CAPE-OPEN

I have supply water at 90F to use source of cooling and l want it to heated to 120 to avoid fouling. I want to use a temperature approach of 10F. So do l use 90+ 10= 100F or 120 + 10 = 130 to get the condenser pressure. Thanks

Gooday,
I meant the pressure of the condenser, so as to determine the pressure of the column based on Tdew of the distillate

If you are using 120 F water to cool with a 10 F approach temperature, you should probably have your condensor at 130 F.