Ultrasonic Assisted Flotation Of Coal Gasification Fine Slag For Carbon-Ash Separation And Water Migration Characteristics

Coal gasification is the basis of high value utilization of coal,and also an important way to realize efficient and clean transformation of coal resources.The market scale of Coal gasification technology in China ranks first in the world,and a large amount of Coal gasification fine slag is generated every year.The gasification fine slag is difficult to dehydrate and the two components of carbon and ash are closely cross-linked,so the utilization of resources is relatively difficult.Currently,the main disposal methods are stacking and landfilling,which will not only threaten the ecological environment,but also leading to serious pollution.In this thesis,the causes of dehydration and carbon-ash separation difficulties were revealed by comparing and analyzing the physical and chemical properties of two kinds of entrained flow gasification fine slags.The separation of carbon ash components was realized by two foam flotation methods,and the flotation quality improvement process was enhanced by ultrasonic field assisted.At the same time,combined with the physical and chemical characteristics of carbon residue and tail ash,the mechanism of ultrasonic assisted separation process was studied.On the foundation of clarifying the water migration characteristics of carbon and ash components,the ceramic membrane filter plate was used to realize efficient vacuum dehydration of two components,and the law of water migration is expounded respective.The problem of poor direct dehydration effect of gasification fine slag was effectively improved,and the technical route of foam flotation of gasification fine slag-carbon ash separation-vacuum dehydration was formed,which will contribute to the realization of high-quality and high-value resource utilization of gasification fine slag.Relevant studies have shown that:（1）The physical and chemical properties of gasification fine slag make it have poor floatability and strong water occurrence ability,which intensifies the difficulty of carbon-ash separation and dehydration.In this thesis,the fine slag of Ningmei and Yankuang coal used in the experiment shows the particle characteristics of fine particle size and flourishing pore structure.In terms of microscopic morphology,the cross-linking state between residual carbon and mineral ash particles in fine slag is complex,and a large amount of hydrophilic Si O₂ exists in residual carbon pores,which has a certain synergistic water-holding effect.Compared with the raw coal,the content of hydrophilic oxygen-containing groups and chemical bonds on the surface of fine slag after high temperature gasification reaction is increased,resulting in poor surface hydrophobicity,which has an adverse effect on the flotation separation process.（2）The difference of particle size distribution and carbon-ash cross-linking state of gasification fine slag will significantly affect the difficulty of carbon-ash separation.Ultrasonic assisted with a certain power can improve the quality improvement effect of flotation of difficult fine slag in terms of particle and surface properties.Compared with Yankuang fine slag,the fine particle size and high content of free mineral ash particles of Ningmei fine slag make the fixed carbon content of concentrate reach55.25%under conventional flotation conditions,which can be directly used as fuel.Concentrate fixed carbon content was only 33.66%under the conventional flotation condition of Yankuang fine slag,but when pulsed ultrasonic assisted flotation with450 W power was applied,concentrate fixed carbon content was increased by 12.08%and ash content was reduced by 12.86%compared with conventional flotation,which effectively enhanced the flotation quality improvement process.But ultrasonic power had the best range of action.The flotation concentrate will have serious ash entrainment under high ultrasonic power,which is not conducive to carbon-ash separation.（3）The dewatering ability of the carbon ash component obtained by flotation is improved in different degrees compared with the original fine slag gasification,and the comprehensive water content of filter cake obtained from the separation-dehydration process is significantly reduced.Compared with the original gasification fine slag,the stretching vibration peak of hydrophobic functional groups derived from hydrocarbon flotation agents can be observed by the infrared spectrum of the flotation residual carbon.At the same time,as the ash content of hydrophilic quartz is reduced,the surface hydrophilic point is significantly reduced,which reduces the water holding capacity.At the same time,because the flotation residual carbon stripped away some of the mineral ash particles blocked in the pore entrance,the water-saturated pore information based on LF-NMR showed that the proportion of water molecules in the macropore was significantly increased,which reduced the difficulty of water migration,and thus had a positive impact on the dehydration process.The micro-morphology of flotation tail ash is spherical particles with relatively smooth surface and less pore distribution,which is not conducive to the occurrence of water,so the difficulty of water removal is relatively low.Under the same vacuum dewatering conditions of ceramic membrane filter plate,the moisture content of each material showed a nonlinear decreasing trend with the action time of vacuum force field.The weighted moisture content of carbon residue and tail ash filter cake was less than 35%,while that of original filter cake was more than 40%.It can be concluded that the separation-dehydration process can recover water resources,recycle carbon-ash components,reduce transportation and land cost,and reduce the damage to the ecological environment,so as to produce considerable environmental and economic benefits.This thesis has 44 figures,31 tables and 137 references.