A Predictive Multi-Step Kinetic Model of Coal Devolatilization - Summary

A Predictive Multi-Step Kinetic Model of Coal Devolatilization – Summary

1-Sentence-Summary: A predictive multi-step kinetic mechanism for coal devolatilization is developed that requires only elemental analysis and operating conditions to use.

Authors: S. Sommariva, T. Maffei, G. Migliavacca, T. Faravelli, and E. Ranzi

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A Predictive Multi-Step Kinetic Model of Coal Devolatilization - Summary

A model for coal devolatilization is developed based on a multi-step kinetic mechanism. The model is designed in such a way that only elemental analysis of the coal and the operating conditions are needed. This is achieved by weighting the particular coal used between three reference coals based on carbon, hydrogen, and oxygen atom content.

The final model is able to capture coal particle devolatilization times and weight loss. Furthermore, detailed profiles of volatile species, tar, and char production can also be achieved. The model is validated through a range of operating conditions including heating rates from K/min to 105 K/s, and increased ambient pressure.

Three of the main findings from this paper are:

  1. Several approaches to modeling coal devolatilization are available in the literature.
  2. Linearly weighting the kinetic parameters from three reference coals based on elemental composition can be used as a predictive model.
  3. The linear weighting model compares favorably for different coal ranks under various operating conditions.

The following sections outline the main findings in more detail. The interested reader is encouraged to view the complete article at the link provided below.

Finding #1: Several approaches are available for modeling coal devolatilization

The authors give an extensive review of modeling approaches for coal devolatilization. In general they break the models into the following groups:

  • Empirical models
  • Multi-step kinetic models
  • Structural lattice models
  • Chemical Percolation and Devolatilization (CPD) models

The authors give an extensive review of literature sources for each of the model categories. In brief, empirical models are generally fit to a first-order Arrhenius expression, and are only suitable at a single operating condition. Multi-step kinetic models are more accurate, but have difficulties with defining model parameters and characterization of tar production.

Structural lattice models include detailed information on the coal chemical structure and can use Monte Carlo methods or percolation theory to solve. Defining the statistical lattice structure is the starting point for these models. Lastly, CPD models can use the extrapolation techniques of Solum et al., 1989 to statistically describe the coal lattice. The methods presented by Genetti et al., 1999 can be used to derive the parameters required from proximate and ultimate coal analysis.

Finding #2: Linear weighting of kinetic parameters based on reference coals is an efficient approach to modeling devolatilization

The goal of the current authors is to develop an approach that is simple enough to be used for CFD simulation of coal gasification and combustion. In this vein, they develop a linear weighting technic between three reference coals of known devolatilization properties. In this approach devolatilization is considered as a straightforward weighted combination of the “pyrolysis of the reference coals”.

Finding #3: The proposed model works well for a range of operating conditions

The proposed linear weighting model is validated over a range of operational conditions. Different ranked coals are tested from heating rates ranging from K/min to 105 K/s.

The results show proper characterization of devolatilization rates and tar production for thermogravimetric analysis and Curie point pyrolyzer analysis. Furthermore, drop tube experiments compare quite well although tar production is over-predicted. In general a pressurized drop tube and pressurized flat flame burner show reasonable agreement, although tar is again over predicted. The individual findings are discussed extensively in the paper and supplemental material.

My Personal Take-Aways From
“A Predictive Multi-Step Kinetic Model of Coal Devolatilization”

In addition to providing a useful model for CFD analysis, the current paper gives a good overview of the different methods available for modeling coal devolatilization. It is recommended for anyone studying combustion or flame propagation of pulverized coal. The list of references and descriptions given are good starting point for anyone working in this area.

Full Citation:

  • S. Sommariva, T. Maffei, G. Migliavacca, T. Faravelli, and R. Ranzi, “A predictive multi-step kinetic model of coal devolatilization,” Fuel, vol. 89, pp. 318-328, 2010.
    title={A Predictive Multi-Step Kinetic Model of Coal Devolatilization},
    author={Sommariva, S. and Maffei, T. and Migliavacca, G. and Faravelli, T. and Ranzi, R.},
    link ={http://www.sciencedirect.com/science/article/pii/S0016236109003548},
    summary = {http://www.mydustexplosionresearch.com/predictive-multi-step-kinetic-model-coal-devolatilization},

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