Optimal design of inter-plant hydrogen networks with intermediate headers of purity and pressure

This paper addresses the optimal design of inter-plant hydrogen networks with intermediate headers of purity and pressure. A superstructure for inter-plant integration of hydrogen networks is presented, where all hydrogen sources and hydrogen sinks are indirectly matched with each other through intra-plant hydrogen headers and inter-plant hydrogen headers. The corresponding mathematical programming model is constructed and a tailored two-step strategy is proposed to solve the model. In this solving method, the topology of the inter-plant hydrogen network and the purity levels of the hydrogen headers are first determined to minimize the cost of hydrogen utilities. The placements of compressors and pressure levels of hydrogen headers are then optimized to reach the lowest total annual cost of the inter-plant hydrogen network. The application of the proposed method is illustrated via a practical industrial case of inter-plant hydrogen network in China.     

Design of a hydrogen compressor for hydrogen fueling stations

Hydrogen compressors dominate the hydrogen refueling station costs. Metal hydride based thermally driven hydrogen compressor (MHHC) is a promising technology for the compression of hydrogen. Selection of metal hydride alloys and reactor design have a great impact on the performance of the thermally driven MHHC. A thermal model is developed to study the performance characteristics of the two-stage MHHC at different operating conditions. The effects of heat source temperature and hydrogen supply pressure on the compression ratio and isentropic efficiency are investigated. Finite volume method is used for discretizing the reaction kinetics, continuity, momentum and energy equations. Metal hydrides selected for this analysis are Mm_0.2La_0.6Ca_0.2Ni₅ and Ti_1.1Cr_1.5Mn_0.4V_0.1. The thermal model was validated with the results extracted from an experimental study. Validation results demonstrated that the numerical results are in good agreement with the data reported in literature.     

Selection of structural materials for hydrogen pipelines and storage vessels

The feasibility, both of using present transmission lines, and of developing new resistant line pipe and pressure vessel steels, is explored. Both appear possible but simple extrapolation of existing conditions for natural gas storage and transmission is inappropriate. Specifically, composition, heat treatment and weldability requirements are more severe for hydrogen transport; pressure vessel steels are susceptible to hydrogen embrittlement and thus seamless vessels and/or protective liners are required; and high-strength resistant steels must be developed for compressors, valves and related equipment. These problems, while solvable, provide an urgent challenge to the materials engineer.     

Design of multiperiod hydrogen network with flexibilities in subperiods and redundancy control

To ensure the operational flexibility of multiperiod hydrogen network and reduce the capacity redundancy of compressors, a method for design of multiperiod hydrogen network is proposed based on flexibility analysis. In the proposed method, an initial multiperiod hydrogen network is obtained by solving the single period optimization models of hydrogen networks for each subperiod, where the minimal capacities of compressors in different subperiods are assigned. Then, the flexibility of the initial multiperiod hydrogen network is examined and improved by solving a proposed flexible design model to identify the bottlenecks of operational flexibility of each subperiod. The additional capacities of compressors and flowrates of hydrogen utility in each subperiod are then determined to finalize the design of the flexible multiperiod hydrogen network with the redundancy control of compressors capacities. The application of the proposed method are illustrated via a hydrogen network of a refinery in China.     

A non-destructive fault diagnosis method for a diaphragm compressor in the hydrogen refueling station

Costly and time-consuming maintenance of the hydrogen compressors due to their frequent breakdown severely hinders the deployment and promotion of hydrogen refueling station (HRS), and effective condition monitoring and fault diagnosis is the key to reduce the unscheduled downtime of the compressor. This paper proposes a non-destructive method for fault diagnosis of diaphragm compressors for HRSs based on the acoustic emission (AE) signal. The AE signals in the time domain are segmented into angle-domain signals correspond to a working cycle. The feature events of the moving components are determined through the measured AE signal in both angle-domain and angle-frequency domain based on short-term Fourier transform (STFT). Those feature events signals are innovatively applied to identify the typical abnormal conditions of excessively high oil pressure, slightly inadequate oil pressure and seriously inadequate oil pressure, replacing the traditional and destructive pressure measuring method. The results show that this method can be used to effectively diagnose abnormal working conditions and indicate that this method can be utilized as a powerful tool in the non-destructive condition monitoring and fault diagnosis of the diaphragm compressors.     

Exergy analysis on the simulation of a small-scale hydrogen liquefaction test rig with a multi-component refrigerant refrigeration system

This study investigates the simulation of a proposed small-scale laboratory liquid hydrogen plant with a new, innovative multi-component refrigerant (MR) refrigeration system. The simulated test rig was capable of liquefying a feed of 2 kg/h of normal hydrogen gas at 21 bar and 25 °C to normal liquid hydrogen at 2 bar and −250 °C. The simulated power consumption for pre-cooling the hydrogen from 25 °C to −198 °C with this new MR cycle was 2.07 kWh/kg_GH2 from the ideal minimum of 0.7755 kWh per kilogram of feed hydrogen gas. This was the lowest power consumption available when compared to today’s conventional hydrogen liquefaction cycles, which are approximately 4.00 kWh/kg_GH2. Hence, the MR cycle’s exergy efficiency was 38.3%. Exergy analysis of the test rig’s cycle, which is required to find the losses and optimize the proposed MR system, was evaluated for each component using the simulation data. It was found that the majority of the losses were from the compressors, heat exchangers, and expansion valves. Suggestions are provided for how to reduce exergy in each component in order to reduce the exergy loss. Finally, further improvements for better efficiency of the test rig are explained to assist in the design of a future large-scale hydrogen liquefaction plant.     

Modeling and development of a liquid piston hydrogen compressor with a double buffer structure: A new insight

Liquid piston hydrogen compressors (LPHCs) are promising used in hydrogen refueling stations. Piston braking is crucial to LPHCs since the solid piston works under a high stroke frequency, which may result in piston collision. The on-off valve in the previous studies requires complicated control program to ensure the piston positions at dead centers. In this paper, a novel LPHC with a double buffer structure and an improved hydraulic driving system are proposed. A simulation involving the flow through the buffer aperture confirms the braking effect of the proposed design. Some parameters affecting piston braking are studied. A light piston can produce a lower velocity pulsation and lower peak pressure in the buffer chamber. The minimal piston displacement decreases with an increase in the bottom throttle diameter, while the maximal piston displacement increases with an increase in the top throttle diameter. The results also show that the slight pulsation of the piston velocity is attributed to the spool insertion, the piston reverse motion, and the opening of valves. This study can provide a technical reference for the optimization of LPHCs.     

Hydrogen decompression analysis by multi-stage Tesla valves for hydrogen fuel cell

Hydrogen fuel cell is an ideal power source for electric vehicles. For a hydrogen fuel cell electric vehicle, the hydrogen is reserved in a high pressure level to promote the recharge mileage while relatively low-pressure hydrogen is demanded for proper functioning of the fuel cell stack, so that decompression of hydrogen is needed before hydrogen flowing into the fuel cell. With a reverse flow through Tesla valves, there appears a large pressure drop between the inlet and outlet, which can be used for hydrogen decompression nicely. However, a single-stage Tesla valve cannot meet the pressure drop requirement, so multi-stage Tesla valves are utilized. In this paper, numerical simulations of reversed hydrogen flow through multi-stage Tesla valves are carried out. The stage number of multi-stage Tesla valves and the inlet/outlet pressure ratio are both studied, and the distributions of temperature, pressure, and velocity inside multi-stage Tesla valves are all investigated. Results show that as the stage number increases or the inlet/outlet pressure ratio decreases, the pressure and the velocity inside multi-stage Tesla valves decrease, and the less the stage number, the more possibility for the velocity higher than local acoustic speed. Besides, a power-law relationship between the flow rate, the stage number and pressure ratio is summarized.     

Analysis of Ontario's hydrogen economy demands from hydrogen fuel cell vehicles

The ‘Hydrogen Economy’ is a proposed system where hydrogen is produced from carbon dioxide free energy sources and is used as an alternative fuel for transportation. The utilization of hydrogen to power fuel cell vehicles (FCVs) can significantly decrease air pollutants and greenhouse gases emission from the transportation sector. In order to build the future hydrogen economy, there must be a significant development in the hydrogen infrastructure, and huge investments will be needed for the development of hydrogen production, storage, and distribution technologies. This paper focuses on the analysis of hydrogen demand from hydrogen FCVs in Ontario, Canada, and the related cost of hydrogen. Three potential hydrogen demand scenarios over a long period of time were projected to estimate hydrogen FCVs market penetration, and the costs associated with the hydrogen production, storage and distribution were also calculated. A sensitivity analysis was implemented to investigate the uncertainties of some parameters on the design of the future hydrogen infrastructure. It was found that the cost of hydrogen is very sensitive to electricity price, but other factors such as water price, energy efficiency of electrolysis, and plant life have insignificant impact on the total cost of hydrogen produced.     

A novel mathematical model for integrating the hydrogen network of refinery with compressor allocation considered

The allocation and cost of compressors have significant influence on hydrogen network. A novel mixed integer nonlinear programming method is proposed for optimizing hydrogen network with the allocation of compressors considered. This model considers the streams compressed stage by stage with multiple compressors and all possible compression paths. The compression power cost of multiple compressors is deduced to optimize the number of compressors in each compression process. The trade-off between the power loss and capital cost of compression is analyzed for different compression paths. The superstructure and mathematical model are built to optimize the hydrogen network in terms of minimizing the total annual cost. The proposed model is flexible and efficient. Three literature cases are studied by the proposed method, and the optimal flowsheets are identified. Compared with previous methods, the computing time is significantly reduced and the total cost of compressors is reduced by 3.38%–8.46%.     

Model-based design of an automotive-scale,metal hydride hydrogen storage system

Sandia and General Motors have successfully designed, fabricated, and experimentally operated a vehicle-scale hydrogen storage demonstration system using sodium alanates. The demonstration system module design and the system control strategies were enabled by experiment-based, computational simulations that included heat and mass transfer coupled with chemical kinetics. Module heat exchange systems were optimized using multi-dimensional models of coupled fluid dynamics and heat transfer. Chemical kinetics models were coupled with both heat and mass transfer calculations to design the sodium alanate vessels. Fluid flow distribution was a key aspect of the design for the hydrogen storage modules and computational simulations were used to balance heat transfer with fluid pressure requirements.     

CFD modelling of accidental hydrogen release from pipelines

Although nowadays hydrogen is distributed mainly by trailers, in the future distribution by means of pipelines will be more suitable if larger amounts of hydrogen are produced on industrial scale. Therefore from the safety point of view it is essential to compare hydrogen pipelines to natural gas pipelines, whose use is well established today. Within the paper we compare safety implications in accidental situations. In the analysis we do not consider technological aspects such as compressors or seals.     

Power-to-liquid hydrogen: Exergy-based evaluation of a large-scale system

Hydrogen as an energy vector is seen as a key for the energy transition. Recently, more than 30 countries have launched their hydrogen strategies and roadmaps. Hydrogen storage and transportation are challenging steps of the hydrogen economy since all available options have significant drawbacks. This paper evaluates a power-to-liquid hydrogen process; the system is “charged” with electricity from renewable sources to produce hydrogen via water electrolysis; the produced hydrogen gas is liquefied and stored at ambient pressure and cryogenic temperature. The purpose of this paper is to report the first evaluation results of a system including a polymer electrolyte membrane electrolyser and a hydrogen liquefier. The evaluation was conducted using exergy-based methods, i.e. exergetic, exergoeconomic and exergoenvironmental analyses. The process of hydrogen liquefaction was simulated with the aid of the Aspen Plus software. The exergetic efficiencies for the liquefaction process and for the electrolyser are 42% and 47%, respectively. While the total exergetic efficiency of the power-to-liquid hydrogen system amounts to 44%. The total exergy destruction for the liquefier amounts to 9.3 MW and for the polymer electrolyser membrane electrolyser amounts to 19.3 MW. The electrolyser followed by the hydrogen compressors were identified as the components with the highest exergy destruction values and investment costs, while the compressors and the recuperators account for the highest exergoenvironmental impact. The sensitivity analysis shows that the specific liquefaction cost of hydrogen strongly varies with the electricity price and the cost of green hydrogen.     

Description and characterization of an electrochemical hydrogen compressor/concentrator based on solid polymer electrolyte technology

Proton-exchange membrane (PEM) technology is commonly used for manufacturing water electrolysers, H₂/O₂ fuel cells and unitized regenerative fuel cells. It can also be used to develop electrochemical compressors, for the purpose of concentrating and/or pressurizing gaseous hydrogen. The aim of the work reported here was to evaluate the main operating characteristics of a laboratory scale (≈10 N liter/h) monocell compressor. The role of various operating parameters (current density, temperature of electrochemical cell, water vapor partial pressure in the hydrogen feed gas, anodic gas composition, etc.) has been evaluated and is discussed. It is shown that the relative humidity of hydrogen oxidized at the anode of the compressor should be adapted to the current density during operation to avoid mass transfer limitations or electrode flooding. A cell voltage of 140 mV is required at 0.2 A cm⁻² to compress hydrogen in one step from atmospheric pressure up to 48 bar, corresponding to an energy consumption of ca. 0.3 kW h/Nm³. Experiments have been performed up to 130 bar. Series connection of several compressors is recommended to reach output pressures higher than 50 bar. To reduce gas cross-permeation effects which can negatively impact the efficiency of the compressor, additional experiments have been made using Nafion membrane modified by addition of zirconyl phosphate. Finally, data related to the extraction of hydrogen from H₂-N₂ gas mixtures are also reported and discussed.     

A quantitative risk assessment of hydrogen fuel cell forklifts

With the increasing deployment of hydrogen fuel cell forklifts, it is essential to understand the risks of incidents involving these systems. A quantitative risk assessment (QRA) study was conducted to determine the potential hydrogen release scenarios, probabilities, and consequences in fuel cell forklift operations. QRA modeling tools, such as fault tree analysis (FTA) and event sequence diagrams (ESD), were used together with hydrogen systems data. This work provides insights into the fatality risk from a hydrogen fuel cell forklift and the reliability of its design and components. The analysis shows that the expected fatal accident rate of a hydrogen forklift is considerably higher than current fatal injury rates observed by the Bureau of Labor Statistics for industrial truck operators and material handling occupations. Nevertheless, the average individual risk posed to forklift drivers was found to be likely tolerable based on current risks accepted by industrial truck operators. Jet fires are found to dominate the system's risk, however, the risk of explosions is also considerable. An importance measures analysis shows that these risks could be mitigated by improving the design and reliability of pressure relief devices, as well as other components prone to leak such as filters and check valves. We also identify sources of uncertainty and conservatisms in the QRA process that can guide future research in hydrogen systems. These results provide powerful insight into improvements in the design of fuel cell forklifts to reduce risk and enable the safe deployment of this key technology for a decarbonized future.     

Alloy selection for multistage metal-hydride hydrogen compressors: A thermodynamic model

A thermodynamic model is presented to aid the selection of compatible pairs of hydrogen storage alloys for service in a multi-stage metal-hydride compressor. The model is built around the concept of an ideal compressor in which all pairs of hydrides operate between the same working temperatures. The key feature of the model is a link between the thermodynamic characteristics of the hydrides in each pair (the entropy change ΔS and enthalpy change ΔH when the hydride is formed from the metal) that results from requiring that the heated low-pressure hydride is able to desorb to the cooled high-pressure metal at a unique intermediate pressure. This necessary linking places severe constraints on the choice of alloys, since ΔS and ΔH cannot be freely chosen and are in fact strongly correlated for hydrides with similar operating temperatures. The model is based on the van ‘t Hoff relation, which is derived from first principles and shown to be only approximately valid at the high hydrogen pressures of interest for vehicle filling stations. Pressure hysteresis and plateau slope are incorporated into the model. A case study of a two-stage compressor is presented, based on the curved van ‘t Hoff line and the experimentally determined effects of pressure hysteresis and plateau slope.     

Transient flow performance and heat transfer characteristic in the cylinder of hydraulic driving piston hydrogen compressor during compression stroke

With the advantages of large flow capacity and high pressure, the use of hydraulic driving piston compressors in hydrogen refueling stations is becoming the development trend. Understanding transient flow and heat transfer characteristic is the key issue for the design and application of hydrogen compressors. The transient model of the hydraulic driving piston compressor is constructed by dynamic mesh and the National Institute of Standards and Technology (NIST) real hydrogen model, which accurately predicts flow field and heat transfer. Moreover, the effect of piston reciprocating cycle frequency on hydrogen parameters variation and heat transfer characteristic is investigated. Adiabatic compression theory is commonly applied in the design of reciprocating compressors. The results show that due to the heat transfer, the exhaust temperature predicted by the adiabatic compression theory is 6.29 K higher than the actual value. This study provides beneficial references for the design optimization and reliable operation of hydraulic driving piston hydrogen compressors.     

Analytical modelling and experimental validation of proton exchange membrane electrolyser for hydrogen production

Proton Exchange Membrane (PEM) Electrolysers (ELSs) are considered as pollution-free with enhanced efficiency technology. Hydrogen can be easily produced from different resources like biomass, water electrolysis, natural gas, propane, and methanol. Hydrogen generation from water electrolysis, which is the splitting of water molecules into hydrogen and oxygen using electricity, can be beneficial when used in combination with variable Renewable Energy (RE) technologies such as solar and wind. When the electricity used for water electrolysis is produced by a variable RE source, the hydrogen stores the unused energy for a later use and can be considered as a renewable fuel and energy resource for the transport and energy sectors.This paper aims to propose a novel graphical model design for the PEM-ELS for hydrogen production based on the electrochemical, thermodynamical and thermal equations. The model under study is experimentally validated using a small-scale laboratory electrolyser. Simulation results, using Matlab-Simulink?, show an adequate parameter agreement with those found experimentally. Therefore, the impact of the different parameters on the electrolyser dynamic performance is introduced and the relevant analytical-experimental comparison is shown. The temperature effect on the PEM-ELS dynamic behaviour is also discussed.     

Research on diagnosis of pre-ignition of hydrogen engine based on SOM-MAS

Abnormal combustion is an important factor in the development process of hydrogen engine and it mainly includes pre-ignition, backfire and knocking, among which pre-ignition has the most serious impact on hydrogen engine. In this paper, it is divided into four types: normal combustion, slight pre-ignition, moderate pre-ignition and severe pre-ignition according to different crankshaft rotation angles. In order to identify different combustion types, this paper proposes a fault diagnosis model based on the fusion of SOM neural network and Multi-Agent System (SOM-MAS). Firstly, different combustion types are identified by SOM. Secondly, the abnormal combustion is tracked and located mainly through the Multi-Agent System, and the location of the abnormality is identified. Finally, based on 44 sets of pressure data samples collected from the in-cylinder combustion of a hydrogen engine on the experimental bench, different combustion types were diagnosed and identified, and the location of abnormal combustion faults was tracked, which verifies the effectiveness of the proposed method shows that the method has certain feasibility and superiority for the diagnosis of hydrogen engine pre-ignition.     

Three dimensional channel effect on the flow characteristics and the performance of hydrogen Knudsen compressors

As a new type of the micro fluidic device, Knudsen compressor can provide the potential utilizations on the hydrogen transport in the micro systems. Considering actual structure of the compressor is three-dimensional, flow characteristic studies are the key issue for the performance predictions. Firstly, the model of three-dimensional Knudsen compressor is built, and the validity of the model is proved by comparison with the experimental result. Secondly, the flow behaviors in the three-dimensional model is investigated, and the distributions of pressure and velocity are investigated. Also, the performance of the hydrogen Knudsen compressor in two-dimensional structure and three-dimensional structure are compared and discussed. Thirdly, the three-dimensional hydrogen Knudsen compressors with different width are analyzed, and the pressure increase in different cases of the hydrogen Knudsen compressors are studied.