Used Oil refinery process problems

[mab2008]

We are operating a used oil re-refining plant to produce lube base oils. The process involves distillation in vacuum operated columns. We are experiencing following operating problems:
1. Coking in direct fired heater tubes. We have tried chemical cleaning, pigging, etc but no results.
2. Colum bottom circulation pumps ( centrifugal type) often experiende cavitation, less discharge pressure,less flow problems, resulting in process upsets.
Appreciating potential solutions from friends with practical experiences.

 

[EmmanuelTop]

If you are experiencing fired heater coking, you have to change something in the way you are running the plant - cleaning activities are just "treating the consequence instead of treating the cause". It could be that radiant duty is exceeding the maximum value, or maybe mass flux of oil is below recommended minimum. I am uploading one document for your reference:

http://www.revamps.com/Revamps/documents/170.pdf

Other method could be to use velocity steam, but this involves heater and column overhead system revamp.

Best regards,

http://antwrp.gsfc.nasa.gov/apod/astropix.html

 

[djack77494]

Coking is a function of your particular fluid (not adjustable) and the time-temperature history of that fluid. You must either reduce the temperature and/or the time that the fluid sits at the highest temperatures. Remember that this is a local phenomenum and that the T-T history going through Heater pass "A" may be different from going through pass "B". Ensure the flows are balanced so all are near the average.

There are often provisions in heaters for decoking using steam or a steam/air mixture. Discuss with your heater manufacturer.

As previously mentioned, coking is a problem best dealt with by avoidance techniques.

 

[25362]

The common procedure adopted by those lube re-refiners not using solvent extraction is composed of settling/filtration [→] water and lights removal by distillation [→] wiped film evaporation [→] polishing with hydrogen or clay [→] vacuum fractionation of lube cuts.

Is your system similar ?