A graphical method for simultaneous targeting and design of multiple utility systems

Abstract

Multiple utility targeting has been one of the most important steps in process integration and has direct effect on total cost. Indeed, the majority amount of investments in any plant especially chemical plant is allocated for supplying hot and cold utilities. Regarding to this fact having realistic design to show the exact amount of the minimum hot and cold utility has been serious concerns among designers and plant owners. Composite Curves (CCs), Grand Composite Curves (GCC), Balanced Composite Curves (BCC) and Balanced Grand Composite Curves (BGCC) have been the common graphical tools to achieve this aim. The current graphical methods may have acceptable results in terms of energy targeting. However, these tools cannot offer sufficient guidance for individual stream matching which is vital to have realistic surface area targeting as well as multiple utility targeting. This research presents a new graphical method for simultaneous targeting and design of multiple utility systems based on stream temperature versus enthalpy plot (STEP) method. Systems including variabletemperature utilities (Flow Gas, Cooling Water) are considered and some limitations of current graphical method (CCs, GCC, BCC, BGCC) have been highlighted. In addition, some examples are provided to demonstrate different limitations of mentioned graphical tools in terms of utility targeting and minimum surface area targeting. The presented method is more realistic as compared to the current graphical methods and can helps designers to have better understanding of multiple utility systems including variable temperature utilities as well as constant-temperature utilities.