## 3 Results and Discussion  
After optimization, baffles were installed in the expansion duct. The corresponding configuration is shown in Figure 5. The specific sizes and locations of the baffles are shown in Figure 6.  
A group of crossed baffles were installed before the AIG. The corresponding configuration is shown in Figure 7. Figure 8 illustrates the specific sizes and locations of the baffles. The consumption of the 6 mm steel plate was about 1.13 m\({}^{3}\) and the corresponding surface area of the baffles was about 188 m\({}^{2}\), which is quite small compared with the sectional area of the catalyst layer of 430 m\({}^{2}\). Figure 9 shows the contours of gas velocity at the observation plane for the optimal design. According to Figure 9, the RSD of gas velocity is 11.90% and the maximum velocity is 6.64 m/s. Figure 4: The sketch map of detection spots over the perforate plate. Figure 10 gives the injection divisions of AIG and Figure 10 gives the corresponding non-uniform NH\({}_{3}\) injection strategy. Figure 11 shows the contours of NH\({}_{3}\) concentration with the non-uniform NH\({}_{3}\) injection strategy applied. The RSD of NH\({}_{3}\) concentration is 3.37% and the range varies from 1.53 \(\times\) 10\({}^{-3}\) to 1.86 \(\times\) 10\({}^{-3}\) kg/m\({}^{3}\), indicating that the flue gas and the NH\({}_{3}\) are mixed adequately. Figure 5: The baffles installation in the expansion duct for the optimal design (unit mm). Figure 6: The sizes and locations of the baffles installation in the expansion duct: (**a**) Y-positive view; (**b**) X-negative view. Figure 8: The sizes and locations of the crossed baffles installation at the upstream side of the AIG: (a) Y-positive view; (b) X-negative view. Figure 7: The crossed baffles installation at the upstream side of the ammonia injection grid (AIG) (unit mm). Figure 9: Contours of gas velocity at the observation plane for the optimal design (unit: m/s). Comparisons were made to evaluate the effect of the crossed baffles. Figure 12 illustrates the influence of the crossed baffles on gas velocities and NH\({}_{3}\) concentration. After installing the crossed baffles shown in Figures 7 and 8, the RSDs of gas velocity and NH\({}_{3}\) concentration decreased by 18.2% and 25.6%, respectively. It is revealed that the crossed baffles are helpful in regulating the flow field. Moreover, when optimizing the tower type SCR-deNO\({}_{x}\) facility with spatial constraints, regulating the flow field at the AIG may provide an effective way to achieve a more homogeneous distribution at the entrance of catalyst layers. Figure 11: Contours of NH\({}_{3}\) concentration at the observation plane for the optimal design (unit kg/m\({}^{3}\)). Figure 6.0 (**a**) The injection divisions of AIG (top view); (**b**) The corresponding non-uniformed NH\({}_{3}\) injection strategy (unit: m/s). In addition, in order to control pressure loss, all of the small-sized baffles were installed at the upstream side of the facility. Simulation results showed that the total pressure loss for the optimal design was 330.61 Pa, which is less than the requirement of 400 Pa.  
Table 1 summarizes the statistic indices of the tower type SCR-deNO\({}_{x}\) facility before and after the optimal design. According to Table 1, the RSDs of gas velocity and NH\({}_{3}\) concentration decreased by 18.30 and 5.50 percentage points, respectively. It is indicated that the flow field inside the SCR facility is regulated remarkably after the optimal design. The maximum velocity at the observation plane decreased by 6.83 m/s, which would greatly reduce the risk of catalyst breakage. Additionally, the existence of the optimal baffles provides an extra pressure loss of 195.44 Pa. Tables 2 and 3 show the measured values of air velocity and CO\({}_{2}\) concentration for the FMT experiments. According to Table 2, the RSD of air velocity is 11.24% and the maximum velocity is 4.76 m/s. FMT results show that the lower velocity areas are located in the upper edge and the bottom edge.