To recover liquid sulfur from hydrogen sulfide (H2S)-containing gases such as acid gas from gas-sweetening units, acid gas from sour-water strippers or offgas from sulfur degassing facilities.
The main reactions are well-known Claus reactions. Ammonia (NH3), present in the sourwater stripper offgas, is processed in the main burner (1) directly with other feed gas streams. Practical complete NH3 destruction is ensured by choosing the proper high-intensity burner and preheating feed gas. The Claus unit is designed to suppress SO3 formation at the reaction furnace and subsequent line burners. The sulfur complexes, even with ammonia in the feed, can typically run for 3 to 4 years without a maintenance shutdown.
The Claus tail gas is routed to a SCOT unit, where the sulfur components are recovered (see SCOT). Upsets, such as those based on partial oxidation, usually pass almost unnoticed in the SCOT unit. For example, a hydrocarbon upset in the feed to the Claus will not have any other effect on the SCOT, other than a slight increase in H2S content from the SCOT absorber. A temporary NH3 breakthrough from the SRU has no other effect than a slight pH increase in the quench water.
Liquid sulfur produced in the Claus unit is degassed in the Shell sulfur degassing facilities (see “sulfur degassing” for more details). In this process, the H2S level in liquid sulfur is reduced to below 10 ppmw, without using catalyst, which improves safety during liquid sulfur handling. Offgas of the sulfur stripper can be routed to the Claus unit or to an incinerator.
The incinerator downstream the Claus/SCOT unit is designed such that a maximum of 10 ppmv H2S can slip through, the remainder of the H2S and any other sulfur component are oxidized to SO2. A thermal incinerator can be designed with a heat-recovery section for superheating steam produced in the Claus unit or gas preheating. A catalytic incinerator, using propriety catalyst, more selectively oxidizers sulfur compounds, thus significantly reducing the risk from temperature runaways.
Licensor: Shell Global Solutions International B.V.
