Research On On-line Monitoring Of SO₂ And NO Gas In Flue Gas Based On Differential Optical Absorption Spectroscopy

In recent years,with the development of society,environmental issues have gradually attracted the attention of people around the world.Large pollutant discharge facilities such as thermal power plants and petrochemical plants have become the focus of pollution detection.Gases such as SO₂ and NO in the flue gas emissions of thermal power plants have also become the top priority of monitoring and control.The emission of both SO₂ and NO is the main reason for the formation of acid rain,which will lead to soil acidification,crop yield reduction and other hazards.The prerequisite for effective management of SO₂ and NO in flue gas is accurate monitoring of their concentrations.Based on ultraviolet Differential Optical Absorption Spectroscopy（DOAS）technology,this paper studies the monitoring methods of SO₂ and NO gas in flue gas.The main contents are as follows:First,the detection methods of various gas pollutants are discussed,and the advantages and disadvantages of various methods are compared.The basic principles of DOAS were selected and studied.Combined with light scattering theory,considering the influence of Mie scattering and Rayleigh scattering on light absorption,the main basis of DOAS Lambert Beer’s law formula was modified.Secondly,the development of the Doas Monitor System software and the implementation of the detection function are completed.Starting from determining the software requirements and key technologies and files needed to implement the functions,the software is divided into two parts,the interface and the code,and the code and design of the various parts including menus,functional interfaces,data interaction,and spectrum drawing are designed and written.The software uses the least square method,Fourier filter,and SG smooth filter to perform gas concentration inversion.In addition,Dynamic Link Library（DLL）technology is used in the software development and production process to facilitate subsequent improvements and extensions.Finally,a set of experimental system was built,and the software and detection system were tested.The single gas and mixed gas of SO₂ and NO were measured respectively.The absorption cross sections of the two gases under the experimental conditions were measured to ensure the accuracy of the measurement results.The error analysis of the single-component gas measurement results is performed,and the measurement results are reliable.In addition,the measurement results of SO₂ and NO mixed gas are processed by three different algorithms.The experimental results show that the comprehensive error of SG smoothing filter is the smallest.At the same time,the final experimental results are within the national standard,which proves the feasibility of the gas detection system and the software developed.