Microwave Drying Scheelite Process Optimization Studies

Drying treatment is a very important process of metallurgy industry, which commonly uses hot air, combustion gas, steam (superheated steam) or electric heating as heat source. The driving force for energy transfer is the temperature gradient between heat source and materials. Due to the conventional heating taking from the outside into the inside, it needs to heat up the whole material to remove water from the inside of material during drying process. The driving for mass transfer is the moisture concentration gradient between the inside and outside of material. The moisture is transferred from the inside to the surface, and then evaporated into atmosphere. For conventional drying process, it needs high external temperature to form a temperature gradient to speed up the drying process. Microwave irradiation has advantages for the internal and selective heating. The water specific dielectric constantε'of 60～78 is much higher than common minerals or compounds, so the moisture always quickly absorb electromagnetic wave and is rapidly transferred to vapors. So, it can significantly reduce the drying time. The selective heating reduces the thermal loss of material integral heating and can significant reduce the energy consumption. Apart from this, an inside to outside temperature gradient is formed due to microwave internal heating characteristic during drying process. The temperature gradient has a same direction as that of moisture diffusion, which can promote the mass transfer and improve the drying efficiency. Therefore the microwave drying technology has been received much attention and obtained rapid development.This paper concentrates the typical white particles of metallurgical materials, carried out by microwave drying and microwave drying process theory, as follows:(1) of the microwave drying scheelite concentrate in the new process. In the single factor experiment based on the establishment of a credible response to the value of each factor and the mathematical model:dehydration curve= 67.83-19.36x1+15.03x2+18.47x3-3.6x1x2-1.28x1X3+5.5x2X3-7.05x12-15.98x22-10.06x32Response Surface Method scheelite concentrate on the microwave drying process conditions were optimized, the results showed that:Microwave time, the amount of materials and material thickness on the drying effects of anthracite in order for the microwave significant time>> the amount of material> material thickness; microwave time, the amount of material, material thickness on the rate of dehydration is not a simple linear relationship, a quadratic term and significant influence on the dehydration rate, interaction term was less affected. Response Surface Optimization of microwave drying of ilmenite optimal conditions were:microwave time 174s, the material amount of 135g, bed temperature 92℃. At this time the actual results of the relative dehydration rates of 82.4%. At this time experimental and predicted deviation is 0.03%.(2) Conducted a scheelite concentrate the microwave drying kinetics. Characterized by drying rate curves can be classified as speed up the drying process of drying, drying constant and falling rate drying stages. The intensity of microwave power effects on the drying rate is remarkable. With the microwave power increases, the drying rate significantly increased, the corresponding microwave drying time is required for the shorter. Thin layer microwave drying of materials by the results of a series of analysis to determine the Page model is suitable for the microwave drying process of dialogue concentrates described and fit, so the model can be a variety of conditions, fine scheelite Mineral materials to predict the drying time(3) Research on the experimental results and theoretical analysis, the microwave drying characteristics of the conclusions different from the traditional drying process. Microwave drying characteristics of which is due to polar molecules within the material in the microwave field oscillating rapidly generate heat, prompting an enormous internal vapor pressure gradient from the inside out, pushing the spread of water to achieve the purpose of drying. Microwave Drying of scheelite concentrate for the whole process, and concentrate treatment capacity wet wet mineral variation in the water, build a mathematical model, and according to the model, calculations of mineral water content at different time, the experimental data and calculation analysis comparing the results obtained a better response to the above model can Microwave Drying of scheelite concentrate.