The problem of designing crude fractionation units is not only a distillation design. It has the added complexity that these units should be able to process different types of crude, sometimes from heavy to light. Important heat exchange also takes place, and the energy efficiency is related to the column design parameters. Part I of this two-part series presents a rigorous targeting methodology to design this multipurpose plant, which can be implemented using a commercial simulator. Part II deals with the heat exchanger network design.