable energy sources) plants. A difference has been found between the optimal energetic layouts and the best economic solutions, showing that the current incentives still not promote the most efficient solutions for energy production from wood biomass.