Fuel Processing Technology, Vol.185, 38-45, 2019
Mercury distribution in Guizhou bituminous coal and its releasing behavior during mild pyrolysis process
The multistep solvent extraction is an effective way for evaluating the original structure of coal, however, it is seldom used for studying the Hg distribution in coal and its release behavior during mild pyrolysis process. In this work, the Guizhou bituminous coal was divided into organic-rich class C-1 and minerals-rich class C-2, the C-1 was further subdivided into 4 groups (EG(1)-EG(4)) using multistep solvent extraction method. The Hg species in different samples and their fate during pyrolysis was investigated using sequential chemical leaching methods and temperature-programmed experiments. The results showed the dominant Hg forms in different samples are quite different, the HCl-soluble and HNO3-soluble Hg are the dominant forms in C-2, while organic matrix combined Hg is the most abundant form in C-1, EG(1) and EG(2) samples. The Hg contents in EG(1) to EG(4) groups are in the order of EG(4) < EG(3) < EG(2) < EG(1), and have little correlation with the total sulfur contents. The thermal stability of different Hg species are quite distinct, the Hg in EG(1) sample is the most thermal unstable and almost released completely before 400 degrees C. The Hg release of GZB, C-1, and C-2 are similar, > 60% and 95% of Hg in the three samples can be released at 400 degrees C and 600 degrees C, respectively. The Hg-OM+ combined with aromatic clusters in EG(2), is difficult to decompose during pyrolysis process, it mainly released in the temperature range of 400-800 degrees C. Except the Hg-Ole combined with aromatic clusters in EG(2), > 95% of Hg can be released before 600 degrees C for other samples. When the heating rate increased from 5 degrees C/min to 20 degrees C/min, the Hg releasing peaks ranged from 150 to 400 degrees C shifted gradually to higher temperature zones, but there was no obvious change in the positions of peaks ranged from 400 to 800 degrees C.