Hydrogen Blending

The author discusses in this paper the potential of a micro gas turbine (MGT) combustor when operated under unconventional fuel supplied. The combustor of C30 gas turbine is a reverse flow annular combustor. The CFD analysis of the reacting flow is performed with the 3D ANSYS-FLUENT solver. Specific computational experiments refer to the use of hydrogen – natural gas mixtures in order to define the optimal conditions for pilot and main injections in terms of combustion stability and NOx production. The author's methodology relies on an advanced CFD approach that compares different schemes like eddy dissipation concept together with the flamelet- PDF based approach coupled with an accurate study of the turbulent chemistry interaction. Extended kinetic mechanisms are also included in the combustion model. Some test cases are examined to make a comparison of combustion stability and efficiency and pollutant production with high hydrogen / natural gas ratios.

Natural gas distribution companies are developing ambitious plans to decarbonize the services that they provide in an affordable manner and are accelerating plans for the strategic integration of renewable natural gas and the blending of green hydrogen produced by electrolysis powered with renewable electricity being developed from large new commitments by states such as New York and Massachusetts. The demonstration and deployment of hydrogen blending have been proposed broadly at 20% of hydrogen by volume. The safe distribution of hydrogen blends in existing networks requires hydrogen blends to exhibit similar behavior as current supplies which are also mixtures of several hydrocarbons and inert gases. There has been limited research on the properties of blended hydrogen in low-pressure natural gas distribution systems. Current natural gas mixtures are known to be sufficiently stable in terms of a lack of chemical reaction between constituents and to remain homogeneous through compression and distribution. Homogeneous mixtures are required both to ensure safe operation of customer-owned equipment and for safety operations such as leak detection. To evaluate the stability of mixtures of hydrogen and natural gas National Grid experimentally tested a simulated distribution natural gas pipeline with blends containing hydrogen at up to 50% by volume. The pipeline was outfitted with ports to extract samples from the top and bottom of the pipe at intervals of 20 feet. Samples were analyzed for composition and the effectiveness of odorant was also evaluated. The new results conclusively demonstrate that hydrogen gas mixtures do not significantly separate or react under typical distribution pipeline conditions and gas velocity profiles. In addition the odorant retained its integrity in the blended gas during the experiments and demonstrated that it remains an effective method of leak detection.

Operators of public electricity grids today are faced with the challenge of integrating increasing numbers of renewable and decentralized energy sources such as wind turbines and photovoltaic power plants into their grids. These sources produce electricity in a very inconstant manner due to the volatility of wind and solar power which further complicates power grid control and management. One key component that is required for modern energy infrastructures is the capacity to store large amounts of energy in an economically feasible way.<br/>One solution that is being discussed in this context is “power-to-gas” i.e. the use of surplus electricity to produce hydrogen (or even methane with an additional methanation process) which is then injected into the public natural gas grid. The huge storage capacity of the gas grid would serve as a buffer offering benefits with regards to sustainability and climate protection while also being cost-effective since the required infrastructure is already in place.<br/>One consequence would be however that the distributed natural gas could contain larger and fluctuating amounts of hydrogen. There is some uncertainty how different gas-fired applications and processes react to these changes. While there have already been several investigations for domestic appliances (generally finding that moderate amounts of H2 do not pose any safety risks which is the primary focus of domestic gas utilization) there are still open questions concerning large-scale industrial gas utilization. Here in addition to operational safety factors like efficiency pollutant emissions (NOX) process stability and of course product quality have to be taken into account.<br/>In a German research project Gas- und Wärme-Institut Essen e. V. (GWI) investigated the impact of higher and fluctuating hydrogen contents (up to 50 vol.-% much higher than what is currently envisioned) on a variety of industrial combustion systems using both numerical and experimental methods. The effects on operational aspects such as combustion behavior flame monitoring and pollutant emissions were analyzed.<br/>Some results of these investigations will be presented in this contribution.

To avoid the potential adverse impacts of climate change from global warming it is suggested that the target of net zero emissions should be reached by this mid-century. Thailand is aiming to achieve carbon neutrality by 2050. Since electricity generation is one of the largest producers of carbon dioxide emission the associated emissions must be greatly reduced to achieve the targets mentioned above. Thus new generation expansion plans must be well developed. This paper discusses the development of generation expansion plans considering Thailand’s latest policies along with enhancement of the existing multi-period linear programming model allowing new electricity generation technologies having low emissions e.g. solar PV with battery and hydrogen blending in natural gas to be integrated into generation expansion planning. Then four generation expansion plans with different levels of hydrogen blending in natural gas are proposed and discussed. It is found that Thailand can achieve carbon neutrality by 2050 by promoting more use of renewable energy altogether with trade-off between land for solar PV installation and amount of hydrogen blended in natural gas. The lesson learned from this study provides crucial information about possible pathways to achieve carbon neutrality in the electricity sector for policy makers in other countries.

The development of hydrogen-blended natural gas (HBNG) increases the risk of gas transportation and presents challenges for pipeline security in utility tunnels. The objective of this study is to investigate the diffusion properties of HBNG in utility tunnels and evaluate the effectiveness of various ventilation mechanisms. The numerical simulation software Fluent 2023 R1 is applied to simulate and analyze the leakage of small holes in a HBNG pipeline in the natural gas compartment. By examining the leaking behavior of HBNG through small holes in different circumstances we aimed to identify the most unfavorable operational situation for leakage. Subsequently we analyzed the ventilation strategy for sub-high-pressure pipes at various pressure levels in this unfavorable condition. This study’s findings demonstrate that blending hydrogen improves the gas diffusion capacity and increases the likelihood of explosion. The primary factors that influence the pattern of leakage are the size of the leaking holes and the pressure of the pipeline. The gas compartment experiences the most unfavorable working conditions for natural gas pipeline leaks when there are higher pressures wider leak openings higher hydrogen blending ratios (HBRs) and leaks in close proximity to an air inlet. When the HBR is 20% the minimum accident ventilation rates for pressures of 0.4 MPa and 0.8 MPa are 15 air changes per hour and 21 air changes per hour respectively. The maximum allowable wind speed for accident ventilation is 5 m/s as regulated by China’s national standard GB 50838-2015. This regulation makes it difficult to minimize the risk of leakage in a 1.6 MPa gas pipeline. It is recommended to install a safety interlock device to quickly shut off the pipeline in the event of a leak in order to facilitate the dispersion of the substance.

Hydrogen is of great significance for replacing fossil fuels and reducing carbon dioxide emissions. The application of hydrogen mixing with natural gas in gas network transportation not only improves the utilization rate of hydrogen energy but also reduces the cost of large-scale updating household or commercial appliance. This paper investigates the necessity of a gas mixing device for adding hydrogen to existing natural gas pipelines in the industrial gas network. A three-dimensional helical static mixer model is developed to simulate the mixing behavior of the gas mixture. In addition the model is validated with experimental results. Parametric studies are performed to investigate the effect of mixer on the mixing performance including the coefficient of variation (COV) and pressure loss. The research results show that based on the the optimum number of mixing units is three. The arrangement of the torsion angle of the mixing unit has a greater impact on the COV. When the torsion angle θ = 120◦ the COV has a minimum value of 0.66% and when the torsion angle θ = 60◦ the COV has a maximum value of 8.54%. The distance of the mixing unit has little effect on the pressure loss of the mixed gas but has a greater impact on the COV. Consecutive arrangement of the mixing units (Case A) is the best solution. Increasing the distance of the mixing unit is not effective for the gas mixing effect. Last but not least the gas mixer is optimized to improve the mixing performance.

The use of hydrogen as a non-emission energy carrier is important for the innovative development of the power-generation industry. Transmission pipelines are the most efficient and economic method of transporting large quantities of hydrogen in a number of variants. A comprehensive hydraulic analysis of hydrogen transmission at a mass flow rate of 0.3 to 3.0 kg/s (volume flow rates from 12000 Nm3/h to 120000 Nm3/h) was performed. The methodology was based on flow simulation in a pipeline for assumed boundary conditions as well as modeling of fluid thermodynamic parameters for pure hydrogen and its mixtures with methane. The assumed outlet pressure was 24 bar (g). The pipeline diameter and required inlet pressure were calculated for these parameters. The change in temperature was analyzed as a function of the pipeline length for a given real heat transfer model; the assumed temperatures were 5 and 25 ◦C. The impact of hydrogen on natural gas transmission is another important issue. The performed analysis revealed that the maximum participation of hydrogen in natural gas should not exceed 15%–20% or it has a negative impact on natural gas quality. In the case of a mixture of 85% methane and 15% hydrogen the required outlet pressure is 10% lower than for pure methane. The obtained results present various possibilities of pipeline transmission of hydrogen at large distances. Moreover the changes in basic thermodynamic parameters have been presented as a function of pipeline length for the adopted assumptions.

DNV has carried out an investigation into potential uses for smart gas meter data as part of Phase 1 of the Modernising Energy Data Applications competition as funded by UK Research & Innovation. In particular a series of calculations have been carried out to investigate the possibility of differentiating accidental gas leaks from normal appliance use in domestic properties. This is primarily with the aim of preventing explosions but the detection of leaks also has environmental and financial benefits.

Three gases have been considered in this study:

• A representative UK natural gas composition.
• A blend of 80% natural gas and 20% hydrogen.
• Pure hydrogen.

An established method was used to calculate the gas outflow rate from leaks into buildings downstream of the meter regulator. These gas leak rates were compared with the gas use by typical domestic appliances and these leaks were considered in the context of the smart gas meter data that is currently available in 30-minute periods. A representative set of gas accumulation calculations was performed. It was found that the following three general cases apply to all three gases:

• Small holes of up to 1 mm rarely reach flammable gas/air concentrations for any gas except under the most unfavourable conditions such as small volumes combined with low ventilation rates. These releases would likely be detected within 6 to 12 hours.
• Medium holes between 1 mm and 6 mm give outflow rates equivalent to a moderate to high level of gas use by appliances. The ability to detect these leaks is highly dependent on the hole size the time at which the leak begins and the normal gas use profile in the building. The larger leaks in this category would be detected within 30 to 60 minutes while the smaller leaks could take several hours to be clearly differentiated from appliance use. This is quick enough to prevent some explosions.
• Large holes of over 6 mm give leak rates greater than any gas use by appliances. These releases rapidly reach a flammable gas/air mixture in most cases but would typically be detected within the first 30-minute meter output period. Again some explosions could be prevented in this timescale.

An event tree has been used to quantify the approximate success rate of detecting and preventing explosion events. Using the currently available 30-minute smart meter data and functionality it is estimated that around 7% of explosions could be prevented with a slight variation depending on the gas type in use. Additional functionality could be included in the meter to improve this performance. Typically one of the risk mitigation measures in isolation increases the explosion prevention rate to around 15%. If multiple improvements are made then the detection rate is predicted to increase to around 30%.

An examination of detailed historical incident information suggests that the explosions that lead to fatalities or significant damage to houses are typically of the type that would be more likely to be detected and prevented. It is estimated that between 25% and 75% of the more severe explosions could be prevented depending on which potential improvements are implemented.

Based on the conservative estimates of explosion prevention a cost benefit analysis suggests that it is justifiable to spend between around £1 and £10 per meter installed to implement the proposed technology. This is based purely on lives saved and does not take account of other benefits.

The deployment of low-carbon hydrogen in gas grids comes with strategic benefits in terms of energy system integration and decarbonization. However hydrogen thermophysical properties substantially differ from natural gas and pose concerns of technical and regulatory nature. The present study investigates the blending of hydrogen into distribution gas networks focusing on the steady-state fluid dynamic response of the grids and gas quality compliance issues at increasing hydrogen admixture levels. Two blending strategies are analyzed the first of which involves the supply of NG–H2 blends at the city gate while the latter addresses the injection of pure hydrogen in internal grid locations. In contrast with traditional case-specific analyses results are derived from simulations executed over a large number (i.e. one thousand) of synthetic models of gas networks. The responses of the grids are therefore analyzed in a statistical fashion. The results highlight that lower probabilities of violating fluid dynamic and quality restrictions are obtained when hydrogen injection occurs close to or in correspondence with the system city gate. When pure hydrogen is injected in internal grid locations even very low volumes (1% vol of the total) may determine gas quality violations while fluid dynamic issues arise only in rare cases of significant hydrogen injection volumes (30% vol of the total).

This study has been commissioned by the gas transporters as part of the Gas Goes Green (GGG)2 work programme to develop and report a ‘gas transporter view’ on how to facilitate hydrogen blending from industrial clusters which are likely to form the initial source for hydrogen blending in the gas network. This view has been developed through engagement carried out with industrial clusters and other stakeholders as well as drawing on learnings from a previous hydrogen blending study.3 The key takeaways of this study are that: l Enabling hydrogen blending from industrial clusters can be done in a pragmatic way with limited need for change to existing gas frameworks. l Where frameworks do need to change the changes are incremental rather than involving overhaul of existing frameworks and are highly workable. l While there remain uncertainties as to the nature of blending at each cluster (e.g. the volume and profile of hydrogen injections) in general the changes required to commercial and regulatory frameworks are the same implying that they are low regret. Below we summarise gas transporters’ preferred approach to facilitating hydrogen blending from industrial clusters including both the policy decisions needed and the changes required to commercial and regulatory frameworks. We note that this work has not involved a legal review and that one will be required as part of the process of implementing the framework changes described below.