A heuristic method to introduce hot feed into chemical process for energy saving with minor structure modification

Abstract

Hot feed is a relatively inexpensive strategy to improve the energy utilization in chemical plants. Since hot feed is often an afterthought, retrofitting the heat exchanger network (HEN) with hot feed becomes a key step to decide the energy saving. This paper proposes a heuristic method to introduce hot feed into the existing HEN with minor structure modifications. The concept of heat flow path is extended to fit the hot feed problem. The possible changes of heat exchangers in a path are analyzed in details referring to the heat flow direction. Based on this, the bottleneck and the maximum shift capability of each path can be determined quantitatively. Rules for the creation and selection of new paths are presented to achieve more hot utility saving. A wax oil hydrogenation unit is analyzed to illustrate the proposed method, where heat carried by hot feed can be fully used to save the hot utility. The proposed method obtains more hot utility reduction (3349.0 kW versus 783.8 kW) by the hot feed strategy and a simpler retrofitting scheme than a previous method based on the grand composite curve. Besides, this method can show clear insights in the HEN retrofit with hot feed and it is easy for industrial application.