Review on the Development of Sorbents for Calcium Looping

Abstract

The calcium looping (CaL) process is a promising CO 2 capture technology, which uses CaO-based sorbents by employing a reversible reaction between CaO and CO 2 , generally named carbonation and calcination for each direction of the reaction. Although CaO-based sorbents possess many advantages, including wide availability, relatively low cost, and high theoretical CO 2 uptake (∼0.786 g of CO 2 /g of CaO), it mainly suffers from a rapid decline in CO 2 capture performance during cyclic operation, which has remained an urgent issue required to be addressed for industrial applications of the CaL process. Extensive studies have been conducted thus far, attempting to prevent and/or alleviate the rapid performance decay of the sorbents. Thus, this paper reviews the recent development of the CaL process worldwide with an emphasis on its development in China, mainly focusing on the advancement in the design and reinforcement of CaO-based sorbents. These activation strategies mainly include doping, chemical pretreatment, incorporation of supports with high Tammann temperatures, and structural modification, which do enhance the cyclic performance of the sorbents. However, some challenges still exist in the development of the CaO-based sorbents, such as the cost of the synthesis route, the scale-up pathways of the sorbents, the assessment of cyclic performance under mild conditions, and the ignorance of mechanical strength and attrition resistance of the sorbents. Therefore, life cycle assessment together with techno-economic analysis is essential when synthesizing CaO-based sorbents. In addition, more work should be conducted under industrially relevant conditions in fluidized bed reactors and even pilot-scale reactors, which are much closer to industrial situations. In this case, mechanical strength and attrition resistance are also assessed during cyclic operation.

CO2 capture using solid sorbents: Fundamental aspects, mechanistic insights and recent advances

“…Reported activation energies for the carbonation reaction are low and typically < 30 kJ mol -1 , often ~ zero [97]- [99]. Various conceptually different reaction models were found suitable for the kinetic modelling of the carbonation reaction [46], [96], [100], including shrinking core, pore and grain models. Similar to many gas-solid reactions, the observed rate of carbonation decreases once all readily available surface CaO has been covered with a product layer of CaCO3.…”

“…The following two subsectionsdealing with stabilizers that alternatively do not or do form mixed phases with CaO or CaCO3review recent works that have led to a better understanding of how stabilizers function within a sorbent; for a comprehensive list of works on synthetic sorbents we refer to some recent reviews on the topic [44]- [46], [360].…”

“…Wet chemistry methods (e.g. sol-gel or coprecipitation) enable a much higher degree of dispersion than mechanical mixing or impregnation methods, which is reflected by the higher cyclic stability of stabilized sorbents when prepared through such methods [46]. One aspect that has not been given much attention yet is the potential segregation of the support and the active phases upon cycling, such that the stabilizer would no longer function as intended [371].…”

Blending Wastes of Marble Powder and Dolomite Sorbents for Calcium-Looping CO2 Capture under Realistic Industrial Calcination Conditions

“…The use of concentrated CO 2 atmospheres approximating realistic industrial CaL calcination conditions for generating an exit gas stream with a high concentration of CO 2 is still a challenge [3], and the sorbents are rarely tested using laboratory scale reactors under severe regeneration calcination conditions. In a recent review focused on the development of sorbents for CaL, only~6% of experimental tests were performed under high CO 2 concentration using laboratory scale reactors [52]. In our previous work, it was shown that WMP are promising waste materials to be used as sorbents for CaL, but the calcination was carried out under a mild calcination atmosphere (N 2 , 800 • C).…”

Dual Anti‐Sintering Mechanism of Highly Stable CaO‐Based Sorbent and Enhanced Kinetics

“…Carbon capture and utilization technologies are widely acknowledged as the most important approaches that can reduce CO 2 emissions and supply fuel-related products [1][2][3][4]. The use of natural limestone as multicyclic absorbent is an attractive option for the separation of CO 2 from flue gases due to its high CO 2 capture capacity, high carbonation temperature, easy availability, and relatively low cost [5][6][7]. However, because the operating temperature of calcium looping is higher than the Tammann temperature of CaCO 3 [8,9], and the adsorption/desorption process of CO 2 has a catalytic effect on CaO sintering [10,11], the CO 2 capture capacity of calciumbased sorbents reduces rapidly after only a few carbonate looping cycles [12,13].…”