Chemical looping gasification of maceral from low-rank coal: Products distribution and kinetic analysis on vitrinite

Abstract

The product distribution and kinetic analysis of low-rank coal vitrinite were investigated during the chemical looping gasification (CLG) process. The acid washing method was used to treat low-rank coal, and the density gradient centrifugation method was adopted to obtain the coal macerals. By combining thermogravimetric analysis and online mass spectrometry, the influence of the heating rate and oxygen carrier (Fe2O3) blending ratio on product distribution was discussed. The macroscopic kinetic parameters were solved by the Kissinger-Akahira-Sunose (KAS) method, and the main gaseous product formation kinetic parameters were solved by the iso-conversion method. The results of vitrinite during slow heating chemical looping gasification showed that the main weight loss interval was 400–600 °C, and the solid yield of sample vitrinite-Fe-10 at different heating rates was 64.30%–69.67%. When β = 20 °C·min−1, the maximum decomposition rate of vitrinite-Fe-10 was −0.312%·min−1. The addition of Fe2O3 reduced the maximum decomposition rate, but by comparing the chemical looping conversion characteristic index, it could be inferred that the chemical looping gasification of vitrinite might produce volatile substances higher than the pyrolysis process of vitrinite alone. The average activation energy of the reaction was significantly reduced during chemical looping gasification of vitrinite, which was lower than the average activation energy of 448.69 kJ·mol−1 during the pyrolysis process of vitrinite alone. The gaseous products were mainly CO and CO2. When the heating rate was 10 °C·min−1, the highest activation energy for CH4 formation was 21.353 kJ·mol−1, and the lowest activation energy for CO formation was 9.7333 kJ·mol−1. This study provides basic data for exploring coal chemical looping gasification mechanism and reactor design by studying the chemical looping gasification process of coal macerals.