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

该项目将研究钙钛矿型载氧材料在水煤气变换反应（CO + H2 <=> CO2 + H2O）中通过化学循环制氢中的应用，特别关注三反应器化学循环（TRCL）工艺，该工艺涉及增加空气氧化步骤，并可使用CH 4或合成气作为还原剂。该工艺无需分离H2和CO2产物流，因为反应物不会相互接触;产物和氧载体材料中间体处于不同的相态。钙钛矿型材料由于其非化学计量比而能够表现出各种不同的氧化电位。此外，它们在其立方ABO 3结构内结合不同价态的许多不同金属阳离子的能力允许具有点缺陷化学的所需性质的材料工程。在来自水煤气变换反应的化学循环中，这些材料通常是La 1-xSrxFeO 3-o形式的锶掺杂的铁酸镧氧化物。CO是涉及化学循环的实验室规模实验中使用的理想还原剂，因为它直接氧化成CO2，从而避免选择性复杂化并简化所涉及的建模。然而，它不是一种在工业规模上使用的现实进料气体，因为它不会自然地以高浓度存在，并且其主要生产方法是通过反向Boudouard反应。来自天然气的CH 4更丰富，并且已被确定为作为还原剂的更可能的替代物之一。然而，当载氧材料通过CH 4的氧化而被还原时，反应的大吸热导致在具有水煤气变换反应的两步化学循环系统中的能量不足。已经提出TRCL方法作为该问题的解决方案，其中添加空气氧化步骤，允许该方法潜在地在工业规模上自热操作，并保持氧载体材料的完全氧化。使用具有金属氧化物氧载体材料的蒸汽压缩和燃烧涡轮机的系统效率的研究已经预测，可以从气流中回收大量的热，以使TRCL方法在电力消耗方面接近自给自足。对于本研究，将使用具有逆流气流的现有单填充床反应器。在反应器内固定就位的钙钛矿型氧载体材料经历一系列的循环还原和氧化，因为惰性平衡中的碳基燃料（例如CH 4）和H2O的单独进料随后空气进入反应器，从而允许产生H2流。在循环中的每个步骤之后，用惰性流（通常为氩气）吹扫反应器，以除去任何痕量的反应物或产物。这是为了防止不受控制的氧化的反应物或产品存在的浓度高于其爆炸下限，这是一个重要的安全问题，这项工作将提供一个比较的TRCL过程的好处与两步化学循环配置使用钙钛矿型氧载体材料通过开发一个数学模型，显示化学循环的原则可能会被应用到一个工业规模。现有的两步工艺模型是基于一个缺陷化学模型，该模型将虚拟氧分压与δ参数和锶掺杂量联系起来。将使用实验室规模的反应堆装置来验证模型，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.