Clay flash calcination for supplementary cementitious materials: Single-particle model and its experimental assessment

A one-dimensional particle model based on the finite volume method is proposed for studying the flash calcination of raw clay. The model incorporates intra-particle mass and heat transport as well as relevant kinetics such as dehydroxylation and recrystallization. Kinetics for clay dehydroxylation derived from Thermogravimetric analysis (TGA) was found to obtain a best fit by a third order reaction with A = 3.76 × 1 0 10 s − 1 and E a = 189.4 kJ/mol . The particle model was evaluated with kaolinite conversion and mullite content experimental data from two laboratory scale flash calciners. The particle model is in good quantitative agreement with experimental conversion data at gas residence times of 0.7 and 1.4 s and reactor temperatures of 500 – 900 ° C . Local sensitivity analysis is performed with the model to reveal the key process parameters affecting the conversion of raw clay and the final amount of produced pozzolanic material. It is discovered that kinetic parameters of clay dehydroxylation and recrystallization, particle size and temperature are the most sensitive parameters, whilst the modeling results are insensitive to pressure and initial particle temperature. For kaolinite-bearing clays of particle size under 100 μ m , temperatures between 800 °C and 930 °C are preferred to maximize the amount of metakaolin. At a representative residence time for industrial flash calciners of 2.5 s , a reactor temperature of 900 °C ensures optimum metakaolin yield for particle radii below 200 μ m .