Economic competitiveness of compact steam methane reforming technology for on-site hydrogen supply: A Foshan case study

On-site hydrogen production through steam-methane reforming (SMR) from city gas or natural gas is believed to be a cost-effective way for hydrogen-based infrastructure due to high cost of hydrogen transportation. In recent years, there have been a lot of on-site hydrogen fueling stations under design or construction in China. This study introduces current developments and technology prospects of skid-mounted SMR hydrogen generator. Also, technical solutions and economic analysis are discussed based on China's first on-site hydrogen fueling station project in Foshan. The cost of hydrogen product from skid-mounted SMR hydrogen generator is about 23 CNY/kg with 3.24 CNY/Nm³ natural gas. If hydrogen price is 60 CNY/kg, IRR of on-site hydrogen fueling station project reaches to 10.8%. While natural gas price fall to 2.3 CNY/Nm³, the hydrogen cost can be reduced to 18 CNY/kg, and IRR can be raised to 13.1%. The conclusion is that skid-mounted SMR technology has matured and is developing towards more compact and intelligent design, and will be a promising way for hydrogen fueling infrastructures in near future.     

Multi-hub hydrogen refueling station with on-site and centralized production

In recent decades, the consequences of climate changes due to greenhouse gas (GHG) emissions have become ever more impactful, forcing international authorities to find green solutions for sustainable economic development. In this regard, one of the global targets is the reduction of fossil fuels utilization in the transport sector to encourage the diffusion of more environmentally friendly alternatives. Among them, hydrogen is emerging as a viable candidate since it is a potentially emission-free fuel when produced by exploiting renewable energy sources (RES). Nevertheless, to allow widespread use of this gas in the transport sector, several technoeconomic barriers, including production cost, and lack of distribution and storage infrastructure, have to be overcome. Distributed hydrogen production via renewable energy-powered electrolysis could be an effective solution to reduce cost and lead to economies of scale. In this study a multi-hub configuration with on-site production from PV-powered electrolysis and centralized production from steam methane reforming (SMR) is proposed. In particular, an infrastructure network for a bus refueling station located in Lazio is considered as a case study. First, each hub, composed of PV panels, an electrolyzer, a compression system, high-pressure and low-pressure storages, and hydrogen dispensers with chiller, is modeled in a Matlab/Simulink environment. Then, a design perturbation analysis is carried out to determine the impact of the configuration on the refueling station performance in terms of carbon emissions levels and the Levelized Cost of hydrogen (LCOH). The results show a significant influence of the station size on the economic performance highlighting significant benefits (reduction up to 40% in the LCOH) for a 80 bus HUB with a saturating trend towards larger sizes. CO₂ emissions per unit mass of hydrogen are kept limited for all the stations thanks to the synergistic effects of SMR and Electrolyzer. Interconnecting more than one station each other further benefits can be achieved from the environmental perspective (savings up to 5 tons of CO₂ are demonstrated for a typical summer case study).     

Analysis of the economy of scale and estimation of the future hydrogen production costs at on-site hydrogen refueling stations in Korea

This paper deals with the analysis of the economy of scale at on-site hydrogen refueling stations which produce hydrogen through steam methane reforming or water electrolysis, in order to identify the optimum energy mix as well as the total construction cost of hydrogen refueling stations in Korea. To assess the economy of scale at on-site hydrogen stations, the unit hydrogen costs at hydrogen stations with capacities of 30 Nm³/h, 100 Nm³/h, 300 Nm³/h, and 700 Nm³/h were estimated. Due to the relatively high price of natural gas compared to the cost of electricity in Korea, water electrolysis is more economical than steam methane reforming if the hydrogen production capacity is small. It seems to be the best strategy for Korea to construct small water electrolysis hydrogen stations with production capacities of 100 Nm³/h or less until 2020, and to construct steam methane reforming hydrogen stations with production capacities of 300 Nm³/h or more after 2025.     

Addition of hydrogen refueling for fuel cell bus fleet to existing natural gas stations: A case study in Wuhan,China

Hydrogen refueling is an essential infrastructure for fuel cell vehicles, and currently, it appears to be a critical service needed to initiate the highly anticipated hydrogen economy in China. A practical selecting procedure of adding hydrogen refueling service to existing natural gas (NG) stations is proposed in this study. A case study in Wuhan, China, is established to assess the feasibility and future planning. The demand for hydrogen fuel and initial supply chain of hydrogen in Wuhan are estimated based on the deployment objective of fuel cell buses. The existing NG stations are evaluated based on 300 kg/day to determine whether they meet the hydrogen safety requirement using Google map or field investigation. The safety space requirement of the hydrogen refueling area on existing NG station is determined as 25.9 × 27.1 m². The optimal hydrogen refueling plan for fuel cell buses is calculated with multi‐objective analysis in economic, environmental, and safety aspects from the view of the hydrogen refueling supply chain. It is shown that adding hydrogen refueling stations to existing NG stations is feasible in technology, economics, regulation, and operation considerations. This study provides guidelines for building the hydrogen infrastructure for fuel cell buses at their early stage of commercial operation.     

Development of membrane reformer system for highly efficient hydrogen production from natural gas

A membrane reformer is composed of a steam reformer equipped with palladium-based alloy membrane modules and can perform steam reforming reaction of natural gas and hydrogen separation processes simultaneously, without shift converters and purification systems. We have developed a membrane reformer system with nominal hydrogen production capacity of 40 Nm³/h. The system has demonstrated the potential advantages of the membrane reformer: simple system configuration as benefited by single-step production of high-purity hydrogen (99.999% level), compactness, and high-energy efficiency of 70–76%. We are promoting development towards commercialization of the membrane reformer technology, focusing on further improvement of energy efficiency, proof of long-term durability and reliability, and establishment of system engineering technologies. The target of our current project is to develop a membrane reformer system that can produce 99.99% or higher-purity hydrogen from natural gas at a rate of 40 Nm³/h with hydrogen production energy efficiency of over 80%.     

Experimental study of the processes in hydrogen-oxygen gas generator

The paper presents a hydrogen-oxygen gas generator, which could be a key element of a novel scheme of hybrid hydrogen-air energy storage system, which proposes to store energy in both compressed air and hydrogen. At a power generation mode, hydrogen is combusted in oxygen, the produced steam is mixed with air and the gas mixture is used in a conventional gas turbine. The experimental hydrogen-oxygen gas generator has produced gas with temperatures 953–1163 K at pressures 2–4 MPa and has reached the thermal capacity up to 210 kW and thermal efficiency up to 95–99%. Separation of the combustion zone and air injection has helped to reduce NO_x content in the product gas to 11 mg/st.m³.     

Nickel-iron modified natural ore oxygen carriers for chemical looping steam methane reforming to produce hydrogen

Chemical looping steam methane reforming (CL-SMR) is a promising and efficient method to produce hydrogen and syngas. However, oxygen carrier (OC) prepared by synthesis are complex, expensive and poor mechanical performance, while natural ore OCs are low activity and poor selectivity. In order to avoid these problems, Ni/Fe modification of natural ores were proposed to improve the reactivity and stability of OC to CL-SMR. The results indicated that the modified calcite recombined and improved the structural phase during the reaction, enhancing performance and inhibiting agglomeration. Moreover, high ratio of iron to nickel was easy to sinter and decline the OC performance. In addition, with the increase of steam flow, both CH₄ conversion and carbon deposition decreased. Thereinto, the highest H₂ concentration, CH₄ conversion efficiency and H₂ yield were obtained when the ratio of steam to OC was 0.05. Furthermore, CH₄ flow rate had a great impact on CL-SMR performance. When the ratio of CH₄ to OC was 0.04, it achieved the highest CH₄ conversion efficiency of 98.96%, the highest H₂ concentration of 98.83% and the lowest carbon deposition of 3.23%. However, the carbon deposition increased with the increase of CH₄ flow rate. After a long-time chemical looping process, the Ni/Fe modified calcite showed a consistently stable performance with average H₂ concentration of 93.08%, CH₄ conversion efficiency of 88.03%, and carbon deposition of 2.15%.     

The economic and environmental impact of power to hydrogen/power to methane facilities on hybrid power-natural gas energy systems

The curtailment of renewable energy would be reduced by converting it to hydrogen or methane using power to hydrogen (P2H) facilities or power to methane (P2M) facilities. Both hydrogen and methane can be injected into the existing natural gas system which has significant potential to unlock the inherent flexibility of integrated energy systems. The coordinated operation strategy of the hybrid power-natural gas energy systems considering P2H and P2M is proposed aiming to minimize the operational cost. In addition, a method to calculate the higher heating value of hydrogen-natural gas mixture is presented along with a strategy for handling the constraints of hydrogen mixture level limits. The simulation results of three case studies demonstrate the economic and environmental benefits of P2H/P2M in terms of reductions in cost, CO₂ emissions and wind power curtailment. The differences in benefits between P2H and P2M have also been compared and analyzed.     

Dynamic planning and energy management strategy of integrated charging and hydrogen refueling at highway energy supply stations considering on-site green hydrogen production

The layout of electric vehicles charging stations and hydrogen refueling stations (HRSs) is more and more necessary with the development of electric vehicles (EVs) and progress in hydrogen energy storage technology. Due to the high costs of HRSs and the low demand for hydrogen, it is difficult for independent HRSs to make a profit. This study focuses on the dynamic planning of energy supply stations on highways in the medium and long term, considering the growth of EV charging demand and the change in the proportion of hydrogen fuel cell vehicles (HFCVs). Based on the perspective of renewable energy generators (REGs), this study seeks the dynamic optimal configuration and comprehensive benefits of adding HRS and battery to existing EVCS considering the travel rules of new energy vehicles (NEVs). The results show that (1) It is profitable for REGs to invest in HRSs; (2) The economy of investment in batteries by REGs depends on the source-load matching. It is feasible only when the output of renewable energy is difficult to meet the demand. (3) The business model of REGs producing hydrogen on-site and supplying both electricity and hydrogen is feasible.     

Numerical investigation of the leakage and explosion scenarios in China's first liquid hydrogen refueling station

Promoting fuel cells has been one of China's ambitious hydrogen policies in the past few years. Currently, several hydrogen fueling stations (HRSs) are under construction in China to fuel hydrogen-driven vehicles. In this regard, it is necessary to assess the risks of hydrogen leakage in HRSs. Aiming at conducting a comprehensive consequence assessment of liquid hydrogen (LH2) leakage on China's first liquid hydrogen refueling station (LHRS) in Pinghu, a pseudo-source model is established in the present study to simulate the LH2 leakage using a commercial CFD tool, FLACS. The effects of the layout of the LHRS, leakage parameters, and local meteorological conditions on the LH2 leakage consequence has been assessed from the perspectives of low-temperature hazards and explosion hazards. The obtained results reveal that considering the prevailing southeast wind in Pinghu city, the farthest low-temperature hazard distance and lower flammable limit (LFL) -distance occurs in the leakage scenario along the north direction. It is found that the trailer parking location in the current layout of the LHRS will worsen the explosion consequences of the LH2 leakage. Moreover, the explosion will completely destroy the control room and endanger people on the adjacent road when the leakage equivalent diameter is 25.4 mm. The performed analyses reveal that as the wind speed increases, the explosion hazard decreases.     

Development and CFD analysis for determining the optimal operating conditions of 250 kg/day hydrogen generation for an on-site hydrogen refueling station (HRS) using steam methane reforming

The objective of this study to develop and undertake a comprehensive CFD analysis of an effective state-of-the-art 250 kg/day hydrogen generation unit for an on-site hydrogen refueling station (HRS), an essential part of the infrastructure required for fuel cell vehicles and various aspects of hydrogen mobility. This design consists of twelve reforming tubes and one newly designed metal fiber burner to ensure superior emission standards and performance. Experimental and computational modeling steps are conducted to investigate the effects of various operating conditions, the excess air ratio (EAR) at the burner, the gas hourly space velocity (GHSV), the process gas inlet temperature, and the operating pressure on the hydrogen production rate and thermal efficiency. The results indicate that the performance of the steam methane reforming reactor increased significantly by improving the combustion characteristics and preventing local peak temperatures along the reforming tube. It is shown that EAR should be chosen appropriately to maximize the hydrogen production rate and lifetime operation of the reformer tube. It is found that high inlet process gas temperatures and low operating pressure are beneficial, but these parameters have to be chosen carefully to ensure proper efficiency. Also, a high GHSV shortens the residence time and provides unfavorable heat transfer in the bed, leading to decreased conversion efficiency. Thus, a moderate GHSV should be used. It is shown that heat transfer is an essential factor for obtaining increased hydrogen production. This study addresses the pressing need for the HRS to adopt such a compact system, whose processes can ensure greater hydrogen production rates as well as better durability, reliability, and convenience.     

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.     

Research on sealing performance and self-acting valve reliability in high-pressure oil-free hydrogen compressors for hydrogen refueling stations

Piston ring sealing and valve design play an important role in high-pressure oil-free reciprocating compressors for hydrogen refueling stations. The severe non-uniformity of the pressure distribution was suggested to be the root cause of the premature failure of the sealing rings, and therefore a mathematical model was established to simulate the unsteady flow within the gaps of piston rings, based on which the pressure distribution was obtained and the mechanism of the non-uniform abrasion of the rings was disclosed. The method to equalize the pressure difference through each ring was proposed by re-distributing the cut size of each ring, and it was validated experimentally. Aiming at the problem that the self-acting valves in hydrogen compressors could be easily destroyed by severe impact, this paper investigated the motion and impact of valves theoretically and experimentally, based on which the methodology was explored to design the parameters of valves for hydrogen compressors.     

Experimental correlations and integration of gas boosters in a hydrogen refueling station

Air driven gas boosters are often deployed in small scale compression systems. Manufacturers specifications, reporting outlet flow for a fixed inlet pressure, do not reflect the batch operation from a limited source storage. Thus, the dynamic variation of critical process parameters such as efficiency, temperature and flow are not documented.Using a hydrogen refueling station demonstrator, the data from more than 20′000 compression cycles is compiled and analyzed. Experimentally derived correlations are determined for an air driven gas booster feeding a cascade storage. A specific analysis of the clearance volume and the working air pressure is introduced.An engineering tool was developed in MATLAB for performance forecasting. It allows the user to simulate the process trends with an accuracy of ±5%. In the context of a hydrogen refueling station, duration, temperature, compression cycles and air consumption data can be used for process management and maintenance planning.     

Optimization and analysis of an integrated energy system based on wind power utilization and on-site hydrogen refueling station

An integrated energy system coupled with wind turbines and an on-site hydrogen refueling station is proposed to simulate the future scenario, which can meet the demands of cooling, heating, power and hydrogen. The system was modeled to calculate the capacity and annual operation of each equipment with the total annual cost as the optimization objective. This study evaluates the performance of the system based on the results. When the system is configured with 0–10 wind turbines, the economics, energy consumption and carbon emissions improve as the scale of wind turbines increases. Energy utilization and wind power utilization are above 66.79% and 99.73%, respectively. The on-off coefficient of the power generation unit can affect energy efficiency. When the system contains 5 turbines, 91% of the hydrogen can be self-produced with the minimum amount of energy redundancy.     

A numerical study of hydrogen leakage and diffusion in a hydrogen refueling station

Studies focused on the behavior of the hydrogen leakage and diffusion are of great importance for facilitating the large scale application of the hydrogen energy. In this paper, the hydrogen leakage and diffusion in six scenarios which including comparison of different leakage position and different wind effect are analyzed numerically. The studied geometry is derived from the hydrogen refueling station in China. Due to the high pressure in hydrogen storage take, the hydrogen leakage is momentum dominated. The hydrogen volume concentration with the variation of the leakage time in different scenarios is plotted. More importantly, profiles of the flammable gas cloud at the end of the leakage are quantitatively studied. Results indicate that a more narrow space between the leakage hole and the obstacle and a smaller contact area with the obstacle make the profile of the flammable gas cloud more irregular and unpredictable. In addition, results highlight the wind effect on the hydrogen leakage and diffusion. Comparing with scenario which the wind direction consistent with the leakage direction, the opposite wind direction may result in a larger profile of the flammable gas cloud. With wind velocity increasing, the profile of the flammable gas cloud is confined in a smaller range. However, the presence of the wind facilitates the form of the recirculation zone near the obstacle. With an increase of the wind velocity, the recirculation zone moves downward along the obstacle. Thus, the hydrogen accumulation is more prominent near the obstacle.     

Dispersion modeling and assessment of natural gas containing hydrogen released from a damaged gas transmission pipeline

This paper performs a simulation and assessment of dispersion of natural gas containing hydrogen released from transmission pipeline using a Computational Fluid Dynamics (CFD) approach. A 3D CFD model is established to evaluate the dispersion behavior of hydrogen-enriched natural gas in the hydrogen-natural gas mixing station. The simulations include a matrix of scenarios for hydrogen doping ratios, gas release rates, wind speeds and wind directions. The development process of flammable gas cloud is predicted, and the dangerous area generated in the hydrogen-natural gas mixing station is assessed. Additionally, the effects of some critical factors on flammable gas dispersion behavior are analyzed. The simulations produce some useful outcomes including the parameters of flammable gas cloud and the dangerous area in the station, which are useful for conducting a prior risk assessment and contingency planning.     

Dry and steam reforming of biomass pyrolysis gas for rich hydrogen gas

Biomass pyrolysis gas (including H₂, CO, CH₄, CO₂, C₂H₄, C₂H₆ and etc.) reforming for hydrogen production over Ni/Fe/Ce/Al₂O₃ catalysts was presented in this study. This study investigated how the operating conditions, such as the calcinations temperature of catalysts, the reaction temperature, the gas hourly space velocity (GHSV) and the ratio of H₂O/C, affect the conversion of CH₄ and CO₂ and the selectivity of hydrogen from dry and steam reforming of pyrolysis gas. The experimental results indicated that, under the conditions: the reaction temperature of 600 °C, the GHSV of 900 h⁻¹ and H₂O/C of 0.92, the reaction efficiency is the optimal. Especially, the concentration of H₂, CO, CH₄, CO₂, and C₂H_n (C₂H₄ and C₂H₆) were 36.80%, 10.48%, 9.61%, 42.62%, 0.49% respectively. The conversion of CH₄ and CO₂ reached 45.9% and 51.09%, respectively. There were all kinds of reactions during the processing of reforming of pyrolysis gas. And the main reactions changed with the operation condition. It was due to the promoting or inhibiting interaction among different constituents in the pyrolysis gas and the different activity of catalysts in the different operation condition.     

Effect of the vacancy close to heat exchange wall on the heat transfer performance of the solid particles steam generator using waste heat in a methanol steam reforming hydrogen production system

With the massive consumption of fossil fuels and it resulted in significant carbon emissions, it is urgent to find an alternative clean energy source. Hydrogen has been regarded as one of the most promising energy candidates for the next generation. It is a great approach that methane steam reforming for hydrogen production by rational utilization of industrial waste heat, which significantly minimizes carbon emissions and develops methanol steam reforming technology. A solid particle steam generator based on the primary heat exchange method has been proposed, which can provide the heat and steam in the methanol steam reforming hydrogen production system. The quasi-two-dimensional packing heat transfer model of solid particles steam generator was set up.The effect of distance change between the vacancy and the cold wall and distance change between vacancies on heat transfer performance of the steam generator and hydrogen production capacity were studied. As the distance between the vacancy and the wall increases, the heat transfer performance of the steam generator gradually deteriorates, so the steam production of the steam generator decreases, and the system's hydrogen production capacity is reduced, the maximum of the heat flux and the minimum of the apparent thermal resistance are 34.67 kW/m² and 12.02 K/W, respectively. As the distance between vacancies increases, the heat transfer performance of the steam generator is gradually optimized slightly. To maintain the hydrogen production capacity, vacancies should be avoided to appear 2 layers of particles away from the heat exchange wall in the particles steam generator. From the results of the study, the farther the distance between vacancies, the better the steam production and hydrogen production capacity.