Sour water stripper satbilization tank 1

[sqsqsq]

Hi everybody,
In some articles a stabilization tank for sour water stripperes is recommended. Could anybody give suggession(s) for the following questions:
1) Justifications and references for stabilization tank installation.
2) What would be an optimum residence time in this tank (in economic and separation points of view)? Why?
Thanks

 

[Jason5000]

Sour water strippers can be rather challenging units to keep operating, depending on your feed quality. Dissolved solids, heavy hydrocarbon contamination, and other issues can foul towers and exchangers occasionally causing out of cycle shutdowns to address the fouling issues. A nice big storage tank can provide you some surge capacity to avoid sour water curtailment in upstream units during an (some say inevitable) outage. Three day storage is a design point I've heard suggested.

As you suggest, a feed tank will also give you a polishing level of feed stabilization. Plenty of skim points and a design to avoid short circuiting are a must. A good tank will help to break some emulsions that may be too tight for upstream separators and protect downstream units from upsets. Again, just a rule of thumb I've heard is 24 hours of residence time with the tank operated at 60% level.

If the downstream acid gas handling unit is a Claus plant, then a storage tank can give you something of a capacity play if the Claus plant capacity is ever limiting. Building sour water in the tank to runback later can provide Claus plant peak shaving capability.

Ultimately, your sour water source and potential comtaminants should play into your feed tank decision. Is this water from a wellhead facility, gas plant, refinery etc? What do you expect in the water that may foul a tower when you boil it and strip it? How much extra capacity is built into your stripper? How expensive is an outage?

This link covers some of the basics of sour water handling if you're interested.

http://www.kps-engr.com/pdf/Fundamentals of Sour Water Stripping.pdf

Good luck,

Jason

 

[Egbertvh]

Agree with all the comments made.
One further thing is that a buffer tank will stabilize the composition of the sour process water.
In an oil refinery there is often a lot of variations in the compostion. This means that without buffer tank, you should regularly check the effluent of the stripper and adjust the operating conditions, which you do not do in actual practice.
The buffer tank would allow you to design your SWS for the average composition and not for the peak.

Regards
Egbert van Hoorn
Amine Experts

 

[25362]

Whether the stabilization tank has a fixed or a floating roof it has been recommended to keep about two feet of hydrocarbons floating on top of the sour water for odor reduction. Hydrocrabons should be removed before emptying the tank, to prevent them from entering the SWS.

Fixed conical roof tanks may require N₂ blanketing for for complete odor control and prevent the formation of explosive mixtures.

 

[mbeychok]

If the tank has a vent to the atmosphere, it will emit H2S vapors whenever the tank level rises. Rather than depending upon a hydrocarbon layer (floating on top of the sour water) to absorb the H2S, it is better to:

Route the vent through a small amine absorber using lean amine from the refinery's main amine unit and returning rich amine to same main amine unit.

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

 

[CJKruger]

Milton, I assume this means that amine will come into contact with air. Has that been a problem ?

 

[mbeychok]

CJKruger:

To the best of my knowledge, it has not been a problem. Do you have info otherwise?

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