Damage associated with interactions between microstructural characteristics and hydrogen/methane gas mixtures of pipeline steels

There is no common standard for blended hydrogen use in the natural gas grid; hydrogen content is generally based on delivery systems and end-use applications. The need for a quantitative evaluation of hydrogen-natural gas mixtures related to the mechanical performance of materials is becoming increasingly evident to obtain long lifetime, safe, and reliable pipeline structures. This study attempts to provide experimental data on the effect of H₂ concentration in a methane/hydrogen (CH₄/H₂) gas mixture used in hydrogen transportation. The mechanical performance under various blended hydrogen concentrations was compared for three pipeline steels, API X42, X65, and X70. X65 exhibited the highest risk of hydrogen-assisted crack initiation in the CH₄/H₂ gas mixture in which brittle fractures were observed even at 1% H₂. The X42 and X70 samples exhibited a significant change in their fracture mechanism in a 30% H₂ gas mixture condition; however, their ductility remained unchanged. There was an insignificant difference in the hydrogen embrittlement indices of the three steels under 10 MPa of hydrogen gas. The coexistence of delamination along with the ferrite/pearlite interface, heterogeneous deformation in the radial direction, and abundance of nonmetallic MnS inclusions in the X65 sample may induce a high stress triaxiality at the gauge length at the beginning of the slow strain rate tensile process, thereby facilitating efficient hydrogen diffusion.     

Effects of CH4 and CO on hydrogen embrittlement susceptibility of X80 pipeline steel in hydrogen blended natural gas

The slow strain rate tensile experiments are carried out to investigate the tensile properties of X80 pipeline steel in hydrogen blended natural gas environments with different H₂/CH₄/CO contents. Mechanical properties and fracture morphologies are further analyzed. The results show that the hydrogen embrittlement susceptibility of X80 steel can be inhibited by the presence of CH₄/CO, and the inhibition mechanisms are discussed. When the CH₄ contents increase above 20 vol%, the inhibition on hydrogen embrittlement of X80 steel is stabilized. By comparison, the inhibitory effect of CO is more significant.     

Study on the stratification of the blended gas in the pipeline with hydrogen into natural gas

When blending hydrogen into existing natural gas pipelines, the non-uniform concentration distribution caused by the density difference between hydrogen and natural gas will result in the fluctuations of local hydrogen partial pressure, which may exceed the set one, leading to pipeline failure, leakage, measurement error, and terminal appliance. To solve the problem, the H₂–CH₄ stratification in the horizontal and undulated pipe was investigated experimentally and with numerical simulations. The results show that in the gas stagnant situation, hydrogen-methane blending process will cause an obvious stratification phenomenon. The relations between the elevation, pressure, hydrogen fraction, etc., and the gas stratification are figured out. Moreover, even when the blended gas flows at a low rate, the hydrogen-caused stratification should also be considered. Thereafter, the blended gas should be controlled into a situation with low pressure and high speed, which could help to set the pressure, speed, the fraction of H₂.     

Dissociative adsorption of hydrogen and methane molecules at high-angle grain boundaries of pipeline steel studied by density functional theory modeling

Pipelines provide an economic and efficient means for hydrogen transport, contributing to accelerated realization of a full-scale hydrogen economy. Dissociative adsorption of hydrogen molecules (H₂) occurring on pipe steels generates hydrogen atoms (H), potentially resulting in hydrogen embrittlement of the pipelines. This is particularly important for existing pipelines transporting hydrogen in blended form with methane (CH₄). In this work, a density functional theory model was developed to investigate the dissociative adsorption of H₂ and CH₄ at high-angle grain boundaries (HAGB), a typical type of hydrogen traps contained in steels, and the stable adsorption configurations. Results demonstrate that the dissociative adsorption of both H₂ and CH₄ at the HAGB is thermodynamically feasible under pipeline operating conditions. Compared with crystalline lattice sites, the HAGB possesses the most negative free energy change, a lower energy barrier and the lowest H-adsorption energy, making the HAGB, especially the quasi three-fold site, become the most stable site for hydrogen adsorption. The saturation coverage of hydrogen at HAGB is calculated to be 1.33. The iron-H bonds are formed at the HAGB by charge consumption at Fe atoms and electron accumulation at H atoms, following a so-called electron hybridization mechanism. The CH₄ adsorption at HAGB affects the H₂ adsorption. Without pre-adsorption of CH₄, the hydrogen adsorption at the HAGB is more stable. Although an elevated CH₄ partial pressure decreases the thermodynamic tendency for H₂ adsorption, it cannot hinder occurrence of the H₂ dissociative adsorption.     

Explosion-prevention strategies of airflow controlling and closed-inerting for hydrogen dilution in utility tunnel

Under the large-scale application of hydrogen energy and the acceleration of utility tunnel construction in China, the hydrogen pipeline would enter the utility tunnel soon. The explosion-prevention strategy is of important to hydrogen transportation in utility tunnel. Thus, a series of comparative studies were carried out in the present study, to explore the high efficiency dilution methods for unexpected hydrogen leak scenarios. (1) Effects of source type and domain extension were further validated based on our previous numerical model. The small-hole model was found to be simple and feasible for pipe release simulation, and has the same high accuracy like the notional nozzle model. The influence of unexpanded domain is acceptable. (2) Investigation of the explosion-prevention strategies was performed based on the finding of the worst leakage case, and hydrogen leaks at the middle of the upwind tunnel with upward leak direction was found to be the worst leakage case for the normal utility tunnel. (3) Compared with the layouts of lateral vents and the single horizontal air distributor, the middle exhaust vent was found to be the optimal airflow controlling strategy. (4) Furtherly, compared to the optimal airflow controlling strategy, closed-inerting was validated to be the most efficient dilution method. In the closed-inerting cases, the peak value of the flammable gas volume which is only ∼40% of the unimproved case appears. After that, the flammable cloud volume decays gradually, while the value increases steadily in the initial unimproved case. No obvious difference was found between the N₂ and CO₂ injection cases.     

A new energy efficient process for hydrogen purification using ZIF-8/glycol–water slurry: Experimental study and process modeling

Effective recovery of hydrogen from refinery off-gas and coke oven gas, in which hydrogen and methane are key components, is increasingly important for the development of hydrogen energy. In this paper, we introduced a new energy efficient process for hydrogen purification from CH₄/H₂ mixture. Firstly, we conducted a phase equilibrium experimental study for CH₄/H₂ in zeolitic imidazolate framework-8 (ZIF-8)/glycol–water slurry. The simple absorption and desorption configuration is adopted for the continuous separation of CH₄/H₂ using ZIF-8/glycol–water slurry. The multi-stage pseudo-absorption modeling approach was introduced for the modeling and simulation of the absorption–adsorption and desorption columns via using multiple flash modules in Aspen Plus. The binary interaction parameters in the thermodynamic model were fitted by experimental data within an acceptable error (4.93%). The operating conditions (i.e., the number of theoretical stages, feed stage, flash pressure, and desorption pressure) were determined to increase H₂ concentration in product and H₂ recovery ratio. The energy performance of the process was also evaluated. Given the feed gas contains 50 mol% H₂, the gas–slurry volume ratio of 43.27 is required to produce 95 mol% H₂ with a high recovery of 97.94%. The total energy consumption per unit volume of product is 0.06254 kW·h/Nm³. Results indicate that the hybrid absorption-adsorption process is a promising energy efficient technique to separate CH₄/H₂ in the future.     

Development and modelling of a novel electricity-hydrogen energy system based on reversible solid oxide cells and power to gas technology

Compared to the conventional thermal units and electrolytic devices, reversible fuel cells have very high efficiencies on both fuel cell mode of generating electricity and electrolysis mode of producing hydrogen or CH_x. However, previous studies about fuel cells and its benefits of power to gas are not fully investigated in the electricity-gas energy system. Moreover, state-of-art studies indicate that hydrogen could be directly injected to the existing natural gas (NG) pipeline within an amount of 5%–20%, which are considered to make a slight influence on the natural gas technologies. This work proposes a novel electricity-hydrogen energy system based on reversible solid oxide cells (RSOCs) to demonstrate the future vision of multi-energy systems on integrating multiple energy carriers such as electricity, pure hydrogen, synthetic natural gas (SNG) and mixed gas of H₂-natural gas. The P2G processes of RSOC are sub-divided modelled by power to H₂ (P2H) and power to SNG (P2SNG). The co-electrolysis/generation processes and time-dependent start-up costs are considered within a unit commitment model of RSOC. The proposed electricity-hydrogen energy system optimization model is formulated as mixed-integer linear programming (MILP), where the H₂-blended mixed gas flow is linearized by an incremental linearize relaxation technic. The aim of the optimization is to reduce the energy cost and enhance the system's ability to integrate sufficient renewables through NG networks. Besides quantified the benefits of renewable level and H₂ injection limit on the P2G process, the numerical results show that RSOC combined with H₂/SNG injection results in productive economic and environmental benefits through the energy system.     

Effects of hydrogen addition on combustion and flame propagation characteristics of laser ignited methane/air mixtures

In this study, effects of hydrogen addition on combustion and flame propagation characteristics of methane/air mixtures were investigated in a constant volume combustion chamber. Tested gas mixtures are 100% CH₄, 05% H₂ – 95% CH₄, 10% H₂ – 90% CH₄ and 15% H₂ – 85% CH₄, and such mixtures were ignited using a passively Q-switched Nd:YAG laser ignitor which has a pulse energy of 12.3 mJ, pulse duration of 2.4 ns and wave length of 1064 nm. A Schlieren setup coupled with a high-speed camera enabled evaluating flame propagation behavior, while pressure curve analysis provided necessary data for characterization of combustion properties. Additionally, lean flammability limits of gas mixtures were also determined at the test conditions. The unique properties of hydrogen (such as low density, high reactivity, high diffusivity etc) widened lean flammability limit. Rate of pressure rise and measured pressure values increased with hydrogen addition, regardless of the air-fuel equivalence ratio (λ). Lastly, hydrogen addition uniformly affected flame propagation characteristics and flame luminosity. Combustion process became more stable with hydrogen addition.     

Prediction of the liftoff,blowout and blowoff stability limits of pure hydrogen and hydrogen/hydrocarbon mixture jet flames

The paper presents experimental studies of the liftoff and blowout stability parameters of pure hydrogen, hydrogen/propane and hydrogen/methane jet flames using a 2 mm burner. Carbon dioxide and Argon gas were also used in the study for the comparison with hydrocarbon fuel. Comparisons of the stability of H₂/C₃H₈, H₂/CH₄ and H₂/CO₂ flames showed that H₂/C₃H₈ produced the highest liftoff height and H₂/CH₄ required highest liftoff, blowoff and blowout velocities. The non-dimensional analysis of liftoff height was used to correlate liftoff data of H₂, H₂/C₃H₈, H₂/CO₂, C₃H₈ and H₂/Ar jet flames tested in the 2 mm burner. The suitability of extending the empirical correlations based on hydrocarbon flames to both hydrogen and hydrogen/hydrocarbon flames was examined.     

Hydrogen permeation studies of composite supported alumina-carbon molecular sieves membranes: Separation of diluted hydrogen from mixtures with methane

One alternative for the storage and transport of hydrogen is blending a low amount of hydrogen (up to 15 or 20%) into existing natural gas grids. When demanded, hydrogen can be then separated, close to the end users using membranes. In this work, composite alumina carbon molecular sieves membranes (Al-CMSM) supported on tubular porous alumina have been prepared and characterized. Single gas permeation studies showed that the H₂/CH₄ separation properties at 30 °C are well above the Robeson limit of polymeric membranes. H₂ permeation studies of the H₂–CH₄ mixture gases, containing 5–20% of H₂ show that the H₂ purity depends on the H₂ content in the feed and the operating temperature. In the best scenario investigated in this work, for samples containing 10% of H₂ with an inlet pressure of 7.5 bar and permeated pressure of 0.01 bar at 30 °C, the H₂ purity obtained was 99.4%.     

Hydrogen separation and purification using crosslinkable PDMS/zeolite A nanoparticles mixed matrix membranes

The transport properties of gases in polydimethylsiloxane (PDMS)/zeolite A mixed matrix membranes (MMMs) were determined based on pure gas permeation experiments. MMMs were prepared by incorporating zeolite 4A nanoparticles into a PDMS matrix using a new procedure. The permeation rates of C₃H₈, CH₄, CO₂, and H₂ were evaluated through a dense homogeneous pure PDMS membrane and PDMS/4A MMMs to assess the viability of these membranes for natural gas sweetening and hydrogen purification. SEM investigations showed good adhesion of the polymer to the zeolite in MMMs. Permeation performance of the membranes was also investigated using a laboratory-scale gas separation apparatus and effects of feed pressure, zeolite loading and pore size of zeolite on the gas separation performance of the MMMs were evaluated. The MMMs exhibited both higher selectivity of H₂/CH₄ and H₂ permeability as compared with the neat PDMS membrane, suggesting that these membranes are very promising for gas separations such as H₂/CH₄ separation.     

Dry and steam reforming of biomass pyrolysis gas for rich hydrogen gas

Biomass pyrolysis gas (including H₂, CO, CH₄, CO₂, C₂H₄, C₂H₆ and etc.) reforming for hydrogen production over Ni/Fe/Ce/Al₂O₃ catalysts was presented in this study. This study investigated how the operating conditions, such as the calcinations temperature of catalysts, the reaction temperature, the gas hourly space velocity (GHSV) and the ratio of H₂O/C, affect the conversion of CH₄ and CO₂ and the selectivity of hydrogen from dry and steam reforming of pyrolysis gas. The experimental results indicated that, under the conditions: the reaction temperature of 600 °C, the GHSV of 900 h⁻¹ and H₂O/C of 0.92, the reaction efficiency is the optimal. Especially, the concentration of H₂, CO, CH₄, CO₂, and C₂H_n (C₂H₄ and C₂H₆) were 36.80%, 10.48%, 9.61%, 42.62%, 0.49% respectively. The conversion of CH₄ and CO₂ reached 45.9% and 51.09%, respectively. There were all kinds of reactions during the processing of reforming of pyrolysis gas. And the main reactions changed with the operation condition. It was due to the promoting or inhibiting interaction among different constituents in the pyrolysis gas and the different activity of catalysts in the different operation condition.     

Optimization of tri-reformer reactor to produce synthesis gas for methanol production using differential evolution (DE) method

This paper presents a study on optimization of a fixed bed tri-reformer reactor (TR). This reactor has been used instead of conventional steam reformer (CSR) and auto thermal reformer (CAR). A theoretical investigation has been performed in order to evaluate the optimal operating conditions and enhancement of methane conversion, hydrogen production and desired H₂/CO ratio as a synthesis gas for methanol production. A mathematical heterogeneous model has been used to simulate the reactor. The process performance under steady state conditions was analyzed with respect to key operational parameters (inlet temperature, O₂/CH₄, CO₂/CH₄ and steam/CH₄ ratios). The influence of these parameters on gas temperature, methane conversion, hydrogen production and H₂/CO ratio was investigated. Model validation was carried out by comparison of the reforming model results with industrial data of CSR. Differential evolution (DE) method was applied as a powerful method for optimization. Optimum feed temperature and reactant ratios (CH₄/CO₂/H₂O/O₂) are 1100 K and 1/1.3/2.46/0.47 respectively. The optimized TR has enhanced methane conversion by 3.8% relative to industrial reformers in a single reactor. Methane conversion, hydrogen yield and H₂/CO ratio in optimized TR are 97.9%, 1.84 and 1.7 respectively. The optimization results of tri-reformer were compared with the corresponding predictions from process simulation software operated at the same feed conditions.     

Development of a novel simulator for modelling underground hydrogen and gas mixture storage

Underground hydrogen storage can store grid-scale energy for balancing both short-term and long-term inter-seasonal supply and demand. However, there is no numerical simulator which is dedicated to the design and optimisation of such energy storage technology at grid scale. This study develops novel simulation capabilities for GPSFLOW (General Purpose Subsurface Flow Simulator) for modelling grid-scale hydrogen and gas mixture (e.g., H₂–CO₂–CH₄–N₂) storage in cavern, deep saline aquifers and depleted gas fields.The accuracy of GPSFLOW is verified by comparisons against the National Institute of Standard and Technology (NIST) online thermophysical database and reported lab experiments, over a range of temperatures from 20 to 200 °C and pressure up to 1000 bar. The simulator is benchmarked against an existing model for modelling pure H₂ storage in a synthetic aquifer. Several underground hydrogen storage scenarios including H₂ storage in a synthetic salt cavern, H₂ injection into a CH₄-saturated aquifer experiment, and hydrogen storage in a depleted gas field using CO₂ as a cushion gas are used to test the GPSFLOW's modelling capability. The results show that GPSFLOW offers a robust numerical tool to model underground hydrogen storage and gas mixture at grid scale on multiple parallel computing platforms.     

Separation of H2/CH4 gas mixture through graphenylene membrane with functionalized nanopore: A computational study

Using molecular dynamics (MD) simulations, we investigated the performance of graphenylene membrane with functionalized nanopore in the H₂/CH₄ separation. In the present work, we studied the impact of functionalized nanopore, system temperature (298, 323, and 348 K), applied difference pressure (up to 2 MPa), and feed composition on the H₂/CH₄ separation performance. The passage of gas molecules across the nanopore was monitored within the simulations, and the permeance was determined under applied conditions. The results revealed that the size of gas molecules and its interaction with the membrane nanopore are two important factors in the separation performance of H₂/CH₄ gas mixture. It is also found that H₂ molecules can easily pass through the studied membranes, whereas no CH₄ molecule was seen in the permeate side, which confirms the ultrahigh selectivity of H₂ over CH₄. Furthermore, the maximum H₂ permeance of 1.95 × 10⁵ GPU through the pore 1 was obtained at 1.5 MPa, which was higher than that of 1.93 × 10⁵ GPU through pore 2. The results also demonstrated that the system temperature doesn't have any effect on the membrane performance. To this end, the permeance of H₂ molecules through the studied membranes obviously increased with raising the ration of H₂ molecules in the feed composition. Due to high selectivity and permeance, the graphenylene membrane with functionalized nanopore is expected to have promising applications in hydrogen separation from H₂/CH₄ mixed gas.     

Thermally rearranged (TR) HAB-6FDA nanocomposite membranes for hydrogen separation

Thermally rearranged (TR) polymers exhibited a good balance of high permeability and high selectivity. For this purpose HAB-6FDA polyimide was synthesized from 3,3 dihydroxy-4,4-diamino-biphenyl (HAB) and 2,2-bis-(3,4-dicarboxyphenyl) hexafluoro propane dianhydride (6FDA) by chemical imidization. Initially, the sample was modified from pure polymer to silica nanofiller doped polymer membrane. Further the modification was done by thermal rearrangement reaction at 350 °C temperature. This modification causes a mass loss in polymer structure and therefore enhances the fractional free volume (FFV). The gases used for the permeation test were H₂, CO₂, N₂ and CH₄. Selectivity was calculated for H₂/CO₂, H₂/N₂ and H₂/CH₄ gas pairs and plotted in the Robeson's 2008 upper bound and compared with reported data. The transport properties of these gases have been compared with the unmodified membrane. Permeability of all the gases has increased to that of unmodified polymer membrane. Thermally rearranged polymer nanocomposite exhibits higher gas permeability than that of silica doped and pure polymer. Also the selectivity for H₂/CO₂ and H₂/N₂ gas pairs exceeds towards Robeson's upper bound limit. It crosses this limit dramatically for H₂/CH₄ gas pair. Polymer nanocomposite can be utilized to obtain high purity hydrogen gas for refinery and petrochemical applications.     

Experimental study on premixed hydrogen/air and hydrogen–methane/air mixtures explosion in 90 degree bend pipeline

Nowadays, hydrogen is being utilized massively in industries as a clean fuel. Displacing of hydrogen due to unique chemical and physical properties has adversely affect on pipeline network, hence increases the potential risk of explosion. This study was carried out to determine the flame propagation of hydrogen/air and hydrogen–methane/air mixtures in pipeline. A 90° pipeline with L/D ratio of 40 was used. Pure hydrogen/air mixture with equivalence ratio, φ = 0.13, 0.17, 0.2, 0.24, 0.27 and 0.30 were used in this work. Different composition of hydrogen–methane–air mixtures were tested in this study i.e. 3%H₂ + 97CH₄, 4%H₂ + 96CH₄, 6%H₂ + 94CH₄ and 8%H₂ + 92CH₄. All mixtures were operated at ambient condition. The results show that bending is the critical part of pipeline and higher concentration of hydrogen can affect on maximum overpressure, flame speed and temperature rise of both pure hydrogen/air and methane-hydrogen/air mixtures.     

Effect of impurities of CH3OH,CH3COOH,and KOH on aqueous phase reforming of glycerol over mesoporous Ni–Cu/CeO2 catalyst

Impurities are inevitable in crude glycerol, a by-product of biodiesel, which has a great influence on aqueous phase reforming (APR). This work investigates three impurities (CH₃OH, CH₃COOH, and KOH) in the aqueous phase reforming of glycerol (GAPR) using a mesoporous Ni–Cu/CeO₂ catalyst at three temperatures. The experiment results indicate that the increase of temperature is beneficial to the conversion of glycerol into gas products, but not favor to the proportion of H₂ in the gas phase. The presence of CH₃OH almost has not affected the total gas volume, while CH₃COOH and KOH decreased and increased the gas volume, respectively. The deactivation of the catalyst occurs under acidic conditions because the active phase Ni on the catalyst surface is lost in the hydrogen evolution reaction. KOH has the greatest influence on the gas phase composition, which greatly increases the H₂ production and the proportion of H₂. The results of liquid-phase solution analysis show that the addition of CH₃COOH promoted the dehydration of glycerol, which is contrary to the results obtained by adding KOH. CH₃OH, as the final product of glycerol dehydrogenation and decarbonization, is added to the initial solution, which will be conducive to the dehydration reaction. The addition of CaO can increase the H₂ production in the APR of glycerol solution containing impurities.     

Ammonia-hydrogen-air gas turbine cycle and control analyses

Blending ammonia with hydrogen has the potential of replacing conventional hydrocarbon fuels to reduce carbon emissions. However, the uncertainties of determining safe, stable, and efficient operating conditions remain a great challenge. Furthermore, although control technologies have been in the scope of interest for gas turbine manufacturers, those are not yet specialized for NH₃–H₂/air gas turbines. Therefore, this paper identifies the cycle performance of an NH₃–H₂/air gas turbine in comparison to a CH₄/air gas turbine, thus highlighting the operating conditions in which the NH₃–H₂/air gas turbines show higher performance compared to the CH₄/air gas turbines. The results have been obtained by developing a LabVIEW code which has also been utilized to serve as a control code for the NH₃–H₂/air and CH₄/air gas turbines. The system identification stage of calibrating the controller has been achieved for both gas turbines by determining the system's sensitivities, thus providing an accurate calibration of the controlling parameters.     

Effect of low partial hydrogen in a mixture with methane on the mechanical properties of X70 pipeline steel

In this study, the effect of a low partial hydrogen in a mixture with natural gas on the tensile, notched tensile properties, and fracture toughness of pipeline steel X70 is investigated. An artificial HE aging is simulated by exposing the tested sample to the mixture gas condition for 720 h. In addition, a series of tests is conducted in ambient air and 10 MPa of 100% He and H₂. Overall, 10 MPa of 100% H₂ significantly degrades the mechanical properties of an X70 pipeline steel. However, it is observed that the 10 MPa gas mixture with 1% H₂ does not affect the mechanical properties when tested with a smooth tensile specimen. In the notched tensile test, a significant reduction in loss in the area is observed when tested with a notched specimen with a notch radius of 0.083 mm. It is also confirmed that a 10-MPa gas mixture with 1% H₂ causes a remarkable reduction in the toughness. The influence of the exposure time to 1% hydrogen in a mixture with natural gas was found to be minor.