Experimental Study On Desulfurization And Denitrification Performance Of Calcium Based Sorbents Modified By NaHCO₃

SO₂ is the leading cause of acid rain,seriouly harmful to soil,water,forests and other ecosystems.It can also cause a variety of diseases,and even death.China’s coal-fired boiler has the characteristics of large output,poor coal quality,wide use area,high desulfurization cost,low desulfurization efficiency and so on.Compared with other methods of desulfurization,desulfurization in coal combustion has the advantages of simple operation,small space occupation and less investment.But there is a big defect that the desulfurization effect is poor.In order to improve the effect of desulfurization in combustion,a lot of researchers put forward the modification of calcium based sorbents.Inorganic salt solution is the most commonly used modification method,especially sodium salt.Na HCO₃ has good desulfurization effect,and has also been confirmed for the succedaneum of calcium based sorbents preliminarily and good denitrification effect,but because of its strong corrosion,it could couse seriously damage to equipments.So this paper proposed the idea of Na HCO₃ in modification of calcium based sorbents,and explored the influence of different ratio,O₂ concentration,the concentration of water vapor,the simultaneous desulfurization and denitrification on SO₂ and NO absorption.The results indicate Na HCO₃ can effectively improve the absorption rate of SO₂,and the ratio increasing is conducive to the absorption of SO₂.O₂ and water vapor can promote the absorption of SO₂ also,the optimal concentration of O₂ is 5%,and as the increasing of water vapor concentration,SO₂ absorption rate increases.When the ratio is 30%,simultaneous desulfurization and denitrification contributes to NO absorption,there are some effects of SO₂ concentration on the absorption of NO,increasing the concentration of SO₂,NO absorption is enhanced.The mechanism of Na HCO₃ modifying calcium based sorbents was studied by SEM analysis,mercury intrusion analysis,XRD analysis and XPS analysis.The influence of pore structure on SO₂ absorption effects was observed.The results show change of calcium based sorbent in morphology,pore size distribution,porosity and specific surface area before and after modification.The pore size distribution and porosity are increased as the ratio increasing,but the specific surface area shows the contrary law.Through the analysis,the positive influence and dominant position of pore volume on pore diffusion were determined.Through the XRD test on the phase composition analysis,the process of modification and desulfurization were established.CO₂ and Na2 O have been found and identified in the process,they have a positive effect on pore creation and expansion,and also open up a new path for desulfurization.It is also found that as grain size decreases,the sintering speeds up,which plays an important role in the decomposition of calcium based absorbent.Finally,through the XPS analysis of the surface,the composition of Ca2+ was determined,and found a lower level of surface Ca（OH）2 after modification,indicating promoted calcination,while the increasing of Ca SO4 and Ca S content after reaction illustrates the extention of the desulfurization.The presence of Na+ increases the concentration of vacancy defects in calcium based sorbents,which promotes the diffusion of solid ions.