Study On Desulphurization And Denitration Of Flue Gas By Calcium Carbide Slag Dry Process

Calcium carbide（calcium carbide,CaC₂）can react with water to produce acetylene（C₂H₂）,which is an important chemical raw material.In the process of using calcium carbide to produce acetylene,how to deal with a large number of calcium carbide slag is an urgent problem for enterprises.In addition,with the increasingly strict emission standards of air pollution,SO₂,NO purification technology needs to be developed.Calcium carbide slag is mainly composed of Ca（OH）₂,which is a kind of desulfurization agent rich in calcium and low cost.At present,the simultaneous desulfurization and denitrification technology of calcium carbide slag has some problems,such as complicated operation,high operating temperature.In addition,the removal of NO requires pre-oxidation or the addition of reducing agents,which makes the investment and operation cost high.In order to realize the resource utilization of calcium carbide slag and reduce the cost of desulfurization and denitrification of coal-fired flue gas,relevant research was carried out in this paper,aiming at developing a modified calcium carbide slag desulfurization and denitrification agent with high low temperature activity,which provided a certain experimental and theoretical basis for the resource utilization technology of solid waste and the collaborative removal of multi-flue gas.In this paper,the key technologies of dry desulphurization and denitration of calcium carbide slag are developed:（1）Compared with raw calcium carbide slag,KOH modification can significantly improve the NO removal performance of calcium carbide slag.When the reaction temperature is 300℃,the NO conversion of K1.5/CS reaches 94%within 60 min,and the adsorption capacity is 0.301mmol/g,which is 5 times higher than that of CS.The results showed that potassium metal modification modification can effectively improve the oxygen activity of the modified materials.K₂O is the main active component of the modified materials,and O_ads/Oxygen vacancies and oxygen-containing functional groups C=O are key to promote the oxidation reaction.The removal of NO by modified calcium carbide slag is an adsorption oxidation process.NO is oxidized by chemisorption to NO₃^-under the action of K₂O,NO₃^-reacts with K⁺to produce KNO₃and KNO₂,and NO₃^-reacts with Ca（OH）₂to produce Ca（NO₃）₂.The nitro compounds formed during the reaction promote the formation of NO and reduce the removal efficiency.（2）The addition of potassium can obviously improve the desulphurization and denitration performance of calcium carbide slag.The results demonstrate that the calcium carbide slag modified by KOH exhibits superior effectiveness,with lower activation energy and higher reaction rate.Potassium modification effectively reduces the energy barrier of desulfurization and denitration reactions,while altering the distribution of alkaline sites in calcium carbide slag.The strength of weak alkaline sites in KOH/CS slightly decreases,whereas the strength of strong basic sites significantly increases.The removal of SO₂is mainly by chemisorption and acid-base neutralization reaction.The content of KOx,C=O,and Oads in the materials is the main factor contributing to differences in activity.（3）The freeze-drying method significantly enhances the desulfurization and denitrification performance of calcium carbide slag,particularly in terms of NO removal.Within 240 minutes,the NO removal rate consistently exceeds 90%,while the SO₂removal rate remains at approximately 100%.These findings demonstrate that potassium（K）dispersion on the surface of calcium carbide slag becomes more regular and uniform,resulting in higher oxygen adsorption intensity compared to K_1.5/CS.When the solid-to-liquid ratio is set at 1:4,calcium carbide slag exhibits optimal performance with a smooth surface and layered structure.Manipulating the freezing angle effectively regulates the pore structure of calcium carbide slag,with an increase in mesoporous characteristics being crucial for enhancing its activity.Furthermore,both conditional experiments and response surface optimization confirm that O₂content,NO concentration,and SO₂concentration are significant parameters influencing the simultaneous desulfurization and denitrification activity of FD-K_1.5/CS.Further investigation reveals that increasing SO₂concentration facilitates NO removal through synergistic effects between these two pollutants.The presence of SO₂indirectly promotes C=O formation,thereby augmenting surface active sites and promoting oxidation reactions.（4）The kinetic equation of NO/SO₂adsorption-oxidation on the surface of FD-K_1.5/CS was deduced using a power function kinetic model,and the activation energy was calculated.Based on correlation results and in situ characterization,the possible reaction mechanism of NO/SO₂on FD-K_1.5/CS surface was inferred.The surface of FD-K_1.5/CS is characterized by a significant abundance of Oads,which imparts a pronounced oxidative effect on calcium carbide slag.Both NO and SO₂gases are converted to their respective adsorbed forms,namely NO（ads）and SO₂（ads）.The K₂O species present on the material’s surface exhibits strong oxidation performance,leading to conversion of SO₂（ads）into SO₃（ads）,while NO（ads）is transformed into NO₂（ads）.During this reaction process,there is a synergistic transformation between S-O group and N-O group.Initially,S-O bond conversion occurs followed by N-O bond conversion.Ultimately,CaSO₃,CaSO₄,Ca（NO₃）₂,KNO₂and KNO₃compounds are formed on the calcium carbide slag’s surface.By comparing the adsorption energies of active species Ca（OH）₂（101）and K₂O（001）,it was observed that K₂O（001）exhibited lower adsorption energy but stronger adsorption capacity.