2 replies to this topic

[florentj]

Greetings,

 

I would like some help on a conversion problem.

 

We have a De-ethaniser with an analyser measuring the C3 content of the top stream. The units of this analyser are [mol %] and the flow instrument measuring that stream is in Nm3/h. How can I find out the volumetric flow of C3 in m3/h with respect to the analyser's reading? 

 

This is probably a rather simple calculation but I am no chemical engineer (actually a junior process control) and I am a bit confused as to what should I understand by [mol %].

 

Thanks a lot in advance!

[fseipel]

N m^3/hr means normal cubic meters per hour -- normalized to standard conditions.  Because a 'mole' of C2 or a 'mole' of C3 or any other species present, represents the same number of gas molecules, you simply multiply the mole % (concentration) by the flow rate, to give N m^3/hr of C3.  Note that this is a special case; if the flowmeter did not read 'normal' volumetric flow rate you'd need to correct for density and you can't multiply this way with liquid mixtures, because they do not obey the ideal gas law.  Also if you need to report the flow in m^3 C3/hr at process conditions rather than 'normal' reference conditions (N m^3/hr), you must apply the ideal gas law using measured process temperature and pressure, to correct the flow rate.

[florentj]

Thanks for the explanation fseipel.