Heat integration, simultaneous structure and parameter optimisation, and techno-economic evaluation of waste heat recovery systems for petrochemical industry

Energy conservation in the petrochemical sector holds the key to its financial viability. The pervasive application of Heat Exchanger Networks (HEN) exemplifies the industry's efforts in heat recovery. Yet, despite its widespread adoption, an alarming quantum of low-grade heat remains squandered, underscoring the potential for augmenting energy savings through more effective utilization of this heat. Recognizing the pivotal role of the synergistic interaction between the process and the heat recovery system in maximizing energy retrieval, an innovative approach is proposed. This methodology initially entailed the development of a process model and an enhanced heat recovery system, the latter embodying the integration of an organic Rankine cycle (ORC) with HEN. Subsequently, a strategic diagnostic was proposed to incorporate these sub-systems into a cohesive, optimisation framework. Following this, an array of energy, exergy, and economic analyses were conducted to appraise the system's performance. The findings suggest a considerable improvement in heat recovery and an amplification in ORC efficiency from a mere 7.64%–11.38%. The enhanced heat recovery further translated into a reduced need for cold utility, thereby minimizing cooler deployment. Given the substantial exergy destruction associated with coolers, their lesser usage bolstered the system's exergy efficiency. Moreover, the optimised ORC manifested in heightened net power generation, consequently elevating electricity revenues. Despite a nominal surge in equipment costs, the aggregate profit witnessed a substantial hike from 165.19 M$/year to 178.79 M$/year. The proposed system substanitally improved thermodynamic and economic performance. This study offers valuable guidance for the design and operation of petrochemical industries, serving as a roadmap to energy conservation and enhanced profitability.