Flame Coal Research Articles

Thermodynamic characteristics of methane adsorption on coals from China with selected metamorphism degrees: Considering the influence of temperature, moisture content, and in situ modification

A better understanding of the thermodynamic characteristics of methane (CH4) adsorption on coal surfaces is needed for the high-efficiency coalbed methane (CBM) preextraction or prevention of coal and gas outbursts. In this study, atomistic representations of selected coal samples with different degrees of metamorphism, such as long flame coal, coking coal, and anthracite coal obtained from China were created; CH4 adsorption isotherms considering the temperature, moisture content, and microwave in situ modification for CBM preextraction were simulated and analysed. The coal molecular structural results showed that as the degree of coal metamorphism increased from long flame coal to coking coal and anthracite coal, the functional groups in the molecular structure of the coal reduced, while the degree of graphite increased. In situ modification of coal facilitated this process. The saturation adsorption capacity of CH4 decreased and then increased with increasing coal metamorphism degree and decreased linearly with increasing temperature. When water molecules were present, the adsorbed CH4 showed different degrees of decreasing trends with increasing moisture content. The isosteric heat of CH4 adsorption followed the order of coking coal > anthracite coal > long flame coal. The isosteric heat gradually decreased with increasing methane adsorption, and the presence of water molecules had a limited effect on the isosteric heat. In situ modification disrupted the self-conjugated hydrogen bonds, reduced the oxygen-containing functional groups, and decomposed some associated minerals in the coal samples. After in situ modification, the amount of methane adsorption decreased due to a greater contribution from the functional group change than that from the pore volume change, and the modification effect was more evident for the low-rank coal samples than for the middle and high metamorphism degree coal samples. In situ modification applied in the coal seams could contributed to designs for CBM exploration, and the results of this experiment and simulation could provide a novel theoretical basis for in situ modification technology.

Study on flame propagation characteristics of coal dust explosion in horizontal straight pipe

AbstractCoal dust explosion is one of the common accidents in mines. The flame generated in the explosion process spreads rapidly, and the high-temperature flame will cause personal injury and equipment damage in the working environment. In order to study the flame propagation characteristics of coal dust explosion, four kinds of coal dust explosion flame propagation experiments were carried out by using the intelligent coal dust explosion identification device, and the flame propagation process was simulated by computational fluid dynamics (CFD) simulation. The results show that the flame length of lignite dust explosion is obviously longer than that of long flame coal, non-caking coal and gas coal. From the ignition of lignite coal dust, the flame length increases continuously, reaches the maximum of 52 cm at a certain time and then gradually decreases to 0. While the flame length increases, the flame propagation rate also experiences the propagation process of accelerating and decelerating. By comparing the explosion flame length obtained by CFD numerical simulation with the experimental results, it is found that the simulation error is within the acceptable range. Further statistical analysis is made on the simulation results of overpressure generated by explosion, and it is found that the change law is consistent with the theoretical formula, so as to further verify the feasibility of numerical simulation for explosion research. The research results lay a theoretical foundation for predicting the disaster scope of coal dust explosion accidents, and have practical significance for taking explosion suppression and flameproof measures in mines.

CO2 adsorption-deformation-percolation characteristics of coals with different degrees of metamorphism and improvement of dynamic prediction model

The deformation and permeability changes occurring during CO2 adsorption in the coal body are important factors affecting CO2 injectability. In order to reveal the characteristic laws of adsorption, deformation and permeability of coal in the process of CO2 adsorption by different coal rank coals, the test experiments of adsorption, deformation and permeability of different coal rank coals under the condition of constant external force were carried out. The adsorption capacity of different coal samples for CO2 was obtained as anthracite > coking coal > long flame coal; The radial deformation ɛ2 and axial deformation ɛ1 of coal after CO2 gas adsorption by anthracite are the closest (ɛ2/ɛ1 is about 1.37), coking coal is the second (ɛ2/ɛ1 is about 1.73), long-flame coal is the largest (ɛ2/ɛ1 is about 2.72), In other words, the higher the coal rank, the more significant the degree of internal homogeneity and isotropy of the coal body, and the mean value of the volume deformation of CO2 adsorbed by long-flame coal is 1.07 and 1.17 times higher than that of coking coal and anthracite. The permeability curves of CO2 adsorption in all three coal samples decreased first and then increased, and the permeability of CO2 in coking coal was the largest, and the sensitivity coefficient of CO2 permeability in coal to adsorption pressure showed a trend of rapid decrease and then small increase. Based on the CO2 adsorption-deformation-percolation variation law of coal, an improved dynamic prediction model of adsorption (fitting accuracy 0.9850 ∼ 0.9963), an improved dynamic prediction model of coal body deformation (fitting accuracy 0.9889 ∼ 0.9921) and an improved dynamic prediction model of permeability (fitting accuracy 0.9848 ∼ 0.9914).

Адсорбція хлорфенолу активованим вугіллям з сумішей довгополуменевого вугілля та вторинних продуктів коксування.

ADSORPTION OF CHLOROPHENOL BY ACTIVATED CARBON FROM MIXTURES OF LONG FLAME COAL AND SECONDARY COKING PRODUCTS © V.А. Кucherenko, Doctor of Chemical Sciences, Ju.V. Таmarkina, PhD in Chemical Sciences, V.А. Sabierova, PhD in Chemical Sciences, I.B. Frolova, PhD in Chemical Sciences (L.M. Litvinenko Institute of Physical-Organic and Coal Chemistry of the National Academy of Sciences of Ukraine, 02160, Kyiv, Kharkiv Highway St., 50, Ukraine) The purpose of this work is to evaluate the effect of secondary coking products (SCPs) on the adsorption properties of activated carbons (ACs) from mixtures of SCP and long-flame coal D. AC samples with specific surface area SBET = 885–1173 m2/g were prepared from coal D and mixtures of coal (85 %) and SCP (15 %). Fuses (F), acid tar (AT) of the sulfate department, polymers (P) of the benzene department, cube residue (CR) and coal tar (T) were used, and the corresponding samples are designated as AC(D), AC(F), AC(AT), AC(P), AC(CR), AC(T). The adsorption capacity for 4-chlorophenol (CP) (ACP) was determined at the AC content of 1 g/L (25°C) and the CP initial concentration СCP(0) ≤ 600 mg/L. The CP concentration was determined from the solution optical density at 280 nm (Perkin-Elmer Lambda 20 spectrophotometer). The specific adsorption capacity АCP(S) (mg/m2) was determined by the ratio АCP(S) = ACP/SBET, which is proportional to the concentration of adsorption centers on the AC surface. The degree of CP extraction and the degree of surface coverage were calculated. The CP adsorption kinetics were approximated by pseudo-first order, pseudo-second order and intraparticle diffusion models. The adsorption isotherms were approximated by the Langmuir and Freundlich models. The SCP type was established to have a significant effect on the AC adsorption activity which is expressed by significant differences in the values of adsorption capacity, kinetic characteristics, and isotherm parameters. The CP adsorption kinetics was found to obey the pseudo-second order model (determination coefficient R2 ≥ 0.996) with constants varying from 2,78·10-4 g/mg·min to 6,29·10-4 g/mg·min depending on the SCP type. By comparing the calculations of the kinetics by the pseudo-first order and intraparticle diffusion models, the rate-determining stage was found to be the physical sorption and chemisorption of СP. In the range of equilibrium concentrations of СCP(е) ≤ 350 mg/l, the adsorption isotherms were approximated by the Langmuir model (R2 ≥ 0,994) better than by the Freundlich model (R2 ≥ 0,887). The calculated capacitances of the monolayer for the obtained ACs differ by a factor of ~2 and are in the interval of АCP(L) =214,3 – 414,3 mg/g, Langmuir constants are from 1,89·10-2 l/mg to 5,29·10-2 l/mg. The CP adsorption capacity was found to increase almost linearly with increasing SBET (R2 = 0.931), but the AC(AT) sample sharply drops out of this dependence and shows a 2-fold lower capacity value, which is due to the AT composition. It is determined that the CP capacity and degree of extraction increase in the series of АC(AT) < АC(D) < АC(F) < АC(T) < АC(P) < АC(CR). Judging by the effect on the AC properties, the most effective SCP is the cube residue, which maximally contributes to the formation of adsorption centers being active in relation to CP. The AC(CR) sample exhibits the highest adsorption capacity (414 mg/g), specific capacity (0.353 mg/m2), surface coverage (80.6 %), and initial CP uptake rate. During the first 5 min, AC(CR) absorbs 35.8 % of the CP total amount at CCP(0) = 600 mg/l. The values of this parameter for other samples are lower and range from 11.5 % (AC(AT)) to 29.2 % (AC(P)). Namely SPS composition is concluded to determine the set of chemical reactions forming the AC spatial framework. All SPCs (except acid tar) promote the formation of AC with a higher capacity and an increased adsorption rate, which makes their use promising for improving the ACs adsorption characteristics. Key words: long flame coal, secondary coking product, activated carbon, adsorption, 4- chlorophenol Corresponding author: Таmarkina Ju.V., e-mail: Tamarkina@nas.gov.ua

Experimental Study on Fractal Characteristics of Adsorption Pore Structure of Coal

The adsorption pore structure is the key affecting the technology of enhanced coal bed methane recovery (ECBM). In this paper, nitrogen adsorption measurement (NAM) and low-field nuclear magnetic resonance (NMR) methods are used to test the structural parameters of adsorption pores of four coal samples with different metamorphic degrees. Combining with the fractal theory, the applicability and the physical significance of fractal dimensions obtained from different models are analyzed. Finally, the main factors affecting the complexity of the pore size structure and the influence of fractal characteristics on the adsorption properties of coal are discussed. The results show that with the increase in the degree of metamorphism, the ranking order of the volume and the specific surface area of adsorption pores of four coal samples are long flame coal > anthracite > gas coal > coking coal. The fractal dimension D2 calculated by the Frenkel–Halsey–Hill (FHH) fractal model ranges from 2.5 to 2.9, representing the degree of the pore surface irregularity, and D3 calculated by the FHH fractal model ranges from 2.004 to 2.037, representing the complexity of pore size distribution. There is no clear quantitative relationship between the fractal dimension and the single structure parameters of adsorption pores. The more the pore diameter distribution is concentrated in the range of 2–5 nm, the larger the fractal dimension is, the higher the complexity of adsorption pore structure is; D2, which represents the irregularity of the surface of coal, has a good linear positive correlation with the maximum adsorption capacity of N2.

Effect of active composite ionic liquids treatment on chemical structure and wettability of coal

To investigate the effect of different ionic liquid composite solutions on the wettability and chemical structure of coal dust, 14 ionic liquid compound solutions with various composite ratios were selected to act on long flame coal. Through the contact angle measuring instrument, 14 ionic liquid compound solutions were optimized, and 4 ionic liquid compound solutions with the same anion/cation were selected. The wetting agent with good water retention performance in the 4 kinds of composite solutions was selected by the water retention experiment. FTIR was used to research the change of functional group content in the coal treated by the 4 kinds of composite solutions. The results displayed that the contact angle of [Bmim][BF4]/[Emim][BF4] solution with the mixture ratio of 1:5 on the coal surface reached the min value of 34.483°. The [Bmim][BF4]/[Bmim][Cl] solution with a compounding proportion of 1:5 had the best water retention performance. The hydrophilic and hydrophobic functional groups of long flame coal treated by ionic liquid composite solutions had changed significantly. The [Bmim][BF4]/[Emim][BF4] composite solutions with the compounding proportion of 2:4 and 1:5 and the [Bmim][BF4]/[Bmim][Cl] composite solutions with the compounding proportion of 2:4 and 1:5 can not only increase the content of hydrophilic functional groups OH⋯O, Si–O–Si, COC, CO, and CO, but also decrease the content of hydrophobic functional groups CH2 and 2H. By analyzing the relationship between coal wettability and functional groups, it was discovered that the hydrophilic functional group CO was the primary functional group affecting the contact angle, and –OH and COC were the primary functional groups affecting the moisture content of coal samples. In this essay, the novel composite wetting agent type was prepared by compounding ionic liquid solutions with the same anion/cation in pairs, which has certain guiding significance for further using the novel composite moistening agent to improve the wettability of coal and preventing and control mine dust.

Clean two-step oxidative degradation of Yima long flame coal for benzenecarboxylic acid production

Low rank coals are promising raw materials to afford oxygenated organic chemicals due to the high oxygen contents. This study reported a clean two-step coal oxidative degradation approach for low-carbon and high value-added chemical production. Oxidative degradation of Yima long flame coal (YLFC) was performed in aqueous hydrogen peroxide solution (AHPS) to activate the aromatic ring structures in YLFC, followed by the further oxidation with aqueous sodium hypochlorite solution (ASHS) to degrade the macromolecular networks in YLFC into soluble portions. Meanwhile, oxidation of YLFC with ASHS was also performed to investigate the role of pretreatment with AHPS in the oxidative degradation of YLFC in ASHS. The results show that 95.5% of the macromolecular structure in YLFC was converted by the two-step oxidation, while the conversion rate of YLFC in ASHS is only 59.3%. Noteworthily, the pretreatment with AHPS is more effective to increase the yields of more valuable pentacarboxy benzene and mellitic acid compared with benzenecarboxylic acids with fewer carboxylic groups. The sharp increase in the yield of oxidation products by pretreatment with AHPS could be related to .OH produced from H2O2 decomposition, which can break the weak oxygenated linkages and generate oxygenated functional groups. Thus, the activated aromatic ring structures and improved hydrophilicity of YLFC contribute to the deep decomposition of condensed aromatic rings caused by aggression of the reactive intermediate O2–. generated from ionization equilibriums in ASHC. The synergistic effect of the two-step oxidation leads to the complete degradation of macromolecular networks in YLFC.

Evolution of Chemical Component and Physical Properties of Datong Long-Flame Coal After Superheated Water Vapor Pyrolysis

ABSTRACT Datong long-flame coal from China was pyrolysis with superheated water vapor at 300°C to 536°C. Chemical and physical changes of long flame coal, including composition, weight loss, pore fracture structure, density, and water absorption were tested, and the qualitative and quantitative relationships among these changes were analyzed. superheated water vapor pyrolysis removes moisture and volatile components from long flame coals and increases the fixed carbon content. After superheated water vapor pyrolysis, the O/C and H/C atomic ratios of long flame coal decreased due to the decomposition of oxygen-containing functional groups and chain aliphatic hydrocarbons. superheated water vapor pyrolysis increased the porosity of long flame coal by material removal and matrix fracture. Material removal occurs throughout the pyrolysis process but matrix fracture occurs only at the initial stage of the conversion of solid organic matter to oil and gas products. The expansion of pore fractures in long flame coal caused a significant decrease in apparent density and an increase in water absorption. Quantitative analysis revealed the forced water absorption of long flame coal was quadratically polynomial with respect to porosity.

EXPERIMENTAL COMPARISON OF THE WEIGHT LOSS DYNAMIC DURING PYROLYSIS BETWEEN LONG FLAME COAL AND OIL RICH COAL

For the isothermal pyrolysis of oil rich coal, the activation energy E =235.92 KJ/mol, and the pre-exponential factor lnA=32.324. The activation energy of oil rich coal under isothermal pyrolysis condition is larger than that of long flame coal, E =162.15 KJ/mol, which means that the conversion rate of long flame coal is larger than that of the oil rich coal. For the constant heating rate pyrolysis of oil rich coal, the activation energy E =39.81 KJ/mol, and the pre-exponential factor lnA=5.239. The activation energy of oil rich coal under constant heating rate pyrolysis condition is larger than that of long flame coal, E =27.86 KJ/mol, which means that the conversion rate of oil rich coal is larger than that of the long flame coal.

Thermal maturity and chemical structure evolution of lump long-flame coal during superheated water vapor–based in situ pyrolysis

Oil and gas products can be successfully obtained from low-rank coal using superheated water vapor in situ pyrolysis technology, and investigating the pyrolysis properties of coal during this process is crucial. Herein, the in situ pyrolysis of lump long flame coal with superheated water vapor using a proprietary superheated water vapor pyrolysis system was simulated. The vitrinite reflectance (Ro) and functional groups of coal samples were analyzed using a microscope photometry and Fourier transform infrared spectroscopy. Moreover, the relationship between the chemical structural parameters and vitrinite reflectance during different thermal maturation processes was examined. The results indicate that the vitrinite reflectance increased from 1.01% for raw coal to 2.2% at 550 °C as the pyrolysis temperature increased. The ranges of the critical temperature for the removal of aliphatic structures, C–O, CO, –OH, and aromatic structures from the coal were 271°C-506 °C, 333°C-550 °C, 220°C-550 °C, RT–333 °C, and 333°C-550 °C, respectively. As Ro increased, the aromaticity and condensation both increased linearly and then decreased; the CH2/CH3 ratio first decreased and then increased; the C-factor exhibited negative exponential reduction. Artificial thermal maturation was more effective than natural thermal maturation in promoting the evolution of the aliphatic structure but less effective in promoting the condensation of aromatic rings. Both types of thermal maturation have the same effect on the evolution of aromaticity and C-factor.

Effects of CO2 intrusion on pore structure characteristics of mineral-bearing coal: Implication for CO2 injection pressure

CO2 intrusion has a crucial effect on the pore structure of mineral-bearing coal. In this study, we selected long flame coal, lean coal, and anthracite after CO2 adsorption at different pressures and tested the coal samples using X-ray diffraction, mercury intrusion porosimetry, and N2 (77 K) adsorption methods. The tests were conducted to determine the variations in mineral content, pore structure, and fractal characteristics. The results showed that supercritical CO2 had a greater ability to dissolve minerals in coal than that of subcritical CO2. Although the total pore volume and BET specific surface area gradually increased with the increase in CO2 intrusion pressure in coal, the transformation of different pores and partial new pores caused by the dissolution of minerals and the adsorption swelling of coal matrix caused the micro-macropores in the three coal samples to exhibit different trends. The pore surface roughness and pore structure complexity of seepage pore in the long-flame coal after CO2 adsorption increased while those of the lean coal and anthracite decreased. Meanwhile, CO2 intrusion caused the surface of the adsorption pore in coal to become smooth, and the pore structure was more regular, except for the lean coal. A conceptual model of the mineral-bearing coal was developed to describe the relationship between the mineral composition and pore structure induced by CO2 intrusion. These findings help to understand the transformation effect of CO2 on coal seams. Thus, a higher CO2 injection pressure should be used to obtain a larger injection volume and shorter injection time during CO2 storage implementation.

Acoustic emission (AE)–based study on low-temperature pyrolysis characteristics of long flame coal

Investigating crack formation and propagation in the low-temperature pyrolysis of coal is beneficial for optimising the pyrolysis process and improving the coal utilisation rate. In this study, the low-temperature pyrolysis processes of long flame coal at different temperatures (150–450 ℃) were monitored by acoustic emission (AE) technology. In addition, the effects of temperature and holding time on crack development were also analysed. The results demonstrated that 300 ℃ was a threshold for depicting low-temperature pyrolysis characteristics of long flame coal. The AE signals were weak before 300 ℃ and improved with an increase in temperature. Next, the AE signals increased significantly and were negatively correlated with the temperature. According to the generation development model proposed in this paper, the increase in temperature led to the rapid development of the primary cracks before 300 ℃, which were then slowed down. Notably, the secondary cracks began to expand after 300 ℃. The AE b-values reflected different crack development modes at 350 ~ 450 ℃. The increasing pyrolysis temperature and holding time were conducive to the development of secondary cracks. The rapid decrease and then sudden disappearance of b-values could be regarded as the criterion of macro failure of coal samples.

Pyrolysis characteristics and microstructure evolution of different coal types

Coal pyrolysis is the basis of coal gasification, as it is the necessary reaction step in the coal conversion process. To study the pyrolysis characteristics of different coal grades under temperature, thermal simulation tests of three different ranks of coal were conducted, and the pore structure and gas products were analyzed by using liquid nitrogen adsorption and gas chromatographic, and perform fractal fitting for pores of different size. The results show that the pyrolysis gas output of Inner Mongolia lignite is higher than that of Xinjiang long flame coal and Hancheng bituminous coal. With the increase of coal rank, the gas output of each gas component also shows a decreasing trend and the initial temperature and peak temperature of various gases gradually shift to high temperature. With the increase of temperature, the average pore size, volume, specific surface area, and fractal dimension of the three kinds of coal char show an increasing trend. The average pore size and pore volume of coal char increase, and the fractal dimension increase with the increase of coal rank. The comprehensive comparative analysis of the gaseous products, average pore size, pore volume, and fractal dimension of the three coal chars shows that Inner Mongolia lignite has high gas production, large average pore size, good connectivity, and simple pore structure, which is conducive to the escape of pyrolysis gas and the transportation of gasification agent and is the best favorable coal for gasification. The research results are expected to provide experimental guidance for the actual production of underground coal gasification.

Study on pore structure change and lean oxygen re-ignition characteristics of high-temperature oxidized water-immersed coal

After coal seam mining is over, the coal left in the goaf is prone to spontaneous combustion accidents due to air leakage. To explore the oxygen-lean re-ignition characteristics of long flame coal after high-temperature oxidation and water immersion. Using scanning electron microscopy (SEM), nitrogen adsorption experiment method, characterize the high-temperature oxidized water-immersed coal sample. Using programmed temperature rise and synchronous thermal analysis experimental methods, the oxidation and re-ignition characteristics of coal samples under oxygen lean conditions were studied. The results show that compared with the untreated coal sample, the surface of the water-immersed coal sample is rougher, with more pores below 10 nm. The high-temperature oxidized water-immersed coal sample has the phenomenon of pore-to-pore, and the proportion of medium-to-large pores increases. The average pore diameter of the oxidized 200℃ water immersion (O200I200) coal sample is the largest, which increases the number of coal oxygen reaction adsorption sites. The crossover temperature of the O200I200 coal samples is lower at various oxygen concentrations, and the 2–10 nm pores affect the maximum exothermic temperature and initial exothermic temperature changes of the low-temperature oxidation process. Mesopores and macropores mainly affect the change in total heat release during high-temperature oxidation. A high oxygen concentration (above 10%) will promote the oxidation and re-ignition process of the pre-oxidized immersed coal sample. This result provides a theoretical basis for preventing the spontaneous combustion of coal in water immersed by high-temperature oxidation in shallow coal seams.

Experimental study on acoustic emission characteristics of high-temperature thermal damage in an oxygen-rich environment of long flame coal

Experimental study on acoustic emission characteristics of high-temperature thermal damage in an oxygen-rich environment of long flame coal

Experimental simulate on hydrogen production of different coals in underground coal gasification

Research on hydrogen production from coal gasification is mainly focused on the formation of CO and H2 from coal and water vapor in high-temperature environments. However, in the process of underground coal gasification, the water gas shift reaction of low-temperature steam will absorb a lot of heat, which makes it difficult to maintain the combustion of coal seams in the process of underground coal gasification. In order to obtain high-quality hydrogen, a pure oxygen-steam gasification process is used to improve the gasification efficiency. And as the gasification surface continues to recede, the drying, pyrolysis, gasification and combustion reactions of underground coal seams gradually occur. Direct coal gasification can't truly reflect the process of underground coal gasification. In order to simulate the hydrogen production laws of different coal types in the underground gasification process realistically, a two-step gasification process (pyrolysis of coal followed by gasification of the char) was proposed to process coal to produce hydrogen-rich gas. First, the effects of temperature and coal rank on product distribution were studied in the pyrolysis process. Then, the coal char at the final pyrolysis temperature of 900 °C was gasified with pure oxygen-steam. The results showed that, the hydrogen production of the three coal chars increased with the increase of temperature during the pyrolysis process, the hydrogen release from Inner Mongolia lignite and Xinjiang long flame coal have the same trend, and the bimodality is obvious. The hydrogen release in the first stage mainly comes from the dehydrogenation of the fat side chain, and the hydrogen release in the second stage mainly comes from the polycondensation reaction in the later stage of pyrolysis, and the pyrolysis process of coal contributes 15.81%–43.33% of hydrogen, as the coal rank increases, the hydrogen production rate gradually decreases. In the gasification process, the release of hydrogen mainly comes from the water gas shift reaction, the hydrogen output is mainly affected by the quality and carbon content of coal char. With the increase of coal rank, the hydrogen output gradually increases, mainly due to the increasing of coal coke yield and carbon content, The gasification process of coal char contributes 56.67–84.19% of hydrogen, in contrast, coal char gasification provides more hydrogen. The total effective gas output of the three coal chars is 0.53–0.81 m3/kg, the hydrogen output is 0.3–0.43 m3/kg, and the percentage of hydrogen is 53.08–56.60%. This study shows that two-step gasification under the condition of pure oxygen-steam gasification agent is an efficient energy process for hydrogen production from underground coal gasification.

Experimental investigation of mechanical characteristics of coal samples at different drying temperatures

The drying and mechanical properties of long flame coal and anthracite after exposure to various drying temperatures were investigated in this study. Coal samples were processed and screened, treated with a nondestructive water immersion device, and dried separately at different temperatures. Uniaxial compression experiment, acoustic emission tests, and fractal dimension calculation were then conducted. Experimental results show that the degree of drying of coal samples rose as the drying temperature increased. Peak stress and elastic modulus decreased while the damage variables and brittleness rose in dried anthracite samples with increasing drying temperature. The Acoustic emission characteristics were consistent with the mechanical characteristics. The stress-strain curves changed from stepped type to perpendicular type in the post-peak stage. This was accompanied by intense damage of the coal samples and increases in the fractal dimension of the broken blocks. Our findings shed light on how coal samples dry and provide recommendations for enhancing drying methods in laboratory mechanics tests.

Coupling effect of Fe-based catalyst on Nitrogen oxides control in the process of nitrogen reduction and combustion denitration of long flame coal pyrolysis

ABSTRACT Civil dispersed coal combustion has become an important source of Nitrogen oxides (NOx), which has caused serious pollution to the ecological environment. In order to control NOx emission in the combustion process of civil coal, coal-based solid clean fuel should be used instead of dispersed combustion of coal, so as to achieve the purpose of reducing NOx emission. The pyrolysis and combustion tests of different iron additives loaded coals were performed. The raw and pyrolytic chars were prepared and characterized by X-ray photoelectron spectroscopy (XPS), nitrogen adsorption, scanning electron microscope (SEM) and X-ray diffraction (XRD). The results indicate that iron additives introduced into raw coal in one step have coupling effect on NOx emission control during pyrolysis and combustion. The addition of iron can lead to more Fe2O3, Fe3O4 and α-Fe in coke and promote coke cracking. Supporting iron catalysts could make coke structure more porous, which increases the contact area of gas. These all make the conversion of N2 increase from 16.71% to 29.64% during pyrolysis. The existence of iron catalyst can also promote the proportion of pyridinic N (N-6) and quaternary nitrogen (N-Q) relatively increase. At the same time, the existence of iron catalyst is beneficial to catalytic reduction of NOx by C and CO. The emissions of NOx during combustion can be reduced by 34.01%. The iron catalyst introduced in one step has a coupling effect on NOx control in coal pyrolysis-combustion process, which realizes a two-step nitrogen reduction effect in combustion. It provides theoretical basis for ultra-low NOx emission in clean fuel combustion.

Critical pore size for micropore filling in coal samples with different rank coals.

The objectives of this study were to explore the occurrence and migration of coalbed methane in coals of different ranks and reveal the microscopic reservoir space and the mechanism of coalbed methane. To meet these objectives, this study selected six coal samples of different coal ranks for low-pressure N2 adsorption experiments, explored the critical pore filling characteristics of packed N2 molecules in the coals, and analyzed the low-pressure N2 adsorption/desorption experimental isotherms using the DFT method and DA equation based on the micropore filling theory. Finally, the critical filling pressure and pore size range for micropore filling were determined, and the analysis results were verified by combining the Langmuir, DA, and BET equations. The results showed that, from low to high coal rank, the N2 adsorption/desorption isotherms of the coal samples transition from type Ⅱ to type Ⅰ. The proportion of N2 molecules in low-rank coals in the form of micropore filling and monolayer adsorption was higher than that in high-rank coals. The critical pressure and critical pore size for micropore filling exhibited U-shaped correlations with the coal rank. Low-rank coals (lignite and long flame coal) were gradually filled in the relative pressure range P/P0 ≈ 1E-4–0.03, and medium- and high-rank coals (gas coal, 1/3 coking coal, lean coal, and anthracite) were filled in the relative pressure range P/P0 ≈ 1E-4–0.01; the corresponding critical pore size ranges were 1.7–2.19 and 1.61–2.00 nm, respectively.

Effect of preoxidation treatment with H2O2 on ruthenium ion-catalyzed oxidation of Yima long flame coal

Environmental concerns have led researches to investigate carbon neutral and sustainable strategies to satisfy well-being of present and future generations, in which coal oxidation becomes a promising approach to achieve this goal. In this study, Yima long flame coal (YLFC) was subjected to ruthenium-ion-catalyzed oxidation (RICO) after peroxidation with H2O2 (PO). The results indicate that the organic matter in YLFC is mainly oxidized into benzenecarboxylic acids, accounting for 70.36% of all the oxidation products, and the yields of the valuable resulting carboxylic acids are significantly elevated by PO from 12.99 wt% to 35.06 wt%, leading to a higher utilization of carbon and lower CO2 emission. Moreover, PO can enhance remarkably the reactivity of the macromolecular precursors of coals, especially highly condensed aromatic species to produce benzenepentacarboxylic acid and mellitic acid more efficiently with a 20-fold increase and 200-fold increase, which is ascribed to the formation of carboxyl groups from other oxygen-containing groups or bonds in coals via PO. The reactive intermediates OH and OOH generated from H2O2 decomposition can attack the carbon atom of alkyl side chains, ether bonds, C=O bonds, and the bridged linkages to undergo a preliminary degradation of macromolecular networks in coals and produce more active sites for the subsequent RICO, leading to the yield and species number increase of carboxylic acids via PO.