为了实现低体积分数(10^-9数量级)NH3测量以满足电厂脱硝过程中的氨逃逸检测要求,采用可调谐激光吸收光谱技术,选取2.25μm附近的ν2+ν3 NH3谱线,在常温常压下进行了低体积分数NH3的测量实验,并重点研究了不同调制电压和调制频率对信噪比的影响.结果表明:通过选取最佳调制电压和调制频率,在调制电压为0.07V,调制频率为14.02kHz时,可以使用二次谐波法测量体积分数最低为4×10^-7的NH3,所测得的二次谐波信号与气体体积分数具有良好的线性关系,此方法可以用于测量电厂脱硝过程的低体积分数氨气.
To meet the detection requirements of ammonia slip in denitrification process of power plant, the low-concentration (10^-9 magnitude) ammonia was experimentally measured at ambient temperature and pressure using tunable diode laser absorption spectroscopy by taking the NH3 absorption spectrum in v2 + v3 band of about 2.25 μm as the detection spectrum, so as to analyze the effects of modulation voltage and frequency on the ratio of signal to noise. Results show that when the modulation voltage and frequency are set at their optimum values of respectively 0.07 V and 14.02 kHz, the second harmonic method can be used to measure the NH3 concentration of as low as 4×10^-7 , and the second harmonic signal thus obtained has a good linear relationship with the gas concentration, indicating that the method can be used for measurement of low-concentration ammonia in denitrification process of power plant.