燃煤发电中痕量NO与NH3的高灵敏度激光吸收光谱原位测量技术研究

The nitrogen oxides (NOx) gases are serious atomspherical pullants and 35% of NOx gases originate from the coal-fired power plant. Meanwhile the concentrations of the trace NOx and NH3 are the most significant parameters for the selective catalytic reduction and selective non-catalytic reduction (SCR/SNCR) in the coal-fired power plant. Comparison with the traditional electrochemistry and gas chromatographic measurements, the tunable diode laser absorption spectroscopy (TDLAS) has fast, in-situ, and high sensitive advantages, so it has become the developed detection technology. However, the measurement precision of TDLAS is subject to the scattering effects interface of considerable flay particles and the varied parameters of the absorption spectroscopy which are affected by the anisotropies of the velocity, pressure and temperature of the mixed flow. In the proposal, the broadening and frequency shift parameters of the absorption spectroscopy which are induced by the various carrier gases, velocity, pressure and temperature will be investigated to realize the in-situ fast measurement with ppm sensitivity based on near 2μm strong absorption band combination with frequency modulation and long optical path technology. At the same time, van der Waals potential-energy surfaces that are formed between the trace gas and the carrier gases such as N2, H2O, O2, et al. will be computed by using ab initio method. The spectral parameters are evaluated by the collision model of Close-Coupling and Coupled-States. And then the gas molecules collision law will be revealed in combination of experiment. The high temperature absorption spectroscopy parameters will also be added to the HITEMP data base. Finally, we will achieve a high accuracy fast in-situ measurement for the trace gases, and construct the relation between with each other gas to provide the optimized parameters for SCR/SNCR.

氮氧化物是一种主要的大气污染物，其35%来源于燃煤发电。氮氧化物和氨气（痕量气体）含量是燃煤发电中选择性（非）催化还原（SCR/SNCR）的主要参数。与电化学、色谱等方法相比，激光吸收光谱技术具有快速、原位、高灵敏等优点，已成为气体污染物最新检测手段。然而，其测量精度受到颗粒物的散射效应的干扰以及复杂载气的压强、温度随机波动对光谱参数的影响。本项目拟采用2μm附近强吸收带，结合频率调制和长光程，研究痕量气体在不同载气、速度、压强、温度环境下碰撞引起的增宽、频移等光谱参数，实现气体ppb量级原位快速测量；并采用从头计算研究痕量气体与氮气、水、氧气等形成范德瓦尔斯势能曲面，利用Close-Coupling与Coupled-States碰撞模型计算增宽和频移，结合实验揭示气体分子碰撞规律，补充高温吸收光谱参数，实现痕量气体高精度快速原位测量，建立痕量气体相互关系，为SCR/SCNR优化提供依据。

氮氧化物是一种主要的大气污染物，其35%来源于燃煤发电。氮氧化物和氨气（痕量气体）含量是燃煤发电中选择性（非）催化还原（SCR/SNCR）的主要参数。与电化学、色谱等方法相比，激光吸收光谱技术具有快速、原位、高灵敏等优点，已成为气体污染物最新检测手段。然而，其测量精度受到颗粒物的散射效应的干扰以及复杂载气的压强、温度随机波动对光谱参数的影响。本项目开展了燃煤电厂尾气中的NH3和NO激光光谱测量与分子光谱理论研究。.实验上：采用硅碳棒加热方式，利用PID控制技术，在实验室模拟了一套高温尾气温度和浓度测量实验装置。自行设计、加工制作和调试新型多光程池，在30cm空间尺寸上实现了17m长的有效吸收光程，此技术将光谱检测灵敏度提高了近2个数量级，创造性地提出了一种螺旋型长光程池。根据电厂在线测量需求，设计了高稳定、小型化的激光温度和电流驱动板，并基于FPGA研制了双通道的模拟锁相放大器和基于STM32F429控制的数字锁相放大器，结合波长调制、平衡差分、小波去噪、频率抑制等技术测量了NH3、NO、CO和CH4气体，实现了ppm到ppb的探测灵敏度下限，解决了NH3浓度和温度同时测量难题；针对尾气中的氮化物，实验利用中心波长为5.2μm的中红外激光吸收光谱技术，实现了NO气体28 ppb的探测极限。.理论上：标识了NO分子的b4Σˉ-a4π系统(3,0)带Q12支，利用PGOPHER程序提供的b4Σˉ-a4π标准的哈密顿量矩阵元和非线性最小二乘拟合程序拟合了NO分子的光谱常数。基于从头计算理论，利用Hartree-Fock结合CASSCF和MRCI计算其低激发态的势能曲线，跃迁电偶极矩等物理参数，并通过求解一维薛定谔方程得到了分子的F-C因子、分子振-转常数及辐射寿命。提出了基于1Σ-1Σ最简单电子系统的激光直接冷却分子方案，并以AgH和AgD自由基分子为例进行模拟，结果表明冷却效率大大提高，且所需激光器数目减少了一半。