Application of the Carbon Looping (CarboLoop) Concept in a Novel Twin-Bed Reactor

CarboLoop is an innovative method, developed and patented by Senneca and Salatino [1], for combustion of coal with inherent separation of CO2 which represents an alternative to chemical looping combustion (CLC) for solid carbons. Unlike other CLC processes, in CarboLoop there is no need for oxygen carriers because the property of carbons to uptake oxygen at low temperatures, forming oxygenated surface complexes, and to release them as CO and CO2 at higher temperatures is exploited. The CarboLoop concept requires the utilization of two reactors (in particular two interconnected fluidized beds): an Oxidizer, where the coal is kept in contact with air at relatively mild temperature (200-300°C) to foster oxygen chemisorption, and a Desorber, operating at higher temperature (700-800°C) where the oxygenated C-O compounds are desorbed in an almost pure CO2 stream. The first proof-of-concept of CarboLoop has been given by discontinuous experiments in a thermogravimetric analyzer. Experiments have been carried out using different solid carbon materials and aimed at assessing the extent and rate of oxygen uptake at different temperatures. In this study the CarboLoop concept is tested for the first time on a bituminous char in an innovative lab-scale fluidized bed apparatus purposely developed for the characterization of looping processes. Cycles of oxidation/desorption have been carried out and CO and CO2 concentrations have been monitored at the exhaust. Results demonstrate the capability of char to uptake oxygen at low temperature and release CO and CO2 at higher temperature.