Relationships between structural features and reactivities of coal-chars prepared in CO2 and H2O atmospheres

Qing, Mengxia; Xiang, Jun; Xu, Jun; Sun, Zhaolin; Gao, Jian; Xu, Kai; Su, Sheng; Wang, Lele; Hu, Xun; Xiang, Jun

doi:10.1016/j.fuel.2019.116087

Cited by 31 publications

(11 citation statements)

References 38 publications

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“…The effect of CO 2 and H 2 O in an impure pyrolysis atmosphere on char structure and properties have been investigated recent years. ,,− In the impure CO 2 /H 2 O pyrolysis stage, both CO 2 and H 2 O gasification reactions may affect char structure and char reactivity. It is reported that char–H 2 O and char–CO 2 follow different reaction pathways, resulting in different char structure and properties .…”

Section: Introductionmentioning

confidence: 99%

“…In the view of a physical structure, H 2 O and CO 2 greatly decrease the char yield and have influence on char density . In the view of a chemical structure, compared to pyrolysis in N 2 atmosphere, H 2 O and CO 2 would also accelerate the aromatic ring condensation and result in additional oxygen-containing functional groups in char. , Particularly, high aromatic and structural order, low hydrogen, and aliphatic functional groups have been found in char generated from a CO 2 atmosphere, which are responsible for the low char reactivity . In the view of a chemical reaction, we have investigated it in our previous studies and found that char–CO 2 and char–H 2 O reactions compete for carbon active sites but follow different mechanisms. ,,, Different reaction pathways may result in different char structure and properties.…”

Section: Introductionmentioning

confidence: 99%

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Effect of CO₂ and H₂O on Char Properties. Part 1: Pyrolysis Char Structure and Reactivity

et al. 2020

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CO2 and H2O have great influence on pyrolysis char structure and its reactivity. Particularly, the effect of CO2 and H2O on pyrolysis char kinetic parameters are unrevealed. Char structure and the corresponding combustion kinetic parameters play a very important role for designing and modeling oxy-fuel combustion. This work focuses on the effects of CO2 and H2O on pyrolysis gas, coal burnout degree, char structure, and corresponding combustion kinetic parameters. The volatile compositions were measured by gas chromatography. Coal burnout degree, char structure, and reactivity were measured by a drop tube furnace, Raman spectroscopy, scanning electron microscopy and thermogravimetric anaylsis, respectively. Our results indicate that a H2O-containing atmosphere results in decreasing char yield, developed and disordered char structure, and high reaction rate constant. All of these features are more obvious in a H2O-containing atmosphere than in a CO2-containing atmosphere. Moreover, a H2O-containing atmosphere reduces char–O2 reaction rate, as well as coal burnout degree in a low oxygen atmosphere at early and middle combustion stages (i.e., burnout degree <80%), but increases at the end stage of combustion (i.e., burnout degree >80%). Our investigation will give basic kinetic parameters and features of char properties obtained in CO2 and H2O atmospheres.

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Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Effect of CO₂ and H₂O on Char Properties. Part 1: Pyrolysis Char Structure and Reactivity

et al. 2020

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“…After the reaction, I D : I G and I D : I Gr decreased significantly, and the S R band disappeared. The reason for the phenomenon is that, during the N-sorption reaction, the large aromatic ring disordered carbon represented by the D band is more active and easier to participate in the reaction; it can be broken into smaller aromatic ring structures . Some graphited carbon structures containing SP 2 chemical bonds converted into SP 3 chemical bonds as temperature increased .…”

Section: Results and Discussionmentioning

confidence: 99%

Using Coal Coke for N-Sorption with an Al-based Nitrogen Carrier during Chemical Looping Ammonia Generation

Feng

Zhang

et al. 2020

Energy Fuels

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Chemical looping ammonia generation (CLAG) is thought to be another method for clean utilization of fossil fuels, because fossil fuels can be thoroughly converted into chemical material, CO, and noncarbon fuel, NH 3 . Intensive studies have been conducted to increase the N-sorption/desorption performances by modifying the N-carrier with single structured carbons (graphite or carbon-black). However, what the N-sorption performances or kinetics of the N-carrier with the real coal coke (with complex structure) are is still not clear, the determination of which will be a big breakthrough for the chemical looping ammonia generation process with coal. In this paper, the N-sorption performance of Al-based nitrogen carrier (γ-Al 2 O 3 ) mixing with coal coke was investigated in detail. Results showed that the reactivity of different coal cokes increases in the order of anthracite, lignite, and bitumite due to the increase of disordered carbon content. In order to further increase the N-sorption performance of the N-carrier, the bitumite coke was prepared with the different pyrolysis conditions, including different heating rates, atmospheres, and temperatures, and it was found that the bitumite coke prepared under 700 °C with heating rate of 10 °C/min in CO 2 was suitable for N-sorption reaction.

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“…In addition, it is generally accepted that the microcrystalline structure plays an important role in the whole reaction process. Generally, the physicochemical structure was significantly affected by pyrolysis conditions, which have long been recognized and studied by many investigators. , Obviously, it is of great significance to explore the char structure under different pyrolysis conditions, which is considered to be an essential factor affecting the gasification reactivity. Meanwhile, the heterogeneous gasification reactivity of coal char is of great importance to design and optimize the industrial systems and whole process.…”

Section: Introductionmentioning

confidence: 99%

Correlation between Char Gasification Characteristics at Different Stages and Microstructure of Char by Combining X-ray Diffraction and Raman Spectroscopy

Liu

Bai

et al. 2020

Energy Fuels

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A comprehensive and reliable correlation between the gasification characteristics and char structure will be helpful to propose a tentative reaction pathway. The rapid-pyrolysis char samples were prepared with a novel high-temperature vertical quenching furnace at high temperatures from 900 to 1500 °C with different residence times. The physicochemical structure and gasification reactivity of chars were systematically analyzed. Results demonstrated that the chemical structures were slightly influenced by the residence time at lower pyrolysis temperatures (900 and 1000 °C), while the graphitization degree was increased by the prolongation of the residence time at 1100 °C. With the increase of the pyrolysis temperature, L c,a/d 002,a and I G/I all monotonously increased, while I D1/I G and I D3/I G monotonously decreased. Additionally, the specific surface area was not considered in the correlations because it was not the main factor affecting the reactivity. The isothermal and non-isothermal gasification reactivities of coal char gradually decreased with the increase of the pyrolysis temperature to some extent. However, I D1/I G could act as a rough indicator for evaluating the characteristic temperatures of chars. It was also revealed that the reaction rate was controlled by various chemical structural factors at different stages. Hence, the correlations based on the chemical structure parameters by combining X-ray diffraction and Raman spectroscopy showed credibility on the prediction of char characteristic temperatures as the critical factor varied with the gasification stage.

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Relationships between structural features and reactivities of coal-chars prepared in CO2 and H2O atmospheres

Cited by 31 publications

References 38 publications

Effect of CO₂ and H₂O on Char Properties. Part 1: Pyrolysis Char Structure and Reactivity

Effect of CO₂ and H₂O on Char Properties. Part 1: Pyrolysis Char Structure and Reactivity

Using Coal Coke for N-Sorption with an Al-based Nitrogen Carrier during Chemical Looping Ammonia Generation

Correlation between Char Gasification Characteristics at Different Stages and Microstructure of Char by Combining X-ray Diffraction and Raman Spectroscopy

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Relationships between structural features and reactivities of coal-chars prepared in CO2 and H2O atmospheres

Cited by 31 publications

References 38 publications

Effect of CO2 and H2O on Char Properties. Part 1: Pyrolysis Char Structure and Reactivity

Effect of CO2 and H2O on Char Properties. Part 1: Pyrolysis Char Structure and Reactivity

Using Coal Coke for N-Sorption with an Al-based Nitrogen Carrier during Chemical Looping Ammonia Generation

Correlation between Char Gasification Characteristics at Different Stages and Microstructure of Char by Combining X-ray Diffraction and Raman Spectroscopy

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Effect of CO₂ and H₂O on Char Properties. Part 1: Pyrolysis Char Structure and Reactivity

Effect of CO₂ and H₂O on Char Properties. Part 1: Pyrolysis Char Structure and Reactivity