Integrated solar system for hydrogen production using steam reforming of methane

Abstract

Integrating renewable technologies has emerged as a promising option in pursuing sustainable and efficient energy solutions. The primary source of industrial hydrogen is steam methane reforming (SMR); however, this process is based on fossil fuels with massive carbon byproduct emissions. The solar thermal tower appears to be a suitable renewable source for powering SMR by providing high temperature heat to drive the process reactions. This approach aims to harness the abundance of solar energy for natural gas reforming to produce hydrogen at minimum environmental impact. This research establishes the viability of combining external central receiver concentrated solar power with SMR integrated with thermal energy storage (TES), revealing general insights into the system energy and exergy performance. The analysis of the current system is performed using the thermodynamic and thermochemical approaches to conduct a parametric study. A 543 MW central receiver is first modeled with a high-temperature molten salt as a working fluid. The SMR process model is then developed, considering both reforming and shift reactions, and solved using Engineering Equation Solver (EES). The subsystem models are validated before being integrated into the overall system model. The performance of the SMR reactor is found to affect the overall system performance considerably. The results also show that when increasing the temperature above 760 ° C, no remarkable improvement in the reforming process is observed. In contrast, the higher the temperature in the water gas shift reactor, the lower the system's performance. Moreover, the impact of wind velocity on the overall system is considered due to the large central receiver surface area. The overall system performance in terms of energy, exergy, and effectiveness is evaluated for one day of operating through charging and discharging operations. In charging mode, the overall energy and exergy efficiencies are 46.5% and 57.2%, respectively, while the overall effectiveness is 61.8%; on the discharging operation, the overall energy efficiency and effectiveness have a similar definition with a value of 82.4% and the overall exergy efficiency achieves a value of 78.7%. Additionally, the amount of hydrogen produced at a central receiver of 543 MWth capacity is about 7.3 kg/s at a 2.1 steam-to-carbon ratio. This integration mitigates a minimum of 12 kg/s of CO2 emissions that would be generated due to methane combustion.