To remove dissolved hydrogen sulfide (H2S) and H2Sx from liquid sulfur coming from Claus units.…
Sulfur Degassing Process by Black & Veatch Pritchard
Hydrogen sulfide (H2S) removal from sulfur.
Sulfur, as produced by the Claus process, typically contains from about 200–500 ppmw H2S. The H2S may be contained in the molten sulfur as H2S or as hydrogen polysulfides (H2Sx). The dissolved H2S separates from the molten sulfur readily, but the H2Sx does not.
The sulfur degassing process accelerates the decomposition of hydrogen polysulfides to H2S and elemental sulfur (S). The dissolved H2S gas is released in a controlled manner. Sulfur temperature, residence time, and the degree of agitation all influence the degassing process. Chemical catalysts, including oxygen (air) that accelerate the rate of H2Sx decomposition, are known to improve the degassing characteristics.
In fact, the majority of successful commercial degassing processes use compressed air, in some fashion, as the degassing medium. Research performed by Alberta Sulphur Research Ltd. has demonstrated that air is a superior degassing agent when compared to nitrogen, steam or other inert gases. Oxygen present in air promotes a level of direct oxidation of H2S to elemental S, which reduces the gaseous H2S partial pressure and increases the driving force for H2Sx decomposition to the more easily removed gaseous phase H2S.
The MAG degassing system concept was developed to use the benefits of degassing in the presence of air without relying on a costly compressed air source. With the MAG system, motive pressure from a recirculated degassed sulfur stream is converted to energy in a mixing assembly within the undegassed sulfur. The energy of the recirculated sulfur creates a high air-tosulfur interfacial area by generating intense turbulence within the jet plume turning over the contents many times, thus exposing the molten sulfur to the sweep air. Intimate mixing is achieved along with turbulence to promote degassing. This sulfur degassing system can readily meet a 10 ppmw total H2S (H2S + H2Sx ) specification.
Tests show degassing rate constants nearly identical to traditional air sparging for well-mixed, airswept degassing systems. Thus, comparable degassing to air sparging can be achieved without using a compressed air source. The assemblies are designed to be self-draining of molten sulfur and to be easily slipped in and out for maintenance through the pit nozzles provided. The mixing assemblies require no moving parts or ancillary equipment other than the typical sulfur-product-transfer pump that maximizes unit reliability and simplifies operations.
The process is straightforward; it is inherently safer than systems using spray nozzles and/or impingement plates because no free fall of sulfur is allowed.
Economics: Typically does not require changes to existing sulfur processing infrastructure.
Licensor: Black & Veatch Pritchard, Inc.
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