Contents lists available at ScienceDirect International Journal of Greenhouse Gas Control journal homepage: www.elsevier.com/locate/ijggc Chemical-looping combustion of solid fuel in a 100 kW unit using sintered manganese ore as oxygen carrier C. Linderholm ⁎ , M. Schmitz, M. Biermann, M. Hanning, A. Lyngfelt Department of Space, Earth and Environment, Chalmers University of Technology, S-41296 Göteborg, Sweden ARTICLE INFO Keywords: Chemical-looping combustion Carbon capture and storage Oxygen carrier Manganese ore Solid fuels ABSTRACT Carbon capture and storage (CCS) offers the opportunity to avoid CO 2 emissions from for example power plants and cement factories. Chemical-looping combustion (CLC) is one of the most promising capture technologies with potentially very low cost of CO 2 capture. In this study we present findings from a solid-fuel 100 kW che- mical-looping combustor. A new oxygen carrier – a sintered manganese ore called Sinaus – has been studied in the Chalmers 100 kW unit. The material has been investigated for an operational time of 51.5 h using five fuels: two bituminous coals, two types of wood char, and petcoke. The operational results clearly demonstrate the viability of the CLC process. In comparison to previously used iron-based oxygen carriers, the Sinaus material showed higher gas con- version – up to 88% – and lower loss of char to the air reactor, with carbon capture reaching as high as 100%. Furthermore, the solid-fuel conversion was higher, which is mainly an effect of the choice of fuel size. It was found that the choice of fuel has a crucial impact on performance. Previous experience has shown that the use of large fuel particles gives low carbon capture, whereas pulverized fuel leads to low solid-fuel conversion. By choosing the appropriate – intermediate – size of fuel, it is possible to combine high carbon capture with high solid-fuel conversion. Previous studies indicate that the drawback of many manganese ores is the mechanical stability. Hence, a lot of emphasis was put on an in-depth study of the lifetime of the Sinaus material. Analyzing the production rate of fines, it was found the expected lifetime of the Sinaus particles was 100–400 h. This is lower than what has been found for iron-based material, but most likely sufficient for operation in full-scale chemical-looping applications. Whilst the production of fines was highest during operation with fuel, a lot of fines were produced also during operation without fuel. Seven experiments without fuel, i.e when the observed mechanical degradation was only due to high-velocity impacts and not chemical stress caused by phase transformations, gave a lifetime in the interval 220–1230 h. In conclusion, this first-of-its-kind investigation shows that the lifetime of the oxygen carrier is related to both the change in oxygen-carrier conversion and high-velocity impacts. 1. Introduction Carbon capture and storage is an economically attractive method of avoiding CO 2 emission into the atmosphere, with negative emissions being possible if biomass is used as fuel. Chemical looping combustion (CLC) is a technology that can drastically reduce the cost of CO 2 cap- ture, featuring systems based on interconnected fluidized beds com- prising metal oxide particles as oxygen carriers. These particles trans- port oxygen from combustion air to fuel, making CO 2 capture an inherent feature of the CLC process. The possibility to use CLC for CO 2 capture was suggested by Ishida et al. in the 1990s (Ishida and Jin, 1999), but the general process scheme of chemical looping was pa- tented already in 1954 by Lewis and Gilliland (2017), who realized the potential for CO 2 production. The steps of fuel conversion in a CLC process with solid fuels have been described in detail by Linderholm et al. (2012) Power production by solid-fuel CLC would share a substantial number of characteristics with state-of-the-art CFB combustion. Utility- scale power generation by CLC of solid fuels can be accomplished by an atmospheric, dual CLC-CFB, as suggested by Lyngfelt and Leckner (2015). On the path toward utility-scale CLC, continuous chemical- looping pilot systems are instrumental in the sense that they allow exploration of optimal reactor design solutions, and investigation of oxygen-carrier particles during relevant conditions. Several CLC units for solid fuels have been designed and operated in the size 0.5–50 kW (Linderholm et al., 2012; Berguerand and Lyngfelt, 2008; Shen et al., http://dx.doi.org/10.1016/j.ijggc.2017.07.017 Received 27 February 2017; Received in revised form 15 July 2017; Accepted 20 July 2017 ⁎ Corresponding author. E-mail address: carl.linderholm@chalmers.se (C. Linderholm). International Journal of Greenhouse Gas Control 65 (2017) 170–181 1750-5836/ © 2017 Elsevier Ltd. All rights reserved. MARK