A Calibration Experiment On Gas Phase Alkalis Detecting System Based On Flame Emission Spectrum

The higher alkali metal content of Zhundong coal,biomass and municipal waste,will release into the gas phase in a large number in the combustion process,which may cause lagging,corrosion and deposition on the heat exchange surface.These problems have a strong impact on the life of the boiler and reduce the efficiency of heat exchange.Noncontact spectrum detection technology has a promising future in the field of alkali metal detection.The alkali metal of K and Na in the flame can unleash the characteristic spectral lines in the visible spectral bands.In order to attain quantitative detection of alkali metal in the flame,calibration relationship between the gas phase concentration of alkali metal in the flame and the corresponding intensity of characteristic spectral line is needed.This paper conducted a serious of calibration experiments about alkali metal flame using the flame emission spectrum detection technology.The specific tasks are as follows:Experimental platform about alkali metal premixed flame was set up,which contains flow control system,ultrasonic atomization system,premixed burner,spectrum detection system and high-speed camera system.When achieving the accurate quantitative control of fuel and oxidant,the atomization system made the alkali solution atomization.Then spectrograph collected the data of flame emission spectrum when the fuel and oxidant are combusted in the burner after complete mixture.The flame emission spectrum was detected by adjusting the fuel flow and premixed air flow.There were 6 operating conditions(equivalent ration=2.99,3.11,3.24,3.36,3.49 and 3.61,respectively),each condition was added water(0.14mL/min).The temperature was calculated by two-color method.The temperature of each operating condition fluctuated at 2093-2042 K,and the error was within 5%.The gas phase concentration of alkali metal in the flame was obtained by formula conversion,when Na,K solution with different concentration(1ppm,2ppm,3ppm,4ppm,5ppm)was added to the above operating conditions.By measuring the characteristic spectrum lines of alkali metal with different concentration in each operating conditions,it can be found that with the temperature decreased 51 K,the intensity of characteristic spectrum line about Na and K reduced 12.2% and 14% respectively.It means the temperature has a great influence on the intensity of spectrum line.In addition,the calibration relationship between the gas phase concentration of alkali metal in the flame ethylene and the intensity of characteristic spectral line of Na and K was obtained.And measuring error of Na and K was 2% and 0.2% through the verification calculation.