6 replies to this topic

[abolghasem202]

Dear all,

 

 

I have a problem in designing a deethanizer column. The main task of this column is to separate light components (e.g. H2, ethylene and ethane) from a propylene/propane mixture. The feed contains about 6mole% propane, 2mole% lights and the rest is propylene.

 

My main problem is in determining column' diameter. I know that a jet flood of 80% is commonly assumed for determining column' diameter. But I came across an operating column with similar feed composition but different flow rate. After simulation of this operating column, I found out that it is designed based on jet flood of  35%. I mean the column can handle a much larger vapor flow rate. This column is operating properly. Downcomer back up and downcomer choke flood of this column are about 50%, based on my calculations.

 

So, I don't know if I should design my column based on jet flood of 80% or 35%? 

 

 

I would very much appreciate your kind responses.

[Bobby Strain]

What pressure does the column operate? Feed source? What capacity? Product specs?

 

Bobby

[abolghasem202]

Bobby, 

 

Feed to this column is the non-reacted gas from polymerization of propylene. Column pressure is about 18 barg. In the existing column, feed flow rate is about 3ton/h. The bottom product should be ethylene-free and condenser temperature is set at -10 C.  The main components in bottom are propylene and propane but a small fraction of propylene is also present in the top product.

[Bobby Strain]

For the 3 T/h feed, only a small diameter is required. So, no need to push it. In fact, a packed tower may be better for you. I presume that you have a process simulator, so it will be easy to check.

 

Bobby

[abolghasem202]

Bobby,

 

Thanks for your suggestion.

Yes, The 3T/h tower should have a relatively small diameter. But, based on my calculations, a diameter of about 0.52m is required (jet flood of 80%) while its diameter is 0.8m. A diameter of 0.8m for this column corresponds to a much smaller jet flood (35%). I do not know which value of jet flood should I consider for designing my new column with higher capacity. 

[Bobby Strain]

I would design for 75% flood or less. You don't want to push it for a new fractionator. It's not a difficult separation.

 

Bobby

[abhi_agrawa]

Abolghasem202,

 

I usually consider 1000 mm as the minimum tower diameter, as someone has to go inside and install the internals. It seems that your reference tower was based on considering 800 mm assuming that in this diameter someone would be able to install the tower internals.

 

Abhishek