Maximize Sour Water Stripper Inlet Feed Rates 2

[cronopioespedro]

Greetings,

Recently I have been posed with a question of how to maximize the SWS inlet feed rates. I know that one of the problems is that the sour water composition is not constant. And that the stripped sour water concentration of H2S and NH3 is usually dictated by environmental regulations. I'm trying to determine whether a simplified mass balance around the stripper tower. But I'm not convinces that this will solve the problem. Are there any equations specifically for sour water stripping that could help me with this problem? Any information will be greatly appreciated.

Thanks!

 

[mbeychok]

cronopioespedro

The key parameter in sour water performance is the amount of stripping steam used per unit of total feed (i.e., fresh feed + reflux). For example, increasing that parameter from 1 pound of steam per gallon of total feed to 1.5 pounds per gallon of total feed will dramatically increase how much ammonia and H2S will be stripped out.

Therefore, if your tower can accomodate a higher stripping steam rate and a higher total feed rate, that is one way of accomodating more feed and still doing a good job of stripping out the NH3 and H2S. Read the article "Program Calculators for Design Study" in the September 1976 issue of Hydrocarbon Processing. It has a typical material balance around a steam stripper and has a graph of NH3 and H2S removal versus equilibrium stages required for the above two rates of steam per gallon of total feed.

Milton Beychok
(Visit me at www.air-dispersion.com)
.

 

[cronopioespedro]

Thanks Mr. Beychok,

Your response was very, very helpful. Just wondering one more thing. Is there a limit to steam to feed ratio that can operate a Sour Water Stripper? Also, for purposes of mass balances, can I assume the density of the sour water to be the same of normal water at a given temperature? As always, any info will be greatly appreciated. Thanks again.

 

[25362]

One way to reduce additional water circulation from using additional live stripping steam is to commission instead a reboiler, with the added advantage that the condensate can be returned to the boiler house.

The recommended maximum useful stripping steam rate for duely preheated sour water is about 0.37 kg per liter of combined sour water + reflux, depending on the degree of preheat and the operating pressure. Greater preheat and lower pressures allow using lower steam rates for equal feed and stripped water quality.

 

[mbeychok]

Just for clarification, 25362's answer of 0.37 kg/liter of total feed converts to 3.1 pounds per U.S. gallon ... which is quite high in my experience. However, my experience is rather old and perhaps modern sour water strippers do indeed use that much steam. In any event, I agree with 25362 that using a reboiler is better than using live steam injection, but it has a higher capital cost.

Milton Beychok
(Visit me at www.air-dispersion.com)
.

 

[25362]

Cronopioespedro

Amigo, it's probably a bit late but I feel obliged to tell you that the stripped water contains phenols, alcohols, aromatics, etc., which are mostly re-absorbed in the crude oil desalter.

And most important: because of fouling problems, reboilers are sometimes replaced by live steam.

Buena suerte.