Performance of Ca-Based Oxygen Carriers Decorated by K₂CO₃ or Fe₂O₃ for Coal Chemical Looping Combustion

Abstract

Chemical looping combustion (CLC) of coal is an attractive technology with inherent CO 2 separation and high energy utilization efficiency. The large-scale preparation of a cheap oxygen carrier with high attrition resistance challenges the scale-up step of CLC reactor systems. To improve the reactivity between the CaSO 4 /bentonite (CaBen) oxygen carrier and coal, CaSO 4 −Fe 2 O 3 /bentonite (CaFeBen) and CaSO 4 −K 2 CO 3 /bentonite (CaKBen), decorated by Fe 2 O 3 and K 2 CO 3 , respectively, were prepared in this work. The active component content, multi-cycle reactivity, and enhancement mechanism of two decorated oxygen carriers were investigated in a fluidized bed with steam as the gasification−fluidization medium. Finally, three types of coals, including lignite, bitumite, and anthracite, were used as fuel. The addition of Fe 2 O 3 and K 2 CO 3 can improve the reactivity of the CaBen oxygen carrier but degrade the attrition resistance slightly. The multiple-cycle experiments indicated that Fe 2 O 3 itself is the oxygen carrier for coal CLC with high reactivity, while K 2 CO 3 acts as the catalysis for coal gasification. The carbon conversion rate of the three coals that reacted with the CaKBen oxygen carrier was higher than that with CaFeBen as the oxygen carrier because of catalysis of potassium on the coal gasification reaction. However, the CaKBen oxygen carrier particles were seriously sintered, and the potassium content in the oxygen carrier reduced with the increasing redox cycles. The coals with high volatile and ash contents have a high instantaneous rate of carbon conversion reacted with two decorated oxygen carriers.

Use of natural ores as oxygen carriers in chemical looping combustion: A review

“…This work also investigated Na and Ca additions but noted that K had the best effect (Bao et al, 2013). Potassium addition was also found to improve gasification rates in coal combustion when coupled with a CaSO 4 ore (Guo et al, 2014). Ca(OH) 2 addition to various Mn ores was also investigated.…”

Investigation of Chemical-looping Gasification Characteristics of Chinese Western Coals with Hematite-CuO Oxygen Carrier

“…[2][3][4][5][6] Guo et al suggested that multifunctional oxygen carrier compounds, such as Ca-based oxygen carriers with K or Na pendant groups, coupled with catalytic gasification, could effectively accelerate coal gasification, but the systems suffered alkali metal loss during the recycling process. [7,8] Moreover, Cu-based oxygen carriers usually exhibit greater oxygen donating capacity and much higher reactivity, which can effectively accelerate char gasification. [9] Sintering of the oxygen carrier occurs and the syngas produced is consumed, which leads to degradation in the quality of the product gas.…”

Non-isothermal oxidation of coal with Ce(NO3)3 and Cu(NO3)2 additives

“…One of such approaches is focused on intensification of the coal combustion process by using of activation additives in order to improve the efficiency of coal combustion (Tikhov et al 2013). Existing experience in the activation additives for solid fuel combustion is based on using the alkalineearth oxides (MgO, CaO) and transition metals oxides (MnO 2 , CuO) (Li et al 2007;Gong et al 2009Gong et al , 2010aWei et al 2012;Huang et al 2013), different salts (MgCl 2 , Ni(NO 3 ) 2 , LiCl) and alkalis (NaOH, KOH) (Zhao et al 2011;Abbasi-Atibeh and Yozgatligil 2014;Guo et al 2014;Yin et al 2012;He et al 2013;Kim et al 2012;Fangxian et al 2009).…”