Dr Soonho Lee

Advancements in supercritical (SC), ultrasupercritical (USC), and advanced USC coal-fired power plants have been achieved through the development of enhanced materials utilized in advanced steam cycles and through the deployment of advanced emission control systems. These are referred to as high-efficiency low-emission (HELE) technologies, which may solve numerous issues associated with coal-based power generation. There is a clear global transition from subcritical to advanced power plant types and significant R&D work on HELE technologies. Therefore, this comprehensive review covers the latest HELE technology deployment in major coal-consuming countries and their R&D roadmaps to advance HELE technologies. In spite of the various advantages of HELE technologies, there have been numerous technical challenges relevant to achieving the HELE steam conditions and deploying low emission control technologies in the HELE systems. Hence, this review covers the technical challenges and the relevant recent research by using various coal combustion test facilities. The current focus for the progression from USC boilers to advanced USC boilers is a successful demonstration of the developed high-performance alloys under the advanced steam conditions. This review covers the current status of research and development of advanced USC (A-USC) materials and challenges based on the major material research programs.

High-efficiency, low-emissions (HELE) coal-fired power plant technologies operate with a higher thermal efficiency of the steam cycle for coal-fired power generation, reducing CO2 emissions per unit energy generation. They represent some of the primary and intermediate solutions to the world's energy security. Extensive numerical modeling efforts have been undertaken over the past several decades, which have increased our understanding of the technical problems in HELE boilers, including combustion and boiler performance optimization, ash deposition, and material problems at higher operating temperatures and pressures. Overall, the differences in the physical and chemical models, boiler performance, and ash deposition of oxy-fuel combustion in HELE boilers that recirculate CO2 and H2O in the boilers are also discussed in comparison with the combustion of coal in the air. This Review comprehensively summarizes the current research on numerical modeling to offer a better understanding of the technical aspects and provides future research requirements of HELE coal-fired boilers, including boiler performance optimization, ash deposition, and material problems. The effects of changes in the configuration and operating conditions are discussed, focusing on the optimization of boiler performance in aspects such as unburnt carbon and NOx emissions. The paper also reviews the retrofit and optimization of operating conditions and the burner geometry with the low-NOx coal combustion technologies necessary to operate the HELE power plants. In terms of ash deposition, the development of submodels, including particle sticking and impacting behaviors and their effects on the deposit growth predictions under different temperatures, are discussed. Numerical models of the material oxidation and creep in the austenitic and nickel-based alloys generally used in HELE conditions have been developed using the finite element method to predict the availability of advanced alloys and creep life in the actual service time of the boiler parts. The predictions of oxide scale growth and exfoliation on the steam-side and fire-side and the creep strength are analyzed. The review also identifies some further research requirements in numerical modeling to achieve the optimization of coal combustion processes and address the technical problems in advanced HELE power plant operations.

The changes in chemical structures over the plastic layer region during the coking of coals have a significant impact on coke formation and coke quality. This paper employed the Solid-state 13Carbon Nuclear Magnetic Resonance (13C NMR), and the Synchrotron attenuated total reflection Fourier transform infrared (ATR-FTIR) microspectroscopy (Synchrotron IR) to study the transformation of the chemical structures in plastic layer samples. The light gases (mainly methane and hydrogen) released from coking process were analyzed using micro gas chromatography (micro-GC) connected to a small coking reactor heated in an electric furnace that simulated the formation of the plastic layers. The results show clearly that the total aromaticity increased consistently in the plastic layers for all coals tested, while the amounts of side-chains decreased significantly during the plastic layer. There was a clear trend showing that the total number of bridge bonds and the looped structures, indicating that the degree of cross-linking would increase through the plastic layer. The plastic layer samples from low fluidity exhibited cross-linking structures with a high degree of branching and aromaticity, while those from high fluidity coals formed cross-linking structures with a relatively low degree of aromaticity and branching but with a large number of bridge bonds and looped structures. The transferable methyl, methylene and hydrogen were strongly correlated to the cross-linking reaction and side-chain elimination in the thermoplastic region, which is reflected by the release profiles of methane and hydrogen gas during the plastic layer stage.