reboiler to column distance 1

[rogered]

Naphtha Splitter Reboiler Return Line
This discussion refers to the Naphtha Splitter Column (1 off) and its reboiler (2 off) and the likely option for heating this reboiler. For the fired heater option the reboiler outlet line could potentially be long, approx. 23m from column - this is due to concerns over the safety of a fired heater close to a column containing a significant hydrocarbon inventory.

Preliminary Pipesim software hydraulics analysis suggests following findings:

1. Flow regime is on border of intermittent / slug flow and annular dispersed flow regime for 24" pipe size.

2. Pressure drop < 0.2 bar

3. Temperature drop < 2°C (for insulated pipe)

4. Velocity < 13 m/s & roh-v 2 <15000 kg/m2 s

The concerns relate to:-

1. Reboiler Return Piping Design for 2 phase flow (vapour 93% vol.) to column bottom.
2. Possible Slug flow in reboiler outlet piping and slug handling measures required. Normal & Turndown (50% of normal) condition)
4. Impact on NS column bottom design
5. Any past reference with such separation distance

The properties of the fluid (crude oil) and possible layout is attached for reference.

 

[CJKruger]

rogered, my comments are:

- Use another flow regime map. I recommend Dukler-Taitel.

- Your vapour fraction is low. You can go up to 50wt% for fired heaters. This will reduce you pumps, pipes, heaters, etc.

I assume your vapour fraction is so low as you use some kind of once-through arrangement. Don't, just let the liquid drop to the bottom of the tower and feed the heater from there.

- The rho.v^2 is too high for the tower. Increase the pipe size 8-10 pipe diameters upstream of the tower.

- If you do not have a once-through arrangement, the reboiler feed is from the tower bottom and you typically do not turn it down. You just reduce the vaporization.

Cilliers

 

[Compositepro]

Place the control valve in the return line to the column so the liquid does not flash into vapor until it returns to the column.

 

[dcasto]

to add to compo's, do not pocket the return line.

 

[CJKruger]

Compositepro, I strongly recommend against putting the control valve downstream of the reboiler heater.

Cilliers

 

[dcasto]

I switched to the downstream on a direct fired amine still because the two phase flow in the furnance was eating up tubes faster than we could replace them.

 

[CJKruger]

dcasto, I am curious, what was the % vaporization before and after the valve ?

Still, I will only consider a control valve in a 2-phase heater outlet line if all other options are way too expensive. I assume in your case you did look at upgrading metallurgy, reducing heat flux, reducing film temperature, improving amine quality, larger tube size, etc.

rogered has a new naphtha splitter reboiler, and I think he has plenty of alternatives that are better (than a control valve in heater outlet).

Cilliers

 

[Compositepro]

My point was to not have boiling in the reboiler so that you do not have two phase flow through a long return line which requires larger pipe and boiler tubing, and more hydrocarbon inventory in the heater. A control valve in two phase flow would not be a good idea.

Even using a heat transfer fluid seems a better concept than a remote reboiler.

 

[dcasto]

the pumps put out enough pressure that the amine was 99% or more. After the valve the "steam" was about 15% to 19% on a molar basis. The solution was DIPA sulfanol solution. I can't find my simulation runs, but thats about what I remember.

 

[CJKruger]

dcasto, thanks for sharing this (very interesting) info.

 

[dcasto]

wow, nice stars y'allll, to the poster?