7 replies to this topic

[Art Montemayor]

Saeid:

I deleted your previous, duplicate query because it becomes very confusing responding to duplicated queries. Additionally it is a waste of Forum space, time and controls. In the future, please only post the same query one time. That is sufficient for members to respond efficiently.

Now for your basic questions:

1. It is normal for the Amine solution to leave a slight, dark, film residue on the steel or stainless steel valve trays in those areas where the velocities are low; it is natural for the high velocity areas (as those around the valve plate holes) to be "wiped" clean.

2. How do you know you have a "foaming" problem? Have you actually seen the "foam" yourself? Or are you responding to reports from others? Foaming is very difficult to detect. Experienced and knowledgeable engineers in the field can detect foaming problems usually by taking dP reading across the Amine absorber or Stripper. Foaming is caused by a variety of specific items. Most often foaming is attributed to hydrocarbons in the solution. What seems to be your suspected cause?

3. There is no "fix" required for the valve trays if they are not broken. I would strongly advise you to leave them alone unless you have to make physical repairs. IF IT AIN'T BROKE, DON'T FIX IT! Changing to a different type of valve isn't going to do anything to resolve your suspected foaming problems. For a clear and definitive explanation, you should refer your problem directly to the engineering company or contractor who designed and built your Amine plant.

4. Please be more concise and specific as to what your problem is by furnishing detailed basic data. For example:
a) What "Amine" solution and strength are you employing?
b ) What are the solution flowrates?
c) Who designed and constructed the plant?
d) What specific gas stream are you treating in the Amine absorber?
e) What is your Stripper design specifications and is this part of the process also exhibiting "foaming" characteristics?
f) What are your solution gas loadings?
g) Are you treating for CO2 & H2S simultaneously? ...or just for one or the other?
h) Do you use an Amine re-distillation still? Do you use an activated carbon in your solution stream?
i) Who is the fabricator of the valve trays and what type are they?

We'll wait for your response.

Art Montemayor
Spring, TX

[Art Montemayor]

saeid:

With the revelation of the +55 oC inlet sour gas I believe you've conceded some of the reason for your foaming problem. As you state, at that temperature some hydrocarbons are being carried over and into the MDEA absorber. Getting the inlet gas temperature down to a design level should be your first priority. Are you stating that you are operating this MDEA unit beyond (or outside of) the design specifications? If so, the results should have been expected.

You still have not responded with the identification of who designed the unit. You merely gave the licensor. Did the licensor design the MDEA unit and specifiy solution rates, temperatures, pressures, and total gas loadings in the Rich solution? Are you following 100% of the licensor and designer specifications? The final answer may lie somewhere in the responses to these questions.

I believe that you now agree with me that identifying the valve trays as the cause of any foaming is incorrect when you have an operation that is outside specificaitons. I hope you resolve the carry-over of hydrocarbons into the absorber, clean up the MDEA solution 100% and get the unit back into rated, design operating conditions.

Art Montemayor
Spring, TX

[rxnarang]

I believe that the temperature of the gas should be above the temperature of the Amine. This prevents condensation of hydrocarbons, the chief source of foaming problems. However, there is a limit on the temperature of the gas, beyond which absorption of CO2/H2S is affected. In addition, below a certain temperature there could be problems with hydrate formation. So actually we have a range of operating tempertaures, bounded on either side with the above considerations.

Of course, there are other reasons for foaming.

Art could you confirm the above?

[rxnarang]

Saeid,

You are correct on the temperature difference between the amine and the gas. To be precise, the lean amine should be 5C higher than the outlet gas hydrocarbon dew point. As mentioned below, this is to prevent condensation of hydrocarbons.


Regards

[Pronab]

Saeid

You can increase lean amine temperature and can maintain temperature difference between amine and sour gas inlet temperature more than 5 deg. C . We maintain this temperature even sometimes 15 deg.C untill Absorber outlet gas specification are ok ( mainly concern about out H2S < 20 ppm). Our rich amine loading is 0.60 ( design ) . I feel your amine circulation is more. We have a amine filtration package which contains a main cellulose filter followed by a carbon bed and a cartidge filter. Untll our filtration package is running normal quality of amine is ok . You should check solvent foam height and break down time, we maintain 2~3cm and less than 5 sec. skimming is done on regular interval. MDEA concentarion is maintain ~45%.

Pronab.