Organic sulphur as a main index for determining the genetic type of low-rank coals

Ludmila Butuzova
Oksana Turchanina
Gennadij Butuzov
Donetsk National Technical University

Achim Bechtel
University Bonn, Mineralogisch-Petrologisches Institut, Poppelsdorfer Schloss

Vladimir A. Safin
Lubov Isayeva
National Academy of Sciences of the Ukraine, L. M. Litvinenko Institute of Physical Organic and Coal Chemistry

Источник: Bulletin of Geosciences, Vol. 80, No. 1, 3-8, 2005.

ABSTRACT

It is well known that the content of heteroatoms, mostly of oxygen and sulphur, is a basic indicator of coal quality. Van Krevelen and Schuyer considered the value of the atomic ratio O/C as a primary indicator of coal rank. There is no evidence for a straightforward relationship between nitrogen and sulphur content and coal rank.

In the Donetz Basin 734 mined seams out of the total of 1009 (ca. 73%) are comprised of reduced-type coals with sulphur contents >1,5%. Low-rank coals and long-flame coals (brand D, GOST 3472-96, Ukraine), including high-sulphur coals, make up a considerable part of coal deposits in Ukraine. In determining the most expedient way of utilising them it is important to establish the relationship between the various types of sulphur content and the basic properties of solid fuels. When investigating this type of question it is desirable to use mathematical statistics for the analysis, which permits a quantitative description of the effects of the contribution of various elements into the formation of coal properties.

Earlier, Gagarin, and Ulanov and Gagarin proposed a reliable method for the regression analysis of the contribution of macerals (liptinite, vitrinite and inertinite) in the formation of the properties of petrographically heterogeneous coals. They have investigated the low-rank coals of the Donbas, Kuzbas, Pechorsky, and Zabaikalye basins.

The objectives of the present paper are to evaluate the contribution of the total and organic sulphur contents to the main classification parameter (the volatile matter yield) and to identify the structural parameters that correlate with S_o^daf for low-rank coals of the same rank but different genetic type by reductivity (GTR).

MATERIALS AND METHODS

The statistical analysis was performed using the Microsoft Excel and Origin 6.1 software package. Qualitative characteristics of the mined coal seams of the Donetz Basin given in a reference book on the quality of variously ranked coals and anthracites of the Donetz and Lviv-Volyn basins were used as the data base. All Middle Carboniferous long-flame coals mentioned in the reference book were selected. From this selection thirty seven samples were used for the statistical analysis. These samples were characterized by the following indices: the total sulphur content (of the seam sample), the volatile matter yield (wt%), the plastometric indicator (i.e. y), the elemental composition (i.e. carbon, hydrogen, sulphur, and the total nitrogen and oxygen contents), and the atomic ratios of the individual elements to carbon.

The coals under examination display a rather broad range for the total (S_t^d,%) and organic (S_o^daf) sulphur variations, whereas their petrographical and brand characteristics remain virtually homogeneous. They are therefore suitable for establishing the relationship between composition and volatile matter yield by the methods of regression and correlation analysis. Assessment of the correlation between the variables C^daf, H^daf, S_t^d, S_o^daf, (N^daf+O^daf) and their atomic ratios on the one hand, and the V^daf value on the other, indicates that the volatile yield does not strictly correlate with the oxygen and hydrogen contents (the pair correlation coefficients r were -0,1988 and 0,4272, respectively). Higher coefficient values were obtained for the pair C^daf-V^daf: r=- 0,6006.

A correlation is observed between the (S_o^daf) or S_o^daf/C^daf parameters and the volatile matter yield, with correlation coefficients of r=0,8746 and r=0,8726. This is much higher than the tabular values (r=0,449 with the value of 0,01).

We have obtained the following line equation for the long-flame coals:

V^daf=(35,98±0,46) + (1,78±0,15)*S_o^daf

Similarly, statistical dependence between the volatile matter yield and the organic sulphur content has been found for the Donetsk DG and G brand coals, with the correlation coefficients being r=0,91 and r=0,95, respectively. The regression equation for the DG brand coals is as follows:

V^daf=(33,24±0,69) + (2,31±0,27)*S_o^daf

The regression equation for the G brand coals is the following:

V^daf=(33,21±0,59) + (2,24±0,19)*S_o^daf

Therefore, the results presented in this paper permit prediction of the technological properties of the Donetz low-rank coals using the sulphur content within a single brand. The coefficient value for the correlation between the V^daf and S_o^daf values is unequivocally indicative of their parallel variation; in other words, it proves the synchronous transformation of the sulphur-containing (and other) components of the organic mass of solid fuels during the coalification process.

CONCLUSIONS

A statistical analysis of the characteristics of the Donetz low-rank coals of different genetic types demonstrates the possibility of improving the classification scheme for solid fuels using the organic sulphur content as a major indicator of the coal genetic type by reductivity.