Publications

In this paper the broader perspective of green hydrogen (H2) supply and refueling systems for aircraft is provided as an enabling technology brick for more climate friendly H2-powered aviation. For this two H2 demand scenarios at exemplary airports are determined for 2050. Then general requirements for liquid hydrogen (LH2) refueling setups in an airport environment are derived and techno-economic models for LH2 storage liquefaction and transportation to the aircraft are designed. Finally a cost tradeoff study is undertaken for the design of the LH2 setup including LH2 refueling trucks and a LH2 pipeline and hydrant system. It is found that for airports with less than 125 ktLH2 annual demand a LH2 refueling truck setup is the more economic choice. At airports with higher annual LH2 demands a LH2 pipeline & hydrant system can lead to slight cost reductions and enable safer and faster refueling. However in all demand scenarios the refueling system costs only mark 3 to 4% of the total supply costs of LH2. The latter are dominated by the costs for green H2 produced offsite followed by the costs for liquefaction of H2 at an airport. While cost reducing scaling effects are likely to be achieved for H2 liquefaction plants other component capacities would already be designed at maximum capacities for medium-sized airports. Furthermore with annual LH2 demands of 100 ktLH2 and more medium and larger airports could take a special H2 hub role by 2050 dominating regional H2 consumption. Finally technology demonstrators are required to reduce uncertainty around major techno-economic parameters such as the investment costs for LH2 pipeline & hydrant systems.

Decentralised renewable energy production in the form of fuels or electricity can have large scale deployment in future energy systems but the feasibility needs to be assessed. The novelty of this paper is in the design and implementation of a mixed integer linear programming optimisation model to minimise the net present cost of decentralised hydrogen production for different energy demands on neighbourhood urban scale while simultaneously adhering to European Union targets on greenhouse gas emission reductions. The energy system configurations optimised were assumed to possibly consist of a variable number or size of wind turbines solar photovoltaics grey grid electricity usage battery storage electrolyser and hydrogen storage. The demands served are hydrogen for heating and mobility and electricity for the households. A hydrogen residential heating project currently being developed in Hoogeveen The Netherlands served as a case study. Six scenarios were compared each taking one or multiple energy demand services into question. For each scenario the levelised cost of hydrogen was calculated. The lowest levelised cost of hydrogen was found for the combined heating and mobility scenario: 8.36 € kg− 1 for heating and 9.83 € kg− 1 for mobility. The results support potential cost reductions of combined demand patterns of different energy services. A sensitivity analysis showed a strong influence of electrolyser efficiency wind turbine parameters and emission reduction factor on levelised cost. Wind energy was strongly preferred because of the lower cost and the low greenhouse gas emissions compared to solar photovoltaics and grid electricity. Increasing electrolyser efficiency and greenhouse gas emission reduction of the used technologies deserve further research.

Hydrogen production by electrolysis is considered an essential means of consuming renewable energy in the future. However the current assessment of the potential of renewable energy electrolysis for hydrogen production is relatively simple and the perspective is not comprehensive. Here we established a Combined Wind and Solar Electrolytic Hydrogen system considering the influence of regional wind-solar-load characteristics and transmission costs to evaluate the hydrogen production potential of 31 provincial-level regions in China in 2050. The results show that in 2050 the levelized cost of hydrogen (LCOH) in China’s provincial regions will still be higher than 10 ¥/kg which is not cost-competitive compared to the current hydrogen production from fossil fuels. It is more cost-effective to deploy wind turbines than photovoltaic in areas with similar wind and solar resources or rich in wind resources. Wind-solar differences impact LCOH equipment capacity configuration and transmission cost composition while load fluctuation significantly impacts LCOH and electricity storage configuration. In addition the sensitivity analysis of 11 technical and economic parameters showed differences in the response performance of LCOH changes to different parameters and the electrolyzer conversion efficiency had the most severe impact. The analysis of subsidy policy shows that for most regions (except Chongqing and Xizang) subsidizing the unit investment cost of wind turbines can minimize LCOH. Nevertheless from the perspective of comprehensive subsidy effect subsidy cost and hydrogen energy development it is more cost-effective to take subsidies for electrolysis equipment with the popularization of hydrogen

In water-cooled nuclear power plants hydrogen gas can be generated by various mechanisms during an accident. In case combustion of the resulting hydrogen-air mixture within the facility occurs existing containment structures may be compromised and excessive radio-active material can be released to the environment. Thus an improved understanding of the propagation of lean hydrogen deflagrations within buildings and structures is essential for the development of appropriate accident management strategies associated with these scenarios. Following the accident in Fukushima Japan the application of three-dimensional computational fluid dynamics methods to high-fidelity detailed analysis of hydrogen combustion processes in both closed and vented vessels has become more widespread. In this study a recently developed large-eddy-simulation (LES) capability is applied to the prediction of lean premixed hydrogen deflagrations in vented vessels. The LES methodology makes use of a flamelet- or progress-variable-based combustion model coupled with an empirical burning velocity model (BVM) an anisotropic block-based adaptive mesh refinement (AMR) strategy an accurate finite-volume numerical scheme and a mesh independent subfilter-scale (SFS) model. Several different vessel and vent sizes and configurations are considered herein. The LES predictions are compared to experimental data obtained from the Large-Scale Vented Combustion Test Facility (LSVCTF) of the Canadian Nuclear Laboratories (CNL) with both quiescent and turbulent initial conditions. Following descriptions of the LES models LES results for both variable chamber sizes and single- and double-vent cases are presented to illustrate the capabilities of the proposed computational approach. In particular the predicted time histories of pressure as well as the maximum overpressure achieved within the vessels and combustion compartments are compared to those from the LSVCTF experiments. The influences of the modelled ignition process initial turbulence and mesh resolution on the LES results are also discussed. The findings highlight the potential and limitations of the proposed LES approach for accurately describing lean premixed hydrogen deflagrations within vented vessels.

The hydrogen production technology by wind power is an effective mean to improve the utilization of wind energy and alleviate the problem of wind power curtailment. First the basic principles and technical characteristics of the hydrogen production technology by wind power are briefly introduced. Then the history of the hydrogen production technology is reviewed and on this basis the hydrogen production system by wind power is elaborated in detail. In addition the prospect of the application of the hydrogen production technology by wind power is analyzed and discussed. In the end the key technology of the hydrogen production by wind power and the problems to be solved are comprehensively reviewed. The development of hydrogen production technology by wind power is analyzed from many aspects which provides reference for future development of hydrogen production technology by wind power

Accurate estimation of mass flow rate and release conditions is important for the design of dispersion and combustion experiments for the subsequent validation of CFD codes/models for consequence assessment analysis within related risk assessment studies and for associated Regulation Codes and Standards development. This work focuses on the modelling of the discharge phase of the recent large scale LH2 release and dispersion experiments performed by HSE within the framework of PRESLHY project. The experimental conditions covered sub-cooled liquid stagnation conditions at two pressures (2 and 6 bara) and 3 release nozzle diameters (1 ½ and ¼ inches). The simulations were performed using a 1d engineering tool which accounts for discharge line effects due to friction extra resistance due to fittings and area change. The engineering tool uses the Possible Impossible Flow (PIF) algorithm for choked flow calculations and the Helmholtz Free Energy (HFE) EoS formulation. Three different phase distribution models were applied. The predictions are compared against measured and derived data from the experiments and recommendations are given both regarding engineering tool applicability and future experimental design.

The present paper deals with the investigation at conceptual level of the performance of short–medium-range aircraft with hydrogen propulsion. The attention is focused on the relationship between figures of merit related to transport capability such as passenger capacity and flight range and the parameters which drive the design of liquid hydrogen tanks and their integration with a given aircraft geometry. The reference aircraft chosen for such purpose is a box-wing short–mediumrange airplane the object of study within a previous European research project called PARSIFAL capable of cutting the fuel consumption per passenger-kilometre up to 22%. By adopting a retrofitting approach non-integral pressure vessels are sized to fit into the fuselage of the reference aircraft under the assumption that the main aerodynamic flight mechanic and structural characteristics are not affected. A parametric model is introduced to generate a wide variety of fuselage-tank cross-section layouts from a single tank with the maximum diameter compatible with a catwalk corridor to multiple tanks located in the cargo deck and an assessment workflow is implemented to perform the structural sizing of the tanks and analyse their thermodynamic behaviour during the mission. This latter is simulated with a time-marching approach that couples the fuel request from engines with the thermodynamics of the hydrogen in the tanks which is constantly subject to evaporation and depending on the internal pressure vented-out in gas form. Each model is presented in detail in the paper and results are provided through sensitivity analyses to both the technologic parameters of the tanks and the geometric parameters influencing their integration. The guidelines resulting from the analyses indicate that light materials such as the aluminium alloy AA2219 for tanks’ structures and polystyrene foam for the insulation should be selected. Preferred values are also indicted for the aspect ratios of the vessel components i.e. central tube and endcaps as well as suggestions for the integration layout to be adopted depending on the desired trade-off between passenger capacity as for the case of multiple tanks in the cargo deck and achievable flight ranges as for the single tank in the section.

Microbial electrolysis cells (MECs) have attracted significant interest as sustainable green hydrogen production devices because they utilize the environmentally friendly biocatalytic oxidation of organic wastes and electrochemical proton reduction with the support of relatively lower external power compared to that used by water electrolysis. However the commercialization of MEC technology has stagnated owing to several critical technological challenges. Recently many attempts have been made to utilize nanomaterials in MECs owing to the unique physicochemical properties of nanomaterials originating from their extremely small size (at least <100 nm in one dimension). The extraordinary properties of nanomaterials have provided great clues to overcome the technological hurdles in MECs. Nanomaterials are believed to play a crucial role in the commercialization of MECs. Thus understanding the technological challenges of MECs the characteristics of nanomaterials and the employment of nanomaterials in MECs could be helpful in realizing commercial MEC technologies. Herein the critical challenges that need to be addressed for MECs are highlighted and then previous studies that used nanomaterials to overcome the technological difficulties of MECs are reviewed.

Enhancing the efficiency of industrial water electrolysis for hydrogen production is important for the energy transition. In electrolysis hydrogen is produced at the cathode which forms bubbles due to the diffusion of dissolved hydrogen in the surrounding supersaturated electrolyte. Hydrogen (and oxygen) bubbles play an important role in the achievable electrolysis efficiency. The growth of the bubbles is determined by diffusive and convective mass transfer. In turn the presence and the growth of the hydrogen bubbles affect the electrolysis process at the cathode.<br/>In the present study we simulate the growth of a single hydrogen bubble attached to a vertical cathode in a 30 wt KOH solution in a cathodic compartment represented by a narrow channel. We solve the Navier-Stokes equations mass transport equations and potential equation for a tertiary current distribution. A sharp interface immersed boundary method with an artificial compressibility method for the pressure is employed. To verify the numerical accuracy of the method we performed a grid refinement study and checked the global momentum and hydrogen mass balances. We investigate the effects of flow rate and operation pressure upon bubble growth behaviour species concentrations potential and current density. We compare different cases in two ways: for the same time and for the same bubble radius. We observe that increasing the flow velocity leads to a small increase in efficiency. Increasing the operation pressure causes higher hydrogen density which slows down the bubble growth. It is remarkable that for a given bubble radius increasing the pressure leads to a small decrease in efficiency.

Fluctuations in renewable energy production especially from solar and wind plants can be solved by large‐scale energy storage. One of the possibilities is storing energy in the form of hydrogen or methane–hydrogen blends. A viable alternative for storing hydrogen in salt caverns is Lined Rock Cavern (LRC) underground energy storage. One of the most significant challenges in LRC for hydrogen storage is sealing liners which need to have satisfactory sealing and mechanical properties. An experimental study of hydrogen permeability of different kinds of polymers was conducted followed by modeling of hydrogen permeability of these materials with different additives (graphite halloysite and fly ash). Fillers in polymers can have an impact on the hydrogen permeability ratio and reduce the amount of polymer required to make a sealing liner in the reservoir. Results of this study show that hydrogen permeability coefficients of polymers and estimated hydrogen leakage through these materials are similar to the results of salt rock after the salt creep process. During 60 days of hydrogen storage in a tank of 1000 m2 inner surface 1 cm thick sealing liner and gas pressure of 1.0 MPa only approx. 1 m3STP of hydrogen will diffuse from the reservoir. The study also carries out the modeling of the hydrogen permeability of materials using the Max‐ well model. The difference between experimental and model results is up to 17% compared to the differences exceeding 30% in some other studies.