SWS_sripped water high ammonia content

[iulian1]

We are operating a SWS, 22 trays, non-refuxed, steam reboiled as followed:
Top presure = 1.1barg
Top temperature = 122oC
Bttm temperature = 127oC
Feed flow rate = 48m3/h, on top tray
Feed temperature = 115oC
Feed composition: Ammonia = 1545mg/l; H2S = 11.9mg/l; total cyanide = 4.25mg/l;pH = 9.2
Stripped water composition: Ammonia = 1479mg/l; H2S = 0mg/l; total cyanide = 3.85mg/l; pH = 10
main feed streams are fromC, FCC SWS and Hydrotreaters

As you can see, we have a big problem with ammonia and cyanide content. we checked the internal(visual inspection) 1 week ago. we face the problem about 1 month.
The column have the possibility to be refluxed on feed tray.
Please support me with some help.

Regards

 

[chemjock]

Are you injecting caustic?

 

[iulian1]

No

 

[siretb]

I think that a pH of 9.2 at feed id too low. So you'll probably need to add caustic soda at feed. I'd say that ph 10.5 is about what you need.

Reflux is needed only if you need to enrich the distillate in ammonia.
Do you subcool the condenser?

Also, beware of scaling, I have had problems with CaCO3 scaling in a similar column.

 

[iulian1]

Thanx siretb,

condenser temperature 95oC.
about pH, attached is a set of lab.data, please have a look on it.

Regards

 

[alweea]

I would assume that this is already a running plant hence there should not be an issue with the design.

Looking at your in and Out NH3, looks like the colum is not working at all, what does the visual inspection result? Any flooding issues (PDI ok ?)

Where is your stripped water sample point? Do you have feed/bottom cooler? Could the cooler be leaking hence high NH3 cotent?

Caustic Injection would help to released low volatility NH3 but only at bottom of part of the column.

 

[iulian1]

Yes, it`s an existing one.
from visual inspection trays are OK, no flooding(stable pressure)
for stripped water, the sample point is in front of the pump, no leaking because according with Lab. data(as an example for yesterday: inlet outlet(bottom)
NH3 content,mg/l 1815 880
pH 8.84 10.07

no changing in operating conditions.

Regards.