Modelling of char-gas reaction kinetics

Gasification of char derived from sewage sludge was studied under different oxidizing atmospheres containing CO 2 , O 2 or H 2 O. The gasification tests were carried out in thermobalance at different temperatures and oxidizing reagent concentrations. The most efficient were the gaseous mixtures containing oxygen. The reaction took place at temperature 400-500°C, whilst in the case of CO 2 and steam much higher temperatures (700-900°C) were necessary to complete the conversion. Two rate models for gas-solid reaction were applied to describe the effect of char conversion on reaction rate. The shrinking core model for reaction-controlled regime was found to be the best for predicting the rate of char gasification in CO 2 and O 2 atmosphere. The experimental data for steam gasification of the char were fitted best by the first-order kinetics. The kinetic parameters estimated from the experimental data are in accordance with the literature for lignocellulosic char gasification and are the first published for sewage sludge char gasification.

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“…This is because gasification is a slower process than the initial pyrolysis [20]. Gasification results in continuous changes in char composition.…”

Section: Introductionmentioning

confidence: 99%

The kinetics of gasification of char derived from sewage sludge

Nowicki

Antecka

Bedyk

et al. 2010

J Therm Anal Calorim

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“…Several authors have investigated the effect of inter- actions between various reactive gases on gasification reactivity, but their results remain questionable [11,12]. Nevertheless, in cases where interactions were observed, their impacts on the particle conversion rate were relatively weak.…”

Section: The Particle Modelmentioning

confidence: 99%

Prediction of the gasification kinetics of a single wood char particle from a limited set of parameters

Teixeira¹,

Steene²,

Ponthieux³

et al. 2014

Fuel

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. Prediction of the gasification kinetics of a single wood char particle from a limited set of parameters. Fuel, Elsevier, 2014, 123, pp.194-204 Three functions were built to calculate particle conversion rate of steam gasification, Boudouard reaction and combustion. Function determination includes the use of a validated particle model and a numerical experimental design. The functions take into account all phenomena controlling particle conversion rate of a char particle under a reactive atmosphere.The functions depend on a limited set of operating conditions -T, p i -and particle properties: e 0 , e p,0 and A i .The functions can be easily adapted to a new wood char by confronting 3-5 experimental results to the function. Keywords:Gasification Particle conversion rate Char particle Modeling a b s t r a c t Many biomass gasification models have been developed at reactor scale with the objectives of understanding the phenomena involved and optimizing the processes. Most of usual models consist in solving equations of heat, mass and momentum balance in a multiphase media. These equations call for source terms that provide production or consumption of heat and species by the reactions. The heat and mass source terms are directly derived from the particle conversion rate, dX/dt. This paper focuses on the determination of these source terms regarding the char gasification stage of the gasification process.We propose three simple functions to calculate wood particle conversion rate of steam gasification, Boudouard reaction and combustion. The determination of each function is based on a validated char gasification model at particle size and a numerical experimental design. The model of char particle gasification includes all the complexity of the transformation: intrinsic reaction kinetic and both internal and external heat/mass transfer limitations. The experimental design was used to define simulations to be carried out, and to establish a relevant correlation between the particle conversion rate and a limiting set of 5 influencing parameters. Two of them are representative of the operating conditions -temperature and partial pressure of the reactant gas, the three others corresponds to particle properties: porosity, thickness, and reactivity constant.The three functions were determined for the gasification of a wood chips char particle in a H 2 O/N 2 , CO 2 / N 2 , and O 2 /N 2 atmosphere respectively. And finally, considering wood pellet char, we showed that the functions could be adapted to this new char from only 3 to 5 experiments, showing a good correspondence between prediction functions and experimental results.

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“…The rate of conversion of a single particle due to chemical reaction, under chemical reaction control, may be expressed as [18,19]:…”

Section: Problem Description and Definitionsmentioning

confidence: 99%

Gas–solid conversion in fluidised bed reactors

Gómez–Barea

Leckner

Santana

et al. 2008

Chemical Engineering Journal

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A simplified model for gas-solid reactions in fluidised bed (FB) is proposed. Such models already exist for catalytic gas-solid reactions (CGSRs), providing general description of the system in terms of main governing parameters. Expansion of this approach to non-catalytic gas-solid reactions (NCGSRs) is difficult, because the solid reactant takes part in the reaction. Therefore, FB reactor models for NCGSR are usually devised only for specific cases, and a general analysis has not been presented up to date. The present model allows analysis of different types of NCGSR in a generalised way, handling catalytic reactions as a particular, simpler, case. It is shown that the reactor behaviour can be described by three governing dimensionless parameters. Two additional parameters, quantifying the importance of diffusion effects in single particles are also identified, and their impact on reactor behaviour is analysed. Possible simplifications are explored. Model limitations, that is, assumption of isothermal bed and particle and the occurrence of only one reaction, are discussed. Examples are outlined to show the applicability of the method.

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Modelling of char-gas reaction kinetics

Cited by 49 publications

References 20 publications

The kinetics of gasification of char derived from sewage sludge

The kinetics of gasification of char derived from sewage sludge

Prediction of the gasification kinetics of a single wood char particle from a limited set of parameters

Gas–solid conversion in fluidised bed reactors

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