天然气管道掺氢输送的风险分析

氢气能源在利用过程中没有任何“碳排放”,环保优势突出,未来具有广阔的发展前景。如果利用现有天然气管道进行掺氢输送,是将来大规模利用氢气的一种有效思路,但由于氢气容易导致管材失效,且氢气相比于天然气更容易扩散且爆炸极限更宽,所以管道掺氢输送也面临若干风险。本文从现有管道、介质泄漏及其火灾爆炸风险等几个方面展开分析,探讨现有天然气掺氢输送的可行性。     

考虑输气功率的掺氢天然气管道运行优化研究

将氢气掺混入天然气并利用现有天然气管道基础设施输送是实现氢气长距离、大规模、低成本输送的有效方式,但氢气的掺入会对原有天然气管道基础设施的运行产生影响。为此,文章建立了掺氢天然气管道运行能耗优化模型,以压气站最小能耗为目标函数,压缩机开机台数和压缩机转速为决策变量,在掺氢比不同的工况下,分别对保持掺氢天然气的体积输量恒定和输气功率恒定的两种情况进行优化求解分析,对不同掺氢比下管道系统优化后的工况进行分析讨论。研究结果表明：在保证天然气掺氢输送的热值供应的基础上,当掺氢比超过15%时,现有天然气管道设施已无法满足最优工况的平稳运行,可以通过增设压缩机站的方式提高管段压力,以保证现有天然气管道输气功率的稳定,或在下游建设储气调峰设施,以平衡管存气体能量下降的影响。     

多气源天然气管网掺氢位置研究

利用相对完善的天然气管网输送氢气,是现阶段实现氢气低成本运输的有效途径之一。为了确定多气源天然气管网的最优掺氢位置,文章采用沃泊热值指数、A.G.A指数、韦弗指数3种判定方法分析了氢气和天然气的互换性,确定了满足天然气互换性要求的最大掺氢比例。为了满足天然气管网掺氢后的水力工况,采用Pipeline Studio软件对掺氢后的天然气管道和某20节点天然气管网系统的运行工况进行仿真,从天然气管网节点压力和节点气质两个方面分析了掺氢比例对管网输送工况的影响,从而确定了天然气管网中的最优掺氢位置。研究结果表明：不同判定方法对掺氢比例的要求不同,需要综合考虑多种判定方法允许的掺氢比例;某20节点多气源天然气管网系统的最优掺氢位置为节点N14。     

双碳背景下氢能产业发展及混氢输送工艺研究

氢能由于具有清洁、绿色、安全性高等特点,正成为我国能源结构转型升级的新方向。天然气管道掺氢输送对于加快我国构建清洁绿色,安全高效的能源体系,实现“碳达峰、碳中和”能源战略目标具有十分重要的意义。首先阐述了氢能在实现双碳目标中的作用,既可以减少化石能源的消耗,又可以促进终端能源消耗的绿色化发展。其次,总结了天然气掺氢产业发展现状,天然气掺氢输送作为氢能发展的重要环节,需要从上游制氢到下游终端利用全产业链技术的支持。最后,从燃气的互换性、设备与管道的适应性以及泄漏的安全性等方面对混氢输送工艺关键问题进行了分析。研究建议从管材氢脆腐蚀机理、储气设备泄漏危险分析、掺氢输送标准体系建设等方面继续深入研究,以期为双碳目标的实现提供有力的技术支持。     

掺混氢气对甲烷/空气一维层流火焰的影响

当前社会对燃气的需求量巨大,通过可再生能源产生的氢气可以作为供给终端用户的燃料,但由于修建纯氢气的输运管道存在投资成本较高的问题,因此,通常选择将氢气掺入天然气管道进行输送应用。使用Chemkin-Pro软件对甲烷掺氢层流预混燃烧进行模拟,从化学动力学的角度探究掺混氢气对火焰的影响。结果表明：随着氢气比例的提高,火焰温度提高,但幅度不大,而当量比对燃烧温度的影响相对更大。掺氢后CO浓度的减少是因为甲烷的含量减少,掺混氢气后火焰燃烧速度增加。研究成果可为氢气掺混天然气的应用提供一定参考。     

管道输运高压氢气与天然气的泄漏扩散数值模拟

基于有限体积法,建立了管道运输高压氢气及天然气的泄漏扩散模型,考虑到氢气与天然气的管道泄漏事故危险性不同,进行了数值模拟与对比,得出了管道泄漏后氢气与天然气的不同泄漏扩散特性.结果表明:高压氢气的泄漏扩散形成的危险云团较大而且集中;氢气初始的泄漏速度比天然气大得多,与周围环境达到压力平衡所需时间较天然气短;随着扩散时间的增加,氢气危险气体云团扩散最大高度较天然气增加得快;在近地面区氢气泄漏扩散产生的危险后果较天然气小.     

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。     

天然气发动机掺氢燃烧的探讨

根据氢气、天然气和天然气掺氢燃烧的一些特性，结合世界各国对天然气掺氢燃烧在发动机上应用的研究状况。探讨天然气发动机掺氢燃烧应用的前途和可行性。     

天然气发动机掺氢燃烧的探讨

本文根据氢气、天然气和天然气掺氢燃烧的一些特性，结合世界各国对天然气掺氢在燃烧发动机上应用的研究的状况。探讨了天然气发动机掺氢燃烧应用的前途和可行性的方式。     

不同掺氢比的HCNG燃料对天然气发动机怠速性能影响研究

为了研究在天然气中掺入不同体积比氢气对发动机怠速性能的影响,针对一台6缸天然气发动机开展了不同体积掺氢比的氢气/天然气混合燃料(HCNG)的怠速性能试验研究.试验证实掺氢后热效率提高,要达到相同的怠速转速可减少怠速旁通阀开度;在怠速情况下,掺氢使CH4、CO、NMHC排放下降,Nox排放上升,可通过点火提前角推迟来有效降低怠速Nox排放;在天然气中掺入适量氢气后有利于改善发动机怠速燃烧,从而增加怠速稳定性.在怠速条件下,掺氢后CO、CH4排放随转速升高先减小后增加;怠速转速升高,怠速稳定性变好.在天然气中掺入适量氢气后,发动机热效率提高,经济性改善.     

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.     

A review of technical and regulatory limits for hydrogen blending in natural gas pipelines

There is rising interest globally in the use of hydrogen for the provision of electricity or heat to industry, transport, and other applications in low-carbon energy systems. While there is attention to build out dedicated hydrogen infrastructure in the long-term, blending hydrogen into the existing natural gas pipeline network is also thought to be a promising strategy for incorporating hydrogen in the near-term. However, hydrogen injection into the existing gas grid poses additional challenges and considerations related to the ability of current gas infrastructure to operate with blended hydrogen levels. This review paper focuses on analyzing the current understanding of how much hydrogen can be integrated into the gas grid from an operational perspective and identifies areas where more research is needed. The review discusses the technical limits in hydrogen blending for both transmission and distribution networks; facilities in both systems are analyzed with respect to critical operational parameters, such as decrease in energy density, increased flow speed and pressure losses. Safety related challenges such as, embrittlement, leakage and combustion are also discussed. The review also summarizes current regulatory limits to hydrogen blending in different countries, including ongoing or proposed pilot hydrogen blending projects.     

Exploration of critical hydrogen-mixing ratio of quenching methane/hydrogen mixture deflagration under effect of porous materials in barrier tube

To improve the safety of the methane/hydrogen mixture pipeline network, The experimental deflagration quenching behavior of porous materials on hydrogen mixed methane in barrier tubes was studied, the influence of the hydrogen mixing ratio on the quenching results of porous materials and the transient change of overpressure was discussed, the critical quenching hydrogen mixing ratio of porous materials was explored. Results show that the hydrogen mixing ratio has a significant effect on the quenching results of porous materials. According to the different quenching results of porous materials under different hydrogen mixing ratios, the successful quenching zone (φ<19%) and the quenching failure zone (φ ≥ 19%) can be divided. It can be determined that the critical quenching hydrogen mixing ratio is φ = 19%. The critical quenching speed is 33.0 m/s. When the porous material is coupled with hydrogen mixing, the pressure curve appears as a “multi-peak” phenomenon, and the maximum pressure peak is generated by the “multi-peak” game. If the hydrogen mixing ratio is greater than the critical quenching hydrogen mixing ratio, it may bring about the uncertainty of the maximum pressure peak and increase the unpredictability of the explosion hazard to the gas pipeline network. Therefore, reasonable hydrogen mixing is conducive to improving the safety of methane/hydrogen mixture pipeline network transportation. The research results could provide an important reference for the engineering application of methane/hydrogen mixture flame arrester design and the selection of safe hydrogen concentration.     

Leakage and diffusion behavior of a buried pipeline of hydrogen-blended natural gas

Buried pipelines are one method of conservation transfer for widely used gases such as natural gas and hydrogen. The safety of these pipelines is of great importance because of the potential leakage risks posed by the flammable gas and the special properties of the hydrogen mixture. Estimating the leakage behavior and quantifying the diffusion range outside the pipeline are important but challenging goals due to the hydrogen mixture and presence of soil. This study provides essential information about the diffusion behavior and concentration distribution of underground hydrogen and natural gas mixture leakages. Therefore, a large-scale experimental system was developed to simulate high-pressure leaks of hydrogen mixture natural gas from small holes in three different directions from a pipeline buried in soil. The diffusion of hydrogen-doped natural gas in soil was experimentally measured under different conditions, such as different hydrogen mixture ratios, release pressures, and leakage directions. The experimental results verified the applicability of the gas leakage mass flow model, with an error of 6.85%. When a larger proportion of a single component was present in the hydrogen-doped natural gas, the leakage pressure showed a greater diffusion range. In addition, the diffusion range of hydrogen-doped natural gas in the leakage direction was larger at 3 o'clock than that at 12 o'clock. The hydrogen blend carried methane and diffused, which shortened the methane saturation time. Moreover, a quantitative relationship between the concentration of hydrogen-doped natural gas and the diffusion distance over which the hydrogen-doped natural gas reached the lower limit of the explosion was obtained by quantitative analysis of the experimental data.     

The synergistic effects of hydrogen embrittlement and transient gas flow conditions on integrity assessment of a precracked steel pipeline

We are reporting in this study the hydrogen permeation in the lattice structure of a steel pipeline designed for natural gas transportation by investigating the influence of blending gaseous hydrogen into natural gas flow and resulted internal pressure values on the structural integrity of cracked pipes. The presence of cracks may provoke pipeline failure and hydrogen leakage. The auto-ignition of hydrogen leaks, although been small, leads to a flame difficult to be seen. The latter makes such a phenomenon extremely dangerous as explosions became very likely to happen. In this paper, a reliable method is presented that can be used to predict the acceptable defect in order to reduce risks caused by pipe failure due to hydrogen embrittlement. The presented model takes into account the synergistic effects of transient gas flow conditions in pipelines and hydrogen embrittlement of steel material due to pressurized hydrogen gas permeation. It is found that blending hydrogen gas into natural gas pipelines increases the internal load on the pipeline walls due to overpressure values that may be reached in a transient gas flow regime. Also, the interaction between transient hydrogen gas flow and embrittlement of API 5L X52 steel pipeline was investigated using Failure Assessment Diagram (FAD) and the results have shown that transient flow enhances pipeline failure due to hydrogen permeation. It was shown that hydrogen embrittlement of steel pipelines in contact with the hydrogen environment, together with the transient gas flow and significantly increased transient pressure values, also increases the probability of failure of a cracked pipeline. Such a situation threatens the integrity of high stress pipelines, especially under the real working conditions of hydrogen gas transportation.     

Research and demonstration on hydrogen compatibility of pipelines: a review of current status and challenges

Hydrogen transportation by pipelines gradually becomes a critical engineering route in the worldwide adaptation of hydrogen as a form of clean energy. However, due to the hydrogen embrittlement effect, the compatibility of linepipe steels and associated welds with hydrogen is a major concern when designing hydrogen-carrying pipelines. When hydrogen enters the steels, their ductility, fracture resistance, and fatigue properties can be adversely altered. This paper reviews the status of several demonstration projects for natural gas-hydrogen blending and pure hydrogen transportation, the pipeline materials used and their operating parameters. This paper also compares the current standards of materials specifications for hydrogen pipeline systems from different parts of the world. The hydrogen compatibility and tolerance of varying grades of linepipe steels and the relevant testing methods for assessing the compatibility are then discussed, and the conservatism or the inadequacies of the test conditions of the current standards are pointed out for future improvement.     

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.     

From the perspective of new technology of blending hydrogen into natural gas pipelines transmission: Mechanism,experimental study,and suggestions for further work of hydrogen embrittlement in high-strength pipeline steels

Blending hydrogen into high-strength pipeline steels for high-pressure transmission may cause materials' hydrogen embrittlement (HE) failure. Although the hydrogen-induced failure of metallic materials has been studied for a long time, the process of hydrogen into the materials, hydrogen-induced delayed failure, and dynamic mechanisms of high-strength pipeline steels under high pressure have not been fully understood. This paper aims to provide a detailed review of the latest research on the hydrogen-induced failure of high-strength pipeline steels in hydrogen-blended natural gas transmission. First, introduced the typical hydrogen blending natural gas pipeline transmission projects and their associated research conclusions. Then, described the physical process of the HE in high-strength pipeline steels and the principle, development, and latest research progress of typical hydrogen embrittlement mechanisms in detail. Third, reviewed the research methods and progress of experimental and theoretical simulations for the HE in steels, including hydrogen permeation (HP) experiments, hydrogen content measurements, hydrogen distribution detection, mechanical property tests, and molecular dynamics simulations. The shortcomings of existing experimental and theoretical simulation methods in the hydrogen-induced analysis of high-strength natural gas pipeline steels under high pressure are discussed. Finally, the future research directions and challenges of this problem are proposed from three aspects: the multimechanism synergy mechanism, the improvement of experimental methods, and the establishment of a new interatomic multiscale model.