Sulfur Behavior in the Sasol−Lurgi Fixed-Bed Dry-Bottom Gasification Process

Abstract

This article reports on the findings of a study regarding the sulfur behavior across a Sasol-Lurgi gasifier. This was undertaken to understand the behavior of the various sulfur-bearing components in the coal, as they are exposed to the conditions in the gasifier. In this study, conventional characterization techniques were employed to monitor the behavior of sulfur-bearing mineral matter across the gasifier. It was observed from the study that the sulfur-bearing mineral (pyrite) in the coal structure undergoes various changes with pyrite being transformed to pyrrhotite and then to various oxides of iron with the subsequent loss of sulfur to form H 2 S. A low proportion of the sulfur species including the organically associated sulfur was encapsulated by a melt that was formed by the interaction between kaolinite and fluxing minerals (pyrite, calcite, and dolomite/ ankerite) present in the coal at elevated temperatures and pressure, thereby ending up in the ash. The remaining small proportions of sulfur-bearing mineral matter including pyrite and organically bound sulfur in the unburned carbon in the carbonaceous shales also report to the ash.

Green coal development for application in fixed-bed catalytic gasification

“…It can be observed that in this highly reducing atmosphere, pyrite decomposes at 125°C forming pyrrhotite (FeS) with the release of H 2 S gas according to the reaction FeS 2 +H 2 Fe (1-x) S + H 2 S. FeS is stable up to a temperature of 525°C, whereafter it decomposes, and is not present above 725°C. At this point, all of the sulphur (in the form of H 2 S) is present in the gas phase, in agreement with the literature (Skhonde et al, 2009). Figure 11 shows the simulation output for the dolomiteadded scenario under reducing conditions.…”

Sulfur Transformation during Hydrothermal Dewatering of Low Rank Coal

“…The organic form, which is bound directly to the hydrocarbon matrix, generally occurs in the forms of sulfides (R–S–R), disulfides (R–S–S–R), thiols (R–SH), thiophenes (heterocyclic), sulfoxides (R–S–O–R), and sulphones (oxidized forms). A significant amount of research has been conducted on sulfur transformation behavior during the combustion, gasification, and pyrolysis of coal. − Nevertheless, relatively few papers have reported the evolution of sulfur when LRCs are upgraded via HTD process. Temperature and atmosphere are the two crucial factors that affect the sulfur evolution.…”

A Critical Review of Mineral Matter Related Issues during Gasification of Coal in Fixed, Fluidized, and Entrained Flow Gasifiers

“…It was reported that transformation of pyrite begins in the pyrolysis zone of a Lurgi dry bottom gasifier and disappears completely in the combustion zone [23,28]. Sulfur in pyrite is predominantly released as H2S as pyrite transforms to pyrrhotite/Fe-S-O/Fe-oxides under reducing conditions [23].…”

“…In the combustion zone where the temperature usually exceeds 1373 K, oxygen interacts with iron species to form various iron oxides. In the gasification and combustion zone, the partially oxidized iron species (Fe-S-O/Fe-oxide) from pyrite, and calcium oxide from carbonates interact with high temperature products of clay minerals to form molten iron aluminosilicates and calcium aluminosilicates at temperatures usually greater than 1273 K [23]. Other products of aluminosilicates such as sodium calcium aluminosilicates (with a melting point of ~1173 K [29]) and potassium aluminosilicates can also contribute to agglomeration of bed ash.…”