A fractionation is a unit operation utilize to separate mixture into individual products. The separation involves separating components by relative volatility. Below is the example of fractionation schematic diagram:
Heat is introduced to the reboiler to produce stripping vapors. The vapor rises through the column contacting the descending liquid. The vapor leaving the top of the column enters the condenser where heat is removed by some type of cooling medium. Liquid is returned to the column as reflux to limit the loss of heavy components overhead.
Some type of fractionators are demethanizer (top product is methane, C1), deethanizer (top product is ethane, C2), depropanizer (top product is propane, C3), debutanizer (top product is butane), distillation column (products are naphta, kerosene, etc) and many other type fractionators, depends on the products to be made and the feed composition.
The interesting thing is the diameter of fractionation column can be different between the top and bottom section. Why? Let's see the example below:
Demethanizer
Atmospheric Distillation Unit
On demethanizer figure above, it shows that the top section has larger diameter than bottom section, looks like a bottle upside down. While on atmospheric distillation unit, the bottom section has larger diameter than top section and looks like a bottle.
After having some discussions and reading some references, I try to conclude the answer of this question. It depends on the feed composition that enters the column. When light components is more than heavy components, the top section column might be having larger diameter than the bottom (like demethanizer). Vice versa, when heavy components is more than light components, the bottom section might be having larger diameter than the top (like distillation column). This answer is only a philosophical answer (I know this is still a shallow answer hehehe). Further calculation and sizing is needed to get more precise and detailed answer. Anyone would be adding or correcting my answer? I am very welcoming it. Let's discuss! :D
Reference:
- GPSA Section 19 Fractionation & Absorption
- http://nptel.ac.in/courses/103102022/evaluation%20of%20crude%20oil/images/2.5.3.jpg
- Discussion with senior and friend: Abang Joni, Mas Andri, and Togel (thank you)
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