Hydrogen Recycling Research Articles

Artificial Intelligent Modeling and Optimizing of an Industrial Hydrocracker Plant

The main objective of this study is the modelling and optimization of an industrial Hydrocracker Unit (HU) by means of Adaptive Neuro Fuzzy Inference System (ANFIS) model. In this case, some data were collected from an industrial hydrocracker plant. Inputs of an ANFIS include flow rate of fresh feed and recycle hydrogen, temperature of reactors, mole percentage of H2 and H2S, feed flow rate and temperature of debutanizer, pressure of debutanizer receiver, top and bottom temperature and pressure of fractionator column. The network was employed to calculate the flow rate of gas oil, kerosene, Light Naphtha (LN), and Heavy Naphtha (HN).Unseen data points were used to check generalization capability of the best network. There were good adjustment between network estimations and unseen data. Finally optimization was performed to maximize the production volume percent of gas oil, kerosene, HN and LN and to identify the sets of optimum operating parameters in order to maximize yields of mentioned product. Optimum conditions were found as feed flow rate of 90.9 m3/h, reactor temperature of 378.4 °C, hydrogen flow rate of 54.31 MSCM/h and LN (feed vol.%) of 9.34.

First EMC3‐EIRENE Simulations with Divertor Legs of LHD in Realistic Device Geometry

AbstractAn extended mesh system for EMC3‐EIRENE has been developed to simulate peripheral plasma including the ergodic and the divertor leg regions of LHD. Both the open and the closed divertor configurations are available. A series of simulations for 8MW input power, five different electron densities at the LCFS (last closed flux surface) and the open/closed configurations were carried out. Approximately 10 times larger neutral pressure was observed under the dome structure compared with the open configuration, which is in good agreement with experimental measurements. In the case of the closed configuration, the leg regions have a large contribution of ionization to hydrogen recycling. In the case of high density discharges, however, electron temperature in the legs becomes low and the major contribution of ionization moves to the ergodic region. Significant influence of configurations is observed in the inboard side of LHD, where closed divertor components are installed but little influence is seen near the LCFS. (© 2014 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

A first-principle study of calcium-decorated BC2N sheet doped by boron or carbon for high hydrogen storage

Hydrogen adsorption and storage on calcium-decorated BC2N sheets doped by Boron or Carbon were investigated using the first-principles calculations. Unlike the weak bond between Ca atoms and pristine BC2N, doping boron or carbon atoms on BC2N sheet can significantly strengthen the Ca atoms on the BC2N, especially for BC2NBC and BC2NCN. It is observed that Ca decorated BC2NBC and BC2NCN possess strong donation and back-donation of Ca with the sheets, which is responsible for enhanced binding energy to eliminate the clustering problem. Up to four hydrogen molecules can stably attach to a Ca atom with an average adsorption energy of ∼0.3 eV, which is in the range that permits hydrogen recycling at ambient conditions. The Ca decorated BC2NBC and BC2NCN complexes can work as high-capacity hydrogen storage materials with the practical usable capacities of 8.36 wt% and 8.38 wt%, respectively.

Compact Design of 10 kW Proton Exchange Membrane Fuel Cell Stack Systems with Microcontroller Units

In this study, fuel, oxidant supply and cooling systems with microcontroller units (MCU) are developed in a compact design to fit two 5 kW proton exchange membrane fuel cell (PEMFC) stacks. At the initial stage, the testing facility of the system has a large volume (2.0 m × 2.0 m × 1.5 m) with a longer pipeline and excessive control sensors for safe testing. After recognizing the performance and stability of stack, the system is redesigned to fit in a limited space (0.4 m × 0.5 m × 0.8 m). Furthermore, the stack performance is studied under different hydrogen recycling modes. Then, two similar 5 kW stacks are directly coupled with diodes to obtain a higher power output and safe operation. The result shows that the efficiency of the 5 kW stack is 43.46% with a purge period of 2 min with hydrogen recycling and that the hydrogen utilization rate µf is 66.31%. In addition, the maximum power output of the twin-coupled module (a power module with two stacks in electrical cascade/parallel arrangement) is 9.52 kW.

Failure analysis of a slot-welded impeller of recycle hydrogen centrifugal compressor

A recently failed slot-welded impeller of recycle hydrogen centrifugal compressor has been investigated by material tests, theoretical calculation and numerical simulation, which focus on the environmental susceptibility of material, the corrosivity of environment and the characteristic components of the stress state. It is found that the matrix of FV520B precipitated hardening stainless steel used in the failed impeller did not match the optimal combination of strength, toughness and corrosion resistance, and large volumes of δ ferrite with banded appearance further increased the environmental susceptibility of material; the electrochemical corrosion environment came into being due to the presence of hydrogen sulfide and condensed water vapor in the recycle medium; the high hoop stress in the failed impeller was mainly caused by the shrink fit during manufacturing and the centrifugal force during operation. Based on these results, the failure of this slot-welded impeller can be mainly attributed to sulfide stress cracking (SSC), and hydrogen induced cracking (HIC) is found to accelerate SSC by breaking the continuity of material and hence increasing local stress. Additionally, the prevention and mitigation measures against failure have been discussed, which can provide some insight into improving the reliability of centrifugal compressor impeller.

High Ion Temperature Plasmas using an ICRF Wall-Conditioning Technique in the Large Helical Device

An ew effective wall-conditioning technique was proposed for realizing high ion temperature (Ti) plasmas in the Large Helical Device using the ion cyclotron range of frequency (ICRF) wave under the established magnetic confinement field. A series of ICRF heating discharges using He as the working gas was conducted ahead of the high-Ti plasma discharges. After sufficient repetitive wall-conditioning discharges, we observed a decrease in the line-averaged electron density, the formation of a peaked electron density profile, a reduction in the Hα emission, and an increase in the central Ti. The results suggest that the stored hydrogen inside the vacuum vessel structures, such as the first wall, the diverter, and other components, sputtered out owing to the He plasmas of the ICRF wall-conditioning discharges and the hydrogen recycling was decreased. Consequently, the ion heating power of NBI increased in the plasma core region, leading to higher central Ti.

Failure Analysis and Transformation of Hydrogen Compressor Dry Gas Seal

Recycle hydrogen compressor group is the core equipment of heavy coker gas oil hydrotreater unit of refinery. This compressor adopts tandem structure with intermediate labyrinth seal as its dry gas seal type. The compressor dry gas seal has officially been put into operation for six months, it damaged twice and caused the device to unplanned shutdown, seriously affected the long term operation of the device. During research and analysis on the seal of the unit, a series of problems were found, such as gas anti-channeling, sealing gas with oil etc. After transformation on the sealed gas supply system, the compressor achieved the purpose of long term stable running.

Chemical recycling of carbon dioxide emissions from a cement plant into dimethyl ether, a case study of an integrated process in France using a Reverse Water Gas Shift (RWGS) step

Recycling of carbon dioxide (CO2) and hydrogen (H2) into liquid fuel technology has recently gained wide public interest since it is a potential pathway to increase the liquid fuel supply and to mitigate CO2 emissions simultaneously.In France, the majority of the electricity production is derived from nuclear and renewable energy which have a low CO2 footprint. This electricity power enables a potential for massive hydrogen production with low carbon emissions.We studied the possibility to develop this technology at an industrial scale in the French context on a typical industrial example of a cement manufacture in the south of France.An integrated process is proposed, which enables the use of the heat released by the CO2 to fuel process to help to capture the CO2 released by the cement manufacture. Some technological issues are discussed, and a potential solution is proposed for the catalyst used in the critical step of the Reverse Water Gas-Shift reaction (RWGS) of the process.

Desorption of hydrogen trapped in carbon and graphite

Thermal desorption behavior of deuterium (D2) from isotropic graphites and a carbon fiber carbon composite (CFC) charged with D2 gas has been investigated to obtain information concerning hydrogen recycling and tritium inventory in fusion experimental devices as well as a futuristic fusion reactor. After thermal desorption experiments were conducted at temperatures up to 1740K, a desorption peak at approximately 1600K (peak 4) was discovered. This is in addition to the previously known peak at approximately 1300K (peak 3). Peak 3 can be attributed to the release of deuterium controlled by the diffusion process in a graphite filler grain and peak 4 can be attributed to the detrapping of deuterium released from an interstitial cluster loop edge site. Activation energies of peaks 3 and 4 are estimated to be 3.48 and 6.93eV, respectively.

Deuterium Uptake in Magnetic-Fusion Devices with Lithium-Conditioned Carbon Walls

Lithium wall conditioning has lowered hydrogenic recycling and dramatically improved plasma performance in many magnetic-fusion devices. In this Letter, we report quantum-classical atomistic simulations and laboratory experiments that elucidate the roles of lithium and oxygen in the uptake of hydrogen in amorphous carbon. Surprisingly, we show that lithium creates a high oxygen concentration on a carbon surface when bombarded by deuterium. Furthermore, surface oxygen, rather than lithium, plays the key role in trapping hydrogen.

Improvement of Plasma Performance with Lithium Wall Conditioning in Aditya Tokamak

Lithiumization of the vacuum vessel wall of the Aditya tokamak using a lithium rod exposed to glow discharge cleaning plasma has been done to understand its effect on plasma performance. After the Li-coating, an increment of ∼100 eV in plasma electron temperature has been observed in most of the discharges compared to discharges without Li coating, and the shot reproducibility is considerably improved. Detailed studies of impurity behaviour and hydrogen recycling are made in the Li coated discharges by observing spectral lines of hydrogen, carbon, and oxygen in the visible region using optical fiber, an interference filter, and PMT based systems. A large reduction in O I signal (up to ∼40% to 50%) and a 20% to 30% decrease of Hα signal indicate significant reduction of wall recycling. Furthermore, VUV emissions from O V and Fe XV monitored by a grazing incidence monochromator also show the reduction. Lower Fe XV emission indicates the declined impurity penetration to the core plasma in the Li coated discharges. Significant increase of the particle and energy confinement times and the reduction of Zeff of the plasma certainly indicate the improved plasma parameters in the Aditya tokamak after lithium wall conditioning.

Hydrogen isotope recycling at a tungsten target

Abstract Hydrogen recycling has been studied focusing on the neutral behavior in front of tungsten target in the plasma–wall interaction simulator APSEDAS and the tandem mirror GAMMA 10. The line intensity of hydrogen Balmer series decreased toward the target corresponding to a decrease in the electron density in APSEDAS. The relative population of n = 3 and n = 4 increased and that of n = 5 and n = 6 decreased just in front of the target ( Z α ) line decreased exponentially with distance from the target with two decay lengths: ∼16 mm and ∼53 mm. These two short decay lengths are attributed to the fact that a fraction of the reflected atoms and atoms dissociated from molecules are at excited energy states.

Detailed OEDGE modeling of core-pedestal fueling in DIII-D

Abstract The OEDGE code is used to model core fueling for attached L-mode plasmas and between edge localized modes (ELMs) for attached H-mode plasmas in DIII-D. Empirical plasma reconstruction has been used to determine the plasma conditions in these discharges. EIRENE is used to model the hydrogen recycling. Divertor recycling accounts for 65–100% of the core fueling. The fraction of the total divertor target flux ionized inside the separatrix ranges from 5% to 20%. The fraction of total wall flux ionized inside the separatrix ranges from 20% to 50%. Neutrals originating from wall regions closer to the separatrix are more likely to ionize in the confined plasma. Ionization in the confined plasma is concentrated below the midplane with peaks in the poloidal profiles just above the X -point. Radial core ionization in high density H-mode is peaked strongly near the separatrix.

Influence of Wall Conditioning on ADITYA Plasma Discharges

ADITYA (R0 = 75 cm, a = 25 cm), an ohmically heated circular limiter tokamak is regularly being operated to carry out several experiments related to controlled thermonuclear fusion research. In recent operational campaign, various experiments have been carried out to enhance the discharge performance as well as improve the plasma parameters. A comparative plasma discharges study with SiC and Graphite limiter was carried out to increase the plasma heating and reduce runaways. Excellent plasma heating has been observed in many discharges using Graphite limiter. Good repeatability of low hard X-rays, high temperature discharges was obtained. The control of plasma impurities and hydrogen recycling is very much essential for high performance discharges. The wall conditioning in ADITYA tokamak is carried out by hydrogen glow discharge cleaning (GDC), Pulse discharge cleaning and electron cyclotron resonance (ECR) discharge cleaning techniques with and without lithium wall coating. GDC assisted Lithiumization was found to be the most effective technique for substantial reduction in Ha and low Z (CIII & O-I) impurities. The partial pressure of mass number 18 (H2O) and 28 (N2/C2H4/CO) were regularly monitored before plasma discharge operation. Furthermore, experiment on optimization of pulse gas feed was helped in reducing wall loading and recycling. However, hard X-rays suppression with the application of multiple gas puff has been successfully achieved during negative converter operation, which led to the extension of plasma pulse length up to ∼ 250 ms. All the supporting facts and operation aspects are reported.

Calcium-decorated graphyne nanotubes as promising hydrogen storage media: A first-principles study

First principles calculations based on density functional theory are carried out to study the hydrogen storage properties of Ca-decorated graphyne nanotubes. The results show that Ca atoms can be adsorbed stably on the acetylenic ring of the graphyne nanotube (GNT) without Ca atom clustering. Both the polar interactions and the orbital hybridizations contribute to the adsorption of H2 molecules. The average adsorption energy is in the range of 0.13–0.33eV/H2 which is almost independent of the tube diameter. Each Ca atom can adsorb up to four H2 molecules due to the steric hindrance of the H2 molecules. With a hydrogen uptake of 7.44–8.96wt%, the Ca-decorated GNT is an optimal choice for hydrogen recycling at near ambient conditions.

Flowsheet development, process simulation and economic feasibility analysis for novel suspension ironmaking technology based on natural gas: Part 1 – Flowsheet and simulation for ironmaking with reformerless natural gas

A novel gas–solid suspension ironmaking process with much less energy consumption and carbon dioxide emissions than the current blast furnace technology is under development at the University of Utah. The proposed process is based on flash reduction of iron ore concentrate with a gaseous reagent, such as hydrogen, syngas and/or natural gas. This series of papers reports on the results of process simulation for the proposed process operated with natural gas. This Part 1 deals with simulation of a commercial scale reformerless ironmaking process with heat recovery and hydrogen recycling steps. Ironmaking was simulated in one-step and two-step process configurations. The results indicated that the proposed process would, depending on the process configuration, reduce carbon dioxide emissions by 39–51% and energy consumption by 32–44% compared with the average blast furnace process (61–66% if the lower heating value of natural gas is used). The sensitivity of the energy requirement to operating conditions was also examined.

Dynamic Models for Plasma-Wall Interactions

In theory and modeling of plasma-wall interactions, very different spatial and temporal scales need to be resolved. Hierarchy of material models (e.g. macroscopic transport, Kinetic Monte Carlo, Molecular Dynamics, and quantum models) used in fusion applications is reviewed and a way of their integration is highlighted. Physics background, theory and applications of macroscopic transport models, which are the main focus of the paper, are thoroughly discussed. The results on self-consistent macroscopic modeling of major physics phenomena, e.g. hydrogen recycling, retention, chemistry, chemical sputtering, and radiation enhanced sublimation for fusion related materials are presented. An example of coupled plasma and material transport simulations is given. The results on Molecular Dynamics modeling of deuterium irradiation of carbon leading to formation of supersaturated surfaces and chemical sputtering are presented (© 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Hydrogen Selective NH2‐MIL‐53(Al) MOF Membranes with High Permeability

AbstractHydrogen‐based energy is a promising renewable and clean resource. Thus, hydrogen selective microporous membranes with high performance and high stability are demanded. Novel NH2‐MIL‐53(Al) membranes are evaluated for hydrogen separation for this goal. Continuous NH2‐MIL‐53(Al) membranes have been prepared successfully on macroporous glass frit discs assisted with colloidal seeds. The gas sorption ability of NH2‐MIL‐53(Al) materials is studied by gas adsorption measurement. The isosteric heats of adsorption in a sequence of CO2 > N2 > CH4 ≈ H2 indicates different interactions between NH2‐MIL‐53(Al) framework and these gases. As‐prepared membranes are measured by single and binary gas permeation at different temperatures. The results of singe gas permeation show a decreasing permeance in an order of H2 > CH4 > N2 > CO2, suggesting that the diffusion and adsorption properties make significant contributions in the gas permeation through the membrane. In binary gas permeation, the NH2‐MIL‐53(Al) membrane shows high selectivity for H2 with separation factors of 20.7, 23.9 and 30.9 at room temperature (288 K) for H2 over CH4, N2 and CO2, respectively. In comparison to single gas permeation, a slightly higher separation factor is obtained due to the competitive adsorption effect between the gases in the porous MOF membrane. Additionally, the NH2‐MIL‐53(Al) membrane exhibits very high permeance for H2 in the mixtures separation (above 1.5 × 10−6 mol m−2 s−1 Pa−1) due to its large cavity, resulting in a very high separation power. The details of the temperature effect on the permeances of H2 over other gases are investigated from 288 to 353 K. The supported NH2‐MIL‐53(Al) membranes with high hydrogen separation power possess high stability, resistance to cracking, temperature cycling and show high reproducibility, necessary for the potential application to hydrogen recycling.

Lithium-based surfaces controlling fusion plasma behavior at the plasma-material interface

The plasma-material interface and its impact on the performance of magnetically confined thermonuclear fusion plasmas are considered to be one of the key scientific gaps in the realization of nuclear fusion power. At this interface, high particle and heat flux from the fusion plasma can limit the material’s lifetime and reliability and therefore hinder operation of the fusion device. Lithium-based surfaces are now being used in major magnetic confinement fusion devices and have observed profound effects on plasma performance including enhanced confinement, suppression and control of edge localized modes (ELM), lower hydrogen recycling and impurity suppression. The critical spatial scale length of deuterium and helium particle interactions in lithium ranges between 5–100 nm depending on the incident particle energies at the edge and magnetic configuration. Lithium-based surfaces also range from liquid state to solid lithium coatings on a variety of substrates (e.g., graphite, stainless steel, refractory metal W/Mo/etc., or porous metal structures). Temperature-dependent effects from lithium-based surfaces as plasma facing components (PFC) include magnetohydrodynamic (MHD) instability issues related to liquid lithium, surface impurity, and deuterium retention issues, and anomalous physical sputtering increase at temperatures above lithium’s melting point. The paper discusses the viability of lithium-based surfaces in future burning-plasma environments such as those found in ITER and DEMO-like fusion reactor devices.

Experimental investigation of density regimes in the helical divertor at TEXTOR

Using the capabilities of the dynamic ergodic divertor in the limiter tokamak TEXTOR, we have experimentally investigated the hydrogen recycling in a complex, three-dimensional, helical divertor structure similar to divertor structures found in stellarators. The observations were then compared with results from modelling with the three-dimensional transport code EMC3-EIRENE. The measurements showed that the recycling flux at the divertor target increases linearly with increasing plasma density, a high recycling regime is not observed. At highest plasma densities before the density limit disruption, the formation of a poloidally structured and helically inclined radiating belt, a helical divertor MARFE, is observed. The radial penetration depth of the neutral hydrogen particles (λn ≈ 3 cm) estimated from spectroscopic measurements was found to be often larger than the varying radial extent of the scrape-off layer of the helical divertor (few mm up to 6 cm) which points to convective heat transport reducing parallel temperature gradients and inhibiting flux amplification. The detailed comparison of the experimental observations and the modelling results showed agreement in this high density behaviour confirming the absence of a high recycling regime. Also agreement in the absolute values of the calculated and measured target particle fluxes was observed. Simulations using different cross-field transport coefficients showed, that this agreement is only found above a certain level of cross-field transport (D⊥ = 1 m2 s−1).