Why do we degas? Crude oil and natural gas contain sulfur compounds which get concentrated as they makes their way to the SRU in the form of hydrogen sulfide (H2S). H2S is present in liquid sulfur in two forms: dissolved and chemically bound (known as polysulfides or H2Sx). The residual H2S content in produced liquid sulfur can be in excess of 600 ppm and the Lower Explosive Limit (LEL) for H2S in air is 4% which is easily reached if liquid sulfur is not degassed. The main goal then of degassing is to reduce the potential safety risk to people, the environment, and equipment. Increasing product purity may also be a reason for degassing to lower levels. The industry standard for safe handling of sulfur product is 10 ppm or less.
Degassing typically consists of two stages, an agitation stage followed by a sweeping stage. Air is typically used in both stages as it is readily available and cheap, oxygen also promotes the direct oxidation of hydrogen sulfide and polysulfides. That being said, other gasses such as nitrogen, steam, and Claus tail gasses can also be used for sweeping the released H2S from the pit.
There are several processes that can be seen in industry and that have been implemented around the world. It is likely that if you have worked in a sulfur plant that you have experience with one or more of these processes.
Comprimo (Formerly Exxon) Degassing Process
Air used for sparging and sweeping
Catalyst added to pit to promote decomposition of polysulfides
Aquisulf (SNEA)
Aquisulf catalyst
Multiple compartments
Shell
Uses air for agitation
Stripping column within the pit
Enersul HySPEC
Series of CSTRs (Continuous Stirred Tank Reactors)
Air used to sweep and catalyst added
Fluor D’GAASS
Pressurized above-ground contactor
Air used for agitation
CSI ICOn
Fixed catalyst bed contactor before or after pit
Operates at pressure of SRU
Finally, we’ll talk about operation and troubleshooting fundamentals. Knowing the basics of degassing chemistry, such as the kinetics, effects of catalyst, and flow characteristics provide a solid foundation for any issues that you may encounter. The next step is knowing your design, understanding how your particular process works compared to others is necessary to being able to identify problem areas. Lastly, ensure that your data is accurate and reliable when monitoring KPIs. To help with this, get onsite verification of your process, including fact checks of technical drawings and data, and liquid sulfur testing.
Reach out to us at SRE for more information on troubleshooting tips and support as well as some interesting case studies from our experience.
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