Dynamic Modeling and Control of a Hydrogen Energy System

The population is expected to continue to rise in the future. A greater amount of automobile utilization is expected, leading to a rapid increase in the transportation sector, a sector heavily dependent on CO2 emission fuels. It would be beneficial to introduce an alternative technology of high efficiency and low emission levels to mitigate the currently increasing GHG emissions to the environment. Among the fossil fuels, hydrogen is the one with the highest energy density per unit volume when stored in solid form and has the highest abundance on earth. Hydrogen can be stored in solid form within metal hydrides. Due to the fact that hydrogen is initially obtained in very low densities, high pressure must be applied to be stored efficiently. Hence, a high pressure metal hydride, HPMH, tank is suggested for its storage. The next step is the means of converting hydrogen into energy. Proton exchange membrane fuel cell, PEMFC, is the suggested technology. The major advantage of this technology is that it converts the fuel directly into energy electrochemically, allowing zero GHG emissions, making it sustainable and of high efficiency. The main disadvantage of hydrogen storage is the long fueling time, which makes it challenging for automobile usage. The next issue is the rate of hydrogen supply to the fuel cell for energy production. As the fuel is initially in solid form it is hard to establish a desired steady flow rate to the engine when required. Finally, the absorption and desorption reactions of hydrogen are temperature-dependent, a variable that must be better analyzed due to its great impact to the system, making it a key component for the improvement of the safety and operability of the system. This thesis combines pre-established detailed dynamic models of an HPMH tank and of a PEMFC system by utilizing the model building platform named gPROMS. The thesis investigates the filling time parameters, discharge rate parameters and the thermal management of an HPMH and PEMFC units. A PI controller is added for the automatization iii of the system that regulates the water flow in the heat exchanger, depending on the hydrogen inflow in the HPMH and the energy output requirements from the PEMFC. The model results provide a clear visualization of the impact of flow rate, pressure and temperature in the operability of the system. It is concluded that one of the most significant variables in the system is the temperature that can be controlled by the flow rate of the water in the heat exchanger. That variable can lead to a higher fueling rate and steadier desorption rate. Furthermore, the PI control is able to efficiently manage the flow rate of water in the heat exchanger and enhance the operability of the system, allowing higher fidelity and safety. The overall outcome of the thesis supports the claim that the future utilization of this system has potential to mitigate the GHG emissions in the transportation sector as well as introduce higher energy efficiencies compared to the current commercial technology and fuel