Study On Enhanced Dewatering Performance Of Coal Gasification Fine Slag By Compound Filter And Process Regulation Research

Coal gasification fine slag is a solid waste produced in the process of coal gasification,and the collected particles exist in the form of black water.An efficient dewatering process will reduce the cost of filter cake treatment and bring considerable economic and environmental benefits to the coal gasification industry.The dewatering performance of gasification fines can be improved by adding filtering aids,but currently there are disadvantages of low dewatering efficiency and difficulty in obtaining low water content filter cake.Therefore,the construction of a suitable filter system is the key problem to be solved in the current process of improving the dewatering of gasification fine slag,and the main work of this thesis is as follows:In this study,the basic physicochemical properties and the state of water content of the coal gasification fine slag were investigated with the help of X-ray diffraction（XRD）,scanning electron microscopy（SEM）,Fourier transform infrared spectroscopy（FTIR）,mercury intrusion porosimetry（MIP）and low-field nuclear magnetic resonance（¹HNMR）.The pore structure is mainly mesoporous and macropore,with the porosity up to 68.51%.The type of water in the coal gasification fine slag is mainly bound water in mesopore and macropore,and the water molecules tend to be stored in smaller pores after dehydration,which makes further dehydration more difficult.On this basis,the effects of cationic surfactants and anionic surfactants on the vacuum dewatering efficiency of gasified fine slag were explored and their mechanisms of action were explored.It was found that the cationic surfactants reduced the electrostatic repulsion between particles in the system under the effect of electro-neutralization and significantly reduced the water content of the filter cake,and the dodecyl trimethyl ammonium bromide（DTAB）and benzyl trimethyl ammonium chloride（TMBAC）could reduce the water content by 7.14%and 7.99%,respectively,at a dosing rate of 500 g/t;the anionic surfactants increased the water content of the filter cake,which may be related to the hydrophilic group of sulfonic acid contained in the molecules of sodium dodecyl sulfate（SDS）and sodium dodecyl benzene sulfonate（SDBS）and the increased negative charge of the solution.In addition,changes in the hydroxyl functional group explained the increased dewatering rate of all four agents,which was related to the decrease in the proportion of hydroxyl self-conjugated hydrogen bonds（OH-OH）in the hydroxyl absorption region.Secondly,based on the obtained surfactant system,organic polymer flocculants and inorganic flocculants were compounded with surfactant DTAB to investigate their effects on the dewatering process,and the mechanism of the action of the compound filtering aid was revealed by the test methods such as zeta potential analysis and suspension viscosity analysis.The results showed that the polyacrylamide polymer flocculants were more effective than the inorganic flocculant composite system,in which the non-ionic polyacrylamide（NPAM）significantly improved the flocculation and sedimentation characteristics of the suspension,and the NPAM-DTAB composite system could increase the dewatering rate by 195.61%at the highest,while the suspension viscosity increased due to its flocculation characteristics,which caused the water to be retained in the flocs,but Compared with the DTAB system,the water content of the filter cake only increased by 1.71%,the effect is better than that of surfactant systems;the combination of cationic polyacrylamide（CPAM）and inorganic flocculant ferric chloride（Fe Cl₃）with DTAB reduced the absolute value of the zeta potential of the system,and the CPAM-DTAB and Fe Cl₃-DTAB combination systems could increase the dewatering rate by 99.41%and 55.26%,respectively;unlike the other three composite systems,the combination of polymeric aluminum chloride（PAC）and DTAB significantly inhibited the dewatering process of coal gasification fine slag.Finally,the effects of feed concentration,filtration pressure and particle size composition on the dewatering process of coal gasification fine slag were explored,and their influence patterns were revealed by laser particle size test and viscosity test.The results showed that the best dewatering efficiency of coal gasification fine slag was obtained when the feed concentration was 100 g/L,the filtration pressure was 0.1 MPa and the grinding time was 9 min,and the dewatering efficiency of gasified slag increased and then decreased with the increase of feed concentration and grinding time,while the higher filtration pressure always brought higher solid-liquid separation effect.The thesis contains 38 figures,20 tables,and 116 references.