3 replies to this topic

[Enrico Lammers]

Hi there,

 

I was wondering how the length and opening size of an half-open pipe in a knock-out drum shall be determined. The relating Shell DEP and API 12J don't give an answer to that. Criteria are described to comply with maximum momentum of the inlet nozzles (rho x v^2 shall be less than xxx Pascal), but the actual size of the opening in the pipe and the length are not described.

 

Is it that simple as the open area of the pipe shall be at least or larger then the area of the nozzle? That's almost in all instances the case. I assume "half-open" refers to the half of the diameter, but it's doesn't say anything about the total open area.

 

Kind Regards,

 

Enrico Lammers

Edited by Enrico Lammers, 21 June 2013 - 02:49 AM.

[Bobby Strain]

Provide the half-pipe across the vessel. Presuming the vessel is vertical.

 

Bobby

[Pilesar]

The pipe should be long enough so that there is a couple of inches clearance between the end of the pipe and the vessel wall to avoid metal/metal contact. If a long pipe, you may need to support the end of the pipe at the vessel wall to keep it from vibrating. The pipe should have an open slot at the bottom. The slot will start aseveral inches into the vessel (about 10% of the vessel diameter) and the slot will end several inches from the closed terminal end. Cut less than half of the pipe ... so that the slot in the pipe wall is about one-fourth or less of the cylinder wall. So you are removing a pie slice of 90 degrees or less for most of the pipe length. If you want better distribution, your slot will narrow as the distance from the inlet nozzle increases. You can calculate the distributor pressure drop if you need exact figures for open area if you want. I just set it the design and move on to the next phase of the project. The frictional pressure drop should mostly be balanced by the recovered momentum closely enough to give a reasonable distribution.

[Enrico Lammers]

All,

 

Thanks for your reply. It's a non critical application, just to separate flash steam from condensate in an atmospheric storage tank.