Reactivity of Some Metal Oxides Supported on Alumina with Alternating Methane and OxygenApplication for Chemical-Looping Combustion

Abstract

Chemical-looping combustion (CLC) is a combustion technology with inherent separation of the greenhouse gas CO2. The technique involves the use of a metal oxide as an oxygen carrier, which transfers oxygen from the combustion air to the fuel. Two reactors are used in the process: (i) a fuel reactor where the metal oxide is reduced by reaction with the fuel, and (ii) an air reactor where the reduced metal oxide from the fuel reactor is oxidized with air. The possibility of using oxides of Cu, Co, Mn, and Ni as oxygen carriers was investigated. Particles were prepared by deposition of the metal oxides on γ-Al2O3 particles by so-called dry impregnation. The reactivity of the oxygen carrier particles was evaluated in a thermogravimetric analyzer (TGA), where the alternating atmosphere which an oxygen carrier encounters in a CLC system was simulated by exposing the sample to alternating reducing (10% CH4, 5% CO2, 10% H2O) and oxidizing (10% O2) conditions at temperatures between 750 and 950 °C. The particles of Ni and Cu showed high reactivity at all temperatures and cycles, with reduction rates of up to 100%/min for CuO and 45%/min for NiO and oxidation rates of up to 25%/min for the oxidation of both reduced metals. Oxides of Mn and Co showed a limited extent of reaction, which was explained by the chemical reaction of the metal oxide with the alumina, with the formation of highly irreversible phases which do not react with methane and oxygen. Thus, Mn and Co are not suitable as oxygen carriers for CLC when supported on Al2O3. From the reactivity data of the nickel and copper oxygen carriers, it was estimated that 460−620 kg/MW oxygen carrier would be needed in the reactors. Similarly, from the oxygen transfer capacity of the particles, the solids circulation rate between the fuel and air reactor would need to be between 1 and 8 kg MW-1 s-1.

Chemical Looping Process - A Novel Technology for Inherent CO2 Capture

“…Ni-, Fe-, Cu-, Mn-and Co-based metal oxides are the typical materials to be employed as oxygen carrier for chemical looping process (Mattisson et al, 2003). CaSO 4 was also used for transferring oxygen for methane combustion in fluidized bed reactors (Song et al, 2009 (Adanez et al, 2004).…”

Effect of support on reactivity and selectivity of Ni-based oxygen carriers for chemical-looping combustion

“…In addition, other characteristics such as easy preparation to reduce costs are interesting. Iron, nickel, copper, and manganese have been selected as the most promising active metals to be used in a CLC process [4][5][6]. Also the selection of a suitable support material is very important.…”

Establishment of an Environmental Control Technology Laboratory with a Circulating Fluidized-Bed Combustion System

“…The metal oxides with its reduced metal oxides or metals, which are used as oxygen carriers in the CLC must have sufficient reaction activity in reduction and oxidation and enough strength to limit particle breakage and attrition. A number of metals have been discussed in the literature 21,[22][23][24][25][26][27][28][29][30][31][32][33][34][35][36][37][38] , such as Fe, Ni, Co, Cu, Mn, and Cd, as well as some metal composites. Based on an oxygen transfer capability, energy balance analysis and thermodynamics analysis, copper (Cu) seems to be the better choice as an oxygen carrier for the CLC system of solid fuels.…”

“…Previous studies indicated that Cu-based oxygen carriers had reactivity of 100 % reduction within minutes at lower temperatures (600-900 o C) [37][38][39][40] in the fixed bed or fluidized bed testing facilities. When copper oxide was doped on substrate, it indicated that most of its oxygen is active for reaction with methane, and the highest efficiency could be achieved with reduction rates up to 100 %/min and oxidation rates up to 25 %/min.…”