| In recent years,with the increase of environmental protection,clean and efficient utilization of coal is the goal of long-term development,Ultra Clean Coal is a kind of clean coal with little mineral content and high added value.It is used to prepare coal-based high-purity electrode,ultra clean coal water slurry and high-quality coal-based carbon materials.When Ultra Clean Coal is used as fuel,carbon and nitrogen oxides can achieve zero emissions by special process conditions.It is a very good clean fuel,which has practical significance to reduce air pollution.In the future,it is imperative to develop Ultra Clean Coal,no matter the large demand for coal-based materials or the high-quality environmental and ecological requirements.Therefore,it is urgent to find an effective method to prepare Ultra Clean Coal.At present,the preparation methods of Ultra Clean Coal mainly include chemical method,physical method and physical chemical method.In this paper,different methods are reviewed.It is found that acid and alkali corrode the equipment seriously and destroy the structure of coal matrix in the process of chemical preparation of Ultra Clean Coal.In addition,the energy consumption in the preparation process is very high.In this paper,through the review of different methods,it is found that the acid and alkali corrode equipment seriously and damage to the structure of coal matrix in the process of chemical preparation of ultra clean coal,the process is a high energy consumption.The ash content of Ultra Clean Coal prepared is higher by physical method.Compared with other methods,it is found that Ultra Clean Coal prepared by selective agglomeration method has certain advantages,but the disadvantage of this method is low yield,which limits the development of Ultra Clean Coal prepared.The problem to be solved is how to improve the yield of clean coal and reduce the ash content of clean coal in the selective agglomeration process,so as to expand the advantages of this process for the preparation of ultra clean coal.In order to study the process conditions of Ultra Clean Coal by selective agglomeration,the anthracite samples from Taixi,Yangquan and Dayugou were selected as the research objects,and the coal particle size was ground to less than 15 ?m by ball mill.The effect of the grinding time,collector(kerosene),frother(dioctyl alcohol),inorganic electrolyte(aluminum chloride,ferric sulfate,ferric chloride),inorganic polymer electrolyte(polyaluminium chloride,polymeric ferric sulfate,polymeric ferric chloride,polysilicate aluminum),stirring strength,dispersant and modifier(acetic acid,propionic acid,butyric acid,maleic acid,fumaric acid and ethylenediamine)on the ash content and yield of clean coal were investigated by selective agglomeration.The reaction surface method was used to optimize the selective agglomeration process,and the orthogonal design was used to optimize the acid-base coupling process.Based on DLVO theory,the mechanism of the interaction between coal and minerals was discussed with inorganic polymer electrolyte in the selective agglomeration.The structure of anthracite was constructed by Materials Studio software,and the kinetic simulation of kerosene/water/anthracite system was carried out.The surface properties and composition of coal samples were analyzed by means of X-ray diffractometer(XRD),X-ray fluorescence spectrometer(XRF),Fourier transform infrared spectrometer(FTIR)and Scanning point microscope X-ray microanalyzer(SEM-EDS),The macerals of coal and vitrinite reflectance of coal were measured by microscope.The zeta potential value of coal and mineral surface was measured by Zeta potential meter.The contact angle tester measures the contact angle between coal and minerals.The moisture and ash content of coal were analyzed by industrial analyzer.The particle size of coal was measured by laser particle size analyzer.The following conclusions are obtained by the analysis of the above methods.1.The effects of aluminum chloride,polyaluminium chloride with 26%mass fraction and 29%mass fraction on the separation were compared.The results show that under the same dosage of agent,the yield of flotation clean coal increased by 19.38%and the ash content of clean coal reduced by 0.18%.Adding 26%PAC was better than 29%PAC.When the dosage of kerosene was 1.19 kg·t-1,the dosage of sec-octanol was 0.40 kg·t-1,the dosage of PAC was 50 g·t-1,the content of ultra clean coal ash was 0.64%,and the yield of clean coal was 68.91%.The evaluation results of M-curve are consistent with the experimental results.Polyaluminium chloride and aluminum chloride can promote the removal of minerals from coal,and the separation effect of polyaluminium chloride was better than that of aluminum chloride at low dosage.2.The effect of separation effect of polymerized ferric sulfate and ferric sulfate was compared.In addition,the effects of the dosage of polymerized ferric sulfate and mixture of polymerized ferric sulfate and polyaluminium chloride on the ash content and yield of clean coal were also investigated.The results show that the separation effect of polymeric ferric sulfate was better than that of ferric sulfate at the same dosage.The separation effect of adding polyaluminium chloride with the dosage of 29w%polyaluminium sulfate(PSB)was better than that 26w%polyaluminium sulfate(PSA).The results of M-curve evaluation are consistent with the experimental results.It is concluded that the separation effect of adding polymeric ferric sulfate was better than that of ferric sulfate,and the separation effect of adding PSB was better than that of PSA.Inorganic polymer electrolytes(polyaluminium chloride,polymeric ferric sulfate and mixtures)can be used to prepare Ultra Clean Coal by selective agglomeration.When the dosage of kerosene was 1.19kg/t,the amount of sec-octanol was 0.4kg·t-1 and the grinding time was 30min,the dosage of PSB was 287.87 g·t-1,the content of ultra pure coal ash was 0.63%,and the yield of clean coal was 66.84%.3.The zeta potential of coal increased from-28.7mV to-20.63mv with the increase of polyaluminium chloride.The ash content of clean coal increased from 0.64%to 0.84%.With the increase of the amount of polymerized ferric sulfate,the zeta potential decreased first and then increased,from-21.4 mV to-25.4 mV and then to-14.3 mV The ash content of clean coal first decreased from 0.76%to 0.64%and then increased to 0.92%.The results show that the change trend of ash content of clean coal is consistent with that of electric potential.The results show that polyaluminium chloride can hydrolyze into various metastable forms of polyhydroxy,including positive ions such as Al(OH)2+,Al(OH)2+,Al3+,Al2(OH)24+,Al3(OH)25+and Al13(OH)27+,and cations such as Fe3+ and FeOH2+will be produced in the solution of polymeric ferric sulfate.These positive charges neutralize the negative charges on the surface of coal and inorganic minerals,resulting in the double electric layer compression of coal and inorganic minerals,agglomeration of mineral particles in coal,reducing the cover of inorganic minerals on the surface of coal particles,thus reducing the ash content of clean coal.At the same time,the net trapping and adsorption of inorganic polymer electrolyte were proposed,which complemented the limitation of DLVO theory.4.The effects of the dosage of dispersant(sodium hexametaphosphate),kerosene,organic regulators(propionic acid,butyric acid,maleic acid,fumaric acid and ethylenediaminetetraacetic acid)and stirring speed on the ash content and yield of fine coal in Taixi Coal were studied.The results show that dispersant can be used in selective agglomeration to reduce Ultra Clean Coal ash.It is found that acetic acid and propionic acid can improve the yield of Ultra Clean Coal without increasing the ash content of Ultra Clean Coal.The yield of clean coal increased by 19.42%and the ash content of raw coal decreased from 2.58%to 0.65%.When the dosage of sodium hexametaphosphate,stirring speed and kerosene were 1.0 kg·t-1,1962rpm,1.19 kg·t-1 respectively,the Ultra Clean Coal prepared by the selective agglomeration method was the Optimal,the ash content of clean coal was 0.53%,and the yield of clean coal can reach 40.57%.By changing System of flotation reagents,ultra clean coal with lower ash content can be obtained,and the ash content of Ultra Clean Coal was 0.41%.An effective method was put forward to increase the production of ultra pure coal after the ash reduction and dispersion,and a micro bubble flotation method was also obtained,which can be used in the separation of fine coal.Furthermore,a new process for the preparation of Ultra Clean Coal by in situselective dispersed micro agglomerations was proposed.The feasibility of this technology was proved theoretically.5.Taking polymeric ferric sulfate as an example,response surface method was used to optimize the process conditions of selective agglomeration.In view of this process,the dynamic equation of staged flotation was put forward.The regression equations of three indexes of clean coal yield,clean coal ash and clean coal kinetics constant are established,which provide theoretical basis and technical parameters for practical production.A new technology of selective agglomerate acid alkali coupling deashing was put forward.The process conditions were determined as follows:the acid concentration was 1.2mol/l,the acid amount was 45ml,the temperature was 80?,the reaction time was 60min,the coal amount was 10g,the alkali concentration was 5%,the alkali leaching time was 60min,the alkali leaching temperature was 200?,the ash content was the lowest and the deashing effect was the optimal.The ash content decreased from 0.41%to 0.09%.The ash content of Ultra Clean Coal obtained has reached the level of Ash Free Coal by the process of selective agglomerating acid-base coupling deashing.6.The mechanism of the application of inorganic polymer electrolyte in selective agglomerations was clarified,and the theory of preparing Ultra Clean Coal by dispersion and ash reduction before agglomerating to increase production is put forward.The measurement of contact angle shows that the hydrophobicity of coal surface is enhanced by adding polyaluminium chloride,the surface difference between coal and artificial mineral increased,the results show that polyaluminium chloride is helpful to the separation of coal and inorganic minerals.According to the calculation of DLVO theory,it is indicated that polyaluminium chloride can promote the separation of coal and montmorillonite.It loses selectivity to the separation of coal and hematite.The results show that the agglomerate of polymerized ferric sulfate to coal increases the yield of clean coal.With the addition of polymerized ferric sulfate,the repulsion between quartz and hematite decreases first and then increases as the distance between particles approaches.The results show that polymerized ferric sulfate is selective for the separation of quartz and hematite.The results of extended DLVO theory show that the agglomeration effect increases with the addition of polyaluminium chloride and aluminium chloride,which is consistent with the results of particle size analysis.7.The anthracite and kerosene models were established by MS software,and the energy changes of kerosene/water/coal system were simulated.The results show that the smaller the roughness is,the more hydrophobic the surface is.The hydrophobicity of a small amount of kerosene is greater than that of a large amount of kerosene.The hydrophobicity of the modifier is propionic acid>acetic acid>butyric acid.The results are consistent with the experimental values.The order of interaction between acid modifier and coal molecule is small kerosene>large kerosene;propionic acid>acetic acid>butyric acid;20 propionic acid molecule>40 propionic acid molecule.The approximate order of MSD curve slope of kerosene molecule is propionic acid/small kerosene>acetic acid/small kerosene>butyric acid/small kerosene>small kerosene>large kerosene,which indicates that the order of adsorption rate of three acid regulators is propionic acid>acetic acid>butyric acid.The order of interaction energy was from strong to weak:butyric acid>acetic acid>propionic acid,20 propionic acid molecule>40 propionic acid molecule.Compared with the experimental results,the weak interaction energy is beneficial to flotation.Spoelstra oil agglomeration model is introduced.According to the model,the corresponding coefficients are calculated by using MATLAB software to obtain the oil quantity change model during the wetting process of oil and coal. |
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