Combined Flexibility and Energy Analysis of Retrofit Actions for Heat Exchanger Networks

Journal article, 2019

Retrofitting of industrial process heat recovery systems can contribute significantly to meeting energy efficiency targets for industrial process plants. One issue to consider when screening retrofit design options is that industrial heat recovery systems must be able to handle external variations, e.g. in ambient temperature, in such a way that operational targets are reached. There exist different approaches to incorporate flexibility considerations in the design process of retrofit proposals for heat exchanger networks (HEN). However, due to mathematical complexity, lack of suitable cost data, and difficulty to handle large-scale systems, the adoption of those methods in industrial retrofit projects has been limited. Therefore, this paper proposes to decouple the design and analysis steps in retrofitting processes. This allows well-proven retrofit design methods to be used in the design step to generate different alternatives. These design alternatives are thereafter evaluated in a separate analysis step in which the initial set of designs is narrowed down to one or several design options that are operable and energy efficient for a priori defined variations of operating conditions. The proposed approach is based upon traditional flexibility analysis combined with energy performance analysis. With such performance data available, a fair evaluation over different operating points can be obtained. The proposed approach is used for analysing the flexibility and energy performance of a HEN case study to illustrate its application.