An experimental study of sulphate transformation during pyrolysis of an Australian lignite

• Published in: Fuel processing technology Vol. 91; no. 3; pp. 313 - 321
• Main Authors: Yani, Setyawati, Zhang, Dongke
• Format: Journal Article
• Language: English
• Published: Amsterdam Elsevier B.V 01.03.2010; Elsevier
• Subjects: Applied sciences; Char; Energy; Exact sciences and technology; Fuel processing. Carbochemistry and petrochemistry; Fuels; Lignite; Pyrolysis; SO 2; Solid fuel processing (coal, coke, brown coal, peat, wood, etc.); Sulphate; Sulphur transformation; Australia; Oceania; SO 2; Sulphur transformation; Pyrolysis; Sulphate; Lignite; Char; Infrared spectrometry; Fixed bed reactor; Thermogravimetry; X ray diffractometry; Experimental study; Sulfates; SO
• ISSN: 0378-3820; 1873-7188
• DOI: 10.1016/j.fuproc.2009.11.002

The transformation of sulphate minerals during pyrolysis of an Australian lignite has been studied using pure sulphates (CaSO 4, FeSO 4 and Fe 2(SO 4) 3), a high mineral (HM) lignite sample and a low mineral (LM) lignite sample collected from different locations of the same deposit, and samples of acid-washed LM doped with sulphates (CaSO 4+ LM and FeSO 4+ LM), respectively. Thermogravimetric analysis and fixed-bed reactor techniques were used for the pyrolysis experimentation and the lignite samples and their chars were analysed using FTIR and XRD. The TGA experiments showed that CaSO 4 decomposes between 1400 and 1700 K in nitrogen and a 50/50 N 2/CO 2 mixture, while in air CaSO 4 decomposes between 1500 and 1700 K. Using a TGA–MS it was found that only a small fraction of CaSO 4 in CaSO 4+ LM decomposed at 653 K, releasing SO 2. CaSO 4 was still observed in the char recovered at 1073 K as confirmed by the FTIR and XRD analysis. FeSO 4·7H 2O released the bound water below 543 K and the remaining FeSO 4 decomposed between 813 and 953 K. FeSO 4 in FeSO 4+ LM decomposed at 500 K to release SO 2. The inherent sulphates in HM were dominated by iron sulphates which started to decompose and release SO 2 at around 500 K and all sulphate had been decomposed at 1073 K. It was observed that during the fixed-bed pyrolysis at 1073 K in nitrogen, approximately 36% of the total sulphur in the CaSO 4+ LM decomposed, 88% of the total sulphur in the FeSO 4+ LM decomposed and around 76% of the total sulphur in HM decomposed. It was also confirmed that FeSO 4+ LM produced more volatile sulphur than CaSO 4+ LM during pyrolysis.