以菱镁矿尾矿为脱硫剂的高温烟气脱硫机理及动力学研究

Mechanism and kinetics of high-temperature flue gas desulfurization with magnesia tailings as a desulfurization sorbent

以菱镁矿尾矿粉体为脱硫剂实现高效烟气脱硫,对有效利用菱镁矿尾矿废弃物,降低烟气脱硫成本具有重要的环保和经济价值。为探索该技术思路的可行性,利用微型流化床反应分析仪(MFBRA)研究菱镁矿尾矿粉体高温烟气脱硫反应的机理和动力学特性,揭示菱镁矿粉体煅烧和硫化反应的动态特性及其与颗粒内孔结构演变的关系。结果表明:在菱镁矿粉体所含碳酸镁与二氧化硫气体反应过程中,同时存在碳酸镁分解为MgO的煅烧反应和新生MgO与SO_(2)气体反应生成MgSO_(4)的硫化反应2个反应过程,其中煅烧反应速率大于硫化反应速率。在反应初期,随着反应时间延长,煅烧反应速率不断加快,MgO生成量增多,颗粒内部孔隙与SO_(2)气体接触面积逐渐增大,硫化反应随之增强。在此阶段,由于MgSO_(4)的生成量较小,新生MgO有大量剩余。在反应中期,硫化反应速率增大,但随着生成的MgSO_(4)层逐渐覆盖在MgO表面,导致煅烧速率逐渐降低,MgO的生成量逐渐减小。在反应后期,致密的MgSO_(4)层堵塞了大部分孔隙,硫化反应速率受MgSO_(4)产物层的扩散控制,反应速率明显降低。到硫化反应完全停止时,颗粒中仍有少量MgCO_(3)和大量MgO未发生反应。研究结果对进一步开发以菱镁矿尾矿粉体为脱硫剂实现高效烟气脱硫技术提供基础数据支持。

High-temperature flue gas desulfurization using magnesite tailings as a sorbent has economic and environmental benefits.In order to assess the feasibility,the reaction mechanism and kinetic characteristics of high-temperature flue gas desulfurization using magnesite tailings as the sorbent were studied via a micro fluidized bed reaction analyzer(MFBRA).The dynamics of magnesite calcination and sulfation,and the evolution of the inner pore structure of magnesite particles were studied.The results show that the reaction process includes a calcination reaction of magnesite to MgO,and a sulfation reaction between MgO and SO_(2)to form MgSO_(4).The calcination reaction rate is faster than the sulfation reaction.Decomposition of magnesite is fast at beginning that resulted in quick increase of MgO and also the sulfation reaction between MgO and SO_(2).The amount of nascent MgO consumed by the sulfation reaction is low and the available MgO is excessive.After that period the sulfation reaction rate increases,thereby the formation of MgSO_(4)increases accordingly.The increased MgSO_(4)covers MgO surface that leads to a reduction of sulfation rate.The calcination rate of MgCO_(3)reduces in the later stage and the internal pore formation slows down with dense MgSO_(4)layer covers small pores.Consequently,the sulfation reaction rate tends to be controlled by the diffusion through the MgSO_(4)layer,leaving some MgCO_(3)and MgO unreacted at the end of the operation.