Empirical Kinetic Models for the Combustion of Charcoals and Biomasses in the Kinetic Regime

Várhegyi, Gábor; Wang, Liang; Skreiberg, Øyvind

doi:10.1021/acs.energyfuels.0c03248

Cited by 6 publications

(14 citation statements)

References 37 publications

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“…A review, published more than 10 years ago, puts into evidence that pyrolysis conditions and substrate properties are the key issues for the oxidation and gasification rates of biomass chars. As for the oxidation process, studies carried out afterward have contributed in clarifying these aspects, confirming the important role played by the pyrolysis temperature, heating rate and pressure, the macrocomponent content and nature, the microstructure, and mainly the content and composition of inorganics. − Despite significant advancements, − the improved understanding of these effects has not yet been fully incorporated into intrinsic kinetics of general validity, that is, capable of describing, through the kinetic parameters, the variability of char reactivity. Kinetics is needed for coupling with the description of transport phenomena aimed at the development of predictive models of practical systems for gasification and combustion …”

Section: Introductionmentioning

confidence: 99%

Burning Dynamics of Straw Chars under the Conditions of Thermal Analysis

Branca¹,

Blasi

2021

Energy Fuels

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Burning is investigated, by means of thermogravimetry, of 17 straw chars produced from packed-bed pyrolysis at moderate temperatures, using wood chars for comparison. The exothermic process always consists of an oxidative devolatilization stage followed by actual burning, generally leading to almost complete conversion for temperatures around 750 K. The majority of straw chars exhibits two-stage burning taking place, first in a catalytically (alkali) activated kinetic regime, with peak rates at temperatures around 650−690 K, and then in a thermally activated kinetic regime, with peak rates at temperatures around 700−730 K. In the other cases, burning is a one-stage process occurring either in a catalytically activated regime, with temperatures of the peak rates around 675−685 K, or in a thermally activated regime which also includes wood chars (temperatures of the peak rates again around 700−730 K). Moreover, burning of the residual char is completed at temperatures above 750 K (in a very few cases with further local peak rates around 825−875 K) in a diffusive regime.

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Section: Introductionmentioning

confidence: 99%

Burning Dynamics of Straw Chars under the Conditions of Thermal Analysis

Branca¹,

Blasi

2021

Energy Fuels

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“…The Polynomial in the Model and the Preexponential Factor. Based on our experience with this type of modeling, 18,19 fifth-order polynomials were chosen for eqs 3 and 4. There is a strong compensation effect between the high-order coefficients of the polynomials, as explained by figures in the Supporting Information.…”

Section: Methodsmentioning

confidence: 99%

“…In a subsequent work, this type of modeling was extended for the description of the combustion of biomasses and chars, and it was tested on 38 TGA experiments. 19 The present work examines the applicability of this type of modeling on the CO 2 gasification of biomass chars. Here again, earlier experiments are reevaluated, and particular care is taken to check the reliability of the results.…”

Section: Introductionmentioning

confidence: 99%

“…Equation 3 follows directly from the combination of eqs 5 and 6 in the work of Vaŕhegyi et al, 2020. 19 The term (1 − X) in eq 3 ensures that Af(X) is zero at the end of the reaction for any polynomial coefficients. Substituting eq 3 into eq 1, we get…”

Section: Introductionmentioning

confidence: 99%

“…The first approach is simpler and also gave appropriate results. In a subsequent work, this type of modeling was extended for the description of the combustion of biomasses and chars, and it was tested on 38 TGA experiments . The present work examines the applicability of this type of modeling on the CO 2 gasification of biomass chars.…”

Section: Introductionmentioning

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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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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Empirical Kinetic Models for the Combustion of Charcoals and Biomasses in the Kinetic Regime

Cited by 6 publications

References 37 publications

Burning Dynamics of Straw Chars under the Conditions of Thermal Analysis

Burning Dynamics of Straw Chars under the Conditions of Thermal Analysis

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

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

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Empirical Kinetic Models for the Combustion of Charcoals and Biomasses in the Kinetic Regime

Cited by 6 publications

References 37 publications

Burning Dynamics of Straw Chars under the Conditions of Thermal Analysis

Burning Dynamics of Straw Chars under the Conditions of Thermal Analysis

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

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