## 3 Results and Discussion
### In-Situ Electro-Chlorination Experiment with CFD Simulation
\begin{table}
\begin{tabular}{c c c c c c c c c c} \hline \hline \multirow{2}{*}{**Flow Rate**} & \multicolumn{3}{c}{**Chlorine Concentration**} & \multicolumn{6}{c}{**Sampling Ports**} & \multirow{2}{*}{**Avg.**} \\ \cline{3-3} \cline{5-10}  & & **(mg L\({}^{-1}\))** & & & & & & & & \\ \cline{3-3} \cline{5-10}  & Experiment & 1.32 & 1.11 & 0.99 & 0.94 & 0.86 & No data & 0.50 & \\ \cline{3-3} \cline{5-10}  & Simulation with decay kinetics & 1.37 & 1.09 & 0.93 & 0.83 & 0.75 & 0.60 & 0.58 & \\ \cline{3-3} \cline{5-10}  & Simulation without decay kinetics & 1.37 & 1.10 & 0.94 & 0.84 & 0.77 & 0.63 & 0.63 & \\ \cline{3-3} \cline{5-10}  & Error with decay kinetics (\%) & 4 & 1 & 6 & 12 & 13 & - & 16 & 9 \\ \cline{3-3} \cline{5-10}  & Error without decay kinetics (\%) & 4 & 0 & 5 & 11 & 11 & - & 26 & 9 \\ \hline \multirow{3}{*}{\(700\) L min\({}^{-1}\)} & Experiment & 1.26 & 0.94 & 0.82 & 0.65 & 0.71 & 0.57 & 0.49 & \\ \cline{3-3} \cline{5-10}  & Simulation with decay kinetics & 1.17 & 0.95 & 0.81 & 0.72 & 0.66 & 0.52 & 0.50 & \\ \cline{3-3} \cline{5-10}  & Simulation without decay kinetics & 1.18 & 0.96 & 0.82 & 0.73 & 0.67 & 0.54 & 0.54 & \\ \cline{3-3} \cline{5-10}  & Error with decay kinetics (\%) & 7 & 1 & 0 & 11 & 7 & 9 & 2 & 5 \\ \cline{3-3} \cline{5-10}  & Error without decay kinetics (\%) & 6 & 2 & 1 & 13 & 5 & 4 & 10 & 6 \\ \hline \multirow{3}{*}{\(800\) L min\({}^{-1}\)} & Experiment & 1.29 & 0.88 & 0.67 & 0.85 & 0.62 & 0.55 & 0.36 & \\ \cline{3-3} \cline{5-10}  & Simulation with decay kinetics & 1.01 & 0.84 & 0.72 & 0.64 & 0.58 & 0.45 & 0.44 & \\ \cline{3-3} \cline{5-10}  & Simulation without decay kinetics & 1.02 & 0.85 & 0.72 & 0.65 & 0.59 & 0.47 & 0.47 & \\ \cline{3-3} \cline{5-10}  & Error with decay kinetics (\%) & 21 & 5 & 7 & 25 & 6 & 18 & 23 & 15 \\ \cline{3-3} \cline{5-10}  & Error without decay kinetics (\%) & 21 & 4 & 8 & 24 & 5 & 14 & 31 & 15 \\ \hline \multirow{3}{*}{\(900\) L min\({}^{-1}\)} & Experiment & 0.78 & 0.76 & 0.56 & 0.52 & 0.53 & 0.37 & 0.51 & \\ \cline{3-3} \cline{5-10}  & Simulation with decay kinetics & 0.89 & 0.71 & 0.60 & 0.53 & 0.49 & 0.41 & 0.40 & \\ \cline{3-3} \cline{5-10}  & Simulation without decay kinetics & 0.89 & 0.71 & 0.60 & 0.54 & 0.50 & 0.42 & 0.42 & \\ \cline{3-3} \cline{5-10}  & Error with decay kinetics (\%) & 13 & 7 & 7 & 2 & 8 & 11 & 22 & 10 \\ \cline{3-3} \cline{5-10}  & Error without decay kinetics (\%) & 14 & 6 & 8 & 4 & 7 & 15 & 17 & 10 \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Free chlorine concentrations in the electro-chlorination experiment. simulation. Figure 9a compares the chlorine concentration along the surface of the pipe between the cases of in-situ electro-chlorination and direct chlorine injection. After passing through the first 50 m of pipe, the chlorine concentration of the in-situ case was reduced to 0.5 mg L\({}^{-1}\) mainly due to diffusion. As a result, the second electrode should be installed at 50 m apart within such a system. On the other hand, the chlorine concentration of the direct injection case in which water mixed well with chlorine was stable around 0.65 mg L\({}^{-1}\), which was expected to be lower than 0.5 mg L\({}^{-1}\) at the end of the pipe due to chlorine decay. Figure 9b presents the relative chlorine demands of each case. It was estimated that in-situ electro-chlorination would demand only 1/3 of chlorine dose that is required by the direct chlorine injection, even though in-situ electro-chlorination could generate higher chlorine concentrations along the surface of the pipes (exceeding 0.5 mg L\({}^{-1}\)) (Figure 9a). While the simulation provides insight into the feasibility of in-situ chlorination for practical applications, this estimation does not consider pipe curvature, fluid elevation, or any other structures that might be placed in the fluid path. Real chlorine demands can vary depending on the conditions in individual power plants. Figure 8: Chlorine concentration contour in the simulation of full-scale in-situ electro-chlorination with different cathode positions.