5 replies to this topic

[ashokg9]

Hi,
In order to calculate the diameter of a distillation column, we have to consider the optimum vapor velocity as 50% to 70% of flooding velocity.

If we maintain vapor velocity much less, then weeping takes place and much more vapor velocity leads to flooding.

What is the effect on separation if we consider the operating vapor velocity less than 50% and more than 70% ?


Thanks,
Ashok

Edited by ashokg9, 03 October 2011 - 06:54 AM.

[latexman]

Efficiency suffers resulting in a poorer separation.

[S.AHMAD]

More vapor (low L/V ratio) results in liquid entrainment, distillate contains more heavy ends. Less vapor (high L/v ratio) results in weeping, more light ends in the bottom product.

[ashokg9]

Thank you Ahmad and latexman.

[katmar]

The 70% of flooding point is not selected because of maximum efficiency and separation. It is used to give some safety factor for wrong data, poor fit of flooding correlations and potential growth in business. If you are confident of your design - for example if it is a direct scale up/down of an existing well know process - then you can design for more than 70% of the calculated flood point and you will get better tray efficiencies and separation than you would at 70%.

Fortunately the efficiency curve is generally fairly flat between 60% at 90% of flooding and the effect of a slight design error is usually not too bad. And in my experience the flooding correlations are mostly fairly conservative. I have done analysis on several columns that were operating well, but should have been flooding according to the correlations. It also depends on the quality of your operators and control system. As you get closer to flooding the column does need to run as steadily as possible and any excursions in the operating parameters can result in process instability. This is another reason why the 70% value is used for design.

[dips]

Ashok,
If suppose my column operates at 90 % of flooding velocity then, which parameters should be monitored to reduce the degree of flooding velocity ?
Means how we maintain the flooding velocity in range of 50-70 % of flooding velocity ?
Please Guide.