Assessment of energy and exergy efficiencies in steam generators

Nowadays, more elaborate instruments are progressively required to evaluate the performance and efficiency of power plants, due to increasing concerns on climate change and the negative influence of carbon-fueled power plants on the greenhouse effect. Conventional approaches, such as mass and energy balances, result insufficient when considering solutions aimed at increasing global energy efficiency. The study presented herein focuses on the application of exergy analysis to the assessment of boilers, which are responsible for considerable exergy destruction in traditional, Rankine-based power plants. The study case considered a coal-fueled water tube boiler with 100 ton/h steam flow rate capacity. Even though exhaust gases presented high energy content, exergy analysis revealed that strategies aimed at minimizing the destruction of the capability to generate work should focus on: (1) heat transfer between exhaust gases and working fluid; and also the (2) combustion process itself. Technological advances applied to the reduction of exergy destruction in (1) and (2) are presented and discussed herein.