Melting Characteristics of Coal Ash and Properties of Fly Ash to Understand the Slag Formation in the Shell Gasifier

Hui Wang; Lihua Cheng; Jianglong Pu; Jigang Zhao

doi:10.1021/acsomega.1c01949

Melting Characteristics of Coal Ash and Properties of Fly Ash to Understand the Slag Formation in the Shell Gasifier

ACS Omega. 2021 Jun 9;6(24):16066-16075. doi: 10.1021/acsomega.1c01949. eCollection 2021 Jun 22.

Authors

Hui Wang¹, Lihua Cheng², Jianglong Pu¹, Jigang Zhao³

Affiliations

¹ College of Biological, Chemical Sciences and Engineering, Jiaxing University, 118 Jiahang Road, Jiaxing, Zhejiang Province 314001, China.
² Guangdong Provincial Engineering Technology Research Center of Petrochemical Corrosion and Safety, Guangdong University of Petrochemical Technology, Maoming, Guangdong Province 525000, China.
³ International Joint Research Center for Green Energy Chemical Engineering, East China University of Science and Technology, 130 Meilong Road, Shanghai 200237, China.

Abstract

The flow temperature (FT) of the coal ash from the Liuqiao no. 2 mine in North Anhui Province (C00) is too high (∼1520 °C) to fit the Shell gasifier due to its relatively high content of SiO₂ and Al₂O₃. To solve this problem, a series of coals were blended with C00 with different ratios, and the relations between FT and the ash composition were investigated. The coal ash was analyzed by X-ray diffraction, Fourier transform infrared (FTIR) spectroscopy, and scanning electron microscopy-EDX to elucidate the mechanism of the improved ash fusion performance and the slag formation in the waste heat boiler of the gasifier. It is shown that FT is relevant to the coal ash compositions as well as the structures formed at high temperatures. The existence of alkaline oxides (CaO, MgO, and Fe₂O₃) decreases the coal ash FT to a low level. The FT can decrease to <1350 °C to cater to the Shell gasifier by blending C00 and C03 with a mass ratio of 4:6 owing to the plentiful alkaline oxides in C03. The FTIR results indicate that the high flow temperature of C00 is attributed to the formation of mullite at high temperatures. The coal blending with various ratios changes the compositions of CaO, MgO, and Fe₂O₃, which can form some low-melting-point eutectic compounds with SiO₂ and Al₂O₃ under high temperatures, inhibit the formation of mullite, and thus decrease the ash FT. The coal ash FT was found to have a good linear relation with the ash compositions, which can sever as a reference to the coal blending. According to the model parameters, it is shown that Mg has the most significant promoting effect on the decrease in FT of the coal ash. The caking tendency of fly ash increases with the rising Ca content and an excessive Ca-based fluxing agent used in the coal blending will lead to the aggregation of the Ca-rich clasts around the fly ash particle, resulting in the plugging of the waste heat boiler in the gasifier. Therefore, the Mg-based fluxing agent is more promising to improve the ash fusion performance and reduce the caking tendency of the coal fly ash.