heat exchangers

The efficiency of isomerization reactors can be significantly increased by modifying the design of heat exchangers, and this leads to the reduction of production costs and environmental effects. In this research, the modification of the heat exchangers around the reactor of the isomerization unit of Persian Gulf Star Oil Compani (PGSOC) using pinch technology has been studied by Aspen HYSYS V9 and Aspen Energy Analyzer V9 software. Pinch analysis in this unit showed that the cross pinch of the heat exchangers around the reactor is 50% of the total cross pinch of the unit's heat exchangers, and in order to reduce it, a retrofit case was investigated. The results of this project show that by adding two new heat exchangers, in addition to removing 7 Ton/hr of medium pressure steam in the E-13 heat exchanger, also 9 Ton/hr of low-pressure steam is produced in the E-28-R2 heat exchanger, that causes to reduction of 10.7 MW in the consumption of utility services. This case saved energy 3 million dollars per years and with the purchase of two heat exchangers, the investment return of this case is less than 1 month.

Using of twisted tubes is one of the most promising technique to increase heat transfer between hot and cold fluids. In this study, the ratio of oval cross sections and number of twists in the Reynolds range of 1000 to 15000 were analyzed by computational fluid dynamics tools. The ratio of oval cross sections between 1 and 2.5 and the number of twists between 0 and 3 are considered for a case study. Basically, increasing the Reynolds number, increasing the cross section diameter ratio, and increasing the number of twists increase the Nusselt number and the friction factor simultaneously. In this case study, the ratio of oval cross sections 1.67 and the length of the twisted of 3 (0.6 m), reveal the best performance to achieve the optimal pressure drop and Nusselt number, respectively.