Towards an Inherently Safer Hydrogen Economy
Abstract
With the rising demand for renewable energy sources, Hydrogen is gaining increased attention due to its potential for zero emissions in transportation and stationary applications. Various Hydrogen-based technologies such as proton exchange membrane fuel cells and Hydrogen refueling stations to support fuel cell electric vehicles have begun commercialization, paving the path towards an environmentally sustainable Hydrogen economy. However, one of the major hindrances towards establishing the Hydrogen economy are the safety issues and safety incidents relevant to Hydrogen.
An example of such incidents is the explosion in a proton exchange membrane fuel cell (PEMFC) powered forklift in Louisiana, USA in May 2018 and the resulting fatality which highlights the need for the improved safety of this technology. Apart from the safety concerns, PEMFC durability has been an important issue towards its further commercialization. Both the safety and durability concerns associated with this technology can be attributed to the temporal degradation of its components. In Chapter II, a mathematical model has been developed that relates the microscale PEMFC degradation to the probability of a macroscale explosion in a Fuel Cell Electric Vehicle (FCEV). Using the model and the inherent safety principle of intensification, it was observed that increasing the operating temperature of the PEMFC system can significantly improve both its safety and durability while intensifying membrane design parameters i.e., membrane thickness and membrane conductivity do not provide any significant improvements. A key inference from this study is that the durability (expressed in voltage loss) and safety (expressed in explosion probability) of a PEMFC system are not perfectly correlated.
Another example of a Hydrogen related incident is the recent Hydrogen Refueling Station (HRS) explosion in Norway in June 2019 that confirms the need for improved design of these facilities to further facilitate the commercialization of a Hydrogen economy. Currently HRS designs are primarily based on the consideration of economics to supply Hydrogen at a competitive price and their safety is evaluated through Quantitative Risk Assessment as dictated by the codes and the standards. However, the lack of relevant safety perspective in the design stage itself leads to a possibility of HRS being overdesigned in terms of safety. In Chapter III, we propose an integrated model using queuing theory, process synthesis, QRA and economic analysis for designing HRS. The application of the integrated model is also proposed using the inherently safer design philosophy. For the base design under consideration, it was observed that reducing liquid storage capacity can significantly reduce the risk associated with explosion along with an improvement in HRS economics, while reducing dispenser hose diameter can reduce the risk associated with jet-fire with a slight detriment to HRS economics.
Apart from Hydrogen dispensing and application, Hydrogen production remains an area of concern from the safety perspective as witnessed from the explosion at a steam reforming facility in California, U.S. in June 2019. In Chapter IV, we have developed an integrated model consisting of process synthesis, quantitative risk assessment and economic analysis sub-models that facilitate a holistic design for the SMR process. The usefulness of the integrated model is demonstrated by evaluating alternatives based on the inherently safer design philosophy. For the base design, the results indicate that decreasing the pressure of purge gas exiting the purge gas compressor leads to a reduction in the jet-fire axial risk distance of purge gas with slight economic benefits. Also, increasing the temperature of syngas entering the condensation unit leads to a reduction in the jet-fire axial risk distance for both purge gas and syngas with slight decrease in process economics.
Citation
Ade, Nilesh (2021). Towards an Inherently Safer Hydrogen Economy. Doctoral dissertation, Texas A&M University. Available electronically from https : / /hdl .handle .net /1969 .1 /196306.