Coal Reactivity Research Articles

Experimental and Theoretical Study on Surface Reactivity and CO Generation Mechanism of Bituminous Coal during Room-Temperature Oxidation.

To investigate the evolution of the microscopic chemical structure during the oxidation of bituminous coal at room temperature (25 °C) and infer the formation mechanism of carbon monoxide (CO), a self-designed closed-system coal oxidation experimental setup was employed to measure the CO generation from three bituminous coal samples [Duanwang (DW), Linsheng (LS), and Kunning (KN)]. 13C nuclear magnetic resonance and X-ray photoelectron spectroscopy were used to determine the structures and contents of different carbon atoms and surface elemental compositions and chemical states of the coal samples. Molecular models were constructed on the basis of the experimental data, and reactive force field pyrolysis simulation was used to trace the carbon atoms in the generated CO molecules. In combination with the results of interactive Mantel correlation analysis on the Fourier transform infrared experimental data of coal samples oxidized at room temperature for 0, 12, 24, 36, 48, and 60 h, the main functional groups, structures, and evolution of coal involved in CO formation during normal temperature oxidation were determined. The constructed molecular formulas for the coal samples were C154H122O28N2S for DW, C145H114O16N2S2 for LS, and C155H92O16N2S for KN. The formation of CO was related to the transformation of carbonyl (C═O), phenolic hydroxyl (-OH), ether (C-O-C), aromatic, and aliphatic structures in the coal.

Analyzing the combustion characteristics of Thar coal block XI: A comprehensive study

Coal is a key energy resource in the world that is available at low cost and the high energy content in coal makes it a fuel of choice in many developed and developing countries. Regardless of massive reserves, Thar coal of Pakistan is low-rank lignite coal with high moisture contents and has very limited use. The proximate analysis, ultimate analysis and X-ray diffractometry analysis were performed to investigate the combustion characteristics, morphological and mineral characteristics of Thar coal block XI. Thar coal samples in this study are characterized as low-rank lignite coal. The proximate analysis showed a significant difference in moisture content, volatile content, fixed carbon content and ash residue. The ultimate analysis provided the details of elemental contents (Carbon, Hydrogen, Nitrogen and Sulfer) in coal. The combustion characteristics such as combustion performance of lignite at high temperatures (950 °C) was investigated in thermogravimeter and the results showed the variations in the ignition temperature, burnout tempearature, combustion index and burnout index. The marphological characteristic were determined by X-ray diffraction. The mineral congregations, ash yields, major and minor elements (SiO2, Al2O3, CaO,MgO, Fe2O3) varied significantly in the coal. These analyses integrate various results for assessing major monitoring parameters of coal reactivity, its temperature ranges and combustion products.

SIMULATION HEATING PROCESS FOR WEAKLY REACTIVE COAL IN THE HORIZONTAL REACTOR

In this study results of the active medium parameters influence formed by hot air on the thermal heating process of weakly reactive coal from the formation «Maikubensk 3B» for the extraction of additional heat are represented. In the course of the research the regularities of the hygroscopic moisture and volatile combustible substances release for the obtaining additional heat have been determined. Optimal temperature ranges of the stage heating taking into account thermal destruction of coal in the temperature range from 20 C to 600 C, the main steps of the insulated heating process, the moisture content gradient propagation lines and dependence of the heat transfer and mass transfer coefficients on the temperature and the humidity during the thermal heating process in the horizontal coal heating reactor. The results show that it is possible to release volatile combustible gases with a gradual increase of temperatures in the obtained mode. The heating mode comprises a pre-heating stage with hydroscopic moisture release, in the temperature range from 20 C to 105 C, the stage of isothermal heating in the temperature range from 105 C to 400 C and the phase of flame-free combustion in the temperature range from 400 C to 600 C with the temperature rise above the set value. Process simulation was carried out in the Comsol Multiphisics software environment for the weakly reactive coal real-world heating conditions. Keywords: coal heating, weakly reactive coal, isothermal heating, step-by-step heating, Lagrange method, non-liner equation, non-stationary process.

Regulation mechanism of phenol on intermediates during supercritical water gasification of coal

Supercritical water (SCW) gasification technology can enable the efficient utilization of coal by converting it to hydrogen-rich gas. However, poly-cyclic aromatic hydrocarbons and heavy components, which are intermediates of supercritical water gasification, tend to generate char, hindering the complete gasification of coal. In this work, phenol is recycled to enhance the gasification process and reduce the formation of these intermediates during SCWG, and the regulation mechanism is investigated. The results demonstrate that both gas yield and gasification efficiency increase with the presence of phenol, reaching approximately 98.5% at 750 °C, concentration of 2%with the effect of phenol, which is 27% higher than that in the coal-water system. Organics removal rate reaches about 98% with the addition of phenol. Phenol can enhance the gasification performance by facilitating the conversion of heavy components to lightweight components. The transient reactivity of coal in the poly-condensation stage is increased by about 50 times with the presence of phenol. The regulation mechanism of phenol in the poly-condensation stage during coal gasification involves the decomposition of SCW forming hydroxyl radicals, which replaces the substituents on the benzene ring, facilitating the dissociation of benzene ring into small molecules that are prone to polymerize. The interacting force between phenol and multi-rings disrupts the conjugate structure, aiding in the decomposition of polycyclic organics into small molecules.

Comparative experimental study of ash formation behaviors during the fixed-bed gasification of coal water slurry and dry pulverized coal prepared from Shenmu coal

The mechanism of ash formation during coal gasification is very important for the safety and stability of gasifier operation. This study comparatively investigated the ash formation behaviors during the gasification of coal water slurry and dry pulverized coal. Shenmu coal was gasified in a CO2 atmosphere at 900 °C using a fixed-bed reactor to prepare chars and ashes. Computer-controlled scanning electron microscopy was employed to characterize the compositions and particle sizes of minerals in the raw coal, coal water slurry gasification ash, and dry pulverized coal gasification ash. Morphological characteristics reveal that, during gasification, coal water slurry gasification char exhibits obvious agglomeration compared to the dry pulverized coal gasification char. The changes of mineral compositions indicate that, during both coal water slurry and dry pulverized coal gasification, minerals follow nearly identical transformation pathways, but the degrees of transformation are different. The influence of char agglomeration on heat transfer may be the reason for the less transformation of K Al-silicate and kaolinite during the coal water slurry gasification. Furthermore, in comparison to dry pulverized coal gasification, more Ca in calcite and S in pyrite transfer into gypsum during the coal water slurry gasification. The results from thermodynamic equilibrium calculations indirectly suggest that this may be attributed to the limited internal diffusion of CO2 within coal water slurry gasification char resulting from char agglomeration during gasification. Overall particle size distributions of minerals in raw coal, coal water slurry gasification ash, and dry pulverized coal gasification ash demonstrate that the degrees of mineral fragmentation are almost consistent during both coal water slurry and dry pulverized coal gasification. However, differences in the degrees of mineral transformation led to different particle size distributions of various minerals between coal water slurry gasification ash and dry pulverized coal gasification ash. This study mainly focuses on the influence of water in coal water slurry on ash formation, and it has not considered the influence of other factors, such as ash content, hydrophilicity, caking property, and gasification reactivity of coal, which need further research to explore.

Experimental Combustion of Different Biomass Wastes, Coals and Two Fuel Mixtures on a Fire Bench

When designing settlements according to the “Green Building” principle, it is necessary to develop a heating system based on climatic conditions. For example, in areas with a sharply continental climate (cold and prolonged winters), it is sometimes necessary to use solid fuel boilers (in the absence of gas). However, to use these, it is necessary to use biomass or biomass-coal blends as fuel to increase their combustion heat. The addition of biomass waste to coal can be aimed at achieving various objectives: utilization of biomass waste; reduction of solid fossil fuel consumption; improvement of environmental performance at coal-fired boiler houses; improvement of the reactivity of coals or to improve the technical and economic performance of heat-generating plants due to the fact that biomass is a waste from various types of production, and its cost depends only on the distance of its transportation to the boiler house. In this work, combustion of various biomass wastes, including sewage sludge, was carried out on a fire bench emulating the operation of a boiler furnace. Fuel particles were ignited by convective heat transfer in a stream of hot air at a velocity of 5 m/s in the temperature range of 500–800 °C, and the experimental process was recorded on a high-speed, color video camera. The obtained values were compared with the characteristics of different coals used in thermal power generation (lignite and bituminous coal). The aim of the work is to determine the reactivity of various types of biomass, including fuel mixtures based on coal and food waste. The work presents the results of technical and elemental analysis of the researched fuels. Scanning electron microscopy was used to analyze the fuel particle surfaces for the presence of pores, cracks and channels. It was found that the lowest ignition delay is characteristic of cedar needles and hydrolyzed lignin; it is four times less than that of lignite coal and nine times less than that of bituminous coal. The addition of hydrolysis lignin to coal improves its combustion characteristics, while the addition of brewer’s spent grain, on the contrary, reduces it, increasing the ignition time delay due to the high moisture content of the fuel particles.

Activation kinetics of biochars from peanut shells, cashew nut shells, and millet stalks under isothermal conditions in CO2 atmosphere

This study investigates the reactivity kinetics of biochar from biomass. The biochars were obtained by pyrolyzing peanut shells (PNS_800), cashew nut shells (CNS_800), and millet stalks (MS_800) at 800 °C in a fixed bed reactor. The chemical composition of the biochar samples shows that silicon (Si), potassium (K), and magnesium (Mg) are the major elements in the biochar of peanut shells (PNS_800) while potassium and magnesium are the major elements in the biochar of cashew nut shells (CNS_800) and millet stalks (MS_800). The biochars were activated in a CO2 (200 Nml/min) atmosphere at temperatures 1123 K, 1173 K, and 1223 K under atmospheric pressure. The random pore model (RPM) and a modified random pore model (MRPM) were used to correlate the reactivity profiles versus carbon conversion and to determine the kinetic parameters. It was observed that biochar reactivity increases as the temperature increases, attaining at least three times at 1173 K than those corresponding to 1123 K. Furthermore, the increase in reactivity is more pronounced with the biochar MS_800. It was observed that the RPM model cannot follow the kinetic of the experimental reactivity of all biochar samples. However, a better fitting of the reactivity is obtained when using the MRPM model. The activation energies (Ea) are distributed in the range of 98.11–148.46 kJ/mol while the pre-exponential factors (k0) are in the range of 19.31–249.53 s-1. It was observed that for the MRPM model, the lower activation energy and the lower pre-exponential factor were obtained by the biochar CNS_800. However, Ea et k0 are well evaluated for PNS_800 and MS_800 with a coefficient of determination of 99.76%. The proposed modified random pore model could be used to describe the reactivity of biochar from biomass as well as the reactivity of coal.

Microscopic Structural Evolution of Oxidized Coal Residues with Different Oxidation Degree.

Coalfield fires represent a critical environmental and safety concern, warranting a comprehensive understanding of the factors influencing the reactivity of oxidized coal residues within fire zones. This study investigates the influence of the oxygen volume fraction and oxidation temperature on the residual structure of oxidized coal, elucidating the underlying mechanisms driving reduced coal reactivity. The representative oxidation conditions for coalfield fire zones were determined. Through industrial and elemental analyses, complemented by methods such as infrared diffuse reflection, specific surface area determination, and pore size analysis, results indicate that higher temperatures and oxygen levels decrease volatile matter and fixed carbon, notably above 400 °C due to oxygen-deficient combustion. Hydroxyl groups decrease with a rising temperature in high oxygen conditions, while carboxyl groups increase at lower temperatures with elevated oxygen. Oxygen-lean and high-temperature conditions reinforce the coal structure, evidenced by the reduced condensation index in aromatic hydrocarbon. Oxidation alters the pore morphology, progressing from micropores to larger irregular pores through various stages, including pore formation, expansion, and merging. Elevated oxygen levels intensify oxidation, consuming the coal carbon matrix and reducing micropores, hindering internal gas diffusion, which is the key to a reduced coal reactivity in fire zones.

Study on detonation characteristics of pulverized coal and evolution law of detonation residue

This study explores the detonation characteristics and compositional changes of pulverized coal, focusing on its use in Rotary Detonation Wave (RDW) technologies. While pulverized coal has shown high fuel efficiency in RDW settings, transitioning from theory to practical detonation engineering presents substantial scientific and technical hurdles. A key issue is the reprocessing of detonation byproducts for in-situ coal mine gob filling, a topic that has received little attention. Utilizing advanced methods like X-ray diffraction (XRD) and Fourier transform infrared spectroscopy (FTIR), this paper investigates the micro-morphology, composition, and aromatic structures of gas–solid products pre and post-detonation at the Tashan Coal Mine's 2305 working face. Results indicate that coal dust from the underground mining face has enhanced detonation characteristics, with the addition of coal powder fuel extending the gas detonation limits. This benefits economic aspects by reducing reliance on gas fuel and lowering detonation fuel costs. The highest recorded detonation wave velocity was 2450 m/s, 14.8% greater than that of coal dust from external sources, suggesting more effective energy release and pressure gain. Furthermore, the study links detonation combustion intensity to coal's aromatic properties, noting a post-detonation aromaticity index (I) of 0.4941. This indicates an improvement in the aromatic structure under high-temperature conditions, vital for coal's reactivity and energy efficiency in RDW applications. This research not only deepens the understanding of coal dust combustion mechanisms but also advances clean coal utilization and deep coal fluidization mining, addressing significant RDW technological challenges.

A novel coal purification-combustion system: Product and efficiency of coal purification process

A novel coal purification-combustion technology is presented to realize the efficient and clean utilization of coal under carbon peaking and carbon neutrality goals. Central to this technology is the implementation of a purification process, the product characteristics, and energy properties of which are the focus of this study. An experimental test of coal purification was conducted using Shenmu coal. The results demonstrate increased coal reactivity following the moderate temperature activation (MTA) process. The high temperature reduction (HTR) phase promotes the production of higher amounts of amorphous carbon, reduces aromatic carbon content, and further decreases fuel particle size. The composite combustion characteristic index(S) of the purified fuel reaches its peak when the excess air coefficient of secondary air (λ2) is 0.36. As λ2 increases from 0.1 to 0.36, the energy in the gas product of the purification system increases from 13700 kJ/kg coal to 25351 kJ/kg coal, while exergy increases from 6530 kJ/kg coal to 11030 kJ/kg coal. The energy efficiency of the purification process ranges from 74.74 % to 80.88 %, with exergy efficiency varying between 60.51 % and 70 %. These findings offer significant insights into refining the coal purification process, ultimately contributing towards maximizing the utility of coal resources.

Synergistic effects of mechanochemical activation and selective O-alkylation on the chemical structure and gaseous products evolution during coal flash pyrolysis

Mechanochemical activation offers significant advantages in enhancing the pore structure and active sites of materials, while selective O-alkylation boosts both the homogeneous and heterogeneous reactivity of coal. In this work, mechanochemical activation and selective O-alkylation are synergistically applied to modify pulverized coal. The evolution of the chemical structure was thoroughly characterized using ultimate analysis, Fourier-transform infrared spectroscopy (FTIR), and nuclear magnetic resonance (NMR). Pyrolysis gas chromatography-mass spectrometry (PY-GC-MS) was utilized to investigate the release of crucial gaseous products during the pyrolysis. Additionally, this study focuses on the synergistic effects of mechanochemistry and selective O-alkylation on the chemical structure and pyrolysis characteristics. The results reveal that alkylation boosts the formation of C-O bonds and aliphatic carbon while reducing the presence of aromatic carbon. Moreover, by disrupting intermolecular forces, alkylation induces the fragmentation of expansive aromatic layers into smaller aromatic fragments, thereby generating additional structural defects. Furthermore, the electron transfer process facilitates the conversion of aromatic carbon into aliphatic forms through ring-opening reactions. On the other hand, incorporating alkyl functional groups and initiating ring-opening reactions of aromatic carbons lead to a rise in aliphatic hydrocarbons during the pyrolysis of alkylated coal. However, intensified mechanochemical action hinders the production of aliphatic hydrocarbons. Additionally, during alkylation, the creation of esters and ethers with elevated thermal stability delays the release of oxygen-containing gas products. The findings propose a new pretreatment method for coal utilization, promoting the development of new low-NOx combustion technology.

Rapid pyrolysis mechanism and product distribution of coal model compounds containing typical C–O bonds

The structure and reactivity of coal is the core problem of coal chemistry, and solving it at the molecular level has been an international unsolved problem. The chemical similarity-based coal chemistry group elevates the study from the macroscopic to the molecular level. However, the previous free radical mechanism lacks experimental confirmation and theoretical computational support. Here, the pyrolysis products of model compounds are first utilized to predict pyrolysis. The hydrogen-donating solvent is then used as a radical trap to confirm the reaction. Subsequently, density functional theory calculations are utilized to aid in the validation. Finally, family components are utilized to demonstrate the universality of the free radical mechanism of coal pyrolysis. This work combines radical trapping with quantum chemical calculations to analyze the radical reaction mechanism of coal pyrolysis in depth at the molecular level. This will provide a theoretical basis for coal pyrolysis and clean and efficient utilization.

Co-gasification of coal and biomass: synergistic effects on gasification reactivity induced by inherent organic components

ABSTRACT It is widely recognized that the synergistic effects during co-gasification process of coal and biomass are caused by the inherent alkali/alkaline earth metals (AAEM). However, the compositions of biomass and coal are complex, with main components being not only AAEM, but also aromatic, aliphatic, and heteroatom-containing compounds. Therefore, whether these organic components can also result in synergistic effects during co-gasification is necessary to be investigated. In this work, to reveal the reaction characteristics of organic components in co-gasification process, two raw materials with little content of ash were selected. The gasification behaviors of coal and biomass were studied and the influences of blending ratio and gasification temperature were mainly examined. The results showed that gasification reactivity of pure biomass was the strongest and its carbon conversion reached 100% within 33 min. With the increase of biomass ratio, gasification reactivity of mixtures was gradually enhanced, which could be ascribed to active functional groups, porous structures, and incompact macromolecular structures of biomass. At high temperature, the gasification reactivity difference was lessened among different samples. As for coal, the reactivity index at 800°C was 0.012. With the increase of biomass blending ratio from 25% to 100%, the reactivity index slowly went up to 0.023 at maximum. When temperature rose to 900°C, the reactivity index was enlarged nearly eight times compared with that of 800°C. At temperatures tested, the shrinking core mode was appropriate to describe gasification process, especially for coal and coal/biomass mixtures. Kinetic analysis showed the theoretical activation energies were all higher than the experimental values, indicating that the interaction between coal and biomass diminished activation energy. The synergy index suggested that gasification reactivity of coal was indeed enhanced during co-gasification process. However, a high-temperature environment might cover up the positive roles of biomass and the synergistic effect was hence weakened. In conclusion, the synergistic effects during co-gasification process could be induced by the organic components in coal and biomass.

Reactivity and catalytic effect of coals during combustion: Thermogravimetric analysis

Catalytic coal combustion is a promising technology to realize efficient utilization of coal, however, the catalysis in the coal combustion process is unclear. This paper focused on the effects of two type catalysts (metal oxides and metal compounds) on the combustion reactivity of lignite, bituminous coal and anthracite using thermogravimetric analyzer, and discussed the catalytic mechanisms combining with catalytic thermal decomposition and catalytic char combustion. All catalysts decreased the ignition temperature and burnout temperature of coals to the extent of 0.25–81.25 °C, 24.75–73.25 °C, and increased the exothermic values. The catalytic effect was influenced by coal rank and had the greatest promoting effect on anthracite. Besides, the pyrolysis conversion rates of coals were increased by catalysts, resulting in ignition advance and made the subsequent reaction easier. The results of catalytic char combustion showed that both catalysts significantly reduced the ignition temperature of char, the Na2CO3 had the best catalytic effect on fixed carbon combustion, while CaO mainly affected the release of volatile matter. Finally, the catalytic mechanism in coal combustion was discussed. This article aims to provide theoretical reference for the practical comprehensive application of coal catalytic combustion.

Experimental Study on the Influence of Pore Structure and Group Evolution on Spontaneous Combustion Characteristics of Coal Samples of Different Sizes During Immersion.

To study the influence of water immersion on the evolution of the groups and spontaneous combustion characteristics of coal samples with different sizes, raw coal from the Fengshuigou Coal Mine operated by Pingzhuang Coal Company in Inner Mongolia was studied. The infrared structural parameters, combustion characteristic parameters, and oxidation reaction kinetics parameters of D1-D5 water immersion coal samples were tested, and the mechanism of spontaneous combustion during the oxidation of submerged crushed coal was investigated. The results were as follows. The water immersion process promoted the re-development of coal pore structure, and the micropore volume and average pore diameter were 1.87-2.58 and 1.02-1.13 times those of raw coal, respectively. The smaller the coal sample sizes, the more significant the change. At the same time, the water immersion process increased the contact point between the active group and oxygen in the coal, and the C=O, C-O, and -CH3/-CH2- groups in coal were further promoted to react with oxygen to generate -OH functional groups and improve the reactivity of coal. The characteristic temperature of water immersion coal was affected by the temperature rise rate, coal sample size, coal voidage, and other factors. Compared with the raw coal, the average activation energy of the water immersion coal with different sizes decreased by 12.4-19.7%, and the apparent activation energy of the coal sample with a size of 60-120 mesh was the lowest on the whole. In addition, the apparent activation energy in the low-temperature oxidation stage was significantly different.

Reactivity of Biomass, Coal, and Semicoke in Different Heating Conditions

Reactivity of Biomass, Coal, and Semicoke in Different Heating Conditions

Investigation on the quantitative evaluation method of coal combustion situation in O2-CO2-N2 atmospheres based on dynamic artificial neural network

ABSTRACT Due to the semi-enclosed space of underground coal seams and the implementation of nitrogen injection measures, most coalfield fires occur in multi-atmosphere environments. At present, there is little research on the combustion situations and kinetics of coal under multi-atmosphere conditions. In this paper, simultaneous thermal analysis experiments were conducted to investigate the combustion behaviors of bituminous coal and anthracite in O2-CO2-N2 atmospheres with different volume fractions. A new index for quantitative characterization of coal combustion situation in multi-gas mixing atmospheres was proposed based on the combustion situation intensity index and heat release rate. Furthermore, a method to predict the coal combustion situation using artificial neural network (ANN) was proposed. The results showed that the combustion rate decreased with the increase in CO2 volume fraction and the decrease of N2 volume fraction under multi-gas mixing atmospheres. The volume fraction changes in inert gases had little effect on the ignition temperature or burnout temperature and had a greater effect on the combustion reactivity of bituminous coal. In a 15% O2-5% CO2-80% N2 atmosphere, the combustion could be inhibited for bituminous coal, while being promoted by anthracite. The combustion situation of bituminous coal in a 15% O2-25% CO2-60% N2 atmosphere was greater than that in air. Based on the proposed coal combustion situation index and the selected optimal ANN model, the coal combustion situation in O2-CO2-N2 atmospheres could be well predicted. This paper provides a reliable theoretical basis for judging the coal combustion spread in the coalfield fire area.

Co-combustion of pulverized coal and walnut shells in air and oxy-fuel atmospheres: Thermal behavior, synergistic effect and kinetics

In this work, the combustion characteristics of pulverized coal, walnut shells, and their blends in the oxy-fuel atmosphere (21% O2/79% CO2) and air atmosphere (21% O2/79% N2) were investigated by the thermogravimetric analyzer (TGA). The interaction between the blends was quantified by the overlap ratio (OR) and the difference between theoretical and experimental weight loss (ΔW). The results showed that the combustion characteristics of walnut shells were better than coal attributed to its higher volatile components, whereas co-combustion of walnut shells with coal could improve the reactivity of coal. The replacement of the air atmosphere with the oxy-fuel atmosphere had a negligible effect on the ignition temperature of the selected materials but generated an increase in the burnout temperature to some extent. The activation energy was calculated by using Kissinger-Akahira-Sunose (KAS) and Flynn-Wall-Ozawa (FWO) methods, and the order of reaction and pre-exponential factor of the selected samples was determined by the master plots method. The results of this study confirmed the feasibility of the co-combustion of walnut shells with coal under the oxy-fuel atmosphere and provided certain theoretical guidance to realize the operation of existing boilers in the oxy-fuel atmosphere.

Preparation of K-N co-doped commercial cylindrical carbon via the coal partial steam gasification for CO2 adsorption

The formed activated carbon is a promosing carbon based absorbent for CO2 adsorption in fossil energy industrial process. In this paper, the preparation method of commercial formed activated carbon and the partial steam gasification of coal via the addition of K2CO3 and melamine were combined to prepare cylindrical activated carbon with high abrasive resistance and well-developed pore structure. The CO2 adsorption capacity and mechanism of the prepared carbons were also explored. The results showed that the steam gasification reactivity of coal was enhanced by the addition of K2CO3 and melamine. The prepared cylindrical carbons had the abrasive resistance higher than 95% and their specific surface area reached 1451 m2/g after K was added to coal. Nearly 70% of microporous proportion was obtained for the cylindrial carbons from the N doped and K-N co-doped coals as 1.3 times as that from undoped carbon. Both the CO2 chemisorption and physical adsorption were improved by the K/N doping. It was concluded that the N species content and narrow micropore volume (<1 nm) showed the more important role on CO2 total and physical adsorption capacity respectively. Good cyclic stability of CO2 adsorption was also observed for the doped cylindrical carbons.

Effect of microwave pretreatment on oxidization behaviors of bituminous coal: Experimental measurement and quantum chemistry calculation

The poor heat conduction and mass transfer of coal seam causes unsatisfying performance of gas production for in situ combustion, while microwave pretreatment is a promising technology to solve this problem. In this work, microwave heating is adopted as pretreatment method to prepare coal samples at different microwave time. The low temperature oxidization and high temperature combustion behaviors of raw coal and modified coal samples were studied with programmed temperature rising method. The functional group content in coal samples were measured with Fourier transform infrared spectrometer, while the relationship between microstructure and reactivity was studied with quantum chemistry calculation. As microwave heating time extends from 0 s to 180 s, the crossing point temperature decreases, while the combustion reaction rate increases. As microwave time prolongs from 180 s to 240 s, the crossing point temperature becomes larger, while the combustion reaction rate becomes smaller. As microwave time increases from 0 s to 240 s, hydroxyl content and carbonyl content in coal samples reduce while ether content rises. The reduction of hydroxyl and increase of ether result in an enhancement of oxidization reactivity. The decrease of carbonyl is unfavorable for oxidization reactivity. Therefore, the effect of microwave heating on coal reactivity has two sides. This explains why the microwave pretreatment time has a non-monotonic effect on the coal reactivity in both low temperature and high temperature range.