Optic Diagnostics On Pulverized Coal Particles Combustion Dynamics And Alkali Metal Release Behavior

Coal combustion is a complex physical and chemical process,including heterogeneous reaction.Even though the coal combustion research has been conducted for a hundred years,there still have a lot of problmes to be solved to meet the challenges of higher efficiency.At the meantime,pollutant dynamic generation like SOx,NOx and PM also increases the difficulties in coal combustion process exploring.Therefore,this thesis develops several optic diagnostic methods for the coal combustion research.For example,novel multi filter array and visible light signal methods are separately adopted to investigate the devolatilization and ignition process.Low intensity selective laser induced breakdown spectroscopy and RGB color pyrometry are also used to study the alkali metal dynamic behavior and char surface burnout temperature.In the end,transient ignition model and carbon burnout kinetic(CBK)model offer theoretical analyses for the devolatilization,ignition and burnout process.Firstly,this work design a novle multi filter techinique to detect the CH* signal during coal ignition,which can be used to characterize the volatile release and reaction process.This method is found to be useful in elimating the extra interference from the particle blackbody emission.The results imply that the temperatre has a dominate effect on the volatile release.After that,on the basis of devolatilization time scale analysis,this thesis isalsoassessing a study of the collective ignition behaviors of dispersed coal particle streams.The prevalent transition from heterogeneous ignition to hetero-homogeneous ignition due to ambience temperature is observed.Then,the effects of ambience temperature,oxygen mole fraction,oxy-fuel ambient and coal rank on the characterized ignition delay are examined.Besides,the transient model is developed,which not only well interprets the observed ignition transition phenomena,but also approximately predicts a variation of heterogeneous ignition time as a function of oxygen fraction.Since the Na relase behavior is strongly related to the coal devolatilization and ignition process.We furtherexamine the dynamic behavior of sodium(Na)release during the pulverized coal combustion of Zhundong lignite on Hencken burner.By utilizing the gap between the excitation energies of the gas and particle phases,a new low-intensity laser-induced breakdown spectroscopy(PS-LIBS)is developed to distinguish the existence of sodiumin the particle or gas phase along the combustion process.For the first time,thein situ verification of the gas phase Na release accompanying coal devolatilization is fulfilled when the ambient temperature is high enough.Furthermore,the effects of ambient temperature,coal rank and oxygen concentration are discussed.Based on the sampling results,it is founed that the devolatilization time,Na transition time and the particulate matter formation time are all strong related.In fact,particle temperature plays a very important role in coal burnout process and ash particle formation.The last part of this work use RGB color pyrometry and CBK model to study the char particle temperature on Hencken burner.An emissivity model based on the spectral emission measurement is employed to modify the RGB pyrometry.RGB method successfully detect the accurate surface temperature of burning char particles.The effect of temperature,oxygen mole fraction and oxy-fule ambient are also considered in this work.The CBK model also well predicts the char particle temperature history and investigate diameter,density and surface area changing behavior during char burnout.