4 replies to this topic

[gvdlans]

Bubble cap trays are nowadays only installed in cases where large turndown and/or a positive liquid seal are very important. Because of the high investment and maintenance cost, normally valve trays are preferred above bubble cap trays.

[Art Montemayor]

Zili:

Everything gvdlans tells you is not only true, but is only part of the "negative baggage" involved with using bubble caps. Valve trays can do all that bubble caps used to do - so why insist on using bubble caps? Bubble caps require you keep an inventory of the varied parts to assemble them (since the parts are forever loosening and coming apart while in service) - so why insist on keeping an inventory of parts solely for the bubble caps? Bubble caps probably give you the largest pressure drop across a given distillation column - so why would anyone be determined to suffer this handicap and efficiency loss? Bubble caps require you furnish a tray-to-tray spacing of 24" to 30" (as a minimum!) just to gain access to the caps and do the necessary maintenance and cleaning - this increases the physical height of any column as well as the capital and installation costs. Why would you consider this desirable? Bubble caps -because of the maintenance and cleaning requirements - also require ladders, platforms, and manways on just about every tray. When this is compounded to the physical height of the column, why would you opt for this design?

But the "killer" feature of bubble caps that breaks the camel's back is the feature that requires you and/or your maintenance personnel to have to enter the trays themselves in order to effect maintenance, inspection, and cleaning. This is considered a HAZARDOUS ENTRY into a process vessel and the nightmare of every plant engineer and maintenance person. This is to be avoided, in my opinion, whereever it is possible. Far too many human fatalities have resulted due to hazardous entries into process vessels throughout the world and we engineers would be well advised to eliminate them where we can.

I could go on and on about bubble caps, but I believe the above suffices to re-inforce what gvdlans is trying to advise you to take into consideration as part of your student key learnings. As an engineer, you have to apply your common sense whereever possible. The scientist always fails to do this; we are expected to do it successfully. So you as an engineering student should always use your original thinking well beyond what you read in any engineering text book. Try to visualize what you would have to do to make the process work successfully and safely - from the design, installation and operational point of view.

Don't think of me or other engineers as "Anti-bubble cap" individuals. I have designed and employed many bubble caps and "tunnel" caps in the past. But that was in the old days (over 30 yrs ago) when we had no viable options on hand. Today, you have those proven and viable options. I would use them in the interests of safety and common sense.

I hope this experience is of help to you.