Q & A > Question Details
We are operating a small refinery processing sweet crude (less than 0.4 wt % sulphur). The crude is heated in a heat exchanger network and sent to a preflash column. The overhead from preflash column are condensed as naphtha and sent for stabilization after removing free water in overhead reflux receiver boot followed by coalescer. The naphtha is reboiled in the column and refluxed by a overhead stab in condenser. Vapour from the column are sent as fuel.
Recently when the column was opened up after one year of service the overhead condenser was badly corroded. In fact all the tubes had holes (condenser uses cooling water in the tubes). The strange thing which was noted that elemental sulphur embedded in the corrosion product covering the outside of tubes.
We are wondering where this elemental sulphur was formed? The overhead operating temperature is 100°F.
We are using antifouling agent in our crude but the vendor says that there is no possibility of elemental sulphur from their product.

1. Preflash overhead goes through a prefilter followed by a sand bed coalescer. We have observed no emulsion and water haze after these filters and coalescers. However, we are recycling boot water to overhead condenser in the preflash. There is no water wash in the stabilizer as it is a simpler stripper with no overhead condenser and drum.
2. No outside naphtha is being processed; however, demin water solution is prepared with neutralizer which is injected in preflash overhead. We are wondering about this Claus type reaction that take place under these mild conditions without catalyst.
30/12/2018 A: Lindsay McRae, Pall Corporation, Lindsay_McRae@pall.com
Sounds like sour water is carrying over and salts being concentrated in the reflux stream. The IFT of this stream can be single digit (6-8 dynes/cm usually ) so it is a pretty stable emulsion particularly if corrosion inhibitors are being used too. You might need a good high efficiency coalescer with prefilter to break this type of emulsion. If you have a bulk separator like mesh pad , plate separator or other low efficiency coalescer device then it’s likely emulsion is not being broken and sour water being recycled back to column from the OH drum.
What type of coaeslecer are you using ?
29/12/2018 A: Eric Vetters, ProCorr Consulting Services, ewvetters@yahoo.com
If you get some oxygen in your unit it can react with H2S to form SO2. The SO2 then reacts with more H2S in a Claus type reaction to form elemental sulfur. I have seen this before in a crude overhead system, but it's not common. I'm not sure how you get oxygen into the overhead of naphtha stabilizer though, unless you are also processing some purchased naphtha through the same tower.