Optimal design and integration of solar thermal collection, storage, and dispatch with process cogeneration systems

• A hierarchical approach addresses design of cogeneration systems.
• Separates steady-state optimization from diurnal variability.
• A multiperiod approach optimizes energy mix.
• Integrates expected operation into design.
• A case study involves actual solar data in Saudi Arabia.

This paper introduces an optimization approach to the design of process combined heat and power systems that integrate the thermal profile of the process, an external fossil fuel, and solar energy. A hierarchical design approach is proposed to stage the implementation of steady-state and dynamic calculations. Initially, energy integration is used to identify minimum heating and cooling utility targets. Next, a genetic algorithm approach is employed to optimize the external heating load and generated power of the cogeneration system that includes a steam Rankine cycle. An outer loop is used to optimize the flowrate, temperature, and pressure of the steam entering and exiting the turbine. A multiperiod optimization approach is developed to account for the diurnal variability of solar energy. Direct usage of collected solar energy is considered along with the option of thermal storage and dispatch. The solution of this mixed integer nonlinear program determines the optimal mix of energy throughout the year. A case study for a petrochemical plant in Jeddah, Saudi Arabia was solved to illustrate the applicability of the devised approach.