John Sczesny - MPR Services, Inc.
It is understood the sulfur plant is a necessary component in refinery operations with a sour crude slate. Hydrocarbons, such as methanol, BTEX and others have different flash points and BTU values other than the normal fuel gas. The burner in the sulfur plant requires a certain BTU range in order to burn efficiently. Poor burning of the acid gas can result in the emissions going off spec. Also, the sulfur produced from the sulfur plant must meet a color spectrum specification in order to be sold and market prices. Hydrocarbon discolors that as well. Thus hydrocarbon carryover into becomes a serious concern. The source of the hydrocarbon carryover is almost exclusively from the amine treater. The sour water stripper mostly provides the sour gas and carries very little HC to the sulfur plant.
Since amine is derived from hydrocarbon it also has a high affinity for absorbing it. The hydrocarbon that accumulates into amine treaters depend on the feed stock and how the amine system is configured. In my experience, there could be lubrication oils from compressors, methanol from upstream processes, and light hydrocarbons, BTEX, and paraffins all coming from the gas feed.
The hydrocarbons that end up accumulating in the amine treater cause all sorts of interesting problems. Hydrocarbons cause foaming, burping and other upset conditions in the amine treater. The upset in the amine plant consequently causes amine and its absorbed hydrocarbon to be whisked away with the sour gas stream from the top of the regeneration tower in the amine system. So hydrocarbon in the amine system is bad for the sulfur plant and the amine plant.
What can be done? Typical mitigation for hydrocarbon is:
- Skimming the HC from the flash drum due to different densities (this only works for some of the hydrocarbon )
- Knockout drums installed upstream of the amine treater and upstream of the sulfur plant
- Activated carbon
- Use better separation techniques employed ahead of the amine plant
- Other novel ways for removing hydrocarbon in the amine plant.