Today, sulfur is produced from petroleum, natural gas, and related fossil resources, from which it is obtained mainly as gaseous hydrogen sulfide (H2S). In petroleum refineries, gases with an H2S content of over 25% are suitable for recovery of sulfur in Claus plants.
The Claus process (see figure 1) is the most significant gas desulfurizing process, recovering elemental sulfur from gaseous hydrogen sulfide. This process is divided into two main steps, thermal (in burners above 850°C) and catalytic. The catalytic recovery of sulfur consists of three sub steps:
– Reheating: the gas is reheated and introduced to the catalyst bed.
– Catalytic reaction: the remaining H2S is reacted with SO2 at lower temperatures (about 200-350°C) over a catalyst to make more sulfur. The reaction does not go to completion even with the best catalyst. For this reason two or three reactors are used.
– Cooling and condensation: In the sulfur condensers, the process gas coming from the burner and from the catalytic reactors is cooled to between 150 and 130°C, sulfur being removed between each stage.
Over the years many improvements have been made to the Claus process in order to adapt it to different feed gas compositions (e.g. high content of CO2 or ammonia) and in order to improve its effectiveness (conversion, energy balance, installation cost). Most sulfur recovery plants utilize one of three basic variations of the Claus process «straight-through», «split-flow» or «direct-oxidation».
Uses of Liquid sulfur
Sulfur is used for manufacturing sulfuric acid, fertilizers, pesticides and rubber products.