Modelling approach and technical solutions for characterization and performance improvement of real biomass powered m-CHP system

Energy valorisation of organic waste material is nowadays an assessed practice of circular economy. The valorisation of residual biomass plays a decisive role in specific rural areas, where biomass represent a renewable energy source and may be abundant. The collection and energy valorisation at the local level of biomass from forest management practices and wildfire prevention cutting can be settled in protected areas to contribute to local decarbonization, by removing power generation from fossil fuels. Biomass gasification is a thermo-chemical process that converts the solid material into a gaseous fuel called syngas (from synthesis gas) mainly composed of CO, H2, CH4, CO2, N2. This syngas can be used, for energy purposes, in reciprocating engines, turbines and even in fuel cells. The main driver to choose biomass gasification as a technology for biomass exploitation is its potential flexibility in input as well as at output. Different woody sources can be used as feedstock for a biomass gasifier, such as dedicated energy crops, forest and agricultural residues, by-products and wastes of the pulp and paper industry, food industry and specialties industry. The Ph.D work, developed in a joint activity between the University of Rome “Tor Vergata”, the National Research Council – Istituto Motori today known as STEMS and the company Costruzioni Motori Diesel (CMD) SpA, intends to give a tangible contribution to improving the performance of a CHP plant of micro scale of power, the CMD ECO20, developed and marketed by the company CMD. The work intends to give an increase the diffusion of energy production from biomasses for heat and power generation, making the waste a resource to get local energy. After an initial phase of documentation about the gasification technique and the actual state of art of biomass gasification for energy production, an fully analysis of the real micro-scale CHP system consisting of a downdraft gasifier coupled with an internal combustion engine was exploited to characterize the energy flows and highlighting the inefficiencies of the system, with particular attention to the genset section for electricity production and heat recovery. The analysis was carried out both through the experimental and the numerical approach, thanks to the construction of an appropriate engine model using the most widespread and modern simulation codes. The numerical simulation provides useful information both in the design and verification phase of all the engine components, even those that would be difficult to access for experimental measurements. In this way it is possible to obtain data on engine performance and emissions and to identify any inefficiencies at every operating configuration of the engine, with a considerable saving of time and costs if compared to the same analysis conducted through experimental measurements. Results are more accurate when more input data are available, hence the need to instrument the entire system in order to characterize the thermodynamic conditions of each individual element and build a matrix of operating point. A multi-objective optimization based on CFD was applied to the syngas powered engine to identify the better calibration of the engine for syngas use and verify it with appropriate experimental campaign. The matured know-how of the system and the effect of main variable on the analysed process led to identification of different technical solution that led to important improvement of the performance, environmental impact and the reliability of the system. The management and automation of the engine have been improved thanks to the use of an Electronic Control Unit capable of monitoring the state of the engine and managing the various phases of operation with closed-loop logics. Finally, a real operation demonstration of the analysed and improved biomass-powered plant was conducted within a national park in Southern Italy replacing a diesel genset and by proving a decisive improvement of air quality in the real environment during exercise.