These units process sulphur containing gases from both the Amine Unit and the Sour Water Stripping Unit. There are two, identically designed, parallel Claus trains, each with a capacity to produce 70% of the normal sulphur production of the entire Upgrader. Paralleling is employed to ensure the Upgrader can stay on stream at a reduced rate should an equipment failure occur on one sulphur recovery train.
The Claus units partially oxidize hydrogen sulphide to produce elemental sulphur in two stages: first at a high temperature in the main reaction furnace without using a catalyst; then in the vapour phase at a low temperature in two catalytic stages. Sulphur produced at each stage is removed from the system by condensation of liquid sulphur from the various streams.
The acid gas stream (principally hydrogen sulphide), from the Amine Unit regenerators and from the Sour Water Stripping Unit, passes through knockout drums where any free liquids are removed. The acid gas streams from each knockout drum are split and fed, with a controlled flow of combustion air, to the combustion chambers of each Claus Unit. In the combustion chamber, complete combustion of the ammonia to elemental nitrogen and water vapour occurs and one-third of the hydrogen sulphide is converted to sulphur dioxide.
The sulphur dioxide reacts with the remaining hydrogen sulphide to produce sulphur and water vapours via the Claus reaction: 2H2S + SO2 » 3S + 2H2O.
The hot gases from the combustion chamber are cooled to condense the elemental liquid sulphur which is removed from the process by gravity. The partially cooled gases are reheated and fed to a converter where, in the presence of a catalyst, the reaction of sulphur dioxide and hydrogen sulphide is driven towards equilibrium. The sulphur produced is condensed and removed from the process in liquid form.
The gases are again reheated and fed to another converter where the reaction is again driven towards equilibrium, producing more sulphur, which is removed.
The gases from the last sulphur condenser in each Claus Unit, now containing less than 5% of the sulphur entering the units, is fed to a single train Tail Gas Clean-Up Unit for further processing.
The condensed liquid sulphur is collected, degassed to remove dissolved hydrogen sulphide, and exported from the site on railcars or trucks.
Used with permission (© SAIT Polytechnic, MacPhail School of Energy, 2009)