Kinetics of Calcination of Partially Carbonated Particles in a Ca-Looping System for CO₂ Capture

Abstract

Post-combustion CO 2 capture based on Ca-looping process, CaL, is a promising technology under development based on the reversible reaction between CaO and CO 2 to form CaCO 3 and the regeneration of the CaO by calcination of CaCO 3 in a rich CO 2 atmosphere. This work is focused on the study of the calcination kinetics with typical solid conditions expected in these systems. Calcination rates of carbonated materials derived from two limestones have been measured at different number of carbonationcalcination cycles, as a function of temperature and CO 2 partial pressure. It has been observed that calcination reaction is chemically controlled for particles below 300 m of particle size, as internal mass transfer is negligible even under the presence of CO 2 in the reaction atmosphere. Calcination rate (expressed per mol of initial CaO) depends on calcination temperature and CO 2 partial pressure, whereas CaCO 3 content and/or particle lifetime do not affect the reaction rate. The basic kinetic model of Szekely et al. (1970) is shown to be valid to fit the new data. Based on these results it is shown that calcination temperatures between 880-920ºC could be sufficient to achieve nearly

In situ X-ray diffraction of CaO based CO2 sorbents

“…Particle size has been shown to influence the mechanism of CO 2 capture and calcination in CaO based materials like for example effects regarding heat and mass transfer. 32,[69][70][71] TEM analysis showed the presence of Ca(OH) 2 crystallites nominally 83×16 nm in size, which compares well with the values calculated from synchrotron diffraction of 75×16 nm. The good agreement between these two very different methods provides strong evidence that the analysis of the anisotropic broadening is robust, and that the calculations of strain and stress presented here are also reliable.…”

CaCO3 calcination by the simultaneous reduction of CuO in a Ca/Cu chemical looping process

“…To describe the calcination kinetics of the calcium carbonate, the shrinking core model proposed by Martínez et al (2012) was chosen: dX cal dt ¼ k cal ð1 À X cal Þ 2=3 ðC CO 2;eq À C CO 2 Þ ð 4Þ Table 1 Mass and energy balances used in the model. Ergun equation (Ergun, 1952) dP dZ ¼ À150 ug 1 À ε ð Þ 2 dp 2 ε 3 þ 1:75 ug 2 1 À εÞ dp ε 3 Table 2 The axial mass and heat dispersion coefficients.…”

On the negative activation energy for limestone calcination at high temperatures nearby equilibrium

“…On the other hand, the calciner reactor in pilotscale tests is operated in the fast fluidization regime, which provides a high efficiency of heat and mass transfer in the typically short residence times (of just a few minutes). Calcination of the partially carbonated solids (with a typical molar carbonate content of 15% after many cycles) is conceivably attained at about T C 900 1C in relatively short times as inferred from thermogravimetric analysis (TGA) tests (Martinez et al, 2012a;Valverde et al, 2014a). Yet, the calciner temperature in practice has to be increased up to T C 930 1C (or, equivalently, the ratio P=P eq decreased to P=P eq C 0:6) in order to achieve a high calcination efficiency of the make-up flow of natural limestone (Charitos et al, 2011;Arias et al, 2013;Ströhle et al, 2014), which imposes an important energy penalty to the technology (Martinez et al, 2012b.…”