Energy-exergy analysis and energy efficiency improvement of coal-fired industrial boilers based on thermal test data

Energy conservation and emission reduction in coal-fired boilers are significant to mitigate climate change and alleviate environmental pollution. In this study, the potential for efficiency promotion is assessed by understanding the factors affecting boiler performance. The results are based on thermal tests of 141 coal-fired industrial boilers in Liaoning province, China. Additionally, an exergy analysis model suitable for coal-fired industrial boilers is proposed under the framework of the first and second laws of thermodynamics to improve the operation of boilers. The energy and exergy efficiencies as well as CO2 emissions have been discussed as well. The results indicate that the heat loss of flue gas and unburnt carbon represent the main heat losses. Exergy loss is dominated by destruction due to irreversibility in coal combustion and heat transfer. Average energy efficiency and CO2 emission of 141 boilers were estimated to be 76.08% and 147.13 kg-CO2/GJ, respectively. Exergy efficiencies of typical samples were estimated at about 12.88% for hot water boiler and 27.97% for steam boiler. Raising the efficiencies of 141 boilers to the target level proposed in the standard will lead to a decrease of coal consumption by 155 kt, emission reduction of 341 kt for CO2, 3.72 kt for SO2, and 3.48 kt for NOx per year.