Comparative Investigation of Liquid Products from Various Pyrolysis Treatments of Lignite Coals

摘要

All solid fuels studied in the conditions of steam pyrolysis treatment give higher yields of LP (from 120% for the bituminous shales to 144% for the Chukurovo coals) which is on account of the reduced amount of semi-coke. The different disproportion of the organic mass of the fuel during SWVP shows that the WV vapour is not only an efficient heat transfer medium but also a chemical reagent participating in the thermal destruction process. The comparison with literature data reveals the advantage of water vapour over the high cost hydrogen. The replacement of water vapour by inert gas does not result in an increase of the yield of liquid products. It has been shown that the tar obtained by SWVP has a lower density, average molecular mass, a lower content of asphaltenes and resinous components. The use of WV has a desulphurizing and denitration effect on the LP. The content of hydrogen and carbon in the LP by steam pyrolysis is larger, the same refers for the neutral oil and paraffino-naphthenic hydrocarbons. In the aromatic fraction of the LP obtained by steam pyrolysis are dominating mono-, bi- and tricyclic aromatic structures which are different from the structures in the LP obtained by the Fisher method. These differences in the yield and composition of the LP for the two treatments suggest different mechanism in the proceeding of the thermal destruction in the presence of WV. The interaction of WV with the organic mass leads to more complete and deep degradation of the fuel resulting in greater amounts of lowmolecular products. On the other hand the observed differences in the composition of the liquid products from the two types of coals - Maritza Iztok and Chukorovo - could be explained by the differences in their petrographic composition. While the coals from Maritza Iztok are typical lignite, those from Chukurovo are younger xylites. For the latter the yield of LP is lower and the content of aromatic hydrocarbons, mainly with polycyclic structures, is considerably lower at the thermal treatment by WV.