Decomposition Characteristics And Experimental Study Of Limestone Powder In Converter High Temperature Flue Gas

At present,lime is mainly prepared by calcining the limestone in lime kiln,but this process has problems,such as great investment,high energy consumption and unstable product quality.Large amounts of high-temperature flue gas are discharged from the vaporization cooling flue of a converter in the steelmaking process,with the temperature of 1400～1600℃,and the heat energy availability is also low.Considering the above two problems,this work proposes a new process that limestone powder is injected into the vaporization cooling flue for calcining using high temperature waste heat to prepare lime.Both decomposition characteristics of limestone and feasibility of the process are studied by theoretical analysis and experiments.This paper mainly involves three parts:1)The Gibbs free energy of the reaction was calculated by thermodynamics,and the decomposition of calcium carbonate in limestone and the release of CO₂ were simulated;2)The thermal decomposition characteristics of calcium carbonate under various atmospheres,compositions of raw material and heating rates were studied by thermogravimetric experiments,and the reaction activation energy was calculated by thermal analysis curve;3)The effects of temperature,particle size,atmosphere,and soot content on the decomposition behaviour and characteristics of limestone powder under different calcination conditions were studied by static calcination in tube furnace and fluidized calcination in drop tube furnace.Thermodynamic study shows that Ca CO₃ began to decompose at 800～900℃in CO₂atmosphere,and the decomposition rate increased with the increase of temperature.After adding soot,the initial decomposition temperature of Ca CO₃ was in range of 600～700℃.At the same time,the main component of soot,such as iron oxides,reacted with Ca O to form the multi-component low-melting compounds,which increased the decomposition pressure of the reaction and promoted the reaction.Thermogravimetric experiments show that the initial decomposition temperature of Ca CO₃ increased with increasing the heating rate.Under a same heating rate,the initial decomposition temperature and activation energy of Ca CO₃ in CO₂ atmosphere were higher than those in N₂ atmosphere.The initial decomposition temperature increased by about 200℃,the termination temperature was close,and the activation energy increased by about 400 k J/mol,indicating that the initial decomposition rate of Ca CO₃ was larger in CO₂ atmosphere than in N₂ atmosphere,by absorbing more heat.Tube furnace experiments show that limestone can be rapidly decomposed at high calcination temperature.When calcined at 1300℃for 1 min,the decomposition ratio of limestone was about 0.8.If the high temperature calcination time is too long,the surface of limestone particles will burst and sinter.At high temperature,the change of trace CO₂atmosphere hardly affected the decomposition of limestone.The calcination of fluidized limestone powder in the drop tube furnace shows that the higher the temperature in the furnace and the smaller the particle size of limestone,and the better the decomposition and activity.Therefore,the calcination conditions of 1400℃and the 200-300 mesh size of limestone were obtained.Two-type calcination experiments show that the atmosphere conditions in the converter vaporization flue have no obvious effect on the decomposition characteristics of limestone powder,and soot promotes the decomposition of limestone powder.Therefore,this study verifies the method of preparing active lime by injecting limestone powder into the converter vaporization cooling flue.It turns to be feasible.