Calcium-based sorbents behaviour during sulphation at oxy-fuel fluidised bed combustion conditions

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• 作者：Francisco Garc&#xed ; a-Labiano ; ^a ; ^{glabiano@icb.csic.es"" rel=""nofollow} ; Ará ; nzazu Rufas^a ; Luis F. de Diego^a ; Margarita de las Obras-Loscertales^a ; Pilar Gayá ; n^a ; Alberto Abad^a ; Juan Adá ; nez^a
• 关键词：Oxy-fuel combustion ; SO₂ retention ; Sulphation ; Fluidised beds ; Calcium-based sorbents
• 刊名：Fuel
• 出版年：2011
• 出版时间：October 2011
• 年：2011
• 卷：90
• 期：10
• 页码：3100-3108
• 全文大小：1599 K

文摘

Sulphur capture by calcium-based sorbents is a process highly dependent on the temperature and CO₂ concentration. In oxy-fuel combustion in fluidised beds (FB), CO₂ concentration in the flue gas may be enriched up to 95 % . Under so high CO₂ concentration, different from that in conventional coal combustion with air, the calcination and sulphation behaviour of the sorbent must be defined to determine the optimum operating temperature in the FB combustors.

In this work, the SO₂ retention capacity of two different limestones was tested by thermogravimetric analysis at typical oxy-fuel conditions in FB combustors. The effect of the main operating variables affecting calcination and sulphation reactions, like CO₂ and SO₂ concentrations, temperature, and sorbent particle size, was analysed.

It was observed a clear difference in the sulphation conversion reached by the sorbent whether the sulphation takes place under indirect or direct sulphation, being much higher under indirect sulphation. But, in spite of this difference, for a given condition and temperature, the CO₂ concentration did not affect to the sulphation conversion, being its major effect to delay the CaCO₃ decomposition to a higher temperature.

For the typical operating conditions and sorbent particle sizes used in oxy-fuel FB combustors, the maximum sorbent sulphation conversions were reached at temperatures of about 900 °C. At these conditions, limestone sulphation took place in two steps. The first one was controlled by diffusion through porous system of the particles until pore plugging, and the second controlled by the diffusion through product layer. As a consequence, the maximum sulphation conversion increased with decreasing the particle size and increasing the SO₂ concentration.