Advanced exergy analysis of a steam power plant with second-level decomposition of exergy destruction

Conventional exergy analysis of thermal systems does not fully reveal the inter-component interactions that result in sub-optimal performances nor the full potentials for improving performance. The advanced exergy analysis overcomes these limitations by determining avoidable and unavoidable, endogenous and exogenous exergy destructions in energy system components. This paper reports the advanced exergy analysis of a steam power plant. Exogenous exergy destruction rates were determined using the recent decomposition method, while a second-level splitting of component exergy destruction rates was implemented. More of the exergy destruction rates (83%) were also found to be endogenous, indicating a limited contribution of inter-component interactions to reduced component performances. The contributions of the avoidable endogenous and avoidable exogenous exergy destruction rates to overall plant exergy destructions were 17.1% and 3.6%, respectively. The modified exergy efficiencies in the boiler section were, respectively, 81.8% and 79.57% for the superheater and the reheater. These were obtained by realistically excluding the avoidable exergy destruction portions and were significantly higher than the respective conventional exergy efficiencies (41.08% and 44.86%). The resulting ranking of the plant components (based on the advanced exergy performances) prioritizes the boiler section the most for improvement, while the least prioritized component is the deaerator.