Transformation And Resourizable Formation Of Inorganic Composition In The Calcium-based Desulfurization Process

In order to improve our country's lower present status in the comprehensive utilization of desulfurization residues formed during the coal combustion, the ployphase reactions among inorganic minerals must be lucubrated and the residues' mineral constituents be controlled. With focus on the idea of resource-energy-environment integration, the desulfurization process transforming inorganic composition into resource and the control mechanism of the sulfur-contained mineral matters were investigated by the means of chemical analysis, XRD and SEM in this paper. The results are of important practical meaning and can instruct to efficiently solve coal-burning pollution problems.After various desufurizing systems were studied, the combustion temperature, Ca/S ratio, coal type and addictive have been found to have great influences on the mineral constituents of the residues. The desulfurization reaction occurs mainly at low temperature, while the solid phase reaction and the decomposition reaction of some mineral matters do at high temperature. So higher temperature and Ca/S ratio can both promote CaSO4 to grow at temperatures ranging from 850 C to 1050 C, then mainly accelerate C4AF, C2AS and C2S to form and further transform at temperatures above 1050 C. The sulfur content and other inorganic constituents of coal can also affect the desulfurization process. The higher sulfur content is, the more easily CaSO4 forms. Aluminate can be attained largely after adding Al2O3 into the desufurizing system, so the free CaO is reduced effectively and C4A3S- was promoted to form in the residues. Yet aluminate can be totally transformed into C4A3S- only in a higher Ca/S ratio.The transformation of inorganic composition in desulfurization process was studied. The results show that the releasing of sulfur at high temperature can be prolonged effectively for the formation of C4A3S- when Ca/S 6 or Al2O3 largely added synchronously, and more silicate mineral phase is promoted to form in the clinker. And the inorganic particle is more likely to be transformed into resource. The suitable desufurizing system is 1050-1150 C, Ca/S=2~3 with a quantitative Al2O3 or 1200-1350 C , Ca/S=8. Their desulfurization efficiency is higher than 38%. The mineral constitute of the former residue's system aremainly aluminate and C4A3S , while the mineral phases of the latter are mainly silicate and C4A3S-.The desulfurization efficiency is decided by the existence form of mineral constituents and the content of sulfur-contained mine in the desulfurization products. The desulfurization product is mainly CaSO4 when Ca/S 5. However, the desulfurization efficiency at high temperature is usually very low for the bad stability of CaSO4. Several sulfur-contained mines were reseached, and the results show that C4A3S- is the perfect desulfurization product for its higher stability at high temperature, its easily controlling to form and the possible recycle of the desulfurization clinker with it. C4A3S- can be synthesized by C2AS and CaSO4 at 1050C or by aluminate and CaSO4 at 950C, and it will decompose at 1350C.