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Chemical looping combustion of solid fuels

机译：固体燃料的化学循环燃烧

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Chemical Looping Combustion (CLC) has arisen during last years as a very promising combustion technology for power plants and industrial applications, with inherent CO2 capture which reduces the energy penalty imposed on other competing technologies. The use of solid fuels in CLC has been highly developed in the last decade and currently stands at a technical readiness level (TRL) of 6. In this paper, experience gained during CLC operation in continuous units is reviewed and appraised, focusing mainly on technical and environmental issues relating to the use of solid fuels. Up to now, more than 2700 h of operational experience has been reported in 19 pilot plants ranging from 0.5 kW(th) to 4 MWth. When designing a CLC unit of solid fuels, the preferred configuration for the scale-up is a two circulating fluidized beds (CFB) system. Coal has been the most commonly used solid fuel in CLC, but biomass has recently emerged as a very promising option to achieve negative emissions using bioenergy with carbon dioxide capture and storage (BECCS). Mostly low cost iron and manganese materials have been used as oxygen carriers in the so called in-situ gasification CLC (iG-CLC). The development of Chemical Looping with Oxygen Uncoupling (CLOU) makes a qualitative step forward in the solid fuel combustion, due to the use of materials able to release oxygen. The performance and environmental issues of CLC of solid fuels is evaluated here. Regarding environmental aspects, the pollutant emissions (SO2, NOx, etc.) released into the atmosphere from the air reactor are no cause of concern for the environment. However, the presence of SO2, NOx and Hg at the exit of the fuel reactor affects CO2 quality, which must be taken into account during the later compression and purification stages. The effect of the main variables affecting CLC performance is evaluated for fuel conversion, CO2 capture rate, and combustion efficiency obtained in different CLC units. Solid fuel conversion is normally not complete during operation, due to the undesired loss of char. A methodology is presented to extrapolate the current information to what could be expected in a larger CLC system. CO2 capture near 100% has been reported using a highly efficient carbon stripper, highly reactive fuels (such as lignites and biomass, etc.) or by the CLOU process. Operational experience in iG-CLC has showed that it is not possible to reach complete fuel combustion, making an additional oxygen polishing step necessary. For the further scale-up, it is essential to reduce the unburnt compounds at the fuel reactor outlet. Proposals to achieve this reduction already exist and include both improvement to the gas-oxygen carrier contact, or new design concepts based on the current scheme for iG-CLC. In addition, CLOU based on copper materials has shown that complete fuel combustion could be achieved. Main challenges for the future development and scale-up of CLC technology have been also identified. A breakthrough in the future development of CLC technology for solid fuels will come from developing long-life materials for CLOU that are easy to recover from the ash purge stream. (C) 2017 Elsevier Ltd. All rights reserved.
机译：近年来，化学循环燃烧（CLC）已经成为发电厂和工业应用中非常有前途的燃烧技术，它具有固有的CO2捕集功能，可减少对其他竞争技术的能耗。在过去的十年中，CLC中固体燃料的使用已得到高度发展，目前处于技术准备水平（TRL）为6。在本文中，本文将对连续单元在CLC操作过程中获得的经验进行评估和评估，主要侧重于技术以及与使用固体燃料有关的环境问题。截止到目前，据报道在19个试点电厂中有2700 h以上的运行经验，范围从0.5 kW（th）至4 MWth。在设计CLC固体燃料单元时，按比例放大的首选配置是两个循环流化床（CFB）系统。煤炭一直是CLC中最常用的固体燃料，但是生物质最近已成为一种非常有希望的选择，它可以利用具有捕获和存储二氧化碳（BECCS）的生物能源来实现负排放。在所谓的原位气化CLC（iG-CLC）中，大多数低成本的铁和锰材料已被用作氧气载体。由于使用了能够释放氧气的材料，因此，通过氧气解偶联（CLOU）进行化学循环的发展使固体燃料燃烧向前迈出了质的一步。此处评估了固体燃料CLC的性能和环境问题。在环境方面，空气反应堆释放到大气中的污染物排放（SO2，NOx等）与环境无关。但是，燃料反应器出口处SO2，NOx和Hg的存在会影响CO2的质量，在以后的压缩和净化阶段必须考虑到这一点。针对在不同CLC单元中获得的燃料转化率，CO2捕集率和燃烧效率，评估了影响CLC性能的主要变量的影响。由于不希望的炭损失，在操作期间固体燃料转化通常不能完成。提出了一种将当前信息外推到更大的CLC系统中可以预期的方法。据报道，使用高效的碳汽提塔，高反应性燃料（例如褐煤和生物质等）或通过CLOU工艺可捕获近100％的二氧化碳。 iG-CLC的操作经验表明，不可能完全燃烧燃料，因此需要额外的氧气抛光步骤。为了进一步扩大规模，必须减少燃料反应堆出口处的未燃化合物。已经存在实现这种减少的提议，并且包括改善气-氧载体接触或基于当前的iG-CLC方案的新设计概念。此外，基于铜材料的CLOU显示可以实现完全的燃料燃烧。还确定了CLC技术未来发展和规模扩大的主要挑战。固体燃料CLC技术未来发展的突破将来自为CLOU开发长寿命材料，该材料很容易从除灰流中回收。 （C）2017 Elsevier Ltd.保留所有权利。

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