[enggstudent11]

Hi all!

I am currently doing a design project for a pair of TLE's for an ethylene plant that steam cracks ethane.  The first TLE is immediatly after the reactor and must cool the gas stream from 875 C to 600 C.  High pressure steam will be generated from this which is recycled to be mixed with fresh feed.  The second TLE will generate low pressure steam that will be used in the reboilers of our fractionation train.

I am trying to do preliminary sizing and have run into trouble.  I was planning using the basic heat transfer equation of q = u*a*tlogmean to calculate the area, then use that to estimate the size of the TLE.

I found q from HYSIS, tlm but am having difficulty estimating a value for U.  I think the fact that water is being vaporized to cool a vapour stream which is giving me inaccurate values. I have looked in the GPSA handbook but any equation for U needs area.

Any help would be greatly appreciated!