DETERMINATION OF REACTIVITY AND THERMODYNAMIC ANALYSIS OF NICKEL-BASED OXYGEN CARRIERS FOR CHEMICAL-LOOPING COMBUSTION

Abstract This work aimed to study nickel-based oxygen carriers (OC) for Chemical Looping Combustion (CLC) using H2 and CH4 as fuel. The reactivity and reaction kinetics of the OC were investigated, applying the shrinking core, nucleation and diffusion models in three dimensions, as well as whether the OC is thermodynamically favorable for the reaction. The results showed that the OC achieved high conversion for both fuels, proving to be quite reactive, while the fuel gas concentration and the temperature have a strong effect on the solids conversion. For the H2 combustion, the reaction rate can be described well by the shrinking core model, whereas for CH4 the nucleation model may better represent the experimental data. With respect to reactions that occur in the reduction reactor with the NiO/Ni redox system, it was observed that, for the investigated temperatures used in CLC, high values of the equilibrium constant were obtained, showing that practically complete conversion of the fuels is possible.

摘要 本研究旨在针对以氢气（H₂）与甲烷（CH₄）为燃料的化学链燃烧（Chemical Looping Combustion, CLC）体系，开展镍基氧载体（nickel-based oxygen carriers, OC）的相关研究。本研究针对该氧载体的反应活性与反应动力学展开探究，采用三维缩核模型、成核与扩散模型，并分析了该氧载体用于该反应的热力学可行性。研究结果表明，该氧载体对两种燃料均表现出较高的转化率，展现出优异的反应活性；同时燃料气体浓度与温度对固体转化率均具有显著影响。针对氢气燃烧过程，其反应速率可通过缩核模型进行良好拟合；而对于甲烷燃烧过程，成核模型更能匹配实验数据。针对还原反应器内发生的NiO/Ni氧化还原体系反应，研究发现在化学链燃烧所采用的探究温度范围内，该体系的平衡常数较高，表明燃料几乎可实现完全转化。