Research into the Kinetics of Hydrogen Desorption from the MNTZV-159 Metal Hydride Storage Tank in the Operating Conditions of a Low-Pressure Refuelling Station

A form of long-term hydrogen storage with high volume efficiency is hydrogen absorption into the host lattice of a metal or an alloy. Unlike high-pressure hydrogen storage, this form of storage is characterised by a low operating pressure. By employing metal hydride (MH) materials in a low-pressure refuelling station, it is possible to significantly increase the safety of hydrogen storage and, at the same time, to facilitate the refuelling of external devices that use MH storage tanks without the necessity of using a compressor. In this article, a methodology for the identification of the mathematical correlations among the hydrogen pressure in the storage tank, the hydrogen concentration in the alloy and the volumetric flow rate of hydrogen is described. This methodology may be used to identify the kinetics of the process and to create simplified simulations of the hydrogen release from an absorption-based storage tank by applying a finite difference method. The mathematical correlations are based on measurements of hydrogen desorption, during which hydrogen was released from the storage tank at stabilised pressure levels. The resulting mathematical description facilitates the identification of the approximate hydrogen pressure, depending on its flow rate, for a particular MH storage tank, while respecting the complexity of its internal structure, heat transfer and the hydrogen’s passage through a porous powder MH material. The identified mathematical dependence applies to the certified MNTZV-159 storage tank at pressures ranging from 7 to 29.82 bar, with hydrogen concentrations ranging from 0.223 to 1.342%, an input temperature of 59.5 ◦C and a cooling water flow rate of 4.36 L·min−1 . This methodology for the identification of a correlation between the flow rate, pressure and hydrogen concentration applies to this particular type of storage tank, and it depends not only on the alloy used and the quantity of this alloy but also on the internal structure of the heat exchanger.