Effect of different forms of Na and temperature on soot formation during lignite pyrolysis. (15th November 2020)

• Record Type: Journal Article
• Authors: Dong, Heming; Zhang, Yu; Du, Qian; Li, Dun; Feng, Dongdong; Gao, Jianmin; Wu, Shaohua
• Is Part Of: Fuel. Volume 280(2020)
• Publication Date: 2020-11-15
• Subjects: Soot -- Na -- Coal pyrolysis -- Temperature; Fuel -- Periodicals; Coal -- Periodicals; Coal; Fuel; Periodicals; 662.6
• DOI: 10.1016/j.fuel.2020.118514
• Languages: English
• ISSNs: 0016-2361

Abstract

Highlights: Small aromatics and aliphatic in lignite volatile are important to soot formation too. In most cases, soot yield of acid-washed coal is higher than that of Na loaded coal. Ion-exchangeable Na has stronger inhibitory effect on soot than adsorbed Na. Vaporized Na improved the reactivity of various substances in pyrolysis gas. Abstract: Current research on coal-derived soot lacks understanding of the role of Na, and also lacks of comparative studies between physically adsorbed Na (ANa) and ion-exchangeable Na (INa). In this study, different analytical methods were used to study the yield, particle size distribution and surface/bulk chemical characteristics of the soot generated by the pyrolysis of acid-washed Yimin lignite loaded with blank, ANa and INa in a drop-tube reactor. The results showed that: small-molecular aromatic compounds and aliphatic substances in lignite volatiles began to form soot around 1175 °C; and the oxygen-containing substances had the strongest inhibiting effect on soot formation near 1250 °C. As a result, "inflexion points" were caused in curves of soot yield with the changing temperature. Different forms of Na had different effects on soot generation characteristics. Some INa organically combine with char or volatiles. INa on char greatly reduced primary tar release, and INa in volatiles promoted the combination of volatiles with oxygen-containing and sulfur-containing substances. Without the chemical connection with coal matrix, ANa was partially gasified during pyrolysis and had no obvious effects on primary tar release. Vaporized Na (both ANa and INa) had multiple effects on soot formation. At a low temperature, Na + promoted the aggregation of small-molecular aromatic compounds and aliphatic substances, contributing to the soot formation. However, when the temperature was higher than 1100 °C, vaporized Na usually presented an inhibiting effect on soot formation. Generally, vaporized Na can improve volatile reaction activity and reduce the temperature of two "inflection points".