Study On Dewatering Kinetics Of Lignite And Its Re-adsorbed Moisture Sample Of Dried Coal

Coal, as the main energy in our country, supports the rapid growth of national economy by means of its industrial development. Since the excessive consumption of high quality coal resources, the reserve is relatively insufficient in the near future. In order to guarantee the sustainable and stable development of Chinese economy and realize the goal of low-carbon green simultaneously, exploiting and utilizing low rank coal becomes imperative.The primary problem in the utilization of lignite is the high moisture content, which seriously hinders its subsequence utilization. For the dried coal samples, the flourishing pore structure and abundant hydrophilic oxygen-containing groups may cause re-adsorption of water. Therefore lignite must be reasonably and effectively upgraded before its large scale utilization.In this research, the dehydration mechanism of raw lignite and the dry behaviors of re-adsorbing water of dewatered coal must be made certain. The existing forms of moisture in lignite and its drying process have been currently given enough attention, but the forms of re-adsorbing water in dewatered coal and its drying were rarely involved. This study focus on the discussions about the drying mechanism and kinetics from two drying processes of raw lignite and re-adsorbed moisture sample of dewatered coal, meanwhile the nitrogen adsorption characterization was used to assistant analysis the structure changes. The results are as follows:The higher the drying temperature of lignite, the faster the drying rate and the shorter drying time. Drying process of raw coal contains three periods, which are the increasing rate, constant rate and falling rate, respectively. During dewatering, the bulk water is released at first, soon afterwards the capillary water and multilayer water are removed, and monolayer water is the last one removed. The liberation rate of bulk water is constant in isothermal drying experiments and the internal water removed at falling rate period. Irreversible structure changes of the sample produced by temperature have taken place during drying. It is found from kinetics based on thermal analyses that three-dimension diffusion mechanism model g(α)= [1-(1-α)1/3]2 fits the lignite falling drying rate periods well, and the dehydration active energy of inherent water in raw coal is 41 kJ/mol.Drying rate increases with rising temperature when drying lignite directly, while pretreatment makes it different. Modified Henderson and Pabis model fits the lignite thin-layer drying process well and the average active energy is 25 kJ/mol while the active energy needed to remove adsorbed water is 31 kJ/mol.The drying process of re-adsorbed moisture sample of dewatered coal has no constant rate period, which indicates that the proportion of bulk water of the re-adsorbed water is little. The non-segmental phenomenon at the falling rate period shows that vast majority of water in re-adsorbed coal is inherent water and the water forms in the re-adsorbed moisture coal are simpler compared with that in raw coal. The degree of pore structure collapse in lignite is anabatic with the elevated temperature, which brings weaker ability of dewatered coal to adsorb water. During drying, falling rate period is controlled by two-dimension diffusion mechanismg(α)= α+(1-α)1n(1-α). The dehydration active energy of inherent water in re-adsorbed coal is 32 kJ/mol.