What is the difference between packed bed column and tray(plate)column?

[Rami Khader]

Dear Sir :
I would like to know the difference between packed bed column
and tray column,Usese for each column, characterstics for each one..... such
like that.
Thanks
Rami Khader

[Ralf Lukner]

Rami,

It's been a while since I have dealt with these columns, but I can give you a
couple of ideas. Since the applications are so diverse, if you want more than
very general comments, you will need to be more specific in your question. In
the petrochemical industry, tray type columns have been quite common for
distilling product, apparently because they are simple to maintain and operate,
especially when the throughput varies (there might be cost advantages as well).
When more capacity is needed, It is common to retro-fit these types of columns
with packing, perhaps at the expense of throughput flexibility. I think in some
applications such as absorbers, packed columns may be more common, perhaps due
to mass transfer issues.

Hope that helps,
--Ralf

[GlennShiv]

There are many subtile differences between trayed and packed towers. Each
device has its respective advantages and disadvantages, and different process
vessels are serviced better by either of the two devices.

Advantages of Trayed Columns
+ low initial equipment cost
+ proven technology & design experience
+ able to handle multiple feeds and draw-offs
+ can easily handle flashing feeds
+ can be designed to resist fouling & corrosion
+ easy for maintence personel to service
+ easy to gamma scan to identify problems

Disadvantages of Trayed Columns
- once constructed, may be difficult to modify to improve capacity or increase
number of separation stages
- high pressure drop (about 5 mmHg per tray)
- not always a good choice for applications that operate below atmospheric
pressure
- some services experience foaming, and require use of foam derating factors

Advantages of Packed Columns
+ low pressure drop (about 1/5th or 1/10th pressure drop compared to trays)
+ great for applications that operate below atmospheric pressure
+ new packed vessels can be designed with smaller vessel diameters compared to
trayed vessels
+ can be utilized to retrofit a trayed column to improve capacity or increase
the number of separation stages
+ deals with foamy systems better than trays

Disadvantages of Packd Columns
- can suffer severe problems from liquid and/or vapor maldistribution
- requires good performance from liquid distributors (i.e. if liquid
distributor has a problem, the entire column suffers)
- does not accomidate multiple feeds and draw-offs without special equipment
- requires special internals to handle flashing feeds
- requires multiple packed sections and internals for applications requiring a
large number of separation stages
- more prone to fouling compared to trays
- higher equipment cost
- packing is thinner than trays, and may require expensive alloys or heavy
ceramic materials to resist corrosion
- more difficult for maintenance personnel to service

Trays tend to be utilized for many new column designs. Packing tend to be
utilized for vacuum applications and certain services, and for the capacity
retrofit of trayed columns. Each device needs to be reviewed in light of its
respective advantages and disadvantages for an application. These days, I
think these is about a 50/50 split between industrial vessels that are packed
and trayed.

You might want to check out the website, http:\\www.Nutter1.com.

Hope this helps.

Glenn Shiveler
Sulzer ChemTech USA
Shiv...@Nutter1.com