Q & A > Question Details
We want to increase the capacity of the stripper in our hydrocarbon unit. There is an aerocondeser for the stream leaving the top of the column. We want to increase condensing capacity by means of a trim cooler that would be placed next to the condensers.
It will receive a total of 7,3 tones/h, 1,3 t/h vapour and 6 ton/h liquid.
I have simulated with ASPEN EDR the new trim-cooler that will operate with cooling water (tubeside).
To avoid revaporization downstream of the trim-cooler the liquid needs to be cooled down as well as the condensing vapour.
The software indicates that the required area for cooling the liquid is 45% of the total number of tubes.
I am specifying 30% cut baffles but doing a quick number tells me that liquid will just pass and there won't be any flooding.
Has anyone ever designed a trim-cooler? How do you accomplish the flooding of the heat exchanger?
There are several options, I find that the most suitables ones are:
1)A dam baffle that will flood the shell until the desired level.
2) A level control loop (level transmitter control valve)
We have other trim-cooler installed in other units, hydrocracker for example, but I have reviewed the trim-coolers drawings but there is not dam baffle or any level controlling loop.


 
Answers
03/01/2018 A: Eric Vetters, ProCorr Consulting Services, ewvetters@yahoo.com
In my experience I would say such a dam/baffle arrangement is unnecessary. Liquid condensing on upper tubes drips down to lower tubes, which causes a natural subcooling of the liquid. In a crude oil vs. overhead exchanger I have seen the overhead liquid leaving the exchanger at least 30-40 F cooler than the vapor as measured by infrared skin temperature measurements.
03/01/2018 A: Celso Pajaro, Sulzer Chemtech, celso.pajaro@sulzer.com
If you want the trim cooler to operate partially flooded you either place them below the reflux drum or add a control valve downstream of the them
03/01/2018 A: Ralph Ragsdale, Ragsdale Refining Courses, ralph.ragsdale@att.net
The vendor should design the shell and tube condenser based on your heat and material balance data. Elevation and instrumentation are an integral part of what you are doing. Forget the flooding issue. It will take care of itself. The instrumentation selected depends on whether there will be non-condensables from the receiver. Only an experienced process engineer can design something that will perform properly.