Abstract
Eight different oxygen carriers (OC) containing CuO (60 wt %) and different mass ratios of CaO to Al2O3 as the support were synthesized by wet-mixing followed by calcination at 1000 °C. The method of synthesis used involved the formation of calcium aluminum hydrate phases and ensured homogeneous mixing of the Ca2+ and Al3+ ions in the support at the molecular level. The performance of the OCs for up to 100 cycles of reduction and oxidation was evaluated in both a thermogravimetric analyzer (TGA) and a fluidized bed reactor, covering a temperature range of 800 to 950 °C. In these cycling experiments, complete conversion of the OC, from CuO to Cu and vice versa, was always achieved for all OCs. The reactivity of the materials was so high that no deactivation could be observed in the TGA, owing to mass transfer limitations. It was found that OCs prepared with a mass ratio of CaO to Al2O3 in the support >0.55 agglomerated in the fluidized bed, resulting in an apparent deactivation over 25 cycles for all tempe...
Highlights
In the chemical looping combustion (CLC) of solid fuels, achieving a sufficiently high rate of gasification of the char to synthesis gases in the fuel reactor is often difficult.[1−3] at typical operating temperatures (∼900 °C) some metal oxides, e.g., those containing Cu(II) or Mn(III), decompose to a lower metal oxide with the production of gas-phase oxygen. These materials are of interest for chemical looping with oxygen uncoupling (CLOU), a variant of CLC in which the char is largely oxidized by the gaseous oxygen released by certain oxygen carriers (OC), rather than being gasified to synthesis gas, which in turn reduces the OC.[1]
The method of preparation involved the formation of calcium aluminum hydrate phases, which transformed into Ca− Al layered double-hydroxide (LDH) and ensured homogeneous mixing of the Ca2+ and Al3+ ions at the molecular level
In the fluidized bed reactor (FBR), the OCs were exposed to harsher reaction conditions that, in some cases, resulted in significant differences in the cyclic performance compared with the thermogravimetric analyzer (TGA)
Summary
In the chemical looping combustion (CLC) of solid fuels, achieving a sufficiently high rate of gasification of the char to synthesis gases in the fuel reactor is often difficult.[1−3] at typical operating temperatures (∼900 °C) some metal oxides, e.g., those containing Cu(II) or Mn(III), decompose to a lower metal oxide with the production of gas-phase oxygen.these materials are of interest for chemical looping with oxygen uncoupling (CLOU), a variant of CLC in which the char is largely oxidized by the gaseous oxygen released by certain oxygen carriers (OC), rather than being gasified to synthesis gas, which in turn reduces the OC.[1]Leion et al.[2] showed that, compared to conventional CLC, the overall rate of conversion of, e.g., petroleum coke to products of combustion was enhanced in CLOU (with a CuObased OC) by a factor of ∼80. In the chemical looping combustion (CLC) of solid fuels, achieving a sufficiently high rate of gasification of the char to synthesis gases in the fuel reactor is often difficult.[1−3] at typical operating temperatures (∼900 °C) some metal oxides, e.g., those containing Cu(II) or Mn(III), decompose to a lower metal oxide with the production of gas-phase oxygen. Circulating fluidized bed (CFB) reactors would probably be used for CLC at large scale, i.e., several hundred MWth.[4,5] The OC particles in such reactors would undergo significant mechanical stress, and the priority should be to improve their mechanical stability,[6] to minimize losses by attrition and particle breakup This is especially important where CLOU is to be used, because the oxides suitable for CLOU, e.g., CuO, are more costly than those used in conventional CLC, e.g., iron oxide, possibly by a factor of ∼10.7
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