Feasibility of the Constrained Free Energy Method for Modeling NO Formation in Combustion

Kangas, Petteri; Koukkari, Pertti; Brink, Anders; Hupa, Mikko

doi:10.1002/ceat.201400633

Cited by 6 publications

(3 citation statements)

References 39 publications

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“…28 Quite often all of these three phenomena are combined in the (iv) overall reaction rate, which can be experimentally defined for certain types of processes and raw materials. 26,27,40 A simplified example of the CFE method for modeling mass-transfer kinetics in a closed system is attached as Supporting Information.…”

Section: ■ Methodsmentioning

confidence: 99%

“…While the matrix extension directly affects the chemical changes involved, all previous aspects can be encompassed in the CFE method. For example, (i) elementary reaction kinetics in the gaseous phase are incorporated to CFE models; , (ii) the changes because of the reaction enthalpy when calculating the local thermodynamic equilibrium are linked to the temperature-dependent reaction rates in adiabatic processes (or with an iterative algorithm, which connects the enthalpy of the system to an external heat-transfer model); and (iii) restrictions in the rate of dissolving in aqueous suspension are coupled to the models . Quite often all of these three phenomena are combined in the (iv) overall reaction rate, which can be experimentally defined for certain types of processes and raw materials. ,, A simplified example of the CFE method for modeling mass-transfer kinetics in a closed system is attached as Supporting Information.…”

Section: Methodsmentioning

confidence: 99%

“…The respective methodology has been introduced for the conservation of “aromaticity” in benzene combustion and for describing the extent of the reaction for internal combustion problems. , The authors of this paper have applied the methodology to other areas of thermal biomass conversion; biomass gasification and related super-equilibrium conditions of tars, char, ammonia, and light hydrocarbons are described using the CFE method in ref . The super-equilibrium of sodium, potassium, chlorine, and sulfur in the fume of a kraft pulp mill recovery boiler is discussed in ref . Other reported applications of the CFE method are, for example, partitioning of electrolytes in an aqueous membrane, , surface energy in a multicomponent system, and reaction pathways .…”

Section: Introductionmentioning

confidence: 99%

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

2014

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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.

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