sieve trays

[picasa]

I am posting this message in this forum in hope of a better response. I used a wrong forum previously.

What is the definition of foam derating factor for a sieve tray?
What is HCBN ? It is some sort of fluid name in a stabilizer vessel. I dont know what HCBN stands for.
For a sieve tray what does the ratio "Hole Area / Bubbling Area" stand for?

 

[sshep]

Picasa,

The bubbling area should be be the area between the chords defining the downcomer inlet (or inlet weir if there is one), and the outlet weir. The hole area is the number of holes times the area of one hole. This sort of poorly defined input parameter is used for some rating programs, also known as open area/active area- typically a number between 9% and 16%.

Because you are not actually entering the number of holes, the best advice is to double check the output which usually restates how much open area (i.e. how many holes) is actually being used, and verify that it matches the number of holes in the plate. It is uncertain to me why this rating definition is so common when most tray drawings explicitly state the number of holes, but that is the way it is often done.

best wishes, sshep

 

[25362]

I think may be HCBN stands for hydrocarbons.

 

[katmar]

Hi Picasa,

I see you have received answers for two of your three questions, so I will address the foam derating factor only.

There are basically two ways that a sieve tray column can flood. If there is too much vapor traveling up the column it can entrain liquid from one tray to the tray above it. The second route to flooding is if the liquid cannot flow freely down the downcomers because there is too much liquid or the tray pressure drop is too great.

The foam derating factor addresses the first flooding mechanism described above.

The way to work out the required diameter of a column to prevent flooding is to use a correlation that gives you the so-called "Capacity Factor" as a function of the liquid and gas relative flowrates, their densities and the tray spacing. Once you have the capacity factor you can calculate the maximum permissable vapor velocity and therefor the required bubbling area. The derating factor is simply a multiplier that is used with the Capacity Factor. If your derating factor is 0.85 you reduce your permissable vapor velocity to 85% of what it was, i.e. you increase your bubbling area by a factor of 1/0.85 = 1.176.

The reason for this is because a foaming system will more easily allow liquid to be carried upwards in the column so lower velocities must be used.

Foaming is also important in downcomer design, but that is a different question.

 

[TD2K]

What is feeding the stabilizer vessel? That may give us a better idea what HBCN could stand for.

 

[Lblopez]

Hello,I hope can help you

What is the definition of foam derating factor for a sieve tray?

May have relation with the rate to form foam in the liquid surface because of vapor velocity and system characterist

What is HCBN ?
What refer it? Where do you read it?

It is some sort of fluid name in a stabilizer vessel.
When you say stabilizer vessel, you refer to reflux vessel or vessel in the top of a distillation coulumn


For a sieve tray what does the ratio "Hole Area / Bubbling Area" stand for?

The hole area is these area of tray where the vapor passes. When the vapor pases the tray and enter in the liquid sin, the vapor open the area while move upward in liquid (like inverted cone without peak, you know?). The ratio is a mesurement for opening of this cone. This ratio is used in hydraulic calc to mechanical desing of trays.

In TREYBAL. "transfer mass operation";
WALAS."Desing operation equipments"
LUDWIG "Desing in chemical process"
KISTER "Destilation desing"
this book are so old but very good, there you can find it.