Operating oil refinery units under uncertainty: Thermodynamic and economic implications

The effects of the variations of process stream properties on the energy targeting of a heat exchanger network were investigated. The thermodynamic properties of a process stream mixture, including the specific heat capacity, viscosity, thermal conductivity, heat transfer coefficient, and the Nusselt, Reynolds, and Prandtl numbers, were examined for two scenarios with different temperature segmentation. In the first scenario, the process stream properties were assumed to be constant within temperature intervals defined by the supply and target temperatures (base case). In the second scenario, the process stream properties were considered to be constant within temperature intervals defined by the bubble and dew points (phase change case). Our study revealed the sensitivity of the process stream properties to temperature variations, demonstrating an increase in the density and thermal conductivity and a decrease in the enthalpy of the mixture with decreasing temperature. The energy targeting results showed lower pinch point temperatures and higher utility demands in the phase change case relative to the base case. This study demonstrates that the incorporation of phase change is vital to the design of a heat exchanger network.