Sulfur recovery from hydrogen sulfide (H2S) contained in ammonia (NH3) bearing feeds, typically acid gases from sour water strippers (SWS). Product: Bright yellow high-purity sulfur and NH3 decomposition in elemental species like nitrogen and water (H2O).
Conventional straight-through Claus plant configuration applying a single zone reactor furnace that can operate when NH3 volume concentration in the feed gas is lower than a few tenths of a percent. At higher NH3 concentrations, especially from a SWS gas stream, which is mainly NH3, H2S and H2O, it becomes necessary to destroy NH3 in order to avoid severe operational problems that may occur in the sulfur recovery units (SRU).
In fact, NH3 in the presence of H2S forms ammonium (poly) sulfide, which solidifies at temperatures below 150°C and tends to plug sulfur condensers, sulfur run-down lines and seal pots. In addition to plugging problems, NH3 in sulfur recovery gas feeds increases plant size, related cost and decreases sulfur recovery.
To fully destroy NH3, the straight-through type plant can still be applied but with different burn configurations conceived to attain the operating conditions needed for NH3 decomposition. In ACT, a dualstage burn strategy is used by applying a “two zone furnace” design in which NH3 bearing stream is burned with part of the amine acid gas (NH3 “free” stream) in zone 1 at high temperature, followed by reinjecting the remaining amine acid gas into zone 2 of the reaction furnace. In addition a high intensity properly designed burner, having excellent mixing characteristics, is used to easily reach the required high temperature levels.
Operating conditions: The operating temperature in the ACT “two zone furnace” configuration can vary between 1,350°C and 1,650°C and the ACT pressure drop is around 0.3 bar. By adopting ACT, an NH3 bearing feed can be treated up to a level of NH3 concentration in the furnace effluent gas that is not harmful for regular SRU operation.
Economics: ACT uses standard equipment and carbon steel almost everywhere.
