Experimental and Numerical Investigation of the Primary Fragmentation of a Lignite during Fluidized-Bed (FB) Devolatilization

Abstract

The paper presents a comparison between experimental and model results of primary fragmentation of a lignite coal in a fluidized bed (FB). In the experiments, the char particle size distribution and the general indicators of primary fragmentation (intensity and index) were determined. The same parameters were calculated using a mathematical model of the process, fed by data of the fuel (the amount of volatiles and fixed carbon), fluidized bed temperature, and inlet particle size distribution. The size distribution and number of the char particles in fluidized bed significantly differ from the size distribution and number of inlet coal particles. Char population has a bimodal distributionseparate distributions for the smaller and larger sets of fragments. The experimental and model results show the same tendency: a coal particle partially breaks at the beginning of devolatilization, giving a large number of fine fragments, while, as the process continues, the rest of the parent particle sometimes breaks down into a smaller number of larger pieces, and sometimes does not fragment at all. Review of the Weibull distribution coefficients enables prediction of the char particle size distribution for the characteristic fluidized bed conditions and inlet coal particle sizes.

Primary Fragmentation Behavior of Indian Coals and Biomass during Chemical Looping Combustion

“…The FI value depends mainly on the F d value. F d would always be less than 1 if the fuel is of nonswelling type and when the fuel is of a swelling nature, the F d will be ≥1 . Since FI is inversely proportional to F d , the FI value will be ≤1 for swelling types and ≥1 for nonswelling and shrinking types.…”

“…If the crack develops in the inner radial positions of the fuel structure (due to the high volatile content of the fuel), it results in the formation of a larger daughter particle . The fracture originating in the outer radial locations due to the thermal stresses leads to exfoliation of outer layers, resulting in generation of fine particles . Thus, it can be understood that if most of the resulting fragments lie in the smaller particle size range, it denotes that the thermal stresses are predominant in creating fragments.…”

“…41 The fracture originating in the outer radial locations due to the thermal stresses leads to exfoliation of outer layers, resulting in generation of fine particles. 40 Thus, it can be understood that if most of the resulting fragments lie in the smaller particle size range, it denotes that the thermal stresses are predominant in creating fragments. If mass fraction is higher for larger particle sizes, the fragmentation cause could be the outburst due to excessive internal pressure developed at high temperatures.…”

Modeling of the axial distributions of volatile species in a circulating fluidized bed boiler

“…In his experiments and simulation, the fragmentation probability of lignite is significantly higher than that of sub-bituminous coal. Paprika (Paprika et al, 2015) and Scala (Scala, 2016) also found the lignite coal particles partially breaks at the beginning of devolatilization, giving a large number of fine fragments. However, detailed description of the fragmentation behavior will make the model much more complex.…”

Prediction and minimization of NOx emission in a circulating fluidized bed combustor: A comprehensive mathematical model for CFB combustion

“…1.0 (ii) The primary fragmentation of large fuel particles are considered, and the PAPSD is modified based on the model proposed in Ref. [61] (iii) The attrition of fuel and char particles is neglected due to the short time of devolatilization or combustion process.…”