3 replies to this topic

[dsahmed]

Boil up vapor returnnozzles into the LPG/NGL Splitter is noticed to be located low into the bottom liquid (liquid sum), which is causing entrainment of vapor making LPG & NGL off-spec.

I do not have design data and would like to know where the nozzle should have been located in relative to liquid height in the kettle reboiler (weir height), last tray or any other location. Only reference I gather is kern article appeared in Deecmebr-1968 hydrocarbon processing, unfortunately I do not have the article therefore unable to understand the theory and required design consideration.

The Boil up vapour return should be between the vapour space of the bottom most tray and still. Ideally the return line should have deflector. The sizing and the height from the bottom to be calculated depending upon the vapour load and the pecularity of the liquid to be distilled. Remember the reboiler is eqivalent to one tray and contributes to the seperation.

[Zauberberg]

Hello dsahmed,

The data you are searching for can be found at: "Distillation Design" and "Distillation Operation" books, both by Henry Kister, as well as in "Process Design for reliable Operations", by Norman Lieberman.

Since the tower bottom level is driven by reboiler hydraulics (you actually control the level in the kettle-side), there isn't much you can do about it - from operational point of view - if reboiler and piping system is clean from deposits and there isn't any physical blockage (deposits, corrosion products etc.) If this is a problem in your plant from day No.1, you are faced with inadequate design.

Concerning the operational changes, you can try to lower the heat input into the column (if there is any margin for tower bottoms product quality) and watch if decrease in system deltaP makes any improvements in tower operation.

[Zauberberg]

dsahmed,

Please find attached two pages from H. Kister's "Dist.Op.", chapter related to reboiler return piping arrangement. This is all that you need.

Best regards

[attachment=361:Reboiler_Return.pdf]