针对燃煤电厂颗粒物超低浓度排放在线检测的需求,在激光散射法的基础上提出了利用光强调制技术的颗粒物浓度在线测量方法。结合波长调制技术提出了气体与颗粒物浓度同步测量的方法,同时建立了波长调制下散射光信号的数学模型。理论分析及仿真结果表明:气体浓度与归一化二次谐波幅值的峰值成正比,颗粒物浓度与消除气体吸收后的散射光信号的一次谐波幅值成正比。利用1392 nm的近红外激光器对蚊香燃烧时产生的颗粒物与水蒸气浓度进行同步测量。实验结果表明:测量的水蒸气浓度值与温湿度传感器测量值之间的偏差小于3%,颗粒物浓度的特征值与粉尘仪测量值具有高度线性关系,拟合因子为0.9973,实现了基于波长调制技术的颗粒物与气体浓度的同步测量。

To satisfy the online detection requirements of the ultralow emission of particulate matter in a coal-fired power plant, this paper proposes the online detection method by the light intensity modulation technique based on the laser-scattering method. In addition, the wavelength modulation technique is combined to propose the synchronous measurement method of gas and particle concentrations. Meanwhile, a mathematical model of the scattered-light signal under wavelength modulation is built. The theoretical analysis and simulation results show that the gas concentration is proportional to the height of the normalized second harmonic amplitude peak and that the particulate matter concentration is proportional to the amplitude of the first harmonic of the scattered-light signal from which the gas absorption has been subtracted. A 1392-nm near-infrared laser is used to simultaneously measure the particulate matter and water vapor concentrations during mosquito coil combustion. The experimental results show that the deviation between the measured water vapor concentration value and that by the temperature-humidity sensor is less than 3%. Moreover, the characteristic value of particle concentration has a high linear relationship with the measured value by the dust meter and the fitting factor R2 is 0.9973. The synchronous measurement of particulate matter and gas concentrations is successfully confirmed based on the wavelength modulation technique.