纳米助燃固硫添加剂的催化作用机理

溶胶.凝胶法制备的纳米TiO2作为CaO固硫添加剂,用热分析法对纳米TiO2催化煤燃烧以及催化CaO固硫的过程进行了实验研究.对燃烧后煤灰的孔径分布进行了分析.采用未反应收缩核模型对固硫反应的动力学过程进行表征.研究结果表明,纳米TiO2与CaO共同作用条件下对煤燃烧有明显的促进作用,即燃烧反应活化能E下降,同时纳米TiO2还能增大燃烧后煤灰的孔径,提高固硫率.氧气的存在抑制氧化钙的固硫转化率,纳米TiO2可以消弱氧气的抑制作用.对固硫反应的影响表现为在反应后期(即产物层扩散控制阶段),与固硫转化率和孔径分布的实验结果非常吻合;讨论了纳米TiO2催化燃烧催化固硫的机理,纳米TiO2导致碳晶格的扭曲,增加表面活性部位,加快氧气的吸附速度,使添加剂周围燃烧速度加快,煤灰孔隙增大从而强化燃烧,促进SO2转化成SO3的本征反应,促进二氧化硫向氧化钙内部的扩散从而提高CaO的固硫效果.

Catalysis mechanism of nano-additive on combustion and sulfur fixation

The nanometer TiO₂ prepared by sol-gel method as additive for CaOfixation of sulfur was studied.The catalysis effects of sulfur fixation and combustion were investigated by thermogravimetric analysis.The coal ashes pore diameter distributions were analyzed.The unreacted shrinking reaction core model of the reaction kinetic was used.The experimental results showed that this model can describe the course of sulfur fixation;the apparent activation energy of combustion with nano-TiO₂ addition and CaOdecreased;the sulfur fixation efficiency of analytical grade CaOcatalyzed by nanometer TiO₂ increased than that without nanometer TiO₂;the pore diameter and surface area of coal ashes with nano-TiO₂ addition increased.The sulfur fixation reaction was inhibited in the presence of oxygen.The inhibition was decreased by the nano-TiO₂ addition.In the end of the reaction,the product-layer diffusion shows the slow rate.This agrees with the experimental results of sulfation conversion and pore distribution.The mechanisms of combustion and sulfur fixation by nanometer TiO₂ addition were discussed.In the presence of nano-TiO₂,which serves as a catalytic active center,the gas(oxygen)-solid(catalyst)-solid(carbon and CaO)catalytic burning reaction takes place.In the burning of the coal,many holes and grooves on the surface of the coal particles are formed because the carbons around the catalytic active center burn faster than those away from the catalytic active center.The controlling course of the reaction changes from outer oxygen and SO₂ diffusion to inner oxygen and SO₂ diffusion.The oxygen transfer speeds up.Finally,the accelerating effects of nano-TiO₂ on the burning and sulfur fixation of the coal are observed.