| The results show that the performance of artificial magnetite is better than that of natural magnetite.However,the artificial magnet concentrate has strong surface activity,hydrophilic and porous surface,that shows artificial magnetite can absorb water easily.Artificial magnetite green pellets have high moisture which is difficult to remove.Secondly,it also affects its shock temperature.So the artificial magnetite pellet shock temperature is much lower than the natural magnetite.The shock temperature of artificial magnets green pellet is in the range of 280?500?.And natural magnetite green pellets shock temperature is generally higher than 600?.Shock temperature can also restrict drying process.That makes the drying process slow,which seriously affects the production efficiency.In this paper,Fujian artificial magnetite is the raw material.Firstly,we explore its ballability and the pellet strength.The characteristic of pellet has a certain impact on the drying of the pellet.So it must use its best pellet conditions.Secondly,the drying process and drying kinetics of artificial magnets pellets were studied.The drying mechanism of artificial magnetite was analyzed by compared with the drying process of the nature magnetite pellets,which can provide the theoretical basis for the selection of heating path of artificial magnetite pellets?The test determines the optimum pelletizing process parameters.The effects of the experimental conditions on the drying of artificial magnetite were investigated by orthogonal test.The results of the drying test were analyzed.The medium temperature and the medium flow rate have a significant effect on the drying time.Increasing the medium temperature and the medium flow rate can speed up the drying process.But when the medium temperature and medium flow rate are too high,it can cause the pellets to burst.And the impact of the diameter of the ball on the drying time is not very obvious.Second,there is an interaction between the medium temperature and the medium flow rate,that is to say,changing the medium flow rate at different media temperatures has different effect on the test results.As the diameter of the ball itself is less affected,the associated interactions are negligible.Since the drying process involves the interaction of materials with water and the heat and mass reverse transfer,the drying mechanism is very complex,so the drying dynamics behavior is often described by a relatively simple empirical model.Through theoretical analysis,the correction of Page model???as a semi-empirical model can be a good explanation of artificial magnetite and natural magnetite drying process.The kinetic equation of artificial magnetite is deduced:MR=aexp?-ktn?.The parameters are as follows.a=0.9997+2.0105×10-11T3+9.9810×10-27T 9k=0.021+3.0105×10-9T3+2.0010×10-25T9+3.3222×10-4TV-1.7475×10-13T4V4+6.1720×10-22T7V7+3.5318×10-4V3+4.4055×10-6V9-8.0117×10-6L3+2.0013×10-13L9n=1.53+1.1008×10-9T3+1.601×10-25T9+7.0686×10-5TV-7.4895×10-14T4V4+1.4989×10-22T7V7+1.7659×10-4V3+3.0838×10-6V9-3.0012×10-6L3+2.0001×10-14L9It is proved that the calculated values of the dry kinetics equations of artificial magnetite and natural magnetite pellets are higher than those of the measured values.Through the function expression,it can accurately predict the change of moisture ratio of superfine silica pellets at any time.The drying mechanism analysis showed that artificial magnetite pellet drying is divided into three stages,namely,speed drying stage,constant speed drying stage and slow drying stage.The drying stage and the constant speed drying stage account for a lower proportion of the drying process.Therefore,the factors that determine the drying rate of the green ball are mainly the slow drying stage,that is,the removal of the pellet molecular water.Compared with natural magnetite,artificial magnetite is finer and finer in shape,irregular in shape and larger in specific surface area,and has more unsaturated bonds on the surface.The artificial magnetite is more hydrophilic and high molecular water,especially high molecular water which is difficult to remove in the drying process and easily lead to pellet burst. |
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