An experimental and modeling study of softening coal pyrolysis

Oh, Myongsook; Peters, William A.; Howard, Jack B.

doi:10.1002/aic.690350509

Cited by 124 publications

(106 citation statements)

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“…This is related to the low volatiles content, the low local permeability and longer duration of the plastic phase of these coals (Gavalas, 1982;Oh, 1985;Perera et al, 2011). This shows that secondary reactions are difficult to prevent in TG experimental equipment.…”

Section: Effect Of Pyrolysis Atmosphere By Tgamentioning

confidence: 99%

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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Section: Effect Of Pyrolysis Atmosphere By Tgamentioning

confidence: 99%

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 transformation of coal to coke involves chemical reaction, mass transfer and phase separation, which produces many bubbles in coke. [1][2][3][4] Figure 1 shows the chemical and transport rate processes contributing to volatiles evolution during pyrolysis of softened coal particles. The pyrolysis of coal produces gas, metaplast and char.…”

Section: Introductionmentioning

confidence: 99%

“…When the pressure is released to atmospheric Chemical and transport rate processes contributing to volatiles evolution during pyrolysis of a softened coal particle. 4) level, the dissolved gas molecules form nucleus of bubble, which is super saturated state. One of the nuclei is expanded by two driving forces: (1) pressure difference between bubble pressure and atmosphere, and (2) mass transfer of dissolved gas into the bubble.…”

Section: Introductionmentioning

confidence: 99%

A Simplified Bubble Nucleation, Growth and Coalescence Model for Coke Production Process

Taki

Hayashizaki

Fukada³

2014

ISIJ Int.

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Coke production process, which involves gas generation, cross-linking, gas foaming as well as solidification phenomena, is extremely complex and is difficult to model them without simplification. In this study, a simple phenomenological model was developed based on a gas foaming simulation model of polymer foaming, which enabled us to simulate the number density of bubbles and their distributed size. The model was extended to account their kinetics of bubble nucleation, growth and coalescence in nonisothermal chemical reactions of gas generation and cross-linking. The bubbles size and morphology obtained from the numerical simulation of two different coals agreed with the pictures of the experiment qualitatively. Five different coals were investigated to understand the relationship between the kinetic and final morphology of coke.

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“…Thus, several investigators [Unger and Suuberg, 1984;Oh et al, 1989;Solomon et al, 1990] have studied the molecular weight distribution of coal tars released in rapid pyrolysis and noted its strong dependence on pyrolysis conditions (temperature, pressure, effect of different reactors and pyrolysis environment) and coal rank. There are relatively few data on the characterization of "primary" tars.…”

Section: A2 General Nature Of Coal Tarsmentioning

confidence: 99%

“…In fact, there is a concern that using THF as solvent results in a shift of the molecular weight to unrealistically high values. Oh et al [1989] obtained a molecular weight distribution between 150 and 1500 daltons for a Pittsburgh bituminous tar using pyridine as the solvent. The difference was attributed to association of tar species in the THF, since pyridine is generally a stronger solvent for coal, and presumably, its tar.…”

Section: A21 Molecular Weight Characterizationmentioning

confidence: 99%

Vapor pressures and heats of vaporization of primary coal tars

Suuberg¹

1992

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Executive SummaryThis project had as its main focus the determination of vapor pressures of coal pyrolysis tars. It involved performing measurements of these vapor pressures and from them, developing vapor pressure correlations suitable for use in advanced pyrolysis models (those models which explicitly account for mass transport limitations).This report is divided into five main chapters. Each chapter is a relatively "stand-alone" section. Chapter A reviews the general nature of coal tars and gives a summary of existing vapor pressure correlations for coal tars and model compounds. It is shown that the heterogeneous nature and the complexity of coal tars have made it unrealistic to apply detailed vapor pressure correlations which take into account the variation in the chemical structure of the tars. The significant product of this study is a much improved understanding of the volatility and thermal behavior of coal tars. The volatility was studied by vacuum sublimation and Knudsen effusion experiments. The volatility behavior is considerably more complicated than had been earlier believed.The tars evaporate in a "distillation-like" fashion. More volatile species are lost earlier in the process, leaving behind a progressively less volatile residue. The results suggest that there are three very different classes of compounds, and therefore, at least three different vapor pressure behaviors. The first corresponds to compounds of high molecular weight and significant alkyl character, the second to compounds with significant hydroxyl group content and medium molecular weight, and the third to medium molecular weight aromatic compounds without hydroxyl groups. Hydrogen bonding plays a major role in the determining the tar volatility. vi There has been concern in pyrolysis modeling about how closely Raoult's law is followed in coal tar. It appears from our results that the assumption of ideal mixture behavior could be acceptable for rough models of pyrolysis despite the possibility of strong specific interactions between certain functional groups.The results from the current work show that measuring the vapor pressures of complicated and thermally unstable mixtures is possible at low temperatures. There has also been some concern about condensation-type reactions influencing the results of vapor

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An experimental and modeling study of softening coal pyrolysis

Cited by 124 publications

References 39 publications

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

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

A Simplified Bubble Nucleation, Growth and Coalescence Model for Coke Production Process

Vapor pressures and heats of vaporization of primary coal tars

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