Steam system network synthesis with hot liquid reuse: I. The mathematical model for steam level selection

• A systematic technique to analyse the effect of multiple steam levels on a HEN.
• The cases of utilising only latent heat and hot liquid reuse are addressed.
• Novel simple models to determine the minimum steam flowrate required.
• An optimum set of steam levels exists providing the minimum steam flowrate.
• Hot liquid reuse yields lowest flowrate when only high pressure steam is used.

In this first of a series of two papers, the effect of varying steam levels on the total steam flowrate within steam systems is analysed mathematically for the traditional parallel configuration as well as for the case of hot liquid reuse. It is demonstrated that in the case of parallel heat exchangers utilising only latent heat, a minimum total steam flowrate is obtained by optimally selecting steam levels, but that in the case of hot liquid reuse, introducing multiple steam levels increases the minimum total steam flowrate attainable under those conditions. The flowrate attained utilising hot liquid reuse, however, remains lower than when only utilising latent heat. It is concluded that the lowest steam flowrate is attained using hot liquid reuse and only a single level of steam, but that the presence of additional steam levels resulting from turbines requires a more holistic approach to the synthesis of steam networks.