Why are fractionating towers in a refinery always tall?
Length plays a part in how long it takes for the vapor to travel from inlet to outlet and length plays a part in how well the fractions are separated.
Fractionating towers in a refinery are always tall because they utilize the process of fractional distillation to separate crude oil into its different components based on their boiling points. The main reason for the height of these towers is to accommodate this process effectively.
To explain this further, here is how fractional distillation works:
1. Crude oil enters the fractionating tower and is heated at the bottom.
2. Different components of crude oil have different boiling points. As the oil is heated, high boiling point components (such as heavy hydrocarbons) tend to condense and remain at the bottom, while low boiling point components (such as gasoline) vaporize and rise to the upper sections of the tower.
3. Inside the tower, there are trays or packing material installed at regular intervals. These surfaces increase the contact area between the rising vapors and the descending liquids, allowing for better separation.
4. As the vapors rise through the tower, they gradually cool down. The different components condense back into liquid form at their respective boiling points and collect on the trays or packing material.
5. The separated liquid fractions are then withdrawn from different levels in the tower.
Now, the reason for the height of the tower becomes clear. The taller the tower, the more stages of separation can be achieved because there is a greater distance for the vapors to travel and cool as they rise. This results in a better separation of the different components based on their boiling points. A tall tower also allows for a longer residence time, meaning more thorough separation can occur.
So, in summary, fractionating towers in a refinery are tall to facilitate the fractional distillation process, allowing for effective separation of different components of crude oil based on their boiling points.