An assessment of electrolytic hydrogen production from H2S in Black Sea waters

In the deeper parts of the Black Sea basin, water is anoxic. Hydrogen sulfide (H₂S) occurs naturally, and its concentration is nearly constant, around 9.5 mg/L at 1500 m depth. Its high solubility, and the existing chemical environment facilitate its accumulation and containment in the seawater, and its extraction poses a challenge.Possibility of hydrogen and sulfur production from H₂S contained in the waters of Black Sea is investigated conceptually. A multistage process is considered which involves extraction of seawater, adsorption of H₂S, electrochemical production of hydrogen and polysulfides; fresh water production by desalination of seawater and further hydrogen production from the resulting salty solution through chlorine-alkaline electrolysis. Some consideration is included regarding the economic and environmental aspects of the process.     

Investigation of the electro-oxidation of artificial Black Sea water using cyclic voltammetry on metal sulfide electrodes (I)

Black Seawater is an alternative hydrogen source because it has hydrogen sulfide content. Seawater electrolysis is a promising method to produce hydrogen. The anodic oxidation of hydrogen sulfide is a novel approach for directly generating electricity via fuel cells. Therefore, four materials (Cu, Stainless Steel 304 (SS), V₂O₅ and Ni) were examined in artificial seawater containing hydrogen sulfide (HS⁻). We developed active metal sulfide electrodes for oxidizing HS⁻. Alongside the corrosion potentials, the progression of the oxidation and reduction reactions was obtained by the cyclic voltammetry method. The active behaviors of the metal sulfide (MS_x) layers were determined by applying Electrochemical Impedance Spectroscopy (EIS). Although the Cu₂S electrode acts as the active catalyst during HS⁻ ion oxidation, NiS is the most suitable metal sulfide because it exhibits a higher corrosion resistance than Cu₂S. While V₂O₅ demonstrates catalytic activity at high temperatures (≥30 °C), FeS layers corrode easily in the artificial seawater environment.     

Blue sky mining: Strategy for a feasible transition in emerging countries from natural gas to hydrogen

Natural gas is often considered a transition fuel to a deep decarbonized world. However, for this to happen, new technologies should be fostered, among which a natural gas-based H₂ industry can become a key-option. This study tests the hypothesis that the development of a natural gas-based H₂ industry equipped with CO₂ capture can monetize natural gas remaining resources, mitigate CO₂ emissions and facilitate the transition to the renewable energy-based H₂. To do that, this study evaluates a stepwise strategy for setting up the development of H2, departing from the idle capacity in the existing natural gas industry, to progressively create a H₂ independent supply. Findings indicated that this strategy can be feasible, according to the case study assessed at relatively moderate crude oil prices. Nevertheless, CO₂ storage can become a constraint to deal with the co-produced CO₂ from the steam methane reforming units. Therefore, it is worth developing storage options.     

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.     

Investigation of the electro-oxidation of artificial Black Sea water by cyclic voltammetry on molybdenum (II)

The electro-oxidation of H₂S in Black Sea water to generate electricity was investigated. MoS₂ exhibited catalytic activity toward the oxidation of H₂S in artificial sea water. The catalytic activity of molybdenum sulfide was found to depend on the electrolyte pH and on the temperature. Cyclic voltammograms taken in the artificial sea water containing hydrogen sulfide at pH = 14 exhibited a peak at 500 mV related to the oxidation of HS⁻. Furthermore, the peak current of the MoS₂ electrode increased to 400 mA g⁻¹ from 250 mA g⁻¹ (approximately 1.6-fold) when the temperature was increased from 353 K to 363 K.     

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.     

Technical,economic, and environmental analyses of the modernization of a chamber furnace operating on natural gas or hydrogen

The paper presents a technical, economic and environmental analyses of a chamber furnace used to heat the charge before forging. The energy efficiency of the furnace before the modernization was 18%, after the modernization it was 31% (partial modernization due to large financial outlays). Other variants were also analysed: complete modernization, the variant of furnace modernization with 30% hydrogen content in the gas and the variant with 100% hydrogen as fuel. The analyses showed that with the current gas price (0.025 EUR/kWh) and the price of emission allowances (nearly 60 EUR/MgCO₂) and 100 cycles/year, the difference in Net Present Value (NPV) before base variant and partial modernization is around 900,000 EUR and before base variant and full modernization is 1,200,000 EUR. The introduction of the gas and 30% of hydrogen co-combustion option versus the base scenario option for 150 cycles per year results in a NPV difference of at least 2 million EUR. The option of 100% hydrogen as a fuel is the most advantageous from the point of view of reducing CO₂ emissions - it is largely influenced by the rising prices of CO₂ emission allowances.     

Utilization of waste heat from cement plant to generate hydrogen and blend it with natural gas

In this paper, a waste heat recovery system for a cement plant is developed and analyzed with the softwares of Engineering Equation Solver (EES) and Aspen Plus. This system is novel in a way that hydrogen is uniquely produced from waste heat obtained from the cement slag and blended with natural gas for domestic use. The presented system has a steam Rankine cycle combined with an organic Rankine cycle, an alkaline electrolyzer unit, oxygen and hydrogen storage tanks, a blending unit, and a combustor. Moreover, multiple useful outputs are obtained, such as power, hydrogen, and natural gas, as well as hydrogen blend. The power obtained from the organic Rankine cycle becomes the highest when the organic fluid R600a is used as a working fluid. The power generated from turbines is fed to the grid externally and the cement plant for internal use. Also, some power is utilized to produce hydrogen via an alkaline electrolyzer which has an efficiency of 62.94%. With the change of the percentage of hydrogen in the blend from 0% to 50%, the annual consumption of natural gas reduces from 48.261 billion m³ to 37.086 billion m³. Furthermore, the overall exergy and energy efficiencies for the plant are found at 55% and 22%, respectively. The carbon dioxide emissions in the released exhaust gas reduce from 34% to 28% when the same volumetric flow rates of the blend and oxygen gas are fed to the reactor. NO and NO₂ emissions increase from 4.06 g/day to 7.45 g/day, and from 0.02 g/day to 0.09 g/day when the hydrogen content is increased from 5% to 20%. Moreover, carbon monoxide emissions decrease from 0.05 g/day to 0.02 g/day, accordingly. As a result, both combustion energy and exergy efficiencies increase with the addition of hydrogen. Furthermore, CO and CO₂ emissions decrease with the hydrogen content increases.     

A parametric investigation of hydrogen energy potential based on H2S in Black Sea deep waters

In this study, a parametric investigation is carried out to estimate the hydrogen energy potential depending on the quantities of H₂S in Black Sea deep waters. The required data for H₂S in Black Sea deep waters are taken from the literature. For this investigation, the H₂S concentration and water layer depth are taken into account, and 100% of conversion efficiency is assumed. Consequently, it is estimated that total hydrogen energy potential is approximately 270 million tons produced from 4.587 billion tons of H₂S in Black Sea deep waters. Using this amount of hydrogen, it will be possible to produce 38.3 million TJ of thermal energy or 8.97 million GWh of electricity energy. Moreover, it is determined that total hydrogen potential in Black Sea deep waters is almost equal to 808 million tons of gasoline or 766 million tons of NG (natural gas) or 841 million tons of fuel oil or 851 million tons of natural petroleum. These values show that the hydrogen potential from hydrogen sulphur in Black Sea deep water will play an important role to supply energy demands of the regional countries. Thus, it can be said that hydrogen energy reserve in Black Sea is an important candidate for the future hydrogen energy systems.     

Hydrogen separation from blended natural gas and hydrogen by Pd-based membranes

Hydrogen separation membranes based on a heated metal foil of a palladium alloy, offer excellent permeability for hydrogen as a result of the solution-diffusion mechanism. Here, the possibility to separate hydrogen from the mixture of Natural Gas (NG) and hydrogen (NG+H₂) with various NG concentrations using Pd, PdCu₅₃ and PdAg₂₄ hydrogen purification membranes is demonstrated. Hydrogen concentrations above ∼25% (for Pd and PdCu₅₃) and ∼15% (for PdAg₂₄) were required for the hydrogen separation to proceed at 400 °C and 5 bar pressure differential. Hydrogen permeability of the studied alloys could be almost fully recovered after switching the feed gas to pure hydrogen, indicating no significant interaction between the natural gas components and the membranes surface at the current experimental condition. Hydrogen flux of the membranes at various pressure differential was measured and no changes in the hydrogen permeation mechanism could be noticed under (NG 50%+H₂) mixture. The hydrogen separation capability of the membranes is suggested to be mainly controlled by the operating temperature and the hydrogen partial pressure.     

Detecting hydrogen concentrations during admixing hydrogen in natural gas grids

The first applications of hydrogen in a natural gas grid will be the admixing of low concentrations in an existing distribution grid. For easy quality and process control, it is essential to monitor the hydrogen concentration in real time, preferably using cost effective monitoring solutions. In this paper, we introduce the use of a platinum based hydrogen sensor that can accurately (at 0.1 vol%) and reversibly monitor the concentration of hydrogen in a carrier gas. This carrier gas, that can be nitrogen, methane or natural gas, has no influence on the accuracy of the hydrogen detection. The hydrogen sensor consists of an interdigitated electrode on a chip coated with a platinum nanocomposite layer that interacts with the gas. This chip can be easily added to a gas sensor for natural gas and biogas that was already developed in previous research. Just by the addition of an extra chip, we extended the applicability of the natural gas sensor to hydrogen admixing. The feasibility of the sensor was demonstrated in our own (TNO) laboratory, and at a field test location of the HyDeploy program at Keele University in the U.K.     

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.     

Techno-economic analysis of PSA separation for hydrogen/natural gas mixtures at hydrogen refuelling stations

Logistics of hydrogen is one of the bottlenecks of a hydrogen economy. In this study, a pressure swing adsorption (PSA) system is proposed for the separation of hydrogen from natural gas, co-transported in the natural gas grid. The economic feasibility of hydrogen supplied by a PSA system at a refuelling station is assessed and compared with other alternatives. The adsorbent material is key to the design of a PSA system, which determines the operation performance and cost. It is concluded that a refuelling station with hydrogen supplied by a PSA system is economically feasible. The final hydrogen price including hydrogen supply, compression, storage, and dispensing is compared with two other hydrogen supply methods: on-site electrolysis and tube-trailer transported hydrogen. Currently, PSA supplied hydrogen is a more economical option. On-site electrolysis can become a more economical option in the future with improved cell efficiencies and reduced electricity prices. Tube-trailer transported hydrogen is highly influenced by the distance travelled. The findings of this study will help with more efficient distribution of hydrogen.     

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.     

The exploitation of hydrogen sulfide for hydrogen production in geothermal areas

Hydrogen is a valuable energy resource and it is widespread in nature. As a matter of fact, researches on hydrogen production are currently experiencing an increasing interest from scientists around the world since this resource is clean and renewable. Several methods of producing hydrogen have been developed in industrialized countries such as the United States of America and Germany.This paper is interested in the process by which hydrogen sulfide of geothermal areas is exploited for hydrogen production. In fact, research advances in this field have concluded that hydrogen sulfide of geothermal resources can contribute significantly and economically in the process of hydrogen generation.The present paper was principally conducted from a literature study and a synthesis of works achieved in recent years in order to highlight the various aspects of hydrogen production from hydrogen sulfide and particularly to study the possibility of the exploitation of Algeria’s thermal resources in this field.     

The emerging hydrogen economy and its impact on LNG

Hydrogen is gaining prominence as a critical tool for countries to meet decarbonisation targets. The main production pathways are based on natural gas or renewable electricity. LNG represents an increasingly important component of the global natural gas market. This paper examines synergies and linkages between the hydrogen and LNG values chains and quantifies the impact of increased low-carbon hydrogen production on global LNG flows. The analysis is conducted through interviews with LNG industry stakeholders, a review of secondary literature and a scenario-based assessment of the potential development of global low-carbon hydrogen production and LNG trade until 2050 using a novel, integrated natural gas and hydrogen market model. The model-based analysis shows that low-carbon hydrogen production could become a significant user of natural gas and thus stabilise global LNG demand. Furthermore, commercial and operational synergies could assist the LNG industry in developing a value chain around natural gas-based low-carbon hydrogen.     

Low carbon hydrogen production in Canada via natural gas pyrolysis

Large scale, low cost, and low carbon intensity hydrogen production is needed to reduce emissions in the energy and transportation sectors. We present a techno-economic analysis and life cycle assessment of natural gas pyrolysis technologies for hydrogen production, with carbon black (CB) as a co-product. Four designs were considered based on the source of heat to the pyrolysis system, the combustion medium, and use of carbon capture (CC) technology. The oxygen-fired-CB design with CC is the most attractive from financial and environmental perspectives, superior to a conventional steam methane reformer (SMR) process with CC. The estimated pre-tax minimum hydrogen selling prices for the pyrolysis technologies range between $1.08/kg and $2.43/kg when natural gas (NG) costs $3.76/GJ. Key advantages include near-zero onsite GHG emissions of the oxygen-fired-CB design with CC and up to 41% lower GHG emissions compared to the SMR + CC process. The results indicate that natural gas pyrolysis may be a feasible pathway for hydrogen production.     

The effects of hydrogen enriched natural gas under different engine loads in a diesel engine

Natural gas, which is among the alternative fuels, has become widespread in the transportation as it is both economical and environmentally friendly. While the use of natural gas is at a significant level in spark ignition engines, it has not yet been implemented in compression ignition engines (CI) as it worsens combustion due to ignition delay. In CI engines, however, the combustion properties of natural gas (NG) can be improved by adding hydrogen (H₂) to NG. This is one of the methods applied to use natural gas in CI engines. In this experimental study, two different volumetric rates of NG and NG/H₂ mixtures were added to the combustion air in a CI engine, and engine performance and emissions were examined under different engine loads. The experiments were performed at two different engine speeds, four different engine loads and no-load condition. An engine cylinder pressure of 59.16 bar, which is the closest value to the 59.39 bar obtained in the use of diesel fuel, was obtained at 1500 rpm for “Diesel + NG(500 g/h)” and 59.9 bar (highest values) was obtained for “Diesel + (500 g/h) [80%NG+20%H₂]" at 1750 rpm. For “Diesel + NG(250 g/h)” (Mix1) and “Diesel + NG(500 g/h)” (Mix2), as the engine speed increases, at the point where the maximum in-cylinder pressure is obtained occurs further to the right from top dead center (TDC). With the addition of 500 g/h NG, an increase of 4.5% was achieved in the cylinder pressure at full load, while an increase of 6.5% was achieved in the case of using “Diesel + (500 g/h) [80%NG+20%H₂]". Although the effect of the NG and NG/H₂ mixtures on in-cylinder pressure was small, the fuel consumption and thermal efficiency improved. Substantial improvements in hydrocarbon (HC) emissions were observed with the use of “Diesel + (250 g/h)[80%NG+20%H₂]”. Carbon dioxide (CO₂) emissions decreased with speed increase, but no significant differences in terms of CO₂ emissions were observed between the mixtures. There was a maximum difference of 15% between the diesel and the mixtures in CO₂ emissions. Although there was a decrease in nitrogen oxide (NO_x) levels with the increase in engine speed, the lowest NO_x emissions of 447.6 ppmvol was observed in “Diesel + NG(250 g/h)” (Mix1) at 1750 rpm at maximum load.     

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.     

Technical potential for developing natural gas use in the Brazilian red ceramic industry

The red ceramic industry in Brazil, consisting of over 7000 companies, requires large amounts of thermal energy, currently being met mainly by native fuelwood, which causes serious deforestation and soil erosion problems. The use of firewood does not allow achieving good energy performance in industrial ceramic kilns, causing high energy losses, low productivity and low quality products (bricks and roof tiles). Thus, to implement higher added value products, besides mitigate environmental problems caused by deforestation, the use of natural gas by the sector seems to be a promising alternative. Brazil’s natural gas market has grown at a fast pace in recent years. Its share in the country’s primary energy consumption increased from 3.7% to 9.3% between 1998 and 2007, compared to almost 21% in the world. The development of the Brazilian natural gas industry was grounded on stepping up supplies through integration with Bolivia from where natural gas is imported, together with fiscal incentives for promoting the demand. This paper estimates that the natural gas market that could be developed in the Brazilian red ceramic industry corresponds to less than 5% of the total industrial natural gas consumption, meaning that a major technological transformation of the country’s red ceramic industry will not severely affect the natural gas market equilibrium, contributing to reduce the country’s high rates of deforestation.