Reboiler return line design

[Chetan VYas]

We have a forced circulation reboiler in Xylene rerun column. Reboiler is furnace heater. The reboiler outlet line is pocketed. We had some hammering effect during start up after power failure ( 4 hours) and pipe dislocated. Is this pocketed line design causing this issue.

 

[pennpiper]

Chetan VYas,
You wrote:
"Is this pocketed line design causing this issue."
The answer is YES!.
That return line back from the Heater is a mixed phase flow line.

The fluid in the line is much the same as Boiler Feed Water (FFW), right at the boiling point and the result (in the BFW case) is Water Hammer.
This Water Hammer effect in your line is causing the problems.

The line should have been designed slopping up, with no pockets back to the column.

Sometimes its possible to do all the right things and still get bad results

 

[pennpiper]

Chetan VYas,,
Please provide a sketch of the existing piping showing"
- the horizontal runs,
- the vertical runs
- all dimensions
- the starting and ending elevations
- include all current support points

Sometimes its possible to do all the right things and still get bad results

 

[georgeverghese]

Can think of 3 requirements to avoid slugging in 2phase reboiler return lines
a) @pennpiper's post
b) Set the pump recirculation rate such that the resulting weight ratio of the liquid in the 2phase return line is at about 70% or higher.
c) Right selection of the return line size.

 

[pennpiper]

Chetan VYas,
A little feed back would be nice and polite.

Sometimes its possible to do all the right things and still get bad results