Multiphase CFD-based models for chemical looping combustion process: Fuel reactor modeling
Multiphase CFD-based models for chemical looping combustion process: Fuel reactor modeling
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DOI：
10.1016/j.powtec.2008.01.019
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发表时间：
2008-04
影响因子：
5.2
通讯作者：
Jonghwun Jung;I. Gamwo
中科院分区：
文献类型：
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作者：
Jonghwun Jung;I. Gamwo
化学链燃烧（CLC）是一种无火焰的两步燃料燃烧，产生纯CO2流，准备压缩和封存。该方法由两个互连的流化床反应器组成。空气反应器是传统的循环流化床，燃料反应器是鼓泡流化床。其基本原理是通过引入高活性金属颗粒（称为氧载体）将氧从空气输送到燃料中，从而避免燃烧期间空气和燃料的直接接触。在该过程中，燃烧产物与其余烟道气（即氮气和过量氧气）保持分离。该工艺消除了从富氮烟气中分离CO2的能源密集型步骤，该步骤降低了热效率。气固流动的多相反应流体动力学行为的基础知识对于化学循环燃烧室的优化和操作至关重要。我们最近全面的文献综述表明，多相CFD为基础的模型还没有适应化学链燃烧过程中的公开文献。在这项研究中，我们已经开发了燃料反应堆的反应动力学模型，并实施了动力学模型到多相流体动力学模型，MFIX，开发早期在国家能源技术实验室。模拟燃料反应器流揭示了高重量分数的未燃烧的甲烷燃料的烟道气沿着与CO2和H2O。这种行为意味着在反应器出口处的高燃料损失，并表明有必要增加停留时间，例如通过降低燃料流速，或在冷凝和除去CO2后再循环未燃烧的甲烷。
Chemical looping combustion (CLC) is a flameless two-step fuel combustion that produces a pure CO2stream, ready for compression and sequestration. The process is composed of two interconnected fluidized bed reactors. The air reactor which is a conventional circulating fluidized bed and the fuel reactor which is a bubbling fluidized bed. The basic principle is to avoid the direct contact of air and fuel during the combustion by introducing a highly-reactive metal particle, referred to as oxygen carrier, to transport oxygen from the air to the fuel. In the process, the products from combustion are kept separated from the rest of the flue gases namely nitrogen and excess oxygen. This process eliminates the energy intensive step to separate the CO2from nitrogen-rich flue gas that reduce the thermal efficiency. Fundamental knowledge of multiphase reactive fluid dynamic behavior of the gas–solid flow is essential for the optimization and operation of a chemical looping combustor. Our recent thorough literature review shows that multiphase CFD-based models have not been adapted to chemical looping combustion processes in the open literature. In this study, we have developed the reaction kinetics model of the fuel reactor and implemented the kinetic model into a multiphase hydrodynamic model, MFIX, developed earlier at the National Energy Technology Laboratory. Simulated fuel reactor flows revealed high weight fraction of unburned methane fuel in the flue gas along with CO2and H2O. This behavior implies high fuel loss at the exit of the reactor and indicates the necessity to increase the residence time, say by decreasing the fuel flow rate, or to recirculate the unburned methane after condensing and removing CO2.