Contents lists available at ScienceDirect Energy Conversion and Management journal homepage: www.elsevier.com/locate/enconman Enhancement of Ca 2 Fe 2 O 5 oxygen carrier through Mg/Al/Zn oxide support for biomass chemical looping gasification Guicai Liu, Yanfen Liao ⁎ , Yuting Wu, Xiaoqian Ma Guangdong Key Laboratory of Efficient and Clean Energy Utilization Institutes, School of Electric Power, South China University of Technology, Guangzhou 510640, PR China ARTICLE INFO Keywords: Chemical looping gasification Oxygen carrier Brownmillerite Biomass gasification Phase transfer ABSTRACT Oxygen carriers (OCs) determined the performance of biomass chemical looping gasification (CLG). This work focused on the potential effects of Mg/Al/Zn oxides on the CLG reactivity of brownmilerite-type Ca 2 Fe 2 O 5 , and the interactions between them were studied. The results showed Al oxide was unsuitable as support for Ca 2 Fe 2 O 5 , because it broke the crystalline structure of Ca 2 Fe 2 O 5 and weakened the syngas selectivity in CLG. ZnO could enhance the syngas production property, but reduced into metal Zn, thus was also unacceptable to be added into Ca 2 Fe 2 O 5 . MgO addition enhanced the oxygen release capacity of Ca 2 Fe 2 O 5 , and the TGA and fixed bed tests showed the improvement in biomass CLG performance. MgO also provided a solvent for the reduced OC, which would raise its melting temperature by the dissolution, thus enhance the OC ability in multiple redox reactions. The 10 redox times test also showed the prepared MgO/Ca 2 Fe 2 O 5 could almost kept stable reactivity. The study also provided a strategy for designing other redox materials operated in high temperature, like chemical looping or calcium looping. 1. Introduction Gasification is an efficient method to promote its fuel quality for biomass [1,2]. The produced syngas could be directly combusted for power generation, or adopted as the source of Fischer–Tropsch synth- esis for gasoline production [3]. Generally, biomass gasification needs some oxygen to realize the partial oxidation purpose. Using air as ga- sification agent will bring high content of nitrogen, which lowers the heating value of synthesis gas and might produce the thermal NO X ; pure-oxygen gasification would highly increase the energy consumption and cost. Chemical looping gasification (CLG) provides an approach to overcome these problems [4], and attracts more and more concerns [5]. Different from conventional gasification, the oxygen source in CLG is from the oxygen carriers (OCs), which provide the oxygen for biomass partial oxidation, avoiding the nitrogen introduction or the high cost of pure oxygen preparation. CLG needs two reactors, including fuel re- actor (FR) and air reactor (AR). The OC is reduced by solid fuel with syngas production in FR, then transferred into AR to recover the lattice oxygen through oxidizing by air. In this process, the gas products could also be adjusted by different kinds of OC materials. Different from other chemical looping process, CLG requires that OCs have high reactivity with biomass pyrolysis products, but low re- activity of CO/H 2 oxidation, because OCs are required to react with char through solid–solid reaction, and avoid the complete oxidation. Fe 2 O 3 -based OC was most widely used in CLG study, due to its low cost and acceptable reactivity. Researchers generally used Fe 2 O 3 [6–8], Fe 2 O 3 /Al 2 O 3 [9–12] and hematite [11–16] as OC to study the basic characteristics of solid fuel CLG. In order to obtain higher reactivity and selectivity for synthesis gas production, some Fe-contained composite oxides were prepared by researchers. Some of them focused on the reactivity, and prepared spinel oxide NiFe 2 O 4 [17–19] and Fe-Ni-Al composite oxides [20]. The results verified the activity enhancement in CLG with Ni addition forming composite oxides. Others concentrated on the selectivity improvement. Their results showed that the synthe- sized BaFe 2 O 4 , CaFe 2 O 4 [21], Ca 2 Fe 2 O 5 [22] and FeAl 2 O 4 [23] had greater CO/H 2 production and lower CO 2 production than Fe 2 O 3 . The unit cell of brownmillerite-type oxide Ca 2 Fe 2 O 5 was composed of alternating FeO 4 tetrahedron and FeO 6 octahedron, with an ordered oxygen-deficiency structure [24]. Due to the existence of oxygen va- cancy in the structure, O 2- ion was easier to transfer, and it could keep a great reactivity with solid fuel. Furthermore, the calcium at the A site had effects on catalytic tar crack. The application in chemical looping hydrogen generation (CLHG) [25–28] showed that Ca 2 Fe 2 O 5 directly reduced into Fe 0 , without other ferric oxides like Fe 3 O 4 or FeO, and it would be oxidized back to Fe 3+ and revived into Ca 2 Fe 2 O 5 after steam oxidation. In solid fuel CLG, Ca 2 Fe 2 O 5 had greater selectivity than https://doi.org/10.1016/j.enconman.2019.04.087 Received 1 April 2019; Received in revised form 22 April 2019; Accepted 28 April 2019 ⁎ Corresponding author. E-mail address: yfliao@scut.edu.cn (Y. Liao). Energy Conversion and Management 195 (2019) 262–273 0196-8904/ © 2019 Elsevier Ltd. All rights reserved. T