Analysis of the kinetic characteristic of water emission during low-rank coal drying process

The drying processes of Yimin lignite (YM) and Tianchi subbituminous ( TC) were studied using thermo- gravimetric analysis. Isoconversion method was used to analyze the TG data to obtain the drying activation energy E. Based on the activation energy obtained,the most probable mechanism function was determined by Achar equation and Coats-Redfern equation,and then the reaction order n and the pre-exponential factor A were obtained. At the same time,the differential scanning calorimetry (DSC) method was used to quantitatively analyze the moisture contained in the coals and verified the thermogravimetric results. The experimental results show that the activation energy E of the water emission process is 45-55 kJ / mol and the drying process follows the simple series model for the low-rank coals. For YM coal,E = 53. 28 kJ / mol,n = 1. 82-1. 95,A = (3. 52 -3. 96) ×108 s-1 and for TC coal,E = 47. 44 kJ / mol,n =1.39-1． 44,A = (6. 62-8. 17) ×107 s-1 . The quantitative analysis on the water existence form using DSC method indi- cates that the content of unstable water mainly in the form of free water and weak bound water is 70% -80% . During the drying process,the free water first releases from the coal particle and the strong bound water releases at the end of the period. The activation energy of the strong bound water emission increases abruptly with the drying process and is much larger than that of pure water.