Packed bed combustion of non-uniformly sized char particles

Coal particle chemical transformational behaviour after thermochemical conversion in a fixed bed

“…The concentration profile inside the packed bed is expected to scale with the height to particle diameter ratio at constant flux, and in turn change the exit gas composition. It was however observed that this theory breaks down for excessively deep beds with particle sizes smaller than 10mm [27] and for height to diameter ratios in excess of 40, as is the case presented here.…”

“…By not using a chemical accelerant for the initial start-up of the reactor the gas composition was measured from the start to observe the transient gas variations occurring during initial heat up of the packed bed of particles before the equilibrium combustion front is formed. It is generally accepted that a narrow oxidation zone exists with a length in the order of 1 particle diameter of the original size fuel particle where oxygen content is rapidly reduced [25,27]. The end of this oxidation zone is marked by a peak in CO₂ concentration and accompanied by the indicated maximum temperature.…”

“…However, detailed and comprehensive experimental data sets are not readily available [26]. In overfeed operations, where the reaction front moves up in the reactor, a great deal of research was conducted on uniform fuel particle sizes and recently, Hallett et al [27] validated the use of the Sauter mean diameter when modelling reacting fuel beds where the particle size distribution is wide. Hobbs et al [26], however noted a lack in experimental data in the form of bed dissection results especially in the millimetre size range, also citing that most modelling efforts attempting to explain the complex gasification phenomena is validated based on exit gas composition and temperature profiles measured on laboratory scale reactors.…”

A study on the dynamic combustion behavior of a biomass fuel bed

“…In that study, the pyrolysis activation energy was adjusted to improve the model fit of the experimental results. Hallett et al [11] studied the effect of char particle size non-uniformity on combustion and gasification in an overfed reactor both experimentally and with a model. They found that a volume-surface mean diameter can be used to describe non-uniformly sized particles.…”

2‐D approximation of a structured packed bed column

“…Recently, more advanced 1‐D mathematical models have been developed . Generally, new models are based on Euler‐Euler models used in computational fluid dynamics (CFD), which allow more precise calculation of the temperature and species distributions along FxB by taking into account gas‐phase and solid surface reactions, fuel particle consumption and motion, heat conduction and radiation in the solid phase, and heat and mass transfer between phases (see the representative work Hallett et al). However, in spite of the relatively good performances of 1‐D models (e.g.…”