Study On The Electrostatic Characteristics Of Particles In The Gas-solid Dense Medium Fluidized Bed

Coal is one of the main energy sources in the world,and China is both a large consumer and producer of coal.The development of coal industry directly impacts the social development and industrial construction process of China.In the national "Fourteenth Five-Year Plan" to "promote green development,improve environmental quality,and deepen the fight against pollution" requirements,the clean,efficient and sustainable use of coal has become the main development direction of the coal mining and utilization industry.In order to solve the problem of uneven distribution of coal resources and water resources in China(a large number of high-quality coal resources are distributed in arid,water-scarce and alpine areas)where the traditional wet sorting technology is difficult to apply,dry coal sorting technology is bound to become a hot spot in this field.At present,gas-solid fluidized dense medium dry separation equipment and technology have been theoretically verified and industrially practiced,and have been effectively promoted and applied.However,there are still urgent problems in the gas-solid fluidized sorting process,such as difficulties in demeshing and dust handling,which need to be solved and improved,and on the other hand,there is still a gap in the related research on the charge characteristics and properties of dense medium.Studies have shown that the constant collision and friction of particles in the fluidization process inevitably leads to the generation and accumulation of static electricity,which causes problems such as adhesion,spark discharge and local defluidization affecting normal production and causing difficulties in desmearing and dust handling.To solve this problem,it is necessary to investigate the charge characteristics of particles in gas-solid dense medium fluidized beds.In this dissertation,based on electrostatic measurement,differential pressure measurement and material motion measurement,the charge characteristics of monoand binary mixed dense medium particles in gas-solid fluidized bed were studied,and a low-cost and efficient electrostatic control means was proposed.Based on the wall adhesion phenomenon of monolithic particles,an image processing algorithm was developed based on the adaptive threshold binarization,and the adhesion behavior of particles in fluidized bed was studied.It was found that significant wall adhesion phenomenon of particles appeared under low humidity.Further theoretical analysis combined with particle adhesion mechanics revealed the particle-wall adhesion mechanism,and the particle-wall electrostatic adhesion force equation was proposed.An electrostatic measurement system based on an attractive Faraday cup was developed to study the charge characteristics of particles and walls in the bed,and the variation of the charge characteristics of monolithic particles under gas-solid fluidization with particle properties and operating conditions was revealed.The charge characteristics of binary dense medium particles in different mixing states were investigated using a combination of online and offline based electrostatic measurements.The effects of two particle properties,particle size and material,and two operating conditions,relative humidity and gas velocity,on the charge characteristics of dense medium particles were investigated separately.The interaction of particle size variability and material variability in three types of mixed heavy media particles,homogeneous heterogeneous,homogeneous heterogeneous and heterogeneous heterogeneous,was investigated.The binary mixed particles were found to have an enhanced effect on the overall charge state of the particles,revealing the mechanism of binary particles charge enhancement and the charge mechanism.The charge characteristics of the particles at each position in the semi-industrial fluidized sorting equipment were further studied using an online electrostatic measurement device and revealed the charge distribution pattern in the bed during the actual separation process.Based on the experimental results of mono-and binary particles,the influence significance of each factor was analyzed by combining the tribological charge theory and fluidization theory,and the interaction effect of each factor on the surface charge density of particles in the gas-solid fluidization process was clarified to lay the foundation for the subsequent research and development of electrostatic control means.Machine learning methods such as support vector machines and artificial neural networks are compared and analyzed to address the limitations of complex nonlinear systems,accurately predict the surface charge density of mono-and binary particles and construct an efficient prediction model.A non-invasive online material motion monitoring system was developed and designed based on the cutting-edge technologies such as microelectromechanical systems(MEMS)and capacitance tomography(ECT),which realized the online measurement of the motion behavior of the material in the gas-solid fluidized bed.The kinetic characteristics and motion mechanism in the vertical and horizontal directions are revealed.The material settling fluctuation discrimination method was proposed.The kinetic equations of the material were constructed by combining the kinetic theory.The charge characteristics of the material were studied by combining the settling motion of the material with the surface properties,and the charge mechanism of the sorted material is revealed.The results of the study on the charging characteristics of mono-and binary particles and the mechanism and law of particle charging were integrated,and the effectiveness and durability of the two methods of particle surface modification and addition of antistatic substances were compared respectively.It was found that carbon fiber can be used as a better electrostatic inhibitor.A good electrostatic suppression effect can be achieved by adding only 0.05% wt.of carbon fiber(at low air velocity)or 0.15% wt.of carbon fiber(at high air velocity).Considering the advantages and disadvantages of all parties,a low-cost and high-efficiency electrostatic control method based on the cooperative use of carbon fiber/carbon fiber powder was proposed to provide a new method for the electrostatic control of large industrial-scale fluidized dry sorting equipment.There are 145 figures,18 tables and 199 references in this dissertation.