5 replies to this topic

[arvind]

Hi,

I am wondering for how to calculate/ decide optimum column operating pressure if I knows (limit) the cooling water outlet temperature to 42°C. and the available low pressure steam is at 4 bar gauge. for depropaniser.


Thanks and regards,

Arvind

[dave2001]

If your are talking about depropanizer, use 300 psig

[fallah]

Hi,

I am wondering for how to calculate/ decide optimum column operating pressure if I knows (limit) the cooling water outlet temperature to 42°C. and the available low pressure steam is at 4 bar gauge. for depropaniser.


Thanks and regards,

Arvind

What about the cooling water flowrate? Can the available flowrate absorb latent heat of saturated propane considering the limitation of cooling water outlet temperature (42 C)?

In the cases i have ever faced Air Cooler has been used as overhead condenser in depropanizer.

Edited by fallah, 20 February 2010 - 02:40 AM.

[fallah]

Dear All,
when deciding the operating pressure at column top, the following procedure should be followed:

1) Determines the maximum cooling water or ambient air temperature that is typically expected on the hottest summer day in the locale where the plant has to be built.
2) Calculates the condenser outlet (reflux drum temperature) that results from the above water or air temperature. How?, taking an approach about 10C
3) Assuming that the condensed liquid is at its bubble point (as normally is), then you must calculate the reflux drum pressure (saturation pressure @ temperature calculated in point 2).
4) Adding 5 or 10 psi to the pressure calculated in 3, allowing some pressure drop in the overhead system (condenser and associated piping) you calculate the tower top pressure.

Beware about the CW return temperature. If hot (above 45-50C) the carbonates starts to precipitate increasing the fouling in the exchanger tubes and pipes.

Best regards,

GERARDO VILLAMIZAR PLATA

Certainly you mean maximum operating pressure in your above statement.Please clarify.

[arvind]

Dear All,
when deciding the operating pressure at column top, the following procedure should be followed:

1) Determines the maximum cooling water or ambient air temperature that is typically expected on the hottest summer day in the locale where the plant has to be built.
2) Calculates the condenser outlet (reflux drum temperature) that results from the above water or air temperature. How?, taking an approach about 10C
3) Assuming that the condensed liquid is at its bubble point (as normally is), then you must calculate the reflux drum pressure (saturation pressure @ temperature calculated in point 2).
4) Adding 5 or 10 psi to the pressure calculated in 3, allowing some pressure drop in the overhead system (condenser and associated piping) you calculate the tower top pressure.

Beware about the CW return temperature. If hot (above 45-50C) the carbonates starts to precipitate increasing the fouling in the exchanger tubes and pipes.

Best regards,

GERARDO VILLAMIZAR PLATA

Thank you very much GERARDO.
That means if my cooling water outlet temperature is 42°C then I can keep condensate propane temperature about 52°C and calculate the saturation vapour pressure of propane at this temperature and additional piping losses @5-10 psi will give me the column top pressure.
This is when my cooling media is cooling water if it is Air cooler then then temperature approach may have increase up to 20°C
and follow the same procedure.


arvind

[Himanshu Sharma]

i am off the topic but still want to share my word of caution about MOC of the Depropaniser column.Normally i have seen it to be LTCS(low temp carbon steel )

In case you have PSVs or Depressurization control valve on this column make sure that temperature doesn't drop beyond -45 deg c .