7 replies to this topic

[chandru]

I am designing C4(butane mixtures) unloading compressor. In that i have to size compressor knockout drum.
Can any one tell me on what basis i have to calculate amount of liquid fraction will be formed/carried out in the compressor suction line which is taken from top of sphere.

[Zauberberg]

Be conservative - consider the worst possible scenario (i.e. the highest flow from C4 spheres and lowest ambient temperature).
The knockout drum will be sized based on the gas flow anyway, so you cannot mistake.

[djack77494]

Often the only source of information you have will be a simulation output. This is one instance where a simulator will not furnish you the answer. As Zauberberg said, you size the K.O. Drum on the basis of gas flow, but you must imagine that for some crazy unknown reason there will be some liquid phase present. In most situations like this that I have seen you have no liquid phase present according to the model. NEVER omit a K.O. Drum (a.k.a. Scrubber) however, because the model says there is no liquid. Trust me, there will be liquid present at times, and it would be easy to damage or destroy the compressor if the drum is not present. While it is difficult to quantify the amount of liquid that might be present, just do the design based on some nominal (very small) quantity of liquid. Never mind that its residence time might be centuries; that is not a problem.

Edited by djack77494, 04 January 2010 - 04:48 PM.

[S.AHMAD]

I am designing C4(butane mixtures) unloading compressor. In that i have to size compressor knockout drum.
Can any one tell me on what basis i have to calculate amount of liquid fraction will be formed/carried out in the compressor suction line which is taken from top of sphere.

Hi,
Consider condensation due to heat loss to surrounding. so need to know temperature of fluid and ambient. If it is insulated, consider worst case of bare pipe since insulator can damage badly during operations.
Possibility liquid carry over from sphere is very unlikely.

For sizing KO drum what we need is the vapor and liquid density and the gas stream flowrate. The quantity of liquid is not being used except for level control valve sizing.

[chandru]

Hai all
Thanks for your reply,
Can you please clear few more doubts,

What partice size i have consider for gravity settling in KOD and particle size across mist eliminator for reciprocating compressor.
What is length between LLL and HLL, i have consider since liquid flow rate is very low,

Thanks in advance.

[mbeychok]

Chandru:

You will find it very useful to read this article in the online Citizendium encyclopedia:

Souders-Brown equation

[Profe]

Hi Chandru
For design purposes of a knockout drum, it is first necessary the conditions of stream: mass flow rate, pressure, temperature and gas composition, its physical state: liquid or gas. Then with the above data, if it is gaseous state, is necessary an adiabatic flash calculation to determine the fraction of liquid and gas. The knockout drum is designed to completely retain the liquid fraction; therefore the design is done as a gas liquid separator. In the case of a knockout drum suction of a compressor must be designed for the worst case of liquid entrainment that may arise under operating conditions (apply a safety factor). The design must consider besides fog retainers (Demister pad) for improved performance in the KO drum.

I thik this little bit of knowledge will be usefull.

Good luck with your design.

Edited by Profe, 12 January 2010 - 08:09 AM.

[sheiko]

I am designing C4(butane mixtures) unloading compressor. In that i have to size compressor knockout drum.
Can any one tell me on what basis i have to calculate amount of liquid fraction will be formed/carried out in the compressor suction line which is taken from top of sphere.

check this out: http://cat.inist.fr/...cpsidt=14878780.