Reaction furnace, front end

The production of COS in the front end reaction furnace presents special problems since sulfur in this form may be difficult to remove in the downstream catalytic beds under conditions that are optimal for the Claus redox reaction between H2S and SO COS (and CS2) were known to be generated from hydrocarbon impurities carried over in the acid gas feed thus the efficiency of the up-stream sweetening process became an important factor. The reaction of CO2, a common constituent of the acid gas feed, with H2S and/or sulfur under furnace temperature conditions has also been shown to be an important source of COS. 

Recent improvements in the operation of the front end reaction furnace have not only increased sulfur recovery at this stage in the plant but have reduced the production of undesirable by-products which, ultimately, leads to a reduction in the environmental impact of the processes. 

The Claus Catalytic Cbnverters. These units represent the heart of any sulfur recovery plant. While the bulk of the sulfur yield may be obtained in the front end reaction furnace the high overall recovery levels demanded by environmental regulations are largely dependent on the efficiency of the Claus catalytic converters. 

It should be noted that the sulfation reaction requires the presence of oxygen. This serves to highlight the importance of air/acid gas ratio control in the front end furnace feed and the prevention of oxygen breakthrough into the catalyst beds. This can be of particular importance when oxygen enriched air feed is used in the front end reaction furnace (31). 

Elsewhere in this review we have commented on the problem of COS production as a result of high temperature reactions occurring in the front end furnace. Sulfur in this form is not subject to conversion to elemental sulfur in the catalytic redox Claus reaction and thus appears as COS in the tail gas where it is incinerated to SO2 thus adding to losses to the environment. The COS and any CS2 can be hydrolyzed to H2S which can then be converted by the redox Claus reaction. 

The gas-phase sulfur chemistry occurring in the front-end furnace of the Claus process is presumably similar to reactions occurring under fuel-rich conditions in combustion. However, in both systems the chemistry is quite complex and involves a number of unresolved issues. 

If air flow to the reaction furnace is much too high, SOj will be formed in the incinerator and a white plume will result. A yellowish plume indicates insufficient air to the front end of the sulfur plant. 

Front-end pressure will vary with the square of the moles of air plus acid gas that enters the reaction furnace. 

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