小型化燃煤电厂逃逸氨气激光测量仪

A miniaturized laser measurement instrument of ammonia escaping from coal-fired power plants

为了准确测量高温下逃逸氨的体积分数,采用可调谐半导体激光吸收光谱技术、波长调制光谱技术(WMS)和长光程技术,开发了一套高温小型化的逃逸氨气测量仪;为了减小逃逸氨气的吸附效应和提高探测灵敏度,研制了新型高温长光程样品吸收池。在前期研制的激光驱动模块基础上,采用74HC4046锁相环芯片作为可调正弦调制信号源,以EPM7064为移相和倍频逻辑控制芯片,同时采用两片AD630作为一次解调(WMS-1f)和二次解调(WMS-2 f)同步解调乘法器,实现了吸收信号的1 f和2f同步解调。此外,以STM32F429为主控制器,将解调滤波后的信号输入到AD7606进行模数转换,并进行数字滤波和体积分数的反演。结果表明,氨气体积分数与WMS-1f幅值、WMS-2f幅值以及同步解调WMS-2 f/WMS-1 f归一化幅度值的线性拟合系数分别为0.998,0.997以及0.998;Allen方差表明在优化时间228s时,其测量的体积分数最低为0.496×10-6,在体积分数为20×10-6~100×10-6范围内测量误差小于±2%。该测量仪可以为燃煤电厂氨逃逸的高温测量提供高精度的原始数据。

In order to accurately measure volume fraction of the escaping ammonia at high temperature, tunable diode laser absorption spectroscopy, wavelength modulation spectroscopy (WMS) and long-path technology were used. A set of miniaturized measurement instrument for escaped ammonia gas at high temperature was developed. In order to reduce the adsorption effect of escaping ammonia and improve the detection sensitivity, a new type of sample absorption cell with high temperature and long optical path was developed. On the basis of the laser driving module developed earlier, phase-locked loop chip 74HC4046 was used as an adjustable sinusoidal modulation signal source. EPM7064 was used as phase shifting and frequency doubling logic control chip. At the same time, two AD630 chips were used as simultaneous demodulation multiplier of the first demodulation (WMS-1 f ) and the second demodulation (WMS- 2f ). The synchronous demodulation of 1f and 2f absorption signals was realized. In addition, STM32F429 was used as main controller and the demodulated and filtered signal was input to AD7606 for analog-to-digital conversion. Digital filtering and volume fraction inversion were performed. The results show that linear fitting coefficients of volume fraction of ammonia gas with WMS- 1f amplitude, WMS- 2f amplitude and the normalized amplitude of WMS- 2f /WMS- 1f are 0.998, 0.997 and 0.998, respectively. Allen variance shows that when the optimization time is 228s, the lowest volume fraction is 0.496× 10^-6 . In the range of volume fraction 20×10^-6 ~100×10^-6 , the measurement error is less than ±2%. The instrument can provide high precision raw data for high temperature measurement of ammonia escaping from coal-fired power plants.