Hamed Alavi Nejad - Islamic Azad University, Shiraz Branch, Member of Young Research Club, Shiraz, Iran
Farhad Shahraki - Department of Chemical Engineering, University of Sistan and Baluchestan, Zahedan, Iran
Mahmud Reza Hojjati - Department of Chemical Engineering, Islamic Azad University, Shiraz Branch, Shiraz, Iran

Due to the increase of economic competition,many refineries have tried to reduce production cost by decreasing energy consumption in the process. One way to improve energy efficiency of the refinery is recovering heat from hot product streams to preheat cold streams of crude by complex heat exchanger networks (HENs). Important feature of heat exchanger network design is the energy-capital tradeoff. This paper presents HEN design for the FCC unit by economical calculation for selecting optimum temperature difference and minimum energy consumption. At first to determine the all of hot and cold streams in the FCC unit, steady state simulation was carried out by the Aspen- HYSYS Refinery software. In many of HENs design a value for Tmin , base on designer experience, was assumed. In this study tradeoff between energy and capital cost has been considered for choosing optimum Tmin. According to result the optimum value of Tmin for this case study was 12ºC. The grid diagram for HEN in the FCC unit has been presented. The HEN that was designed in this study needs minimum energy by using 10 process-process heat exchangers that exchange energy about 76.5MW. With consideration tick-off rules, this network has also a minimum number of units.

Keywords: Heat Exchanger Network, Fluid Catalytic Cracking, Energy target, Optimum temperature difference