## 3 Results and Discussion
### DTF Experiment Results
#### 3.2.2 DTF NOx Index  
The material properties of coal used to predict NOx emissions are listed in Table 3, using moisture content, according to the industrial analysis, fixed carbon, In(FR/FN), and NOx concentration calculated by an empirical formula using these three factors. The calculated and actual NOx concentrations created using the DTF test indicate a relation in Figure 5, which shows a correlation coefficient of 0.9020 and R\({}^{2}\) = 0.8137, which was calculated using the following equation. \[[\text{Calculated NOx concentration}]=\text{a}+\text{b}\times[\text{ Moisture}]+\text{c}\times[\text{Fixed carbon}]+\text{d}\times\text{In}[\text{FR/FN}] \tag{2}\]  
where a, b, c, and d are function system indicators (coefficients), which are values that change according to the type of reactor and the operating conditions. Therefore, using this empirical formula, we compared it to the NOx concentration before entering SCR using the properties of the coals used in the practical operations of boiler #2 in the Hadong Thermal Power Site. At this site, two to three types of coals used for combustion were selected to meet the heat value standard and cofired. Therefore, the factors were determined by arithmetical calculation in accordance with the ratio of used coal from a single type of coal property. In Figure 6, one data dot on the X-axis represents NOx concentration at the SCR entrance generated from used coal combustion during each 8-hour time slot during the daytime shift (D/S), after time shift (A/S), and nighttime shift (N/S). NOx concentrations that were measured in the actual boiler are confidential data so are expressed as an arbitrary unit. NOx concentrations in the actual boiler were measured at two ducts located on the front of the SCR entrance and expressed as average values and actual data. The NOx concentrations measured from the same coals show a 20% to 50 % difference. This error in the difference could be from the turbulent flow inside the duct or from an error in the measuring instrument. The green dots that are calculated as evidence of a difference error must show the same NOx values calculated from the same coals used. However, we observed that the NOx concentration from actual combustion shows a major error, in some cases, in the differences in values. It is clear that, because the actual and calculated NOx concentrations do not always show the correct \begin{table}
\begin{tabular}{c c c c c c} \hline \hline \multirow{2}{*}{**No.**} & \multirow{2}{*}{**Sample**} & \multicolumn{2}{c}{**Moisture**} & \multicolumn{2}{c}{**Fixed Carbon**} & \multirow{2}{*}{**FR/FN(-)**} & \multirow{2}{*}{**Calculated**} \\  & & **Content (as/rec** & & & \\  & & **basis, wt \%)** & & & **NOx (ppmv)** \\ \hline
1 & Anglo & 4.71 & 54.75 & 141.7 & 218.17 \\
2 & Clermont & 2.73 & 58.84 & 115.7 & 246.31 \\
3 & Cloud peak & 19.73 & 39.25 & 52.7 & 50.42 \\
4 & Flame & 1.98 & 48.27 & 82 & 205.38 \\
5 & Glencore & 12.37 & 45.59 & 61.8 & 125.16 \\
6 & Indominco & 14.29 & 39.31 & 57.3 & 86.46 \\
7 & Lanna & 16.95 & 38.45 & 106.1 & 70.09 \\
8 & Light House & 18.35 & 42.11 & 87.9 & 74.7 \\
9 & Light House & 6.33 & 47.33 & 116.7 & 175.89 \\
10 & Macquarie & 9.18 & 47.62 & 86.6 & 156.52 \\
11 & Mercurai & 4.2 & 53.67 & 109.3 & 215.2 \\
12 & Moolarben & 1.86 & 52.3 & 103.4 & 224.33 \\
13 & NCA & 13.68 & 47.85 & 71.1 & 126.95 \\
14 & Noble & 3.19 & 55.39 & 140.9 & 230.59 \\
15 & Rio & 3.82 & 51.63 & 78.6 & 206.96 \\
16 & Trafigura & 3.94 & 51.43 & 128 & 208.82 \\
17 & Trafigura & 6.76 & 47.56 & 95.2 & 172.61 \\
18 & Trafigura & 4.87 & 47.29 & 65.7 & 181.09 \\
19 & Tugnuisky & 4.14 & 45.59 & 59 & 178.08 \\
20 & Vitol & 9.68 & 47.46 & 130 & 155.52 \\ \hline \hline \end{tabular}
\end{table} 
Table 3: Fuel sample properties to the NOx emission prediction. t trends when applying the empirical formula, as some researchers have reported, it appears correct to trust a drift in the generation of NOx concentrations since the combustion products are produced from the actual chemical reactions.