Review of Carbonaceous Annealing Effects on O<sub>2</sub> and CO<sub>2</sub> Coal Reactivity

Holland, Troy; Fletcher, Thomas H.; Senneca, Osvalda

doi:10.1021/acs.energyfuels.9b02698

Cited by 6 publications

(6 citation statements)

References 64 publications

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“…The thermal deactivation (annealing) of chars has been known for decades. 25 Accordingly, the reactivity of the chars depends on their thermal history prior to the gasification. This dependence can be approximated by a change in the preexponential factor.…”

Section: Resultsmentioning

confidence: 99%

“…Accordingly, the reactivity of the chars depends on their thermal history prior to the gasification. This dependence can be approximated by a change in the preexponential factor. , Some annealing differences may develop during the heat up of the samples within the TGA at different heating programs. Besides, the annealing continues during the gasification as well, and hence, the difference in the temperature programs may affect the reactivity during the gasification as well.…”

Section: Resultsmentioning

confidence: 99%

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Empirical Kinetic Models for the CO₂ Gasification of Biomass Chars. Part 1. Gasification of Wood Chars and Forest Residue Chars

2021

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The gasification kinetics of charcoals and biomass chars is complicated by several factors, including chemical and physical inhomogeneities, the presence of mineral matter, and the irregular geometry of the pore structure. Even the theoretically deduced gasification models can only provide empirical or semiempirical descriptions. In this study, an empirical kinetic model from the earlier works of the authors was adapted for the CO2 gasification of biomass chars. It is based on a versatile polynomial approximation that helps to describe the dependence of the reaction rate on the progress of the conversion. The applicability of the model was tested by the reevaluation of 24 thermogravimetric analysis (TGA) experiments from earlier publications. The adjustable parameters of the model were determined by the method of least squares by evaluating groups of experiments together. Two evaluation strategies were tested. In the regular evaluations, the same kinetic parameters were employed for all the experiments with a given sample. The use of experiments with modulated and constant reaction rate (CRR) temperature programs made it possible to employ another approach too, when the preexponential factor was allowed to vary from experiment to experiment. The latter approach allows a formal kinetic description of the differences in the thermal deactivation of the samples caused by different thermal histories as well as of some inevitable systematic errors of the TGA experiments. The evaluations were carried out by both approaches, and the results were compared. The evaluations were based on 12 experiments. As a test, each evaluation of the study was repeated with only 8 experiments. The results of the latter test calculations indicated that the information content of the employed experiments is sufficient for the evaluation approaches of this work.

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Section: Resultsmentioning

confidence: 99%

Section: Resultsmentioning

confidence: 99%

Empirical Kinetic Models for the CO₂ Gasification of Biomass Chars. Part 1. Gasification of Wood Chars and Forest Residue Chars

2021

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“…The most convincing and predictive models for pyrolysis of coal and biomass at a high heating rate are probably the chemical percolation devolatilization (CPD) and FLASHCHAIN models. − The kinetics of thermal annealing have been described through the power law of eq , according to the thermal annealing model proposed by Senneca et al and already introduced. This formulation is chosen in the present work too, because it is particularly simple and provides estimates of the thermal annealing rate similar to more complex DAE models, shown recently by ref .…”

Section: Thermal Annealing Model For Biomassmentioning

confidence: 99%

“…Thermodeactivation of coals has been well-documented and assessed under but not limitedly to EFR conditions and has been quantified for a large suite of coals by several research groups. These topics have been recently reviewed. , Following the common approach of identifying thermal annealing through thermodeactivation, models of the thermal annealing of coal of different complexities have been developed. The most popular models are n th-order power law and differential algebraic equation (DAE) models, ,,, which have also been implemented in comprehensive combustion/gasification models. − …”

Section: Introductionmentioning

confidence: 99%

“…These topics have been recently reviewed. 13,20 Following the common approach of identifying thermal annealing through thermodeactivation, models of the thermal annealing of coal of different complexities have been developed. The most popular models are nth-order power law and differential algebraic equation (DAE) models, 27,31,33,34 which have also been implemented in comprehensive combustion/gasification models.…”

Section: Introductionmentioning

confidence: 99%

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Extension of the Thermal Annealing Concepts Developed for Coal Combustion to Conversion of Lignocellulosic Biomass

et al. 2020

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During the lifetime of coal and biomass particles in a reactor, severe changes in the carbonaceous structure occur. In the early stages of heat treatment, transformations at both the structural and chemical level are dramatic and well-recognized in the literature under the name of pyrolysis. Further heat treatment, even in parallel with heterogeneous reaction, produces less evident changes but is still very impactful on the char reactivity in the late stages of burnoff, which are recognized in the literature under the name of thermal annealing. Thermal annealing of biomass has often been neglected and underestimated. In the present work, a large experimental campaign has been carried out to measure the effects of heat treatment on the reactivity of a lignocellulosic material, namely, walnut shells, and, for comparison, a bituminous coal. The campaign included experiments in a thermogravimetric analyzer, fixed bed reactor, drop tube reactor, heated strip reactor, and flat flame burner, spanning over a very wide range of temperatures (700–2300 K), heating rates (0.1–105 K/s), and residence times (0.02–20 000 s). Results provide a unique set of data useful for testing pyrolysis–annealing models on lignocellulosic materials. Thermal annealing is very relevant also for lignocellulosic biomass and reduces the reactivity of char up to 1 order of magnitude. However, the distinction between pyrolysis and thermal annealing is made complex by the presence of multiple components with different inertia to thermal treatment. The applicability of the concepts developed for thermal annealing of coal to lignocellulosic biomass is therefore open to discussion. It is observed that the boarder line between the stage of pyrolysis and the stage of thermal annealing can be reasonably set when approximately 70–80% of the (ASTM) volatile matter content has been released. The early stages of thermal annealing, involving aromatization and graphitization of the carbon structure, occur in parallel with pyrolysis tails.

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Kinetics of the CO2 gasification of woods, torrefied woods, and wood chars. Least squares evaluations by empirical models

Várhegyi

Wang

Skreiberg

2023

J Therm Anal Calorim

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The gasification kinetics of chars forming from biomass materials was studied by kinetic equations of type dX/dt = Af(X) exp(− E/(RT)) where X is the conversion of the sample, A is the pre-exponential factor, E is the activation energy and f(X) is a suitable model function. The theoretically deduced f(X) models in the literature are rarely applicable for chars of biomass origin because of chemical and physical inhomogeneities and irregularities. Hence, empirical f(X) functions were determined by a method proposed four years ago (Várhegyi in Energy Fuels 33:2348–2358, 2019). The parameters of the models were obtained by the method of least squares. Thermogravimetric experiments from an earlier work were reevaluated to explore the possibilities of the approaches employed. The experiments belonged to untreated birch and spruce woods; torrefied woods; chars prepared at a higher temperature; and chars formed at high heating rates (ca. 1400 °C min−1). Common kinetic features were found for the CO2 gasification of the chars studied. The reliability of the results was carefully tested by evaluating smaller and larger groups of the experiments and comparing the results. The method proved to be suitable for the determination of realistic f(X), E, and A from single modulated experiments, too. The models described well the gasification of chars forming from different woods through a wide range of temperature programs and thermal pretreatments.

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Review of Carbonaceous Annealing Effects on O₂ and CO₂ Coal Reactivity

Cited by 6 publications

References 64 publications

Empirical Kinetic Models for the CO₂ Gasification of Biomass Chars. Part 1. Gasification of Wood Chars and Forest Residue Chars

Empirical Kinetic Models for the CO₂ Gasification of Biomass Chars. Part 1. Gasification of Wood Chars and Forest Residue Chars

Extension of the Thermal Annealing Concepts Developed for Coal Combustion to Conversion of Lignocellulosic Biomass

Kinetics of the CO2 gasification of woods, torrefied woods, and wood chars. Least squares evaluations by empirical models

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Review of Carbonaceous Annealing Effects on O2 and CO2 Coal Reactivity

Cited by 6 publications

References 64 publications

Empirical Kinetic Models for the CO2 Gasification of Biomass Chars. Part 1. Gasification of Wood Chars and Forest Residue Chars

Empirical Kinetic Models for the CO2 Gasification of Biomass Chars. Part 1. Gasification of Wood Chars and Forest Residue Chars

Extension of the Thermal Annealing Concepts Developed for Coal Combustion to Conversion of Lignocellulosic Biomass

Kinetics of the CO2 gasification of woods, torrefied woods, and wood chars. Least squares evaluations by empirical models

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Product

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Review of Carbonaceous Annealing Effects on O₂ and CO₂ Coal Reactivity

Empirical Kinetic Models for the CO₂ Gasification of Biomass Chars. Part 1. Gasification of Wood Chars and Forest Residue Chars

Empirical Kinetic Models for the CO₂ Gasification of Biomass Chars. Part 1. Gasification of Wood Chars and Forest Residue Chars