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We have been facing issues in one of our sour water stripping units wherein we observe continuous plugging of the feed control valve to the stripper column with greenish black hard deposits. The temperature of sour water passing through this control valve is in the range 146-152 deg C. Could anyone suggest the testing we should carry out to understand this heavy deposit? Does anyone have experience with hard greenish black deposits in their sour water stripping units?
 
Answers
06/07/2020 A: Lindsay McRae, Pall Corporation, Lindsay_McRae@pall.com
Fouling in SWS unit (especially feed exchanger and sometime SWS column) is a fairly common issue in in refineries and can often be attributed back to poor separation in the Sour Water drum just before the SWS. This is usually a quite difficult separation to make as this is a quite stable emulsion with a low IFT and the residence time and separation efficiency of a simple large separation drum is just not good enough to for a difficult separation like this.


High efficiency PhaseSep Liquid Coalescers equipped with suitably sized pre-filters have proven to be able to break this emulsion and protect downstream SWS without being disarmed.

It might be worthwhile for you to check for carryover of HC's from SW Drum. Suspended solids ( corrosion products) may also be present due to the very sour service, high temp and various CS materials.


Our commercial experience shows this is often a quite variable and a fouling stream too so it pays to conduct a characterisation study on the SWS feed including PSD, TSS and HC liquid loading to ensure the pre-filter & coalesce is sized correctly.
03/07/2020 A: Pronab Mistry, ADNOC Gas Processing, pronab88@yahoo.com
I presume that your system has feed water filtration before entering the stripping tower. Even after filtration sour water will contain some residual hydrocarbon and at the freed water temperature you mentioned, hydrocarbon could be decomposing and precipitating inside the control valve. Moreover, dissolved H2S also can decompose. You should analyse the greenish black materials. I wonder why the feed water temperature is so high? Normally we maintain a 120-125 Deg C feed water temperature. Which media you are using in the stripper reboiler? If it is steam, it should be low pressure ( 5~ 7 barg) saturated steam. You can try to reduce the feed water temperature gradually to 125 Deg C as a trail and see the effects.