Operation of a cyclonic preheater in the Ca-looping for CO2 capture

Limestone calcination under calcium-looping conditions for CO2 capture and thermochemical energy storage in the presence of H2O: an in situ XRD analysis

The presence of H₂O at very low concentrations in the calciner significantly accelerates decomposition, while the resulting CaO crystal structure and reactivity are not modified.

Effect of dolomite decomposition under CO2 on its multicycle CO2 capture behaviour under calcium looping conditions

The mechanism of dolomite decomposition under CO₂ is responsible for its superior CO₂ capture performance as compared to limestone.

Energy Intensity Reduction of Ca-Looping CO2 Capture by Applying Mixing Loop Seals and Cyclonic Systems

This work faces the challenge of cutting the specific energy demand in the CO2 capture process based on Ca-looping technology. The use of high-temperature sorbents allows an efficient integration of the excess heat flows. Up to now, several investigations studied the Ca-looping integration with external systems such as a steam cycle. In this research, a further step is done by comparing technological solutions for the internal heat integration with the aim of reducing the energy needs. Particles preheating before entering the regeneration reactor appears as an opportunity for energy saving since solids have to be heated up around 250–300°C from one reactor to another. Two different internal heat integration possibilities making use of a particle separation device and a mixing valve are presented and compared. The former consists of the inclusion of a cyclonic preheater. This configuration presents the a priori advantage of a more developed technology since it is widely used in the cement industry but the drawback of a worse gas–solid heat exchange. Although there is a lack of practical experience regarding the use of a single seal valve to feed two reactors, this configuration presents a promising prospective related to the excellent heat exchange features of the solid flows. The aim is to obtain comparative results by means of implementing advanced thermochemical models, in order to make progress on the development of less energy-intensive configurations of the calcium looping.

Crystallographic transformation of limestone during calcination under CO2

The calcination of limestone under CO₂ is determined by a topotactic transformation.

Relevant influence of limestone crystallinity on CO₂ capture in the Ca-looping technology at realistic calcination conditions

We analyze the role of limestone crystallinity on its CO2 capture performance when subjected to carbonation/calcination cycles at conditions mimicking the Ca-looping (CaL) technology for postcombustion CO2 capture. The behavior of raw and pretreated limestones (milled and thermally annealed) is investigated by means of thermogravimetric analysis (TGA) tests under realistic sorbent regeneration conditions, which necessarily involve high CO2 partial pressure in the calciner and quick heating rates. The pretreatments applied lead to contrasting effects on the solid crystal structure and, therefore, on its resistance to solid-state diffusion. Our results show that decarbonation at high CO2 partial pressure is notably promoted by decreasing solid crystallinity. CaO regeneration is fully achieved under high CO2 partial pressure at 900 °C in short residence times for the milled limestone whereas complete regeneration for raw limestone requires a minimum calcination temperature of about 950 °C. Such a reduction of the calcination temperature and the consequent mitigation of multicyclic capture capacity decay would serve to enhance the efficiency of the CaL technology. On the other hand, the results of our study suggest that the use of highly crystalline limestones would be detrimental since excessively high calcination temperatures should be required to attain full decarbonation at realistic conditions.