Options of natural gas pipeline reassignment for hydrogen: Cost assessment for a Germany case study

The uncertain role of the natural gas infrastructure in the decarbonized energy system and the limitations of hydrogen blending raise the question of whether natural gas pipelines can be economically utilized for the transport of hydrogen. To investigate this question, this study derives cost functions for the selected pipeline reassignment methods. By applying geospatial hydrogen supply chain modeling, the technical and economic potential of natural gas pipeline reassignment during a hydrogen market introduction is assessed.The results of this study show a technically viable potential of more than 80% of the analyzed representative German pipeline network. By comparing the derived pipeline cost functions, it could be derived that pipeline reassignment can reduce the hydrogen transmission costs by more than 60%. Finally, a countrywide analysis of pipeline availability constraints for the year 2030 shows a cost reduction of the transmission system by 30% in comparison to a newly built hydrogen pipeline system.     

Potential energy and greenhouse gas emission effects of hydrogen production from coke oven gas in U.S. steel mills

For this study, we examined the energy and emission effects of hydrogen production from coke oven gas (COG) on a well-to-wheels basis and compared these effects with those of other hydrogen production options, as well as with those of conventional gasoline and diesel options. We then estimated the magnitude of hydrogen production from COG in the United States and the number of hydrogen fuel cell vehicles (FCVs) that could potentially be fueled with the hydrogen produced from COG. Our analysis shows that this production pathway can achieve energy and greenhouse gas emission reduction benefits. This pathway is especially worth considering because first, the sources of COG are concentrated in the upper Midwest and in the Northeast United States, which would facilitate relatively cost-effective collection, transportation, and distribution of the produced hydrogen to refueling stations in these regions. Second, the amount of hydrogen that could be produced may fuel about 1.7 million cars, thus providing a vital near-term hydrogen production option for FCV applications.     

Life-cycle assessment of diesel, natural gas and hydrogen fuel cell bus transportation systems

The Sustainable Transport Energy Programme (STEP) is an initiative of the Government of Western Australia, to explore hydrogen fuel cell technology as an alternative to the existing diesel and natural gas public transit infrastructure in Perth. This project includes three buses manufactured by DaimlerChrysler with Ballard fuel cell power sources operating in regular service alongside the existing natural gas and diesel bus fleets. The life-cycle assessment (LCA) of the fuel cell bus trial in Perth determines the overall environmental footprint and energy demand by studying all phases of the complete transportation system, including the hydrogen infrastructure, bus manufacturing, operation, and end-of-life disposal. The LCAs of the existing diesel and natural gas transportation systems are developed in parallel. The findings show that the trial is competitive with the diesel and natural gas bus systems in terms of global warming potential and eutrophication. Emissions that contribute to acidification and photochemical ozone are greater for the fuel cell buses. Scenario analysis quantifies the improvements that can be expected in future generations of fuel cell vehicles and shows that a reduction of greater than 50% is achievable in the greenhouse gas, photochemical ozone creation and primary energy demand impact categories.     

Deployment of fuel cell vehicles in China: Greenhouse gas emission reductions from converting the heavy-duty truck fleet from diesel and natural gas to hydrogen

Hydrogen fuel cells, as an energy source for heavy duty vehicles, are gaining attention as a potential carbon mitigation strategy. Here we calculate the greenhouse gas (GHG) emissions of the Chinese heavy-duty truck fleet under four hydrogen fuel cell heavy-duty truck penetration scenarios from 2020 through 2050. We introduce Aggressive, Moderate, Conservative and No Fuel Cell Vehicle (No FCV) scenarios. Under these four scenarios, the market share of heavy-duty trucks powered by fuel cells will reach 100%, 50%, 20% and 0%, respectively, in 2050. We go beyond previous studies which compared differences in GHG emissions from different hydrogen production pathways. We now combine an analysis of the carbon intensity of various hydrogen production pathways with predictions of the future hydrogen supply structure in China along with various penetration rates of heavy-duty fuel cell vehicles. We calculate the associated carbon intensity per vehicle kilometer travelled of the hydrogen used in heavy-duty trucks in each scenario, providing a practical application of our research. Our results indicate that if China relies only on fuel economy improvements, with the projected increase in vehicle miles travelled, the GHG emissions of the heavy-duty truck fleet will continue to increase and will remain almost unchanged after 2025. The Aggressive, Moderate and Conservative FCV Scenarios will achieve 63%, 30% and 12% reductions, respectively, in GHG emissions in 2050 from the heavy duty truck fleet compared to the No FCV Scenario. Additional reductions are possible if the current source of hydrogen from fossil fuels was displaced with increased use of hydrogen from water electrolysis using non-fossil generated electricity.     

Optimal design of a sleeve-type steam methane reforming reactor for hydrogen production from natural gas

The three-dimensional computational fluid dynamics (CFD) model was used in a sleeve-type steam methane reforming (SMR) reactor for H₂ production of 2.5 Nm³/h from natural gas. The feed and combustion gases acted as a counter-current heat exchange owing to a narrow sleeve equipped between the combustor and catalyst-bed. The CFD results were validated against the experimental data of the SMR reactor with a sleeve gap size of 3 mm. The effect of the sleeve gap size and the flame shape on process performances such as H₂ production rate, thermal efficiency, and uniformity of catalyst-bed temperature was investigated using the CFD model. The sleeve gap size influenced the gas velocity inside the sleeve gap and the convective heat transfer. The SMR reactor with a sleeve gap size of 7 mm showed the highest H₂ production rate and thermal efficiency when comparing six sleeve gap sizes ranging from 2 to 10 mm. A new flame shape for the SMR reactor with the sleeve gap size of 7 mm was proposed to improve the process performances.     

Study on leakage and explosion consequence for hydrogen blended natural gas in urban distribution networks

It appears to be the most economical means of transporting large quantities of hydrogen over great distances by the existing natural gas pipeline network. However, the leakage and diffusion behavior of urban hydrogen blended natural gas and the evolution law of explosion characteristics are still unclear. In this work, a Computational Fluid Dynamics three-dimensional simulation model of semi-confined space in urban streets is developed to study the diffusion process and explosion characteristics of hydrogen-blended natural gas. The influence mechanism of hydrogen blending ratio and ambient wind speed on the consequences of explosion accident is analyzed. And the dangerous area with different environmental wind effects is determined through comparative analysis based on the most dangerous scenarios. Results indicate that the traffic flow changes the diffusion path of the jet, the flammable gas cloud forms a complex profile in many obstacles, high congestion level lead to more serious explosion accidents. Wind effect keeps the flammable gas cloud near the vehicle flow, the narrow gaps between the vehicles aggravate the expansion of the flammable gas cloud. When the wind direction is consistent with the leakage direction, hydrogen blended natural gas is gathered in the recirculation zone due to the vortex effect, which results in more serious accident consequences. With the increase in hydrogen blending ratio, the higher content of H and OH in the gas mixture significantly increases the premixed burning rate, the maximum overpressure rises rapidly when the hydrogen blend level increases beyond 40%. The results can provide a basis for construction safety design, risk assessment of leakage and explosion hazards, and emergency response in hydrogen blended natural gas distribution systems.     

Modeling study on the production of hydrogen/syngas via partial oxidation using a homogeneous charge compression ignition engine fueled with natural gas

The production of hydrogen and syngas from natural gas using a homogeneous charge compression ignition reforming engine is investigated numerically. The simulation tool used was CHEMKIN 3.7, using the GRI-3 natural gas combustion mechanism. This simulation was conducted on the changes in hydrogen and syngas concentration according to the variations of equivalence ratio, intake temperature, oxygen enrichment, engine speed, initial pressure, and fuel additives with partial oxidation combustion. The simulation results indicate that the hydrogen/syngas yields are strongly dependent on the equivalence ratio with maxima occurring at an optimal equivalence ratio varying with engine speed. The hydrogen/syngas yields increase with increasing intake temperature and oxygen contents in air. The hydrogen/syngas yields also increase with increasing initial pressure, especially at lower temperatures, yet high temperature can suppress the pressure effect. Furthermore, it was found that the hydrogen/syngas yields increase when using fuel additives, especially hydrogen peroxide. Through the parametric screening studies, optimum operating conditions for natural gas partial oxidation reforming are recommended at 3.0 equivalence ratio, 530 K intake temperature, 0.3 oxygen enrichment, 500 rpm engine speed, 1 atm initial pressure, and 7.5% hydrogen peroxide.     

The role of hydrogen cars in the economy of California

Hydrogen has been proposed as an alternative transportation fuel that could reduce energy consumption and eliminate tailpipe emissions when used in fuel cell vehicles (FCVs). To investigate the potential effects of hydrogen vehicles on California’s economy over the next two decades, we employed the modified Costs for Advanced Vehicles and Energy (CAVE) model and a California-specific computable general equilibrium model. Results indicate that, even in the aggressive scenario, hydrogen cars can only account for a minor fraction of the on-road fleet through 2030. Although new sales could drop sharply, conventional gasoline cars and carryover pre-2010 vehicles are still expected to dominate the on-road vehicle stock and consume the majority of transportation energy through 2030. Transportation energy consumption could decline dramatically, mainly because of the fuel economy advantage of FCVs over conventional cars. Both moderate and aggressive hydrogen scenarios are estimated to have a slightly negative influence on California’s economy. However, the negative economic impacts could be lessened as the market for hydrogen and FCVs builds up. Based on the economic optimization model, both hydrogen scenarios would have a negative economic impact on California’s oil refining sector and, as expected, a positive impact on the other directly related sectors that contribute to either hydrogen production or FCV manufacturing.     

Assessment of natural gas/hydrogen blends as an alternative fuel for industrial heat treatment furnaces

The present study investigates the application of natural gas/hydrogen blends as an alternative fuel for industrial heat treatment furnaces and their economic potential for decreasing carbon dioxide emissions in this field of application. Doing so, a detailed technological analysis of several influencing parameters on the heating system was performed as well as a consideration of furnace heating technology challenges. Starting with an evaluation of the main thermophysical properties of the blends and their corresponding flue gases, requirements for the heating systems were identified. Potential ways of decreasing flue gas losses and increasing the heat transfer are shown. In the radiant tube application, an increased overall combustion efficiency of about 1.2% was measured at 40 vol% hydrogen in the fuel gas. Influences on the air to gas ratio control system of the furnace is a further important point, which was considered in this study. Two commonly used control systems were evaluated concerning their capabilities to regulate the gas flow rates of blends with varying hydrogen contents and combustion properties, such as Wobbe Index. This is important, since it shows the capability to retrofit existing furnaces. Two types of burners were tested with different natural gas/hydrogen blends. This includes an open jet burner with air-staged and flameless combustion operation modes. A recuperative burner for radiant tube application was considered as well in these tests. Doing so, the nitrogen oxide formation of both systems under different operating conditions and different fuel blends were evaluated. An increase by about 10% at air-staged combustion and about 100% at flameless combustion was measured by a hydrogen content of 40 vol% in comparison to pure natural gas firing. Finally, the additional fuel costs of natural gas hydrogen blends and different cases are presented in an economic analysis. The driving force for the use of hydrogen as a fuel is the price of the CO2 certificates, which are considered in the analysis at a current price of 25.2 €/t CO2.     

Study on the stratification of the blended gas in the pipeline with hydrogen into natural gas

When blending hydrogen into existing natural gas pipelines, the non-uniform concentration distribution caused by the density difference between hydrogen and natural gas will result in the fluctuations of local hydrogen partial pressure, which may exceed the set one, leading to pipeline failure, leakage, measurement error, and terminal appliance. To solve the problem, the H₂–CH₄ stratification in the horizontal and undulated pipe was investigated experimentally and with numerical simulations. The results show that in the gas stagnant situation, hydrogen-methane blending process will cause an obvious stratification phenomenon. The relations between the elevation, pressure, hydrogen fraction, etc., and the gas stratification are figured out. Moreover, even when the blended gas flows at a low rate, the hydrogen-caused stratification should also be considered. Thereafter, the blended gas should be controlled into a situation with low pressure and high speed, which could help to set the pressure, speed, the fraction of H₂.     

Dynamic modeling and characteristic analysis of natural gas network with hydrogen injections

With the transformation of energy structure, the proportion of renewable energy in the power grid continues to increase. However, the power grid's capacity to absorb renewable is limited. In view of this, converting the excess renewable energy into hydrogen and injecting it into natural gas network for transportation can not only increase the absorption capacity of renewable energy but also reduce the transportation cost of hydrogen. While this can lead to the problem that hydrogen injection will make the dynamic characteristics of the pipeline more complicated, and hydrogen embrittlement of pipeline may occur. It is of great significance to simulate the dynamic characteristics of gas pipeline with hydrogen injection, especially the hydrogen mixture ratio. In this paper, the cell segmentation method is used to solve each natural gas pipeline model, the gas components are recalculated in each cell and the parameters of partial differential equation are updated. Additionally, the dynamic simulation model of natural gas network with hydrogen injections is established. Simulation results show that for a single pipeline, when the inlet hydrogen ratio changes, whether or not hydrogen injection has little influence on the pressure and flow. The propagation speed of hydrogen concentration is far less than that of the pressure and flow rate, and it takes about 1.2 × 10⁵ s for the 100 km pipeline hydrogen ratio to reach the steady state again.     

Economic,environmental, and social impacts of the hydrogen supply system combining wind power and natural gas

Hydrogen economy is one of the most attractive alternatives to the current carbon-based energy system, since it can be produced from diverse resources and used as a carbon-free energy carrier from the end-user's perspective. This study proposes a hybrid hydrogen supply system for the transport sector, which includes all the life stages from production, transport, and storage to final distribution (fueling stations). Particularly, we consider two types of resources for hydrogen production (i.e., renewable wind power and conventional natural gas) to identify the benefits and bottlenecks of hydrogen supply systems from the economic, environmental, and social perspectives. To achieve this goal, rigorous process models for the involved processes (i.e., hydrogen production by steam methane reforming from natural gas and water electrolysis using wind power, and hydrogen storage and transport) are developed. To illustrate the capability of the proposed system, we conducted a design problem within the hydrogen supply system in Jeju Island, Korea. In this case study, three scenarios were generated by combining different hydrogen production options: 1) wind power-based hydrogen production, 2) natural gas-based hydrogen production, and 3) integrated hydrogen production. As a result, we discussed the optimal hydrogen supply system, from the life cycle perspective, by identifying technical bottlenecks, major cost-drivers, and CO₂ burdens.     

Experimental investigation on performance of hydrogen additions in natural gas combustion combined with CO2

Natural gas with H₂ is widely used for lean-burn combustion, which leads to NO_x emission as the main problem for it. For decreasing NO_x emission and increasing thermal efficiency, the investigation on seeking the influence of H₂ fractions on the mixture of CH₄ and CO₂ was conducted. Firstly, the ignition timing was decided through thermal efficiency and brake mean effective pressure (BMEP) for CH₄ only. Then, combustion characteristics of CH₄, CH₄+CO₂ and CH₄+CO₂+H₂ were compared with volume percentage of H₂ changing from 5% to 30%. Finally, the H₂ injection strategy was checked between closed and open valve injections. Among these discussions, thermal efficiency, power output, BMEP and fuel consumption were evaluated. Results show that CO₂ addition decreases power output and BMEP, leading to much more fuel consumption and lower thermal efficiency. When H₂ is added, at the rich mixture conditions (λ＜1.0), power output and thermal efficiency decrease sharply as the mixture is enriched. However, at the lean-burn conditions (λ＞1.0), the decrease in flow rate of lower heating value (LHV) and increase in power output finally result in the higher efficiency with H₂ addition. Moreover, when λ＞1.0, both low fuel consumption and high efficiency can be obtained with H₂ addition to achieve the high BMEP. Furthermore, the open valve injection could obtain higher thermal efficiency, power output and BMEP with lower fuel consumption, suggesting that the H₂ injection strategy should be well controlled with the ignition timing.     

The influences of hydrogen on the performance and emission characteristics of a heavy duty natural gas engine

Because blending hydrogen with natural gas can allow the mixture to burn leaner, reducing the emission of nitrogen oxide (NO_x), hydrogen blended with natural gas (HCNG) is a viable alternative to pure fossil fuels because of the effective reduction in total pollutant emissions and the increased engine efficiency.In this research, the performance and emission characteristics of an 11-L heavy duty lean burn engine using HCNG were examined, and an optimization strategy for the control of excess air ratio and of spark advance timing was assessed, in consideration of combustion stability. The thermal efficiency increased with the hydrogen addition, allowing stable combustion under leaner operating conditions. The efficiency of NO_x reduction is closely related to the excess air ratio of the mixture and to the spark advance timing. With the optimization of excess air ratio and spark advance timing, HCNG can effectively reduce NO_x as much as 80%.     

Blending blue hydrogen with natural gas for direct consumption: Examining the effect of hydrogen concentration on transportation and well-to-combustion greenhouse gas emissions

Jurisdictions are looking into mixing hydrogen into the natural gas (NG) system to reduce greenhouse gas (GHG) emissions. Earlier studies have focused on well-to-wheel analysis of H₂ fuel cell vehicles, using high-level estimates for transportation-based emissions. There is limited research on transportation emissions of hythane, a blend of H₂ and NG used for combustion. An in-depth analysis of the pipeline transportation system was performed for hythane and includes sensitivity and uncertainty analyses. When hythane with 15% H₂ is used, transportation GHG emissions (gCO2eq/GJ) increase by 8%, combustion GHG emissions (gCO2eq/GJ) decrease by 5%, and pipeline energy capacity (GJ/hr) decreases by 11% for 50–100 million m³/d pipelines. Well-to-combustion (WTC) emissions increase by 2.0% without CCS, stay the same with a 41% CCS rate, decrease by 2.8% for the 100% CCS scenario, and decrease by 3.6% in the optimal CO₂-free scenario. While hythane contains 15% H₂ by volume only 5% of the gas’ energy comes from H₂, limiting its GHG benefit.     

Catalytic reforming of natural gas for hydrogen production in a pilot fluidized-bed membrane reactor: Mapping of operating and feed conditions

A fluidized-bed membrane reformer was operated in two independent laboratories to map various operating conditions, to investigate the effects of changing the composition of the natural gas feed stream and to verify earlier experimental trials. Two feed natural gases were tested, containing either 95.5 or 90.1 mol% of methane (3.6 or 9.9 mol% of other gaseous higher hydrocarbons). Experimental tests investigated the influence of total membrane area, reactor pressure, permeate pressure and natural gas feed rates. A permeate-H₂-to reactor natural gas feed molar ratio >2.3 was achieved with six two-sided membrane panels under steam reforming conditions and a pressure differential across the membranes of 785 kPa. The total cumulative reforming time reached 395 h, while hydrogen purity exceeded 99.99% during all tests.     

Effect of hydrogen direct injection on natural gas/hydrogen engine performance under high compression-ratio conditions

In traffic transportation, the use of low-carbon fuels is the key to being carbon-neutral. Hydrogen-enhanced natural gas gets more and more attention, but practical engines fueled with it often suffer from low engine power output. In this study, the inner mechanism of hydrogen direct injection on methane combustion was optically studied based on a dual-fuel supply system. Simultaneous pressure acquisition and high-speed direct photography were used to analyze engine performance and flame characteristics. The results show that lean combustion can improve methane engine's thermal efficiency, but is limited by cyclic variations under high excess air coefficient conditions. Hydrogen addition mainly acts as an ignition promoter for methane lean combustion, as a result, the lean combustion limit and thermal efficiency can be improved. As for hydrogen injection timing, late injection can increase the in-cylinder turbulence intensity but also the inhomogeneity, so a suitable injection timing is needed for improving the engine's performance. Besides, late hydrogen injection is more effective under lean conditions because of the reduced mixture inhomogeneity. The current study shall give some insights into the controlling strategies for natural gas/hydrogen engines.     

Combustion performance of low-NOx and conventional storage water heaters operated on hydrogen enriched natural gas

Adding renewable hydrogen into natural gas pipeline would bring down the net gas C/H ratio and hence the CO₂ emissions. Also, it can help stabilize electric grids and maximize the renewable output of intermittent energy sources (solar, wind, etc.) via power-to-gas pathway. However, hydrogen differs in its chemical and physical characteristics (flammability range, flame speed, density, adiabatic flame temperature, energy content, etc.) than natural gas. Before transitioning to hydrogen admixing into pipelines, a general agreement on maximum hydrogen tolerance pertaining to end use (residential appliances) operation needs to be established. Focusing on the combustion performance of two representative models of storage water heaters (conventional and low-NO_x) in California, this research addresses how much H₂ content in natural gas can be tolerated without loss of critical performance parameters with reliable operation. Characteristics like flashback, ignition delay, flame structure, and emissions (NO_x, NO, CO, CO₂, UHC, and NH₃) at different concentrations of H₂ admixed with natural gas is investigated. The present study shows <10% H₂ can be added to natural gas without any loss of efficiency for both the low-NO_x and conventional storage water heater. This work also aims to provide a brief review of burner configuration and emission regulation pertaining to water heating owing to a gap in the literature.     

Hybridizing concentrated solar power (CSP) with biogas and biomethane as an alternative to natural gas: Analysis of environmental performance using LCA

Concentrating Solar Power (CSP) plants typically incorporate one or various auxiliary boilers operating in parallel to the solar field to facilitate start up operations, provide system stability, avoid freezing of heat transfer fluid (HTF) and increase generation capacity. The environmental performance of these plants is highly influenced by the energy input and the type of auxiliary fuel, which in most cases is natural gas (NG). Replacing the NG with biogas or biomethane (BM) in commercial CSP installations is being considered as a means to produce electricity that is fully renewable and free from fossil inputs. Despite their renewable nature, the use of these biofuels also generates environmental impacts that need to be adequately identified and quantified. This paper investigates the environmental performance of a commercial wet-cooled parabolic trough 50 MWe CSP plant in Spain operating according to two strategies: solar-only, with minimum technically viable energy non-solar contribution; and hybrid operation, where 12% of the electricity derives from auxiliary fuels (as permitted by Spanish legislation). The analysis was based on standard Life Cycle Assessment (LCA) methodology (ISO 14040-14040). The technical viability and the environmental profile of operating the CSP plant with different auxiliary fuels was evaluated, including: NG; biogas from an adjacent plant; and BM withdrawn from the gas network. The effect of using different substrates (biowaste, sewage sludge, grass and a mix of biowaste with animal manure) for the production of the biofuels was also investigated. The results showed that NG is responsible for most of the environmental damage associated with the operation of the plant in hybrid mode. Replacing NG with biogas resulted in a significant improvement of the environmental performance of the installation, primarily due to reduced impact in the following categories: natural land transformation, depletion of fossil resources, and climate change. However, despite the renewable nature of the biofuels, other environmental categories like human toxicity, eutrophication, acidification and marine ecotoxicity scored higher when using biogas and BM.     

Influence on hydrogen production of the minor components of natural gas during its decomposition using carbonaceous catalysts

In this work, the catalytic decomposition of the minor hydrocarbons present in natural gas, such as ethane and propane, over a commercial carbon black (BP2000) is studied. The influence of the reaction temperature on the product gas distribution was investigated. Increasing reaction temperatures were found to increase both hydrocarbon conversion and hydrogen selectivity. Carbon produced by ethane and propane was predominantly deposited as long filaments formed by spherical aggregates with diameters on the order of nanometres. Furthermore, the influence of ethane and propane on methane decomposition over BP2000 was also investigated, showing enrichment in hydrogen concentration with the addition of small amounts of these hydrocarbons in the feed. Additionally, the positive catalytic effect of H₂S on methane decomposition over BP2000 is addressed.