Effects of steam and CO2 on the characteristics of chars during devolatilization in oxy-steam combustion process

Xu, Jun; Su, Sheng; Sun, Zhaolin; Qing, Mengxia; Xiong, Zhe; Wang, Lele; Jiang, Long

doi:10.1016/j.apenergy.2016.08.121

Cited by 104 publications

(70 citation statements)

References 46 publications

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“…Raman spectroscopy is one of the most valuable methods to characterize the carbon microcrystalline structure of carbonaceous materials. Actually, the indicator of carbon microcrystalline structure for graphite materials, calcined carbon materials, and non‐carbonized carbon materials exhibit a variation according to the literature reports . Briefly, I G /I D is the common indictor for graphite materials.…”

Section: Resultsmentioning

confidence: 99%

“…Raman spectrum combined with curve‐fitting method was used to determine the carbon microcrystalline structure of MLP and its liquid‐phase carbonization products. Curve‐fitted standards were according to the literature, and presented in Table 3. The Raman spectrum and curve‐fitted spectrum of liquid‐phase carbonization products are shown in Figure .…”

Section: Resultsmentioning

confidence: 99%

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Thermal Conversion Behavior of Medium–Low–Temperature Coal Tar Pitch During Liquid–Phase Carbonization Process

Zhu

Zhao

et al. 2019

ChemistrySelect

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Medium–low temperature coal tar pitch (MLP) is a type of aromatic carbonaceous material obtained by the low temperature distillation of low rank coal, and is considered as a desirable raw material for the production of artificial carbon/graphite material. The thermal conversion behaviors of MLP during the liquid‐phase carbonization process were analyzed in detail in this study. Further, the changes of molecular structure and carbon microcrystalline structure of MLP and liquid‐phase carbonization products derived from it were quantitatively investigated by optical microscopy, fourier transform infrared spectroscopy, Raman spectroscopy, X‐ray diffraction, and curve‐fitting method. Results showed that both branched chain and the contents of C=O functional groups in the MLP played a key role in the reaction reactivity. Moreover, temperature of 450 °C was found to be a rapid changing temperature point on the enhancement of thermal conversion of MLP. The stacking height (Lc), parallel layers (N), average number of aromatic rings in each layer (n), ratio of ‘impurity’ structure (RI), ratio of amorphous carbon structure (RAC), ratio of graphite carbon structure (RGC), and ratio of defects graphite carbon structure (RDGC) exhibited a significant change with the improvement of liquid‐phase carbonization temperature.

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Section: Resultsmentioning

confidence: 99%

Section: Resultsmentioning

confidence: 99%

Thermal Conversion Behavior of Medium–Low–Temperature Coal Tar Pitch During Liquid–Phase Carbonization Process

Zhu

Zhao

et al. 2019

ChemistrySelect

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“…This can be explained by the reactive effects of the atmosphere on some of the volatile species which are released and the development of porous structure (Yin & Yan, 2016). Also, the high temperature (above 600 °C) favors the occurrence of the CO 2 -gasification reaction (Su et al, 2015;Valdés et al, 2016;Xu et al, 2016); which provided a slightly higher reaction rate when the coals were pyrolyzed under a CO 2 -atmosphere compared to N 2 (see Figure 4c and d).…”

Section: Effect Of Pyrolysis Atmosphere By Tgamentioning

confidence: 99%

“…This is consistent with the results reported by A.G. Borrego, Garavaglia, & Kalkreuth (2009), who concluded that CO 2 promotes cross-linking reactions and the formation of more pore volume. gasification reactions occurred (Bu et al, 2016;Xu et al, 2016). Gasification is likely responsible for the variation of surface area in these samples (see Figure 6a).…”

Section: Valdés Betancur López Gómez and Chejnementioning

confidence: 99%

“…To explain the changes that occur during the coal devolatilization, regardless of reaction atmosphere, it is necessary to understand the structure of the coal and char (Xu et al, 2016). It is also important to note that the chars are more sensitive to intraparticle processes such as thermoplasticity, crosslinking, swelling, and fragmentation, among others, hindering their prediction (Khan & Jenkins, 1985;Speight, 2013).…”

Section: Introductionmentioning

confidence: 99%

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Effects of pyrolysis atmosphere on the porous structure and reactivity of chars from middle and high rank coals

Valdés¹,

Guerrero²,

López³

et al. 2018

Ing. Inv.

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The influence of a CO 2 or N 2 -based atmosphere on the porous structure and microstructure of the chars obtained from the nonisothermal slow devolatilization (10 °C/min), from room temperature to 900 °C, of two coals of different rank (Semi-Anthracite (SA) and High Volatile Bituminous type C (HVBC)) and different particle size distribution was studied. Physicochemical characterization (ultimate and proximate analysis), structural and morphological characterization by Raman spectroscopy, FE-SEM, BET surface area, and volume and diameter microporous by CO 2 adsorption measurements were carried out for all the chars. It was found that the kinetic parameters, the physicochemical properties, and reactivity of the chars are different, depending on the pyrolysis atmosphere. It was also determined that for the char from SA coal with particle size greater than 0.7 mm, the BET surface area increases when the atmosphere is enriched with CO 2 . This effect appears to be promoted by the interaction of different processes such as intraparticle side reactions (softening, nucleation and coalescence of bubbles, crosslinking, among others), differences in the thermal diffusivity of N 2 and CO 2 , and the reactive effects of the latter. Additionally, tests of oxidative reactivity of chars showed that the char formed in a CO 2 atmosphere is more reactive than that formed in N 2 . With the results of Raman analysis and kinetic parameters quantified, it was concluded that the reaction atmosphere determined the degree of ordering achieved by the char structure and that the thermodiffusive properties of the reaction atmosphere promoted structural differences in the char even at low heating rates.Keywords: Slow pyrolysis, Pore size distribution, large coal particles, Oxy-combustion, reactivity. RESUMENSe estudió la influencia de una atmósfera basada en CO 2 o N 2 sobre la estructura porosa y la microestructura de carbonizados de carbón obtenidos de la pirólisis lenta no isotérmica desde temperatura ambiente hasta 900 °C de dos carbones de diferente rango (Semi-Antracita (SA) y Bituminosos Alto en Volátiles tipo C (BAVC)), y de diferentes distribuciones de tamaño de partícula. Para todos los carbonizados se realizó la caracterización fisicoquímica (Análisis ultimo y próximo), la caracterización morfológica y estructural por combinación de técnicas como espectroscopia Rama, Microscopia electrónica de barrido por emisión de campo (FE-SEM), área superficial (BET -Brunauer-Emmett-Teller) y volumen y diámetro de microporos por mediciones de adsorción en CO 2 (Horvath-Kawazoe (HK) method). Se encontró que los parámetros cinéticos, las propiedades fisicoquímicas y la reactividad de los carbonizados de carbón son diferentes dependiendo de la atmósfera de pirólisis. También se determinó que para el carbonizado de carbón de SA, con un tamaño de partícula mayor de 0,7 mm, la superficie BET aumenta cuando la atmósfera se enriquece en CO 2 . Este efecto parece ser promovido por la interacción de diferentes procesos como las reacciones secund...

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Investigation of combustion reactivity and NO emission characteristics of chars obtained from the devolatilization of raw and partially dried lignite

et al. 2019

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In an attempt to achieve the clean and efficient utilization of lignite, drying pre‐treatment was performed in this study before lignite combustion. The combustion reactivity and NO emission characteristics of the partially dried lignite samples in the char combustion stage were investigated by means of TG and isothermal combustion tests, and the reactivity could be summarized as the following order: L1>L0.5>raw>L3>LT>L5 (chars obtained from the devolatilization of the raw and partially dried coals at 378 K for 0.5, 1, 3, 5, and 120 minutes) and the NO conversion ratio of L1 was the lowest. When the moisture content in the coal particles was relatively high (19.68%‐35.84%), the drying treatment could increase the combustion reactivity and inhibit NO emission in the char combustion stage; When the moisture content was within a relatively low range (0.17%‐19.68%), the moisture removal had negative effects on the reactivity and NO emission in the char combustion stage. The surface behaviour and microstructure of the raw coal char and chars derived from the partially dried coals were clarified by temperature programmed desorption/reduction (TPD/TPR) and Raman spectroscopy. The results illustrated that L1 derived from Lc1 (19.68%) was the most reactive sample with the largest amount of C(O) on the particle surface. There were also more reactive aromatic structures in L1 than other samples. Compared with direct combustion or excessive drying treatment, lignite should be dried to a certain degree (19.68%) for optimized lignite combustion.

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Effects of steam and CO2 on the characteristics of chars during devolatilization in oxy-steam combustion process

Cited by 104 publications

References 46 publications

Thermal Conversion Behavior of Medium–Low–Temperature Coal Tar Pitch During Liquid–Phase Carbonization Process

Thermal Conversion Behavior of Medium–Low–Temperature Coal Tar Pitch During Liquid–Phase Carbonization Process

Effects of pyrolysis atmosphere on the porous structure and reactivity of chars from middle and high rank coals

Investigation of combustion reactivity and NO emission characteristics of chars obtained from the devolatilization of raw and partially dried lignite

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