Characterization and Optimization of Heat Recovery in a Combined Heat and Power Generation Unit

A sustainable substitute to traditional energy conversion systems to supply energy standards to distributed communities by using locally available resources is micro Combined Heat and Power generation(m-CHP) based on biomass gasification. The circular economy concept, whose need is nowadays rising due to the increasing concerns about the release of greenhouse gases (GHGs) emissions and the connected effects on climate changes, is today intensely incentivizing the use of organic waste material for energy purposes. The proposed work focuses on the possible improvements to be made to an existing micro Combined Heat and Power (m-CHP) unit, manufactured by Costruzioni Motori Diesel S.p.A. (CMD). This system, the CMD ECO20, integrates a downdraft gasifier, syngas cleaning devices, a spark ignition engine linked to an electric generator, and two heat exchangers for the waste heat recovery: a plate heat exchanger along the engine cooling circuit and a shell and tube one along the exhaust gases line. The optimization regards the whole heat recovery system in terms of evaluating the possible uses of the energy content of exhaust gases. The use of a numerical model is presented in this paper, relevant to the direct drying process, made thanks to the use of a 0D model of the Thermoflex™ software. The drying of the poplar woodchip with different intrinsic moisture percentages is analysed and a parametric analysis is made by varying the exhaust mass flow rate. To calibrate the model, an experimental characterization is made on the CMD ECO20 by using thermocouples, pressure and mass flow rate sensors along the whole plant.