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Applications
The Shell Sulfur Degasification Process* has been developed to remove H2S and H2Sx from liquid sulfur eliminating potential toxic and explosion hazards associated with handling, transport and storage of liquid sulfur. Elemental, sulfur produced by the Claus process contains both physically dissolved H2S and chemically bound H2S in the form of hydrogen polysulfides (sulfanes): H2Sx. The principle of sulfur degasification is to accelerate decomposition of the polysulfides according to H2Sx H2S + Sx-1 and to remove the dissolved H2S from the liquid sulfur. In the Shell Sulfur Degasification Process, the sulfur is degassed to less than 10 ppm wt H2S/H2Sx.

Description
Degasification is carried out as a continuous process in the degasification compartment of the Claus plant sulfur pit or in a dedicated vessel. The actual degasification takes place in the stripping column where sulfur is vigorously agitated by bubbling air through the liquid sulfur.

As the stripping column is open at the bottom and the top, the sulfur can circulate through the stripping column and a thorough mixing with the total content of the degasification compartment is achieved. The concept allows for a large number of design variants. it does not use a catalyst and has no moving parts.

The sulfur as it is produced in the Sulfur Recovery Units contains about 300 ppm (weight) H2S. Bubble columns are located in the stripping section.They have a rectangular cross-section. The top and bottom parts are open. Air distribution spargers are provided at their bottom sides. Bubble columns are located in the stripping section.They have a rectangular cross-section. The top and bottom parts are open. Air distribution spargers are provided at their bottom sides. The stripping air to the spargers is supplied by an air blower. The function of the air is to obtain forced sulfur circulation in and around the bubble columns, to strip the dissolved hydrogen sulfide from the liquid sulfur and to oxidize the major part o The stripping air to the spargers is supplied by an air blower. The function of the air is to obtain forced sulfur circulation in and around the bubble columns, to strip the dissolved hydrogen sulfide from the liquid sulfur and to oxidize the major part o The sulfur level in the stripping section is kept constant by means of an overflow wall between the stripping compartment and the downstream storage compartment. The degassed sulfur is pumped by the sulfur pump from the storage compartment to the sulfur handling. Sweep air is added via the air inlet, located on the cover of the stripping section. The total air, together with the H2S released from the sulfur, is drawn off by a steam ejector and discharged to the incinerator.
Operating Conditions
In the Shell Sulfur Degasification Process, air stripping is applied without addition of chemicals. Air is supplied to the stripping column at a pressure of approx. 1.5 bara either as a slipstream from the Claus air blower or by a dedicated blower. Vent gas is charged to an incinerator or can be recycled back to the sulfur plant. The degassified sulfur flows over a weir to the pumping compartment and is pumped on level control to storage. The Shell Sulfur Degasification Process is an inherently safe system that prevents the formation of an explosive H2S/air mixture.

Features
   Safer working conditions for handling liquid sulfur.
   Reduced corrosion in transport and storage equipment.
   Reduced fugitive emissions from the sulfur pit.
   No chemicals present in the product sulfur.
   No moving parts.


References
More than 150 Shell Sulfur Degasification systems ranging in capacity from 10 to 4000 t/d sulfur production are in operation or are under design/ construction throughout the world demonstrating the reliability, simplicity and flexibility of the process.

Licensor
*Jacobs Nederland B.V., Leiden, The Netherlands, is the exclusive worldwide licensor of behalf on Shell Research Ltd. since 1981.
 

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