Limestone calcination kinetics in simultaneous calcination and sulfation under CFB conditions

doi:10.11949/j.issn.0438-1157.20170627

Abstract

Abstract:

The interaction of limestone calcination and sulfation in simultaneous calcination/sulfation under circulating fluidized bed furnace conditions was studied by constant-temperature thermogravimetric setup. The sulfation reaction took place simultaneously with calcination and CaSO₄ was formed in the particles when SO₂ was present. Compared to pure calcination condition, the mass loss rate of limestone calcined in the presence of SO₂ was lower but the final mass was higher. Limestone calcination was slowed down by SO₂ presence and the calcination rate decreased with increase of SO₂ concentration within the range of 0-0.3%. A probable mechanism was proposed that CaSO₄ formation by SO₂ sulfation with CaO of limestone particles upon calcination may fill or plug pores in CaO layer, impede CO₂ transfer, and hinder calcination reaction. The mechanism of SO₂ inhibition on limestone calcination was supported by product pore structure analysis and calculation that some pores were plugged and effective CO₂ diffusion coefficient in pores was reduced. However, the calcination rate of limestone was increased with particle size decreased from 0.4-0.45 mm to 0.2-0.25 mm, no matter whether there was SO₂ or not. Temperature also largely affected calcination, SO₂ impeding effect was less pronounced at 880℃ than at 850℃, which was probably due to reduced pore plug of CaSO₄ at 880℃.

Key words: calcination, sulfation, limestone, reaction kinetics, circulating fluidized bed, diffusion

摘要：

采用恒温热重实验台研究了循环流化床内石灰石同时煅烧硫化反应中煅烧反应与硫化反应的相互作用。当煅烧环境中存在SO₂时，煅烧反应与硫化反应同时发生，并在颗粒中生成CaSO₄。与纯煅烧工况相比，在含有SO₂的气氛中煅烧石灰石时，颗粒的质量下降速率降低，而煅烧终质量升高。SO₂的存在能够降低石灰石的煅烧速率，而且在0～0.3%的范围内，SO₂浓度越高，煅烧越慢。对该现象提出以下机理：当煅烧过程中存在SO₂时，SO₂会与正在煅烧的石灰石颗粒的CaO层发生硫化反应生成CaSO₄，所生成的CaSO₄会堵塞颗粒的孔隙，增加CO₂的扩散阻力，进而减慢煅烧反应速率。对煅烧产物孔结构的测试和计算表明在同时煅烧硫化中部分孔隙被堵塞、封闭，孔内CO₂有效扩散系数下降，证明所提出的机理能够合理解释SO₂对石灰石煅烧的减缓作用。随着粒径由0.4～0.45 mm减小到0.2～0.25 mm，无论反应环境是否存在SO₂，石灰石的煅烧速率均加快。温度对煅烧速率有明显的影响，850℃下SO₂对石灰石煅烧速率的减缓程度大于880℃，这可能是由于880℃下CaSO₄对颗粒孔隙的堵塞作用下降导致的。

关键词: 煅烧, 硫化, 石灰石, 反应动力学, 循环流化床, 扩散

CLC Number:

TK221

CHEN Liang, WANG Ziming, WANG Chunbo. Limestone calcination kinetics in simultaneous calcination and sulfation under CFB conditions[J]. CIESC Journal, 2017, 68(12): 4615-4624.

陈亮, 王子铭, 王春波. 流化床锅炉内石灰石同时煅烧/硫化反应中煅烧动力学特性[J]. 化工学报, 2017, 68(12): 4615-4624.

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