Development of an integrated hydropower system with hydrogen and methanol production

In the present study, a methanol synthesis plant integrated with a hydropower station with river hydro storage option is developed and analyzed thermodynamically to study the ability of increased benefit and sustainability via the generation of multiple useful commodities. The present system is, in this regard, designed to produce methanol steadily throughout the day at baseload and generate power at an increased rate during the on-peak period. This system also cogenerates heat and fresh water through reverse osmosis and oxygen via water electrolysis. The methanol synthesis unit is simulated in the AspenPlus in a recirculation loop based on a plug flow pressurized reactor. The reaction extent for synthesis reaches a maximum at an optimum temperature for any specified pressure. The water electrolysis is conducted at 80 degrees C and 2 kA/m(2) since the parametric study confirms that at higher current density, the duty of the water preheating heat exchanger becomes high, which increases unnecessarily the capital investment. One key focus of the paper is to devise the operating strategy of hydro-storage, which is done for an illustrative case study in which the hourly Ontario electricity price (HOEP) for the year 2020. The system is controlled in such a way that the power generation during the on-peak periods is maximized for increased revenue. A river with a 425 m(3)/s annual average flow rate is assumed for the case study. The gross head for hydro-storage must reach a maximum at about 30 m at 7 a.m., and 6 p.m. and the storage pool is discharged to 23 m after morning peak and to 20 m after evening peak. The overall energy efficiency of the system is found to be 61.6%. The overall exergy efficiency of the system is obtained to be 58.2% with a generation mix of grid-delivered power, methanol, heating, oxygen and fresh water. (C) 2021 Elsevier Ltd. All rights reserved.