Construction And Process Evaluation Of System For Lignite Rapidly Dried By Hot Flue Gas At Low Temperature

Currently,lignite is mainly used for pit plant power generation and coal chemical engineering. However, due to its high moisture, high volatile, low heat, direct combustion of lignite wastes energy very much. Meanwhile, the output of milling system is limited by the high moisture of lignite,resulting in low economy aspects. In this paper, rapidly dried by hot flue gas at low temperature of lignite was put forward, and the device platform was designed, built, and evaluated from three aspects, energy, upgrading efficient and security.The drying gas carries energy, and by online component analysis the content of O2 and CO2 was limited to 8-10% and 4-6%, separately. The analysis of energy shows that upgrading the Mengdong lignite needs 1.315 MJ energy, while the calorific improves 5.06 MJ / kg, so it is economically feasible.In this paper, the physical and chemical characteristics of upgrading lignite was analyzed, and its properties of dewatering, reabsorption and combustion was also studied. Results showed that the moisture dropped to 4.74% from the 29.36% after upgrading while the calorific value increased from 18.32MJ/kg to 23.38MJ/kg. The particle size concentrated in the 50-150μm and the macromolecular skeletal structure does not change obviously, but the free hydroxyl functional groups significantly decreased. We also found that the specific surface area, total pore volume, mean pore size increased which results in increase in the amount of nitrogen adsorbed. The water reabsorption of upgraded lignite increases, and showed good linear relationship with the upgrading temperature. At last, the flammability of lignite also improves after upgrading and the combustion property was enhanced.After analysis of component and energy, main factors of energy consumption was obtained and the process parameters of the system was optimized. The results showed that the flue gas mainly consists N2, O2 and CO2, and the drying medium contains energy of 196.42MJ/h. Main energy consumption factors are lignite moisture,drying medium parameters, system heat release and facilities.With this experimental system, the explosion property of pulverized coal was studied and the safety of this system was systematically assessed. The explosion limit concentration of pulverized coal decreases after upgrading, and the higher the upgrading temperature, the easier the pulverized like to explode. The pressure reaches the maximum when the pulverized coal concentration is 400g/m3. At low oxygen concentration(8%) conditions, the maximum explosion pressure of upgrading lignite was only 0.087 MPa, and we can consider it hard for upgraded lignite explosion under this system.