Effect of H₂S on the behaviour of an impregnated NiO-based oxygen-carrier for chemical-looping combustion (CLC)

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• 作者：Cristina Dueso ; Mar¨ªa T. Izquierdo ; Francisco Garc¨ªa-Labiano ; Luis F. de Diego ; Alberto Abad ; Pilar Gay¨¢n ; Juan Ad¨¢nez
• 关键词：Chemical-looping combustion (CLC) ; Oxygen-carrier ; Nickel oxide ; Sulphur
• 刊名：Applied Catalysis B: Environmental
• 出版年：2012
• 出版时间：25 September, 2012
• 年：2012
• 卷：126
• 期：Complete
• 页码：186-199
• 全文大小：1184 K

文摘

Gaseous fuels for chemical-looping combustion (CLC) process may contain sulphur-compounds which could affect the oxygen-carrier behaviour, especially if NiO is used as active phase. In this work, several samples of a NiO-based oxygen-carrier prepared by impregnation (18 wt. % ) on ¦Á-Al₂O₃, so-called NiO18-¦ÁAl, were extracted from a CLC unit after continuous operation with CH₄ containing 500 vppm of H₂S and characterized subsequently. Part of the sulphur fed to the system was release as SO₂ in the air-reactor during the CLC experiments while the rest remained in the solid particles. Ni₃S₂ was found in the oxygen-carrier extracted from the fuel-reactor, although small amounts of NiSO₄ were also detected. On the contrary, NiSO₄ was the main sulphur compound in the oxygen-carrier from the air-reactor while a low concentration of Ni₃S₂ was present. Despite the accumulated sulphur and the oxygen transport capacity loss during the operation, the oxygen-carrier was capable of recovering the initial reactivity for the CH₄ combustion after some time without H₂S feeding to the CLC system. In addition, a study about the possible regeneration of the oxygen-carrier in the air-reactor working at different temperatures and oxygen concentrations was performed. Independently of the operating conditions, part of the sulphur remained in the solid and total regeneration was not possible. The analysis of the NiO18-¦ÁAl oxygen-carrier after the CLC operation using TPR and XPS techniques revealed that sulphur reacted preferably with free NiO instead of NiAl₂O₄. Although Ni₃S₂ was the majority sulphide in the fuel-reactor, minor amounts of other sulphides such as NiS were detected. Sulphur was preferably concentrated in the outer surface of the particles. Taking into account all these results, a previous desulphuration process of the fuel would be necessary when NiO-based oxygen-carriers are used in a CLC system.