Inappropriateness of the Standard Method in Sulfur Form Analysis of Char from Coal Pyrolysis

Abstract

The solid products of pyrite decomposition during coal pyrolysis under nitrogen atmosphere at different temperatures were investigated by X-ray diffraction (XRD), and the solubilities of the corresponding compounds in hydrochloric acid and nitric acid were examined by inductively coupled plasma atomic emission spectroscopy (ICP-AES). The feasibility of using the standard method for sulfur forms analysis of coal to determine the sulfur forms in char was discussed. It is found that the standard method is unsuitable to analyze the sulfur forms of the char and big error is introduced during calculation of the organic sulfur in char. During pyrolysis, pyrite (FeS2) is converted to pyrrhotite (Fe1–x S) and/or ferrous sulfide (FeS), which dissolve in HCl solution and lead to an elevated value of organic sulfur determined by the standard method. A modified calculation method of sulfur forms in char is recommended. The organic sulfur content in pyrolysis char obtained by this method is much lower and more accurate than that obtained by the standard one. The modified method for the sulfur form analysis of char is superior to the standard one, especially for the chars obtained from coals with high pyrite content and pyrolyzed at high temperatures.

Effect of coal particle size on distribution and thermal behavior of pyrite during pyrolysis

“…Effect of coal particle size on the distribution of sulfur forms in sectioned YZ-Dem coals Sulfur content in coal was analyzed in the light of the standard method [23]. Table 1 indicates that more than half of the total sulfur in each sample is pyritic sulfur.…”

“…2(b) when compared with the other two size-sectioned demineralized coals. Previous experiments [23] showed that pyrite in YZ raw coal decomposed to FeS x and FeS above 600°C. Therefore, the above result of YZ-DemL can be ascribed primarily to its lowest pyrite content and the poor heat and mass transfer in the large size coal particles.…”

“…Sectioned YZ-Dem coal samples have considerable quantity of SO 2 evolved at 530-650°C, while no SO 2 was detected for the pyrite-free sample (YZ-Demp) in this temperature range. Additionally, we previously noticed that part of FeS 2 in YZ raw coal was transformed into Fe 1Àx S at 500°C [23]. Therefore it can be deduced that SO 2 released at 350-530°C for sectioned YZ-Dem coals is attributed mainly to the decomposition of organic sulfur and slightly to that of pyritic sulfur in coal [7].…”

“…Coal samples with a size fraction of <150 lm or around 150 lm were selected in order to find some common or remarkable characters during coal pyrolysis as earlier works did [12,22,23].…”

“…To eliminate the influence of minerals, especially sulfate, in coal on thermal characteristic of pyrite, coal samples were treated by acid leaching [12,23]. The raw coal and the size-selected ones were treated with 5 M HCl, 33.3 M HF and 12 M HCl at 60°C sequentially for 1 h. The suspension was filtered and washed with boiled double-distilled water until no chloride ion was detected from filtrate.…”