Systems modeling, simulation and material operating requirements for chemical hydride based hydrogen storage

Research on ammonia borane (AB, NH3BH3) has shown it to be a promising material for chemical hydride based hydrogen storage. 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 ∼16% by weight for the release of ∼2.5 M equivalents of hydrogen gas) and its stability under typical ambient conditions. Another promising candidate is alane, AlH3 (10.1% by weight). Materials operating requirements to use chemical hydrides for vehicle onboard storage are discussed. A flow-through system concept based on augers, ballast tank, hydrogen heat exchanger and H2 burner was designed and implemented in simulation. In this design, the chemical hydride material was assumed to produce H2 in the auger itself, thus minimizing the size of ballast tank and reactor. One dimensional models based on conservation of mass, species and energy were used to predict important state variables such as reactant and product concentrations, temperatures of various components, flow rates, along with pressure, in various components of the storage system. Various subsystem components in the models were coded as ‘C’ language S-functions and implemented in Matlab/Simulink. Steady state simulation results for all the three candidate materials (solid AB, liquid AB and alane) were presented to show the proof of concept, whereas the drive cycle simulations were discussed only for solid AB using the fuel cell H2 demand for four different US drive cycles. Conditional logic based controllers that control the material flow rate into the reactor and to control the H2 fed to the burner were developed and implemented in drive cycle simulations. Simulation results show that the proposed system meets most of the 2010 DOE targets, and is well above the required > 40% of the DOE targets for fill time, well-to-powerplant efficiency, and volumetric and gravimetric density.

► Representative reactor models for three chemical hydride materials.
► System models for flow-through and slurry reactors for hydrogen storage.
► Transient drive cycle simulations to meet 2010 DOE metrics in hydrogen storage.