Simulation Study Of NH₃ Concentration Measurement Based On QCL-TDLAS

Tunable Diode Laser Absorption Spectroscopy(TDLAS)technology uses a tunable semiconductor laser narrow-band laser to scan the gas molecule absorption spectrum,and obtains gas concentration,pressure,temperature and other parameters by analyzing the changes in the laser signal.It has high measurement accuracy,high sensitivity,and response time.Short and other advantages,it can realize on-line non-contact measurement of gas concentration,especially in extreme environments such as high temperature,strong corrosion,flammability and explosion,and has great advantages.It is widely used in the field of gas concentration measurement.In recent years,with the increasing improvement of nitrogen oxide emission control standards,Selective Catalytic Reduction(SCR)denitration technology has been widely adopted in thermal power plants.As an important reducing agent,NH₃can reduce nitrogen oxides NO_Xto N₂.The NH₃escaped during the flue gas treatment process is directly discharged into the atmosphere,which will cause environmental pollution,especially the formation of haze particles in the atmosphere.Up to now,TDLAS technology mainly uses near-infrared absorption spectroscopy(1-2?m)for gas concentration measurement,and the absorption intensity of gas molecules in the near-infrared band is weak,resulting in low measurement accuracy based on near-infrared absorption spectroscopy.It is difficult to meet the requirements of ammonia escape measurement in industrial sites.According to the theory of spectroscopy,compared with near-infrared absorption spectroscopy,the absorption intensity of gas molecules in the mid-infrared band(4-10?m)is about hundreds of times that of near-infrared.As the mid-infrared band quantum cascade laser(Quantum Cascade Laser—QCL)has made important progress and gradually commercialized,the high-precision gas detection technology based on QCL-TDLAS will have broad application prospects in the field of air pollutant monitoring in the future.Specific research contents include:1.Use Trace Pro optical simulation software to simulate the reflection of the Herriott long optical path gas absorption cell,give the relevant simulation model,and obtain the influence of different parameter changes on the Herriott cell laser reflection times and the total length of gas absorption.2.Use the Simulink module in Matlab software to simulate and analyze the QCL-TDLAS and DFB-TDLAS ammonia emission online measurement process,including the laser signal output,gas absorption and signal detection module.Analyzed the laser absorption under normal temperature and pressure and the different environments of the denitration outlet of thermal motor,and obtained the signal amplitude information and the gas absorption rate function.3.By setting different concentration values,the absorbance spectra of NH₃under two different laser light sources are obtained.Through the absorbance area-concentration fitting curve,the sensitivity,resolution,and detection limit of different systems were calculated and compared and analyzed.