Biomass Microturbine Based EFGT and IPRP Cycles: Environmental Impact Analysis and Comparison

Abstract

The global microturbine market will grow at an interesting Compound Annual Growth Rate during the period 2016–2020 and a key driver will be distributed generation also with unconventional fuels. This paper compares the performances of two different microturbine based technologies for biomass micro CHP. One is the Integrated Pyrolysis Regenerated Plant (IPRP), technology developed by the authors by coupling a pyrolyzer to a mGT fuelled by biomass pyrolysis gas. Two IPRP versions are considered: one in which char is burned to provide pyrolysis energy and one in which it is used as a carbon sink. The second technology is the Externally Fired Gas Turbine (EFGT) based on biomass combustion in a dedicated burner and high temperature heat exchangers used to heat up compressed air which expands in the mGT. Hot air at the turbine exhaust is used as combustion air for biomass. The layout and operational conditions considered were optimized by the authors in previous works. The environmental performance of the two technologies when fuelled with the same biomass at the same power output, is assessed through a Life Cycle Assessment (LCA) analysis, calculating impacts on acidification, carbon footprint and Cumulative Energy Demand (CED). Two sensitivity analysis are also performed on different vegetal oils used for scrubbing and different methods of allocation, referred to CHP products. Results show that both technologies have negative carbon footprints, however the IPRP has the worst performance because of the sunflower oil, used for syngas scrubbing, which offsets the additional carbon sink benefit of biochar. If water it used as a scrubbing medium in the IPRP plant, this configuration obtains similar results in terms of environmental impact, compared to IPRP plant using vegetable oil as a scrubbing medium. However, when the effect of a different vegetal oil is considered, namely a waste frying oil, the former introduces extraordinary benefits resulting in the IPRP outperforming the EFmGT in terms of carbon negative technology.