## 3 Results
### Tests Results  
During the reported tests, 91 measurements were taken for different configurations and parameters of reagent injection into the combustion chamber of the boiler, which operated in the power range from 15 to 30 MW. Figure 14 shows the effect of varying the \(NSR\) on the NOx reductions obtained with respect to the three boiler power ranges, while Figure 15 shows the NOx reduction values obtained as a function of the boiler power.  
Figure 14: NOx reduction as a function of \(NSR\) for different boiler outputs.  
Figure 13: Iso-surfaces of urea concentration (blue) on the background of optimal temperature window and iso-surfaces of visible temperature (orange—1100 \({}^{\circ}\)C, yellow—900 \({}^{\circ}\)C).  
Figure 15: NOx reduction as a function of boiler output for different \(NSR\) values.  
The measurements presented in Figure 14 indicate an increase in NOx reduction in each boiler load range as the \(NSR\) increases. Furthermore, the best NOx reduction rates for the same NSR are obtained for lower boiler loads. The total results range is relatively wide: from a reduction level of approximately 15% (\(NSR\) 0.75, load range of 25-30 MW) to a reduction level of 75% (\(NSR\) 2.15, load range of 15-20 MW). Increasing the \(NSR\) from around 0.75 to a level exceeding 2.5 results in NOx reduction levels of 20%, 30%, and 35% for the 25-30 MW, 20-30 MW, and 15-20 MW load ranges, respectively.  
The measurement results are also presented in a different configuration in Figure 15. Most trials were carried out in the 20-25 MW power range due to the operating characteristics of the individual boiler. The graph shows a general trend of decreasing system efficiency with increasing boiler power, as well as a decrease in efficiency associated with a lower NSR.  
During performance tests of the designed SNCR system, nozzles with different numbers and diameters of holes were used. The test results showed that better performance was obtained with multiple-hole nozzles than with single-hole nozzles. Figure 16 shows a comparison of NOx reduction as a function of the reactant excess ratio for two different injection nozzle designs. During the test, the other SNCR plant operating parameters remained constant. The boiler was operated at approximately 20 MW.  
Based on the results presented in Figure 16, it can be concluded that three-hole nozzles allowed for several percentage points higher NOx reduction than single-hole nozzles. Photographs showing the reagent atomization in the cold boiler with the two-hole and three-hole nozzles taken during plant tests are shown in Figure 17.  
Figure 16: NOx reduction as a function of \(NSR\) for different injection lance nozzle designs.  
Figure 17: Photographs of the reagent spray jet in the boiler. The 3-hole nozzle (**left side**) and 2-hole nozzle (**right side**).  
Figure 18 illustrates the NOx-reduction comparison as a function of the \(NSR\) for three-hole and two-hole nozzles. During the test, the other SNCR plant operating parameters remained constant. The boiler operated at approximately 18-19 MW during the test runs.  
The chart shows that, for the location studied, higher reductions were obtained for the two-hole nozzles. The differences reached 3-4 percentage points.  
An aqueous urea solution was used as the reagent throughout the research cycle. The industrial AdBlue(r) product used has a concentration of 32.5%. In order to check the impact of urea concentration, the SNCR system efficiency was compared by using a 35 and 12% solution. Figure 19 compares the NOx reduction obtained for the different solution concentrations.  
The results confirmed the higher NOx reduction achieved for the lower urea concentration. Differences exceed up to ten percentage points. For the same \(NSR\) values, an improvement in NOx reduction efficiency of between 10% and 13% was achieved. With an NSR of less than 1.5, the installation efficiency using the lower urea concentration was about 55%, while for \(NSR\)s above 2, it was about 65%.