Identification of the Optimal Pressure Levels in total Site Utility Systems Using Variable Physical Properties

Utility system design greatly influences the total site design and operation. Therefore, several design approaches have so far been presented for such systems. However, none has included the variation of physical and thermodynamic properties of steam due to pressure and temperature changes. This research, tries to present a mathematical model for determining optimum pressure level of steam considering variable physical and thermodynamic properties. In this mathematical model the corresponding equations of physical and thermodynamic properties have been added into mass and energy balance equations. Several case studies have been solved with this new model and compared with the results of published literatures. The comparison shows that although considering the variation of physical and thermodynamic properties of steam does not change the final structure of the design but, it can significantly affect the details, specially the optimum distribution of exchangers heat load (in one case study it reached 17%). Thus, it can be suggested that: "First assume constant physical and thermodynamic properties for steam and design the final structure of the steam network. Then considering variation of physical and thermodynamic properties of steam, find the optimum steam pressure levels and heat load of exchangers".

Keywords:

Utility Systems , Total Site , Optimum Pressure Level , Physical and Thermodynamic Properties , Optimization Techniques