Hydrogen Blending

The ability for existing burners to operate safely and efficiently on hydrogen-blended fuels is a primary concern for the many industries looking to adopt hydrogen as an alternative fuel. This study investigates the efficacy of increasing fuel injector diameter as a simple modification strategy to extend the hydrogen-blending limits before flashback. The collateral effects of this modification are quantified with respect to a set of key performance criteria. The results show that the unmodified burner can sustain up to 50 vol% hydrogen addition before flashback. Increasing the fuel injector diameter reduces primary aeration allowing for stable operation on up to 100% hydrogen. The flame length visibility and radiant heat transfer properties are all increased as a result of the reduced air entrainment with a trade-off reported for NOx emissions where in addition to the effects of hydrogen reducing air entrainment further increases NOx emissions.

A transient pipeline flow model with gas composition tracking is solved for studying the operation of a natural gas pipeline under nonisothermal flow conditions in a hydrogen injection scenario. Two approaches to high-resolution pipeline flow modeling based on the WENO scheme are presented and compared with the implicit finite difference method. The high-resolution models are capable of capturing fast fluid transients and tracking the step changes in the composition of the transported mixture. The implicit method assumes the decoupling of the flow model components in order to enhance calculation efficiency. The validation of the composition tracking results against actual gas transmission pipeline indicates that both models exhibit good prediction performance with normalized root mean square errors of 0.406% and 1.48% respectively. Under nonisothermal flow conditions the prediction response of the reduced model against a high-resolution flow model with respect to the mass and energy linepack is at most 3.20%.

With the adjustment of energy structure the utilization of hydrogen energy has been widely attended. China’s carbon neutrality targets make it urgent to change traditional coal-fired power generation. The paper investigates the combustion of pulverized coal blended with hydrogen to reduce carbon emissions. In terms of calorific value the pulverized coal combustion with hydrogen at 1% 5% and 10% blending ratios is investigated. The results show that there is a significant reduction in CO2 concentration after hydrogen blending. The CO2 concentration (mole fraction) decreased from 15.6% to 13.6% for the 10% hydrogen blending condition compared to the non-hydrogen blending condition. The rapid combustion of hydrogen produces large amounts of heat in a short period which helps the ignition of pulverized coal. However as the proportion of hydrogen blending increases the production of large amounts of H2O gives an overall lower temperature. On the other hand the temperature distribution is more uniform. The concentrations of O2 and CO in the upper part of the furnace increased. The current air distribution pattern cannot satisfy the adequate combustion of the fuel after hydrogen blending.

In order to reduce carbon emissions the effects of gas composition and initial turbulence on the premixed flame dynamics of hydrogen-blended natural gas were investigated. The results show that an increase in hydrogen content leads to earlier formation of flame wrinkles. When the equivalence ratio is 1 and hydrogen blending ratio is below 20% Tulip flames appear approximately 2.25 m away from the ignition point. When hydrogen blending ratio exceeds 20% Tulip flames appear approximately 1.3 m away from the ignition point and twisted Tulip flames appear approximately 2.5 m away from the ignition position. During the 0.05 m process of flame propagation downstream from ignition point flame propagation velocity increases by about 2 m/s for every 10% increase in hydrogen content. The increase in hydrogen content has the most significant impact on the flame propagation velocity during the ignition stage. The average flame propagation velocity increases with the increase of hydrogen blending ratio. The greater the initial turbulence the more obvious the stretching deformation of flame front structure. With the increase of wind speed the flame propagation velocity first increases and then decreases. At a wind speed of 3 m/s the flame propagation velocity reaches its maximum value.

In this study a 3D model is developed to simulate multi-hole leakage scenarios in buried pipelines transporting hydrogen-blended natural gas (HBNG). By introducing three parameters—the First Dangerous Time (FDT) Ground Dangerous Range (GDR) and Farthest Dangerous Distance (FDD)—to characterize the diffusion hazard of the gas mixture this study further analyzes the effects of the number of leakage holes hole spacing hydrogen blending ratio (HBR) and soil porosity on the diffusion hazard of the gas mixture during leakage. Results indicate that gas leakage exhibits three distinct phases: initial independent diffusion followed by an intersecting accelerated diffusion stage and culminating in a unified-source diffusion. Hydrogen exhibits the first two phases whereas methane undergoes all three and dominates the GDR. Concentration gradients for multi-hole leakage demonstrate similarities to single-hole scenarios but multi-hole leakage presents significantly higher hazards. When the inter-hole spacing is small diffusion characteristics converge with those of single-hole leakage. Increasing HBR only affects the gas concentration distribution near the leakage hole with minimal impact on the overall ground danger evolution. Conversely variations in soil porosity substantially impact leakage-induced hazards. The outcomes of this study will support leakage monitoring and emergency management of HBNG pipelines.

Hydrogen blending into natural gas networks is a promising pathway to decarbonize the gas sector but requires bespoke fluid-dynamic models to accurately capture the properties of hydrogen and assess its feasibility. This paper introduces a generalizable optimal transient gas flow model for transporting homogeneous natural gashydrogen mixtures in large-scale networks. Designed for preliminary planning the model assesses whether a network can operate under a given hydrogen blending ratio without violating existing constraints such as pressure limits pipeline and compressor capacity. A distinguishing feature of the model is a multi-day linepack management strategy that engenders realistic linepack profiles by precluding mathematically feasible but operationally unrealistic solutions thereby accurately reflecting the flexibility of the gas system. The model is demonstrated on Western Australia’s 7560 km transmission network using real system topology and demand data from several representative days in 2022. Findings reveal that the system can accommodate up to 20 % mol hydrogen potentially decarbonizing 7.80 % of gas demand.

Hydrogen is a promising fuel in the current transition to zero-net CO2 emissions. However most practical combustion equipment is not yet ready to burn pure hydrogen without adaptation. In the meantime blending hydrogen with natural gas is an interesting option. This work reports a computational study of the performance of swirl-stabilized natural gas/hydrogen flames in a novel combustion chamber design. The combustor employs an air-staging strategy introducing secondary air through a top-mounted plenum in a direction opposite to the fuel jet. The thermal load is fixed at 5 kW and the effects of fuel composition (hydrogen molar fraction ranging from zero to one) excess air coefficient (λ = 1.3 1.5 or 1.7) and primary air fraction (α = 50–100%) on the velocity temperature and emissions are analysed. The results show that secondary air changes the flow pattern reducing the central recirculation zone and lowering the temperature in the primary reaction zone while increasing it further downstream. Secondary air improves the performance of the combustor for pure hydrogen flames reducing NO emissions to less than 50 ppm for λ = 1.3 and 50% primary air. For natural gas/hydrogen blends a sufficiently high excess air level is required to keep CO emissions within acceptable limits.

Hydrogen blending in natural gas pipelines facilitates renewable energy integration and cost-effective hydrogen transport. Due to hydrogen’s lower density and higher leakage potential compared to natural gas understanding hydrogen concentration distribution is critical. This study employs ANSYS Fluent 2022 R1 with a realizable k-ε model to analyze flow dynamics of hydrogen–methane mixtures in horizontal and undulating pipelines. The effects of hydrogen blending ratios pressure (3–8 MPa) and pipeline geometry were systematically investigated. Results indicate that in horizontal pipelines hydrogen concentrations stabilize near initial values across pressure variations with minimal deviation (maximum increase: 1.6%). In undulating pipelines increased span length of elevated sections reduces maximum hydrogen concentration while maintaining proximity (maximum increase: 0.65%) to initial levels under constant pressure. Monitoring points exhibit concentration fluctuations with changing pipeline parameters though no persistent stratification occurs. However increasing the undulating height elevation difference leads to an increase in the maximum hydrogen concentration at the top of the pipeline rising from 3.74% to 9.98%. The findings provide theoretical insights for safety assessments of hydrogen–natural gas co-transport and practical guidance for pipeline design optimization.

In the transformation process from fossil-fuel based to carbon-neutral combustion full or partial replacement of natural gas with hydrogen is considered in numerous industrial applications. As hydrogen flames yield significantly higher NOX emissions than natural gas flames understanding what factors influence these emissions in flames of natural gas/hydrogen blends is crucial for the retrofitting process. Our work is concerned with the simplest form of industrial retrofitting where hydrogen is injected into the natural gas line without any modifications to the burner construction while keeping the burner power constant. We provide quantifications of NOX emissions with respect to changes in hydrogen content (pure natural gas to 100% hydrogen) swirl number (S=0.6 to S=1.4) excess air ratio ( = 1 to =4.5) and air preheat (ambient air to 300 ◦C). The changes were determined in small steps and over a large range. The emission data is to be used in industrial CFD for both validation and tuning therefore Laser Doppler Velocimetry was used for precise determination of the burner inlet conditions. Key findings of the investigation include that for hydrogen flames the NOX emission index [mg/kWh] is 1.2 to 3 times larger than for pure natural gas flames at similar firing conditions. The steepest increase in NOX emissions occurs above 75% volume fraction of hydrogen in the fuel. For natural gas flames NOX emissions peak at 1.3 to 1.4 excess air while the maximum for hydrogen and natural gas/hydrogen blends lays at =1.6. NOX emissions decrease slightly as the swirl number increases but this effect is minor in comparison to the effects of hydrogen content excess air ratio and air temperature.