Measurement And Analysis Of Emission Spectrum Of Flame For The Zhundong Coal Combustion

The combustion of Zhundong coal will release a large amount of alkali metal,sodium(Na).The released alkali metal will cause problems such as slagging and corrosion,which will reduce the efficiency of heat exchangers and shorten the service life of the boilers.If alkali metals during the combustion process of Zhuandong Coal can be measured online,it will be of great significance to realize the clean utilization of fuel,improve heat transfer efficiency of boiler and ensure the safe operation of equipment.In this paper,the flame emission spectroscopy(FES)was used to online measure and analysis the combustion of the Zhundong coal.The detailed description is as below.Firstly,an experimental system was designed and built for the alkali metal calibration and coal particle combustion based on FES.Analysis of the spectrum can simultaneously obtain the change of the characteristic spectrum intensity of the alkali metal,temperature and band radiation intensity.There were two distinct peaks at the wavelengths of 589.04 nm and 589.64 nm,which were the characteristic spectrum of Na.The temperature was calculated using the multi-wavelength pyrometry.And the wavelength range of the temperature calculation is from 700 nm to 850 nm.The band radiation intensity was the integral of monochrome radiation energy to wavelength in the wavelength range of the calculative temperatureSecondly,the calibration experiment was carried out by using the standard solution of Na with the known concentration.And the relationship was obtained between the characteristic spectrum intensity of Na and the concentration of Na in gas phase.When the gas concentration exceeded 3ppm,self-absorption occurred.By the self-absorption correction,the proportional relationship was obtained between the characteristic spectrum of Na and the gas phase concentration.The goodness of fit on the corrected data was 0.98 and the detection limit was 0.043 ppm.Finally,in order to study the effect of different coals on the release of Na,experimental measurements were carried out on the emission spectra of two high-sodium Zhundong coals and one low-sodium coal.The results show that the release of Na included three stage(the volatile phase,the coke phase and the ash phase),which could be judged by the change of the alkali metal concentration and band radiation intensity.FES could quantitatively analyze the gas phase concentration of Na in the combustion environment.The amount of alkali metal released from Zhundong coal was much higher than that of the low-sodium coal and the release concentration from Wucaiwan coal was higher than that from Tianchi coal.The duration of Wucaiwan coal in coke stage was longer than that of Tianchi coal,and the release ratio of Wucaiwan coal and Tianchi coal in coke stage was over 45%.Changing the air flow rate could change the environment of Zhundong coal combustion,which affected the temperature of the combustion environment and the concentration of air components,thus affecting the release of Na.After increasing air flow rate,temperature of the combustion environment decreased and the release proportion during ash stage increased,however,the total amount of released alkali metal decreased and the residual Na in the ash was increased.