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Open AccessArticle

Comparative Evaluation of Integrated Waste Heat Utilization Systems for Coal-Fired Power Plants Based on In-Depth Boiler-Turbine Integration and Organic Rankine Cycle

1
National Research Center for Thermal Power Engineering and Technology, North China Electric Power University, Changping district, Beijing 102206, China
2
Shenhua Guohua (Beijing) Electric Power Research Institute, Chaoyang district, Beijing 100025, China
3
Industrial Process and Energy Systems Engineering, Swiss Federal Institute of Technology in Lausanne, Sion 1951, Switzerland
*
Author to whom correspondence should be addressed.
Entropy 2018, 20(2), 89; https://doi.org/10.3390/e20020089
Received: 7 November 2017 / Revised: 30 December 2017 / Accepted: 20 January 2018 / Published: 29 January 2018
(This article belongs to the Special Issue Work Availability and Exergy Analysis)
To maximize the system-level heat integration, three retrofit concepts of waste heat recovery via organic Rankine cycle (ORC), in-depth boiler-turbine integration, and coupling of both are proposed, analyzed and comprehensively compared in terms of thermodynamic and economic performances. For thermodynamic analysis, exergy analysis is employed with grand composite curves illustrated to identify how the systems are fundamentally and quantitatively improved, and to highlight key processes for system improvement. For economic analysis, annual revenue and investment payback period are calculated based on the estimation of capital investment of each component to identify the economic feasibility and competitiveness of each retrofit concept proposed. The results show that the in-depth boiler-turbine integration achieves a better temperature match of heat flows involved for different fluids and multi-stage air preheating, thus a significant improvement of power output (23.99 MW), which is much larger than that of the system with only ORC (6.49 MW). This is mainly due to the limitation of the ultra-low temperature (from 135 to 75 °C) heat available from the flue gas for ORC. The thermodynamic improvement is mostly contributed by the reduction of exergy destruction within the boiler subsystem, which is eventually converted to mechanical power; while the exergy destruction within the turbine system is almost not changed for the three concepts. The selection of ORC working fluids is performed to maximize the power output. Due to the low-grade heat source, the cycle with R11 offers the largest additional net power generation but is not significantly better than the other preselected working fluids. Economically, the in-depth boiler-turbine integration is the most economic completive solution with a payback period of only 0.78 year. The ORC concept is less attractive for a sole application due to a long payback time (2.26 years). However, by coupling both concepts, a net power output of 26.51 MW and a payback time of almost one year are achieved, which may promote the large-scale production and deployment of ORC with a cost reduction and competitiveness enhancement. View Full-Text
Keywords: coal-fired power plants; waste heat utilization; organic Rankine cycle; exergy analysis; in-depth boiler-turbine integration coal-fired power plants; waste heat utilization; organic Rankine cycle; exergy analysis; in-depth boiler-turbine integration
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Huang, S.; Li, C.; Tan, T.; Fu, P.; Wang, L.; Yang, Y. Comparative Evaluation of Integrated Waste Heat Utilization Systems for Coal-Fired Power Plants Based on In-Depth Boiler-Turbine Integration and Organic Rankine Cycle. Entropy 2018, 20, 89.

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