Simultaneous Optimization of the Complex Fractionator and Heat Exchanger Network Considering the Constraints of Variable Heat Removals in Delayed Coking Units

Abstract

Heat exchanger networks in process plants recover usable heat from hot to cold process streams such as feedstock, product, and pumparound streams. In this paper, we focus on the design of a heat exchanger network for removing variable heat from a complex fractionator in delayed coking units. A superstructure-based mixed integer nonlinear programming model is presented to minimize the total annual cost, including the heat exchanger area cost and the utility cost. In the proposed model, duties and operating parameters of pumparounds are optimized and the optimized structure of the heat exchanger network is defined simultaneously. Meanwhile, two modifications are applied to improve the simultaneous optimization model for the integrated system of the complex fractionator and heat exchanger network. First, a predominant calculation method for the log mean temperature difference is introduced in order to obtain the results closest to the actual process; second, nonconstant specific heat of process streams with ...