Severe AntiFoam Injection Needed In BASF aMDEA CO2 Removal System to control foaming

[StanLee28]

In our Ammonia plant CO2 removal section , one of the hardest to deal with problem has become the necessity to continuously and in batches inject antifoam for the following reasons:
The Urea Plant downstream , which uses the CO2 from the CO2 stripper, has the problem of increasing temperatures in their reactor which converts hydrogen to water , in an endothermic reaction . the urea plant has limitations on their temperature increase. Somehow by injecting antifoam to the Absorber The temperature in their reactor is decreased for a short period of time ?(around 2 hour) .
by the time the Urea reactor temperature increases the gas flow from HP flash vessel to flare is also increased ,causing the pressure control valve MV to open more .
CO2 removal system is aligned as Absorber >HP FLASH VESSEL > STRIPPER
What effect does antifoam have on Hydrogen leakage to CO2 stream above stripper column?

 

[georgeverghese]

It seems obvious that the antifoam injection at the CO2 absorber has the effect of reducing carryunder of H2 in the spent aMDEA solvent going to the flash vessel and then onwards to the CO2 stripper. But it is suprising that there is still some residual H2 in the overheads CO2 stream from the stripper going to the urea reactor, since most of the H2 in the spent solvent should have flashed out in the intermediate HP flash vessel.

There is some contaminant in the feed syngas from the low temp shift reactor leading to the CO2 absorber which is cause of foaming in the CO2 absorber. Probably some corrosion inhibitor ?

Though I am not a urea plant specialist, your explanation for the high temp in the the urea reactor does not sound credible:
a) Though the reverse shift reaction could occur in the urea reactor, as you say, this is mildly endothermic and cannot be the cause of high temp
CO2 + H2 <=> CO + H20
b)Reverse decomposition of ammonia in the urea reactor also cannot be a cause, since decomposition is also endothermic.
So there is some other reaction in the urea reactor, brought on by the presence of H2 in the CO2 feed, which is exothermic.

 

[BurrowX]

Hi, It seems like you have multiple problems
1. Injecting Antifoam
2. Increasing temperature in the Urea Reactor
3. Hydrogen evolution/leakage from the system

In my experience, the ideal case is to not need to continuously add antifoam to operate. If your absorber is foaming that issue should be addressed separately.

Adding antifoam, especially if it isn't added appropriately can cause other issues. It will affect your chemistry, add it seems like it has been doing that already. (THEORY) Your Antifoam probably has different chemical properties than your process and a higher thermal capacity which may mean that the more you add, the more it decreases your operating temperature until its all consumed. This may mean that it takes 2 hours for all the excess antifoam to be consumed and then you have to add more antifoam.

These systems are very temperature sensitive. The next time this happens note the temperature swings in the system before and after adding antifoam. Address the need to add antifoam in your absorber with your chemical supplier.

If this continues you may run a high risk of forming heat stable salts and then the party is all over!
I hope this helps and good luck!

Laron B.
Results. Not Recommendations
BurrowX
Sr. Chemical Engineer