(635c) CFD Modeling Development of Onboard Absorptive Hydrogen Storage on Coal-Derived Activated Carbon for Light-Duty Vehicles

Interest in hydrogen as an alternate fuel source has led the automotive industry to search for new power sources for automobiles. The onboard storage of hydrogen represents the current bottleneck in the widespread deployment of hydrogen vehicles and remains a major technological challenge. The U.S. Department of Energy (DOE) has set a technical target of 12 bar and 85 degrees Celsius as the maximum pressure and temperature for onboard storage, alongside goals and time-gated benchmarks for gravimetric and volumetric capacity. Both compressive and cryogenic storage of hydrogen require immense pressures and come with high associated costs and safety concerns. On the other hand, adsorptive storage on activated carbon beds shows promise in addressing the need for safe, reversible hydrogen storage that meets the technical targets set by the DOE.

In this work, computational fluid dynamics (CFD) models of the physisorption of hydrogen on a fixed bed of activated carbon are developed comparing the Eulerian two-fluid model (TFM) approach and the porous media (PM) approach in the commercial CFD solver Ansys Fluent. The different approaches are validated against the bench-scale experiment and PM simulations of Ye et al. [1] and Xiao et al. [2] and contrasted in terms of accuracy and cost and applicability to larger-scale systems. The issue of a creeping error in the calculation of adsorbate mass inside the tank is highlighted and investigated in detail and the causal factors are enumerated. It is shown that despite the reduced numerical complexity of the PM framework, it requires a much smaller time step to accurately account for the mass accumulation and thus incurs a higher simulation cost, and TFM is selected as the optimum simulation methodology.

The validated TFM case is extended to predict the adsorptive storage performance of an activated carbon derived from Blue Gem coal, an exceptionally high-grade coal found in Tennessee and Kentucky with minimal sulfur and ash content. The novel sorbent material, designated BGC-KNa_C850, is developed and characterized by the National Energy Technology Laboratory’s Materials and Manufacturing Division. The bench-scale results with the novel sorbent provide a foundation for scale-up and optimization studies for tank design and operating conditions to establish the feasibility of onboard adsorptive hydrogen storage at vehicle scales.

[1] Ye, F. et al. (2012) Implementation for model of adsorptive hydrogen storage using UDF in Fluent. Physics Procedia, 24, pp. 793–800.

[2] Xiao, J. et al. (2010) Simulation of heat and mass transfer in activated carbon tank for hydrogen storage. Int. J. Hydrogen Energy, 35, pp. 8106–8116.