Research on the dynamic characteristics of natural gas pipeline network with hydrogen injection considering line-pack influence

Hydrogen energy has the advantages of renewable, clean and high energy density, which is considered as the most potential secondary energy in the 21st century. But transportation is a major constraint on development of hydrogen. A possible solution is to inject hydrogen into natural gas network for transport. Due to the obvious differences in the properties of natural gas and hydrogen, it is necessary to establish natural gas pipeline model with hydrogen injection to explore the influence of hydrogen on pipeline. The line-pack of natural gas network can improve the flexibility of the system to deal with uncertainties, and the line-pack has a significant impact on the dynamic characteristics of the natural gas network under the change of external conditions. When hydrogen is injected into the natural gas network, the line-pack is affected by both pressure and hydrogen mixture ratio, and the line-pack influence on the dynamic characteristics of the network is more complicated. In this paper, a natural pipe network with hydrogen injection is established based on the finite difference method, and simulation is carried out under different situations to explore the influence of different line-pack on the dynamic characteristics of the natural gas network. The results show that the response speed of hydrogen mixture ratio is faster under the condition of low line-pack, which is conducive to reducing the risk of hydrogen embrittlement when the hydrogen mixture ratio surges for a short time. However, the pressure loss caused by the increase of flow can be reduced in the high line-pack state.     

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.     

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.     

An MILP model for the reformation of natural gas pipeline networks with hydrogen injection

A mixed integer linear programming (MILP) model is proposed for the reformation of natural gas pipelines. The model is based on the topology of existing pipelines, the load and pressure at each node and the design factors of the region and minimizes the annual substitution depreciation cost of pipelines, the annual construction depreciation cost of compressor stations and the operating cost of existing compressor stations. Considering the nonlinear pressure drop equations, the model is linearized by a piecewise method and solved by the Gurobi optimizer. Two cases of natural gas pipeline networks with hydrogen injection are presented. Several adjustments are applied to the original natural gas pipeline network to ensure that our design scheme can satisfy the safety and economic requirements of gas transportation. Thus, this work is likely to serve as a decision-support tool for the reformation of pipeline networks with hydrogen injection.     

Steady-state analysis of a natural gas distribution network with hydrogen injection to absorb excess renewable electricity

Natural gas networks, thanks to their extensiveness and capillarity, could play a crucial role in the green transition of the energy sector. The decarbonization of a gas network can be achieved by injecting green hydrogen into the grid. This work aims to simulate a low-pressure natural gas distribution network serving industrial and residential users and subjected to one localized injection of hydrogen produced by renewable energy sources. The main quality indexes and fluid dynamics parameters of the gas mixture are analysed to understand the feasibility of injecting hydrogen into a natural gas network. Firstly, the network was examined under nominal steady conditions with a constant hydrogen injection. Then, the same grid was simulated considering a 24-h pattern of hydrogen injection, according to the power daily surplus. The results show that the grid can help to buffer the surplus of renewable power produced. The conclusions derived by the results underline that the effect of H2 injection is maximum during the highest excess of electricity and the importance of an accurate choice of the injection node: a wrong choice leads, at the peak of power production, leads to an amplification of the H2 injection impact and hence to a reduction of the Wobbe Index value that overcomes the safety lower limit.     

Comparison of different system layouts to generate a substitute of natural gas from biomass and electrolytic hydrogen

The production of electrolytic hydrogen is considered among the best solution to mitigate the grid instability problems which arise from the widespread distribution of renewable energy sources, such as wind and solar. However, hydrogen is not easy to stock and distribute. Possible solutions are represented by its direct injection into the existing pipeline for natural gas distribution or its utilisation for the production of a substitute of natural gas. In this last case, which follows the so called approach of “power to gas”, a source of carbon is required. Preferably the carbon should come from biomass, since it can be considered “renewable carbon”.Starting from this idea, this study analyses two different approaches, depending on the grid power demand. In a first layout, biomass is gasified with electrolytic hydrogen to generate directly a methane rich syngas. After water condensation, the syngas is fed to a methanation process to convert almost completely carbon in methane.In the second layouts the biomass is gasified with electrolytic oxygen and the syngas is fed, together with other electrolytic oxygen, to a power unit, such as an internal combustion engine, a gas turbine or a high temperature fuel cells (SOFC). The exhaust gas from these power units is composed almost exclusively by carbon dioxide and water vapour. After water condensation, the carbon dioxide is fed together electrolytic hydrogen to a methanation process to obtain the substitute of natural gas.An overall best efficiency of roughly 74% is obtained when the plant is not connected to the grid. On the contrary, when electricity can be absorbed by the grid, best efficiency of 59.4% is reached utilising, as power unit, a SOFC fed at 6 bars.In all cases the input is low value energy (biomass and unstable electric power) and the output is high value energy constituted by a substitute of natural gas and stable electric power.     

The economic feasibility study of a 100-MW Power-to-Gas plant

Power-to-Gas (PtG) is a grid-scale energy storage technology by which electricity is converted into gas fuel as an energy carrier. PtG utilizes surplus renewable electricity to generate hydrogen from Solid-Oxide-Cell, and the hydrogen is then combined with CO₂ in the Sabatier process to produce the methane. The transportation of methane is mature and energy-efficient within the existing natural gas pipeline or town gas network. Additionally, it is ideal to make use of the reverse function of SOC, the Solid-Oxide-Fuel-Cell, to generate electricity when the grid is weak in power. This study estimated the cost of building a hypothetical 100-MW PtG power plant with energy storage and power generation capabilities. The emphasis is on the effects of SOC cost, fuel cost and capacity factor to the Levelized Cost of Energy of the PtG plant. The net present value of the plant is analyzed to estimate the lowest affordable contract price to secure a positive present value. Besides, the plant payback period and CO₂ emission are estimated.     

Long-distance renewable hydrogen transmission via cables and pipelines

Intermittency is one of the main obstacles that inhibit the wide adoption of the renewable energy in the power sector. Small-scale fluctuations can be tackled by short-term energy storage system, whereas long-term or seasonal intermittencies rely on large-scale energy management solutions. Besides the supply and demand mismatch in temporal domain, renewable energy sources are usually far away from consumption points. To connect the energy sources to the demand cost-effectively, cable transmission is usually the default option, and considering the long distance, other emerging energy carriers such as hydrogen could be a feasible option. However, there is handful studies on the quantitative evaluation of the long-distance energy transmission cost. This paper investigated the economic feasibility of renewable energy transmission via routes of power cable and gas pipeline. In the direct power transmission case, renewable energy is transmitted via HVDC cable and then converted to hydrogen for convenient storage. The alternative case converts renewable energy into hydrogen at the source and transports the hydrogen in the gas pipeline to consumers. Existing data available from public domain are used for cost estimation. Results show that the improvements of capacity factor and transmission scale are the most cost-effective approach to make the renewable hydrogen economically viable. At 4000 km of transmission distance, renewable hydrogen LCOE of 7 US$/kg and 9 US$/kg are achievable for the corresponding optimum cases, respectively.     

Dynamic behaviour of non-isothermal compressible natural gases mixed with hydrogen in pipelines

This paper focuses on non-isothermal transient flow in mixed hydrogen–natural gas pipelines. The effect of hydrogen injection into natural gas pipelines has been investigated in particular the pressure and temperature conditions, Joule–Thomson effect, linepack and energy consumption of the compressor station. The gas flow is described by a set of partial differential equations resulting from the conservation of mass, momentum and energy. Real gas effects are determined by the predictive Soave–Redlich–Kwong group contribution method. The Yamal-Europe gas pipeline on Polish territory has been selected as case study.     

Offshore renewable energy exploitation strategies in remote areas by power-to-gas and power-to-liquid conversion

Chemical storage of electric energy is recognised as a potential solution to improve the penetration of renewable energy. The coupling of renewable power production with offshore oil & gas exploitation by converting electricity into synthetic fuels represents an opportunity to valorize renewables in remote areas in an energy transition panorama. The present study aims at a comparison of alternative power-to-gas and power-to-liquid strategies for the conversion of offshore wind power into different chemical energy vectors (hydrogen, synthetic natural gas and methanol), taking advantage of conventional offshore oil & gas infrastructures for energy conversion and synthetic fuel transportation. A set of technical, economic, environmental and profitability performance indicators was defined to allow the comparison. A case study in the North Sea was analysed. The results showed that electrolyzers capacity and offshore-onshore distance play an important role on economic indicators. Sensitivity analysis was carried out to test the robustness of the results.     

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.     

Hydrogen supply chain scenarios for the decarbonisation of a German multi-modal energy system

Analysing hydrogen supply chains is of utmost importance to adequately understand future energy systems with a high degree of sector coupling. Here, a multi-modal energy system model is set up as linear programme incorporating electricity, natural gas as well as hydrogen transportation options for Germany in 2050. Further, different hydrogen import routes and optimised inland electrolysis are included. In a sensitivity analysis, hydrogen demands are varied to cover uncertainties and to provide scenarios for future requirements of a hydrogen supply and transportation infrastructure. 80% of the overall hydrogen demand of 150 TWh/a emerge in Northern Germany due to optimised electrolyser locations and imports, which subsequently need to be transported southwards. Therefore, a central hydrogen pipeline connection from Schleswig-Holstein to the region of Darmstadt evolves already for moderate demands and appears to be a no-regret investment. Furthermore, a natural gas pipeline reassignment potential of 46% is identified.     

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.     

Hydrogen effects on X80 pipeline steel in high-pressure natural gas/hydrogen mixtures

Blending hydrogen into existing natural gas pipelines has been proposed as a means of increasing the output of renewable energy systems such as large wind farms. X80 pipeline steel is commonly used for transporting natural gas and such steel is subjected to concurrent hydrogen invasion with mechanical loading while being exposed to hydrogen containing environments directly, resulting in hydrogen embrittlement (HE). In accordance with American Society for Testing and Materials (ASTM) standards, the mechanical properties of X80 pipeline steel have been tested in natural gas/hydrogen mixtures with 0, 5.0, 10.0, 20.0 and 50.0vol% hydrogen at the pressure of 12 MPa. Results indicate that X80 pipeline steel is susceptible to hydrogen-induced embrittlement in natural gas/hydrogen mixtures and the HE susceptibility increases with the hydrogen partial pressure. Additionally, the HE susceptibility depends on the textured microstructure caused by hot rolling, especially for the notch specimen. The design calculation by the measured fatigue data reveals that the fatigue life of the X80 steel pipeline is dramatically degraded by the added hydrogen.     

Use of hydrogen as a seasonal energy storage system to manage renewable power deployment in Spain by 2030

Spain has presented a plan (known as PNIEC) to reduce conventional energy sources (shutting down 16 GW) and to increase the use of renewable sources (incorporating 65 GW). This generation portfolio leads to a situation in which there will be a surplus of electrical energy in spring and summer, which will be lacking in autumn and winter. The plan sets a target on batteries, but insufficient to manage more than 10 TWh over 6 months. This paper proposes the deployment of electrolysers to produce hydrogen with the surplus energy, using the already existing Spanish natural gas network to store it. The resulting gas (up to 15% blend of hydrogen in natural gas) could be used subsequently in turbines to alleviate the energy deficit. With this strategy, up to 7.27 TWh of the surplus renewable energy could be reused, and 2.54 million tons of CO2 equivalent would be avoided yearly.     

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.     

Optimal dispatch of HCNG penetrated integrated energy system based on modelling of HCNG process

Hydrogen is injected into the existing natural gas network to form hydrogen-rich compressed natural gas (HCNG), effectively addressing the high cost of hydrogen transmission. However, the traditional IES model cannot be used due to the hydrogen injection's effect on gas properties and the vague characteristics of the transport and separation processes. Therefore, this paper proposes an HCNG penetrated integrated energy system (HPIES) optimal dispatching method by comprehensively modelling the injection, transmission, and separation processes of HCNG. An HCNG mass flow rate model considering variable mixing ratio and unknown beginning flow direction is developed to describe the effect of hydrogen injection. Furthermore, the hydrogen separation model is established by introducing a combined membrane and pressure swing adsorption separation process. The tightening McCormick algorithm is proposed to solve quickly HPIES optimal dispatch problem with an acceptable feasibility check. Finally, case studies on the HPIES consisting of IEEE 39-bus power system and 20-node natural gas system validate the effectiveness of the algorithm and model. The results show that the average error is 0.031% for the bilinear term constraint.     

Investigation of photovoltaic-hydrogen power system for a real house in Turkey: Hydrogen blending to natural gas effects on system design

In the study, the effects of hydrogen mixing studies at the rate of 20% to the natural gas system which is an ongoing study in Turkey, on the photovoltaic system (PV) is investigated using a real house consumption. Providing the annual electrical energy consumption (1936,83  kWh) and 20% of natural gas consumption (62,4 m³) of a real house with hydrogen is included in the study. A PV-hydrogen system is theoretically investigated to provide the energy required for hydrogen production from solar panels. Hydrogen blending effects on PV size, capacity usage, and carbon footprint are analyzed. Thus, the contribution was also made to the “green hydrogen” works and reduction of the carbon footprint of the house. It was found that the required hydrogen for electricity can be provided 52,5 m² solar panel area and 14,28% increase in this area and installed power can provide an amount of hydrogen that need for 20% hydrogen blending to the natural gas system. The overall system capacity usage decreased when the system is used for 20% hydrogen blending to the natural gas system. The carbon footprint of the house was decreased by 67,5%. If the hydrogen has not been blended with 20% natural gas, this ratio would have been 59,2%.     

Hydrogen integration in power-to-gas networks

The share of renewable energy resources is consistently rising in the global energy supply, and power-to-gas technique is being seen as the feasible storage of surplus renewable electricity. In this regard the sensitivity of hydrogen towards various elements of the P2G network needs to be assessed. The study provides an overview of a number of P2G projects mainly concentrated in Europe, and summarizes the results of investigations carried out on the effects of hydrogen injection on the existing natural gas pipeline infrastructure. It has been found that each element of the natural gas infrastructure has a varying degree of acceptability to hydrogen concentration; however the determinant element affects the overall allowable hydrogen concentration. In the transmission network, compressors are the determinant element and have a limiting value of 10% hydrogen admixture. Distribution network and storage elements allow a 50% concentration of hydrogen. End use appliances have a tolerant range of 20–50%. The second portion of the study demonstrates the effect of hydrogen injection on gas quality, which reveals that an introduction of 2% hydrogen in the distribution network has negligible effect however a 10% hydrogen mixture affects the calorific value of the supplied fuel gas below the desired level.