The effect of steam on CO2 uptake and sorbent attrition in fluidised bed calcium looping: The influence of process conditions and sorbent properties

Review on the modifications of natural and industrial waste CaO based sorbent of calcium looping with enhanced CO2 capture capacity

The calcium looping cycle (CaL) possesses outstanding CO2 capture capacity for future carbon-capturing technologies that utilise CaO sorbents to capture the CO2 in a looping cycle. However, sorbent degradation and the presence of inert materials stabilise the sorbent, thereby reducing the CO2 capture capacity. Consequently, the CaO sorbent that has degraded must be replenished, increasing the operational cost for industrial use. CaO sorbents have been modified to enhance their CO2 capture capacity and stability. However, various CaO sorbents, including limestone, dolomite, biogenesis calcium waste and industrial waste, exhibit distinct behaviour in response to these modifications. Thus, this work comprehensively reviews the CO2 capture capacity of sorbent improvement based on various CaO sorbents. Furthermore, this study provides an understanding of the effects of CO2 capture capacity based on the properties of the CaO sorbent. The properties of various CaO sorbents, such as surface area, pore volume, particle size and morphology, are influential in exhibiting high CO2 capture capacity. This review provides insights into the future development of CaL technology, particularly for carbon-capturing technologies that focus on the modifications of CaO sorbents and the properties that affect the CO2 capture capacity.

Effect of Steam Injection during Carbonation on the Multicyclic Performance of Limestone (CaCO3) under Different Calcium Looping Conditions: A Comparative Study

This study explores the effect of steam addition during carbonation on the multicyclic performance of limestone under calcium looping conditions compatible with (i) CO₂ capture from postcombustion gases (CCS) and with (ii) thermochemical energy storage (TCES). Steam injection has been proposed to improve the CO₂ uptake capacity of CaO-based sorbents when the calcination and carbonation loops are carried out in CCS conditions: at moderate carbonation temperatures (∼650 °C) under low CO₂ concentration (typically ∼15% at atmospheric pressure). However, the recent proposal of calcium-looping as a TCES system for integration into concentrated solar power (CSP) plants has aroused interest in higher carbonation temperatures (∼800-850 °C) in pure CO₂. Here, we show that steam benefits the multicyclic behavior in the milder conditions required for CCS. However, at the more aggressive conditions required in TCES, steam essentially has a neutral net effect as the CO₂ uptake promoted by the reduced CO₂ partial pressure but also is offset by the substantial steam-promoted mineralization in the high temperature range. Finally, we also demonstrate that the carbonation rate depends exclusively on the partial pressure of CO₂, regardless of the diluting gas employed.

CO2 Capture at Medium to High Temperature Using Solid Oxide-Based Sorbents: Fundamental Aspects, Mechanistic Insights, and Recent Advances

Carbon dioxide capture and mitigation form a key part of the technological response to combat climate change and reduce CO₂ emissions. Solid materials capable of reversibly absorbing CO₂ have been the focus of intense research for the past two decades, with promising stability and low energy costs to implement and operate compared to the more widely used liquid amines. In this review, we explore the fundamental aspects underpinning solid CO₂ sorbents based on alkali and alkaline earth metal oxides operating at medium to high temperature: how their structure, chemical composition, and morphology impact their performance and long-term use. Various optimization strategies are outlined to improve upon the most promising materials, and we combine recent advances across disparate scientific disciplines, including materials discovery, synthesis, and in situ characterization, to present a coherent understanding of the mechanisms of CO₂ absorption both at surfaces and within solid materials.

Calcium Looping: On the Positive Influence of SO2 and the Negative Influence of H2O on CO2 Capture by Metamorphosed Limestone-Derived Sorbents

The CO₂ capture performance of sorbents derived from three distinct limestones, including a metamorphosed limestone, is studied under conditions relevant for calcium looping CO₂ capture from power plant flue gas. The combined and individual influence of flue gas H₂O and SO₂ content, the influence of textural changes caused by sequential calcination/carbonation cycles, and the impact of CaSO₄ accumulation on the sorbents' capture performance were examined using bubbling fluidized bed reactor systems. The metamorphosed limestone-derived sorbents exhibit atypical capture behavior: flue gas H₂O negatively influences CO₂ capture performance, while limited sulfation can positively influence CO₂ capture, with space time significantly impacting CO₂ and SO₂ co-capture performance. The morphological characteristics influencing sorbents' capture behavior were examined using imaging and material characterization tools, and a detailed discussion is presented. This insight into the morphology responsible for metamorphosed limestone-derived sorbent's anomalous capture behavior can guide future sorbent selection and design efforts.

Thermally induced carbonation of Ca(OH)2 in a CO2 atmosphere: kinetic simulation of overlapping mass-loss and mass-gain processes in a solid-gas system

Thermally induced carbonation of Ca(OH)₂ in a CO₂ atmosphere is a reaction exhibiting particular features, including stoichiometric completeness to form CaCO₃ and a kinetic advantage over the carbonation of CaO particles. This study aims to gain further insight into the reaction mechanisms of CO₂ capture by Ca(OH)₂ and CaO. It focuses on the kinetic modeling of the carbonation of Ca(OH)₂ as a consecutive reaction in a solid-gas system. The kinetic behaviors of the thermal decomposition of Ca(OH)₂ in an inert gas atmosphere and of the overall process of thermally induced carbonation of Ca(OH)₂ in a CO₂ atmosphere were investigated using thermal analyses and other complementary techniques. Based on kinetic results, the overall reaction of the thermally induced carbonation of Ca(OH)₂ in a CO₂ atmosphere was separated by a kinetic deconvolution analysis into two consecutive reaction steps: the thermal decomposition of Ca(OH)₂ and the subsequent carbonation of the CaO intermediate. The relationship between the two component reaction processes was well illustrated by a consecutive shrinkage of the dual reaction interfaces of Ca(OH)₂-CaO and CaO-CaCO₃. The continuous supply of water vapor and CO₂ to the CaO-CaCO₃ interface from different directions was suggested to be the physico-geometrical advantageous feature of the carbonation of Ca(OH)₂.