Investigation of configuration on multi-tank cascade system at hydrogen refueling stations with mass flow rate

Abstract

Currently, the utilization of hydrogen has been focused on transportation sector because it has been expected that the emission of carbon dioxide (CO2) can be largely and effectively reduced by replacing internal combustion engine vehicles (ICEVs) into fuel cell electric vehicles (FCEVs). Light-duty passenger FCEVs are already in the market and the extent of CO2 reduction can be further expanded by applying FCEVs to heavy vehicles.Hydrogen refueling stations (HRSs) are an essential infrastructure for supporting FCEVs and have been developed for effective filling of hydrogen. Currently, most FCEVs store hydrogen in a compressed gaseous state. Therefore, in HRSs, hydrogen stored at high pressure is used to rapidly refuel the vehicles. To reduce energy consumption and ensure high utilization of the stored hydrogen, a cascade system with multi-tank at different levels of pressure is generally applied to commercial HRSs. Usually, three stages of pressure level (low-, mid-, and high-pressure) are composed of the cascade system. Therefore, the proper design on the capacity (stored hydrogen mass or volume) of tanks as well as the pressure of tanks is required to obtain satisfactory performance of HRSs.To date, HRSs for light-duty FCEVs have been mainly studied to reduce refueling time and energy consumption. However, HRSs for heavy-duty vehicles should be investigated to extend the utilization of hydrogen in the transportation sector. Such HRSs should be able to supply hydrogen at increased mass flow rates over 60 g/s which is a known limitation on the light-duty FCEV refueling. In the present study, a thermodynamic model was developed and, then, verified by results from a computational fluid dynamic (CFD) model. The model was applied to a cascade-type HRS with different configurations on storage capacities of low-, mid-, and high-pressure tank. The effect of bore diameter at a nozzle was also explored because the mass flow rate could be increased with lowered pressure drop and the nozzle is a main contributor of total pressure drop through a filling line. It was found that the capacity of the high-pressure tank becomes important to obtain a high flow rate and it can be reduced by increasing a bore diameter of a nozzle of a dispenser at HRS.