# In Situ Measurement of Alkali Metals in an MSW Incinerator Using a Spontaneous Emission Spectrum
## 1 Introduction  
The rapid development of modern society has resulted in the production of an increasing volume of MSW. The disposal, treatment and management of MSW are common problems in the world. Incineration has been widely used for the disposal of MSW in order to conserve fuel and protect the environment by lessening the amount of MSW in landfills [1; 2]. However, emissions of trace organic compounds--particularly polychlorinated dioxins and furans, and heavy metals such as mercury, lead and cadmium--are major environmental hazards caused by MSW incineration. Alkali and alkaline earth metals are typically found in high concentrations in MSW. These alkali metal compounds often contribute to the fouling and corrosion of the heating surfaces of fluidized bed andgrate incinerators. To understand the transfer of heavy metals and alkali and alkaline earth metals, and to control the emission of these metals in MSW incineration, certain methods for measuring the metal species in flue gasses have been applied--including absorption, emission, plasma spectroscopy, and ionization/mass spectrometric methods [3; 4]. In addition, other analysis techniques, such as X-ray fluorescence (XRF), energy dispersive X-ray spectroscopy (EDX), scanning electron microscope combined energy dispersive spectrometer (SEM-EDS) and X-ray diffraction (XRD), have been used to provide supporting/complementary data about the metal species in fuel and ash [5]. However, few in situ measuring systems focus on combustion or flame inside the incinerator. Only two of the studies we reviewed [6; 7] used infrared thermographic cameras to replace thermocouples and to obtain a temperature map inside the combustion chambers of incineration plants. These studies demonstrated that in situ monitoring combustion can be helpful, particularly for control and optimization purposes. Some research has reviewed diagnostic techniques for monitoring and controlling flames [8; 9]. Optical methods based on laser diagnostic techniques have been applied for measuring velocity, temperature, species, and particulate in flames. However, using these latter methods presents some challenges in practical industrial furnaces and incinerators, because of the limited optical access, the laser attenuation by the particulate medium and other factors. Flame emission spectroscopy (FES) is another alternative non-intrusive approach for diagnosing flames. The spontaneous emission spectra of flames contain continuous spectra from the blackbody radiation of solid particles (e.g., soot, char, or ash particles); from the band spectra produced by the radiation of gas molecules (e.g., CO\({}_{2}\) or H\({}_{2}\)O); from the chemiluminescence of excited radicals (e.g., OH, CH, or C\({}_{2}\)); and from the line spectra of free atoms (e.g., alkalis or alkaline earth metals) [10]. Based on the measurement and analysis of the spontaneous emission spectra of flames, FES has been proposed to determine equivalence ratios [9], to monitor flame stoichiometry [9; 11] and to calculate flame temperatures in a natural gas-fired furnace [12], a pulverized coal-fired furnace [13; 14], a gasification facility [15], an aluminum flame [16], and even an MSW incinerator [17]. For the flame of the MSW incinerator, strong characteristic emission lines of Na and K are observed in the visible spectra in the experiments, and more studies are needed to know if this type spectrum could be used for measurement temperature, while related works are relatively few in number. In this paper, experimental investigations involving in situ measuring and analyzing spontaneous emission spectra of MSW flames in a grate incinerator using FES are presented. First, the experimental setup, including the grate incinerator and a spectrometer system, will be introduced, and then the measurement principle will be described. Then, the results of temperature, emissivity and intensities of the emissions lines of the alkali metals derived from MSW flame spectra in the incinerator will be given.