Hydrogen production via a three-reactor chemical-looping (TRCL) process using perovskite-type oxygen-carrier materials.

该项目将研究使用钙钛矿型载氧材料通过水-气变换反应(CO+H2&lt；=&gt；CO2+H2O)的化学环来生产氢气，特别是三反化学环(TRCL)过程，该过程涉及增加一个空气氧化步骤，可以使用CH4或合成气体作为还原剂。这一过程消除了分离H2和CO2产物流的需要，因为反应物不相互接触；产物和氧载体材料中间体处于不同的相。由于钙钛矿型材料的非化学计量比，它们能够展示出广泛的不同的氧化电位。此外，它们能够在其立方ABO3结构中结合许多不同价态的不同金属阳离子，从而允许利用点缺陷化学来进行具有所需性质的材料工程。在水-气变换反应的化学环路中，这些材料通常是掺锶的La1-xSrxFeO-O铁氧体氧化物，CO是一种理想的还原剂，用于涉及化学环路的实验室实验，因为它直接氧化成二氧化碳，从而避免了选择性的复杂性，并简化了所涉及的建模。然而，在工业规模上使用它不是一种现实的原料气，因为它不是以大浓度自然发生的，其主要生产方法是通过反向Boudouard反应。天然气中的甲烷含量更丰富，已被确定为更有可能作为还原剂的替代品之一。然而，当氧载体材料通过CH4氧化还原时，反应的吸热很大，导致水-气变换反应的两步化学环体系出现能量亏损。TRCL工艺已被提出作为这一问题的解决方案，增加了空气氧化步骤，使该工艺有可能在工业规模上自动加热操作，并保持氧气载体材料的充分氧化。对采用金属氧化物载氧材料的蒸汽压缩和燃烧涡轮的系统效率的研究预测，可以从气流中回收大量的热量，使TRCL过程在电力消耗方面接近自给自足。传统上，TRCL过程涉及一个由单独的燃料反应器、蒸汽反应器和空气反应器组成的流态化床系统。在这项研究中，将使用现有的具有逆流气流的单填充床反应器。固定在反应堆内的钙钛矿型氧气载体材料经历了一系列循环还原和氧化，碳基燃料(如CH4)和水在惰性平衡中单独进料，随后空气进入反应堆，从而产生氢气。在循环中的每一步之后，用惰性气体(通常是氩气)净化反应器，以去除任何微量的反应物或产物。这是为了防止存在于其爆炸下限以上的反应物或产品的不受控制的氧化，这是一个重要的安全问题。这项工作将通过开发一个数学模型来比较TRCL工艺和使用钙钛矿型氧载体材料的两步化学环配置的好处，该数学模型展示了化学环的原理如何应用于工业规模。现有的两步过程模型是基于缺陷化学模型，该模型将虚拟氧分压与增量参数和锶掺杂量联系起来。将使用实验室规模的反应堆试验台来验证该模型，并进一步探索TRCL配置的潜力。

This project will investigate the use of perovskite-type oxygen-carrier materials for hydrogen production via chemical looping from the water-gas shift reaction (CO + H2 <=> CO2 + H2O), specifically focusing on the Three-Reactor Chemical Looping (TRCL) process that involves the addition of an air oxidation step and can use CH4 or syngas as the reducing agent. This process eliminates the need to separate the H2 and CO2 product streams since the reactants do not come into contact with each other; the products and the oxygen carrier material intermediate are in different phases.Perovskite-type materials are able to demonstrate a wide range of different oxidising potentials due to their non-stoichiometry. In addition, their ability to incorporate a number of different metal cations of differing valance states within their cubic ABO3 structure allows for materials engineering of desired properties with point defect chemistry. In chemical looping from the water-gas shift reaction, these materials have typically been strontium doped lanthanum ferrite oxides of the form La1-xSrxFeO3-o.CO is an ideal reducing agent to use in laboratory-scale experiments involving chemical looping as it oxidises directly to CO2, thereby avoiding selectivity complications and simplifying the modelling involved. However it is not a realistic feed gas to use on an industrial scale since it does not naturally occur in large concentrations and its main production method is via the reverse Boudouard reaction. CH4 from natural gas is more abundant and has been identified as one of the more likely alternatives as a reducing agent. However the large endothermic heat of reaction when the oxygen-carrier material is reduced via oxidation of CH4 results in an energy deficit in two-step chemical looping systems with the water-gas shift reaction. The TRCL process has been proposed as a solution to this problem, with the addition of the air oxidation step allowing for the process to potentially be operated auto-thermally on an industrial scale, and maintaining full oxidation of the oxygen carrier material. Studies of the system efficiency using a steam compression and combustion turbine with metal-oxide oxygen carrier materials have predicted that significant amounts of heat could be recovered from the gas streams to make the TRCL process near self-sufficient in terms of electrical power consumption.The TRCL process conventionally involves a fluidised bed system with a separate fuel reactor, steam reactor and air reactor. For this study, an existing single packed bed reactor with counter-current gas flows will be used. The perovskite-type oxygen carrier material, which is fixed in place within the reactor, undergoes a series of cyclic reductions and oxidations as separate feeds of carbon-based fuel (such as CH4) and H2O in a balance of inert followed by air enter the reactor, allowing for the production of a H2 stream. Following each step in a cycle, the reactor is purged with a stream of inert, typically argon, in order to remove any trace amounts of the reactants or products. This is to prevent the uncontrolled oxidation of the reactants or products existing in concentrations above their lower explosive limits, which is an important safety concern.This work will provide a comparison of the benefits of the TRCL process with two-step chemical looping configurations using perovskite-type oxygen carrier materials by developing a mathematical model that shows how the principle of chemical looping might be applied to an industrial scale. An existing model for the two-step process is based on a defect chemistry model that relates the virtual oxygen partial pressure to the delta parameter and the amount of strontium doping. A laboratory-scale reactor rig will be used in order to verify the model and further explore the potential of the TRCL configuration.