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Kinetics of coal and char oxycombustion studied by TG–FTIR

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Abstract

Coal and char oxycombustion is a complex process because of very high reaction rate of oxygen with coals and chars carbon. Very important process during oxycombustion is diffusion of O2 to surface of coal and char grain. This process can be minimized using small samples and high flow of the gas, but it is also dependent on temperature. For this reason, it is impossible to eliminate diffusion processes which cause significant impact on calculated kinetic parameters. This paper describes the results of thermogravimetric studies of oxycombustion process with evolved gas analysis by FTIR. Ultimate and proximate analysis of coal and char were made. Thermogravimetric experiments of coal and its char oxycombustion were conducted using five heating rates, namely 2.5, 5, 10, 20 and 40 K min−1, and gas mixture composed of 20 % O2 in CO2. Activation energies of coal and char oxycombustion were calculated by isoconversional methods: integral Vyazovkin and differential Friedman. Activation energies for three ranges of heating rates were calculated. This paper shows influence of heating rate on calculated activation energy. The reason of this phenomenon is due to change of the mechanism of coal and char oxycombustion from the chemical kinetic control regime to mixed chemical kinetic–diffusion control regime.

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Abbreviations

A :

Pre-exponential factor (s−1)

AC:

Ash content (wt%)

β :

Heating rate (K min−1)

E :

Activation energy (kJ mol−1)

m :

Mass (mg)

n :

Number of experiments

M :

Moisture content (wt%)

R :

Universal gas constant (kJ mol−1 K−1)

T :

Absolute temperature (K)

t :

Time (s)

V :

Volatile matter content (wt%)

X :

Fractional conversion degree of solid (−)

ash:

Mineral matter

D:

Diffusion

R:

Reaction

X :

Fractional conversion degree of solid (−)

t :

Total

0:

Initial state

ad:

Air-dried basis

d:

Dry basis

daf:

Dry and ash-free basis

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Acknowledgements

The results presented herein were obtained from research work co-financed by the National Centre of Research and Development in the framework of Contract SP/E/2/6642/10 ‘Advanced Technologies for Energy Generation: Oxy-combustion technology for PC and FBC boilers with CO2 capture’.

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Authors and Affiliations

  1. Institute for Chemical Processing of Coal, 1 Zamkowa, 41-803, Zabrze, Poland

    Piotr Babiński, Grzegorz Łabojko, Michalina Kotyczka-Morańska & Agnieszka Plis

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  1. Piotr Babiński
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  2. Grzegorz Łabojko
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  3. Michalina Kotyczka-Morańska
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  4. Agnieszka Plis
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Correspondence to Piotr Babiński.

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Babiński, P., Łabojko, G., Kotyczka-Morańska, M. et al. Kinetics of coal and char oxycombustion studied by TG–FTIR. J Therm Anal Calorim 113, 371–378 (2013). https://doi.org/10.1007/s10973-013-3002-x

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  • DOI: https://doi.org/10.1007/s10973-013-3002-x

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