Compound Triboelectrostatic Machine Divided The Study Of The Separation Mechanism

Electric separation is a very high efficiency physical separation, which uses different minerals have different electric properties in the high voltage electric field to separate. Electric separation is easy to run, economical, dose not produce waste water and friendly to environment, so electric separation is better than other physical and chemical mineral processing methods, many countries pay great attention to it, and it must be quickly developed in the world.Triboelectrostatic separation is a dry separation process based on the fact that particles can be charged differently upon contact, friction or impact. Triboelectricity can be produced by particles friction each other, and particles friction or impact some materials surface. The cause of tribocharge is electrons transfer. Triboelectricity is small, so the main problems with conventional triboelectrostatic separators are low throughput and poor efficiency, which limit their application.According to the situation of triboelectrostatic separation technology studied and used in the world, this paper presents a new concept that is particles' compound charge for the first time, and bases on the new concept this paper presents and study a compound triboelectrostatic separator, which is made up of a tribocharge device and a compound high voltage electric field. The tribocharge device is formed by a tribotrough and an external electric field. The compound high voltage electric field is formed by an electrostatic electrode and several shutter or sheet sharp electrodes with the roller electrode connected to earth. The tribocharge and corona charge combine to make particles compound charge, this charge principle can let particles charge electricity increase. Using the charge principle we can manufacture a new type of triboelectrostatic separator, which has high throughput and high efficiency.This paper studies the charge mechanism, which combined by the tribocharge and corona charge. Setting up a mathematical model and manufacturing an experimental device of the compound triboelectrostatic separator. Using the experimental device to test particles charge electricity, and prove that the mathematical model of the compound triboelectrostatic separator is right. This paper gets good experimental results by using the experimental device to separate fly ash. We can find that the compound tnboelectrostatic separator is a new technique, which can be widely used in mineral beneficiation, materials purification, food process, etc.1. Conductor particle has big permittivity and high energy level, it is easy polarization and loses outer surface's electrons; Uonconductor particle has small permittivity and low energy level, it is hard polarization and easy gets electrons. While particles are tribocharged, conductor particles get positive charges, and uonconductor particles get negative charges.2. This paper researches the corona electrification mechanism. A corona discharge is produced when a high voltage is applied between two electrodes, one of which has small radius of curvature named the sharp electrode. The electric field causes an electric discharge in a limited region near the sharp electrode, at a voltage below the spark breakdown voltage of the gap. In the region close the sharp electrode the electric field is very high, exceeding the breakdown field of gas to produce electron/ion pair. Usually the sharp electrode is negative, then in the corona electric field positive charges quickly fly to the sharp electrode, and negative charges quickly fly to the positive electrode connected to earth. In the corona electric field both conductor and uonconductor get negative charges. A compound high voltage electric field of the compound triboelectrostatic separator is combined by 4 sharp electrodes and an electrostatic electrode. After particles get corona electrification, they will be affected by electrostatic field immediately. Conductors are influenced and absorbed to electrostatic electrode after quick discharging. But uonconductors are hard discharging, which are absorbed by roller of the positive electrode connected to earth. So conductor and uonconductor particles are separated in the compound high voltage electric field. The separation effect is strengthened by combining 4 sharp electrodes and the electrostatic electrodes. There are two separation theories, one is the Leavings Charge Separation Theory, another is the Steady Charge Separation Theory, this paper finds the first one fits for calculating particles' corona electrification, the second one fits for explaining particles charge and discharge in the corona electric field.3. This paper educes the equation for calculating conductor particles triboelectricity, in which includes tribocharge affected by an external electric field. The first time introduces the new research result of three American scientists who are Schein L.B., Laha M. and Novotny D., which about calculating uonconductor particles triboelectricity, and their theory points out that should think about in the low and high density limit. Analyzing experimental results, the triboelectricity of uonconductor quartz particles is far lesser than conductor phosphate particles' at the same test condition, so it is right that use different equation to calculate conductor and uonconductor particles' triboelectricity. This paper also find uonconductor quartz particles' polarity can't be change with the external electric field's polarity change, quartz particles' triboelectricity is always negative. But conductor phosphate particles' polarity can be change with the external electric field's polarity change for the first time.4. For calculating collision time duration and triboelectricity between particles and roller of the positive electrode connected to earth, this paper uses Newton's second law, Hertzian theory and an electronic theory model of tribocharge developed by Anderson J.H to educe two equations for the first time. The particle specific charge is determined by the work function difference between the particle and roller, particle diameter, and impact velocity. It is clear that the particle specific charge increases linearly with the increase of the work function difference and exponentially decreases with the radius of particles and impact speed.5. This paper introduces the equation of particle charge decay, studies a charged particle affected by some forces in the corona electric field, analyses of the force condition of conductor, semiconductor and uonconductor to be separated three products, supports theory for setting up a mathematical model and manufacturing an experimental device of the compound triboelectrostatic separator.6. In order to design an experimental device of the compound triboelectrostatic separator, this paper analyses the length, obliquity and materials of the tribocharge device. Thinks triboelectricity affected by particles temperature, how to design the external electric field of the tribocharge device, how many sharp electrodes, and how long the distance between two electrodes. The compound high voltage electric field of the compound triboelectrostatic separator is combined by 4 shutter or sheet sharp electrodes and an electrostatic electrode.7. Studying three charge courses which are tribocharge, impact charge between particles and roller, and corona electrification in the compound triboelectrostatic separator. While particles are affected by Coulomb force, using particles leavings charges of three charge courses to set up a mathematical model of the compound triboelectrostatic separator. So we can find particles charges in the compound triboelectrostatic separator are more than conventional triboelectrostatic separators', the compound triboelectrostatic separator's separation effect will be improved. Using a particles charge measurement system including a Digital Charge Measurement and a Faraday Cage to measure particles charge. Experimental results show that the line of tribocharge, trendlines of corona electrification and tribocharge + corona electrification have linear relationship, which can prove the hypothesis of setting up the compound triboelectrostatic separator mathematical model is right.8. The experimental result illuminates that between the triboelectricity and frequency of the tribocharge device vibration does not have linear relationship. When the frequency is low, the triboelectricity is small. With the frequency increases, the triboelectricity also increases. The triboelectricity reaches maximum that is 39×10^-9C/g when the frequency at 400Hz. But the triboelectricity decreases to 34×10^-9C/g when the frequency at 450Hz. This result can explain with the frequency increases, particles tribocharge time in the tribocharge device is decreased, so let triboelectricity reduces. At the same time can be found that the triboelectricity is small when E_F = 0 of the external electric field. Big triboelectricity will be get by using big intensity of the external electric field.9. Using the experimental device of the compound triboelectrostatic separator to separate fly ash. Fly ash is an important mineral resource. Its handling, processing, and ultimate use or disposal are important to the utility industry and our environment. In the last decade, commercial interest in removing unburned carbon from fly ash to get two products which are unburned carbon and fly ash of low LOI. Fly ash of low LOI can be used to produce cement and water reduce agent, which has great value and very important for the construction industry. For separating fly ash and other minerals has stimulated research and development of triboelectrostatic separation technology. The triboelectrostatic separation, a dry processing technology, is one of the best technologies for processing fly ash due to its fine particle size and dry state.10. Fly ash is a crystal mineral containing quartz, magnetite, magnesia, calcium oxide, anhydrite, etc.; the non-crystal mineral contains vitreous body, unformed carbon, hypo-limonite, etc. The fly ash comes from American Crystal River power station, which more than 90% particles size is between 45μm to 106μm. unburned carbon particles' resistance rate is about 10⁴～10⁵Ω·cm, which are conductors; fly ash particles' resistance rate is about 10¹¹ï½ž10¹²Î©Â·cm , which are nonconductors. So unburned carbon particles and fly ash particles have great different electric properties, which is important for separating fly ash by the compound triboelectrostatic separator.11. The result using the experimental device of the compound triboelectrostatic separator to separate fly ash for the first time, which shows that with the electric intensity of the tribocharge device external electric field and the voltage of the compound electric field increases, separation effects are better and better. With feed rate and relative humidity decrease, the separation effects are better and better. Such results accord with the forecast of the compound triboelectrostatic separator mathematical model. The result of testing the relationship between separation effect and roller rotating speed, which shows the separation effect when the roller rotating speed at 35 rpm is better than that when the roller rotating speed at 40 rpm, it is just to prove that the particle specific charge exponentially decreases with the radius of particles and impact speed.12. From original state fly ash, using the experimental device of the compound triboelectrostatic separator we can get fly ash particles of low LOI with the LOI at 8.34% and the yield at 56.67%, unburned carbon particles with the LOI at 27.37% and the yield at 16.84%.