Fundamental Research On Modification Process Of Direct Fiber-Forming By Blast Furnace Molten Slag

Aimed at the situation of lower slag sensible heat recovery, large water consumption and environmental pollution and low utilization of high value-added in water quench process, it can change the condition when using blast furnace slag with proper amount of modification agent to produce the slag wool directly which can use the slag sensible heat recovery efficiently and high utilization of high value-added and no waster consumption and not produce toxic gas such as H2S and SO2. It also can bring large economic benefit and social benefit. But there is less fundamental research on the modification of molten slag, crystallization control and heat-mass transfer so that the direct fiber-forming process can not realize the industrialization application.In this paper, based on method of the thermodynamic calculation simulation, microscopic analysis, hot state experiments and half industrial test, the crystallization behavior, viscosity behavior, modification agent properties, crystallization control mechanism and the heat exchange rule of molten slag were studied, and the slag and modification agent properties were analyzed. Meanwhile, the mathematical models of the conditioning agent dissolution and diffusion coefficient were found. A new production method of slag wool with blast furnace molten slag directly injection was proposed and the half industrial test in the fiber-forming process was done. It supplied the theoretical support for the modification process of direct fiber-forming by blast furnace molten slag.The aim was proposed from the analysis of slag and modification agent's elementary composition, mineral characteristics and viscosity behavior combined with the experience index of producing slag wool. According to the mineral phase exchange characteristics and crystallization thermodynamics calculation in SiO2-CaO-MgO-Al2O3 quaternary melt system, the mineral start crystallization temperature and precipitation proportion and influence with each other were studied; the minimum mineral crystallization area of slag modified by iron tailings was located in eutectic horizontal of akermanite and gehlenite or akermanite and pseudowollastonite and gehlenite. The minimum mineral crystallization area of slag modified by fly ash was situated in the eutectic point of gehlenite and akermanite and spinel or the eutectic point of kamaishilite and akermanite and spinel or the narrow eutectic horizontal line of akermanite and gehlenite.The physical and chemical properties of molten slag were studied which was modified by iron tailings and fly ash basing on the modification slag crystallization behavior. The results showed that the Mk?M? and K/O rose and hydrogen ion index gradually reduced with adding ratio of modification agent increasing. Meanwhile, the appropriate fiber-forming temperature interval became wider. The melting temperature was decreasing before increasing. When the Mk was greater than 1.4, the melting temperature was about 1300? and it also became sticky. The crystallization behavior became lower in cooling process, glass phase increased and the amount of mineral reduced. When Mk was greater than 1.2, there was no mineral precipitation and formed the uniform glass phase. When the modification agent was iron tailings and fly ash, the appropriate acidity coefficient of fiber-forming was between 1.2 and 1.4. When the modification agent was mixture, the appropriate acidity coefficient of fiber-forming was between 1.3 and 1.4. Therefore, the result showed that the best modification agent was iron tailings; the mixture ranked the second, and the fly ash was the last.The effect on the technological condition and various chemical composition to slag's crystallization was studied. The results was shown that it was difficult to form uniform glass phase entirely which was only controlled by slag's crystallization behavior with technological condition. The effect on the crystallization behavior of slag was studied and the crystallization direction was confirmed by the equilibrium solidification modules of FactSage thermodynamic software and Sheil-Cooling module calculation simulation and hot simulation experiment. When the basicity was between 1.1 and 0.8, the start crystallization temperature decreased and the precipitation amount reduced and the glass phase content increased and the granularity of mellilite became larger with basicity increasing. While as the cooling intensity increasing, the mellilite mineral and spinel mineral leucite could not precipitate and garnet disappeared. Meanwhile, it can promote the anorthite and pyroxene group precipitate and the wollastonite group and olivine started to precipitate. When the content of Al2O3 was between 14.0% and 17.5%, with the content increasing, the start crystallization temperature rose slightly. The precipitation amount reduced slightly. The granularity of mellilite became thinner. However, as the cooling intensity increasing, the mellilite and spinel mineral leucite was hard to precipitate and the garnet disappeared. It also could promote the pyroxene group precipitate. When the MgO content was between 9.0% and 11.0%, the start crystallization temperature and precipitated amount had no obvious change. When the cooling temperature was increased, the precipitation amount reduced slightly and the granularity of mellilite became larger. It restrained the anorthite and pyroxene group precipitation and garnet disappeared. The wollastonite and olivine started to precipitate.The heat-mass transfer discipline of modified slag was studied. The mathematical model of molten time in modification process and SiO2 molecular diffusion coefficient was found which could confirm the adding modification agent style and granularity. It was shown that the adding style could choose contact slag directly when the radius of modification agent particles was less than the critical value. When the radium value was greater than critical value, it preferred the upper part to contact slag. It could shorten the melting time by using the smaller particles of modification agent. Above all, the heat-mass transfer discipline was further studied. It explored the rule of modification agent ratio with slag flowing properties and temperature tendency of slag and inner link of supplement energy. It was shown the diagrams of adding ratio to molten temperature and flowing temperature and supplement energy.Finally, the raw material with modified slag whose Mk was between 1.2 and 1.4 could be added to have the slag wool by half industrial test with modification agent injection direct. The diameter of slag wool was less than 3?m and the slag ball's content was lower than 5.14% and cotton rate was greater than 70%. The quality was better than national standard.