Abstract:

Circulating fluidized bed (CFB) boilers are the best device to utilize inferior coal. In-situ SO₂ removal with limestone is easy and low-cost, but the desulfurization efficiency and calcium utilization are not high enough. Under the circumstance of the ultra-low emission of coal-fired boilers, it is still necessary to investigate the way to improve the sulfur removal performance in CFB boilers. In this paper, SO₂ removal with limestone was reviewed. The effect of H₂O on CaO sulfation was introduced, as well as the simultaneous calcination/sulfation reaction and the model. The use of smaller limestone particles and sorbents reactivation was also introduced. The emphasis was put on the simultaneous calcination /sulfation reaction of limestone, in which the phenomenon that CaCO₃ in limestone cannot decompose completely under CFB conditions was analyzed. The research progress of this reaction as well as the work still need to be done was described. A new model was put forward, which is based on the random pore concept and considered the calcination, sintering and sulfation reaction simultaneously. The new model can describe the reaction process of limestone in CFB more accurately. The research of desulfurization in CFB should be based on the real reaction process of limestone, and the simplification of this reaction should be limited to the reasonable bounds, otherwise the research conclusion cannot reflect its real characteristics.

Key words: circulating fluidized bed, limestone, sulfur dioxide, calcination, sulfation, kinetics, desulfurization

摘要：

循环流化床（CFB）锅炉是燃用劣质煤的最佳设备，炉内石灰石脱硫具有操作简单、成本低等优势，但也存在脱硫效率不够高、石灰石利用率低等问题，在当前燃煤超净排放的背景下，有必要探索CFB内石灰石高效脱硫的理论和技术。本文综述了近年来石灰石脱硫研究的新进展，包括水蒸气对CaO硫化反应的影响及机理、石灰石同时煅烧硫化反应及模型等；介绍了近年来提出的改善炉内脱硫效果的方法，包括采用小粒径石灰石和吸收剂的活化等。着重介绍了石灰石同时煅烧/硫化反应新概念，阐述了CFB内石灰石可能无法完全热解的现象及原因，以及该反应的研究进展和需要继续开展的工作。介绍了CaO硫化反应模型的研究进展，并提出了石灰石同时煅烧硫化反应的随机孔模型，将石灰石煅烧、烧结和CaO硫化反应同时考虑在内，更精确地描述炉内石灰石反应的过程。指出研究者应重视炉内脱硫的真实反应过程，避免对CFB脱硫过程做过度简化，否则研究结论很难反映炉内脱硫的真实规律。

关键词: 循环流化床, 石灰石, 二氧化硫, 煅烧, 硫化, 动力学, 脱硫