Generic superstructure synthesis of organic Rankine cycles for waste heat recovery in industrial processes

Waste heat accounts for up to 70% of input energy in industrial processes which enunciates the importance of energy recovery measures to improve efficiency and reduce excessive energy consumption. A portion of the energy can be recovered within the process, while the rest is rejected to the environment as unavoidable [1] waste; therefore, providing a large opportunity for organic Rankine cycle (ORC)s which are capable of producing electricity from heat at medium-low temperatures. These cycles are often regarded as one of the best waste heat recovery measures but industrial applications are still limited due to the lack of comprehensive methodologies for their integration with processes. As such, this work proposes a novel and comprehensive superstructure optimization methodology for ORC integration including architectural features such as turbine-bleeding, reheating, and transcritical cycles. Additional developments include a novel dynamic linearization technique for supercritical and near-critical streams and calculation of heat transfer coefficients. The optimization problem is solved using a bi-level approach including fluid selection, operating condition determination and equipment sizing and is applied to a literature case study. The results exhibit that interactions between these elements are complex and therefore underline the necessity of such methods to explore the optimal integration of ORCs with industrial processes.