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Understanding Flash Column Design

design flash column flash distillation distillation column

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#1 sunny0

sunny0

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Posted 15 February 2015 - 02:45 PM

Hi,

 

I have general design of Flash Column Distillation in attached power point presentation but few things are messing up with my mind that i am unable to understand. It would be a great help if someone can let me understand these things?

 

Kindly see the attached power point presentation.

My Questions:

1. In Power point we have design of Flash column so why we call it Drum instead of Column?

2. In Slide name " Vertical Size Drum " There is an equation in which this "Permissible vapor Velocity" formula is there. In this formula what is row ? (Row type variable is there so what is it?)

3. What would be the formula for Diameter to Height ratio of Drum/Column?

4. In Rachford Rice Solution, what is ment by Trial & Error Method? What is it?

 

Kindly post your replies.

I appreciate your replies.

Thanks.

Attached Files



#2 Pilesar

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Posted 16 February 2015 - 02:08 PM

Some possible answers:

1) The term "column" usually refers to a multi-stage distillation vessel. A flash drum typically means a single stage distillation vessel. The presentation you attached is about flash drums. I saw nothing about "flash columns".

2) The equation you reference on slide 13 is the critical velocity equation. The maximum permissible vapor velocity is the velocity where a gas stream upward will almost begin to carry liquid droplets overhead. The "rho" in the equation is density of the liquid and vapor (depending on the subscript.)

3) The minimum diameter is calculated based on the vapor velocity needed so that liquid is not carried overhead. The height is often a function of vessel cost. The rule-of-thumb shown on the same slide 13 indicates the height is typically three to five times the diameter. There are other considerations such as the need to hold a certain amount of liquid in the drum, the height required to measure level, the height needed between the feed inlet and the overhead to disengage the liquid droplets, etc. The optimum height to diameter ratio also depends on the vessel design pressure due to wall thickness, head diameter, and material cost factors.

4) Trial and Error Method means you propose a value for your unknown parameters and adjust them as needed to satisfy all the required equations. See slide 8 and following. 






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