Study On Plasma Characteristics And Spectral Data Preprocess Of Fly Ash In Particle Flow By Laser-induced Breakdown Spectroscopy

The unburned carbon in fly ash is one of the main parameters to evaluate the boiler combustion efficiency and fuel efficiency of coal-fired power plants,and it represent mechanical incomplete combustion heat loss of boiler.Therefore fast and accurate measurement of unburned carbon in fly ash is one of the important approaches to achieve combustion optimization of coal-fired boiler,correct coal grinding,improve energy efficiency and ensure the stability and economy of power plant operation.Currently,UC content measurement devices which are based on the loss-on-ignition(LOI)method have been widely used in coal-fired power plants,but these instruments must go through many individual steps of analysis before they are accomplished,the 15 minutes measurement period is difficult to meet the demand of on-line measurement.Additionally,the microwave absorption,which is higher commercially oriented of on-line measurement techniques,is very simple and have a high sensitivity,but their measurement accuracy is closely affected by the characteristics of coal.Therefore,developing the technology of on-line measurement and improving the accuracy and stability of the measurement results remains one of the key issues in this field.In this thesis,the laser-induced breakdown spectroscopy,a new atomic emission spectroscopy technology,was used to measure the unburned carbon of fly ash in coal-fired power plants.Based on the research of domestic and foreign scholars,through fierce study the mechanism of the action between laser and fly ash samples,the plasma time evolution characteristics of fly ash were determined,mastered the methods of optimizing the experiment parameters.The fly ash in particle flow as the object of study in this paper,firstly,the true source of the invalid spectrum in the particle flow is studied,and established the method for identifying invalid data in particle flow.Secondly,the factors about the spectrum data instability caused by LIBS were studied.The relationship between the particle size and the element spectral intensity of particle were emphatically studied,and established the method for correcting particle size effects.The experimental conditions were optimized to improve the stability and efficiency of the particle flow spectral data.Finally,for the seriously interference between the Fe 247.98 nm and the C 247.86 nm lines in the analysis of fly ash when using the poor-resolution spectrograph,presented a correction method that using Fe line to correct the C-Fe lines interference.The integrated intensity of the spectral lines is chosen as the input intensity to obtain the intensity ratio of non-interference Fe lines and obtained the C 247.86 nm line integrated intensity from the overlapping peak,the methods of correcting unburned carton in fly ash was also established.To a certain degree,the measurement accuracy of unburned carbon in fly ash is improved.Finally,the thesis summarizes the main conclusions and bring new ideas concisely and briefly,and look ahead to the later study.