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I am working in Diesel Hydrodesulfarisation Unit. In our unit after H2S removed in Amine Absober, Diesel will go to Stripper. Where steam (direct steam) used as stripping medium. The purpose of steam stripping is only to removal of lower ends or it will remove H2S also. Presently we are maintaining Stripper I/L and bottom temperatures 230 and 225 deg respectively. If I decrease the temperatures by 5 deg, I will gain that heat in preheat, but it is believed that if we decrease stripper IlL temperature H2S in product Disesel will be more and copper Strip corrosion problem will appear. Is it true , By decreasing stripper I/L temperature and increasing steam Can I balance it.
 
Answers
11/03/2011 A: Satish Angadi, Haldor topsoe, satish.angadi@gmail.com
I suggest :
1) The bottom temperature be above 220°C.
2) stripping steam to feed, the range is 8-20 t/m3 of feed. 12-15 t/m3 is good. and
3) If you ensure that water/steam will condense in the overhead section and not in the stripper. This is the key.
If you can manage these, you can reduce stripping steam.
07/03/2011 A: Morgan Rodwell, Fluor Canada Limited, morgan.rodwell@fluor.com
I concur with Mr. Bowers statements. I have seen two attempts to recover additional heat from diesel stripper feed and both ran into problems with water condensation in the tower.
You need a simulation of the system, adjusted based on actual H2S in diesel levels (since the simulators are not particularly accurate) to determine if you are too close to the water dewpoint.
07/03/2011 A: Ralph Ragsdale, Ragsdale Refining Courses, ralph.ragsdale@att.net
The direct steam, or “live steam” as sometimes called, strips out some of the H2S and reduces the partial pressure of the hydrocarbon which results in hydrocarbon vaporization to strip out additional H2S. Any superheat in the steam will generate hydrocarbon vapor, too, but that is minimal. Using software simulation, or by test runs, you can determine the most cost effective combination of feed temperature and stripping steam rate for your operation. As Mr. Bowers pointed out, all water must be allowed to go overhead as vapor and not condense in the column.
Most applications use steam to a reboiler, and the hydrocarbon partial pressure effect does not exist.
07/03/2011 A: keith bowers, B and B Consulting, kebowers47@gmail.com
H2S has about the same volatility as propylene. In order to 'lift' the H2S out the top of the column, one MUST make some overhead product. If there are insufficient light ends (C3-C5) in the feed, it will require higher temperature and more stripping steam.
Also remember, the vapor leaving the top tray must contain all the water (stripping steam) contained in the feed and stripping steam if you want dry diesel product. If water builds up enough to have a third phase (liquid water) on the trays, rapid corrosion will take place. The column my also be very unstable with liquid water flashing and condensing irregularly in the trays where it is present.