Comprehensive exergy-based evaluation and parametric study of a coal-fired ultra-supercritical power plant

摘要

In this paper, both conventional and advanced exergy analyses were conducted to a large-scale ultra-supercritical coal-fired power plant. The objectives of the conventional one are to compare the exergetic performances of different components, to identify and quantify the sites with the largest exergy destruction and losses, and to find the fuel-savings potential by improving each component in isolation. The advanced exergetic analysis focuses on the thermodynamic interactions among components and the sources for energy-saving potential of each component. Moreover, comparisons with several subcritical units are conducted and a sensitivity analysis shows the dependencies of the overall exergetic efficiency on a number of key design parameters. The results display the spatial distribution of exergy destruction and losses in detail and three performance ranges for different types of heat exchangers involved in the system. The energy-saving potentials at both the system and the component levels by improving an individual component are not in accordance with the amount of its exergy destruction. Improvement strategies for different components differ significantly due to the varied contributions of endogenous/ exogenous parts to their avoidable exergy destructions. With an increase in the steam conditions, the exergy destruction ratio of the boiler is significantly reduced, contributing mainly to the system improvement. The most effective and achievable measure for reducing the fuel consumption is still the reasonable utilization of available low-grade heat. This framework provides a basis for the quantifying proposals of exergy-driven strategies for improving the system.