Bulk monolithic Ce–Zr–Fe–O/Al2O3 oxygen carriers for a fixed bed scheme of the chemical looping combustion: Reactivity of oxygen carrier. (1st February 2016)

• Record Type: Journal Article
• Authors: Gu, Zhenhua; Li, Kongzhai; Wang, Hua; Qing, Shan; Zhu, Xing; Wei, Yonggang; Cheng, Xianming; Yu, He; Cao, Yan
• Is Part Of: Applied energy. Volume 163(2016)
• Page Start: 19
• Page End: 31
• Publication Date: 2016-02-01
• Subjects: Chemical looping combustion -- Bulk monolithic oxygen carrier -- Fixed bed reactor -- Ce–Zr–Fe–O/Al2O3 -- Redox stability; Power (Mechanics) -- Periodicals; Energy conservation -- Periodicals; Energy conversion -- Periodicals; 621.042
• DOI: 10.1016/j.apenergy.2015.10.177
• Languages: English
• ISSNs: 0306-2619

Abstract

Graphical abstract: In the present work, we describe for the first time the utilization of bulk monolithic oxygen carrier for chemical looping combustion of methane in a fixed bed reactor. Bulk monolithic Ce–Zr–Fe–O/Al2 O3 oxygen carrier owns very high activity and stability during the chemical looping process. For the large scale utilization, the monolith makes introducing of the gas feed in multiple points along the reactor to improve the gas–solid reaction possible. Highlights: The intrinsic reactivity of the powder oxygen carrier for CH4 oxidation can be totally inherited by the monolithic one. The monolithic oxygen carrier represented good performance for the chemical looping combustion of CH4 in high GHSVs. The requirement on the mechanical strength of the monolithic oxygen carrier is much lower compared with the pellets. Abstract: The size and geometry of oxygen carriers are one of the key factors to determine the efficiency of a large-scale chemical looping combustion (CLC) system in fixed bed reactors, because they strongly affect the dynamic conditions of the gas–solid reactions, such as the intra particle mass transfer limitation for reactants, the pressure drop and the flow distribution. In the present work, we describe for the first time the utilization of bulk monolithic oxygen carriers for chemical looping combustion of methane in a fixed bed reactor. The comparison on the structure and reactivity of the monolithic Ce–Zr–Fe–O/Al2 O3 oxygen carrier with the powder one is investigated in detail. The successive CH4 -reduction/air-oxidation redox testing of the monolithic oxygen carrier is also performed. It is found that the Ce–Zr–Fe–O/Al2 O3 oxygen carriers own high activity for methane complete oxidation due to the strong active component (i.e., Ce–Zr–Fe–O) to support (i.e., Al2 O3 ) interaction. The powder and monolithic oxygen carriers show similar reduction behaviors either in hydrogen or in methane atmosphere. This indicates that the utilization of organic binders and additives in the fabrication procedures of the monolith has no significant effect on the reducibility of the oxygen carrier. The monolithic oxygen carriers used in the chemical looping combustion of methane in its natural form (4.5 cm long, 6.0 cm in diameter, square cell size of 2.0 mm, and wall thickness of 0.9 mm) represent high activity in a high gas hourly space velocity (GHSV, 6000 h −1 ). This can be attributed to the special geometric structure and layered microstructure. The activity of the monolithic oxygen carrier is also very stable in the successive redox process. On the other hand, the requirement on the mechanical strength of the monolithic oxygen carrier is much lower than that toward the pellets, which allows the oxygen carrier to have relatively high specific surface area in a large-scale CLC system. The monolith reveals very high structure stability in both macro and micro aspect during the chemical looping process.