基于可调谐激光吸收光谱技术的逃逸氨检测系统研究

发布时间：2019-03-08 08:06

【摘要】：随着环境污染问题受到的社会关注度越来越高,国家对于环境保护也日趋重视。发电厂在生产过程中会产生大量的氮氧化物,是目前大气污染的主要成分之一,加大对氮氧化物的治理力度,安装脱硝装置成为必然的发展方向。在脱硝过程中,氨气被广泛的作为一种光催化还原剂使用,但未反应的NH3从脱硝系统中排除,难免的造成二次污染。由此可见,对于逃逸氨的在线测量,随工况运行精确制定NH3的喷入量,显得尤为重要。目前,基于光谱理论的可调谐激光吸收光谱(TDLAS)技术在痕量气体测量时具有非接触性、无需预处理,响应迅速,测量精确的优势,成为了当前工业污染痕量气体监测的代表性测量方法之一。本文主要研究的目的是利用可调谐吸收光谱技术(TDLAS)实现对发电厂逃逸氨的在线测量,并重点对测量时出现的关键性问题进行了研究。本文首先介绍了光谱学原理、谱线强度及吸收光谱线性函数,重点研究了可调谐激光吸收光谱技术的测量原理、基本技术方法。其次对逃逸氨的监测方法进行了全面的对比分析,调研了国内外应用广泛的、成熟度高的监测设备进行了考察分析,并对测量方法进行了确定。经对比、分析,选用了在线测量取样法的直插式TDLAS技术的监测装置作为测量工具,相对于其他方法,此种方法具有反应快、背景信号小、抗干扰能力强、精度高等优势。结合所在电厂烟道的实际工况,提出了具体的设计搭建方式,并对设计的光路部分和机械部分进行了介绍。之后,在确定了TDLAS测量逃逸氨的中心频率后,对在线监测设备进行了零气实验和标定实验,从而利用具体实验验证设备的可靠性和准确性。在验证后,利用最小二乘法推导气体的反演算法,以满足系统的需要。最后,用实验来分析了温度对氨气浓度测量的影响。并为验证实际现场中因温度变化而导致的对逃逸氨测量影响的情况。温度的影响需要要对浓度反演进行温度校正,本文提出了温度补偿经验公式。通过实验验证,温度补偿公式可大幅提高测量系统的精确度。经过验证,该补充公式能够有效提升测量精度,进一步提高了TDLAS技术的准确性和可靠性。
[Abstract]:With the increasing social concern about environmental pollution, the state pays more and more attention to environmental protection. A large number of nitrogen oxides will be produced in the production process of power plants, which is one of the main components of air pollution at present. It is an inevitable development direction to strengthen the control of nitrogen oxides and install denitrification devices. In the process of denitrification, ammonia is widely used as a photocatalytic reducing agent, but the unreacted NH3 is excluded from the denitrification system, which inevitably results in secondary pollution. It can be seen that for the on-line measurement of ammonia escape, it is particularly important to accurately determine the injection amount of NH3 with the operating conditions. At present, the tunable laser absorption spectroscopy (TDLAS) technique based on spectral theory has the advantages of non-contact, no pretreatment, rapid response and accurate measurement in the measurement of trace gases. It has become one of the representative measurement methods for monitoring trace gases in industrial pollution. The main purpose of this paper is to realize the on-line measurement of fugitive ammonia in power plant by means of tunable absorption spectroscopy (TDLAS), and focus on the key problems in the measurement. In this paper, the principle of spectroscopy, the intensity of spectral line and the linear function of absorption spectrum are introduced, and the measurement principle and basic technique of tunable laser absorption spectroscopy are mainly studied. Secondly, the monitoring methods of ammonia escape are compared and analyzed comprehensively, and the widely used and mature monitoring equipments at home and abroad are investigated and analyzed, and the measuring methods are determined. Through comparison and analysis, the direct-insertion TDLAS monitoring device of on-line sampling method is selected as the measuring tool. Compared with other methods, this method has the advantages of quick response, small background signal, strong anti-jamming ability and high precision. Combined with the actual working conditions of the flue in the power plant, the concrete design and construction methods are put forward, and the optical and mechanical parts of the design are introduced. Then, after determining the center frequency of TDLAS measurement of ammonia escape, zero-gas experiment and calibration experiment of on-line monitoring equipment are carried out, and the reliability and accuracy of the equipment are verified by specific experiments. After verification, the least square method is used to derive the gas inversion algorithm to meet the needs of the system. Finally, the effect of temperature on the measurement of ammonia concentration was analyzed by experiments. In order to verify the effect of temperature change on the measurement of escape ammonia in the field. Temperature effect requires temperature correction for concentration inversion. An empirical formula for temperature compensation is presented in this paper. The experimental results show that the temperature compensation formula can greatly improve the accuracy of the measurement system. It is proved that the supplementary formula can effectively improve the accuracy of measurement and further improve the accuracy and reliability of TDLAS technology.
【学位授予单位】：华北电力大学(北京)
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TP274;O433

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