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Experimental study on principles of isothermal dehydration of anthracite

Laing, Yunpei, Wang, Fakai, Luo, Yongjiang, Wang, Han, Hu, Qianting
Drying technology 2019 v.37 no.1 pp. 38-46
drying, evaporation, liquids, mathematical models, micropores, moieties, particle size, thermogravimetry
Isothermal dehydration experiments were performed and studied on anthracite. A mathematical model is established for anthracite dehydration to improve the efficient utilization of high-moisture anthracite exploited by water addition technology. Three kinds of high-moisture anthracite with different particle size were treated by isothermal drying methods. Experimental results show that there are two clear stage differentiations in the derivative thermogravimetric curve of the anthracite drying process, namely Xc₁ and Xc₂. The dehydration process can be divided into the rapid deceleration phase (X < Xc₁), the steady linear dehydration phase (Xc₁ < X < Xc₂), and the deceleration phase (X > Xc₂). The drying mechanisms of the three dehydration stages are different. When X > Xc₂, the evaporation of the free water and bound water in the large pore of the anthracite is influenced by the capillary force of the curved liquid surface. When Xc₁ < X < Xc₂, the main driving force of water migration is the pressure gradient. When X < Xc₁, the detached water partly comes from the internal micropores of the anthracite and the rest is connected with the functional groups of the anthracite surface. A high drying temperature contributes to increasing the drying rate of the drying process, thereby improving the effects of anthracite dehydration.