In Situ Capturing and Absorption of Sulfur Gases Formedduring Thermal Treatment of South African Coals

摘要

The objective of this study, the first of its kind on these specific South African low-sulfur coals, was to capture H2S and SO2 produced under inert and oxidizing conditions from sulfur compounds present in the coals. The capturing agents were calcium and magnesium oxides formed during the transformation of calcite and dolomite. The effectiveness of two different scrubbing solutions (0.15 M cadmium acetate and 1.1 M potassium hydroxide) for absorption of volatilized H2S and SO2 was also investigated. The bituminous coal (coal A) contained dolomite, calcite, pyrite, and organic sulfur. Lignite (coal B) had a high organic sulfur content and contained gypsum, no or low dolomite and pyrite contents, and no calcite. A third sample (coal C) was prepared by adding 5 wt % potassium carbonate to coal A. Under oxidizing conditions and at elevated temperatures, FeS2 produced Fe2O3, FeO, and SO2. It transformed to FeS and released H2S under inert conditions. Organic sulfur interacted with organically bound calcium and magnesium at 400 °C in an inert atmosphere to form calcium sulfate and oldhamite ((Ca,Mg)S). CaO, produced fromcalcite or dolomite, reacted with SO2 and O2 at 950 °C to form calcium sulfate. Treatment of lignite at400–950 °C resulted in 96–98% evolution of sulfuras gases. Hydrogen sulfide formation increased with the increasingthermal treatment temperature under inert conditions for the threecoals. Under oxidizing conditions, sulfur dioxide formation decreasedwith the increasing temperature when heating coals B and C. The lowestratio (0.01) of H2S to SO2 was achieved duringthermal treatment of the blend of coal and potassium carbonate (coalC), implying that almost all of sulfur was retained in the coal Cash/char samples. In situ capturing of sulfur gases by CaO and MgOand by the added K2CO3 in coal C to form calcium/magnesium/potassiumsulfates and potassium/calcium/magnesium aluminosilicate glasses duringutilization of these and similar coals could reduce the percentageof sulfur volatilized from the coals by 54–100%, thereby potentiallydecreasing their impact on the environment.