# In Situ Measurement of Alkali Metals in an MSW Incinerator Using a Spontaneous Emission Spectrum
## 4 Results and Analysis
### Comparison of Measured Results and Operating Parameters of the Incinerator  
Generally, in order to decrease the pollutant emissions, the incinerator is operated with an excess air coefficient of between 1.4 and 1.6, and at a temperature higher than 850 \({}^{\circ}\)C. The adjustment of the primary air is crucial for controlling the excess air and the temperature in MSW incineration. A test for changing the flow rate of the primary air flow from 28,000 to 35,000 m\({}^{3}\)/h has been conducted. The measured temperature, emissivity, and peak intensities of the alkali metals' emission lines were compared with the recorded primary air, actual evaporative capacity, and oxygen content of the incinerator, respectively. Figure 8 displays the normalized peak intensities of Na (589 nm), K (765.9 nm),  
Figure 7: Intensities of alkali metals’ emission lines calculated from spectral radiation intensities in Figure 3b.  
and Rb (779.4 nm) emission lines, and demonstrates that the flow rates of primary air varied with time. From Figure 8, it can be seen that when the primary air was high, the peak intensities of the alkali metal emissions increased. The increased primary air enhanced the particulate entrainment in the MSW flame, so more alkali metal entered the gaseous medium of the flame instead of staying in the ash. Therefore, the concentrations of alkali metals in the flame increased, which caused the peak intensities of the alkali metals' emission lines to increase. Changes in the peak intensities of the alkali metals' emission lines may be related to changes in the characteristics of the MSW. However, in this experiment, the composition of the MSW used changed only slightly.  
Additionally, the adjustment of the primary air affected the temperature of the MSW flame. Figure 9 displays temperatures derived from the MSW flame spectra and the primary air and shows that they varied with time. The temperature had a similar variation trend as the primary air. The increase in surface temperature on the particles leads to higher K and Na emissions; those results are similar to the release of alkali metal during biomass and coal combustion. The literature [24] shows that the release of K and Na from well-characterized biofuels was quantified as a function of temperature in a lab-scale fixed-bed reactor. [PERSON] et al. [25] investigated the release and transformation fundamentals of sodium during pyrolysis of two Zhundong bituminous coals, with experimental results showing that the release of sodium increases with temperature, indicating that temperature has a profound effect on the volatilization of sodium. The range of temperatures was between 1200 and 1400 K. In this temperature range, the emission of pollutants, such as dioxin, can be controlled.  
Figure 8: Peak intensities of the alkali metals’ emission lines and primary air varying with time.  
Figure 9: Temperatures of the MSW flame and primary air varying with time.  
Another interesting phenomenon was that the peak intensity of the K emission line had a linear relationship with the peak intensity of the Na emission line, as shown in Figure 10. This correlation may be attributed to the wide availability of these two metals in the waste, and also to their similar physicochemical characteristics. Na and K are both important elements in biomass, and because biomass (vegetable, plant, and garden wastes) forms a significant part of household waste, it stabilizes the ratio of Na and K in the MSW.  
Figure 11 displays the emissivity derived from the MSW flame spectra and oxygen content in the blue gas varying with time. It is interesting that the two parameters behaved in an approximately contrary manner, which may be explained by the soot in the flame. The increased oxygen content may have suppressed soot formation. Thus, emissivity from the soot particles generated in the MSW in the furnace may increase as the flame decreases.