Biomass CHP plants represent a viable option to produce distributed energy in a sustainable way when the overall environmental benefit is appraised on the whole life cycle. CHP plants for bioenergy conversion may consist of a gasification (IGC – Integrated Gasification Cycle) or pyrolysis (IPRP – Integrated Pyrolysis Regenerated Plant) pre-treatment unit, producing a syngas that feeds an internal combustion engine or a gas turbine. The external combustion mode is also an option, where exhaust gases from biomass combustion provide heat to either a traditional steam cycle, an ORC (Organic Rankine Cycle) or an EFGT (Externally Fired Gas Turbine). This paper focuses specifically on turbines based technologies and provides a LCA comparison of 4 main technologies suitable for the small scale, namely: EFMGT, ORC, IGC and IPRP. The comparison is carried out considering 3 different biomasses, namely a Short Rotation Forestry, an agricultural residue and an agro industrial residue at 2 different scales: micro scale (100 kw) and small scale (1 MW), being higher scales barely sustainable on the life cycle. From data derived from the Literature or experimental campaign (tests at the IPRP and gasification facilities at the University Perugia), LCA analysis were carried out and the different scenarios were compared based on two impact categories: global warming and human health. Input and output of the derived LCI are referred to the functional unit of 1 kWh electric for upstream, core and downstream processes. Results show the contribution of main processes and are discussed comparing scale, technology and feedstock.
Multi-objective optimization of ORC geothermal conversion system integrated with life cycle assessment
