Systems Modeling of Ammonia Borane Bead Reactor for Off-Board Regenerable Hydrogen Storage in PEM Fuel Cell Applications

Research on ammonia borane (AB, NH₃BH₃) has shown it to be a promising material for chemical hydrogen storage in PEM fuel cell applications. AB was selected by DOE’s Hydrogen Storage Engineering Center of Excellence (HSECoE) as the initial chemical hydride of study because of its high hydrogen storage capacity (up to 19.6% by weight for the release of three molar equivalents of hydrogen gas) and its stability under typical ambient conditions. A model of a bead reactor system was developed to study AB system performance in an automotive application and estimate the energy, mass, and volume requirements for this off-board regenerable hydrogen storage material. The system includes feed and product tanks, hot and cold augers, a ballast tank/reactor, a H₂ burner and a radiator. One-dimensional models based on conservation of species and energy were used to predict important state variables such as reactant and product concentrations, temperatures of various components, flow rates, and pressure in the reactor system. The flow rate of AB into the process and the system pressure were governed by a control system which is modeled as an independent subsystem. Each subsystem in the model was coded as a C language S-function and implemented in the Matlab/Simulink environment. Preliminary system simulation results for a start-up case and for a transient drive cycle indicate appropriate trends in the reactor system dynamics.