How to transform teoritical into real number of trays

[biofan]

Is there someone who can give me a detailed explanation how to transform teoritical into real number of trays for atmosheric tower fed with the effluent from H OIL reactors (hydrocracking of vacuum residue). The feed is described by a definite number of pseudo components. Is it possible to use the O'Connell formula Eoc = 0.492*(?l*?)^ -0.245. In this case concerning for example section for separating high atm gasoil(HAGO) from atm residue (AR) which of the pseudo components, describing the two above fractions must be characterized? I mean to know their liquid viscosity and relative volatility in order to solve O'Connell's correlation. My idea is to seperate them so that 5% boiling from AR to be 360 C and 95% boiling from HAGO to be 370 C

 

[mbeychok]

biofan:

You have not described your problem or explained your question well enough. There really is no reliable equation for converting theoretical distillation trays into actual distillation trays.

Fractionation Research Inc. at

http://www.fri.org/

has been developing such data for various tray types and various types of distillation at various pressures and temperatures for over 50 years. They are a non-profit research organization and access to their data is limited to their member companies.

You might try contacting them to see if such data as you need is available and what it would cost to get saccess to that data.

Milton Beychok
(Visit me at www.air-dispersion.com)
.

 

[SNORGY]

Stupid me for asking, but...

If the number of theoretical trays is always expected to be different than the number of actual trays, is there something about the "theory" that needs review?

Regards,

SNORGY.

 

[mbeychok]

SNORGY:

As they say, "no question is stupid".

A theroretical tray is a tray that is theorectically 100% efficient. Actual trays are not 100% efficient ... their efficiency is a function of the trsy type (bubble cap or sieve or etc.), the distillation temperature and pressure, the components of the liquid being distilled, etc., etc.

Research such as FRI performs using different trays at different temperatures and pressures and for different liquids ... in a fairly large-scale demonstration distillation column is what is required to determine tray efficiencies.

Alternatively, if one can find an actual commercial scale column using the same type of tray and distilling a similar liquid, data from that column can be used to determine the efficiency.

If you cannot obtain access to FRI data. the best bet is to contact some well-known tray manufacturers who have had experience with a similar distillation column and have them do your column design. In fact, that is always a good idea ... rather than trying to "do it yourself".

Milton Beychok
(Visit me at www.air-dispersion.com)
.

 

[25362]

Isn't the planned ASTM distillation overlap between the HAGO and the UCB a bit too narrow ?

 

[biofan]

I just want to understand how designers as a whole, once they have determined the theoritical number of trays convert them into real. Thank you for the answers.

 

[toabhijeet]

Hi Biofan

Broadly

Na = Nt / E

Na: Actual Trays
Nt: Thereotical Trays
E: Tray Efficiency

I suppose you have Na; The E can be decided based on type of tray & manufacturers data.

Please find attached some articles for tray efficiency.