Optimal operation of a multi-generation district energy hub based on electrical, heating, and cooling demands and hydrogen production

Abstract

In this study, a new configuration of a multi-generation energy system is proposed based on waste heat recovery from a regenerative gas turbine cycle (as the driver cycle) for running a district heating heat exchanger, a Rankine cycle, an ejector refrigeration cycle, and a proton exchange membrane electrolyzer cycle. In the first phase of the study, a thorough parametric model of the system is developed in EES software based on the eco-exergy and enviro-exergy analyses. The second phase is focused on the optimal operation of the system utilizing a robust multi-criteria optimization in Matlab software. Results of the parametric study showed that: (i) the share of fuel, capital, and environmental penalty costs rates in the system's total cost rate are respectively 46.95%, 29.38%, and 23.67%, at the optimal conditions. (ii) although the design variables of the bottoming cycles are not effective on the amount of pollutants, they have a significant effect on the enviro-exergy assessment criterion. The optimal system productions are included 21.42 MW of power, 26.81 MW of heat, 8.89 MW of cold, and 11.96 kg/h of hydrogen. The energy and exergy efficiencies are found to be 89.75% 35.21%, respectively. In such conditions, the payback period is approximately 5 years, demonstrating the economic feasibility of the proposal. Recovering the waste heat of conventional cycles to develop an energy production hub with minimal energy loss is one of the most important challenges in the energy matrix and relying on the results of the present study, it can be concluded that the proposed system has done this task well.