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Computational fluid dynamics (CFD) has become an essential tool for optimizing the design and diagnosing the operation of a boiler. However, the validity of the results depends on the degree of numerical diffusion as well as the reliability of the submodels. This study aims to assess mesh sensitivity in the reacting two-phase flow of pulverized coal in a common tangential-firing boiler. Three mesh versions were constructed for the boiler with the number of cells ranging between 1.2 million and 5.4 million, corresponding to 0.0114 -0.0022 m3 per cell in the burner zone. The velocity distribution was found to be highly sensitive compared to temperature, heat flux, and NO concentration. By contrast, the use of key performance parameters such as total wall heat absorption, exit NOx concentration, and carbon conversion, was not appropriate criteria for the mesh sensitivity test. These parameters were determined by integration over the entire surface or volume, which made them sensitive to the overall reaction stoichiometry instead of the mesh fineness. It suggests that the use of a coarse mesh could be acceptable in evaluating the key performance parameters influenced by major operation variables, such as air distribution and fuel properties. However, sufficient mesh fineness is necessary for studies requiring accurate prediction of detailed flow patterns such as the evaluation of burner tilting/yawing or ash deposition on the wall.

The use of separated overfire air (SOFA) has become a standard technique of air staging for NOx reduction in the coal-fired boiler and can also be applied to existing boilers by retrofit. This study was to optimize the air distribution for the proposed SOFA installation in a 500 MWe tangential-firing boiler that has 20 identical units in Korea. Using computational fluid dynamics (CFD) incorporating advanced coal combustion submodels, the reference case was established in good agreement with the design data, and different flow ratios of burner secondary air, close-coupled OFA (CCOFA), and SOFA were evaluated. Increasing the total OFA ratio effectively suppressed NO formation within the burner zone but had a negative impact on the boiler performance. With moderate air staging, NO reduction became active between the CCOFA and SOFA levels and, therefore, the OFA distribution could be optimized for the overall boiler performance. For total OFA ratios of 25% and 30% with respective burner zone stoichiometric ratios of 0.847 and 0.791, increasing the SOFA ratio to 15% and 20%, respectively, was ideal for decreasing the unburned carbon release and ash slagging as well as NO emission. Too high or low SOFA ratios rapidly increased the unburned carbon because of inefficient mixing between the strong air jets and char particles. Based on these ideal cases, the actual air distribution can be adjusted depending on the coal properties such as the ash slagging propensity.

For renewable electricity production, biomass can fully displace coal in an existing power plant with some equipment modifications. Recently, a 125 MWe power plant burning mainly anthracite in Korea was retrofitted for dedicated wood pellet combustion with a change of boiler configuration from arch firing to wall firing. However, this boiler suffers from operational problems caused by high unburned carbon (UBC) contents in the bottom ash. This study comprises an investigation of some methods to reduce the UBC release while achieving lower NOx emissions. The computational fluid dynamics approach was established and validated for typical operating data. Subsequently, it was applied to elucidate the particle combustion and flow characteristics leading to the high UBC content and to evaluate the operating variables for improving the boiler performance. It was found that the high UBC content in the bottom ash was a combined effect of the poor fuel grindability and low gas velocity in the wide burner zone originating from the arch-firing boiler. This prevented the operation with deeper air staging for lower NOx emissions. Reducing the particle size to x emissions with deeper air staging while increasing the boiler efficiency.

A reduced-order model (ROM) for an entrained flow coal gasifier provides a real-time dynamic prediction of key performance parameters under various operating conditions. However, existing 1D ROMs cannot consider coal burners located on the sidewalls in Shell coal gasifiers frequently applied in commercial plants. In this study, a pseudo-2D ROM was developed to consider the characteristic flow pattern of the gasifier and coupled with a discretized slag-layer model for the wall. Some input parameters specific to the gasifier were determined from a detailed computational fluid dynamics study. Further, the measured differences between input coal ash and bottom slag composition were incorporated in the slag viscosity. The ROM was validated in two ways using the design and operation data of a 300-MW IGCC plant. First, the steady-state prediction showed good agreement with the design data at various loads in terms of syngas composition, heat duty, and exit gas temperature. This also implied that the predicted slag thickness on the wall was reasonable. Second, the ROM was applied to actual operation data over 7 h with two events. For a gradual increase in the target O2/coal ratio and sudden changes in the coal throughput, the dynamic response of the measured heat duty was successfully reproduced by the ROM. The predicted exit gas temperature reflected the instantaneous fluctuations of O2/coal ratio and appeared more reasonable than the correlation-based value used by the operators. The ROM clearly showed differences in the response rate between the exit gas temperature, heat duty, cold gas efficiency, and slag thickness for changes in the operation variables. It can be used as a real-time online simulator for advanced gasifier operation.

We systematically analyzed the Wetland Conservation Action Plan of Gyeongsangnam Province to evaluate conservation status in local government level. Project topics were categorized into 1) wetland infrastructure, 2) wetland conservation and wise use, 3) education and awareness, and 4) conservation framework. From 2010 to 2013, 42 projects (145 cases, 88,899 million won) were implemented by 14 affiliated organizations under Gyeongsangnam Provincial Government. The number of projects and budget size has been decreased over 4 years, besides most of main projects were continued. The budgets were largely used for wetland project of cities and counties. Development and implementation of various conservation projects may have considerable potential values in wetland conservation, while it is still difficult to assess their overall effectiveness in the society. Diverse wetland management practices in Gyeongsangnam Provincial Government have accumulated fundamental practices and knowledge for an effective local conservation. These administrative experiences will further benefit other local government to establish wetland management framework. To accelerate policy diffusion to other local governments, Gyeongsangnam Province needs to promote and share leading experiences and information of wetland conservation. Enhanced local government framework by the legislation at central government will further support country-level management plans and practices.