CaO-Based Pellets Supported by Calcium Aluminate Cements for High-Temperature CO₂ Capture

Abstract

The development of highly efficient CaO-based pellet sorbents, using inexpensive raw materials (limestones) or the spent sorbent from CO2 capture cycles, and commercially available calcium aluminate cements (CA-14, CA-25, Secar 51, and Secar 80), is described here. The pellets were prepared using untreated powdered limestones or their corresponding hydrated limes and were tested for their CO2 capture carrying capacities for 30 carbonation/calcination cycles in a thermogravimetric analyzer (TGA). Their morphology was also investigated by scanning electron microscopy (SEM) and their compositions before and after carbonation/calcination cycleswere determined by X-ray diffraction (XRD). Pellets prepared in this manner showed superior behavior during CO2 capture cycles compared to natural sorbents, with the highest conversions being > 50% after 30 cycles. This improved performance was attributed to the resulting substructure of the sorbent particles, i.e., a porous structure with nanoparticles incorporated. During carbonation/calcination cycles mayenite (Ca12Al14O33) was formed, which is believed to be responsible for the favorable performance of synthetic CaO-based sorbents doped with alumina compounds. An added advantage of the pellets produced here is their superior strength, offering the possibility of using them in fluidized bed combustion (FBC) systems with minimal sorbent loss due to attrition.

CO2 capture by calcium aluminate pellets in a small fluidized bed

“…From the point of view of CO2 capture the main difference between the original and pelletized material is the CaO and Al2O3 content. The reduced CaO content in pellets, 86.51 %, results in lower CO2 carrying capacity (mass basis) for the same conversion, but it is compensated on a longer series of cycles due to a sintering mitigation effect by mayenite (Ca12Al14O33) [22]. …”

“…As a result, alternative methods of incorporating supports have been sought. One simple method is the pelletization of CaO powder using calcium aluminate cement and water spray [22,23]. Calcium aluminate pellets have been shown to work effectively over a long series of calcinations and carbonations [24] and with elevated temperatures and concentrations of CO2 expected in the calciner [25].…”

“…Calcium aluminate pellets have been shown to work effectively over a long series of calcinations and carbonations [24] and with elevated temperatures and concentrations of CO2 expected in the calciner [25]. In addition, it has been estimated that the pellets (at $200/t for the calcined pellets, 2009 estimate) should give a competitive cost for avoided CO2 over 60 cycles [22].…”

Cement/CaO-modified iron ore as oxygen carrier for chemical looping combustion of coal

“…For the mixed oxygen carrier, the CaO or lime may face with some potential problems at a high temperature, e.g., attrition and sintering, which could cause the reactivity deterioration of oxygen carrier during long-time operation. Addition of aluminate cement as a binder can improve the mechanical strength, chemical properties and sintering resistance of the particles [22][23][24]. Then, the cement-combined oxygen carrier was developed and the new stable formation of Ca 2 Al 2 SiO 7 was formed with enhanced sintering resistance.…”

Cyclic CO2 capture characteristics of a pellet derived from sol-gel CaO powder with Ca12Al14O33 support

“…The CO 2 capture capacity of natural limestone decreases from 0.61 g CO 2 /g sorbent during the first cycle to 0.18 g CO 2 /g sorbent during the 10 th cycle at 850 o C and 650 o C for calcination and carbonation, respectively [15]. Therefore, new preparation methods need to be developed to enhance the cyclic performance of the calcium-based sorbents [16][17][18][19][20][21][22][23][24]. Recent studies have proposed a solgel process to synthesize calcium-based sorbents with high cyclic reactivity [25][26][27][28][29][30][31].…”