Abstract
The integrated recovery of heat and mechanical work has gained increasing importance in process integration due to the strong thermodynamic coupling between temperature and pressure changes in many industrial systems. This work presents a rigorous framework for the simultaneous synthesis of Work and Heat Exchanger Networks (WHEN), in which heating, cooling, compression, expansion, throttling, and pumping are optimized in a coordinated manner. The problem is formulated using Generalized Disjunctive Programming (GDP), allowing the explicit representation of alternative thermodynamic paths, phase-dependent behavior, and logical equipment choices. Process streams are defined by supply and target states, while only bounds are imposed on intermediate pressures, temperatures, and flow rates. Streams may change classification between hot and cold multiple times and may undergo several phase transitions.Rigorous thermodynamic correlations obtained from Aspen HYSYS are embedded in the optimization model, enabling a physically consistent treatment of condensation, vaporization, and isenthalpic valve expansion without restrictive assumptions. The heat exchanger network is represented implicitly through the Pinch Location Method, avoiding the combinatorial complexity of explicit exchanger matching while accommodating multiple utilities and unclassified streams.The approach is demonstrated through a self-refrigerated alkylation process case study. The optimal solution reveals a non-intuitive thermodynamic path involving alternating vapor and liquid compression stages and multiple phase changes, which enhances internal heat recovery. Compared to a conventional design strategy, the proposed framework reduces total annual energy integration costs by 12.5%. The resulting non-convex MINLP is solved to global optimality within seconds, demonstrating both robustness and computational tractability.