INDUCED BREAKDOWN SPECTROSCOPY; HIGH-TEMPERATURE; PARTICLES

A new route for directly measuring the fly ash unburned carbon in a gas solid flow by laser-induced breakdown spectroscopy (LIBS) was proposed. A homemade gas-solid flow generation system was developed to simulate the gas solid flow in the duct of a coal-fired plant. For improving the measurement performance, the emission characteristics of the laser induced plasma, the influence of the fly ash mass flow rate, and the correlation between the unburned carbon content and the carbon emission intensity were studied in detail. The SNR of the Si spectral line at 288.15 nm was selected as the index for false spectra identification because the distribution of Si is not related to the particle size. The results highlight the change of the plasma shape and volume with fluctuations of the gas solid flow because of the uneven distribution of the fly ash particle size and number in the laser focal spot. The mass flow rate of the fly ash affected the false hit rate, while it did not affect the intensity of the analyte lines. The regression coefficients (R-2) between the normalized intensity of C 247.86 nm and the unburned carbon content improved from 0.93 to 0.98 when the false spectra were rejected. The good agreement between the normalized intensity of C 247.86 nm and the unburned carbon content indicates that LIBS can be developed as a promising tool for directly measuring the fly ash unburned carbon in a gas-solid flow.

SITE QUANTITATIVE-ANALYSIS; LIBS SPECTRA; POWER-PLANTS; ASH CONTENT; WELL LOGS; VALUE GCV; CALIBRATION; PREDICTION; MODEL; PERFORMANCE

Online measurement for the gross calorific Value (GCV) of coal is important in the coal Utilization industry. This paper proposed a rapid GCV determination method that combined a laser-induced breakdown spectroscopy (LIBS) technique with artificial neural networks (ANNs) and genetic algorithm (GA). Input variables were selected according to the physical mechanism and mathematical significance to improve the prediction of the ANN. GA was applied to determine an,optirnal architecture for the network instead of a trial and error method. As a result, the mean standard deviatiori (MSD) of the GCV for four prediction set samples is,0.38 MJ/kg in 50 trials (repetitions of training the ANN with the same; input data but different random initial weights and biases), proving that the ANN model is able to provide high modeling repeatability in the GCV analysis. The mean absolute error (MAE) of the GCV for the prediction set is 039 MJ/kg. The result meets the requirements (0.8 MI/kg) for coal online analyses using the neutron activation method in the Chinese national standard (GB/T 29161-2012).

METHANE-AIR FLAMES; DIFFUSION FLAMES; CH-ASTERISK; OH-ASTERISK; SOOT; DIAGNOSTICS; EMISSION; FRACTION; MIXTURE; ETHANE

Real-time monitoring of the local equivalence ratio is of primary importance for combustion efficiency improvement. Chemiluminescence and laser-inducedbreakdown spectroscopy (LIBS) measurements can be powerful tools for sensing the equivalence ratio. Radicals, such as OH*, CH*, and C-2*, are formed within the flame front, and consequently, the related chemiluminescence emission can be considered as a marker to follow the evolution of combustion processes. From LIBS measurements, the ratio of two characteristic spectral lines of fuel (H) and oxidizer (0) is related to the equivalence ratio. In this work, LIBS measurements have been carried out in premixed flames of known equivalence ratio for calibration purposes. Then, the application to non-premixed flames has been performed to evaluate the local equivalence ratio. Chemiluminescence emission spectra have also been collected, and the values of OH*, CH*, and C-2* have been properly evaluated, taking into account the contribution of CO2* broad band emission. A methane co-flow diffusion flame has been investigated along the centerline as well as at three cross sections, and the local equivalence ratio profiles obtained by LIBS have been compared to CH* chemiluminescence profiles. Finally, the experimental data obtained were compared to the results of a detailed chemical kinetic model.

VICTORIAN BROWN-COAL; FIXED-BED REACTOR; ASH DEPOSITION; ALKALI REMOVAL; ATOMIC SODIUM; SORBENTS; GASIFICATION; TEMPERATURE; MECHANISMS; CORROSION

Zhundong coal represents a large portion of China's future energy supply, because of the large reserve capacity. Although Zhungdong coal has low ash and good ignition characteristics, it also contains large amounts of sodium, which can foul and corrode heat-transfer surfaces. For economically viable use of Zhundong coal or other high-alkali coals, the alkali release must be mitigated prior to or within the burner. This can be done either by washing the coal,, using sorbents to trap the sodium, or a combination of these methods. Additive influence on the release of sodium over the entire coal combustion process was measured using a calibrated laser-induced breakdown spectroscopy (LIBS) technique. The additives used were alumina, silica, and five mineral sorbents comprising blends of silica, alumina, and various other inorganic compounds; different coal/sorbent ratios were assessed (1%, 3%, and 5% additive, by weight). During the three stages of sample coal combustion, it was found that the first stage, devolatilization, releases only similar to 1.2% of the total sodium; the char combustion stage releases similar to 28% of the total sodium; and the ash stage releases the vast majority of sodium (similar to 70%). The peak instantaneous release rate occurs during the char combustion stage. The sodium retention efficiency for all of the sorbents tested was lowest during the devolatilization stage and there was no appreciable change to the duration of the stage. Sodium retention efficiency was greatest in the ash stage, primarily due to the sheer amount of sodium released during this stage. The ash stage was effectively shortened, in proportion to the retention efficiency of the sorbent. The sodium release during the char combustion stage showed an obvious difference in profile for the various types of sorbent tested. Alumina was the least effective in reducing sodium release and retained the characteristic shape of sodium release from raw coal during this stage. Silica and sepiolite demonstrated similar sodium release profiles, which were markedly different than the sodium release profiles of either alumina or aluminosilicate mineral samples. Time-resolved sodium retention plots show an enhancement in the sodium retention by alumina during the char burnout. The addition of sodium sorbent to the coal extended the duration of the char burnout stage, which may indicate that the reduction of available sodium reduces the alkali catalysis of the char decomposition.

ADSORPTION; VALIDATION; REGRESSION; SAMPLES; ARGON; SIZE

From healthcare to cosmetics to environmental science, the specific surface area (SSA) of micro- and mesoporous materials or products can greatly affect their chemical and physical properties. SSA results are also widely used to examine source rocks in conventional and unconventional petroleum resource plays. Despite its importance, current methods to measure SSA are often cumbersome, time-consuming, or require cryogenic consumables (e.g, liquid nitrogen). These methods are not amenable to high-throughput environments, have stringent sample preparation requirements, and are not practical for use in the field. We present a new application of laser-induced breakdown spectroscopy for rapid measurement of SSA. This study evaluates geological samples, specifically organic-rich oil shales, but the approach is expected to be applicable to many other types of materials. The method uses optical emission spectroscopy to examine laser-generated plasma and quantify the amount of argon adsorbed to a sample during an inert gas purge. The technique can accommodate a wide range of sample sizes and geometries and has the potential for field use. These advantages for SSA measurement combined with the simultaneous acquisition of composition information make this a promising new approach for characterizing geologic samples and other materials.