INFLUENCE OF THERMAL EFFECTS DURING FAST FILLING OPERATIONS ON ADSORPTION CAPACITY IN A HYDROGEN CRYO-ADSORPTION STORAGE TANK

Charging and discharging operations of on-board hydrogen adsorption storage systems involve exothermic and endothermic processes. Temperature elevations caused by the released heat of adsorption, compression work and thermal mass introduced from the inlet gas result with a reduction of the storage capacity The main objective of this work was the investigation of the impact of temperature elevations on the decrease of adsorption storage capacity during high-pressure charging of a hydrogen cryo-adsorption storage tank. The experimental operating conditions were compatible with practical applications for hydrogen adsorption on-board storage systems. The analysis was conducted with two adsorbent classes: activated carbon (NORIT R0.8) and metal-organic-frameworks (Cu-BTC-1,3,5). Adsorption isotherms for hydrogen uptake for both adsorbents are measured by a gravimetric method and fitted in accordance to the Langmuir equation. The experimental study was carried out in a cylindrical tank with granular adsorbents in which the bed temperature was measured at various positions. A typical average temperature increase in the core of the storage column during hydrogen charging experiments with the CuBTC and NORIT R0.8 was 16.2 K and 20.4 K at 2 MPa respectively. Such temperature elevation results in a loss in the adsorption storage capacity of 14.75 % for the system packed with the CuBTC adsorbent. Solutions for increased efficiency of the hydrogen cryo-adsorption storage tanks are proposed.