4 replies to this topic

[ramlalithravi]

Hello all,
This clarrification is regarding a existing separator revamping with respect to the derating of the system.

Separator or compressor suction KO drum has been designed for a design pressure of 25 barg. due to constrainnts related to corrosion alowance of the equip. the system is derated to 22.25 barg.

accordingly the size of the separator will get modify based on the results derived from the simulation.

My question is , can it be possible to retain the same dimension but by internals modification, could i get the same separation efficiency??

Inlet condition of the separator:

Vapour rate - 2600 m3/hr
liquid flow rate - 10 m3/hr
density vap. - 28.82 kg/m3
density liq - 550 kg/m3
k factor i chosen - 0.11 m/sec.

with this availble datas, the diameter is coming about 1.6 m..but exisiting diameter is 1m. at this condition only by modifying the internal, can it performs to the same separation efficiency???


Regards,
rame

[Zauberberg]

Please note that you have already used K-value on the higher side of the recommended range, and you ended up with higher flow area requirements anyway. In reality, the K-factor you used should be de-rated even further because of application (compressor/expander suction drum) to 70-80% of the initial value.

Personally, I have bad experience with revamping KO drums with different type of internals. Sure, vendors will always claim that they can achieve whatever you need within the same vessel diameter, but they don't really care - eventually you are the person who operates and who will continue to operate that piece of equipment, and your judgment/decision should be the ultimate one.

The best suggestion I can give is to get in touch with the compressor vendor/OEM, and discuss this subject with their technical group. If you don't get the "green light" from the vendor, that is another reason to consider employing a new vessel, with sufficiently high flow area that will allow for proper gravity separation enhanced by the wire mesh. There isn't such good thing in designing KO drums like relying on gravity separation. Gravity is very simple and beautiful - it always works, and it works everywhere.

[Zauberberg]

Also, if you decide to go for the new, bigger vessel - make it big enough from the beginning. A few centimeters higher diameter will not add so much extra cost, but it will provide an extra margin and room for future revamps. It is always better to go with the conservative design, rather than explaining to the management why the new vessel does not work.

[Erwin APRIANDI]

Dear ramesh r,

What is your operating pressure, you mentioned about the design pressure and the derating design pressure but you don't mentioned the operating pressure.

As I have experienced in my last two project, lower operating pressure will required bigger size than higher operating pressure. And as Zauberberg as mention you have take high K value of 0.11 m/s since we ussually even reduce the factor further more by multiply it by 0.7 or 0.8 for compressor suction scrubbers and expander inlet separators application based on GPSA recommendation. So I will not recommend you to use a simple separator sizing spreadsheet to do the adequacy check.

However if you really persistance on using the existing separator, you can use a computational fluid dynamics simulation for further clarification whether the existing separator is still enough for the new operation or not

Edited by erwin.apriandi, 26 January 2011 - 09:28 PM.

[smalawi]

Hi,

can you go with high K values ? yes, you can install more efficient separator internals e.g. inlet vane device, larger vessel vane packs, cyclones, ... but these wont work for a compressor KO vessel. with a small vessel size, once you build any level you will start re-entraining liquid back to the compressor and damaging it. moreover, if the residence time in the vessel is too low, you cant relay on operators intervention and you open up the door for more expensive instrument protection

I will go with a new vessel if possible,

cheers,

SM