Q & A > Question Details
I work in a UOP licensed DHDS unit. It has one HP amine absorber to absorb H2S from recycle gas. At thr top of the column, a water wash facility with level tray is installed to wash lean amine from recycle gas. We are experiencing foaming. The water tray level quickly fills and goes to the next recycle gas knockout drum. Delta pressure of the column is also increasing and the level increases suddenly in the water tray even after isolating fresh water. The delta temperature between amine and process gas is 12oC. Drained liquid is milky in colour. Please suggest a remedy.

16/02/2021 A: Jake Gotham, InSite Technical Services, jake.gotham@insitetechnical.com
You are probably right that the amine is foaming and being carried over into the water wash section. Flooding is another possibility if the tower internals are fouled or damaged. I’d suggest the following operational response to a foaming incident:
• Reduce the vapour velocity through the absorber. This might be possible by opening the vapour bypass line around the absorber (not all units have this facility), or by reducing recycle gas compressor speed (again, this isn’t always possible and in any case should be limited to the minimum period of time to avoid catalyst deactivation).
• If the problem is flooding rather than foaming, reducing amine circulation rate may or may not help. A reduction in amine circulation rate will increase the amine loading (mols of H2S per mol of amine). If the amine loading exceeds the allowable limit for your amine type, increased corrosion will occur in the rich amine system, so this change would need to be controlled and managed.
• Inject anti-foam if you have the facility to do so. Be aware that too much anti-foam can cause foaming, so make sure the supplier’s recommendations are followed. Short term preventative suggestions:
• Check the amine versus vapour temperatures to make sure you are not condensing liquid hydrocarbon into the amine. You quote a 12°C differential in your message – I assume the amine is hotter than the vapour, not the other way around. An alarm on the temperature difference is useful. Medium term improvements: • Improve amine hygiene. What is the amine quality like? Do you have slip-stream filters and charcoal beds on the amine system? Are the cartridges changed regularly?
•Add an anti-foam injection facility if you don’t already have one.
• Discuss with your catalyst supplier the implications of running without amine. Many DHDS units do not have a HP amine absorber tower at all. The impact of this on your unit will depend on how sour the feed is – if the feed sulphur content is relatively modest, you may be able to operate without amine either permanently, or until the next turnaround when the tower can be inspected and the problem rectified (see below). The increase in recycle H2S may directionally increase corrosion, again whether or not this is significant will depend on the sulphur content of the feed but in many cases it is manageable within the existing metallurgy and inspection regime. Long term:
• The problem may be caused by fouling or damage within the absorber. You should plan to clean and inspect the tower at the next catalyst change or turnaround. Get in touch if you’d like help troubleshooting this problem any further.
09/02/2021 A: Nagarathinam S Murthy, Ashphil Consultancy, Chennai, nssvdvr@gmail.com
I guess the water in the top wash section is seen to have the milky colour. Typically, this could be the result of surfactants being carried into the water wash section. Look at the following. Check the quality of amine which is being used in the HP loop of the amine tower. Any carry over of amine containing HSS could also turn water in the water wash section milky. Simply take a lean amine sample check for foaming tendency. It is possible amine foams are landing in the water wash section. If possible, extract the milky water with n-hexane wash and analyze the contaminant that induces the issue in the water wash section.
08/02/2021 A: RAUL FLORES, PDVSA INTEVEP, fraulf@hotmail.com
This is a cause - effect situation. Please look for the cause, then the effect. Why the foam? It is the stability of the foam then what causes the stability of the foam? Hydrocarbons, dirty (suspended material), tensoactives. Please check the stability of the foam (height and time tests), analyze changes in the gas composition, check the gas inlet separation drum and its maintenance, and changes in the amine circuit processing looking to the filters.