Hydrogen as a direct heat exchange fluid in room temperature hydride systems: Numerical study on the desorption process

Hydrogen, as an energy carrier, is a promising candidate to foster decarbonization. However, its storage poses significant challenges. Common methods, such as compressed gas and liquid hydrogen, have high energy consumption and safety concerns. Recently, solid hydrogen storage in materials like metal hydrides has gained attention for their ability to store hydrogen safely at low pressures and low temperatures. This study aims to develop a numerical model to simulate the performance of metal hydrides using hydrogen as a direct fluid heat exchanger during desorption. The model, formulated as a system of partial differential equations, is implemented in MATLAB with the ODE15s solver and applied to a disk-type lanthanum nickel reactor to minimize pressure drops. Performance is investigated by varying design parameters, including reactor length and diameter, bed porosity, hydride particle diameter, operating pressure and temperature, and hydrogen mass flow rate at the reactor inlet. Additionally, the energy consumption of auxiliary equipment, such as pumping and thermal power, is evaluated. Results show that the system energy requirement is about 8-9% of the hydrogen lower heating value, with most desorption occurring in less than 300 seconds. The reactor dimensions are crucial for fast desorption and low pressure drops, with pumping power under 1 W given the small thickness and flow rate. Particle diameter and porosity have minor impacts, while pressure, temperature, and flow rate are fundamental. High temperatures, low pressures, and high recirculating flow rates favor the reaction, though a trade-off between performance and energy consumption is necessary since all high temperatures high recirculated mass flow rate allows for high consumption.