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Claus plants convert toxic hydrogen sulfide to elemental sulfur by reacting the hydrogen sulfide with oxygen in either a single step, or two step, split-stream process.
In a two step process, part of the hydrogen sulfide is burned with limited air to produce sulfur dioxide, sulfur, and water. These products then flow to a second reaction stage, where the remaining hydrogen sulfide is reacted with the sulfur dioxide over a catalyst to form elemental sulfur and water. Claus plants convert between 95-98% of hydrogen sulfide to sulfur. The remaining balance of hydrogen sulfide, known as tail gas, is typically sent for further processing and is the focus of ever stricter environmental regulations.
These stricter regulations can only be achieved with subsequent tailgas cleanup. Oxygen enrichment is a means to increase the production of a given Claus plant without increasing the pressure drop across the system that would naturally occur by adding more air. The oxygen enrichment can also be used to compensate for the reduced gas volume by adding more crude gas, meaning that more sulfur can be produced in the Claus plant. Capacity increases can be as much as double.
Oxygen enrichment also allows the Claus plant to process additional ammonia, which is more common as refineries pursue deeper hydrotreating, by increasing the temperature to the necessary reaction temperature of 1,300C. The flow of oxygen is controlled to assure reaction of the ammonia while maintaining a safe temperature to protect the reactor walls. |
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