Research On Measurement Of Flue Gas Carbon Dioxide Concentration Based On Direct Absorption Of Multiple Reflections

Excessive carbon dioxide emission is the main cause of greenhouse effect,and with the greenhouse effect becoming more and more serious,it has a far-reaching impact on the global environment and ecosystem.Disasters such as extreme climate constantly appear,which have interfered with human life and health,and even related to the survival of human beings.Therefore,carbon emission monitoring and emission reduction have gradually become the focus of global attention,and China has also actively taken the corresponding responsibility of emission reduction.In the carbon dioxide emission of our country,the carbon emission of power generation and heat supply industry account for the vast majority of the total amount of the country.Therefore,monitoring carbon dioxide emissions from coal-fired power plants and improving the accuracy of carbon dioxide emissions data are of great significance for the measurement of total carbon emissions.At present,China uses the emission factor method to calculate the carbon dioxide emissions,but due to the lack of measured emission factors,the European standard is adopted,resulting in the calculated total carbon emissions far higher than the actual value.Internationally,the online monitoring method is regarded as the highest level method of carbon emission inventory statistics,and China has gradually changed to real-time online monitoring.The stability and accuracy of the monitoring system are directly related to the reliability of carbon emission data,so it is necessary to establish a high-accuracy field measurement method to accurately measure carbon dioxide in the flue.The content of carbon dioxide emitted by enterprise chimneys is generally below 20%.Based on the principle of molecular absorption spectroscopy,a relative method for accurately measuring the concentration of carbon dioxide is established in this paper.The specific research contents are as follows:?1?The theoretical model for measuring the concentration of carbon dioxide in the flue gas of enterprises based on direct absorption spectroscopy is optimized.According to Beer-Lambert's law,the relationship between the incident light intensity and the output light intensity of the gas absorption cell and the carbon dioxide concentration is established,and then a relative measurement method based on a known concentration of carbon dioxide/nitrogen mixture is derived.?2?The experimental device for direct absorption spectrum measurement is built.Firstly,based on the principle of avoiding interference from other gas spectrum lines,the three spectral lines R16e,R18e and R20e near the 1.57?m band are selected for experimental measurement,and then the Herriott multiple reflection optical gas absorption cell is designed and processed,and the indicating light path and working light path are built successively,and then the processing methods of baseline fitting,frequency axis,fitting line type and near weak absorption peak are determined.?3?The line intensity of carbon dioxide at 296 K is calculated.First,at?293±0.005?K and?0,4,6.6,9.3,13.3,16,20,26.8?kPa,the absorption spectra of 15%carbon dioxide/nitrogen mixture at 6359.97 cm^-1?30012???00001?R16e,63612 cm^-1?30012???00001?R18e and6362.5 cm^-1?30012???00001?R20e are obtained.The line intensity values of the three spectral lines are calculated from the absorption peak area.After the line intensity values at 293K are obtained,the temperature and the line intensity values are used as reference values,and the line intensity values at 296 K are calculated and compared with the reference values of HITRAN,GEISA,HITEMP databases.The results show that the average relative error of the calculated intensity of the three spectral lines relative to the HITRAN 2016 database is 0.95%,the average relative error to the GEISA database is 1.05%,and the average relative error to the HITEMP database is 1.61%;?4?The actual concentration of carbon dioxide in the range of flue gas concentration is measured.35%carbon dioxide/nitrogen mixture is used as reference gas of known concentration.At?293±0.005?K and?4±0.002?kPa,the actual concentration of the carbon dioxide/nitrogen mixture with nominal concentrations of 1%,5%,10%,and 15%is measured.The measurement results are in good agreement with the results obtained by the weighing method in the range of 0.1%.The maximum extended relative measurement uncertainty?k=2?is 0.65%?R16e spectral line?and 0.65%?R18e spectral line?and 0.74%?R20e spectral line?respectively,which meet the needs of flue gas concentration measurement.