Distillation columns gamma scanning

[AndreChE]

Dear all

Our C2 and C3 Splitters are with very high DP.

For the C2 Splitter, we have checked all the pressure profile along the column and we know in which section the flooding is located. We were suspecting ice/hydrates but we collected greenoil in the bottom level indicator nozzle.
The column was revamped with new trays, more capacity. At the moment it is distilling onspec bottom and top products just with a very high DP than expected.

For the two C3 Splitters, the situation is diferent. THe columns were not changed. They were hydrotested and closed.
When we started up the plant we experienced very high DP along both columns, with values in which was not possible to distill in the past. However, the situation still remains and both top and bottoms are onspec. Our maximum DP was 700/800 mbar and now we have 1200/1300mbar for 178 trays in each column.

We will perform gamma scanning for these 3 columns. My question are:

- Which conditions should we put the columns for the scan? Max possible load? We already have very high dp but they are distilling. High/low reflux? High/low reboil?

- Were can I learn more deeply how to analyse gamma scan plots? I have read everything in Kister's books and some small papers but I feel I need to study deeper in order to fully understand quickly those plots? Any papers or articles on the net or journals? Any specific book or documentation? The tests will be performed next week.

Thank you all
AndreChE

 

[unclesyd]

When we used Gamma Scanning of our columns we were at operating normal operating conditions. In the days we performed our testing they didn't want any more liquid in the column than was necessary due to instrument sensitivity.

I've only seen one short paper on this procedure that was copied from one of the journals. I'll look around but I don't think I still have it. I would get with the people that are going to do the scan and discuss your problem with them.

 

[0707]

Go to

http://www.tracerco.com/products-processdiagnostics-trutec-truscan.htm

good luck

luis

 

[Jason5000]

Here are a few of my lessons learned from tower scanning.

If the high DP in your towers is intermittent, ie. comes and goes along with swinging rates and level in your towers as is typical with flooding, I would suggest scanning it while it is in an "upset" condition. I've seen a scan done on an absorber column while the column was operating perfectly and the scan results looked normal. Then we asked the board operators to initiate an upset and scanned the tower again, and the second scan showed large holdup from flooding. We were even able to pin it right down to the seventh downcomer. Lesson learned: if its in and out of flood, flood it for the scan!

Also it helps to know a little bit about your tower internals going into the scan, as it sounds you do. Case in point, colleagues of mine were experiencing very poor performace from a rather large amine regenerator. They scanned the tower and everthing looked pretty normal. However, when they opened the tower they found many of the trays blown out. The tower had two pass trays and the side that was scanned was all in good condition; it was the opposite side where all the trays were bent up or just plain missing. Lesson learned: scaffold and scan both sides of a two-pass tower.

 

[STI666]

Gents,

Jason5000 makes some good points on Gamma Scanning. The scanning crew should be a good reference to suggest the best procedure, with your consultation, to obtain good results.

In the first example, the tower was most likely scanned in an unflooded operating condition to verify that the trays were still in position. Trays can be difficult to detect if the tower is liquid stack flooded. The rates would then be turned up to flood the tower and determine the point of origin.

In the second example, on a two pass system (or more), scan one side of the trays. After the data is obtained, the decision can be made on whether to scan the other side. Sometimes the problem is apparent after one scan. A second scan may be performed to confirm the data or obtain additional information if needed.

Scanning companies are pretty eager to help out so give them a call to discuss your problems and options. Talking does not normally cost anything and they can help to lay out the best plan to obtain the required information (hopefully they will also minimize your costs). Gamma Scanning may not always find the problem but if not it can eliminate possibilities so you can look elsewhere.

We have found that plant operators lose far more money in lost production or off spec products than they ever spend on the cost of a Gamma Scan.

Don

http://www.scanningtech.com