A Method for Simultaneous Retrofit of Heat Exchanger Networks and Towers Operations for an Existing Natural Gas Purification Process

Abstract As an essential part of Heat Integration (HI), Heat Exchanger Networks (HENs) are widely used in large-scale industrial sites in the chemical industry. The interface temperatures (supply and target temperatures) of the HEN can change due to the adjustment of operating variables in the process. This paper proposes a new two-stage method for the simultaneous optimisation of the operating variables of the processing plants and the HEN of a natural gas purification process. In the first stage, a Particle Swarm Optimisation (PSO) algorithm is developed to minimise the total energy consumption. The variables representing the tower top pressure, tower bottom pressure, and reflux ratio are optimised, thereby changing the characteristics of the cold and hot streams in a HEN. In the second stage, a Shifted Retrofit Thermodynamic Grid Diagram (SRTGD)-based model and the corresponding solution approach are developed to retrofit the HEN. The objective function of the second stage is to minimise the total annual cost. The case study shows that the total energy consumption of the process is reduced by 41.5 % compared to the existing on-site process.