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Our crude vacuum distillation column bottom pump suction strainer gets full of coke. How can we prevent this?
 
Answers
26/06/2011 A: Sudhakara Babu Marpudi, Dangote Oil Refinery Company, m_sudhakarababu@yahoo.com
Maintaining the bottom temperature, flash zone Vacuum / pressure and lower residence time the short residue piping is the key to prevent the Coking in the bottom of vacuum columns. Bottom temperature can be controlled by optimising the bottoms quench. Vacuum can be controlled by recycling some of the non condensibles to the suction of the vacuum producing equipment. Resindence time can be lowered by optimising piping bends / lengths that are generally given generous margins for managing the piping stresses. If the coking is still uncontrollable install duplex basket strainers in the bottom pump suction. That will reduce the frequency of suction strainer cleaning.
01/08/2010 A: Jayaraj Jayam, Chennai Petroleum Corporation Limited, njayaraj@gmail.com
Full of coke in the suction strainer of the vacuum tower bottom pump indicates that mild thermal cracking takes place at the bottom of your vacuum tower which is an undesirable reaction. Control the bottom temperature of your vacuum column by adding more quench flow. If you do not slip any VGO in VR, then reduce COT of your vacuum heater.
Check design data for the bottom temperature of your vacuum tower and try to maintain that. Also maintain minimum level at bottom of your column so that the hold up residue gets only a minimum residence time. Higher residence time helps thermal cracking even at low temperature.
23/06/2008 A: Berthold Otzisk, Kurita Europe GmbH, Berthold.Otzisk@kurita-water.com
The coke particles in the suction strainer are a clear indication of fouling problems. Coke formation is often a result of precipitation of asphaltenes. Temperature changes may influence the thermodynamic reactions to precipitate more asphaltenes.
Metals like sodium, potassium, iron, chromium, nickel, vanadium and copper accelerate the precipitation of asphaltenes at temperatures around 350°C. You can stabilize the asphaltenes with a suitable Kurita antifoulant program to avoid precipitation. This will help to reduce the coke potential.
18/06/2008 A: Mike Watson, Tube Tech International Ltd, mike.watson@tubetech.com
Coke formation depends very much on the type of crude used, but modification of the column can enable cleaning while on-line.