5 replies to this topic

[sd_shreyas]

Hi,

 

Can anyone educate me on the normal/design margin kept above Cricondentherm temperature of fuel gas when it is pressure let down at KO pot and use for various purposes downstream?

 

Is there any specific standard or guideline?

 

Thanks,

Shreyas

[serra]

by definition cricondentherm is the maximum temperature on VLE area,
usually one calculates the phase envelope to find cricondetherm,
for some examples of phase envelopes see

http://www.prode.com...aseenvelope.htm

for a natural gas mixture, a EOS such as Peng Robinson or Soave Redlich Kwong
can predict VLE lines with errors of 1-3 K
which may be higher for very non ideal mixtures,

as far as I know there are not standards for this topic,
you may correct values for maximum (expected) error,

also don't forget that cricondentherm gives a conservative value,
if you know that a plant operates below a certain pressure

(which is below cricondetherm pressure)
you can, for example, calculate the dew point line up to that
value and select the maximum dew point.

 

Finally, cricondentherm is related to composition,

if for some reason, you add heavy components

cricondentherm must be recalculated.

Edited by serra, 07 July 2014 - 04:54 AM.

[Bobby Strain]

What is really important is the dewpoint temperature. I think you have your definitions confused.

Bobby

[sd_shreyas]

Bobby,

 

You are right. Later on further reading, I show the mention of margin on Hydrocarbon dew point (HDP) and not on Cricondentherm.

 

Question is: What is the normal/design margin kept above HDP of fuel gas when it is pressure let down at KO pot and use for various purposes downstream?

 

Is there any specific standard or guideline?

 

Thanks.

[serra]

cricondentherm is a typical spec. for pipelines as one wish to avoid condensation, with temperatures ABOVE cricondentherm you are safe from condensation in every section of pipeline,
with temperatures BELOW cricondentherm to see if condensation is possible you calculate dew point temperature at operating pressure in the specified section (of pipeline).
 
as said dew point temperature is calculated at a specified pressure,
you say "it is pressure let down at KO pot and use for various purposes downstream"
which means there is a range of operating pressures where you must make
sure to be above dew point to avoid condensation.
for a procedure see post #2, for example calculate dew point line
from Pmin to Pmax (operating pressure range) and select maximum value of temperature.

I do not know if there are accepted standards to set a minimum value above dew point,
as said in post #2, if you adopt a EOS as PR or SRK errors should be in the range 1-3 K,
probably a value of 5 K (above estimated dew point) should appear safe.

Edited by serra, 08 July 2014 - 04:21 AM.

[sd_shreyas]

Thanks Serra