Sulfur Recovery Unit (SRU)

The Sulfur Recovery Unit, Unit 32, has been upgraded to recover at least 96% of the sulfur available as elemental sulfur, with a design capacity of 43 tons per day. The feed to the unit is the hydrogen sulfide rich acid gas stream from the Amine Scrubbers and the No. 1 Sour Water Stripper Overhead stream. The process by which H₂S is converted to sulfur is based on a controlled non-stochiometric combustion with air, in which one-third of the H₂S is burned to form sulfur dioxide (SO₂) which is then reacted with the remaining two-thirds of the H₂S to form sulfur and water vapor.

The acid gas stream is fed to the combustion tunnel at the front of the reaction furnace through a specially designed acid gas burner. Sufficient air is admitted to the combustion tunnel, around the burner, to burn only one-third of the H₂S in accordance with the reaction:

(1)

The SO₂ then reacts with the remaining H₂S according to the reaction:

(2)

Approximately 70% of the sulfur produced in the plant is formed as vapor in the reaction furnace. A portion of the heat produced in the exothermic reaction is removed in the Waste Heat Boiler where steam is generated. Process gas flows from the boiler to the first Sulfur Condenser where the stream is cooled. The elemental Sulfur is condensed, and flows, by gravity, through a seal leg to the Sulfur Pit. The stream is then reheated and charged to the first of three catalytic reactors where further conversion of H₂S to sulfur occurs in the presence of an activated alumina catalyst.

Between each of the reactors, liquid sulfur is recovered in the condenser and then the gas stream is reheated before entering the next reactor. The product stream from the third reactor is cooled and liquid sulfur drains through the seal legs to the sulfur pit. The tail gas from the final unit is charged to the incinerator, where it is burned with excess fuel gas at elevated temperatures to ensure full thermal destruction and that zero hydrogen sulfides are released to the atmosphere.