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Heat Pinch Analysis retrofit projects are typically performed by evaluating and maximising the heat recovery potentials within the individual process units. Once the potential improvements from the individual units have been assessed, the Total Site (TS) Heat Integration analysis is performed. Such approach may steer designers away from the promising retrofit opportunities and to lead towards suboptimal heat exchanger networks (HEN). This paper presents an effective retrofit framework for a TS system to determine the most cost-effective retrofit options and maximise the potential savings. Instead of performing the typical unit-wise process retrofit, the strategy is to determine the baseline total site consumption and benchmark targets, and to identify retrofit options from the TS context. This TS retrofit framework has been tested on a case study involving a petrochemical plant comprising of multiple process sections. The results of the analysis show that significant energy savings can be realised when both direct and indirect heat recovery retrofit options are evaluated. Further energy savings can be achieved via the Plus–Minus Principle that helps pinpoint the correct locations of heat surpluses and deficits and lead to the appropriate TS retrofit solution. As a conclusion, energy retrofit projects should be approached from the TS context, followed by the unit-wise retrofit (i.e., retrofit of the individual process sections). [ABSTRACT FROM AUTHOR]

• Model for heat exchanger network (HEN) retrofit with enhancement technologies is formulated. • HEN retrofit model with long-term investment and maintenance planning model is developed. • Service life, depreciation and reliabilities of heat exchangers are considered in the planning model. • Results obtained yield 14% or higher net present value compared to previous retrofit solutions. • A graphical tool is created to track the reliability and maintenance status of heat exchangers. Process Optimisation has been the core topic in chemical process industries for decades. However, the performance of the asset strongly influences the production efficiency as well. In the case of Heat Exchanger Network (HEN), the retrofit decisions are often aimed to maximise energy savings and minimise the associated cost. However, the age and performance of heat exchangers have a great influence on the HEN efficiency as well. This study brings innovative retrofit algorithms, integrating exchangers' lifetime and reliability functions to visualise the benefits of the hybrid process and asset optimisation. The HEN retrofit structures are optimised, considering various heat intensification methods. The model is formulated based on the novel concept of Shifted Retrofit Thermodynamic Grid Diagram (SRTGD). A Mixed Integer Linear Programming (MILP) model is formulated for the investment and maintenance planning. The operating life of the network is discretised into multiple periods, and a decision is made within each period: whether to upgrade the heat exchangers, purchase new heat exchangers – for replacement or adding to the network, maintain the heat exchangers or perform nothing. Two realistic case studies are used to elucidate the application of the method. Under a 20 y planning horizon, the Net Present Value (NPV) obtained are higher than the previous works, i.e. 17% higher for case study 1 with 51% utility savings, and 14% higher for case study 2 with 74% utility savings. The proposed HEN retrofit decisions are proven to be cost-effective. A graphical tool has been developed to track the reliability and maintenance status of the exchangers to provide a significant guide to the economically optimum decisions. [ABSTRACT FROM AUTHOR]