循环捕集CO2后煅烧石灰石的硫化特性

ZEC(zero emission coal)系统中,粗煤气进入碳酸化/重整炉前需先脱除H₂S,提出利用经过多次碳酸化/煅烧捕集CO₂循环的煅烧石灰石(CaO)脱除H₂S,并研究循环碳酸化/煅烧次数、硫化温度、H₂S浓度和微观结构对循环CaO硫化特性的影响。结果表明,多次循环碳酸化/煅烧捕集CO₂后CaO仍具有较高H₂S吸收性能。前20次循环,CaO硫化转化率随循环次数增加迅速降低;20次循环后,CaO硫化转化率缓慢下降。硫化120 min后,未循环CaO的硫化转化率接近100%,而经历1、20和100次循环后CaO的硫化转化率分别为94%、81%和74%。H₂S浓度对循环CaO硫化性能影响较大。硫化温度(800～1000℃)对循环CaO的硫化性能影响较小,最佳硫化温度为900℃。随循环次数增加,CaO颗粒发生高温烧结,导致比表面积降低和20～150 nm内孔隙减少,而这是与H₂S吸收密切相关的孔隙,导致CaO硫化转化率降低。

Sulfidation performance of calcined limestone from CO2 capture cycles

Zero emission coal (ZEC) process based on calcium looping in which CO₂ is captured through a cyclic carbonation/calcination process is a promising technology for hydrogen production. In this process, H₂S should be removed before raw gas flows into the downstream carbonator/reformer. In this work, the cycled CaO derived from limestone after multiple carbonation/calcination cycles for CO₂ capture was used to remove H₂S from raw gas. Cyclic carbonation/calcination of CaO was performed in a dual fixed-bed reactor and then the cycled CaO was sent to a sulfidation reactor for H₂S removal. The effects of carbonation/calcination cycle number, sulfidation temperature, H₂S concentration and CaO microstructure on sulfidation performance of the cycled CaO from CO₂ capture cycles were investigated. The cycled CaO after the long-term carbonation/calcination cycles for CO₂ capture still had high H₂S removal capacity. Sulfidation conversion of CaO derived from limestone decreased rapidly with increasing number of carbonation/calcination cycles in the first 20 cycles, and then decreased slowly with further increasing cycle number. After sulfidation for 120 min, sulfidation conversion of the CaO after 0 cycle was nearly 100%. And sulfidation conversions of the cycled CaO after 1, 20 and 100 cycles were 94%, 81% and 74%, respectively. H₂S concentration showed a great effect on H₂S removal of the cycled CaO. Sulfidation temperature in the range of 800—1000℃ had a little effect on H₂S removal of the cycled CaO, and the optimum sulfidation temperature was 900℃. As the cycle number increased, specific surface area of the cycled CaO dropped due to sintering. The pores 20—150 nm in diameter of the cycled CaO which were closely related with H₂S adsorption also decreased. Thus, H₂S removal capacity of the cycled CaO decayed with the number of cycles.