Assessment of Thermochemistry aand Preliminary Design of a Carbon Looping Combustion Process (CarboLoop)

The CarboLoop concept proposed by Salatino and Senneca [1] pursues the simple idea that a carbon-based fuel can act itself as oxygen carrier as it is cycled between an Oxidizer, where the fuel uptakes oxygen at moderate temperature (say 300-400°C), and a Desorber where desorption of surface oxides is accomplished in inert atmosphere at higher temperature (in the order of 700°C). Looping of the carbon fuel between the oxidizer and the desorber enables stepwise conversion of carbon over multiple cycles yielding a nearly pure stream of CO2, ready for sequestration, at the exhaust of the Desorber. This study further contributes to the exploitation of the CarboLoop concept by reporting on the thermochemistry of the oxidation and desorption stages and by analyzing issues associated with energy integration between the Oxidizer and the Desorber. A calorimetric study on raw and pre-oxidized carbon samples indicates that carbon oxidation at temperatures in the order of 300-400°C is moderately exothermic, whereas a pronounced exothermicity is displayed upon exposure of the oxidized samples at higher temperature. The proposed mechanistic frame is based on the formation of "metastable" complexes upon exposure to oxygen at moderate temperature, followed by isomerization/rearrangement into "stable" oxides and subsequent desorption at higher temperature. Thermochemical and kinetic data provide the basis for a preliminary layout of the CarboLoop process. Carbon inventory and circulation rate between the Oxidizer and the Desorber and thermal loading in either reactor are assessed with reference to an assigned thermal throughput and set of operating/design parameters.