Multiple utilities targeting in energy integration considering rigorous temperature-enthalpy relations

Energy integration is a strong concern in process synthesis. Most methods are applied with simplifying assumptions for better computational efficiency. Enthalpies are obtained considering constant heat capacities, which is coherent for some processes. However, for streams in near-critical or phase-changing conditions, enthalpy may vary in a strongly nonlinear form. This paper proposes an optimization approach using concepts from Pinch Analysis for utility and heat exchange area targeting considering process and utility stream heat capacity variations with temperature. Decision variables are heat recovery approach temperature (HRAT), final utility temperatures, and energy duties for each available utility. Three case studies were evaluated. Large differences in utility allocations were observed (e.g., in Example 1, for the rigorous cp case, no medium- or lowpressure steam is applied, while high-pressure steam heat duty is 2.32 times the value from the constant cp case). Processing times were reasonable for early design stages (around one minute).

Automated summary

Energy integration is a critical issue in process synthesis, and current methods often rely on simplifying assumptions for better computational efficiency. However, in near-critical or phase-changing conditions, the enthalpy of streams may vary significantly in a nonlinear way. This paper proposes an optimization approach using Pinch Analysis concepts to consider variations in heat capacity with temperature, leading to more accurate targeting of utility and heat exchange areas. Case studies demonstrate significant differences in utility allocations.