ENVIRONMENTAL AND ENERGY ENGINEERING Thermal Effects in Dynamic Storage of Hydrogen by Adsorption Malek Lamari, Asdin Aoufi, and Pierre Malbrunot LIMHP  CNRS, Av. J.B. Clement, Villetaneuse, France 93430 ´ Thermal effects in dynamic hydrogen storage by adsorption at room temperature and high pressure are studied theoretically and experimentally. The system of adsorbate  adsorbent used was hydrogen in granular acti®ated carbon. The theoretical analysis was based on heat- and mass-transfer modeling in a packed-bed adsorber, with particular emphasis on the thermal effects occurring during charge and discharge steps. The influ- ( ) ence of gas flow rate and storage pressure up to 15 MPa on the total amount stored or deli®ered was in®estigated. Operating conditions were compatible with practical applica- tion for onboard ®ehicle storage. The experimental study was carried out in cylindrical 2-L reser ®oirs filled with granular acti®ated carbon in which the bed temperature was measured at ®arious positions. The temperature changes during both charge and dis- charge agreed well with the model predictions. Introduction Hydrogen utilization is receiving increased attention in view of the importance of the world’s demand for energy caused by the simultaneous growth of the world population and of air-pollutant emissions produced by carbonaceous fu- els. As alternative energy, it is the cleanest fuel, and is espe- Ž . cially attractive for electric-vehicle use Nicholetti, 1995 . Im- Ž portant properties of hydrogen such as heat power 2.75 times . higher than gasoline for the same weight make it an ideal Ž . candidate for transport applications Das, 1996 . A more dif- ficult issue facing the transition to its effective utilization is onboard storage; this may influence the vehicle’s cost, per- Ž formance, and fuel economy Berry and Aceves, 1998; Noh et . al., 1987; Hynek et al., 1997 . There are currently four main technologies for onboard ve- hicle hydrogen storage: compressed gas, liquefaction, metal hydrides, and adsorption. Particular attention was focused on carbon sorption systems, since they can store hydrogen of Ž moderate size, weight, and pressure Chahine and Benard, ´ . 1998; Lamari et al., 1997; Chahine and Bose, 1992 . Indeed, when the gas is introduced into a container, a large part of it is stored by adsorption and the rest by compression. This Correspondence concerning this article should be addressed to M. Lamari. contributes to reducing the operating pressure compared to compressed gas technology. Consequently, less weight is re- quired and better security is ensured. This application has been enhanced by the discovery of new graphitic structure materials: nanotubes and nanofibers are considered promis- Ž ing storage adsorbents Chambers et al., 1998; Dillon et al., . 1997; Rodriguez et al., 1997 . However, practical difficulties, such as temperature changes in dynamic charge or discharge that requires thermal control, exist in the storage process. Ž . Considering packed-bed pressurization charge and de- Ž . pressurization discharge , there are two main heat effects: heat released by adsorption and by compression, and reverse temperature drop due to decompression and desorption. This mayhave a detrimental effect on performance of the storage Ž system during both cycles Barbosa et al., 1997a; Chang and . Talu, 1996 . A lower amount of gas is stored at the target pressure during the first operation and a residual amount of stored gas is retained in the container at the depletion pres- sure during the second operation. Ž Several theoretical and experimental studies Kikkinides and Yang, 1993; Lu et al., 1993; Zhong et al., 1992; Sun- . daram and Wanket, 1988; Farooq et al., 1988 describing the thermal effects associated with adsorption have been carried out, particularly in the field of pressure swing adsorption pro- Ž . cesses PSA , which are currently used in gas separation and March 2000 Vol. 46, No. 3 AIChE Journal 632