Controlling sludge in petroleum storage tanks

[roadwhore75]

I am looking at a way to control sludge at the bottom of large >100' diameter above ground storage tanks. These tanks have a significant slope, with perhaps 20% of the capacity in the heal. I toyed with the idea of adding agitators but this idea was scoffed at by an older engineer who said we want the sludge to collect in the heal. We will soon be making ultra low sulfur (ULSD) diesel that he says will have catalyst residue; I assume he means carry-over, in fluid bed terminology. The ULSD obviously goes through a hydrotreater.

My questions are these:
1) How can I predict the settling time for the tanks?Obviously, there will need to be some settling time before we send the ULSD down a pipeline or out to a truck.
2) Does agitation make sense? I was thinking of turning on the agitator prior to conversion from gas oil (20,000 ppm sulfur) to ULSD. Our planners will want to be able to switch back and forth between ULSD and gas oil. Obviously, we would not use the agitator except when converting the tank because we will want to allow sediment to settle.
3) Can someone recommend some references for estimating settling in storage tanks?

Thanks

 

[Glenfiddich]

Maybe an internal ring manifold for the feed to the tank would help to keep the bottom agitated. If not, then a mechanical agitator-nothing wrong with that. The inlet and outlet should be 90 or 180 degrees from eachother.

I wouldn't bother with settling time calcs. I'd just recommend the internal ring header or an agitator-as you already mentioned.