吸附剂修饰铁基氧载体的氧化动力学研究

研究了吸附剂修饰合成Fe_2O_3/Al_2O_3的氧化动力学。其中,吸附剂(K_2O、Na_2O、CaO)用于控制化学链燃烧过程中有毒氯化物、硫化物以及重金属的排放。首先在热重分析仪(TGA)上利用合成气作为还原气氛使氧载体呈还原态(FeO/Al_2O_3),在空气气氛下进行了原FeO/Al_2O_3以及三种吸附剂修饰FeO/Al_2O_3的氧化实验,实验温度分别为850、875、900和925℃。通过八种等温动力学模型对900℃下原FeO/Al_2O_3的氧化过程进行了分析。结果表明,phase boundary-controlled(contracting cylinder)模型能够很好地描述其氧化过程(FeO向Fe_2O_3转化过程)。利用该模型分别计算了原FeO/Al_2O_3、K_2O修饰FeO/Al_2O_3、Na_2O修饰FeO/Al_2O_3和CaO修饰FeO/Al_2O_3的氧化动力学参数,其表观活化能分别为13.71、20.21、21.62和24.20 k J/mol。通过进行比较依据动力学参数计算得到的转化率随时间的函数以及实验获得的转化率随时间的函数,进一步证实了phase boundary-controlled(contracting cylinder)模型的可靠性以及相应动力学参数的准确性。

Oxidation kinetics of adsorbent-decorated Fe-based oxygen carrier for chemical-looping combustion

Adsorbent-decorated Fe₂O₃/Al₂O₃ as oxygen carrier (OC) was proposed for restraining the emission of chloride, sulfide and heavy metals during the chemical-looping combustion process of gaseous or solid fuels. Three adsorbents (K₂O, Na₂O and CaO) were selected for decorating these OC particles. First, the raw Fe₂O₃/Al₂O₃ and three adsorbent-decorated Fe₂O₃/Al₂O₃ were reduced by synthesis gas and then the oxidation kinetics of four reduced OCs (raw FeO/Al₂O₃ and three adsorbent-decorated FeO/Al₂O₃) were investigated by using thermogravimetric analysis (TGA) technique in air atmosphere at four temperatures (850, 875, 900 and 925℃). It was found that the translation of FeO to Fe₂O₃ can be described by the phase boundary-controlled (contracting cylinder) model, and the apparent activation energy (E) was calculated to be 13.71, 20.21, 21.62 and 24.20 kJ/mol for raw FeO/Al₂O₃, K₂O-decorated FeO/Al₂O₃, Na₂O-decorated FeO/Al₂O₃ and CaO-decorated FeO/Al₂O₃, respectively. Last, the reaction mechanism was evaluated through comparing the calculated data from the obtained kinetic parameters and the experimental results, which demonstrated the reliability of the phase boundary-controlled (contracting cylinder) model.