Role of precalcination and regeneration conditions on postcombustion CO2 capture in the Ca-looping technology

• Published in: Applied energy 2014-12, Vol.136, p.347-356
• Main Authors: Valverde, J.M., Sanchez-Jimenez, P.E., Perez-Maqueda, L.A.
• Format: Article
• Language: English
• Subjects: Applied sciences; Ca-looping; CO2 capture; Energy; Exact sciences and technology; Limestone calcination; Solid sorbents
• ISSN: 0306-2619; 1872-9118
• DOI: 10.1016/j.apenergy.2014.09.052

Limestone samples after 20 carbonation/regeneration cycles. [Display omitted] •CO2 capture performance of limestone at Ca-looping conditions is investigated.•CaO is regenerated at high temperature and high CO2%.•Precalcination in air hinders CO2 capture and causes particle fragmentation.•Precalcination at high T/high CO2% mitigates sorbent deactivation.•Heat treatment and recarbonation enhance CO2 capture if limestone is precalcined at high T/high CO2%. The Ca-looping (CaL) technology is already recognized as a potentially viable method to capture CO2 from postcombustion gas in coal fired power plants. In this process, CO2 is chemisorbed by CaO solid particles derived from precalcination of cheap and widely available natural limestone. The partially carbonated solids are regenerated by calcination under high CO2 concentration. Novel CaL concepts are proposed to further improve the efficiency of the technology such as the introduction of a recarbonation reactor in between the carbonation and calcination stages to mitigate the progressive deactivation of the regenerated CaO. Process simulations aimed at retrieving optimum design parameters and operating conditions to scale-up the technology yield results critically dependent on the multicyclic sorbent performance. Nevertheless, technical limitations usually preclude lab-scale tests from mimicking realistic CaL conditions necessarily involving high CO2 concentration for sorbent regeneration and quick transitions between carbonation and calcination. In this work, a lab-scale experimental analysis is reported on the CaO multicyclic conversion at CaL conditions closely resembling those to be expected in practice. The results presented evidence a relevant role of precalcination conditions. Precalcination in air leads to a strongly adverse effect on the activity of the sorbent regenerated under high CO2 concentration, which is further hindered if a recarbonation stage is introduced. On the other hand, sorbent deactivation is mitigated if precalcination is carried out at conditions similar to those used for sorbent regeneration. In this case, recarbonation helps lessening the loss of multicyclic conversion, which is further enhanced by the synergistic combination with heat pretreatment. Moreover, the present study shows that the kinetics of carbonation is strongly dependent on precalcination and regeneration conditions. The diffusion controlled carbonation phase and recarbonation are intensified if the sorbent is p