Repetitive Carbonation−Calcination Reactions of Ca-Based Sorbents for Efficient CO₂ Sorption at Elevated Temperatures and Pressures

Abstract

In an effort to develop a novel hydrogen production process in which coal is gasified with highpressure steam in the presence of CO 2 sorbents, the fundamental CO 2 sorption characteristics of Ca-based sorbents during repetitive carbonation-calcination reactions at different pressures were investigated using a conventional TG/DTA analyzer and a laboratory-scale horizontaltube reactor. The results revealed that, as a result of sintering and crystal growth, Ca-based sorbents were significantly deactivated by high-temperature calcination treatment. As a consequence, the CO 2 uptake capacity of the sorbents decreased with cycle number under both atmospheric and pressurized conditions. An intermediate hydration treatment was found to enhance the reactivity and durability of the sorbents for multicycle CO 2 sorption. Because of the presence of eutectics in the CaO-Ca(OH) 2 -CaCO 3 ternary system, the formation of sorbent melts was observed in repetitive calcination-hydration-carbonation reactions at elevated pressures at 923 and 973 K. Even under eutectic conditions, the sorbents retained their high reactivity for CO 2 sorption.

The Use of a High Limestone Content Mining Waste as a Sorbent for Co2 Capture

“…It can be seen that the carbonations and calcinations are reversible in practice since, after the first and second carbonations, there is only calcium carbonate and after calcinations there is mostly calcium oxide. Kuramoto et al (2003) also reported that the sorbent regenerates, maintaining the CO2 capture capacities of this type of mineral over calcination-hydration-carbonation cycles. The authors compared the results with and without intermediate hydration of CaO, suggesting that the hydration treatment provides the durability of the sorbents in repetitive CO2 sorption.…”

“…Previous studies investigating carbonation of Ca(OH)2 and carbonation of CaO show that Ca(OH)2 reaches a higher conversion than CaO (Nikulshina et al, 2007;Kuramoto et al, 2003), whereas the carbonation of CaO is initially chemically controlled and then becomes controlled by diffusion, while the carbonation of Ca(OH)2 at high temperatures (up to 400 °C) is all chemically controlled (Nikulshina et al, 2007).…”

“…Despite low costs, CaO-based sorbents show a fast deactivation and a decrease in their CO2 capture capacity over reaction cycles because of sintering phenomena, crystal growth and pore blocking during the calcination step (Abanades and Alvarez, 2003;Symonds et al, 2009;Grasa and Abanades, 2006;González et al, 2008;Manovic et al, 2009;Kuramoto, 2003). Previous studies show that high calcination temperatures accelerate this deactivation process (Grasa and Abanades, 2006;González et al, 2008).…”

“…In order to overcome the sintering and enhance the sorbent reactivity, a range of methods has been proposed, such as doping of CaO-based sorbents (AlJeboori et al, 2012) to produce synthetic sorbents, thermal preactivation of fresh sorbent (Valverde et al, 2013) and hydrating (Yu et al, 2012;Phalak et al, 2012;. A number of authors have shown that including an intermediate hydration of CaO improves the sorbent morphology, forming porous agglomerates (Kuramoto, 2003) and enhancing pore size, likely a shift from smaller to larger pores, which avoids the pore pluggage (Yu et al, 2012;Phalak et al, 2012).…”

Development of Superior Sorbents for Separation of Co2 From Flue Gas at a Wide Temperature Range During Coal Combustion

“…Hence, at 225 o C Ca(OH) 2 [11] and CsOH layers were formed on the sorbent's surface due to high water adsorption, namely 27 wt% H 2 O/mass of sorbent. However, with increasing sorption temperature a considerable decrease of the water adsorption was observed.…”