Study On The Tribocharging Mechanism And Separation Of Macerals In Low-rank Coal

Currently,coal direct liquefaction technology winning high attention for its potential in alleviating the pressure of the petroleum resources and atmospheric pollution in China.The key relative to superior of coal liquefaction is that the distribution of active component vitrinite and inert component inertinite in raw coal,and triboelectrostatic beneficiation is an effective dry method for fine macerals.In this presentation,vitrinite and inertinite with high purity were extracted from liquefaction demonstration low-rank coal of Shenhua corporation as targeted subject.Modern precision characterization instruments were applied to obtain the microstructural information of macerals and their tribocharging difference mechanism was revealed.Electrical parameters of macerals were measured,its characteristics and influence mechanism on macerals triboelectrostatic separation were also analyzed.Tribocharging characteristics of macerals were investigated and the optimum tribocharging medium was sought.The triboelectrostatic enrichement and separation experiments were finally performed,previous mechanism analyses were verified and the separation process was improved.The main conclusions are as follows:Tribocharging difference mechanism of macerals with high purity was revealed by their surface microcosmic information characterization.Atomic force microscope(AFM)of macerals showed that surface potential of inertinite is 0.42 v higher than that of vitrinite,which indicated that inertinite easily charges negative while vitrinite gets positive charge in triboelectrostatic separation.The high level of electronegative groups in inertinite displayed by Fourier transform infrared spectroscopy(FTIR)quantitative analyses,and the higher degree of graphitization,tighter internal structure and stronger electrons binding ability in inertinite revealed by X-ray diffraction spectrogram(XRD)characterization both suppoting the higher surface potential.FTIR and X-ray photoelecgon spectroscopy(XPS)both illustrated that macerals have similar content in hydrophobic groups while inertinite has more hydrophilic functional groups,which stated that inertinite should be more susceptible to relative humidity in separation process.Macerals' triboelectrostatic separation behabiors were predicted based on the investigation of their two electrical parameters(resistivity and relative dielectric constant)characteristics and its influence mechanism analyses.Their resistivity both decreased with increasing temperature and declined as the relative humidity growing on account of their natural insulativity,the relative humidity is the more powerful factor in environment.Whatever the circumstances,the inertinite always has higher resistivity than vitrinite in test with sample size below 200 mesh.On the basis of above description,an anticipation was made that inertinite could keeps the surface charge better than vitrinite in the transportation part after they received their charges and before they enter the high voltage electrostatic field.Two maceral both still got relatively higher resistivity and their difference shrank for the better electrons holding ability of active component vitrinite in the environment with high temperature and low relative humidity.The relative dielectric constant of macerals both going down as temperature increasing and increased with relative humidity,the relative humidty is the prior element as well.Inertinite always with higher relative dielectric constant than vitrinite under particle size below 200 mesh.Therefore,it is proposed that path of inertinite with negative charge to the positive plate suffered stronger interference for its intense polarizability while the vitrinite' route would be more stable with weak polarizability in the sorting stage after their transportation.The relative dielectric constant of vitrinite and inertinite and their difference all decresed for the further declining polarization performance of active component vitrinite with higher temperature and lower relative humidity.Reletive humidty plays a more important role in this two environmental factors in macerals' resistivity and relative dielectric constant,so the relative humidity control is needed in both transportion and separation stages.Tribocharging characteristics of macerals with eight tested friction media were measured in order to the perfect one for tribo-charger,the tribocharging characteristics between vitrinite and inertinite was tested as well.The absolute values of charge to mass ratio on macerals with tested materials were all increased with temperature and dropped as growing relative humidity.Preference ranking of eight media is as follows: polyamide(PA)>copper>aluminum>stainless steel>(polyethylene terephthalate(PET)> polyethylene(PE)> polyvinyl chloride(PVC)> silica gel).Inertinite always charged negatively after tribocharging with fixated vitrinite and performed well.Characteristics and rules of tribocharging between two macerals in coordination with their test on media.Ttriboelectrostatic separation and enrichment experiments of macerals in low-rank coal were performed,and second separation stage was established for the enrichment strengthening.As the above predictions,vitrinite was prone to charge positively and enriched in positive product whereas the inertinite easily got negative charge and gathered in nefative collection.The enrichment of macerals was in accordance with the ash remove process of low-rank coal.Content and recovery of vitrinite both rose with decreasing ash content in collection,and the content and recovery of inertinite were both increased with ash content.The recovery of inertinite was always higher than vitrinite under same sorting condition.Macerals' recovery increased with temperature and decreased with rising relative humidity.The impact of temperature on macerals enrichment results was stronger than relative humidity.The order of system operating conditions' influence on macerals separation is as follows: sorting voltage>feeding rate>transport volume.Compared with environmental and system operating conditions,the second stage triboelectrostatic separation had the best macerals enrichment effect(content of vitrinite and inertinite increased 13.99% and 12.88% respectively).The second stage products of negative plate and positive plate could respectively be the concentrate of vitrinite and inertinite.This dissertation contains 42 figures,22 tables and 166 references.