| The increasing improvement of coal upgrading technology ultimately attributes to the continuous expansion of dry sorting technology.The dry separation technology for fine coal has always been a hot issue in the field of dry separation.Among them,the dry separation technology by combining vibration and airflow provides an important separation method for the dry separation field.In this thesis,the separation mechanism has been realized through the separation of fine coal by vibratory gradient dry separator,the purpose of effective separation and quality improvement has been achieved.A study was performed on the motion behavior and force characteristics of the vibratory gradient dry separator.The results show that as the main moving member of the vibratory gradient separator,the vibration of the mandrel during smooth operation is called free vibration,the initial excitation frequency is low.While the vibration during start-up and shutdown stags is called jump-gradient excitation,both of which are within the tolerance range of the mandrel material.The separation bed driven by the mandrel,its motion characteristics are divided into three directions X,Y,Z.The main vibration direction is X,followed by Z,and the last is Y-axis.Displacement amplitude is 6.88 mm and 3.78 mm along the X and Z axes.When the speed of the mandrel is constant,velocity amplitudes of 287.60 mm/s and 161.6 mm/s along the X and Z-axis directions,the acceleration amplitudes are 10.43 m/s~2 and 5.92 m/s~2 along the X and Z-axis directions,respectively.The displacement amplitude along the Y-axis direction is only 1.02 mm.The directions of velocity and acceleration are always opposite to the X and Z.It has the advantages of high amplitude,low frequency and low power consumption.In terms of airflow distribution,air velocity values on the bed were detected to explore the characteristics of airflow distribution in different regions.And the maximum value of air velocity is mainly distributed in the bed feed end.And with the continuous movement of the material group,the air velocity decreases at the same time.When the blower velocity was adjusted from 8.97 m/s to 4.37 m/s,the air velocity distribution on the bed surface showed a tendency of radial decrease from the high-speed area to the surrounding area under no-load state.And when the blower velocity was 7.05 m/s,the measurement point No.3 at the bed feed inlet was the high air velocity peak area,which could reach up to 3.00 m/s.With the gradual reduction of the blower velocity,the area of peak velocity of airflow was always in the functional area of gangue channel,and gradually reduced to 1.76 m/s,1.29 m/s.The analysis of the air pressure resistance on both sides of the air distribution plate shows that the role of air distribution plate makes the air velocity in each area of the bed(ⅠtoⅣ)different,and the angleθof fan blade of air holes in each area varies from 90°,45°,30°and 15°in the order of the area fromⅠtoⅣ.The feed end with a 90°fan blade requires the largest air volume,and the air velocity rises as the fan blade angle decreases,which is conducive to the loose stratification and lateral migration of high-density particles in the thicker material layer,and the 45°blade area is the core constituency.For single particle,the theoretical mechanical analysis and the equilibrium and kinematic processes of the particle under the compound force field along the X,Y and Z directions of motion respectively are described.The variation equations of particle acceleration a_x,a_y and a_z are summarized,and the relationship between the influence of different parameters on acceleration is derived.The mechanism is investigated in terms of regional segregation and gradient separation of fine particles.It was shown that the motion paths through the bed surface of particles with different densities are not the same.The separation bed of the vibratory gradient dry separator can be divided into five major areas according to the functional area,which are the feed end,separation area,transition area,gangue channel and discharge end.When the vibration frequency f is 42 Hz,air velocity V_A is 14.70 m/s,bed lateral inclination A_H is 7°,the separation effect of tracer particles is the most obvious.In the separation conditions for(b)f=36 Hz,V_A=14.70 m/s,A_H=5°,the results show that the material layer in the feed end is thicker,up to a thickness of 10.08 cm.The thickness of the particle layer in the separation area was distributed in the range of 5.52-6.96 cm,and the height of the layer in the gangue channel showed a band distribution phenomenon.For the bed distribution test of white tracer particles(low density particles)under different separation conditions.The results showed that the vibration frequency and airflow speed should be increased correspondingly in the process of gradually increasing the bed lateral inclination angle A_H from 4°to 7°,so as to improve the separation effect of light and heavy particles.The density distribution in different areas was investigated by using the ash content of the-6mm coal sample as the separation index.The results show that,the difference of ash content between the upper and lower layers in the feed end is not obvious under the separation condition of the transverse angle A_H is 5°.With the gradual movement of particles to the separation area,low-density particles and high-density particles gradually achieve stratification,the difference between the upper and lower layers of ash is more obvious,and high-density particles gradually to the gangue channel,the highest ash content in the region,the upper and lower layers of ash content is no obvious difference,indicating that the region of high-density particles has relatively more content.Different parameters for the impact of the characteristics were studied,the results show that the airflow distribution state is not the same under the condition of no-load and load.With the gradual increase of air velocity,the separation effect of the separator gradually improved.The best separation effect was achieved when the air velocity of the blower reached 5.68 m/s,and the ash difference between clean coal and gangue was the largest,which was 12.54%and 81.82%respectively.When the vibration frequency gradually increases,the ash difference between clean coal and gangue gradually increases,and the separation effect first improves and then deteriorates.When the vibration frequency is 34 Hz,the maximum ash separation degree is 1.89.With the gradual increase of bed inclination angle,the transverse inclination angle has a greater influence on the separation effect,and when the lateral inclination angle A_H of the separation bed is 6°,the separation effect is the best.And the effect of bed longitudinal inclination A_Z on the separation effect is smaller with the increasing longitudinal angle,the ash difference of the products is not obvious,and the change of ash separation degree is small.Based on the above analysis,a study was conducted to optimize the interaction of the separation parameters and to improve the quality of low-quality coal.The study showed that the significant effects of different parameters were ranked as follows:vibration frequency>air velocity>lateral inclination angle.When the vibration frequency was 34 Hz,the air velocity was 6.16 m/s,and the lateral inclination angle was6°,the results of the coal separation and quality improvement tests showed that the yield of clean coal and gangue were 57.57%and 42.43%,and the ash content was 12.49%and 78.21%,respectively.Compared with the ash content of raw coal,the ash content of fine coal decreased by 27.04%,the actual separation density was 1.68 g/cm~3,and the possible deviation is 0.12 g/cm~3.The dissertation consists of 54 figures,23 tables and 121 references. |
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