Steam carbon gasification of a nickel based oxygen carrier Francois-Xavier Chiron, Gregory S. Patience ⇑ Department of Chemical Engineering, École Polytechnique de Montréal, C.P. 6079 Succ. ‘‘CV’’ Montréal, H3C 3A7 Québec, Canada article info Article history: Received 15 July 2010 Received in revised form 9 February 2011 Accepted 20 February 2011 Available online 5 March 2011 Keywords: Chemical Looping Combustion Coking Oxygen carrier SCG Micro-fluidized bed abstract Ni-based oxygen carriers are promising candidates for Chemical Looping applications due to a combina- tion of excellent methane conversion performance, mechanical stability, oxygen transfer capacity. How- ever, experiments conducted on NiO/NiAl 2 O 4 in a micro-fluidized bed reactor show that methane forms coke on active nickel sites. In subsequent tests, water vapour was fed to the coked Ni oxygen carrier pro- ducing a highly concentrated stream of CO/H 2 (1/1). In the absence of water vapour, production of hydro- gen dropped with time while a methane/argon mixture was fed to the reactor. Co-feeding water together with methane improves stability – both H 2 production and carbon deposition were constant for over 1 h. Despite the tremendous lay down of carbon, catalytic activity remained stable at levels as low as 3 vol.% water vapour (and 10% methane). Water vapour is an effective oxidant for Ni(0) but is insufficient to entirely re-oxidize the oxygen carrier from Ni to NiO. Ó 2011 Elsevier Ltd. All rights reserved. 1. Introduction The first transport fluidized bed reactors appeared in the 1940s for the catalytic cracking of hydrocarbons, which became known as Fluid Catalytic Cracking (FCC) with improvements in technology. This process evolved and was applied in the 1970s as the first industrial Circulating Fluidized Bed (CFB) to calcine alumina [1]. Since the early 1980s, both industry and academia have shown a great interest in CFB for combustion processes due to their superior environmental characteristics. Besides combustion applications, new processes based on CFB technology where developed to pro- duce chemicals, such as DuPont’s n-butane partial oxidation pro- cess to make maleic anhydride using VPO as a catalyst [2]. VPO in the V 5+ state is a source of oxygen to partially oxidize n-butane. The catalyst is then circulated to a regenerator were it is oxidized by air (from the V 4+ state to V 5+ ). Chemical Looping Combustion (CLC) is based on the same principles as DuPont’s process to pro- duce maleic anhydride. Patience and Bordes-Richard highlighted the main issues related to the development of such a process – from the catalyst development to the hydrodynamics in a commer- cial scale CFB – in the preface of the International VPO Workshop [3]. 1.1. Chemical looping technology Due to environmental pressure towards CO 2 emissions in the last decade, research in this field has greatly intensified. CLC is capable of producing electricity from a wide range of fuels (solids, liquids and gases) with minimal CO 2 and NO x emissions. It is based on circulating a solid oxygen carrier – typically a metal oxide – between two fluidized beds: fuel reactor and air reactor. In the fuel reactor, the metal oxide is reduced by a hydrocarbon and a mixture of H 2 O and CO 2 is produced. In the air reactor, the reduced metal reacts with molecular oxygen to be reconstituted to the oxide. Many metal oxides have been tested [4] and one of the most effective is NiO. Ni oxidation by oxygen from air is extremely exo- thermic (r2) but the reaction between the oxide and the fuel is highly endothermic (r1): 4NiO þ CH 4 ! CO 2 þ 2H 2 O þ 4Ni DH 1200 K ¼ 136 kJ=mol ðr1Þ Ni þ 1=2O 2 ! NiO DH 1200 K ¼234 kJ=mol ðr2Þ Balancing the energy is a key factor for this process. Sufficient heat must be transferred from the air reactor to compensate for the endothermicity of the fuel reactor. It may either be transferred by the particles, or by heat exchangers. A variant of CLC is Chemical Looping Reforming (CLR) where the desired product is syngas (CO + H 2 ) instead of electrical power. The process remains the same but the fuel combustion is limited to partial oxidation: NiO þ CH 4 ! Ni þ 2H 2 þ CO DH 1200 K ¼ 211 kJ=mol ðr3Þ It is possible to promote partial oxidation by controlling both the residence time distribution of the oxygen carrier in the fuel reactor and its oxidation state. A schematic of a prototype is reproduced in Fig. 1 and shows the principal elements including a fuel reactor (fluidized bed), riser-transport bed (air reactor), cyclones, and standpipes. This configuration is adapted from DuPont’s Butane Oxidation process to produce maleic anhydride 0016-2361/$ - see front matter Ó 2011 Elsevier Ltd. All rights reserved. doi:10.1016/j.fuel.2011.02.029 ⇑ Corresponding author. Tel.: +1 514 3404711x3439; fax: +1 514 340 4159. E-mail addresses: francois-xavier.chiron@polymtl.ca (F.-X. Chiron), gregory-s. patience@polymtl.ca (G.S. Patience). Fuel 90 (2011) 2461–2466 Contents lists available at ScienceDirect Fuel journal homepage: www.elsevier.com/locate/fuel