Microstructure evolution of procedural products during limestone simultaneous calcination/sulfation

doi:10.11949/j.issn.0438-1157.20171167

Abstract

Abstract:

The calcination kinetics and pore structure evolution of limestone in simultaneous calcination/sulfation was studied by a self-designed constant-temperature thermogravimetric reactor. Sulfation reaction took place to form CaSO₄ simultaneously with limestone calcination as long as SO₂ gas was present. The presence of SO₂ reduced calcination rate of limestone. Compared to pure calcination, simultaneous calcination/sulfation had slower increase in specific surface area and specific pore volume, which both distribution curves were lower, and these two parameters of small pores with 2-8 nm in diameters decreased with time in the final calcination stage. A mechanism was proposed to describe pore microstructure evolution during simultaneous calcination and sulfation, that is, because limestone calcination occurs from surface to inner core, small amount of CaSO₄ was formed on CaO surface with few plugged pores and CaSO₄ had little effect on calcination rate and pore structure in initial reaction stage (0-75 s), continuous increase of CaSO₄ thickness and coverage enlarged both volume of closed pore and CO₂ diffusion resistance but declined calcination rate in the middle calcination stage (75-225 s), and further accumulation of CaSO₄ accelerated plugging on pores especially smaller ones in the final stage (225-300 s). Calculation of volume of closed pores showed that pore plugging started in initial and middle calcination stages and intensified rapidly in final reaction stage, which validated the proposed mechanism.

Key words: circulating fluidized bed, reaction kinetics, model, calcination, sulfation

摘要：

采用自制恒温热重实验装置，测试了石灰石同时煅烧硫化反应的煅烧动力学特性和颗粒孔结构演变特性，探讨了孔结构演变机理。当煅烧环境中存在SO₂时，石灰石颗粒煅烧的同时发生硫化反应。煅烧环境中SO₂的存在降低了石灰石煅烧速率。与纯煅烧相比，同时煅烧硫化反应的比表面积和比孔容增长均较慢，比表面积和比孔容分布曲线均较低，且在反应后期直径2～8 nm内小孔的比表面积和比孔容随时间降低。提出了描述石灰石同时煅烧硫化反应过程中微观孔结构演变的模型：石灰石颗粒的煅烧由颗粒的表面向内进行，在煅烧前期（0～75 s），少量CaSO₄在CaO表面生成，小部分孔隙被CaSO₄堵塞，CaSO₄对煅烧速率和孔结构的影响较小；在煅烧中期（75～225 s），CaSO₄厚度和覆盖面积不断增加，堵塞孔体积增加，CO₂的扩散阻力增加，导致石灰石的煅烧速率下降；煅烧后期（225～300 s），由于CaSO₄的不断积累，孔隙堵塞加剧，且堵塞主要发生在小孔上。对煅烧过程堵塞孔体积的计算表明，在煅烧前期和中期孔堵塞现象已经发生，在反应后期孔堵塞体积快速增加。

关键词: 循环流化床, 反应动力学, 模型, 煅烧, 硫化

CLC Number:

TK221

WANG Ziming, CHEN Liang, YUE Shuang, WANG Chunbo. Microstructure evolution of procedural products during limestone simultaneous calcination/sulfation[J]. CIESC Journal, 2018, 69(5): 2149-2157.

王子铭, 陈亮, 岳爽, 王春波. 同时煅烧硫化反应中石灰石微观孔结构演变特性[J]. 化工学报, 2018, 69(5): 2149-2157.

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