Volatile matter content is one of the important characteristics of coal, which would inevitably influence the laser-coal interaction process. In this work, the coal samples with different volatile ...matter contents were carried out by laser induced breakdown spectroscopy (LIBS) in argon atmosphere. The temporal and spatial evolution of spectra was captured along with the plasma evolution to investigate the mechanism of the volatile matter effects. The results showed that the spectral emissions for the species that abundant in volatile matter were intense at the plasma front, which indicated that the volatile matter vaporized preferentially as laser irradiating and pushed toward the upper part of the plasma. The distribution characteristics of the atomic carbon emission and ionic calcium emission of different coals demonstrated that the amount of vaporization increased with the volatile content. The more abundant dissociated volatile matter in the plasma plume benefited the generation of molecular carbon (CN and C2) formed by several pathways, resulting in an enhancement on the corresponding emissions. Moreover, effects of volatile content on ablation process contributed to the difference in plasma structure and composition, which would be magnified during the plasma expansion and fluctuation process, contributing to greatly diverse plasma morphology and parameter distribution. Consequently, a conceptual laser-coal interaction model was proposed based on the comprehensive analysis of the measurements to describe the initiation and propagation of the effects of volatile matter on coal plasma.
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•The mechanism of laser-coal interaction was clarified by temporal-spatial resolved LIBS.•Effects of volatile matter on the temporal and spatial evolution of spectra were determined.•The plasma dynamics and parameters characteristics of coal with different volatile matter contents were illustrated.
Pyrolysis of 34 Chinese coals is studied in a TGA coupled with a mass spectrometer. The mass loss registered in TGA during temperature programmed heating is attributed mainly to devolatilization of ...fragments generated from cleavage of covalent bonds because retrogressive reactions of small volatile radical fragments do not produce solid products and that of large volatile radical fragments are slow and occur mainly outside of the sample crucible. Each of the DTG curves is fitted by a set of sub-curves and regression using 6 sub-curves yields the best fitting. Each of the 6 sub-curves is assigned to cleavage of a group of covalent bonds in coal, which is validated by model compounds and literature data. The trends in peak temperature and peak area of the sub-curves with respect to changes in C% in the coals are clear and similar to changes in some of the physical properties of coals. The analysis method presented is useful in analyses of coal structure and pyrolysis reactions. Furthermore, TG analysis is suggested to replace proximate analysis due to the rich volatile-temperature information and easy identification of volatiles generated from decomposition of carbonates.
►Pyrolysis of 34 Chinese coals is studied in a TGA–MS system. ►The DTG curves of the coals are fitted better by 6 sub-curves. ►The sub-curves are assigned to crack of bonds in coal according to the bond energy. ►The trends in peak T vs C% are similar to that in physical properties of coals.
The characteristics of the carbon components emitted during coal and biomass combustion changed sharply, owing to rapid and increasingly complex combustion conditions and changes in fuel variety. ...However, comprehensive experiments on the various factors influencing the characteristics of carbonaceous substance emissions from residential fuel combustion are severely lacking, which makes it difficult to compile accurate emission inventories and source apportionment. In this study, ten types of coal and eight types of biomass burned in a muffle furnace at different combustion temperatures were used to determine the emission characteristics of carbonaceous substances. The ranges of emission factors (EFs) of fine particulate matter (PM2.5), organic carbon (OC), elemental carbon (EC) and a total of 16 United States Environmental Protection Agency (EPA) priority control polycyclic aromatic hydrocarbons (PAHs) ranged from 1.96 to 17.75, 0.83 to 10.97, 0.14 to 1.19 and 0.017 ± 0.01 to 0.009 ± 0.007 g/kg for coal combustion, and 2.44 to 17.7, 1.07 to 9.34, 0.3 to 1.66 and 0.016 ± 0.02 to 0.18 ± 0.30 g/kg for biomass burning, respectively. Combustion temperature and fuel type were important factors affecting carbonaceous substance emissions. The mean EFPM2.5, EFOC for residential fuel, and EFPAHs for coal combustion were significantly greater at lower temperatures than at higher temperatures; however, the trends for mean EFEC for residential fuel and EFPAHs for biomass were opposite. The emission characteristics of PM2.5, OC, EC, and PAHs for coals of varying maturity were different at low and high combustion temperatures, which might indicate that coal maturity was a main influencing factor at low combustion temperatures, whereas other factors were dominant at high combustion temperatures. Finally, the PAHs diagnostic ratios were discussed and found to be inconsistent with previous studies for some conditions, which indicated that they should be used cautiously for source apportionment studies.
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•Comprehensive emission factors of carbonaceous matters were obtained.•Emission factors of carbonaceous matters were affected highly by temperature and fuel types.•Different species formation mechanisms were changed on different temperature.
•Incomplete combustion of coal volatile matter leads to significant PM emission from household stove.•PM emission decrease with increasing coal size and mineral additive in household ...stove.•Controlling coal properties helps to reduce PM emission from household coal combustion.
Aiming to reduce primary particulate matter (PM) emission from household coal combustion, we conducted experimental investigations on several coal properties that affect PM emission factors (EFs). Fourteen coal chunk samples with various volatile matter contents on dry and ash-free basis (Vdaf, 2.84–48.7%) were tested to examine the effect of coal volatile matter content. Eight coal briquette samples with various mineral additives were tested to examine the effect of coal additive. Two coal chunk samples with Vdaf of 32.9% and 9.3%, respectively, were made into three different sizes to examine the effect of coal size. Due to low combustion temperature and low burning efficiency of the volatile matter in household stoves, PMs emitted from household coal combustion often have a high fraction of carbonaceous compositions. Both PM2.5 EF and the fraction of its carbonaceous constituents increase with an increase in the coal volatile matter content till about Vdaf=35% and then stay roughly flat. Addition of extraneous minerals results in a significant reduction of PM emissions. Increasing the coal size from ∼1cm to ∼10cm leads to a reduction of PM EFs by ∼80%. The coal volatile matter content determines the total amount of organic compounds to be devolatilized during coal pyrolysis stage. The coal size and ash content affect the escape of these organic compounds from burning coal chunks or briquettes. Together, they all affect the burning completeness of these organic compounds in household stoves and subsequently the total amount of organic precursors to form carbonaceous constituents in PMs.
This study updated carbonyl compound (CC) emission factors (EFs) and composition for residential solid fuel combustion based on real-world measurements of 124 fuel/stove combinations in China and ...explored the CC formation mechanism using tube-furnace experiments with 19 fuels and low/high temperatures to explain the impact of fuel and stove on CC emission characteristics. The average EFCC values for straw, wood, and coal were 1.94 ± 1.57, 1.50 ± 0.88, and 0.40 ± 0.54 g/kg, respectively. Formaldehyde and acetaldehyde were the most abundant species, accounting for 40–60% of CCs, followed by acetone (∼20%), aromatic aldehydes (∼10%), and unsaturated aldehydes (∼5%). Different from formaldehyde and acetaldehyde, other species showed significant variation among fuel types. All these characteristics could be explained by the difference in the volatile content and chemical structure of fuel, such as aromatic in coal versus lignin in biomass. The improvement in stove technology reduced CC emissions by 30.4–69.7% (mainly formaldehyde and acetaldehyde) among fuels but increased the proportion of aromatic aldehydes by 24.3–89.4%. Various CC species showed different formation mechanisms related to fuel property and burning temperature. The volatile matter derived from thermal pyrolysis of fuel polymers determined CC composition, while higher temperature preferentially degraded formaldehyde and acetaldehyde but promoted the formation of acetone and aromatic aldehydes. This study not only revealed emission characteristic of CCs from RSFC but also contributed to the improvement of clean combustion technology.
Determination of proximate characteristics can be achieved using conventional analyses methods that require a certain amount of time. In cement factories, refuse-derived fuel (RDF) is continuously ...fed to a kiln by a conveyor belt, so even if an inappropriate proximate characteristic is determined, it would be too late to prevent the feeding of RDF to the kiln. To overcome this problem, there is a need for instant measurement of the proximate characteristics (moisture, volatile matter, ash) that enables the feeding to be stopped. In such cases, the deep learning (DL) is a useful method based on the prediction of proximate characteristics. Therefore, in this study, the aim is to estimate the mentioned parameters developed by near-infrared spectroscopy (NIR) combined with deep learning models. For this purpose, the spectrographic measurements taken from RDF samples with an NIR spectrometer, and the results of proximate analysis in a laboratory, were used together as a dataset. A fully convolutional neural network (FCNN) and ResNet were used as a network, and they were trained using images of RDF samples and proximate analysis values. The FCNN model was more successful in prediction studies. According to the FCNN model, the results show that the models in the study can predict the moisture, ash, and volatile matter content of RDF with satisfactory
R
2
values between 0.979, 0.983, and 0.952.
Gaseous inhibitors are used in many industries for the explosion prevention of combustible dusts, mitigating the potential hazard to humans, properties and environments. This work experimentally and ...theoretically studied the inerting effect of gaseous inhibitors on the ignition process of dust clouds in O2/N2/CO2 atmospheres, with an emphasis on the role of the CO2/N2 ratio. 10 different combustible carbonaceous dusts were selected, including grain dust, biomass dust and coal dust. Experimental results showed that the inhibition effect of CO2/N2 is closely related to the ignition mechanism of dust clouds. Specifically, a higher ratio of CO2/N2 yields a stronger inhibition effect on the ignition process of dust samples with relatively low volatile matter contents predominated by heterogeneous ignition. In addition, two novel steady-state ignition mechanism models were developed to interpret the experimental observations. Maxwell-Stefan equations were used to describe the diffusivity in the ternary O2/N2/CO2 gas mixtures. The analytical results were in good agreement with the experimental data of the minimum ignition temperature of dust cloud (MITC) in oxygen-lean atmospheres. The mechanism modelling can be used to estimate the critical ignition temperature of all carbonaceous dust clouds with a wide range of volatile matter content under different inert atmospheres, which will provide a reference for the explosion hazard assessment of dust posed by a hot surface in the process industries.
The degree of coalification is an essential parameter influencing the quality of coal reserves. Modelling of the development of this parameter in the Czech part of the Upper Silesian Coal Basin ...(Carboniferous, Mississippian to Pennsylvanian — Lower Namurian to Westphalian A) revealed the distribution of coalification within the basin in all its stratal units. The grade of coalification was found in principle to be similar but its intensity in general decreases upwards into the hanging wall. Because of different areal extents of individual stratal units the degree of coalification is demonstrated on the oldest and areally most extensive unit — the Petřkovice Member. The studies and their results presented in this paper are based on more than 29,000 analyses of the dry and ash-free volatile matter (
V
daf) in coal samples from surface and underground boreholes drilled in the years 1946–2000. Three zones of enhanced coalification were distinguished: the Ostrava–Příbor Zone, the Rožnov–Frenštát Zone and the Příbor–Těšín Zone. These zones were found to correlate fairly well with the occurrence of gas deposits confined to the weathered Carboniferous rock massif or its mantle. Consequently, the degree of coalification does not only determine the quality of coal reserves but may also be used as an auxiliary tool in the search for gas deposits in coal basins.
Hilt's law (dependence of the coalification degree on depth) is a substantial and long-acknowledged rule. Its validity in the Czech part of the Upper Silesian Coal Basin (Carboniferous, Mississippian ...to Pennsylvanian — Lower Namurian to Westphalian A) is the subject of this study. It is based on over 29,000 analyses of the volatile matter moisture- and ash-free
(V
daf
) from surface and underground boreholes drilled in 1946–1989. Vitrinite reflectance (
R
max) cannot be used as a measure of coalification in the Upper Silesian Coal Basin: the number of reflectance measurements is small and their distribution over the basin area is very uneven. Statistical data on
V
daf for the individual stratal units were processed. Modelling of the trends in the volatile matter moisture- and ash-free (
V
daf) depending on “stratigraphic depth” proved the general applicability of Hilt's law. The distribution of this parameter in selected boreholes and segments of the basin was also studied, and coalification gradients were calculated. Coalification in specific examples (boreholes) is, however, highly variable and shows numerous deviations from Hilt's law even within individual boreholes, which is documented on a real example. The causes of some of the deviations are relatively well known (e.g., effect of elevated pressure in tectonically deformed areas, effect of effusive rocks or paleoweathering zones) while others can be presumed (heat flows due to Variscan and Carpathian orogenies affected by the lithology of the Carboniferous massif). The contribution of these effects in specific examples can be determined with great difficulty only.
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