Study On Detecting Gas Nitrogen Oxides Based On The Research Of Photoacoustic Spectroscopy

Gas detection technology has an important practical significance in the fields ofindustrial development, spaceflight, atmospheric environmental pollution control,people’s daily life and physiological processes of biological organism, as well as a varietyof human disease diagnosis. Since the20th century, China’s economy has developedrapidly, especially in industry which is the fastest one but results in a great increase inindustrial boiler burning fossil fuels. The burning fuels have released a large number ofharmful gas, of which the sulfide and nitrogen oxides cause serious damage to humanhealth and ecological environment. And sulfide and nitrogen oxides are the main gas ofcausing acid rain, making human suffering from respiratory diseases and lung diseases.Environmental pollution is increasingly serious with people`s increasing attention to theenvironment. Under the current situation, traditional gas detection system cannot meetthe demand, and it is necessary to develop an online gas detection system with rapidreaction, high resolution, high sensitivity.Through the comparative analysis of the current gas detection methods, this thesisdevelopes a gas detection system based on photo-acoustic spectroscopy. Gas photo-acoustic spectrum detection technology is a new type of sensing technology and has adynamic detection range with non-consumption and non-separation measured gas, highsensitivity, and good selectivity. This thesis expounds a theory of gas molecular infraredspectrum and gas photo-acoustic spectrum detection principle, introduces the producingprocess photo-acoustic signal and designs a set of photo-acoustic spectrum gas detectionsystem, which mainly states the selection of the radiation source, chopper and the filterand the design of photo-acoustic pool and the design of the core system problems ofmicrophone matching. This thesis also analyzes the influence of water steam in theprocess of measuring, makes a nitrogen oxide photo-acoustic spectrum onlinemeasurement mode and provides the theoretical foundation for the design of the nitricoxide instrument.This thesis shows calibration gas flow distribution, zero gas and vapor fluctuationson the influence of different nitric oxide concentration, and it also analysis of the noise inthe process of detection.It provides comprehensive analysis of gas absorption rate and thecross sensitivity factors and identifies the NO2and NO interference filter centerwavelength of5350nm and6300nm. It has verifies the feasibility of this method todetect boiler flue nitric oxide concentration. Because the single component gas photo-acoustic signals and gas concentration following the linear relationship, this paper adoptsthe least-squares regression method to establish a quantitative analysis model forquantitative analysis of gas concentration. This method is helpful to improve thecalculation accuracy for calculation the gas concentration.