循环捕集CO2后煅烧石灰石的硫化特性

摘要

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。%Zero emission coal (ZEC) process based on calcium looping in which CO2is 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.