Study On The Combustion Characteristics And Na Release Characteristics Of Zhundong Coal Based On Spontaneous Emission Spectrum Analysis

Zhundong coalfield in Xinjiang is the largest integrated coalfield in China,with huge reserves and good development prospects.However,Zhundong coal contains a large amount of Na,which will be released in the form of gas phase in the combustion process of Zhundong coal.As the flue gas flows through the heating surface of the boiler,and the temperature decreases on the heating surface of the boiler,it condenses and forms corrosion slagging,which seriously affects the combustion and utilization of Zhundong coal.The combustion temperature of Zhundong coal and the concentration of sodium in flame are the main factors affecting the slagging corrosion of boiler heating surface.Therefore,it is of great significance to detect the combustion characteristics and Na release characteristics of Zhundong coal for clean and efficient utilization of Zhundong coal.In order to realize the quantitative measurement of Na release concentration in the combustion process,a gas phase sodium concentration measurement method based on spontaneous emission spectrum analysis is proposed in this paper.The quantitative detection experiment of the relationship between the radiation intensity of Na characteristic spectrum in the flame containing Na ion and the Na concentration in the flame and the flame temperature is carried out,and the quantitative relationship between the three is established.During the experiment,the flame radiation spectra under 11 different temperature conditions and 6 different concentrations were collected.The spectral analysis results show that at the same temperature,the radiation intensity of Na characteristic spectral line after spectral self-absorption correction is linearly related to Na concentration.The temperature calibration coefficient is linear with the fitting results of blackbody radiation intensity at the same temperature.Considering the influence of Na concentration and flame temperature on the radiation intensity of characteristic spectral line of Na,the function relation of them is established as:I?589(T,CNa)=1.2966·Ib(I?589,T)·CNa?In this paper,Zhundong raw coal and Zhundong coal washed at 40? and 80?were used as the research objects.The combustion characteristics of Zhundong coal compressed particles and the release characteristics of Na in the combustion process were tested by in-situ spectroscopy based on flame self-radiation spectroscopy.The detected flame spectrum is superimposed by the continuous spectrum and the Na characteristic spectrum at 589 nm.The flame temperature is calculated by the multiwavelength method,and the Na release concentration is calculated by the calculated temperature and the functional relationship established above.The simultaneous detection of flame temperature and Na concentration was realized.Through the change of temperature and Na release concentration of Zhundong coal combustion flame,it can be judged that there are three different combustion stages in Zhundong coal combustion:volatile combustion stage,coke combustion stage and ash stage.The spectral analysis results show that when the heating environment temperature is 1600 K,the peak temperature of Zhundong raw coal,40? washing coal and 80? washing coal volatile combustion stage are 1790 K,1778 K and 1786 K,respectively.The peak release concentrations of Na were 3.48 ppm,1.91 ppm and 1.43 ppm,respectively.The peak values of Na release concentration during coke combustion were 11.01 ppm,6.57 ppm and 5.18 ppm,respectively.Water washing effectively reduced the peak value of Na concentration and the total amount of Na release in different combustion stages of Zhundong coal particles,shortened the ignition time of Zhundong coal particles,prolonged the duration of volatile and coke combustion stages,and reduced the peak temperature of volatile combustion stage and the average combustion temperature of coke combustion stage.This paper also independently designed a drop tube furnace with an optical observation window,and measured the axial temperature distribution on the central line of the furnace.In the glass window about 11cm long range,the furnace centerline temperature can remain stable,fluctuations within 20K.The combustion characteristics of Zhundong coal particle jet flame were tested by using the drop tube furnace.The jet flame images with a height of 20 cm and the flame radiation spectra at 11 different heights were collected.The collected spectra and images can reflect the complete jet combustion process of Zhundong coal particles.Spectral and image analysis results show that the ignition mode of Zhundong coal particle jet flame in drop tube furnace is heterogeneous ignition.After falling about 5cm in the drop tube furnace,the fire started,and the radiation spectrum intensity reached the maximum at about 9cm position.The decrease of Na content in coal after washing treatment does not change the ignition mode,but it will significantly reduce the radiation intensity of the radiation spectrum generated by the flame and the radiation intensity of the sodium characteristic spectrum,and slightly increase the ignition delay time of Zhundong coal particles.