Tray columns weeping point to zero loading ??

[mrtangent]

Dear Sirs,

I am completing a project which defines column operation via a simulator we have been asked to describe how the column trays loss level from weeping point to zero flow. The trays are muti pass sieve trays. Say the weep point is 50% of design would I expect a straight line of loss of liquid level to 25% or is it something which is system specific and difficult to model.

I would be interested in people’s perspectives on this.

 

[sshep]

Hey James,

I hope you will give us some feedback on your experience with implementing a dynamic simulation project once you get finished. Is this for operator training? I know from my own experience that these "out of normal operating range issues" are alot of work. You can be sure that operators will enjoy trying to break the model by dumping and flooding the column, etc, so some reasonable response by the model is desirable.

Kister's Distillation Design (mine is 1992), ISBN 0-07-034909-6, section 6.3.5. has correlations to calculate clear liquid height based on froth density, and the Francis weir formula- this is the tough part. Hopefully this variable (clear liquid head) is already being calculated in the model for liquid tray hold-up. The weeping correlation Kister prefers relating clear liquid head to weeping is given in section 6.2.12 (Lockett-Banik correlation). This correlation relates the weep rate (gpm per ft of hole area) to the vapor velocity through the holes and the clear liquid head and vap/liquid density. It appears that weep rate is inversly related to hole vapor velocity, square-root of clear liquid head, and square root of liquid to vapor density ratio.

Best wishes on your project,
sshep

 

[jamiegla1]

Try downloading a copy of Koch Glitch's "KG Tower". I BELIEVE it has the ability to change the turndown% and see the results. Its pretty good about allowing you to input tray types, # of passes, etc.