Exergy analysis of municipal solid waste incineration processes. The use of O2-enriched air and the oxy-combustion process

This work provides a complete exergy analysis of municipal solid waste incineration process. The work was based on a previous study, and was enriched considering the possibility to increase the O2 %mol in the combustion air, up to oxy-combustion conditions. Two configurations have been considered, with and without flue gas recirculation, and the environmental aspects of oxy-combustion were taken into account, as well as its exergetic cost. The flue gas was used in a boiler for high pressure steam production, expanded in three turbines for power generation. The exergy analysis allowed to identify the process units characterized by major irreversibility and exergy loss as waste. The results showed that the flue gas recirculation led to an exergy efficiency increase of the whole process of about 3% (from 31.1% up to 34% at adiabatic flame temperature equal to 1200 °C). The O2 %mol increase in the combustion air allowed to reduce the flue gas flowrate, leading to environmental benefits. Oxygen-enriched air adoption led to limited exergetic improvements, due to the exergy cost of the air separation unit. The specific energy generation of the plant increased at fixed combustion chamber temperature adopting flue gas recirculation.