Abstract
A total energy system of a chemical plant includes reactors, separators, a heat exchanger network (HEN), and a utility system. For the retrofit to save energy, reactors normally are unchanged. Based on the “onion model”, the total energy system is divided into three subsystems, separation, heat exchange, and utility subsystems. The strategy for total energy system retrofit is proposed in this paper, which considers Heat Integration within each subsystem and coordination between each two subsystems. The first step is to find out the Pinch temperature of the HEN. According to the relative position of the endothermic and exothermic temperatures with the Pinch temperature, different retrofit strategies for separators will be used. For separators above or below the Pinch, Heat Integration between separators and between separators and the HEN should considered. The utility subsystem will be adjusted to fit the other subsystems, and heat engines and heat pumps are involved under economic consideration. To make coordination between each two subsystems, cycling calculation is needed. A caprolactam plant is used as the case study to show the proposed strategy.
