Feasibility analysis of blending hydrogen into natural gas networks

Hydrogen fuel has the potential to mitigate the negative effects of greenhouse gases and climate change by neutralizing carbon emissions. Transporting large volume of hydrogen through pipelines needs hydrogen-specific infrastructure such as hydrogen pipelines and compressors, which can become an economic barrier. Thus, the idea of blending hydrogen into existing natural gas pipelines arises as a potential alternative for transporting hydrogen economically by using existing natural gas grids. However, there are several potential issues that must be considered when blending hydrogen into natural gas pipelines. Hydrogen has different physical and chemical properties from natural gas, including a smaller size and lighter weight, which require higher operating pressures to deliver the same amount of energy as natural gas. Additionally, hydrogen's small molecular size and lower ignition energy make it more likely to permeate through pipeline materials and seals, leading to degradation, and its wider flammability limits make it a safety hazard when leaks occur. In this study, we investigate these potential issues through simulation and technical surveys. We develop a gas hydraulic model to simulate the physical characteristics of a transmission and a distribution pipeline. This model is used throughout the study to visualize the potential impacts of switching from natural gas to hydrogen, and to investigate potential problems and solutions. Furthermore, we develop a Real-Time Transient Model (RTTM) to address the compatibility of current computational pipeline monitoring (CPM) based leak detection methods with blended hydrogen. Finally, we suggest the optimal hydrogen concentration for this model, and investigate the amount of carbon reduction that could be achieved, while considering the energy needs of the system.     

Prediction of confined,vented methane-hydrogen explosions using a computational fluid dynamic approach

Hydrogen is seen as an important energy carrier for the future, with a great benefit being carbon-free emissions at its point of use. A hydrogen transport system between manufacturing sites and end users is required, and one solution proposed is its addition to existing natural gas pipeline networks. A major concern with this approach is that the explosion hazard may be increased, relative to natural gas, should an accidental release occur. This paper describes a mathematical model of confined, vented explosions of mixtures of methane and hydrogen of value in performing consequence and risk assessments. The model is based on solutions of averaged forms of the Navier–Stokes equations, with the equation set closed using k-? and second-moment turbulence models, and the turbulent burning velocity determined from correlations of data on CH₄–H₂ mixtures reported in the literature. Predictions derived for explosions in a 70 m³ vessel, with and without internal pipe congestion, show reasonable agreement with available data, and demonstrate that hydrogen addition can have a significant effect on overpressure generation. Conclusions drawn from the calculations go some way to identifying safe operating limits for hydrogen addition.     

The development of natural gas and hydrogen pipeline capital cost estimating equations

Natural gas pipeline cost data collected by the Oil and Gas Journal (O&GJ) [1] for interstate pipelines constructed from 1980 through 2017 were used to develop capital cost estimating equations that are a function of pipeline diameter, length, and U.S. region. Equations were developed for material, labor, miscellaneous, and right-of-way costs, the four cost components in the O&GJ data, for six different regions of the United States (U.S.). Each equation is a function of pipeline diameter and length.Adjustment mechanisms were then developed for converting the natural gas pipeline equations into equations for estimating the costs of hydrogen pipelines. These adjustments were based in part on an analysis completed by the National Institute for Standards and Technology (NIST) [2,3]. The results of this work were used to update cost models in the Hydrogen Delivery Scenario Analysis Model (HDSAM) [4], developed by Argonne National Laboratory for the U.S. Department of Energy's Hydrogen Program. Our analysis shows a wide range of pipeline cost across different U.S. regions, especially with respect to labor and right-of-way costs. The developed cost formulas for hydrogen pipelines are both important and timely as hydrogen is being considered as a zero-carbon energy carrier with the potential to decarbonize all energy sectors, and the cost of hydrogen transportation is essential for techno-economic analysis of its potential use in these sectors.     

Experimental analysis on the effect of pipe and orifice diameter in inter tank hydrogen transfer

Hydrogen is an energy carrier which can be utilized in many sectors like stationary and transportation energy with nearly zero emission. Hydrogen energy is more efficient when compared to other energy sources. Hydrogen can be a replacement for fossil fuels in future as it emits only water when it is burned. In this work a mathematical model of transfer of hydrogen between two tanks has been developed using MATLAB simulink software version 21. Flow of hydrogen inside the pipe is controlled by orifice and diameter of this orifice and pipe diameter itself has some impact on outcome parameters such as inlet temperature of pipe, outlet temperature of pipe, heat transfer from one tank to other tank and hydrogen gas flow rate. The influence of orifice diameter as well as initial pressures on outcome parameters of hydrogen gas transfer model has analyzed in this work. From the simulation results it is inferred that when one initial pressure kept constant and other initial pressure keep on varying, no change in inlet temperature, decrease in outlet temperature, increase in heat transfer and increase in gas flow rate were observed when orifice diameter increase in size from 2 cm then 4 cm and then 6 cm. The research work has significant guidance for safety and efficient way of transporting hydrogen through pipeline from one tank to other tank.     

Experimental study of hydrogen explosion in repeated pipe congestion – Part 2: Effects of increase in hydrogen concentration in hydrogen-methane-air mixture

Hydrogen is seen as an important energy carrier for the future which offers carbon free emissions. At present it is mainly used in refueling hydrogen fuel cell cars. However, it can also be used together with natural gas in existing gas fired equipment with the benefit of lower carbon emissions. This can be achieved by introducing hydrogen into existing natural gas pipelines. These pipelines are designed, constructed and operated to safely transport natural gas, which is mostly methane. Because hydrogen has significantly different physical and chemical properties than natural gas, any addition of hydrogen my adversely affect the integrity of the pipeline network, increasing the likelihood and consequences of an accidental leak. Since it increases the likelihood and consequences of an accidental leak, it increases the risk of explosion. In order to address various safety issues related to addition of hydrogen in to a natural gas pipeline a EU project NATURALHY was introduced. A major objective of the NATURALHY project was to identify how much hydrogen could be introduced into the natural gas pipeline network. Such that it does not adversely impact the safety of the pipeline network and significantly increase the risk to the public. This paper reports experimental work conducted to measure the explosion overpressure generated by ignition of hydrogen-methane-air mixture in a highly congested region consisting of interconnected pipes. The composition of the methane/hydrogen mixture used was varied from 0% hydrogen (100% methane) to 100% hydrogen (0% methane) to understand its effect on generated explosion overpressure. It was observed that the maximum overpressures generated by methane-hydrogen mixtures with 25% (by volume) or less hydrogen content are not likely to be significantly greater than those generated by methane alone. Therefore, it can be concluded that the addition of less than 25% by volume of hydrogen into pipeline networks would not significantly increase the risk of explosion.     

Investigation of visible light emission from hydrogen-air research flames

Due to the urgency of reducing greenhouse gases in the combustion process, low-carbon renewable gaseous fuels are needed to replace the pipeline natural gas. Hydrogen is a competitive sustainable energy source, and also a promising energy carrier because of its zero-carbon property and low molecular weight. This study analyzed the flame characteristics of a cooktop burner operating on different natural gas/hydrogen mixtures. As hydrogen percentage increasing from 0% to 75% in the fuel mixture, more reddish color was observed in the flame, which is against the scientific fact that hydrogen flame color is usually pale blue color or even invisible under normal light condition. Therefore, combustion experiments and electron microscopy analysis are conducted to track the source of the abnormal color in the flame. The results suggest that the abnormal reddish flame color is from hydrogen embrittlement on the storage and transport facilities.     

A multi-objective model for optimizing hydrogen injected-high pressure natural gas pipeline networks

The paper develops a statistical model for optimizing the Hydrogen-injected Natural gas (H-NG) high-pressure pipeline network. Gas hydrodynamic principles are utilized to construct the pipeline and compressor station model. The model developed is implemented on a pipeline grid that is supposed to carry Hydrogen as an energy carrier in a natural gas-carrying pipeline. The paper aims to optimize different objectives using ant colony optimization (ACO). The first objective includes a single objective optimization problem that evaluates the maximum permissible hydrogen amounts blended with natural gas (NG) for a set of pipeline constraints. We also evaluated the variations in operational variables on injecting Hydrogen into the natural gas pipeline networks at varying fractions. The study further develops a multi-objective optimization model that includes bi-objective and tri-objective problems and is optimized using ACO. Traditional studies have focused on single-objective optimization with minimal bi-objective issues. In addition, none of the earlier research has shown the effect of introducing Hydrogen to the NG network using tri-objective function evaluations. The bi-objective and tri-objective functions help evaluate the effect of injecting Hydrogen on different operational parameters. The study further attempts to fill the gap by detailing the modelling equations implemented through a bi-objective and tri-objective function for the H-NG pipeline network and optimized through ACO. Pareto fronts that show the tradeoff between the different objectives for the multi-objective problem have been generated. The primary objective of the bi-objective and tri-objective optimization problems is maximizing hydrogen mole percent in natural gas. The other objective chosen is minimizing compressor fuel consumption and maximizing delivery pressure, throughput, and power delivered at the delivery station. The findings will serve as a roadmap for pipeline operators interested in repurposing natural gas pipeline networks to transport hydrogen and natural gas blend (H-NG) and seeking to reduce carbon intensity per unit of energy-delivered fuel.     

Comparisons of hazard distances and accident durations between hydrogen vehicles and CNG vehicles

A comparison study is conducted to reveal the differences of hazard distances and accident durations between hydrogen vehicles and CNG vehicles during a representative accident in an open environment, i.e gas release from thermally-activated pressure relief device (TPRD). The analysis is performed for the scenario of impinging jet fires released from 4.2 mm TPRD diameter, with release inventory assumption on the basis of similar driving range: 4 kg hydrogen storage at 35 MPa and 20 kg methane storage at 25 MPa. Results show that the release duration for CNG vehicle is over two times longer than that for hydrogen vehicle, indicating that CNG vehicle jet fire accident is more time-consuming and firefighters have to wait a longer time before they can safely approach the vehicle. For both hydrogen vehicle and CNG vehicle, the longest hazard distance near the ground occur at a few seconds after the initiation of the TPRD. Afterwards the flames will shrink and the hazard distances will decrease. For firefighters with bunker gear, they must stand at least 6 m and 14 m away from the hydrogen vehicle and CNG vehicle, respectively. For general public, a perimeter of 12 m and 29 m should be set around the accident scene for hydrogen vehicle and CNG vehicle, respectively.     

Effect of hydrogen blending on the energy capacity of natural gas transmission networks

In this paper the effects of hydrogen on the transport of natural gas-hydrogen mixture in a high-pressure natural gas transmission system are investigated in detail. Our research focuses on the decrease in transferable energy content under identical operating conditions as hydrogen is blended in the gas transmission network. Based on the extensive literature review the outstanding challenges and key questions of using hydrogen in the natural gas system are introduced. In our research the transmissible energy factor - TEF - is defined that quantifies the relative energy capacity of the pipeline caused by hydrogen blending. A new equation is proposed in this paper to find the value of TEF at specific pressure and temperature conditions for different hydrogen concentrations. This practical equation helps the natural gas system operators in the decision-making process when hydrogen emerges in the gas transmission system. In this paper the change of the compression power requirement, which increases significantly with hydrogen blending, is investigated in detail.     

Operation optimization for gas-electric integrated energy system with hydrogen storage module

Hydrogen is gradually becoming one of the important carriers of global energy transformation and development. To analyze the influence of the hydrogen storage module (HSM) on the operation of the gas-electricity integrated energy system, a comprehensive energy system model consisting of wind turbines, gas turbines, power-to-hydrogen (P2H) unit, and HSM is proposed in this paper. The model couples the natural gas network and power grid bidirectionally, and establishes a mixed integer nonlinear programming problem considering HSM. The linearization model of the natural gas pipeline flow equation and the generator set equation is constructed by piecewise linearization method to improve the efficiency of solving the model. And the energy flow distribution in the gas-electricity integrated energy system is finally solved. In Model 1, compared with not considering the installation of P2H units, when the hydrogen doping ratio is 10%, the operating cost can be reduced by 6.63%, and the wind curtailment cost can be reduced by 17.54%, and the carbon emission can be reduced by 298.7 tons. The optimization results of Model 2 reveal that compared with no HSM, the system operating cost is reduced by 5.96%, the hydrogen content level in the natural gas pipeline network is increased by 42.12%, and the carbon emission of the system is reduced by 117.6 tons, and the fluctuation of wind power is suppressed. This study demonstrates the feasibility of large-scale absorption of renewable energy through HSM.     

Fire prevention technical rule for gaseous hydrogen transport in pipelines

This paper presents the current results of the theoretical and experimental activity carried out by the Italian Working Group on the hydrogen fire prevention safety issues in the field of the hydrogen transport in pipelines [Grasso N, Ciannelli N, Pilo F, Carcassi M, Ceccherini F. Fire prevention technical rule for gaseous hydrogen refuelling stations. Proceedings of the International Conference on Hydrogen Safety, 8–10 September 2005, Pisa, Paper 420064]. From the theoretical point of view a draft document has been produced beginning from the Italian regulations in force on the natural gas pipelines; these have been reviewed, corrected and integrated with instructions suitable to use with hydrogen gas. From the experimental point of view a suitable apparatus has been designed and installed at the University of Pisa; this apparatus will allow simulations of hydrogen releases from a pipeline with or without ignition of the hydrogen–air mixture. The experimental data will help the completion of the above-mentioned draft document with the instructions about the safety distances. However, in the opinion of the Group, the work on the text contents is concluded and the document is ready to be discussed with the Italian stakeholders involved in the hydrogen applications.     

中国规模化氢能供应链的经济性分析

    目的   文章研究规模化氢能供应链的经济性,未来十年,氢能作为战略能源将会重构社会的能源结构,并影响未来社会能源总成本。预测大规模氢能时代的制氢、储氢、输氢、分销、应用的成本,和市场化的趋势有着重要的意义。氢气由于高储运成本,用途、品质的多样性,氢气市场存在分层结构。分析氢能与常规能源的可比价格,提出原油当量价格(POE)的概念,预测未来氢能价格的合理区间。解决供应链问题是获得低成本氢能的关键,由此提出干线门站模式,解决绿氢的资源分布与长距离输送氢能的问题。    方法   利用平准化氢气成本(LCOH)分析模型,测算大型光伏制氢管道输氢LCOH,分析大规模可再生能源制氢输氢的经济性。利用氢能供应链的储、输、卸六个象限成本公式,分析气氢、液氢、固氢、有机氢、管道氢等不同储运技术,短距离氢储运成本,分析门站后输氢的场景和成本,预测短距离输氢的成本趋势。    结果   研究表明:我国有丰富的绿氢资源,随着投资下降,预计大规模绿氢管道输送的城市门站LCOH将低于2.0 RMB/Nm3,将成为未来主要的氢源。当前,氢储运技术气氢、液氢、甲醇、合成氨、有机氢、固氢、管道氢,随着规模的增加实现远距离输送。在现有的技术下,城市门站到终端的输送,氢短距输送（<100 km）测算成本都在1.2 RMB/Nm3以下,由此评估的氢能供应链的总成本,干线门站模式下氢能最终到达终端的价格约为3.2 RMB/Nm3,当量价格POE与汽油价格接近,考虑燃料电池的能效因素,氢能汽车在4.0 RMB/Nm3的氢价下,具有比汽油车更低的百公里燃料费用。    结论   因此,氢能作为战略能源,在无补贴的情况下实现中国氢能源的绿氢替代,在技术经济上是可行的。     

氢气管输技术研究进展

利用现有“全国一张网”的天然气管道设施,将氢气掺入天然气管道输送,可有效解决中国氢气规模化输送难题。该文综述目前关于氢气管道输送的研究成果,总结氢气管道建设现状;分析输氢工艺安全性,阐述管线泄漏的危害性及防护措施,分别讨论高压输送管道、中低压配送管道和管道焊缝的相容性;归纳目前的燃气互换性方法及设备适应性。指出了目前氢气管输面临的问题：掺氢比例等参数对氢气渗透、聚集、泄漏、喷射火灾等安全问题的影响尚不明确;氢气与典型管材的相容性研究不足;缺少纯氢和掺氢管道输送技术相关标准规范体系。     

Development of uniform harm criteria for use in quantitative risk analysis of the hydrogen infrastructure

This paper discusses the preliminary results of the Risk Management subtask efforts within the International Energy Agency (IEA) Hydrogen Implementing Agreement (HIA) Task 19 on Hydrogen Safety to develop uniform harm criteria for use in the Quantitative Risk Assessments (QRAs) of hydrogen facilities. The IEA HIA Task 19 efforts are focused on developing guidelines and criteria for performing QRAs of hydrogen facilities. The performance of QRAs requires that the level of harm that is represented in the risk evaluation be established using deterministic models. The level of harm is a function of the type and level of hazard. The principle hazard associated with hydrogen facilities is uncontrolled accumulation of hydrogen in (semi) confined spaces and consecutive ignition. Another significant hazard is combustion of accidentally released hydrogen gas or liquid, which may or may not happen instantaneously. The primary consequences from fire hazards consist of personnel injuries or fatalities, or facility and equipment damage due to high air temperatures, radiant heat fluxes, or direct contact with hydrogen flames. The possible consequences of explosions on humans and structures or equipment include blast wave overpressure effects, impact from fragments generated by the explosion, the collapse of buildings, and the heat effects from subsequent fire balls. A harm criterion is used to translate the consequences of an accident, evaluated from deterministic models, to a probability of harm to people, structures, or components. Different methods can be used to establish harm criteria including the use of threshold consequence levels and continuous functions that relate the level of a hazard to a probability of damage. This paper presents a survey of harm criteria that can be utilized in QRAs and makes recommendations on the criteria that should be utilized for hydrogen-related hazards.     

Recommendations on X80 steel for the design of hydrogen gas transmission pipelines

By limiting the pipes thickness necessary to sustain high pressure, high-strength steels could prove economically relevant for transmitting large gas quantities in pipelines on long distance. Up to now, the existing hydrogen pipelines have used lower-strength steels to avoid any hydrogen embrittlement. The CATHY-GDF project, funded by the French National Agency for Research, explored the ability of an industrial X80 grade for the transmission of pressurized hydrogen gas in large diameter pipelines. This project has developed experimental facilities to test the material under hydrogen gas pressure. Indeed, tensile, toughness, crack propagation and disc rupture tests have been performed. From these results, the effect of hydrogen pressure on the size of some critical defects has been analyzed allowing proposing some recommendations on the design of X80 pipe for hydrogen transport. Cost of Hydrogen transport could be several times higher than natural gas one for a given energy amount. Moreover, building hydrogen pipeline using high grade steels could induce a 10 to 40% cost benefit instead of using low grade steels, despite their lower hydrogen susceptibility.     

Experimental studies on wind influence on hydrogen release from low pressure pipelines

At the DIMNP (Department of Mechanical, Nuclear and Production Engineering) laboratories of University of Pisa (Italy) a pilot plant called HPBT (Hydrogen Pipe Break Test) was built in cooperation with the Italian Fire Brigade Department. The apparatus consists of a 12 m³ tank connected with a 50 m long pipe. At the far end of the pipeline a couple of flanges have been used to house a disc with a hole of the defined diameter. The plant has been used to carry out experiments of hydrogen release. During the experimental activity, data have been acquired about the gas concentration and the length of release as function of internal pressure and release hole diameter. The information obtained by the experimental activity will be the basis for the development of a new specific normative framework arranged to prevent fire and applied to hydrogen. This study is focused on hydrogen concentration as function of wind velocity and direction. Experimental data have been compared with theoretical and computer models (such as CFD simulations).     

Evaluation of hydrogen concentration effect on the natural gas properties and flow performance

The natural gas flowing through transmission pipeline is impure and has a wide range of non-hydrocarbons components at different concentrations like hydrogen. The presence of hydrogen in the natural gas mixture influences its properties and flow performance. The effect of hydrogen concentration on the natural gas flowing through a transportation pipeline has not been adequately investigated and widely comprehended. In this paper, several mixtures flow through pipeline include typical natural gas and hydrogen at different concentrations up to 10% are evaluated to demonstrate their impact on the flow assurance and the natural gas properties. The string Ruswil – Griespass part from the Transitgas project with 94 km length is simulated applying Aspen Hysys Version 9 and validated using Aspen Plus. The simulation specifications were 1.228 1 10⁶ kg/h mass flowrate, 1200 mm and 1164 mm the outer and inner diameters, and 75 bar and 29.4 °C operating pressure, and temperature. The effect of different hydrogen concentrations has been examined and the differences from the typical mixture are estimated. The results show that the presence of hydrogen in the natural gas mixture reduces its density, 10% hydrogen content records 11.78% reduction in the density of typical natural gas. Interestingly, it has been found that up to 2% of hydrogen concentration turns in elevating the viscosity of the typical natural gas while the viscosity decreases at the point that hydrogen content increases above 2%. In addition, the pressure losses over the transmission pipeline increases due to the presence of hydrogen, 10% hydrogen concentration turns in 5.39% increase in the pressure drop of the natural gas mixture. Also, the temperature drop across the pipeline decreases as the hydrogen concentration increases; 10% hydrogen content can result in a 6.14% reduction in the temperature drop across the pipeline. As well as, the findings prove that the hydrogen strongly impacts the phase envelope by changing from size symmetric to size asymmetric diagram. The effect of pipeline elevations has been investigated by changing the elevation up to 25 m uphill and 25 m downhill. The results state that increase the pipeline elevation turns in increasing the pressure losses over the pipeline length. Along with this, the results illustrate that the presence of hydrogen in the mixture elevates the critical pressure and reduces the critical temperature.     

Hydrogen from natural gas without release of CO2 to the atmosphere

The “Hydrogen economy”, in which hydrogen will be a main carrier of energy from renewable sources, is a long term prospect. In the near and medium term increasing demand for hydrogen--also as an energy carrier in special niches--will probably be covered by hydrogen from fossil sources, mainly natural gas. This can be acceptable from an environment as well as an economical point of view, since hydrogen can be produced from natural gas at acceptable costs, without release of CO₂ to the atmosphere. There are two main options for this: (1) hydrogen from natural gas by conventional technology (e.g. steam reforming) including CO₂ sequestration; (2) high temperature pyrolysis of natural gas, yielding pure hydrogen and carbon black. Technologies for industrial scale realisation of these options have been developed and evaluated in Norway, which is a large producer and exporter of natural gas. The economy and market opportunities are discussed in the paper. It appears that renewable energy costs must come down considerably from present levels before hydrogen from renewables can compete with hydrogen from natural gas without release of CO₂ to the atmosphere.     

Is hydrogen a safe fuel?

The safety aspects of hydrogen are systematically examined and compared with those of methane and gasoline. Physical and chemical property data for all three fuels are compiled and used to provide a basis for comparing their various safety features. Each fuel is examined to evaluate its fire hazard, fire damage, explosive hazard and explosive damage characteristics. The fire characteristics of hydrogen, methane and gasoline, while different, do not largely favor the preferred use of any one of the three fuels; however, the threat of fuel-air explosions in confined spaces is greatest for hydrogen. Safety criteria for the storage of liquid hydrogen, liquefied natural gas (LNG) and gasoline are compiled and presented. Gasoline is believed to be the easiest and perhaps the safest fuel to store because of its lower volatility and narrower flammable and detonable limits. It is concluded that all three fuels can be safely stored and used; however, the comparative safety and level of risk for each fuel will vary from one application to another. Generalized safety comparisons are made herein but detailed safety analyses will be required to establish the relative safety of different fuels for each specific fuel application and stipulated accident. The technical data supplied in this paper will provide much of the framework for such analyses.