Study On Removal Of Fluoride From High Temperature Flue Gas

Fluoride is one of the prime air pollutants.The industries including steels smelting,nonferrous smelting,phosphate fertilizer production,cement manufacturing and coal-fired power generation has been the dominant anthropogenic fluorine pollution sources.With the development of industries,an increasing amount of fluoride emission has caused wide hazard,which poses an increasingly pressing concern.According to the industrial reality of fluoride removal,this paper investigated the removal of fluoride in high-temperature flue gas by alumina adsorption.The reaction mechanism was analyzed using adsorption equilibrium and adsorption kinetics,and thus a shrinking core model of alumina adsorbing-HF was established.Finally,the mechanism of HF adsorped on alumina and a reasonable regeneration process were proposed,which could provide a theoretical basis for industrial application.More details were given as follows.(1)The effects of the particle size,velocity of gas flow,HF concentration and temperature on the adsorption capacity of Al2O3 for HF were studied.The adsorption characteristics of alumina for HF were analyzed based on adsorption equilibrium and adsorption kinetics.The results showed that the amount of adsorped HF increased rapidly in the initial stage and that the adsorption rate got slowed down with the duration of adsorption until reaching equilibrium state.With increasing the particle size of alumina adsorbent,the adsorption efficiency of HF decreased continuously.And the adsorption rate and equilibrium adsorption capacity of alumina were also decreased with the increase of gas flow rate.The adsorption capacity first decreased when the temperature was increased from 30℃ to 120℃,and then increased as the temperature rised to 300℃.With the increase of HF concentration in the feeding gas,both of the initial adsorption rate and equilibrium adsorption capacity of alumina increased.The adsorption equilibrium accorded with Langmuir isothermal equation.The removal of HF by alumina adsorption could be well predicted by quasi-second adsorption kinetic model and Bangham adsorption kinetics model.(2)A shrinking core model was selected to describe the adsorption process for HF using alumina.The corresponding mathematical model was deduced on the basis of the spherical structure of alumina particle.Via a combination of theoretical calculation and experimental data simulation,the key parameters in the model were solved.In addition,the difference between the mathematical model and the experimental data was disscussed.With the proposed empirical correlation,the model parameters could be modified,contributing to a better prediction of the adsorption process with the modified model.(3)The BET specific surface area of alumina decreased from 274.10 m2·g-1 to 145.46 m2·g-1 after adsorption test;the average pore size increased from 53.74 nm to 65.67 nm;the specific pore volume decreased from 0.39 cm3·g-1 by 0.23 cm3·g-1.The morphology of alumina adsorbent was observed by scanning electron microscopy(SEM).It is found that the alumina after adsorption test would get crisper.The alumina samples before and after tests were further characterized using XRD,FTIR and XPS.A potential adsorption mechanism of HF on alumina was discussed.Finally,it is proposed that the alumina could be regenerated in a high temperature aqueous atmosphere.