Study On Detecting System Of Escaping Ammonia Based On Tunable Laser Absorption Spectroscopy Technology

With the increasing concern of environmental pollution,the state pays more attention to environmental protection.The power plant will produce a large number of nitrogen oxides in the production process,which is one of the main components of the air pollution,so it is an inevitable trend to install the denitration equipment and increase the treatment of nitrogen oxides.In the process of denitration,ammonia is widely used as a photocatalytic reductant,but the unreacted NH3 is excluded from the denitration system,which will inevitably cause second pollution.Therefore it is very important to work out the method on accurate injection quantity of NH3 and measure the ammonia escape on-line.At present,based on spectral theory,Tunable Diode Laser Absorption Spectroscopy(TDLAS)technique have the advantages of non-contact,without pretreatment,rapid response,accurate measurement in gas measurement,which has become one of the representative of the current measurement methods of industrial pollution of trace gas monitoring.The main purpose of this paper is to realize the on-line measurement of ammonia escaping from power plant by using Tunable Diode Laser Absorption Spectroscopy(TDLAS),and research the key problems when measuring.In this paper,we first introduce the principle of spectroscopy,the spectral line intensity and the linear function of absorption spectrum,and focus on the basic principle of the Tunable Diode Laser.Secondly,this paper makes a comprehensive analysis and comparison of the monitoring methods of the escaping ammonia,investigates and analyzes the monitoring equipment which is widely used at home and abroad,and determines the measurement method.By contrast,the monitoring device used in line TDLAS on-line measurement sampling method as a measurement tool,compared with other methods,this method has the advantage of fast response,small signal background,strong anti-interference ability,high accuracy.Combined with the actual operating conditions of the power plant flue,the paper puts forward the design and construction methods,and introduces the design of the light path and mechanical parts.After determining the center frequency of TDLAS when measure the escape the ammonia,zero gas and calibration experiments in on-line monitoring equipment,which were carried out to verify the reliability and accuracy of the equipment.Afterverification,the inversion algorithm is used to meet the needs of the system.Finally,to analyzed the influence of temperature on the direct absorption detection and wavelength modulation spectroscopy by experiments.The experimental results show that the influence of temperature on the direct absorption detection and wavelength modulation spectrum detection is the same,that is,the amplitude of the gas absorption signal is smaller and the line width tends to be gentle after the temperature rises.The empirical formula of temperature compensation is presented.The experimental results show that the temperature compensation formula can greatly improve the accuracy of the measurement system.To sum up,the research on the influence of temperature on the system lays the foundation for the field detection of escaping ammonia,and improves the accuracy and stability of TDLAS measurement under bad conditions.