Dewatering Upgradation And Drying/Thermal Decomposition Kinetics Of Lignite

Lignite as a primary energy source is expected to play a key role in energy supplies in the future because of its abundance, easy exploitation, and low mining cost. Lignite is characterized by high moisture content and a low energy yield compared with other coals, although cheap and low in sulfur. This moisture enhances the freight charges per thermal unit of coal and direct combustion of wet lignite for electricity generation may not be energy efficient because a significant portion of fuel energy must be used to evaporate the lignite moisture. Therefore, dewatering is the first and essential step in almost all lignite utilization processes, a novel gas-solids multiregime flow method which include the pneumatic conveying, spouted bed is proposed to dry the lignite. These were analyzed that the various operating parameters effect on the hydrodynamic characteristics of pneumatic conveying and spouted bed respectively, inlet and outlet flue gas temperatures effect on dehydration rate in hot test. TG experiments and drying kinetics experiments of lignite made, and TG curves and drying characteristic curves of lignite were obtained.The research of hydrodynamic characteristics show that the solids to gas mass flow ratio and superficial air velocity are main influencing factors of pressure loss on a unit length of pneumatic tube and empirical correlations of fs are given to predict the pressure loss of pneumatic tube on various air velocity. Besides, the key hydrodynamic parameters such as wms,ΔFm,ΔPs are studied. The correlations of ums and APm for the particular bed geometry are developed.The drying kinetics results indicate that with increasing the drying medium temperature, drying rate increases and particles diameter has the same impact rules on the drying curves when particles diameter is in rang of 0 to 3mm, beyond this range the impact becomes less obvious. The experimental data of drying kinetics were simulated by means of the thin layer-drying models, and the drying equation MR=exp[-(kt)n] and the drying rate equation-dM R/dt=knM R(-ln m R)n-1/n are derived. The pre-exponential factor A is 5.819min-1, the activation energy of interface evaporation Ev is 21347.5kJ/mol, empirical factor Cd is 0.0409m-1 and the drying time index n is 1.516.The investigation of thermal decomposition kinetics of lignite is found that the thermal decomposition kinetics of lignite is three dimensional diffusion, the kinetic equation is (dα)/(dT)=A/βe-E/RT f(a)=(3A)/(2β)e-E/RT(1-α)4-31[(1-α](?)-1]-1,in which the pre-exponential factor A is 1.22×1013min-1and the activation energy E is 193.41kJmol-1...