Xiumin Jiang

Shanghai Jiao Tong University, Shanghai, Shanghai Shi, China

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Publications (71)190.71 Total impact

  • Xiangxin Han, Qingqing Liu, Xiumin Jiang
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    ABSTRACT: The heat transfer occurring within oil shale particle is a dominant fundamental cause affecting shale oil yield and energy consumption of industrial oil shale retorts. For exploring this property, the shape of crushed Gonglangtou oil shale particle is first investigated, showing very obvious platy structure especially in the equivalent diameter range of 4-25 mm. So, it is more appropriate to describe oil shale particle with thin rectangle model. And then, a mathematical heat transfer model is developed to analyze the thermal behavior within oil shale particle in the process of the retorting, incorporating the pyrolytic heat as an internal heat sink. Previous experimental data are applied to validate this model. Furthermore, the central temperature history and heating time of oil shale particles with different sizes are predicted at various heating rates using this heat transfer model, showing that platy structure characteristic offers an important role for the heat transfer process and even for the particle fragmentation. In order to improve retorting efficiency and reduce energy loss, it is recommended at last that the residence time of oil shale in the retorting reactors should fully consider the heating time of oil shale particle.
    International Journal of Heat and Mass Transfer 05/2015; 84:578-583. DOI:10.1016/j.ijheatmasstransfer.2015.01.058 · 2.52 Impact Factor
  • Jiaxun Liu, Xiumin Jiang, Jun Shen, Hai Zhang
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    ABSTRACT: With more stringent regulations being implemented, elucidating the formation mechanisms of nitrogen-containing species during the initial pyrolysis step becomes important for developing new NOx control strategies. However, there is a lack of agreement on the origins of NOx precursors during coal pyrolysis, in spite of extensive investigations. Hence, it is important to achieve a more precise knowledge of the formation mechanisms of nitrogen-contain species during coal pyrolysis. In this paper, pyrolysis experiments of superfine pulverized coal were performed in a fixed bed at low heating rates. The influences of temperature, coal type, particle size and atmosphere on the NH3 and NO evolution were discussed. There is a central theme to develop knowledge of the relationship between particle sizes and evolving behaviors of nitrogen-containing species. Furthermore, the catalytic role of inherent minerals in coal was proved to be effective on the partitioning of nitrogen during coal pyrolysis. In addition, the conversion pathways of heteroaromatic nitrogen structures in coal/char during pyrolysis were recognized through the X-ray photoelectron spectroscopy (XPS) analysis. Large quantities of pyridinic and quanternary nitrogen functionalities were formed during the thermal degradation. Finally, the relationships among the nitrogen-containing gaseous species during coal pyrolysis were discussed. In brief, a comprehensive picture of the volatile-nitrogen partitioning during coal pyrolysis is obtained in this work, involving the formation mechanisms of the main nitrogen-containing gaseous products such as NH3, HCN, NO, NO2 and N2O.
    Energy Conversion and Management 04/2015; 94. DOI:10.1016/j.enconman.2014.12.096 · 3.59 Impact Factor
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    ABSTRACT: Fluidization-suspension combustion technology is an effective method to utilize coal water slurry (CWS) as a fuel in industrial boilers. The evolution of surface morphology and pore structure of CWS spheres under fluidization-suspension combustion is studied. A bench-scale fluidized bed was used for combustion of CWS spheres, with bed temperature of 850°C, fluidization number of 4 and bed height of 90 mm. The samples after 15 s, 30 s and 45 s of combustion were taken out from the bed for scanning electron microscope (SEM) and N2 adsorption tests. The combustion mechanism of CWS spheres in fluidization-suspension combustion state is discussed. Results have shown that: after 15 s, CWS spheres burst due to volatile release, and some particles fragmented with great number of pores produced. So the specific surface area and volume of pores increased rapidly; after 30 s, combustion occurred mainly at the exterior surface of CWS spheres and appeared as layer by layer inward combustion. This was confirmed by that the specific surface area and volume did not change; after 45 s, as the combustion proceeded, flame front entered the interior surface through pores, and burnt interior framework to make pores collapse. So the specific surface area and volume of pores decreased rapidly. In the whole process of combustion, fractal dimension increased firstly and then decreased, which showed that the pore structure had experienced a process from complicated to simple.
    Energy & Fuels 04/2015; 29(5):150415123742008. DOI:10.1021/ef502923t · 2.73 Impact Factor
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    ABSTRACT: Recent research has shown that fly ash may catalyze the oxidation of elemental mercury and facilitate its removal. However, the nature of mercury-fly ash interaction is still unknown, and the mechanism of mercury retention in fly ash needs to be investigated more thoroughly. In this work, a fly ash from a coal-fired power plant is used to characterize the inorganic and organic constituents and then evaluate its mercury retention capacities. The as-received fly ash sample is mechanically sieved to obtain five size fractions. Their characteristics are examined by loss on ignition (LOI), scanning electron microscope (SEM), energy dispersive X-ray detector (EDX), X-ray diffraction (XRD), and Raman spectra. The results show that the unburned carbon (UBC) content and UBC structural ordering decrease with a decreasing particle size for the five ashes. The morphologies of different size fractions of as-received fly ash change from the glass microspheres to irregular shapes as the particle size increases, but there is no correlation between particle size and mineralogical compositions in each size fraction. The adsorption experimental studies show that the mercury-retention capacity of fly ash depends on the particle size, UBC, and the type of inorganic constituents. Mercury retention of the types of sp2 carbon is similar to that of sp3 carbon.
    Surface Review and Letters 04/2015; 22(02):1550018. DOI:10.1142/S0218625X15500183 · 0.37 Impact Factor
  • Jiaxun Liu, Xiumin Jiang, Jun Shen, Hai Zhang
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    ABSTRACT: Free radicals play an important part in coal utilization, such as carbonization, gasification, liquefaction and pyrolysis processes. The diagenesis of organic sediment, pyrolytic reactions during metamorphosis and radiolysis are the three possible geneses of stable free radicals in coal. The influences of different origins on the nature of free radicals and their subsequent behaviors during the coal utilization are of great interest. In this paper, three experimental studies of super-fine comminution, fixed-bed pyrolysis and in situ ultraviolet irradiation were adopted to investigate the behaviors of the paramagnetic centers in coal/char. The nature of different radical species in coal/char during the influential processes was focused through the deconvolution study of the electron paramagnetic resonance (EPR) spectra. Final results indicate that the comminution, pyrolysis and ultraviolet (UV) irradiation are all effective ways to initiate the free radicals. The super-fine comminution has noticeable influence on the aromatic hydrocarbon radicals. The UV irradiation can promote the formation of the σ-type oxygen-containing radicals in coal. Furthermore, the simple aromatic clusters and the σ-type oxygen-containing radicals are the most active types during thermal degradation of pulverized coal particles.
    Powder Technology 03/2015; 272. DOI:10.1016/j.powtec.2014.11.017 · 2.27 Impact Factor
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    ABSTRACT: In this study, combustion experiments of green algae granulations (Enteromorpha clathrata) (EN) were carried out in a bench-scale fluidized bed. The particle diameter was kept constant during the combustion process and combustion model was described as a shrinking core model. Model was divided into water ball, volatile-matter ball, and carbon ball. Ash ball radius was assumed to be the same during the combustion and carbon ball was burned layer by layer. Simulation of single-particle combustion process consists of process of water evaporation, release of volatile matters and combustion, and the process of char combustion. Finally, a mathematical model was established for the combustion of EN single particle in the fluidized bed, validated by the experiment data. The model can be applied for the design of the combustion devices for the combustion of seaweed particles with high content of ash.
    Journal of Renewable and Sustainable Energy 03/2015; 7(2):023137. DOI:10.1063/1.4919357 · 0.93 Impact Factor
  • Hai Zhang, Jiaxun Liu, Jun Shen, Xiumin Jiang
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    ABSTRACT: Using pyridine nitrogen as representative of nitrogen-containing char model, detailed theoretical calculations based on DFT (density functional theory) and conventional TST (transition state theory) are carried out to investigate the thermodynamics and kinetics of the heterogeneous interaction between NO (nitric oxide) and char(N) (char bound nitrogen) during coal combustion. Focus is directed on NO chemisorption of direct nitrogen–nitrogen interaction and N2 desorption from medium chemisorbed surface. It is suggested that side-on chemisorption is a low barrier (2.3 kJ/mol) and high exothermic (178.5 kJ/mol) step, while N-down chemisorption is a high barrier (105.2 kJ/mol) and moderate exothermic (64.4 kJ/mol) step. Worth noticing is that NO chemisorption on char(N) surface is different from that on char surface, largely because there is no unpaired σ electrons located at N atom. After chemisorption, four stepwise reactions with the highest energy barrier of 266.3 kJ/mol are found to produce separated N2. The overall NO reduction rate is expressed as . Reaction rate of rate-limiting step involved in N2 desorption is 2 × 100 s−1 at 1000 K, indicating it can tempestuously take place above 1000 K. The calculated results lend credit to previous experimental phenomenon.
    Energy 02/2015; 82. DOI:10.1016/j.energy.2015.01.040 · 4.16 Impact Factor
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    ABSTRACT: Shale char organic matter was obtained by demineralization of shale char through HCl and HF treatment. XRD technique was applied to determine the minerals in shale char and its ashes from different-temperature combustions. The effect of mineral matrix in shale char on the pyrolysis and combustion of organic matter was explored by the TG-FTIR test to shale char and its organic matter. Minerals in shale char ash changed both in amount and variety during combustion. Both the pyrolysis and combustion of shale char and its organic matter can be divided into two stages. Without confinement of mineral matrix after demineralization, the emission of gaseous products from the pyrolysis of shale char organic matter starts earlier than that of shale char pyrolysis. The effect of inorganic minerals on the oxidation of organic matter displays in two aspects. For one, the earth metal cations contained in inorganic minerals may promote the oxidation of organic matter. Secondly, the presence of inorganic matrix enhances the porosity of shale char. New organic sulfur formed during oil shale retorting is confined by inorganic matrix during combustion. After demineralization, this new organic sulfur can decompose and be released intensively at low temperature.
    Fuel 01/2015; 139:502-510. DOI:10.1016/j.fuel.2014.09.021 · 3.41 Impact Factor
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    ABSTRACT: An experimental investigation of process parameters design by superfine pulverized coal reburning on NOx reduction is carried out in a one-dimensional bench-scale combustion system. Reburning effectiveness for initial levels ranging from 600 to 650 ppm is evaluated. It is found that for Shenhua bituminous coal, NOx reduction performance of superfine pulverized coal owns its unique advantage, 50% higher than conventional particle size. Medium reburning fuel fraction (RF20 similar to RF25) and low oxygen concentration are recommended to be ensured in this experiment. The yield of HCN and CH4 along the furnace axis does not seem to be decisive on the effect of particle size, but is closely related to the effect of reburning fuel fraction. Both exhaust and in-flame measurements are reported in this paper to provide valuable experimental data for practical engineering applications.
    Energy Conversion and Management 01/2015; 89:825-832. DOI:10.1016/j.enconman.2014.10.059 · 3.59 Impact Factor
  • Jiaxun Liu, Xiumin Jiang, Jun Shen, Hai Zhang
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    ABSTRACT: The superfine pulverized coal has a greater potential for reducing NO, emissions in the staged and oxyfuel combustion technologies. The compositions and evolving processes of the volatile species during coal pyrolysis are important for understanding the pyrolysis mechanisms and pollution control strategies. In spite of numerous works focused on the description of coal thermal decomposition, the mechanism of formation reactions for particular gaseous products of coal pyrolysis like CH4 remains unclear. In this paper, the mechanisms of CH4 formation during superfine pulverized coal pyrolysis in N-2 and CO2 atmospheres are investigated under non-isothermal conditions in a fixed-bed reactor. The effects of coal type, particle size and temperature on the evolved CH4 and its formation mechanisms are analyzed. In addition, the total overlapped CH4 evolution curves are resolved applying the deconvolution method through numerical analysis. Five constituent reaction complexes induced by different functional groups are recognized. Five CH4 precursors involving in the CH4 revolution during coal pyrolysis are confirmed, applying the solid-state C-13 NMR analysis. Different CH4 formation mechanisms initiated from the thermal decomposition of the functionalities are concluded, with the products competing for the donatable hydrogen for stabilization.
    Energy Conversion and Management 11/2014; 87:1027-1038. DOI:10.1016/j.enconman.2014.07.053 · 3.59 Impact Factor
  • Jiaxun Liu, Xiumin Jiang, Jun Shen, Hai Zhang
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    ABSTRACT: The oxygen-containing gases released during coal pyrolysis comprise more than a half of the devolatilization products, especially the noncondensible species. The mechanisms of CO formation reactions remain problematic, particularly the identity of the functional group precursors for low-temperature CO. In this paper, pyrolysis experiments of superfine pulverized coal were carried out in the N-2 and CO2 atmosphere under non-isothermal conditions, applying a fixed-bed reactor. The CO formation mechanisms were investigated from a functional-group standpoint. The deconvolution method via numerical analysis was adopted to resolve the multi-component envelop profiles of CO evolution. Five constituent reaction complexes induced by different oxygenated groups and reactions are recognized, combining the X-ray photoelectron spectroscopy (XPS) analysis. In addition, the effects of coal type, particle size, pyrolysis atmosphere and heating rate on the CO evolution were analyzed. Finally, different CO formation mechanisms initiated from the primary decomposition of distinctive oxygenated functionalities, secondary pyrolysis reactions of tars, and gasification reactions of chars are summarized.
    Energy Conversion and Management 11/2014; 87:1039-1049. DOI:10.1016/j.enconman.2014.07.055 · 3.59 Impact Factor
  • Xiangxin Han, Mengting Niu, Xiumin Jiang
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    ABSTRACT: Retorting oil shale can produce shale oil, semicoke, water and fuel gases. Shale oil can be used as an important substitute oil supply, and semicoke and fuel gases may be burnt as fuels. An interesting issue is about how to utilize and distribute the heat from the combustion of semicoke and fuel gases, not only providing enough heat for retorting oil shale, but also producing more available energy products and less energy losses. Based on a combined system of oil shale FB (fluidized bed) retort and semicoke CFB (circulating fluidized bed) boiler, a comprehensive process flow was developed and an optimization calculation was conducted to achieve mass and energy balances of the whole system. Simulation indicated that, burning semicoke and fuel gases from retorting Huadian oil shale at the retorting temperature of 490 °C could not only provide enough energy required for the endothermic oil shale drying and retorting processes, but also supply extra energy for power generation or heat supply. The sensitivity of various operating parameters on the performance of the process was also discussed to optimize the comprehensive utilization system of oil shale. This work provided a reference for developing the new comprehensive utilization technology of oil shale.
    Energy 09/2014; 74:788-794. DOI:10.1016/j.energy.2014.07.050 · 4.16 Impact Factor
  • Jiaxun Liu, Xiumin Jiang, Jun Shen, Hai Zhang
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    ABSTRACT: The CO2 control technologies have been studied extensively in recent years, among which the oxy-fuel combustion shows a vast number of advantages to be explored commercially in the near future. However, unexpected problems, such as bad combustion characteristics and serious slagging and depositing issues, show up with the replacement of N-2 by CO2. These inherent disadvantages in normal O-2/CO2 combustion can be restrained via combining the superfine pulverized coal and oxy-fuel combustion technology. The axial NO emission characteristics of this new technology were focused here. The effects of the oxidizer staging were also studied in detail. Results indicate that the axial NO emissions of the unstaged O-2/CO2 combustion basically showed "M" type of distributions along the furnace. The "M" type can be divided into the main homogeneous and heterogeneous reaction zones. The oxidizer-staged O-2/CO2 combustion can mitigate NO emissions effectively. Coals with smaller particle sizes and higher volatiles are more advantageous for eliminating NO in the staged O-2/CO2 combustion technology. The superfine pulverized coal used with certain low NO combustion technologies shows significant superiority in both combustion performance and NO abatement.
    Energy & Fuels 08/2014; 28(8):5497-5504. DOI:10.1021/ef5009924 · 2.73 Impact Factor
  • Hai Zhang, Xiumin Jiang, Jiaxun Liu, Jun Shen
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    ABSTRACT: Comprehensive theoretical calculations are carried out to investigate the nitric oxide (NO) heterogeneous reduction mechanism in the presence of hydroxyl ( OH) and carbonyl (>C=O) groups. Energetics (activation energy and thermochemistry data) and kinetics (thermal rate constant) for the proposed pathways are provided by density functional theory (DFT) and conventional transition state theory (TST), respectively. The role played by -OH and >C=O has been clarified. In the presence of -OH, four stepwise reactions with the highest energy barrier of 251.7 kJ/mol are found to produce new active sites. Subsequently, a number of elementary reactions with energy barrier below 116.1 kJ/mol take place to reduce NO. The role of >C=O is to yield NCO intermediate. The formation of NCO is highly exothermic with 709.4 kJ/mol, which contributes to the elimination of carbon dioxide (CO2) and nitrogen (N-2). The discovered mechanism is consistent with previous experimental observation that NO heterogeneous reduction is enhanced due to the presence of oxygen.
    Energy Conversion and Management 07/2014; 83:167–176. DOI:10.1016/j.enconman.2014.03.067 · 3.59 Impact Factor
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    ABSTRACT: This is the age of oil when many parts of the economy, particularly transportation, still rely heavily upon oil. The uncertainty in petroleum prices, its growing worldwide consumption and limited availability have motivated many countries rich in oil shale resources to investigate more efficient technologies to produce and use shale oil as an alternative to traditional petroleum. This review considers some aspects of oil shale based technologies. Among many differences in the flow and operational characteristics of several typical industrial oil shale retorting processes, one of the most important concerns how to treat semicoke and transfer the pyrolytic heat required for retorting oil shale. This will not only affect the yield and quality of shale oil, but also involves a series of serious issues related to energy and environment. Semicoke, one of the final products formed after retorting oil shale, is a potentially harmful solid waste often containing some toxic organic compounds and heavy metals, disposal of which can result in very great environmental contamination. However, the organic compounds remaining in semicoke lead to it having a potential heat of combustion, and thus semicoke may be considered for combustion utilization as a fuel. This paper reviews the fundamental characteristics and combustion utilization possibilities for semicoke that would allow treating and utilizing semicoke efficiently and in an environmentally friendly manner. Although properties of semicoke vary widely with both the retorting processes and their operational parameters, it generally contains significant amounts of inorganic minerals from the oil shale matrix, some organic compounds and lesser amounts of trace elements. Its leaching elutes have shown acceptable limit values at a landfill for non-hazardous waste and thus the leaching of heavy metals is not necessarily a problem. However the leaching of organic compounds may often exceed the limits for dissolved organic carbon. Thus, the incineration of semicoke will often be desirable both to ensure relatively low harm to the environment as well as efficient resource recycling for energy. Based on the current status and probable future development of oil shale industries, and the combustion characteristics of semicoke, two technical routes have been recommended for utilizing semicoke. These might also be regarded as references or benchmarks for evaluating the new development of oil shale retorting processes. One method involves an integrated utilization system for oil shale in which semicoke is actively treated and utilized in a circulating fluidized bed boiler for providing heat for both retorting the oil shale and for generating steam. The other option is to employ circulating fluidized bed technology to burn semicoke which has been previously produced and might still be a byproduct of some retorting technologies. With regard to both options, industrial circulating fluidized bed combustion results are discussed, in an effort to establish the feasibility of burning semicoke in a circulating fluidized bed boiler.
    Fuel 06/2014; 126:143–161. DOI:10.1016/j.fuel.2014.02.045 · 3.41 Impact Factor
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    ABSTRACT: Oil shale samples from Huadian were retorted in a stainless-steel cylindrical retort under argon atmosphere to determine retorting temperature effect on the product yield and characteristics of shale oil and non-condensable gases produced. Increasing temperature from 430 °C to 520 °C improved both oil and gas yields, but reduced the oil/gas yield ratio. Raising temperature increased nitrogen content in the derived shale oil and decreased the atomic H/C ratio and oxygen content, but had no significant effect on the sulfur content. It was also noticed that the boiling point of shale oil generated at 490 °C was lowest, and the shale oils obtained at 430 °C and 460 °C showed similar boiling point distributions. The produced shale oils had similar atomic H/C ratio as well as higher light oil content compared to crude oils produced in China, and could be classified as sweet and high-nitrogen oil in terms of the classification method of crude oil. The oil derived at 490 °C contained the lowest amount of saturates and the highest amount of aromatics, asphaltenes and non-hydrocarbons. C1–C4 hydrocarbon gas contents rose with increasing temperature. Higher ethene/ethane, propene/propane, butene/butane and alkene/alkane ratios obtained at higher temperature were linked to secondary cracking reactions.
    Fuel Processing Technology 05/2014; 121:9–15. DOI:10.1016/j.fuproc.2014.01.005 · 3.02 Impact Factor
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    Jiaxun Liu, Xiumin Jiang, Jun Shen, Hai Zhang
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    ABSTRACT: Superfine pulverized coal combustion is a new pulverized coal combustion technology with lots of advantages. A mechanochemical effect exists during the comminution process, which changes the chemical properties of coal significantly. Free radical concentrations and certain functional groups would increase with the decrease of particle sizes. In this paper, we combined electron paramagnetic resonance (EPR) and C-13 solid-state nuclear magnetic resonance (NMR) techniques to study the free radical characteristics of superfine pulverized coal thoroughly. The final results indicate that the EPR spectra of coal are the superimpositions of several lines induced by different paramagnetic centers, which can be fitted by 1 Gaussian and 3 Lorentzian lines. The influences of coal maturities and particle sizes on EPR parameters, such as g-values, linewidths, and spin concentrations, are analyzed in detail. It is shown that with the decrease of particle sizes, more free radicals are induced through bond cleavages. Mechanical forces initiate the accumulation of free radicals in the fractures and inner pore surfaces of coal. Furthermore, the influence of particle sizes on oxygen-containing radicals (i.e., Lorentzian 1 types) is the greatest. This work provides a primary picture of the occurrence modes and spatial distributions of free radicals in superfine pulverized coal. The findings will help form the basis and provide guidance for further studies on revealing the correlations between the free radical reaction pathways and NOx formation mechanisms.
    Advanced Powder Technology 05/2014; 25(3). DOI:10.1016/j.apt.2014.01.021 · 1.64 Impact Factor
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    ABSTRACT: To obtain a deep understanding of the pyrolysis mechanism of oil shale kerogen, critical organic intermediates were firstly prepared by heating Huadian oil shale up to the critical temperature point (∼350 °C), and then analyzed using Gas Chromatograph–Mass Spectrometer (GC–MS), Fourier Transform Infrared Spectrometer (FT-IR), Nuclear Magnetic Resonance Spectrometer (NMR) and X-ray Photoelectron Spectroscopy (XPS), etc. According to the results, there are about 84.3 aliphatic carbons per 100 carbons in the critical organic intermediates, less than that in the kerogen matrix studied previously, showing that the aliphatic carbons will decrease during thermal decomposition from kerogen to the critical organic intermediates. This might be mainly attributed to the breakup of aliphatic carbon chains and the resulting hydrocarbon gas emissions. Meanwhile, aromatic carbon structures are well retained in the critical organic intermediates, resulting in an increase in the aromaticity. In addition, the distributions of some heteroatoms (O, N and S) present in the critical organic intermediates were discussed as well. These results will be important for both the exploration of pyrolysis mechanism of kerogen and the improvement of quality and yield of shale oil.
    Fuel 04/2014; 121:109–116. DOI:10.1016/j.fuel.2013.12.046 · 3.41 Impact Factor
  • Hai Zhang, Xiumin Jiang, Jiaxun Liu, Jun Shen
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    ABSTRACT: New insights into the heterogeneous reduction reaction between NO and char-bound nitrogen [char(N)] were obtained by a combination of density functional theory (DFT) and conventional transition state theory (TST). A detailed description of the nature of NO chemisorption is reported based on the HOMO and LUMO, Mulliken atomic charges, and spin densities. It is suggested that, during chemisorption, char(N) contributes electrons to NO. The seven most stable structures (I–VII) resulting from NO chemisorption were identified, and the exothermicity was found to increase in the order III < V < IV < VI < VII< II < I. This finding is reasonable considering the fact that the HOMO of char(N) is predominantly reflected in the active C(2) atom and the LUMO of NO is mainly concentrated on the N(8) atom. Three stepwise reactions leading to N2 formation have been characterized with low energetic penalty acceptable for occurring at the practical heterogeneous combustion temperature. The highest energy penalty was calculated to be 270.794 kJ/mol. A kinetic similarity over the temperature range of 850–1000 K between the rate-limiting step and char gasification was found (10–3–100 compared to 10–4–10–1 s–1, respectively). By comparison with previous experiments, the calculated results were validated, and on the basis of these results, the reburning of superfine bituminous coal is recommended.
    Industrial & Engineering Chemistry Research 04/2014; 53(15):6307–6315. DOI:10.1021/ie403920j · 2.24 Impact Factor
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    ABSTRACT: Inorganic matter in coal significantly influences its chemical properties and potential utilizations. Electron paramagnetic resonance (EPR) characteristics can be affected by inorganic species, and various groups of paramagnetic centers behave differently after demineralization procedures. In this paper, EPR and the power saturation technique were applied to investigate thoroughly the free radical characteristics of acid-treated superfine pulverized coals. Systematic studies were conducted to explore the behaviors of different groups of paramagnetic centers in demineralized and pyrite-free coals. Focus was directed on comparisons of free radical characteristics of coal samples with different particle sizes, indicating that coals with higher maturities and larger particle sizes are much more easily saturated. Compared to raw coals, the acid-treated samples are more susceptible to saturation. Furthermore, the power saturation technique also served as a quantitative analysis method to study the line-broadening mechanism. This technique revealed that the components in coals with higher molecular weights contain more homogeneous components. Worth noticing is that the concentrations of free radicals residues in the acid-treated coals are determined by two competing mechanisms. The oxidation effects would increase the amounts of free radicals while the removal process of certain components in coals has decreasing effects. Multi-component spectra studies reflect that EPR spectra of acid-treated coals are superimposed by one Gaussian and three Lorentzian lines.
    Fuel 01/2014; 115:685-696. DOI:10.1016/j.fuel.2013.07.099 · 3.41 Impact Factor