# In Situ Measurement of Alkali Metals in an MSW Incinerator Using a Spontaneous Emission Spectrum
## 4 Results and Analysis
### Temperature, Emissivity, and Alkaline Metal Emission Lines from MSW Flame Spectra  
According to measurement principles, the temperature and emissivity can be derived from continuous spectral radiation intensities based on [PERSON]'s emissivity model. The emissivity distributions of the three MSW flame spectra represented in Figure 3b are given in Figure 5. These figures demonstrate that the MSW flame shows non-gray characteristics in a wavelength range of 500 nm to 900 nm, caused by an increased amount of soot particles in the flame. The corresponding temperatures of the three cases are 1282 K, 1335 K, and 1379 K, respectively.  
To validate the accuracy of the results, the spectral radiation intensities were re-calculated by substituting the values of the temperature and emissivity into Equation (3). Comparing the re-calculated and measured spectral radiation intensities, as shown in Figure 6, it was found that they matched well in the continuous wavelength range.  
Figure 5: Emissivity distributions calculated from spectral radiation intensities in Figure 3b.  
Figure 6: Comparison of the re-calculated and measured spectral radiation intensities.  
As mentioned in Section 3, the intensities of the emission lines of the alkali metals were obtained by deducting the continuous spectral radiation intensities from the measured spectral radiation intensities. Figure 7 lists the intensities of the alkali metal emission lines of the three MSW flame spectra depicted in Figure 3b. The intensities of the alkali metal emission lines were taken to compare with those of the background radiation, and the results show that the relationship between them is nearly five times, so uncoupling the continuous spectrum and the characteristic lines is necessary for the temperature measurement of K and Na.  
The strength of the alkali metals' emission lines is a complex function of the concentration of the alkali metals, and it also depends on the self-absorption of the radiation. For small-scale flames enriched by alkali metals, the concentration distributions of the alkali metals are generally assumed to be uniform. Some methods similar to those described in the literature [22] may be used to correct the effect of self-absorption. However, for an industrial MSW incinerator, which has a large furnace cavity, these concentration distributions of the alkali metals in the furnace are inappropriately assumed to be uniform. In such cases, it is difficult to correct for the effect of self-absorption using methods such as those described in the literature [23]. It is best to reconstruct the 2D and/or 3D distribution of local quantities inside the isothermal and homogeneous combustion chambers, as is often done for a large-scale, coal-fired boiler furnace by means of a visible flame image processing system with many detectors [24]. In this article, by means of a single spectrometer detector, line-of-sight values were determined for the measurement of the flame temperature, the radiation intensity of the alkali metals, and the flame emissivity. In this article, the peak intensities of the alkali metals' emission lines are used for in situ monitoring of the alkali metal content in the MSW flame.