A Review on Exergy Analysis of High Pressure Steam Boiler

In thermodynamics, exergy of a system is the maximum useful work possible during a process that brings the system into equilibrium with a heat reservoir. In case the surrounding is the reservoir, exergy is the potential of a system to cause a change as it achieves equilibrium with its environment. Exergy, in other words, is the energy that is available to be used. As energy analysis is based on the First law of Thermodynamics, it has some inherent demerits like not accounting for properties of the system environment, or degradation of the energy quality through dissipative processes. Also, it doesn't characterize the irreversibility of the processes within the system. In contrast, it characterizes work potential of the system. This is when the exergy analysis comes into play. It represents a good standard to estimate the maximum obtainable work from a given form of energy using the state of the surrounding as reference point. Exergy analysis, however, isn't a substitute for first law analysis. Rather, it is a supplement. Various researchers have conducted a thermodynamic analysis of a subcritical boiler-turbine generator under varying parameters of pressure, temperature and flow rate, in order to determine the ways to enhance plant efficiency. Also, the data on exergy loss distribution manifests that boiler and turbine irreversibilities account for the highest exergy losses in the power plant. Therefore, efforts at improving the power plant performance should be directed at improving boiler efficiency, since this will lead to maximization of plant efficiency. Another scholar, in his research, found that sliding pressure operation is better than constant pressure operation at part loads due to reduced throttling losses at part-load operation. Also, a large reduction in rate of exergy destruction has been observed for turbine. Hence, turbine should be operated at varying pressure at part load in order to maximize its efficiency.