## 1 Introduction  
Energy consumption has been increasing explosively throughout the world in both developed and developing countries. Energy production from fossil fuel makes up 80% of the world's energy and all researchers are concerned with the environmental problems caused by the use of fossil fuels. Oxides of sulfur (SOx) and nitrogen (NOx) are emitted from powerplants that use the fine dust of pulverized coal since a power source must be reduced. Therefore, regulations on emissions must be more restrictive, not only those from powerplants but also from cars, ships, and other fossil-fuel vehicles [1; 2; 3; 4]. In countries such as China and India, where there is a rapidly increasing industrial demand for power, the increase in the demand brings increases in the price of coal, which causes several countries, such as Korea, to import low-quality or other types of coal to use as fuel [5]. These pulverized-coal powerplants have several problems related to combustion, particularly exhaust emissions from the fuel combustion process. In general, the main environmental pollutants are greenhouse gases (GHGs), fine dust particles, and precursors of Sox and NOx. Since the fine dust-related social issues are becoming more important, a reduction in SOx and NOx generation is one of the most important issues. Therefore, accurate predictions and measurements of combustion emission gases are very important for establishing better environmental effects from boiler operations and fuel use. The reaction mechanism in SOx production is well known and the number of SOx generated is predictable. Therefore, powerplants already use this information as a basis for estimating fossil fuel shift time using SOx [6]. Conversely, it is difficult to predict the amount of NOx generated, and most efforts to predict the amounts from the complicated mechanisms of action through which this pollutant is generated are formulas based on experiments and experience and cannot be precisely explained [7]. However, guidelines are needed for predictive values that are easy to apply to the emission of exhaust under established operational conditions and powerplant and research and development (R&D) infrastructure facilities continue to create indices to use as experimental factors in a prediction formula. Therefore, R&D on identifying the factors for predicting NOx generation based on experimental and empirical formulas is becoming more important in setting up operational conditions in the backend facilities to decrease NOx and operate boilers in thermal powerplants that use various types of fuel. The prediction of the NOx emissions of coal has been attempted for a long time. Every combustion process of the boilers depends on their own individual combustion technique and operation conditions. Tremendous complicated influence factors affect NOx emissions. Several researchers introduced have experimentally established the NOx prediction formula and used the system indicators (coefficients) to express the operating conditions and boiler types. Researchers, including [PERSON], developed empirical formulas for NOx generation using the characteristics of coal. Based on nine types of coal, researchers conducted the experiments at reactor sites with an electric heating furnace and created an empirical formula for NOx conversion from the amount of carbon monoxide (CO) and CO\({}_{2}\) generated [8]. Other researchers, such as [PERSON], studied the phenomenon of NOx generation based on different types of coal [9]. A linear regression analysis on NOx emissions and the characteristics of coal showed a dispersity between NOx emissions from the coal's volatilized amount and the fuel ratio (FR) and created a coefficient of regression and coefficient of determination. However, the results also showed that, while applying the actual results to the data, they did not correspond to the experimental characteristics.