Dispersion Regulation And Stability Mechanism Of Low-rank High-ash Coal Slurry

The thesis aims at designing and synthesizing dispersan for slime of low-rank,high ash, and fine granularity. From the view of solution and interface chemistry, theeffect and mechanisms of the minerals on the slurry properties were studied.Adsorption kinetics and thermodynamics characteristics of dispersant and slime areinvestigated, and the surface adsorption mechanism of action of prepared dispersantson slime is analysed. According to the factors of dispersant, solution environment,coal to regulate coal slurry dispersed system, and to improve the performance of thecoal slime water slurry(CSWS).According to quantum chemical computational simulation, CSWS dispersant ismolecular structure designed, anionic dispersing agent of the carboxylic acid salts(SAF-A) is screened and consequently synthesized. The effect of SAF-Adispersant onlow-rank coal is studied. The results showed that SAF-A dispersant can effectivelycombined with low-rank coal and the adverse effects of mineral ions to the slurry caneffectively inhibited. The pulping concentration can increase by2.5%and exhibitgood fluidity and stability under the condition that the weight of the dispersant in thereaction all accounting60%of the weight of traditional naphthalene-based(NLS) andwood-based(LS) dispersant.Based on theories and methods of colloid and solution chemistry, the principalsof insoluble minerals and mineral ion pulp on CSWS are researched. The resultsshowed that when the insoluble minerals and slime adsorbed the dispersant, theelectronegativity will be greatly enhanced. The thickness of hydration film willincreased and the slurry were more stabile and liquidity. With DLVO theory adopted,the electrostatic interaction of coal particles and the electrostatic interaction of coalwith calcite, quartz increases with grain spacing, the coal particles and the interfacebetween the coal and various minerals are attractive polarity role; in the same distance,the minerals in coal can improve the total interaction between the particles in thedispersion system, appearing mutual repulsion, helping to restrain particle aggregationand can improve stability of the slurry. The presence of a mineral ion is able toconsume the dispersant in the dispersion system. Under the condition of the samemineral ions concentration, the consumption of SAF-A dispersant by the mineral ionsin dispersion system reduced about10%of the original quantity comparing with theconsumption of lignin sulfonate, with showing the strong anti-mineral ion capacity. Mineral ions are easy to occur complex effects with SAF-A dispersant, weakening theeffect of the SAF-A; they can also compress coal particles in the surface electric doublelayer structure, agglomerating the coal particles easily, increasing the viscosity of theslurry. The mineral ion interactions has a little effect on the consumption of thedispersant and the thickness of the electrical double layer of the coal particles while agreat influence on the coordination between mineral ions and dispersant.The SAF-A dispersant in the solid/liquid interface of the coal slurry were studiedon the adsorption kinetic, adsorption thermodynamics and determined category, actingforce and form of adsorption. The studies found that adsorption was in line withsecond-order equation in different temperature, pH and ionic strength, the adsorptionrate is increased with temperature, while the pH value and ionic strength increases, theadsorption rate decreases. The adsorption behavior is in line with the Langmuir andthe Freundlich equation and is also the spontaneous exothermic process. There areelectrostatic, hydrophobic and hydrogen adsorption in this process.SAF-A dispersant, solution environment, coal quality modification conditionswere studied to establish the suitable prediction model for low-rank high ash slimepulp and pulping performance. The results showed that, with the complex ratio ofSAF-A/LS decreasing, slurry concentration was first increased and then decreased.The slurry performance was best at the complex ratio of7:3. The hydrogen bondinginteraction between SAF-A and coal particles was changed with slurry temperature.The slurry performance first increased and then decreased when the slurrytemperature increased. The slime surface electronegativity decreased with solution pHvalue increased and the electrostatic repulsion between particles increased conducingto the preparation of high performance slime CSWS. Oxygen-containing functionalgroups, internal water content and minerals onthe surface of slime are the key factorsto affect the slime pulp. Temperature less than400℃can effectively reduce theoxygen content and the inner water content in a short time, significantly increasingslurry concentration. Coal slime flotation dropping ash can enhance the combustibleconcentration in the coal slurry, reduce mineral ions concentration, increase theeffective action of SAF-Adispersant and improve the stability of the slurry.