光谱学与光谱分析, 2020, 40 (3): 688, 网络出版: 2020-03-25  

电厂烟羽中SO2柱浓度的紫外非色散二维成像

Ultraviolet Two-Dimensional Non-Dispersive Imaging of SO2 Column Density in Power Plant Plume
作者单位
1 中国科学院安徽光学精密机械研究所, 环境光学与技术重点实验室, 安徽 合肥 230031
2 中国科学技术大学, 安徽 合肥 230026
3 安徽新华学院, 安徽 合肥 230088
摘要
鉴于近年来突发事故和雾霾等污染现象时有发生, 其危害范围广、 危害程度深, 因此迫切需要掌握污染影响的区域、 范围、 强度以及污染扩散的趋势。 而污染源、 污染气体的二维快速成像分布在确定气体泄漏源定位、 鉴别突发事件以及鉴定污染范围和污染影响的过程中占绝对优势。 基于面阵CCD探测器, 利用紫外滤光片分光的成像技术实现了对丰台电厂烟囱排放的烟羽进行快速成像测量; 采用烟气在线监测技术获取的SO2实时浓度作为参考浓度, 经转换之后标定成像系统, 标定结果表明SO2斜柱浓度与光学厚度呈线性关系, 相关系数0.958, 满足成像理论可被解析的先决条件; 考虑到成像系统视场角小, 使镜头在上风向偏离烟羽区域拍摄的图片作为背景, 任取背景图上的一行像素, 这些像素的光学强度表明上风向强度均匀, 无其他干扰影响; 测量过程中, 为了减小烟羽变化带来的误差, 鉴别目标气体的310 nm滤光片与祛除气溶胶影响的330 nm滤光片对烟羽交替成像; 最后根据线性最小二乘拟合获取了2017年5月20日12点30分左右的SO2斜柱浓度的二维分布及其时序图。 测量结果显示在烟囱出口附近出现SO2斜柱浓度高值, SO2斜柱浓度高值约为1.7×1017 molec·cm-2; SO2斜柱浓度分布图直观显示SO2浓度的扩散趋势, 表明下风向SO2斜柱浓度沿着烟羽的扩散轴减小缓慢, 在大气浮力、 烟羽流体动力学以及风向共同作用下, 垂直于烟羽扩散轴的方向上, 扩散轴上方的SO2斜柱浓度小于其下方浓度, 但基本趋势是垂直于扩散轴的两侧SO2斜柱浓度衰减很快; 在下风向距离烟囱中心28米的区域, 取SO2斜柱浓度与高斯曲线进行拟合, 拟合系数0.747, 表明风向方向: SO2斜柱浓度扩散遵循高斯扩散; 根据SO2斜柱浓度时序图, 获得了烟羽的传播速度约为1.2 m·s-1; 为了验证紫外非色散成像系统测量结果的可靠性, 在已知烟羽SO2排放量(9.2 g·s-1)、 烟羽速度(1.2 m·s-1)、 烟羽高度(约140 m)及周边环境的情况下, 采用高斯烟羽扩散模型进行理论预测, 成像系统的测量结果与烟羽模型的模拟结果对比表明: SO2斜柱浓度的测量值及扩散趋势与理论预测基本一致。 利用基于滤光片的快速成像方法实现了对固定点源排放的污染气体SO2斜柱浓度的成像测量, 最终成功获取了烟羽中SO2斜柱浓度的分布及扩散的趋势, 测量结果与模型模拟的一致性表明该成像方法有望为定量、 定性评估污染危害提供测量依据。
Abstract
In view of the frequent occurrence of sudden accidents, haze and other pollution phenomena in recent years, the harm scope is wide and the harm degree is deep. Therefore, it is urgent to grasp the region, the scope and the intensity of the pollution, as well as the trend of the pollution diffusion. The two-dimensional fast imaging distribution of pollution sources has an absolute advantage indetermining the location of gas leakage source, identifying emergencies and identifying the scope and impact of pollution. In this paper, the fast imaging measurement about the plume from the power plant in Fengtai is realized by ultraviolet filter based on a planar CCD detector. The concentration of SO2 obtained by the flue gas on-line monitoring technology is used as the reference concentration. The imaging system is calibrated after the reference concentration is transformed. The calibration result shows that the SO2 column density presents a linear relationship with the optical intensity, the correlation coefficient is 0.958, and the prerequisite that the imaging theory can be analyzed is satisfied. Considering that the angle of view of the imaging system is small, the background is taken as lens deviates from the plume area upwind. The background intensity indicates that the upwind intensity is uniform and there is no other influence. The 310 nm filter identifying the target gas and the 330 nm filter dispelling the influence of aerosol are used alternately to image for the smoke plume in order to reduce the error of the plume change during the measurement process. At last, the two-dimensional distribution and the sequence diagram of SO2 slant column density are obtained according to the linear least squares fitting at about 12:30 on May 20, 2017. The results show that SO2 slant column density is high near the chimney exit, and high SO2 concentration of inclined column is approximately 1.7×1017 molec·cm-2. The figure of slant column density distribution displays visually diffusion trend of SO2 concentration, showing that SO2 inclined column density decreases slowly along the axial diffusion of the plume under the direction of the wind, and under the direction of the perpendicular to the plume diffusion, the figure tells that inclined column of SO2 above the axisis less than its concentration below because of the air buoyancy, fluid dynamics about plume and the direction of wind. However the basic trend of diffusion is that both sides of the SO2 inclined column perpendicular to the axis decrease quickly. In the 28 meters away from the center of the chimney from downwind direction, the concentration of SO2 inclined column and gauss curve are taken for fitting, and the fitting coefficient is 0.747, which indicates that the concentration diffusion of SO2 inclined column in wind direction basically follows gauss diffusion. The plume velocity is about 1.2 m·s-1 according to the time series diagram about SO2 column density. The gauss diffusion model is used to verify the feasibility of ultraviolet non-dispersive imaging system on the basis of the known plume SO2 emissions (9.2 g·s-1), smoke plume speed (1.2 m·s-1), smoke plume height (140 m) and the surrounding environment. Comparing the results about the imaging system with the plume model, it is shown that SO2 slant column density measured and the diffusion trend are consistent with theoretical predictions. This paper for the first time uses rapid imaging method based on filter to image SO2 slant column density from fixed point pollution source, and finally the distribution and diffusion of SO2 in plume are obtained successfully. The consistency between measurement results and model simulation indicates that this imaging method is expected to provide measurement basis for quantitative and qualitative assessment of pollution hazards.

张英华, 李昂, 谢品华, 黄业园, 胡肇焜, 张朝刚. 电厂烟羽中SO2柱浓度的紫外非色散二维成像[J]. 光谱学与光谱分析, 2020, 40(3): 688. ZHANG Ying-hua, LI Ang, XIE Pin-hua, HUANG Ye-yuan, HU Zhao-kun, ZHANG Chao-gang. Ultraviolet Two-Dimensional Non-Dispersive Imaging of SO2 Column Density in Power Plant Plume[J]. Spectroscopy and Spectral Analysis, 2020, 40(3): 688.

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