CO₂ carrying behavior of calcium aluminate pellets under high-temperature/high-CO₂ concentration calcination conditions

Sintering and a resulting loss of activity during calcination/carbonation can introduce substantial economic penalties for a CO₂ looping cycle using CaO-based sorbents. In a real system, sorbent regeneration must be done at a high temperature to produce an almost pure CO₂ stream, and this will increase both sintering and loss of sorbent activity. The influence of severe calcination conditions on the CO₂ carrying behavior of calcium aluminate pellets is investigated here. Up to 30 calcination/carbonation cycles were performed using a thermogravimetric analyzer apparatus. The maximum temperature during the calcination stage in pure CO₂ was 950 °C, using different heating/cooling rates between two carbonation stages (700 °C, 20% CO₂). For comparison, cycles were also done using N ₂ during the calcination stages. In addition, the original Cadomin limestone, used for pelletization, was also examined in its original form and the results obtained were compared with those for the aluminate pellets. As expected, high temperature during calcination strongly reduced CO₂ carrying capacities of both sorbents. However, aluminate pellets showed better resistance to these severe conditions. The conversion profiles obtained are significantly different to those obtained under milder conditions, with significant increased activity during the slower, diffusion-controlled, carbonation stage. Moreover, scanning electron microscopy analysis of samples after prolonged carbonation showed that pore filling occurred at the sorbent particle surfaces preventing diffusion of CO₂ toward the particle interior.