High-pressure Storage Systems Research Articles

Analysis of energy saving potential of an asynchronous refueling process for liquid hydrogen station

Liquid hydrogen station shows a great advantage in the future larger market of fuel cell vehicles. However, the energy-saving potential of the liquid hydrogen station remains underexplored. Therefore, a novel asynchronous refueling process (HRP-as) to refuel the vehicle and the high-pressure storage system is proposed based on a conventional synchronous hydrogen refueling process (HRP-s). Moreover, the imperfect compression of the liquid pump and different initial storage pressure are considered. Accordingly, the thermodynamic models of both processes were established, and the evolution of critical parameters was analyzed. Results indicate that the electricity consumption of the liquid pump rises along with the initial storage pressure increase. Compared to the HRP-s, HRP-as exhibits the ability to achieve electricity savings of up to 9.5% within the restrictions of pump capacity and total refueling time. Therefore, HRP-as provides an excellent option for liquid station design without extra expenditure.

Techno-economic evaluation of hydrogen refueling stations with liquid or gaseous stored hydrogen

In this study, different hydrogen refueling station (HRS) architectures are analyzed energetically as well as economically for 2015 and 2050. For the energetic evaluation, the model published in Bauer et al. [1] is used and norm-fitting fuelings according to SAE J2601 [2] are applied. This model is extended to include an economic evaluation. The compressor (gaseous hydrogen) resp. pump (liquid hydrogen) throughput and maximum pressures and volumes of the cascaded high-pressure storage system vessels are dimensioned in a way to minimize lifecycle costs, including depreciation, capital commitment and electricity costs. Various station capacity sizes are derived and energy consumption is calculated for different ambient temperatures and different station utilizations. Investment costs and costs per fueling mass are calculated based on different station utilizations and an ambient temperature of +12 °C. In case of gaseous trucked-in hydrogen, a comparison between 5 MPa and 20 MPa low-pressure storage is conducted. For all station configurations and sizes, a medium-voltage grid connection is applied if the power load exceeds a certain limit. For stations with on-site production, the electric power load of the hydrogen production device (electrolyzer or gas reformer) is taken into account in terms of power load. Costs and energy consumption attributed to the production device are not considered in this study due to comparability to other station concepts. Therefore, grid connection costs are allocated to the fueling station part excluding the production device. The operational strategy of the production device is also considered as energy consumption of the subsequent compressor or pump and the required low-pressure storage are affected by it. All station concepts, liquid truck-supplied hydrogen as well as stations with gaseous truck-supplied or on-site produced hydrogen show a considerable cost reduction potential. Long-term specific hydrogen costs of large stations (6 dispensers) are 0.63 €/kg – 0.76 €/kg (dependent on configuration) for stations with gaseous stored hydrogen and 0.18 €/kg for stations with liquid stored hydrogen. The study focuses only on the refueling station and does not allow a statement about the overall cost-effectiveness of different pathways.

Prediction of state property during hydrogen leaks from high-pressure hydrogen storage systems

In an actual hydrogen leakage process, heat exchange occurs between the gas in a high-pressure storage system and its surroundings. Therefore, the predictions of models that are established based on the isentropic process assumption have large errors. In this study, a high-pressure gas leakage process model including heat exchange (the HEC model) is established. It includes two parts; one is a high-pressure gas storage model without the isentropic process assumption, and the other is a leakage orifice model with the isentropic process assumption. Formulas for the pressure variation and temperature variation based on the mass and energy conservation equations, the Abel–Noble equation of state, and an enthalpy formula based on the Helmholtz free energy are used to establish the gas storage model. The leakage orifice model is built using a mass flow rate formula based on the van der Waals equation of state and Perry's flow coefficient formula. Finally, the proposed high-pressure gas leakage process model including heat exchange is compared with high-pressure hydrogen leakage process models with the isentropic process assumption based on the Abel–Noble and van der Waals equations of state. The results show that the proposed model can yield more promising results in predicting the gas leakage mass flow rate, gas pressure, and temperature inside hydrogen storage systems compared with previous models.

Energetic evaluation of hydrogen refueling stations with liquid or gaseous stored hydrogen

The future success of fuel cell electric vehicles requires a corresponding infrastructure. In this study, two different refueling station concepts for fuel cell passenger cars with 70 MPa technology were evaluated energetically. In the first option, the input of the refueling station is gaseous hydrogen which is compressed to final pressure, remaining in gaseous state. In the second option, the input is liquid hydrogen which is cryo-compressed directly from the liquid phase to the target pressure. In the first case, the target temperature of −33 °C to −40 °C [1] is achieved by cooling down. In the second option, gaseous deep-cold hydrogen coming from the pump is heated up to target temperature. A dynamic simulation model considering real gas behavior to evaluate both types of fueling stations from an energetic perspective was created. The dynamic model allows the simulation of boil-off losses (liquid stations) and standby energy losses caused by the precooling system (gaseous station) dependent on fueling profiles. The functionality of the model was demonstrated with a sequence of three refueling processes within a short time period (high station utilization). The liquid station consumed 0.37 kWh/kg compared to 2.43 kWh/kg of the gaseous station. Rough estimations indicated that the energy consumption of the entire pathway is higher for liquid hydrogen. The analysis showed the high influence of the high-pressure storage system design on the energy consumption of the station. For future research work the refueling station model can be applied to analyze the energy consumption dependent on factors like utilization, component sizing and ambient temperature.

Performance of a small‐scale compressed air storage (CAS)

The use of renewable energy, such as wind and solar, has significantly increased in the last decade. However, these renewable technologies have the limitation of being intermittent; thus, storing energy in the form of compressed air is a promising option. In compressed air energy storage (CAES), the electrical energy from the power network is transformed into a high-pressure storage system through a compressor. Then, when the demand for electricity is high, the stored high-pressure air is used to drive a turbine to generate electricity. The advantages of CAES are its high energy density and quality, and for being environmentally friendly process. In the existing facilities of University of Auckland, New Zealand, air cavern is not available; thus, a high-pressure tank is used to store the compressed air, which could provide an excellent opportunity for small size applications. There is a limited literature available on the temperature and pressure profiles in a typical high-pressure tank during charging and discharging processes. Therefore, this research investigates how temperature and pressure inside a high-pressure tank change during charging and discharging processes. It will provide a better understanding for heat transfer in such system. Furthermore, it will provide the necessary information needed for the designing of an efficient small-scale CAES. In this work, air is compressed to a maximum pressure of 200 bar and stored into a 2 L tank, which is fully fitted with a pressure transducer and a thermocouple suitable for high-pressure measurements. The charging and discharging process is theoretically modeled, and the results are compared with the experimental measurements, showing a good agreement. The heat balance on the system is used to validate the steady-state condition, while dynamic analysis is used to predict the transient change of compressed air and tank wall temperatures. The theoretical modeling is undertaken by solving the differential equations describing the transient change in temperature of both air and tank wall. The results of this study show that air temperature rises from 24°C to 60°C at 100 bar and from approximately 17°C to over 60°C at 200 bar. During discharging process, air temperature drops from ambient to 5°C at starting pressure of 100 bar and to −20°C at starting pressure of 200 bar.

Development of a solar powered hydrogen fueling station in smart cities applications

This paper reports main criteria for design, realization and validation of a solar-powered hydrogen fueling station in a smart city application relevant to an on-site hydrogen production plant. The program has been developed by CNR-ITAE together with other industrial partners in the framework of the Italian research project called i-NEXT (innovation for greeN Energy and eXchange in Transportation). The i-NEXT hydrogen production plant is located in the Municipality of Capo d’Orlando, Sicily, it is fed by a microgrid able to receive energy from solar radiation by a 100 kW rooftop photovoltaic plant and connected with a battery energy storage of 300 kWh (composed by 16 sodium nickel chloride high temperature batteries). The plant is able to deliver hydrogen and electricity for an electric and hydrogen vehicles fleet. The hydrogen fueling station includes four subsystems: a hydrogen production system by electrolysis, a compression system, a high-pressure storage system and a hydrogen dispenser for automotive applications. It is able to generate in the hydrogen production subsystem through an alkaline electrolyzer of 30 kWh: 6.64 Nm3/h of H2 with a gas purity of 99.995% (O2 < 5 ppm and dew point < −60 °C). The compression subsystem has a three stage compressor with a rated gas flow rate of 5,2 Nm3/h and a delivery pressure of 360 bar. The compressed H2 gas is stored in a high-pressure tanks of 350 L capacity allowing, in this way, a supply through a dispenser system of two automotive's tanks of 150 L @ 350 bar in less than 30 min. This paper reports the design and the development results coming from a first test campaign.

High-pressure release and dispersion of hydrogen in a partially enclosed compartment: Effect of natural and forced ventilation

The study of compressed hydrogen releases from high-pressure storage systems has practical application for hydrogen and fuel cell technologies. Such releases may occur either due to accidental damage to a storage tank, connecting piping, or due to failure of a pressure release device (PRD). Understanding hydrogen behavior during and after the unintended release from a high-pressure storage device is important for development of appropriate hydrogen safety codes and standards and for the evaluation of risk mitigation requirements and technologies. In this paper, the natural and forced mixing and dispersion of hydrogen released from a high-pressure tank into a partially enclosed compartment is investigated using analytical models. Simple models are developed to estimate the volumetric flow rate through a choked nozzle of a high-pressure tank. The hydrogen released in the compartment is vented through buoyancy induced flow or through forced ventilation. The model is useful in understanding the important physical processes involved during the release and dispersion of hydrogen from a high-pressure tank into a compartment with vents at multiple levels. Parametric studies are presented to identify the relative importance of various parameters such as diameter of the release port and air changes per hour (ACH) characteristic of the enclosure. Compartment overpressure as a function of the size of the release port is predicted. Conditions that can lead to major damage of the compartment due to overpressure are identified. Results of the analytical model indicate that the fastest way to reduce flammable levels of hydrogen concentration in a compartment is by blowing through the vents. Model predictions for forced ventilation are presented which show that it is feasible to effectively and rapidly reduce the flammable concentration of hydrogen in the compartment following the release of hydrogen from a high-pressure tank.

Optimum angle of inclination : Deris, Nese, Air Conditioning, Heating, Ventilating, 5 p. Aug. 1961, Illus.

This paper reports main criteria for design, realization and validation of a solar-powered hydrogen fueling station in a smart city application relevant to an on-site hydrogen production plant. The program has been developed by CNR-ITAE together with other industrial partners in the framework of the Italian research project called i-NEXT (innovation for greeN Energy and eXchange in Transportation). The i-NEXT hydrogen production plant is located in the Municipality of Capo d’Orlando, Sicily, it is fed by a microgrid able to receive energy from solar radiation by a 100 kW rooftop photovoltaic plant and connected with a battery energy storage of 300 kWh (composed by 16 sodium nickel chloride high temperature batteries). The plant is able to deliver hydrogen and electricity for an electric and hydrogen vehicles fleet. The hydrogen fueling station includes four subsystems: a hydrogen production system by electrolysis, a compression system, a high-pressure storage system and a hydrogen dispenser for automotive applications. It is able to generate in the hydrogen production subsystem through an alkaline electrolyzer of 30 kWh: 6.64 Nm3/h of H2 with a gas purity of 99.995% (O2 < 5 ppm and dew point < −60 °C). The compression subsystem has a three stage compressor with a rated gas flow rate of 5,2 Nm3/h and a delivery pressure of 360 bar. The compressed H2 gas is stored in a high-pressure tanks of 350 L capacity allowing, in this way, a supply through a dispenser system of two automotive's tanks of 150 L @ 350 bar in less than 30 min. This paper reports the design and the development results coming from a first test campaign.