Exergy analysis of a steam-turbine power plant using thermocombustion

This paper deals with the exergy analysis of a thermal power plant using different fuels, including biodiesel. The main goal is to understand the effect of design parameters and chemical dissociation of combustion products on energy and exergy efficiencies. Mass, energy and exergy analyses are made of the main components of the system, considering six different sources of irreversibilities: combustion chamber, heat transfer process, steam condensation, flue gas emission to the atmosphere, pump and frictional reheat at the steam turbine. Grassmann diagrams highlight the exergy flows and where the potential improvements exist. Results are obtained through ThermoCombustion, a virtual lab for combustion processes. The exergy analysis shows that the maximum source of exergy destruction is the boiler, followed by chimney exhaust, then steam turbine, and the condenser. Unlike the traditional methods, in this work, it was possible to distinguish between the irreversibilities thermal (due to the heat transfer) of the intrinsic irreversibility of the adiabatic combustion (associated with the chemical reactions and the viscous friction) in the steam boiler. The exergy loss distribution indicates that boiler irreversibility yields the highest exergy loss in the power plant. The use of the fuels with a simple molecular structure containing oxygen molecules will reduce the exergy destruction. The destruction of exergy in the reactive process decreases if the combustion temperature is increased, although this would lead to increases in NOx emissions. The regenerative cycle reduces total irreversibilities, increasing exergy efficiency.