Dynamics of a single particle during char gasification

Heat transfer and kinetics in the pyrolysis of shrinking biomass particle

“…On the other hand, experiments conducted for large biomass particles (Lee et al, 1976;Chan et al, 1988) have shown signiÿcant shrinkage of char layer as the pyrolysis front propagates through the solid. Morel et al (1990) have modeled the changes in particle size due to disintegration of the solid structure at some critical conversion during char gasiÿcation. Villermaux et al (1986) described the shrinkage e ects assuming that the solid density remains constant as degradation occurs.…”

Gas–solid conversion in fluidised bed reactors

“…The rate of shrinkage/expansion of a particle's external surface is difficult to generalise because it depends on the nature of the NCGSR. For instance, for gasification reactions, a threshold for the local conversion has been fixed at the instant when the ash layer of particle peels off [38,39]. This threshold condition allows theoretical computation of the particle's boundary at any time.…”

“…The shrinkage of a particle during consumption is not included in F i (x c ) that only measures the change of the internal surface. If a detailed model (integration inside the particle) is used, it is possible to establish the rate of shrinkage as shown by Srinivas and Amundson [38] and Morell et al [39] for the case of gasification of coal particles. However, here we have formulated the model in terms of the global particle conversion x c , and the change in size with particle conversion cannot be calculated.…”

“…(41) ν stoichiometric factor of the reaction ξ kinetic parameter (see Table 1) ρ density of solid (kg m −3 ) τ R solid residence time (s) Θ(x c ) function defined in Eq. (39) Subscripts b bubble, bed, average in the bed c reactive component in the particle crit critical e emulsion i intraparticle in inlet out outlet p particle r reaction s surface 0 initial, superficial consideration of the multiphase nature of the FB by means of a simplified description of two phases, in which the solids and the gas were distributed in the bed. Thereafter the concept of 'contact time distribution' was recognized as a key factor for taking into account the time of gas contact with the solid reactant [2].…”

“…The fourth column is the function defined in Eq. (39). ξ i are kinetic model parameters; NAEF: not analytical expression found.…”