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Considerable studies have been reported on the coal pyrolysis process and the formation of SO 2 and NO x processors such as H 2 S, COS, SO 2 , HCN, and NH 3 in inert atmospheres. Similar studies in CO 2 atmosphere also need to be accomplished for better understanding of the combustion characteristics and the SO 2 /NO x formation mechanism of oxy-fuel combustion, which is one of the most important technologies for CO 2 capture. In this study, thermogravimetry coupled with Fourier Transform Infrared (TG-FTIR) analysis was employed to measure the volatile yield and gas evolution features during coal pyrolysis process in CO 2 atmosphere. Results show that replacing N 2 with CO 2 does not influence the starting temperature of volatile release but seems to enhance the volatile releasing rate even at 480 °C. At about 760 °C, CO 2 prevents the calcite from decomposing. In CO 2 atmosphere, the volatile yield increases as the temperature increases and decreases as the heating rate increases. COS is monitored during coal pyrolysis in CO 2 atmosphere while there are only H 2 S and SO 2 formed in N 2 atmosphere. The COS is most likely formed by the reaction between CO 2 and H 2 S. No NH 3 was monitored in this study. In CO 2 atmosphere, the gasification of char elevates the conversion of char-N to HCN. The HCN yield increases as the temperature increases and decreases as the heating rate increases.

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.

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