Research On Radiative Properties Of MSW Incineration Flames And Their Combustion Optimization

Municipal solid waste?MSW?in China usually has the charateristics of complex and variable fractions,high moisture content and low heating value.When this kind of MSW is feed into the grate type incinerators,there often exist problems,such as partial combustion of MSW and excessive incineration pollutants.Therefore,the combustion diagnosis of the grate type incinerators is very essential to improve the incineration efficiency and reduce the environmental pollution.Flame temperature is one of the most important parameters for characterizing combustion state,and its measurement has become the main method of combustion diagnosis.At present,flame emission spectroscopy?FES?is the most promising technique for flame temperature measurement.Owing to the lack of a model accurately describing the flame emissivity,the FES typically treats the non-gray flames as gray materials.Consequently,this method measures the brightness temperature,instead of the true temperatue,which limits the combustion diagnosis accuracy of grate type incinerators.The primary aim of this doctoral dissertation is to develop a spectral emissivity model of MSW incineration flames.After the emission spectra of various MSW incineration flames were experimentally analyzed,the emission intensity of these flames was found to be dominated by soot particle clouds inside.According to the experimentally-determined soot particle structures,the radiative properties of soot particles were quantitatively calculated,and the spectral emissivity model of MSW incineration flames was developed.Finally,this study propsed a spectral emissivity model-based flame temperature measurement method and implemented combustion diagnostic optimization for a 700 t/d grate type incinerator.Results in this study are listed below:Firstly,the emission spectra of various MSW incineration flames were investigated,which can target the research object for the following work.The results showed that at the wavelengths of?=0.5-0.9?m the emission spectra of MSW incineration flames contain continuous spectra from particulate materials and line atomic spectra from alkalis.Given that the emission spectra of gaseous products of MSW incineration are mainly distributed in the ultraviolet and far-infrared regions and particulate materials inside flames are mainly soot particles,soot particles are thus deemed to dominate the emission intensity of MSW incineration flames.Furthermore,the research on the radiative properties of MSW incineration flames is transformed into those of soot particles inside flames.The morphological structure of soot particles in MSW incineration flames was then determined experimentally,which laid the foundation for accurately calculating the radiative properties of soot particles.In addition,to facilitate the proposal and verification of a general radiative property calculation model for different soot particle clouds,laminar ethylene diffusion flames were adopted to simplify the diffusion flames of olefin volatile gases during MSW prolysis.The results showed that in the separate and mixed incineration flames of MSW and laminar ethylene diffusion flames,the???_p of soot particles was 26.5-46 nm,the???was 48-107,theD_fwas 1.70-1.79,and the k_f was 2.05-2.48 the soot primary particle size distribution PDF?d_p?and the soot primary particle number distribution PDF?N?can be fitted well using the?double?lognormal distribution.According to the experimentally-determined structural parameters of soot particles,a more realistic simulation for the aggregation of soot primary particles was proposed.The simulation results regarding flames under different O₂concentrations showed that the aggregation process of soot primary particles is very rapid,and it took less than 20 ms to generate large-sized soot particle?N=50-150?when the O₂ concentration increased from 21%to 40%,the time required by the aggregation process gradually decreased from 18.5 ms to 8.8 ms,while the D_f and k_f of simulated soot particles were almost unchanged?D_f=1.70-1.74 and k_f=2.13-2.23?.Basd on the simulated three-dimensional structure of soot particles and the discrete dipole approximation?DDA?method,a calculation model was put forward,which can quantitatively calculate the radiative properties of soot particle clouds in MSW incineration flames,such as absorption efficiency?,scattering efficiency?,asymmetry factor g and ?single scattering albedo.The calculation results showed that the?,?,g and?of soot particle clouds would increase or hit plateau with the increasing of???_p?and???when the incident wavelength ?rose from 0.40?m to 3.00?m,the values of?,?,g and?would descend by 70-99%.By analyzing the quantitative calculations of radiative properties of soot particle clouds in MSW incineration flames,a spectral emissivity model for these flames was eventually proposed:????=1-exp(-MX?^-1.23),and a flame temperature method based on flame emission images was developed incorporating this spectral emissivity model.The accuracy of this flame temperature method was confirmed experimentally,and successfully applied for the combustion diagnosis optimization of a 700 t/d grate type incinerator.