The production and application of active lime in steelmaking
With the increasing of the steel production and the speeding up of the smelting cycle, the steelworks has more and more been strict with lime production and quality for the smelting slag, especially more and more emphasized on the research and development of lime. Lime activity degree was shown by the Ca (OH) 2 consumed 4mol/L of hydrochloric acid milliliter (ml) when neutralize quick lime digestive General when the lime average activity degree is more than 300ml/4N-HCl, then could significantly shorten initial slag expenditure time of steel-making convertor, reduce tons of steel lime consumption and greatly benefit for the early off P P, which is called active lime. The production of activity lime should choose limestone raw materials that have fewer impurities. Limestone associated impurities, such as SiO2、Al2O3、Fe2O3 and MgO etc., These impurities will be reacted with burned lime MgO under low temperature, the combination of CaO particles and impurities will reduce the lime activity. In addition, Na2O impurities very easy to form some glass phase, these melting compounds can jam stoma of the lime surface, which reduces the ability of lime reaction as well as jam the exhausting of CO2, which cases lime underfiring. The equipments used for producing active lime, which adopted the advanced technique in the world and double chambers and parallel flow heat-storage Mayers lime kiln. This is because the lime produced by earth kiln has low activity degree, high underfiring rate, high consumption and severe pollutions. Mayers this lime kiln has two main features: the characteristic of parallel flow and recovery of heat storage . The parallel flow enable the hottest flame to contact with the cold air to complete the burn, to make the material stones won’t over-burn, as well as having high exchange rate, and sintering process can achieve the tidy uniform soft burn conditions. Heat-storage recovery enables the preheated stone to absorb exhaust heat, and release to the enter gas, which makes it heated to the burning temperature prior to contact with the fuel ,meanwhile makes the kiln get very high thermal efficiency. Mayers lime kiln produces the high active lime that has small grains, high porosity, small volume& density, large specific surface, and strong reaction capability, and lime activity degree is about 350ml / 4N - HCl. Steelmaking practices show that the lime can improve 80% of the dephosphorise & desulfurize efficiency, while reducing the smelting time, which completely reacted with the acid materials of molten steel within 3-5min, whereas the common lime reaction time is at least 6-10min. Moreover, it improves more than 40%of the furnace life , reduces the consumptions of 5-8kg/t steel burdens, with the calculation of 10 million t, it can save 15 million or so per year and the production benefit is remarkable.