Experimental Study On Drying And Separating Fine Lignite In Vibration Fluidized Bed

For the past few years, on the one hand high quality coal resources were draining off with coal resources continuously mining, on the other hand the wet separation is with high cost, easy to slime especially when sorting lignite and some other shortcomings. In addition, as a kind of low degree of coalification coal, lignite has the characteristics of high moisture content, low density, high volatile, non-caked, chemical reactivity, poor thermal stability and low calorific value, easy to weathering and spontaneous combustion, difficult to sorting and storing, which led to a lot of limiting for the use of lignite. At the same time, as a batch of new coal chemical industry projects start to use coal as their raw material the demand of coal resources rised sharply and the coal sorting and drying gradually be taken seriously. This article dry lignite under low fluidizing gas velocity by adopting the method of single factor experiment and then separate it in the vibration dense medium fluidized bed which will provide technical support for the energy efficiency and efficiently using of lignite.Firstly, this paper compares the fluidization properties and separation properties differences of lignite and a type of coking coal that has a well sorting effect in a fluidized bed. By using the pressure fluctuation acquisition and processing equipment, high-speed dynamic cameras to analyze the two types of coal particles movement rule, bed flow stability, formation and movement of bubbles in fluidized bed. The result shows that coal types, materials input, particle size and density, whether to join the pulverized coal influences the fluidized bed fluidization properties, bed density and stability of pressure fluctuations and finally produce different impact on the separation effect of the two kinds of coal. It can realizes a certain separation effect of low density lignite with the addition 10% of lignite powder whose particle size is 0.5-0.9 mm into magnetite powder. Because of low density and high moisture, lignite separation effect is inferior to coking coal, but can have certain effect of dirt exclusion.For 1-3 mm fine grained lignite, this paper suggested that dry it directly using vibration fluidized bed and analyzed the various factors of amplitude, frequency, gas velocity, temperature and particle size, medium quantity on the drying 1-3 mm fine grained lignite through the single factor experiment method. It turns out that the addition of vibrational energy can produce obvious back-mixing between particles even below the critical fluidization wind speed, which contribute to the drying of lignite efficiently and energy saving. Drying rate increases with the increasing of vibration strength, but the influences of amplitude and frequency differ: the promotion is larger because of the increasing of amplitude than the frequency when both are large. The best value of amplitude and frequency are 15 Hz and 25 mm. The effect direction of temperature and particle size are opposite. The higher the temperature the greater the drying rate, meanwhile 140℃ is the best temperature because the increasing of drying rate is unconspicuous above this temperature. In addition, effect of drying is bad drying the lignite of large particle size in vibration fluidized bed, when we should limite particle size in the scope of following 3 mm.Because of the high ash content of-3+1mm lignite, it is not suitable to use it directly after drying, and the sorting effect in vibration fluidized bed in which there is no dense medium is not good, this experiment sort the lignite after drying by using vibration dense medium fluidized bed. The results show that when the fluidization number reaches 1.35, the separation effect is best, and clean coal ash content reach 10%.At last, this article studied the drying characteristics of-13+6mm lignite in vibration dense medium fluidized bed, the result shows the addition of dense medium lead to lubricating effect among the coarse coal particles, with which the particles become active and the chance of collision are increased; due to the grain size is fine the dense medium will fill the pores between coarse coal particles, thus improving the drying effect of coal especially above 6mm greatly. The drying rate promotion is still obvious with increasing of frequency when it is already large. The best frequency and amplitude are 25 Hz and 25 mm. Apart from this, the influences of other factors basically the same between vibration dense medium fluidized bed and vibration fluidized bed.Based on the above research, this article conducted the drying dynamic analysis of the two different particle size of coal in combination with the Origin software and several typical dry model; compared the the effective diffusion coefficient and activation energy of them in vibration fluidized bed and vibration dense medium fluidized bed under and far more than critical fluidization gas speed. The result shows that the fitting results of Modified Henderson and Pabis are the most similar to the actual experimental data, the correlation coefficient is closest to 1 among each model; mean square error is least, so it’s the best optimum drying model. As other conditions being the same, the activation energy of N=0.9 and vibration dense medium fluidized bed are less than the conditions of N=1.8 and vibration fluidized bed. It will get a good effect if we combine the vibration energy and low wind speed. The addition of dense medium contribute to the promotion of drying effect of coarser lignite tremendously.