Modeling Biomass Conversion during Char Gasification, Pyrolysis, and Torrefaction by Applying Constrained Local Thermodynamic Equilibrium

Petteri Kangas (Corresponding Author), Pertti Koukkari, Mikko Hupa

Research output: Contribution to journalArticleScientificpeer-review

9 Citations (Scopus)

Abstract

The char and biomass conversions during gasification, pyrolysis, and torrefaction were studied using the constrained free energy (CFE) method. The Gibbs free energy minimization method is extended by implementing immaterial constraints for describing partial equilibria in the gaseous phase and for kinetically controlling slow reactions associated with the conversion of char and biomass. The connection between immaterial constraints and the affinities of slow chemical reactions are illustrated. The method presented allows for the Arrhenius type of kinetic model to be incorporated into the calculation of local constrained thermodynamic equilibrium. Thus, the kinetically constrained chemical reactions, equilibrium reactions, and reaction enthalpies can be solved simultaneously by applying CFE methodology. A conceivable approach for introducing pseudo-biomass components into the thermochemical system is evaluated. The technique applies to statistical estimates of standard enthalpy and standard entropy based on assumed molecular compositions. When incorporated into a thermodynamic model, the pseudo-components allow for estimating the composition of biomass during the process and the fast volatilization of oxygen- and hydrogen-containing species at the beginning of the processes. The CFE method was successfully used for modeling the char conversion. The high operating temperature of the gasification process justifies the assumption of local equilibrium in the gas phase. The immaterial constraint can be used for controlling the release of carbon to the gas phase as the reaction proceeds. When pyrolysis and torrefaction were studied, the immaterial constraints could be successfully used for describing biomass conversion in solid phases. However, for these processes, the assumption of local equilibrium in the gas phase is not valid, because no equilibrium reactions occur in the low-temperature conditions.
Original languageEnglish
Pages (from-to)6361-6370
Number of pages9
JournalEnergy & Fuels
Volume28
Issue number10
DOIs
Publication statusPublished - 2014
MoE publication typeA1 Journal article-refereed

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Gasification
Biomass
Pyrolysis
Thermodynamics
Free energy
Gases
Chemical reactions
Enthalpy
Gibbs free energy
Chemical analysis
Vaporization
Hydrogen
Entropy
Carbon
Oxygen
Temperature
Kinetics

Keywords

  • biomass convesion
  • char gasification
  • local thermodynamic equilibrium

Cite this

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title = "Modeling Biomass Conversion during Char Gasification, Pyrolysis, and Torrefaction by Applying Constrained Local Thermodynamic Equilibrium",
abstract = "The char and biomass conversions during gasification, pyrolysis, and torrefaction were studied using the constrained free energy (CFE) method. The Gibbs free energy minimization method is extended by implementing immaterial constraints for describing partial equilibria in the gaseous phase and for kinetically controlling slow reactions associated with the conversion of char and biomass. The connection between immaterial constraints and the affinities of slow chemical reactions are illustrated. The method presented allows for the Arrhenius type of kinetic model to be incorporated into the calculation of local constrained thermodynamic equilibrium. Thus, the kinetically constrained chemical reactions, equilibrium reactions, and reaction enthalpies can be solved simultaneously by applying CFE methodology. A conceivable approach for introducing pseudo-biomass components into the thermochemical system is evaluated. The technique applies to statistical estimates of standard enthalpy and standard entropy based on assumed molecular compositions. When incorporated into a thermodynamic model, the pseudo-components allow for estimating the composition of biomass during the process and the fast volatilization of oxygen- and hydrogen-containing species at the beginning of the processes. The CFE method was successfully used for modeling the char conversion. The high operating temperature of the gasification process justifies the assumption of local equilibrium in the gas phase. The immaterial constraint can be used for controlling the release of carbon to the gas phase as the reaction proceeds. When pyrolysis and torrefaction were studied, the immaterial constraints could be successfully used for describing biomass conversion in solid phases. However, for these processes, the assumption of local equilibrium in the gas phase is not valid, because no equilibrium reactions occur in the low-temperature conditions.",
keywords = "biomass convesion, char gasification, local thermodynamic equilibrium",
author = "Petteri Kangas and Pertti Koukkari and Mikko Hupa",
year = "2014",
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language = "English",
volume = "28",
pages = "6361--6370",
journal = "Energy & Fuels",
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}

Modeling Biomass Conversion during Char Gasification, Pyrolysis, and Torrefaction by Applying Constrained Local Thermodynamic Equilibrium. / Kangas, Petteri (Corresponding Author); Koukkari, Pertti; Hupa, Mikko.

In: Energy & Fuels, Vol. 28, No. 10, 2014, p. 6361-6370.

Research output: Contribution to journalArticleScientificpeer-review

TY - JOUR

T1 - Modeling Biomass Conversion during Char Gasification, Pyrolysis, and Torrefaction by Applying Constrained Local Thermodynamic Equilibrium

AU - Kangas, Petteri

AU - Koukkari, Pertti

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PY - 2014

Y1 - 2014

N2 - The char and biomass conversions during gasification, pyrolysis, and torrefaction were studied using the constrained free energy (CFE) method. The Gibbs free energy minimization method is extended by implementing immaterial constraints for describing partial equilibria in the gaseous phase and for kinetically controlling slow reactions associated with the conversion of char and biomass. The connection between immaterial constraints and the affinities of slow chemical reactions are illustrated. The method presented allows for the Arrhenius type of kinetic model to be incorporated into the calculation of local constrained thermodynamic equilibrium. Thus, the kinetically constrained chemical reactions, equilibrium reactions, and reaction enthalpies can be solved simultaneously by applying CFE methodology. A conceivable approach for introducing pseudo-biomass components into the thermochemical system is evaluated. The technique applies to statistical estimates of standard enthalpy and standard entropy based on assumed molecular compositions. When incorporated into a thermodynamic model, the pseudo-components allow for estimating the composition of biomass during the process and the fast volatilization of oxygen- and hydrogen-containing species at the beginning of the processes. The CFE method was successfully used for modeling the char conversion. The high operating temperature of the gasification process justifies the assumption of local equilibrium in the gas phase. The immaterial constraint can be used for controlling the release of carbon to the gas phase as the reaction proceeds. When pyrolysis and torrefaction were studied, the immaterial constraints could be successfully used for describing biomass conversion in solid phases. However, for these processes, the assumption of local equilibrium in the gas phase is not valid, because no equilibrium reactions occur in the low-temperature conditions.

AB - The char and biomass conversions during gasification, pyrolysis, and torrefaction were studied using the constrained free energy (CFE) method. The Gibbs free energy minimization method is extended by implementing immaterial constraints for describing partial equilibria in the gaseous phase and for kinetically controlling slow reactions associated with the conversion of char and biomass. The connection between immaterial constraints and the affinities of slow chemical reactions are illustrated. The method presented allows for the Arrhenius type of kinetic model to be incorporated into the calculation of local constrained thermodynamic equilibrium. Thus, the kinetically constrained chemical reactions, equilibrium reactions, and reaction enthalpies can be solved simultaneously by applying CFE methodology. A conceivable approach for introducing pseudo-biomass components into the thermochemical system is evaluated. The technique applies to statistical estimates of standard enthalpy and standard entropy based on assumed molecular compositions. When incorporated into a thermodynamic model, the pseudo-components allow for estimating the composition of biomass during the process and the fast volatilization of oxygen- and hydrogen-containing species at the beginning of the processes. The CFE method was successfully used for modeling the char conversion. The high operating temperature of the gasification process justifies the assumption of local equilibrium in the gas phase. The immaterial constraint can be used for controlling the release of carbon to the gas phase as the reaction proceeds. When pyrolysis and torrefaction were studied, the immaterial constraints could be successfully used for describing biomass conversion in solid phases. However, for these processes, the assumption of local equilibrium in the gas phase is not valid, because no equilibrium reactions occur in the low-temperature conditions.

KW - biomass convesion

KW - char gasification

KW - local thermodynamic equilibrium

U2 - 10.1021/ef501343d

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M3 - Article

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SP - 6361

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JO - Energy & Fuels

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SN - 0887-0624

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ER -