Dynamic transportation model for cost targeting and integrated design of process and heat exchanger network

Simultaneous optimization of process flowsheet and heat exchanger network (HEN) is critical for achieving cost-effective and sustainable process design. The superstructure-based method is commonly adopted to perform the holistic design. However, due to the complexity and nonconvexity of the optimization problem, this approach suffers from computational challenges and lacks guarantees on solution quality, limiting its applicability to small-scale problems. To address this issue, this work introduces a novel decomposition-based two-step solution approach. In the first step, a dynamic transportation model is developed for accurate system cost targeting, providing a capability not offered by energy-focused pinch targeting models. The model maintains linear constraints and computational tractability, even when both process stream temperatures and flow rates are decision variables during optimization. In the second step, the strong predictive capabilities of the transportation model in heat matches and stream conditions are leveraged to generate a significantly reduced superstructure, facilitating the attainment of near-optimal solutions. The proposed method effectively addresses scenarios involving unclassified streams, multiple utilities, and isothermal streams, with its robustness demonstrated across four literature examples. Notably, in the final example, the method achieved an 84.9 % reduction in the total annualized cost of the HEN compared to the traditional sequential design, contributing to enhanced process profitability and showcasing its potential for optimizing complex chemical or energy systems.