Ammonia (NH3) and hydrogen sulfide (H2S) are usually encountered in refinery sour water stripper offgas.…
ThioSolv SWAATS Process (sour water ammonia to ammonium thiosulfate)
Converts ammonia (NH3) and sulfur in sour water stripper gas (SWSG) to low-toxicity ammonium thiosulfate (ATS) solution. The process can also oxidize all sulfur species in Claus tail gas and scrub sulfur dioxide (SO2) from that or other dilute streams to achieve low sulfur oxide (SOx) emissions.
Ammonia and a stoichiometric amount of hydrogen sulfide (H2S) are selectively absorbed from the SWSG. Unabsorbed H2S is burned to SO2. Claus tail gas is combined with the burner outlet and all sulfur species therein are oxidized to SO2, which is scrubbed by reaction to thiosulfate with negligible pressure drop.
6 NH3 + 4 SO2 + 2 H2S + H2O › 3 (NH4)2S2O3 (ATS)
SWAATS converts the NH3 in the SWSG; no purchased NH3 is required. The process prevents and reverses equipment plugging by converting any elemental sulfur in Claus tail gas to soluble thiosulfate. The process is highly selective for H2S and SO2 vs. CO2.
Economics: For each ton of sulfur in SWSG diverted to SWAATS, about 2.5 tons of capacity for amine acid gas (AAG) sulfur is freed up in Claus. The value of the effect will increase as deeper desulfurization increases NH3 production. Avoids CAPEX to expand SRU capacity or OPEX for oxygen enrichment. Claus operability and catalyst life are greatly improved by removing NH3 from its feed. OPEX
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