Comprehensive study on the influence of preparation conditions on the physicochemical structure of char and the adaptability of the char reactivity model

Abstract This study was performed to analyse the adaptability of the self-developed char reactivity model and reveal the influence of preparation conditions on the char gasification reactivity. Firstly, six coal samples were selected for the step-by-step extraction of the metal elements. The forms of K elements in the different coal samples were quite different. Na elements were mainly water-soluble, ion-exchanged and acid-soluble states, whilst Ca, Mg and Fe elements were mainly ion-exchanged, acid-soluble and insoluble states. Then, the coal char gasification rate was determined using thermogravimetric analysis (TGA) in the temperature range of 1073–1223 K to verify the self-developed char reactivity model. Results showed that the model could accurately predict the reaction rate of the char samples under different gasification temperatures. Finally, a typical coal sample was selected to prepare char under various heating rates, cooling rates and annealing times and characterised by CO2 and N2 adsorption-desorption, Raman, FTIR, XPS and TGA. Results showed that with prolonged annealing time and decreased heating and cooling rates, the proportion of micro-pores in char increased, the particles tended to possess a graphitisation structure. In addition, the surface reaction functional groups disappeared, reducing the char gasification reaction rate. Comparison of the model calculated values and the experimental values of the char gasification reaction rate obtained under different preparation conditions showed that the self-developed model could provide a reference for the prediction of in situ char gasification reaction rate.