Coal pyrolysis in a rotary kiln: Part I. Model of the pyrolysis of a single grain

Abstract

A mathematical model is presented which describes the pyrolysis of a single grain of coal and is designed to be incorporated into an overall model simulating the rotary kiln coal pyrolysis process. The grain model takes into account the principal physical phenomena occurring during the conversion of coal to coke, namely, heat transfer toward and within the grain, drying of the coal, and the evolution of volatile species. Particular care has been taken in the determination of the thermophysical and kinetic parameters necessary for the model. Thus, the drying kinetics for Lorraine coal were measured by thermogravimetry. The kinetics of pyrolysis were determined by both thermogravimetry and gasphase chromatography, in order to separately monitor the evolution of the nine gaseous species considered. The true specific heat and the thermal conductivity of the solid were also mesured as a function of temperature. The numerical model, based on the finite-volume method, calculates the temperature, composition, and mass flow rates for the different gases evolved at each point in the grain at any instant of time. The model was, finally, validated by comparing the calculated and measured values of the overall conversion of the pyrolysis reaction and the temperature at the center of the grain.

Mathematical modelling of Collie coal pyrolysis considering the effect of steam produced in situ from coal inherent moisture and pyrolytic water

“…Coal pyrolysis is modelled by the single-reaction approach similar to previous work on large particle pyrolysis modelling [9][10][11]. The ultimate volatile yields are taken from fast-heating pyrolysis experiments of pf-sized (90-106 lm) particles using a drop-tube/fixed-bed reactor [4] having features similar to those used by Hayashi and coworkers [5], where the dried coal was fed in one pulse into the reactor with minimised contact between the char and volatiles.…”

“…One approach is assuming drying to be an additional chemical reaction described by an 1st-order Arrhenius expression [9,[15][16][17]. This is adopted here as an empirical approach, due to its good integratability into the present model and it reasonably models moisture evaporation in fuel particles [9,[15][16][17]. The kinetic parameters are fitted from drying experiments on Collie coal pf-sized particles using a thermogravimetric analyser (TGA) at various heating rates.…”

Predictive models and operation guidance system for iron ore pellet induration in traveling grate–rotary kiln process

“…The mathematical models are mass and heat balance equations incorporated with kinetic expressions of physical and chemical phenomena, which includes evaporation and condensation of pellet moisture, oxidation of magnetite, combustion of coke breeze, calcination of lime or dolomite, pellet shrinkage, etc. Rotary kilns are ubiquitous fixtures of the metallurgical and chemical process industries, the mathematical models of rotary kiln generally involve solid motion (Boateng and Barr, 1996;Puyvelde, 2006), heat transfer (Barr et al, 1989;Senegacnik et al, 2007;Shi et al, 2008;Tomaz and Filho, 1999), kinetics of chemical reactions such as pyrolysis, calcination, solid clinkering (Mujumdar et al, 2007;Ortiz et al, 2005;Patisson et al, 2000a) and fuel combustion. Similarly, overall model of rotary kiln is established via mass and heat balance equations, as reported in Marias (2003), Mujumdar and Ranade (2006), and Patisson et al (2000b).…”

Process simulation of activated carbon production using a rotary kiln

“…Likewise, the energy balance for solid is (2) where the terms from the second of the right hand side are the conduction and radiation between gas and solid, the conduction and radiation between wall and solid, and heat consumption for the generation of water vapor, respectively. The last is the heat consumption by the water gas reaction.…”

“…Coal pyrolysis in a rotary kiln has been modeled to examine the role of operating parameters, such as the kiln rotation speed for the process optimization [2,3]. A review of charcoal production technology was published to explain the production technique and its relation to the charcoal properties [4].…”