[Rapid Measurement of Carbon Dioxide with Laser-Induced Breakdown Spectroscopy Based on Atomic and Molecular Spectrum].

With the rapid development of economy and industrialization, global warming is becoming the most serious sensitive global climate issues, which causes the rising of sea level and many other negative effects. The cause of global warming is the emission of greenhouse gases and carbon dioxide is the main component of greenhouse gases. The control of CO2 emssion is beneficial to addressing gobal climate change and environmental degradation. Therefore, it's important to develop a rapid detection of CO2 for accurate control. There are amounts of methods to detect CO2 at present, including titration, electrochemical method, gas chromatography, infrared absorption spectroscopy and so on, however, t they still have the deficiency for online monitoring in industrial field. laser induced breakdown spectroscopy (LIBS), which is developing rapidly in recent few decades, is a detecting technology with characteristics of time-saving and synchronous measuring of multicomponent. What's more, there is no need for sample pretreating. To develop the online monitoring technique of CO2 emission in the industrial field, LIBS was employed to measure CO2 in this study. The mass flow controller was used to adjust the flow of high purity CO2 and N2 to obtain mixed gas with different CO2 concentrations. The mixed gas was firstly mixed in an air mixing chamber for thorough mixing and then sent to the sample cell for LIBS measurement. The evolution of C atomic spectral line and CN molecular band with different delay times were being studied, which demonstrated parts of CO2 react with air ambient to form CN molecular during the plasma generation, the CN molecular band should be taken into consideration for quantitative analysis, and the parameters were optimized for synchronous measurement of C line and CN band: 800 ns was the optimal delay time. During the plasma generation, many factors in the plasma may interact with others, the analysis index had close relationship wih serval measuring parameters. With the consideration of the effect of C, CN and the self-absorption in high concentration, multivariate calibration method was employed to establish calibration models of CO2. The results showed that the correlation coefficients R2 and the slope were 0.978 and 0.981, respectively. Compared with calibrated with single factor, the multivariate method improved the reliability of the model. What's more, the feasibility of the application of LIBS to measure CO2 rapidly was proved.

[A New Calibrated Model of Coal Calorific Value Detection with LIBS].

A set of coal samples were used for laser-induced breakdown spectroscopy (LIBS) experiment to measure the coal calorific value. Traditional channel normalization method didn't consider the physical / chemical mechanism of coal, which would limit the model in precision, accuracy and repeatability. Thus a new calibrated model based on the kinds of the effects of spectral deviation was proposed in this paper. The model selected 19 groups of coal samples, where the random 15 groups were used to establish quantitative analysis model of calorific value while the remaining four for inspection and evaluation. The model based on spectral deviation factors, and the transmission theory combined with the stark broadening formula was used to deduce the absorption effect mechanism and the deviation correction method under the condition of LIBS. The mutual interference between elements and the mechanism of matrix effect were being analyzed while K coefficient method was used to correct mutual interference between the elements in the LIBS. The establishment of numerical model with the electron density, the plasma temperature and the element concentration was used to deeply corrected spectrum deviation caused by matrix effect. Thus taking into consideration of the effect of self-absorption, interfere of inter-elements and matrix effect, the calibration model was established, while R2=0.967, RMSEP=0.49 MJ·kg-1, RMSE=0.45 MJ·kg-1, MRE=2.42%, ARE=1.64%, RSD=5.79% and RSDP=8.10%. Compared with the 0.405, 8.28 MJ·kg-1, 4.14 MJ·kg-1, 22.85%, 52.48%, 18.28% and 32.85% of traditional channel normalized-multiple linear regression method, it demonstrated that the precision and accuracy have been improved significantly and model has good application value.

[Influence of C-Fe Lines Interference Correction on Laser-Induced Breakdown Spectroscopy Measurement of Unburned Carbon in Fly Ash].

In coal-fired plants, Unburned carbon (UC) in fly ash is the major determinant of combustion efficiency in coal-fired boiler. The balance between unburned carbon and NO(x) emissions stresses the need for rapid and accurate methods for the measurement of unburned carbon. Laser-induced breakdown spectroscopy (LIBS) is employed to measure the unburned carbon content in fly ash. In this case, it is found that the C line interference with Fe line at about 248 nm. The interference leads to C could not be quantified independently from Fe. A correction approach for extracting C integrated intensity from the overlapping peak is proposed. The Fe 248.33 nm, Fe 254.60 nm and Fe 272.36 nm lines are used to correct the Fe 247.98 nm line which interference with C 247.86 nm, respectively. Then, the corrected C integrated intensity is compared with the uncorrected C integrated intensity for constructing calibration curves of unburned carbon, and also for the precision and accuracy of repeat measurements. The analysis results show that the regression coefficients of the calibration curves and the precision and accuracy of repeat measurements are improved by correcting C-Fe interference, especially for the fly ash samples with low level unburned carbon content. However, the choice of the Fe line need to avoid a over-correction for C line. Obviously, Fe 254.60 nm is the best

[Influence of laser energy on measurement of unburned carbon in fly Ash particle flow].

The fly ash particle flow was produced by a screw feeder and then ablated by a pulse laser to create plasma. The emission spectra of fly ash were detected by laser-induced breakdown spectroscopy. The present paper focused on the influence of laser energy on the measurement of unburned carbon. Seven groups of pulse laser in the range of 40 to 130 mJ were used to ablate the fly ash particle flow. The results show that the carbon line intensity is increased linearly with the increases in laser energy, but the SNR of carbon line increases in the range of 40 to 90 mJ and then trends to saturation, while the elimination rate of false data decreases. In this experiment, laser energy ranging from 90 to 100 mJ can enhance the plasma emission signal and improve the true spectral data of fly ash particle flow. So laser energy has close correlations with the ablation of the particle flow and the carbon line intensity. Reasonable laser energy is good for the effective ablation of the fly ash particle flow to get plasma spectra signals with good SNR.

[Study of laser energy in multi-element detection of pulverized coal flow with laser-induced breakdown spectroscopy].

The logical range of laser power density and optimum laser power density were explored for multi-element analysis of pulverized coal flow with laser-induced breakdown spectroscopy in the present paper. The range of laser energy was chosen from 20 to 160 mJ in the experiment. Pulverized coal less than 200 microm in diameter of particles fell freely through feeder outlet and the rate of flow was controlled by screw feeder. Emissions were collected with pulse laser at 1 064 nm focusing on pulverized coal flow and plasma was generated. The intensity and cause of fluctuation of emission spectra at various laser energy levels were studied. A suitable range of laser power density is from 14.4 to 34.4 GW x cm(-2), and the optimum laser power density is 19.5 GW x cm(-2) for the determination of pulverized coal flow with LIBS.

[The study on the laser-induced breakdown spectroscopy properties of compound fertilizer with different physical forms].

In order to study the mechanism of laser-induced breakdown spectroscopy for detecting the chemical components content of compound fertilizer in detail, two physical forms of compound fertilizer samples (powder and granular) were used for this study. The authors analyzed the laser-induced breakdown spectroscopy properties of samples with different physical forms made under different preparation pressure. And the spectral characteristics and plasma characteristics of N,P and K in the powder and granules made under the preparation pressure of 0, 0. 5, 2, 4, and 6 MPa, respectively were compared experimentally. The experiments results showed that the spectral characteristics of the two forms have obvious difference when the pressure is small and the grain samples have significant higher line intensity than those of the powder samples. With the increase in the pressure, the difference in the plasma characteristics between these two physical forms was reduced, and all the characteristic spectral lines intensity of the same physical form samples increases firstly and reduces afterward.

[Application of wavelet transform in laser-induced breakdown spectra compression].

A method based on the wavelet transform (WT) was developed for the compression of laser-induced breakdown coal spectral data. By studing the impacts of main parameters such as the order of db wavelet, decompose level and threshold method on compression performance, it can summarize the compression parameter selection rule and select the proper compression scheme. The scheme was evaluated by compression scores and relative deviation of each spectral line between original and reconstructed. By choosing proper parameters for channel 1, channel 2 and channel 5 of LIBS spectrum of coal sample (No. 1-No. 8), the restore score RS and compress score CS are respectively 81%-92.11% and 79.02%-92.07%, with the spectral line relative deviation under 5%. It indicates that the storage space is reduced while the main characteristic of original spectrum is maintained. The result shows that this method is very effective.

[Impact of laser energy on measurement of fly ash carbon content].

A laser induced breakdown spectroscopy-based apparatus for the analysis of element, employing a 532 nm laser and a multi-channel optical spectrometer with a non-intensified CCD array, has been built and tested. It was applied to analyze the carbon content of coal fly ash. Seven groups of pulse laser in the range of 35 to 98 mJ were used to ablate the fly ash samples. The electron densities and plasma temperatures with different laser energy were determined, and the influence of laser energy on the intensity of analysis carbon lines was also analyzed. The results show that carbon line intensity increases slowly with the increase in laser energy in the range of 35 to 46 mJ, and increases fast in the range of 46 to 78 mJ, then trends to saturation and has a little drop. At the same time, air breakdown has increased significantly, and has an obvious effect on sample plasma. Furthermore, the electron density and plasma temperature increase with the laser energy until 78 mJ and then begin to decrease. It indicates that a proper laser energy can enhance the plasma emission signal, and avoid the negative impact of air breakdown that prevent the pulse laser from reaching the surface of sample and ablating it. In this experiment situation, the measurement accuracy of the carbon line can be improved.