Dear experts,
I’m going to retrofit an existing design of crude pre-heat train. I’ve modeled it and compose CDU+VDU unit heat balance, but there are points that confuse me. I found that to agree inlet temperature to first column of CDU I should keep temperature outcoming product streams (before air coolers) much more than it happens to be at existing plant. For example, calculated temperature of vacuum residue is 180 C degrees, but in reality, it’s about 148 C. The same thing happens with VGO stream. Measurements were performed in winter; ambient temperature was minus 12 C degrees. Calculated heat loss is about 6 MW. May it happen to be?
Thank you.