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Chemical looping combustion of solid fuels
Progress in Energy and Combustion Science ( IF 32.0 ) Pub Date : 2018-03-01 , DOI: 10.1016/j.pecs.2017.07.005
J. Adánez , A. Abad , T. Mendiara , P. Gayán , L.F. de Diego , F. García-Labiano

Abstract 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 kWth 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.

中文翻译:

固体燃料的化学循环燃烧

摘要 化学循环燃烧 (CLC) 在过去几年已成为发电厂和工业应用中非常有前途的燃烧技术,其固有的 CO2 捕获减少了对其他竞争技术施加的能量损失。在过去十年中,固体燃料在 CLC 中的使用得到了高度发展,目前处于 6 级技术就绪水平 (TRL)。 本文回顾和评价了 CLC 在连续机组运行过程中获得的经验,主要侧重于技术与使用固体燃料有关的环境问题。截至目前,已在 0.5 kWth 至 4 MWth 的 19 个试点工厂中报告了超过 2700 小时的运行经验。在设计固体燃料 CLC 装置时,放大的首选配置是两个循环流化床 (CFB) 系统。煤一直是 CLC 中最常用的固体燃料,但最近生物质已成为一种非常有前途的选择,可以使用带有二氧化碳捕获和储存的生物能源 (BECCS) 实现负排放。大多数低成本的铁和锰材料已被用作所谓的原位气化 CLC (iG-CLC) 中的氧载体。由于使用了能够释放氧气的材料,带氧解偶联的化学循环 (CLOU) 的发展使固体燃料燃烧向前迈进了定性的一步。这里评估了固体燃料 CLC 的性能和环境问题。在环境方面,空气反应器释放到大气中的污染物排放物(SO2、NOx 等)不会引起环境问题。然而,SO2 的存在,燃料反应器出口处的 NOx 和 Hg 会影响 CO2 的质量,在后期的压缩和净化阶段必须考虑到这一点。评估影响 CLC 性能的主要变量的影响,包括在不同 CLC 装置中获得的燃料转化率、CO2 捕获率和燃烧效率。由于不希望有的炭损失,固体燃料转化通常在操作期间不完全。提出了一种方法来将当前信息外推到更大的 CLC 系统中可以预期的信息。据报道,使用高效碳汽提塔、高反应性燃料(如褐煤和生物质等)或通过 CLOU 工艺可捕获接近 100% 的 CO2。iG-CLC 的运行经验表明,不可能实现燃料完全燃烧,因此需要额外的氧气精制步骤。为了进一步扩大规模,必须减少燃料反应器出口处未燃烧的化合物。实现这种减少的建议已经存在,包括改进气氧载体接触,或基于 iG-CLC 当前方案的新设计概念。此外,基于铜材料的 CLOU 已经表明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化的主要挑战。未来固体燃料 CLC 技术发展的突破将来自于为 CLOU 开发易于从灰清除流中回收的长寿命材料。实现这种减少的建议已经存在,包括改进气氧载体接触,或基于 iG-CLC 当前方案的新设计概念。此外,基于铜材料的 CLOU 已经表明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化的主要挑战。未来固体燃料 CLC 技术发展的突破将来自于为 CLOU 开发易于从灰清除流中回收的长寿命材料。实现这种减少的建议已经存在,包括改进气氧载体接触,或基于 iG-CLC 当前方案的新设计概念。此外,基于铜材料的 CLOU 已经表明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化的主要挑战。未来固体燃料 CLC 技术发展的突破将来自于为 CLOU 开发易于从灰清除流中回收的长寿命材料。
更新日期:2018-03-01
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