(15f) Energy Saving by Simply Feed Preheating at Petrochemical Plant

In general, the feed fluid of distillation column is preheated by utilizing feed/bottom heat exchanger or heat recovery system and the feed condition is close to bubble point. The reboiler load could be reduced by installation of a new preheater which uses cheap low-pressure steam. In order to maintain separation of the column, reflux flow rate should be a little larger than before installing the preheater. Therefore, reboiler duty reduction (ΔHR) becomes smaller than feed enthalpy increase(ΔHF ) and this ratio, ΔHR/ΔHF depends on application systems.

Two practical energy saving jobs relating to feed conditions were performed at Chiba facility of Idemitsu Kosan Co. in Japan. First one is a benzene column of aromatics plant. A new feed preheter was installed and made the feed approximately 90 percent vaporization to reduce the reboiler whose hot medium was hot-oil.

Second job was carried out in styrene monomer plant. When ethyl-benzene production process was converted from aluminum chloride process to liquid phase zeolite process, reboiler duty of the two distillation columns could be reduced by eliminating water washing section.

We investigated necessity of modifications including column internals and auxiliary using process simulator during the basic planning phase of these jobs and finally decided to modify feed pipes and feed nozzles for these three columns. These distillation columns are running well as we expected.