4 replies to this topic

If I have 2-phase flow entering a kettle reboiler, is it better to have the inlet on top or bottom of the reboiler.

I know that for complete liquid flow, the inlet is at the bottom.


thank you

[Nirav]

If I have 2-phase flow entering a kettle reboiler, is it better to have the inlet on top or bottom of the reboiler.

I know that for complete liquid flow, the inlet is at the bottom.


thank you

You should ask little in detail.

On which side of reboiler you are having 2 phase flow?
What is shell side / tube side fluid?

You have asked questions earlier also in this forum. But you don't came back after somebody replies to your query.
So try to respond to the answer you receive on forum. It helps to understand problems and solution to it at the same time.

Warm regards,

As a follow up to my orginal post..........


Saturated fluid will enter the shell inlet of the kettle reboiler. Less than 30% of the flow is vapor. The concern is that if the inlet is at the bottom the large vapor bubbles might form around the tubes thus reducing heat transfer surface area and reduce heat transfer.

There has been a suggestion to enter from the top of the shell giving the 2-phase flow a chance to condense fully to liquid but again there might be situation encountered in reflux condensers where the flow of the vapor has to be greater than the liquid flowing down.

Any thoughts or suggestions would be appreciated.

[Nirav]

Hello Ms.Kellie

In short, in almost all cases of kettle reboilers, process fluid from a column bottom will enter at bottom of reboiler. This fluid is always at its saturation condition and all of the heat transfered to this fluid will be utilzed to convert liquid into vapors at the constant temperature (temp of inlet = temp of outlet). Because, heat is utilized as "latent heat" only. There could be very little difference between inlet and outlet temperature due to the fact that the pressure at inlet and outlet is different and hence, saturation temperature will differ slightly.
There is no "superheating" in kettle reboilers since the vapors will leave the reboiler as soon as it is produced. There is hardly any control over it. Because it is acting on pressure balance with the column. As per standard practice, outlet from reboiler will be two phase flow of about 30% vapors.

Now, I do not understand as why you say as follows.

Saturated fluid will enter the shell inlet of the kettle reboiler. Less than 30% of the flow is vapor.

There can be NO vapor in the fluid before it enters the reboiler. Because "static height" of reboiler will prevent any fluid to get flash before it enters into reboiler. "static height" is the MOST IMPORTANT parameter in reboiler design since total pressure drop of reboiler circuit is compensated only by this driving force which is height of liquid or "static height". I hope you know this aspect well.

I don't know about other readers, but I am getting confused with your following statement.

There has been a suggestion to enter from the top of the shell giving the 2-phase flow a chance to condense fully to liquid but again there might be situation encountered in reflux condensers where the flow of the vapor has to be greater than the liquid flowing down.

How the "reflux condenser" is related to reboiler in your process here? You must provide small flow diagram if you are asking anything specific.

Warm regards,