Experimental Study Of Hydrated Magnesium Slag As Desulfurizer

Magnesium reduced slag comes from the magnesium-smelting plant. The slag is treated as waste being dumped. Fly ash comes from coal combustion process. Small of them can be used for building materials, but most of them are still deposited in the ash field. Drawing lessons from lime and fly ash’s hydration reaction, the magnesium slag are modified as desulfurizer by the fly ash’s Pozzolanic reaction in this thesis. At the same time, the addictive effects on hydration process are also studied.With the help of ICP-AES analyzer and XRD analyzer, the thesis identifies the element composition and the phase composition of magnesium slag and fly ash. The hydration device of the magnesium slag/fly ash is designed and constructed by considering parameters such as the mass ratio of fly ash/magnesium slag, hydration time and hydration temperature. The different hydration desulfurizer’s performances are studied in the desulfurization system which is constructed with TGA as the main instrument. The effects of desulfurization temperature on desulfurizer performance are also studied. Comparing the phase composition changes, the related reaction mechanisms are discussed. In order to explore the hydration desulfurizer’s microscopic characteristics, the specific surface and porosity are investigated by gas adsorption instrument, and the micro-topography is studied by SEM. The research of this thesis has achieved the following results:1) The hydration reaction composition of the magnesium slag is Ca2Si04, whose quality content reaches to90.16%. The corresponding compositions of the fly ash are Al4SiO8and SiO2. The desulfurization composition of hydration desulfurizer are [(CaO)(SiO2)2(Al2O3)(H2O)4] and [(CaO)3(Al2O3)(H2O)x].2) The optimal temperature of desulfurization reaction is920℃in the experimental range, which accord with the circulating fluidized bed boiler furnace temperature.3) The optimal parameters of hydration desulfurizer are MR=20, TH=90℃and tH=8h in this thesis. The calcium conversion rate of the best hydration desulfurizer is improved from3.36%to36.70%.4) Most efficient additive in hydration reaction is oxalic acid, the calcium conversion rate reaches to73.7%by adding0.5%oxalic acid. Adding sodium hydroxide can also enhance the desulfurizer’s performance, the calcium conversion rate reaches to55.54%by adding3.0%sodium hydroxide.5) After hydration of magnesium slag and fly ash, the specific surface area is3.86times more than unhydrated mixtures, and the pore volume is2.16times more than unhydrated mixtures. The performance of hydration desulfurizer is enhanced mainly due to mesoporous being improved.6) After hydration reaction, the outer surface of the fly ash particles is covered by the desulfurizer layer, and internal of fly ash particles is of cavernous porosity. The desulfurization reactions become more thoroughly because sulfur dioxide spread from two directions in the outer and inner surface during the desulfurization reaction.