| As more and more attentions have been paid to the denitration in the modernindustry, the amount of escaping ammonia during the process is increasing, whichurgently demands improvement of techniques in the escaping ammonia detection. Inthis paper, the application of TDLAS in the escaping ammonia detection is introduced,and several key issues are explored based on the current studies.First, principles of the escaping ammonia detection using TDLAS technique,modeling method and experimental setup are introduced. The influences of pressure,temperature, and flow velocity on the profile of ammonia absorption (amplitude,width and frequency shift) are analyzed, which provides correction method based ontheir influence on the absorption profiles. Then, the linear modeling method isadopted for the ammonia concentration prediction.Meanwhile, after noise analysing,several digital filtering method are comparedfor the system noise reduction, and the wavelet transform combining averaging isadopted as the most effective pretreatment of the original spectra based on largeamount of experiments.Moreover, the influence of temperature on the direct absorption profile andwavelength modulation profile (secondary harmonic spectra) is studied, whichindicates similar changes in both situations that ammonia absorption declines inamplitude and broadened in width as temperature increases. The empirical expressionof temperature correction is summarized, based on which the accuracy of escapeammonia detection is greatly improved. On the other hand, the influence of pressureon the direct absorption profile and wavelength modulation profile (secondaryharmonic spectra) is explored, which indicates that, the amplitude of secondaryharmonic spectra decreases despite the positive and negative pressures. The empiricalexpression of pressure correction is studied, which also help improve the escapeammonia detection accuracy. The corrections in these two aspects provide potentialapplication of TDLAS method to the on-line circumstances, with its advantages in theimprovement of detection accuracy and stability. |
