Sulfur Recovery 

1. Amine acid gas KO drum: vertical separator with demister, liquid particle 5-30 microns, efficiency 95-99.5, operating pressure 0.5-0.8 barg, 60C
2. SWS acid gas KO drum: the same as above, but with 85C to avoid amonium salts formation due to NH3 presence
3. Claus burner & 2 zone reactor: the combustion reactions are carried out in the burner and combustion chamber (zone 1) of the Thermal Reactor. In the reaction chamber (zone 2) of the Thermal Reactor, the Claus reaction (60-70% conversion), continues as a result of the high temperature. The expected combustion temperature is approximately 1360°C.
In the two-zone Thermal Reactor design, all the combustion air is supplied to the combustion chamber (zone 1) of the Thermal Reactor with a portion of the amine acid gas and all of the SWS gas.
The quantity of acid gas to zone 1 is restricted to control the combustion chamber’s temperature within the preferred range of 1280-1360°C. This is done to ensure complete destruction of the ammonia.
Additionally, the moles of H2S fed to zone 1 must always be greater than one-third of the total H2S in the feed stream so as to prevent sulphite - SO3 formation and to ensure total oxygen combustion/consumption. Therefore, the minimum recommended operating range for total hydrogen sulphide to zone 1 is 38-42% of the total in the combined feeds. The remainder of the amine acid gas is fed to the reaction chamber (zone 2) of the Thermal Reactor.
The combustion gases from the Thermal Reactor Burner and zone 1 of the Thermal Reactor flow into zone 2 of the Thermal Reactor, where adequate residence time is provided for the Claus sulfur formation reactions, residual ammonia destruction, and destruction of any hydrocarbon in the acid gas fed to zone 2 - typically operates 50-100°C cooler than zone 1.
The Thermal Reactor zone volumes are based on ammonia destruction kinetics.
The Thermal Reactor is refractory lined to protect the metal shell from the high temperatures required to oxidize the gas constituents. The Thermal Reactor shell is also protected from high heat losses by an external thermal shroud.
4. Waste Heat HX: the gas is cooled in a two pass process cooler with the hot gas passing through the inside of the tubes. Saturated steam is produced at high pressure - 40 barg, in the Waste Heat Exchanger while cooling the process gases to approximately 645°C in the first pass and to approximately 315°C in the second pass.
5. Sulfur condensers: 1st cools the sulfur to 120C generating LP steam, 2nd to 170C by LLP steam generation, Final Condenser T = 136C by preheating BFW
6. Sulfur Reheaters: 1st heat the gas from 1st sulfur condenser to 250C by HP steam; 2nd gas T at exit 208C.
7. Conversion Reactors: in 1st reactor the gas pass to activated alumina catalyst at 250C to approach equilibrium of sulfur reaction & the cycle is repeated in 2nd reactor, T=208C (sulfur reaction is favor by lower T, but in the same time the sulfur condensation need to be avoided/15-20C above dew point)
8. Hydrogenation reactor: use 99.9% H2 to transform to H2S any sulfur compounds at 285C by indirect heating with HP steam in preheater HX; keep 2.5-3% H2 excess measured at Quench Column top for complete conversion to H2S
9. Incinerator & stack: gas from TGT is heated to 650C by incinerator burner using combustion air from blower, the Incinerator is a refractory lined carbon steel vessel used to convert any remaining reduced sulfur compounds to SO2 prior to atm. discharge.
The Incinerator has a pilot, a main burner, and inlet air louvers. The Incinerator pilot is specified for continuous operation to ensure the pilot is on even if acid gas processing is interrupted. A continuous pilot maintains draft in the Incinerator as well as ensuring all tail gas combustibles are burned prior to release to the atmosphere. The recommended stack excess O2 operating point is 3% O2. The main issue is the pipe between the incinerator & stack which need to be design to sustain at least one explosion, ask the licensor also what will happens with the stack base if explosion shall occurs.
10. TGT waste HX: gas is cooled in the waste heat exchanger to approximately 176°C by generating low pressure 4.5 barg steam from a mixture of low pressure BFW & condensate from the Reactor Preheater, which both enter the WHE on level control. The steam used in the preheater is only partially condensed as it transfers heat to the SRU tail gas.
11. Reactor Preheater Flash Drum: is placed downstream to separate the condensate from the remaining steam. The steam leaves the flash drum through a pressure control valve which lets it down to low pressure. The condensate leaves the bottom of the drum and is fed to either the TGT Waste Heat Exchanger or the steam system’s Condensate Drum.
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