Techno-economic analysis of hydropower based green ammonia plant for urea production in Nepal

This study presents a detailed design, economic, sensitivity and uncertainty analysis for establishing a hydropower based green ammonia plant for use in urea manufacturing in the context of Nepal. The electrolyzer plant for producing hydrogen was simulated with the help of DWSIM while the air separation and ammonia synthesis units were simulated with the help of Aspen Plus for producing 1245 ton/day of ammonia to meet the annual urea demand of Nepal. The capitalized cost of the electrolyzer, air separation and the ammonia synthesis unit of this size were calculated to be 26 million, 7 million and 9 million USD/year respectively. The levelized cost of hydrogen (H₂) and ammonia (NH₃) were found to be 3602 and 826 USD/ton respectively. Economic profitability analysis showed profitability of the plant with ROI and IRR of 38% and 26% respectively with a payback period of three years after operation. The sensitivity analysis showed strong sensitivity on the utility (electricity) cost for both the electrolyzer and ammonia synthesis unit which presents a strong opportunity for Nepal. The levelized cost for H₂ and NH₃ varied between 2845 USD/ton and 4361 USD/ton and 634 USD/ton and 1018 USD/ton respectively for ±30% variation in the utility (electricity) cost. Uncertainty analysis using Monte Carlo method showed the possible minimum levelized cost of H₂ and NH₃ to be 2340 USD/ton and 418 USD/ton respectively. This study illustrates the potential of hydropower based ammonia synthesis for urea manufacturing and provides an important baseline value for policymakers to make investment decisions and to formulate policies for this pathway of production.     

Sustainable hydrogen roadmap: A holistic review and decision-making methodology for production,utilisation and exportation using Qatar as a case study

Hydrogen is seen as a promising and inevitable energy carrier in the transition towards a carbon-free energy era. This study reviews the potential for carbon-free hydrogen production, utilisation and exportation from the State of Qatar. The study aims to introduce a roadmap for current and future exploration of carbon-free hydrogen production and exportation from Qatar, for which an assessment of several available alternatives for the production of hydrogen in Qatar is performed. These alternatives include the use of natural gas as a feedstock for hydrogen production through steam methane reforming (SMR), solar integrated steam methane reforming with carbon capture, as well as the possibilities for hydrogen production from electrolysis using renewables and ammonia as another intermediate. The potential of each alternative is reviewed based on selected technical, economic and environmental criteria. The findings of this review study indicate that the production and exportation of blue ammonia currently present the best pathway for Qatar, while green hydrogen is expected to become as competitive as blue ammonia in the mid-future. It is widely accepted that as the technologies associated with clean hydrogen production improve, and the cost of renewable energy falls, green hydrogen will become quite competitive in the region.     

Dynamic modelling of a solar hydrogen system for power and ammonia production

A new configuration of solar energy-driven integrated system for ammonia synthesis and power generation is proposed in this study. A detailed dynamic analysis is conducted on the designed system to investigate its performance under different radiation intensities. The solar heliostat field is integrated to generate steam that is provided to the steam Rankine cycle for power generation. The significant amount of power produced is fed to the PEM electrolyser for hydrogen production after covering the system requirements. A pressure swing adsorption system is integrated with the system that separates nitrogen from the air. The produced hydrogen and nitrogen are employed to the cascaded ammonia production system to establish increased fractional conversions. Numerous parametric studies are conducted to investigate the significant parameters namely; incoming beam irradiance, power production using steam Rankine cycle, hydrogen and ammonia production and power production using TEGs and ORC. The maximum hydrogen and ammonia production flowrates are revealed in June for 17th hour as 5.85 mol/s and 1.38 mol/s and the maximum energetic and exergetic efficiencies are depicted by the month of November as 25.4% and 28.6% respectively. Moreover, the key findings using the comprehensive dynamic analysis are presented and discussed.     

Design of an ocean thermal energy plant ship to produce ammonia via hydrogen

The 43°F (24°C) temperature difference that exists between surface water and deep water at selected sites in tropical oceans can be used to drive a heat engine to produce electric power, electrolyze water, and produce ammonia from the resulting hydrogen plus nitrogen from the air. A baseline design has been developed for a 100-MWe Ocean Thermal Energy Conversion (OTEC) plant-ship that would produce 313 tons per day of ammonia. The cost estimates for this design have been extrapolated to 500-MWe plant-ships to produce ammonia (for fertilizers and chemicals) or liquid hydrogen for shipment to the U.S. It is judged that ammonia will be producible at competitive cost ($96/short ton in 1975 dollars) by the sixth and subsequent plant-ships in the mid-1980s. This production by OTEC/ammonia plants would conserve supplies of natural gas or other fossil fuels now used to produce ammonia on shore. For the longer term (1990s), liquid hydrogen from OTEC plants should become competitive as demands for this clean fuel and efficient ways for employing it in larger markets (fuel cells, transportation, etc.) come to maturity.     

Life cycle environmental impact comparison of solid oxide fuel cells fueled by natural gas,hydrogen, ammonia and methanol for combined heat and power generation

This study aims to provide a comprehensive environmental life cycle assessment of heat and power production through solid oxide fuel cells (SOFCs) fueled by various chemical feeds namely; natural gas, hydrogen, ammonia and methanol. The life cycle assessment (LCA) includes the complete phases from raw material extraction or chemical fuel synthesis to consumption in the electrochemical reaction as a cradle-to-grave approach. The LCA study is performed using GaBi software, where the selected impact assessment methodology is ReCiPe 1.08. The selected environmental impact categories are climate change, fossil depletion, human toxicity, water depletion, particulate matter formation, and photochemical oxidant formation. The production pathways of the feed gases are selected based on the mature technologies as well as emerging water electrolysis via wind electricity. Natural gas is extracted from the wells and processed in the processing plant to be fed to SOFC. Hydrogen is generated by steam methane reforming method using the natural gas in the plant. Methanol is also produced by steam methane reforming and methanol synthesis reaction. Ammonia is synthesized using the hydrogen obtained from steam methane reforming and combined with nitrogen from air in a Haber-Bosch plant. Both hydrogen and ammonia are also produced via wind energy-driven decentralized electrolysis in order to emphasize the cleaner fuel production. The results of this study show that feeding SOFC systems with carbon-free fuels eliminates the greenhouse gas emissions during operation, however additional steps required for natural gas to hydrogen, ammonia and methanol conversion, make the complete process more environmentally problematic. However, if hydrogen and ammonia are produced from renewable sources such as wind-based electricity, the environmental impacts reduce significantly, yielding about 0.05 and 0.16 kg CO₂ eq., respectively, per kWh electricity generation from SOFC.     

中国发展煤炭清洁转化制甲醇是替代石油能源的最佳选择

我国年产20×108t煤炭相当10×108t石油,若采用粉煤气化配入水电解氢合成甲醇液体燃料,可使碳元素达99%的利用率;煤中硫化物全部回收成硫磺且免去巨额CO2排放。甲醇合成弛放气中含N2又可用于合成氨加工成尿素。甲醇油除作发动机燃料外,还可加工转化成乙烯、丙烯替代短缺的石油原料。从元素的物料、热量平衡与化学反应分析得出,煤炭纯氧气化同水电解制氢和氧,替代合成气的CO变换成H2和CO2,免去脱除与排放CO2,氧作煤气化用氧替代空分;发动机用甲醇油催化成合成气,可提高发动机的压缩比,使低热值的甲醇油成为同等于汽、柴油作功当量的甲醇汽油。1.3t煤可产1t甲醇,相当产1t石油炼制的成品油,达到节约资源、环境友好循环经济的目的。     

A new synthesis route of ammonia production through hydrolysis of metal – Nitrides

Recently ammonia has emerged as a potential hydrogen storage material because it contains 17.8 wt% hydrogen. Here, we propose a new synthesis route of ammonia production using hydrolysis of nitrides, which is based on the conversion technique using thermal energy, solar heat or exhaust heat to form NH₃ directly. Lithium metal has been tested as a starting material for the above purpose. We present the detailed results on room temperature nitridation of lithium metal, it is found that the nitridation properties are strongly affected by the surface state of lithium metal. The ammonia synthesis via hydrolysis of lithium nitride succeeds and it is strongly dependent on the reaction rate and temperature.     

A bifunctional electrochemical flow cell integrating ammonia production and electricity generation for renewable energy conversion and storage

Renewable energy has rapidly advanced in the global energy system, triggering the visible development of energy storage technologies in recent decades. Among them, the electricity-fuel-electricity approach is an effective way for the storage and utilization of renewable power. In this work, a bifunctional electrochemical flow cell integrating both ammonia production and electricity generation modes is developed for renewable energy conversion and storage. Ammonia, a hydrogen carrier having a high hydrogen content of 17.6 wt %, is relatively easier to convert to liquid phase for large-scale storage. The long-distance ammonia transport can reliably depend on the established infrastructure. In addition, as a carbon-free fuel beneficial for achieving the goal of carbon-neutrality, ammonia is considered as an environmentally benign and cost-effective mediator fuel. This flow cell is able to operate via two modes, i.e., an ammonia-production mode for energy storage in the form of ammonia (via nitrogen reduction reaction) and an electricity-generation mode for energy conversion in the form of electricity (via ammonia oxidation reaction). This flow cell is constituted by a PtAu/C-coated nickel-foam electrode for nitrogen and oxygen reduction reactions, a Pt/C-coated nickel-foam electrode for water and ammonia oxidation reactions, and an alkaline anion exchange membrane for charge-carrier migration. Charging this flow cell with the supply of nitrogen results in a Faradaic efficiency of 2.70% and an ammonia production rate as high as 9.34 × 10^?10 mol s^?1 cm^?2 at 23 °C. Moreover, energizing this flow cell with ammonia results in an open-circuit voltage of 0.59 V and a peak power density of 3.31 mW cm^?2 at 23 °C. A round-trip efficiency of 25.7% is realized with the constant-electrode mode.     

Hydrogen production by supercritical water gasification of coal: A reaction kinetic model including nitrogen and sulfur elements

Researches on reaction kinetics and mechanism are crucial to the application of hydrogen production technology by supercritical water gasification of coal from experiment to industrialization. Based on the migration mechanisms of nitrogen and sulfur in the process, this paper developed a general model including nitrogen and sulfur to study the generation path, consumption path and reaction rate of the gasification products. The parameters of the kinetic model were obtained by fitting the experimental data of the gasification products, and the activation energy of each reaction was obtained by the Arrhenius equation. By comparing the reaction rates among the various reactions, the reaction steps for controlling the production or digestion of the product could be obtained. The main source of ammonia production was pyrolysis of coal followed by steam reforming reaction of fixed carbon. The rate of ammonia contribution from ammonia synthesis was extremely low and could be ignored. The consumption path of ammonia was the decomposition reaction of ammonia though its rate was also slow. The pyrolysis reaction of coal was the main source of hydrogen sulfide, followed by the steam reforming reaction of fixed carbon. The difference of the concentration and reactivity between organic sulfur and inorganic sulfur caused the difference in the generation source of hydrogen sulfide in early and late stage of the gasification. The kinetic model can predict not only the production of hydrogen, methane, carbon dioxide, carbon monoxide, ammonia and hydrogen sulfide under different operating conditions, but also the products for different coal types, which may provide a theoretical basis for the targeted regulation of nitrogen and sulfur elements in supercritical water.     

Optimization of low-carbon hydrogen supply chain networks in industrial clusters

This work presented an optimization-based model to aid in designing and planning a hydrogen supply chain network (HSCN) under different CO₂ emission mitigation policies. The novelty of this approach lies in simultaneously, 1) tracking the resources available in HSCN and 2) designing the spatial interaction production, storage, and transportation. The model was formulated as a Mixed Integer Linear Program (MILP) to identify the minimum cost of HSCN. A case study was solved to assess the techno-economic performance of grey, blue and green hydrogen production while accounting for transport and the full energy system. A Pareto-curve was constructed to understand the trade-off between the Levelized cost of Hydrogen and emission reduction. The model also enabled the investigation of various long-distance hydrogen transport schemes; hydrogen transported as ammonia will cost 19% less than the other alternatives (liquid hydrogen, and liquid organic hydrogen carrier).     

Ammonia as a hydrogen energy carrier

The gravimetric H₂ densities and the heats of combustion of tanks stored ammonia (ammonia storage tanks) were similar to those of the liquid H₂ tanks at the weight of 20–30ton, although the gravimetric H₂ density of liquid H₂ is 100 wt%. The volumetric H₂ densities and the heats of combustion of ammonia storage tanks were about 2 times higher than those of liquid H₂ tanks at 1–4 × 10⁴ m³. Gray ammonia is synthesized from hydrogen through process known as steam methane reforming, nitrogen separated from air and Haber-Bosch process. Blue ammonia is the same as gray ammonia, but with CO₂ emissions captured and stored. Green ammonia is produced by reacting hydrogen produced by electrolysis of water and nitrogen separated from air with Haber-Bosch process using renewable energies. The energy efficiencies of gray, blue and green ammonia were better than those of liquid hydrogen and methylcyclohexane (MCH) with high H₂ density and similar to the efficiency of H₂ gas. The energy efficiencies of ammonia decreased in the order, gray ammonia > blue ammonia > green ammonia. The production costs of green hydrogen energy carried increased in the order, ammonia < liquid H₂<MCH. The amounts of energy consumption by N₂ production and Haber-Bosch process were below 10% compared with the value of H₂ production from water electrolysis.     

Kinetic and thermodynamic analyses of mid/low-temperature ammonia decomposition in solar-driven hydrogen permeation membrane reactor

It is a promising method for hydrogen generation without carbon emitting by ammonia decomposition in a catalytic palladium membrane reactor driven by solar energy, which could also store and convert solar energy into chemical energy. In this study, kinetic and thermodynamic analyses of mid/low-temperature solar thermochemical ammonia decomposition for hydrogen generation in membrane reactor are conducted. Hydrogen permeation membrane reactor can separate the product and shift the reaction equilibrium forward for high conversion rate in a single step. The variation of conversion rate and thermodynamic efficiency with different characteristic parameters, such as reaction temperature (100–300 °C), tube length, and separation pressure (0.01–0.25 bar), are studied and analyzed. A near-complete conversion of ammonia decomposition is theoretically researched. The first-law thermodynamic efficiency, net solar-to-fuel efficiency, and exergy efficiency can reach as high as 86.86%, 40.08%, and 72.07%, respectively. The results of this study show the feasibility of integrating ammonia decomposition for hydrogen generation with mid/low-temperature solar thermal technologies.     

Performance assessment of electrochemical ammonia synthesis using photoelectrochemically produced hydrogen

In this study, an effective hydrogen production for electrochemical ammonia synthesis is performed using a photoelectrochemical hydrogen production reactor. A photoelectrochemical cell is built by electrodepositing photosensitive Cu₂O particles on a cathode stainless steel plate. The produced hydrogen is supplied to a molten salt electrolyte‐based electrochemical ammonia synthesis reactor at ambient pressure where nitrogen gas is co‐supplied from a nitrogen tank. Using photoelectrochemically produced hydrogen, the electrochemical synthesis of ammonia is successfully accomplished. The reactions of nitrogen and hydrogen gases occur in a molten salt ambient consisting of molten hydroxides (NaOH and KOH), whereas the reaction temperature is varied in the range of 180°C to 260°C to investigate the impact of temperature on the performance. The porous nickel‐meshed electrodes with an effective area of 25 cm² are used as cathode and anode. The hydrogen production process is characterized under both concentrated light and non‐concentrated light conditions. The maximum Coulombic efficiency for ammonia synthesis is calculated to be 14.2% with an ammonia production rate of 4.41 × 10^?9 mol/s cm² via nano‐Fe₃O₄ catalyst. Copyright © 2017 John Wiley & Sons, Ltd.     

Recent advances in ammonia synthesis technologies: Toward future zero carbon emissions

As a carbon-free molecule, ammonia has gained great global interest in being considered a significant future candidate for the transition toward renewable energy. Numerous applications of ammonia as a fuel have been developed for energy generation, heavy transportation, and clean, distributed energy storage. There is a clear global target to achieve a sustainable economy and carbon neutrality. Therefore, most of the research's efforts are concentrated on generating cost-effective renewable energy on a large scale rather than fossil fuels. However, storage and transportation are still roadblocks for these technologies, for example, hydrogen technologies. Ammonia could be replaced as a viable fuel for a clean and sustainable future of global energy. More efforts from governments and scientists can lead to making ammonia a clean energy vector in most energy applications. In this review, ammonia synthesis was assessed, including conventional Haber–Bosch technology. Current hydrogen technologies as the key parameters for ammonia generation are also evaluated. The role of ammonia as a hydrogen-based fuel and generation roadmap are discussed for future utilization of energy mix. Further, ammonia generation processes are addressed in depth, including blue and green ammonia generation. A survey of ammonia synthesis catalytic materials was conducted and the role of catalyst materials in ammonia generation was compared, which showed that the Ru-based catalyst generated the maximum ammonia after 20 h of starting experiment. An end-use plan for using ammonia as a clean energy fuel in vehicles, marines, gas turbines as well as fuel cells, is briefly discussed to recognize the potential applications of ammonia use. The practical and future end-use vision of energy sources is proposed to achieve great benefits at low carbon emissions and costs. This review can provide prospective knowledge of large-scale aspects and environmental considerations of ammonia. Herein, we conclude that ammonia will become the “clean energy carrier link” that will achieve the global energy and economy sustainability targets.     

Flexible production of green hydrogen and ammonia from variable solar and wind energy: Case study of Chile and Argentina

We report a techno-economic modelling for the flexible production of hydrogen and ammonia from water and optimally combined solar and wind energy. We use hourly data in four locations with world-class solar in the Atacama desert and wind in Patagonia steppes. We find that hybridization of wind and solar can reduce hydrogen production costs by a few percents, when the effect of increasing the load factor on the electrolyser overweighs the electricity cost increase. For ammonia production, the gains by hybridization can be substantially larger, because it reduces the power variability, which is costly, due to the need for intermediate storage of hydrogen between the flexible electrolyser and the less flexible ammonia synthesis unit. Our modelling reveals the crucial role in the synthesis of flexibility, which cuts the cost of variability, especially for the more variable wind power. Our estimated near-term production costs for green hydrogen, around 2 USD/kg, and green ammonia, below 500 USD/t, are encouragingly close to competitiveness against fossil-fuel alternatives.     

Life cycle assessment of nuclear-based hydrogen and ammonia production options: A comparative evaluation

In this study, nuclear energy based hydrogen and ammonia production options ranging from thermochemical cycles to high-temperature electrolysis are comparatively evaluated by means of the life cycle assessment (LCA) tool. Ammonia is produced by extracting nitrogen from air and hydrogen from water and reacting them through nuclear energy. Since production of ammonia contributes about 1% of global greenhouse gas (GHG) emissions, new methods with reduced environmental impacts are under close investigation. The selected ammonia production systems are (i) three step nuclear Cu–Cl thermochemical cycle, (ii) four step nuclear Cu–Cl thermochemical cycle, (iii) five step nuclear Cu–Cl thermochemical cycle, (iv) nuclear energy based electrolysis, and (v) nuclear high temperature electrolysis. The electrolysis units for hydrogen production and a Haber–Bosch process for ammonia synthesis are utilized for the electrolysis-based options while hydrogen is produced thermochemically by means of the process heat available from the nuclear power plants for thermochemical based hydrogen production systems. The LCA results for the selected ammonia production methods show that the nuclear electrolysis based ammonia production method yields lower global warming and climate change impacts while the thermochemical based options yield higher abiotic depletion and acidification values.     

Methanol production using hydrogen from concentrated solar energy

Concentrated solar thermal technology is considered a very promising renewable energy technology due to its capability of producing heat and electricity and of its straightforward coupling to thermal storage devices. Conventionally, this approach is mostly used for power generation. When coupled with the right conversion process, it can be also used to produce methanol. Indeed methanol is a good alternative fuel for high compression ratio engines. Its high burning velocity and the large expansion occurring during combustion leads to higher efficiency compared to operation with conventional fuels. This study is focused on the system level modeling of methanol production using hydrogen and carbon monoxide produced with cerium oxide solar thermochemical cycle which is expected to be CO₂ free. A techno-economic assessment of the overall process is done for the first time. The thermochemical redox cycle is operated in a solar receiver-reactor with concentrated solar heat to produce hydrogen and carbon monoxide as the main constituents of synthesis gas. Afterwards, the synthesis gas is turned into methanol whereas the methanol production process is CO₂ free. The production pathway was modeled and simulations were carried out using process simulation software for MW-scale methanol production plant. The methanol production from synthesis gas utilizes plug-flow reactor. Optimum parameters of reactors are calculated. The solar methanol production plant is designed for the location Almeria, Spain. To assess the plant, economic analysis has been carried out. The results of the simulation show that it is possible to produce 27.81 million liter methanol with a 350 MW_th solar tower plant. It is found out that to operate this plant at base case scenario, 880685 m² of mirror's facets are needed with a solar tower height of 220 m. In this scenario a production cost of 1.14 €/l Methanol is predicted.     

Feasibility study of renewable energy sources for developing the hydrogen economy in Pakistan

Hydrogen energy can play a pivotal part in enhancing energy security and decreasing hazardous emissions in Pakistan. However, hydrogen energy can be sustainable and clean only if it is produced from renewable energy sources (RES). Therefore, this study conducts feasibility of six RES for the generation of hydrogen in Pakistan. RES evaluated in this study include wind, solar, biomass, municipal solid waste (MSW), geothermal, and micro-hydro. RES have been evaluated using Fuzzy Delphi, fuzzy analytical hierarchy process (FAHP), and environmental data envelopment analysis (DEA). Fuzzy Delphi finalizes criteria and sub-criteria. FAHP obtains relative weights of criteria considered for choosing the optimal RES. Environmental DEA measures relative efficiency of each RES using criteria weights as outputs, and RES-based electricity generation cost as input. The results revealed wind as the most efficient source of hydrogen production in Pakistan. Micro-hydro and Solar energy can also be used for hydrogen production. Biomass, MSW, and geothermal achieved less efficiency scores and therefore are not suggested at present.     

Recent progress towards solar energy integration into low-pressure green ammonia production technologies

Large progress has been made in the last decades to reduce the carbon footprint of ammonia, which is an essential commodity of the food, chemical and energy industry. Apart from alternative routes for green feedstock production, such as hydrogen via electrolysis and nitrogen via solar thermochemical methods, alternatives are explored to replace the Haber-Bosch process. The present article reviews four promising mild condition ammonia production methods: solid state synthesis, molten salt synthesis, thermochemical looping and photocatalytic routes. Contrary to the Haber-Bosch method, which requires high pressures of 200–400 bar, they operate at low-pressures, furthermore such routes open the possibility for direct ammonia production from H₂O and N₂ without the intermediate hydrogen production step. These advantages allow easier renewable energy integration; however, R&D activities are needed for scaling-up. An analysis is given on renewable energy integration with focus on solar resources both in the form of electricity and heat.     

Utilization of green ammonia as a hydrogen energy carrier for decarbonization in spark ignition engines

Rising concerns about the dependence of modern energy systems on fossil fuels have raised the requirement for green alternate fuels to pave the roadmap for a sustainable energy future with a carbon-free economy. Massive expectations of hydrogen as an enabler for decarbonization of the energy sector are limited by the lack of required infrastructure, whose implementation is affected by the issues related to the storage and distribution of hydrogen energy. Ammonia is an effective hydrogen energy carrier with a well-established and mature infrastructure for long-distance transportation and distribution. The possibility for green ammonia production from renewable energy sources has made it a suitable green alternate fuel for the decarbonization of the automotive and power generation sectors. In this work, engine characteristics for ammonia combustion in spark ignition engines have been reported with a detailed note on engines fuelled with pure ammonia as well as blends of ammonia with gasoline, hydrogen, and methane. Higher auto-ignition temperature, low flammability, and lower flame speed of ammonia have a detrimental effect on engine characteristics, and it could be addressed either by incorporating engine modifications or by enhancing the fuel quality. Literature shows that the increase in compression ratio from 9.4:1 to 11.5:1 improved the maximum power by 59% and the addition of 10% hydrogen in supercharged conditions improved the indicated efficiency by 37%. Challenges and strategies for the utilization of ammonia as combustible fuel in engines are discussed by considering the need for technical advancements as well as social acceptance. Energy efficiency for green ammonia production is also discussed with a due note on techniques for direct synthesis of ammonia from air and water.