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

Abstract

. 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.

Simulation of biomass char gasification in a downdraft reactor for syngas production

“…are determined by where C c,0 is the initial concentration of char and the notation ω i denotes the char conversion rate for each heterogeneous reaction (1)–(3). These char conversion rates have been correlated by Teixeira and coworkers to the experimental parameters, temperature T and partial pressure of the reactant gas P j ( i .e., H 2 O, CO 2 , and O 2 ), as well as the char properties, porosity ε p , particle thickness e p and reaction pre‐exponential factor A i , by three functions that take the form …”

The effect of pyrolysis heating rate on the steam gasification reactivity of char from woodchips

“…Compared to empirical modelling approaches based on the mathematical fitting of the results [7], the developed model owns a certain physical meaning.…”

Kinetic modelling of char gasification by accounting for the evolution of the reactive surface area

“…The char conversion rate can be modelled by empirical laws fitted on the mass loss of the solid (Diblasi, 2008;Laurendeau, 1978;Teixeira et al, 2014) but the most advanced models are rather based on the fundamental parameters which control the reactivity of char, namely: the carbon active sites and surface chemistry of char (Bar-Ziv and Kantorovich, 2001;Campbell and Mitchell, 2008;Davis et al, 1995;Geier et al, 2013;Gupta and Bhatia, 2000;Hurt and Calo, 2001;Hurt and Haynes, 2005;Klose and Wölki, 2005;Leistner et al, 2012;Lizzio et al, 1990;Radović et al, 1983), the accessible surface area and porous structure of the particle (Ballal and Zygourakis, Extensive models have emphasized the importance of structural effects on the conversion rate especially for microporous char (Ballal and Zygourakis, 1987;Bhatia and Perlmutter, 1980;Bhatia and Vartak, 1996;Gavalas, 1980;Kantorovich and Bar-Ziv, 1994). It has been shown that the surface chemistry is also a very important parameter and should be considered with the porous structure for a proper modelling of char oxidation (Bar-Ziv and Kantorovich, 2001;Gupta and Bhatia, 2000;Kantorovich and Bar-Ziv, 1994;Leistner et al, 2012;Ma and Mitchell, 2009;Miura et al, 1989;Yaşyerli̇et al, 1996).…”