System level heat integration and efficiency analysis of hydrogen production process based on solid oxide electrolysis cells

The solid oxide electrolysis cells (SOEC) technology is a promising solution for hydrogen production with the highest electrolysis efficiency. Compared with its counterparts, operating at high temperature means that SOEC requires both power and heat. To investigate the possibility of coupling external waste heat with the SOEC system, and the temperature & quantity requirement for the external waste heat, a universal SOEC system operating at atmospheric pressure is proposed, modeled and analyzed, without specific waste heat source assumption such as solar, geothermal or industrial waste heat. The SOEC system flow sheet is designed to create opportunity for external waste heat coupling. The results show that external waste heat is required for feed stock heating, while the recommended coupling location is the water evaporator. The temperature of the external waste heat should be above 130 °C. For an SOEC system with 1 MW electrolysis power input, the required external waste heat is about 200 kW. When the stack operates at thermoneutral state and 800 °C, the specific energy consumption is 3.77 kWh/Nm³-H₂, of which electric power accounts for 84% (3.16 kWh/Nm³-H₂) and external waste heat accounts for 16% (0.61 kWh/Nm³-H₂). The total specific energy consumption remains almost unchanged when operating the SOEC stack around the thermoneutral condition.     

Hydrogen generation by alcohol reforming in a tandem cell consisting of a coupled fuel cell and electrolyser

The performance of a novel electro-reformer for the production of hydrogen by electro-reforming alcohols (methanol, ethanol and glycerol) without an external electrical energy input is described. This tandem cell consists of an alcohol fuel cell coupled directly to an alcohol reformer, negating the requirement for external electricity supply and thus reducing the cost of operation and installation. The tandem cell uses a polymer electrolyte membrane (PEM) based fuel cell and electrolyser. At 80 °C, hydrogen was generated from methanol, by the tandem PEM cell, at current densities above 200 mA cm⁻², without using an external electricity supply. At this condition the electro-reformer voltage was 0.32 V at an energy input (supplied by the fuel cell component) of 0.91 kWh/Nm³; i.e. less than 20% of the theoretical value for hydrogen generation by water electrolysis (4.7 kWh/Nm³) with zero electrical energy input from any external power source. The hydrogen generation rate was 6.2 × 10⁻⁴ mol (H₂) h⁻¹. The hydrogen production rate of the tandem cell with ethanol and glycerol was approximately an order of magnitude lower, than that with methanol.     

Geothermal development in Hungary—country update report 2000–2002

This paper describes the status of geothermal energy utilization—direct use—in Hungary, with emphasis on developments between 2000 and 2002. The level of utilization of geothermal energy in the world increased in this period and geothermal energy was the leading producer, with 70% of the total electricity production, of all the renewable energy sources (wind, solar, geothermal and tidal), followed by wind energy at 28%. The current cost of direct heat use from biomass is 1–5 US¢/kWh, geothermal 0.5–5 US¢/kWh and solar heating 3–20 US¢/kWh. The data relative to direct use in Hungary decreased in this period and the contribution of geothermal energy to the energy balance of Hungary, despite significant proven reserves (with reinjection) of 380 million m³/year, with a heat content of 63.5 PJ/a at ΔT=40 °C, remained very low (0.25%). Despite the fact that geothermal fluids with temperatures at the surface higher than 100 °C are available, no electricity has been generated. As of 31 December 2002, the geothermal capacity utilised in direct applications in Hungary is estimated to be 324.5 MW_t and to produce 2804 TJ/year. Geothermal heat pumps represent about 4.0 MW_t of this installed capacity. The quantity of thermal water produced for direct uses in 2002 was approximately 22 million m³, with an average utilization temperature of 31 °C. The main consumer of geothermal energy is agriculture (68% of the total geothermal heat dedicated to direct uses). The geothermal water is used only in five spas for space heating and sanitary hot water (SHW), although there are 260 spas in the country, and the thermal water produced has an average surface temperature of 68 °C. The total heat capacity installed in the spas is approximately 1250 MW_t; this is not provided by geothermal but could be, i.e., geothermal could provide more than three times the geothermal capacity utilized in direct uses by 31 December 2002 (324.5 MW_t).     

Hydrogen production from wind energy in Western Canada for upgrading bitumen from oil sands

Hydrogen is produced via steam methane reforming (SMR) for bitumen upgrading which results in significant greenhouse gas (GHG) emissions. Wind energy based hydrogen can reduce the GHG footprint of the bitumen upgrading industry. This paper is aimed at developing a detailed data-intensive techno-economic model for assessment of hydrogen production from wind energy via the electrolysis of water. The proposed wind/hydrogen plant is based on an expansion of an existing wind farm with unit wind turbine size of 1.8 MW and with a dual functionality of hydrogen production and electricity generation. An electrolyser size of 240 kW (50 Nm³ H₂/h) and 360 kW (90 Nm³ H₂/h) proved to be the optimal sizes for constant and variable flow rate electrolysers, respectively. The electrolyser sizes aforementioned yielded a minimum hydrogen production price at base case conditions of $10.15/kg H₂ and $7.55/kg H₂. The inclusion of a Feed-in-Tariff (FIT) of $0.13/kWh renders the production price of hydrogen equal to SMR i.e. $0.96/kg H_2, with an internal rate of return (IRR) of 24%. The minimum hydrogen delivery cost was $4.96/kg H₂ at base case conditions. The life cycle CO₂ emissions is 6.35 kg CO₂/kg H₂ including hydrogen delivery to the upgrader via compressed gas trucks.     

Hydrogen production from oil sludge gasification/biomass mixtures and potential use in hydrotreatment processes

Gasification of oil sludge (OS) from crude oil refinery and biomass was investigated to evaluate hydrogen production and its potential use in diesel oil hydrodesulphurization process. Gasification process was studied by Aspen Hysys^® tools, considering different kinetic model for main OS compounds. Air and superheated steam mixtures as gasifying agents were simulated. Gasification parameters like: temperature, syngas chemical composition and gas yield were evaluated. Results showed OS thermal conversion needs a working temperature above 1300 °C to ensure a high conversion (>90%) of OS compounds. Thermal energy requirement for gasification was estimated between 0.80 and 1.25 kWh/kg OS, considering equivalence air (ER) and steam/oil sludge (SOS) ratio between 0.25-0.37 and 0.2–1.5 kg steam/kg OS, respectively. The gas yield was 2.28 Nm³/kg OS, with a H₂ content close to 25 mol%, for a H₂ potential production about 1.84 Nm³ H₂/kg OS; nevertheless, when OS and biomass mixtures are used, hydrogen production increases to 3.51 Nm³ H₂/kg OS, meaning 37% of H₂ (from natural gas) required for diesel oil hydrodesulphurization could be replaced, becoming an added value technological alternative for OS waste conversion as a source of H₂, inducing a considerable reduction of greenhouse gases and non-renewables resources.     

Green hydrogen-based pathways and alternatives: Towards the renewable energy transition in South America's regions–Part B

Hydropower compounds most of the energy matrix of the countries of the Latin America and Caribbean region (LAC). Considering the concern in reducing Green House Gases emissions (GHG) from hydropower plants and hydrogen production from fossil sources, green hydrogen (H₂) appears as an energy vector able to mitigate this impact. Improving the efficiency of the plant and producing renewable energy the element is an interesting alternative from the ecological and economic point of view. This study aims to estimate the potential of H₂ production from wasted energy, through the electrolysis of water in hydroelectric plants in Colombia and Venezuela. The construction of two scenarios allowed obtaining a difference, considering a spilled flow of 2/3 in the first scenario and 1/3 in the second. In Colombia, hydrogen production reached 3.39 E+08 Nm³ at a cost of 2.05 E+05 USD/kWh in scenario1, and 1.70 E+08 Nm³ costing 4.10 E+05 USD/kWh in scenario 2. Regarding the Venezuelan context, the country obtained lower production values of H₂, ranging between 7.76 E+07 Nm³.d^?1 and 4.31 E+07 Nm³.d^?1, and production cost between 9.45 E+09 USD/kWh and 1.89 E+10 USD/kWh. Thus, the final cost for the production and storage of H₂ was estimated at 0.2239 USD.kg^?1. Ultimately, Colombia and Venezuela have a large potential to supply the demand for nitrogen fertilizers with green ammonia production, apply green hydrogen in manufacturing and use the surplus for energy substitution of Liquefied Petroleum Gas - LPG. In Colombia, the chemical energy offered is equivalent to 6.681 E+11 MJ/year^?1 and in Venezuela, the result is equal to 1.697 E+11 MJ/year^?1 in the conservative scenario. Finally, the countries have great potential for the diversification of the energy matrix and the insertion of renewables in the system.     

On the reduction of electric energy consumption in electrolysis: A thermodynamic study

Electricity is the major component in the cost of hydrogen production via electrolysis. This study aims to reduce electric energy consumption in electrolysis and replace it with lower cost thermal energy. An idealized thermodynamic analysis of hydrogen production by electrolysis at higher temperatures is presented, with particular emphasis on isolating the work and thermal components of the required energy. There is significant advantage in using thermal energy from another complementary process to overheat the inlet steam to meet this need. The electricity demand for electrolysis, under reasonable conditions, can thus be reduced to 26.63 kWh kg^?1. Introducing multiple stages can further reduce this to 25.22 kWh kg^?1 and more significantly, greatly reduce the temperature of the thermal energy needed. At lower utilizations, it is possible to reduce the electrical requirement to below 20 kWh kg^?1, which is less than half the most aggressive targets for electrolyzer improvements.     

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.     

Parametric study of an efficient renewable power-to-substitute-natural-gas process including high-temperature steam electrolysis

Power-to-Substitute Natural Gas processes are investigated to offer solutions for renewable energy storing or transportation. In the present study, an original Power-to-SNG process combining high-temperature steam electrolysis and CO₂ methanation is implemented and simulated. A reference process is firstly defined, including a specific modelling approach of the electrolysis and a methanation modelling including a kinetic law. The process also integrates a unit to clean the gas from residual CO₂, H₂ and H₂O for gas network injection. Having set all the units, simulations are performed with ProsimPlus 3™ software for a reference case where the electrolyser and the methanation reactors are designed. The reference case allows to produce 67.5 Nm³/h of SNG with an electrical energy consumption of 14.4 kW h/Nm³. The produced SNG satisfies specifications required for network injection. From this reference process, two sensitivity analyses on electrolysis and methanation working points and on external parameters and constraints are considered. As a main result, we observe that the reference case maximises both process efficiency and SNG production when compared with other studied cases.     

Economics of hydrogen production and liquefaction by geothermal energy

Seven models are considered for the production and liquefaction of hydrogen by geothermal energy. In these models, we use electrolysis and high-temperature steam electrolysis processes for hydrogen production, a binary power plant for geothermal power production, and a pre-cooled Linde–Hampson cycle for hydrogen liquefaction. Also, an absorption cooling system is used for the pre-cooling of hydrogen before the liquefaction process. A methodology is developed for the economic analysis of the models. It is estimated that the cost of hydrogen production and liquefaction ranges between 0.979 $/kg H₂ and 2.615 $/kg H₂ depending on the model. The effect of geothermal water temperature on the cost of hydrogen production and liquefaction is investigated. The results show that the cost of hydrogen production and liquefaction decreases as the geothermal water temperature increases. Also, capital costs for the models involving hydrogen liquefaction are greater than those for the models involving hydrogen production only.     

Operation of first solar-hydrogen system in China

The first solar-hydrogen (S-H) system in China, which consists a 2 kW PV cell array, a 48 V/300Ah lead-acid battery bank, an 0.5 Nm³/h hydrogen production capacity alkaline water electrolyzer, a 10 Nm³ LaNi₅ alloy hydrogen storage tank and a 200 W H₂/air PEM fuel cell, was installed in the Institute of Nuclear and New Energy Technology (INET) of Tsinghua University and has been operated for several months. The goal of the system was to study the technical and economical feasibility of using such a system to produce hydrogen in large scale for the future hydrogen energy society. With two months operation, experimental results reveal 40.68% energy transformed to hydrogen with 7.21 kWh/Nm³ H₂ electricity consumption. Economic analysis results illustrate that the present system is not cost-efficient and the energy conversion efficiencies of PV panel and electrolyzer are suggested to increase in technology improvement to cut down cost.     

Thermoeconomic analysis and artificial neural network based genetic algorithm optimization of geothermal and solar energy assisted hydrogen and power generation

The study aims to optimize the geothermal and solar-assisted sustainable energy and hydrogen production system by considering the genetic algorithm. The study will be useful by integrating hydrogen as an energy storage unit to bring sustainability to smart grid systems. Using the Artificial Neural Network (ANN) based Genetic Algorithm (GA) optimization technique in the study will ensure that the system is constantly studied in the most suitable under different climatic and operating conditions, including unit product cost and the plant's power output. The water temperature of the Afyon Geothermal Power Plant varies between 70 and 130 °C, and its mass flow rate varies between 70 and 150 kg/s. In addition, the solar radiation varies between 300 and 1000 W/m² for different periods. The net power generated from the region's geothermal and solar energy-supported system is calculated as 2900 kW. If all of this produced power is used for hydrogen production in the electrolysis unit, 0.0185 kg/s hydrogen can be produced. The results indicated that the overall energy and exergy efficiencies of the integrated system are 4.97% and 16.0%, respectively. The cost of electricity generated in the combined geothermal and solar power plant is 0.027 $/kWh if the electricity is directly supplied to the grid and used. The optimized cost of hydrogen produced using the electricity produced in geothermal and solar power plants in the electrolysis unit is calculated as 1.576 $/kg H₂. The optimized unit cost of electricity produced due to hydrogen in the fuel cell is calculated as 0.091 $/kWh.     

Exergoeconomic assessment of a geothermal assisted high temperature steam electrolysis system

Exergoeconomic formulations and procedure including exergy flows and cost formation and allocation within a high temperature steam electrolysis (HTSE) system are developed, and applied at three environmental temperatures. The cost accounting procedure is based on the specific exergy costing (SPECO) methodology. Exergy based cost-balance equations are obtained by fuel and product approach. Cost allocations in the system are obtained and effect of the second-law efficiency on exergetic cost parameters is investigated. The capital investment cost, the operating and maintenance costs and the total cost of the system are determined to be 422.2, 2.04, and 424.3 €/kWh, respectively. The specific unit exergetic costs of the power input to the system are 0.0895, 0.0702, and 0.0645 €/kWh at the environmental temperatures of 25 °C, 11 °C, and −1 °C, respectively. The exergetic costs of steam are 0.000509, 0.000544, and 0.000574 €/kWh at the same environmental temperatures, respectively. The amount of energy consumption for the production of one kg hydrogen is obtained as 133 kWh (112.5 kWh power + 20.5 kWh steam), and this corresponds to a hydrogen cost of 1.6 €/kg H₂.     

Economic evaluation with sensitivity and profitability analysis for hydrogen production from water electrolysis in Korea

Economic evaluation for water electrolysis compared to steam methane reforming has been carried out in terms of unit hydrogen production cost analysis, sensitivity analysis, and profitability analysis to assess current status of water electrolysis in Korea. For a hydrogen production capacity of 30 Nm³ h^?1, the unit hydrogen production cost was 17.99, 16.54, and 20.18 $ kg H₂^?1 for alkaline water electrolysis (AWE), PEM water electrolysis (PWE), and steam methane reforming (SMR), respectively with 11.24, 10.66, and 11.80 for 100 Nm³ h^?1 and 8.12, 7.72, and 7.59 $ kg H₂^?1 for 300 Nm³ h^?1. With sensitivity analysis (SA), the most influential factors on the unit hydrogen production cost depending on the hydrogen production capacity were determined. Lastly, profitability analysis (PA) presented a discounted payback period (DPBP), net present value (NPV), and present value ratio (PVR) for a different discount rate ranging from 2 to 14% and it was found that a discounted cash flow rate of return (DCFROR) was 14.01% from a cash flow diagram obtained for a hydrogen production capacity of 30 Nm³ h^?1.     

Effect of introducing a steam pipe to n-dodecane decomposition by in-liquid plasma for hydrogen production

A method has been developed to improve the hydrogen production efficiency (HPE) by in-liquid plasma n-dodecane decomposition. A thin steam pipe is placed over the plasma electrode to recover the thermal energy emitted from the plasma to its surroundings. The steam generated by this energy is supplied to the vaporized n-dodecane around the edge of the plasma to cause a steam reforming reaction (SRR). Water pyrolysis is suppressed by not supplying the steam directly to the plasma. A large amount of CO and a small amount of CO₂ were detected in the produced gas. This indicates that a strong SRR has occurred. The HPE obtained by this method is 0.28 Nm³/kWh, which is two times greater than those obtained by previous methods, and similar to or greater than the yield of water electrolysis. This result is a major advance in the field of plasma heavy hydrocarbon decomposition aimed at hydrogen production. HPE is expected to be further improved by simply increasing the input power, due to synergy between the heat recovery effect of the steam pipe and the bubble stabilization effect. This indicates that this method has a high potential.     

High-temperature electrolysis of water vapor—status of development and perspectives for application

Electrolysis of water vapor using solid-oxide electrolyte cells has been demonstrated to be a very efficient method of hydrogen production from water. As a result of an eight-year development program in Germany, the technology of vapor electrolysis cells and their integration into larger molecules has reached an advanced status: Single cells have been operated during long-term tests with current densities of 0.3 A cm^?2 and 100% Faraday efficiency at a voltage of only 1.07 V [corresponding to a specific electrical energy consumption of 2.57 kWh Nm^?3 (H₂)]. With electrolysis tubes of series-connected cells an enrichment of hydrogen in the vapor stream of up to 85% could be demonstrated without major concentration polarization losses. Concepts for integrated modular electrolysis units made up of serial- and parallel-connected tubular cells have been developed and successfully tested. A pre-prototype unit of 3.5 kW hydrogen output power is under development. The high efficiency of this hydrogen production process will allow an extension of the use of electrolytic hydrogen in the near future. The reasons for such a development will be explained and an example for a modified synfuel process will be given.     

Direct electrification of Rh/Al2O3 washcoated SiSiC foams for methane steam reforming: An experimental and modelling study

Electrified methane steam reforming (eMSR) is a promising concept for low-carbon hydrogen production. We investigate an innovative eMSR reactor where SiSiC foams, coated with Rh/Al₂O₃ catalyst, act as electrical resistances to generate the reaction heat via the Joule effect. The novel system was studied at different temperatures, space velocities, operating pressures and catalyst loadings. Thanks to efficient heating, active catalyst and optimal substrate geometry, complete methane conversions were observed even at a high space velocity of 200000 Nl/h/kg_cat. A specific energy demand as low as 1.24 kWh/Nm³_H2, with an unprecedented energy efficiency of 81%, was achieved on a washcoated foam with catalyst density of 86.3 g/L (GHSV = 150000 Nl/h/kg_cat, S/C = 4.1, ambient pressure). A mathematical model was validated against measured performance indicators and used to design an intensified eMSR unit for small scale H₂ production.     

Potential and costs for the production of electrolytic hydrogen in alcohol and sugar cane plants in the central and south regions of Brazil

This project verified the potential for the production of hydrogen via water electrolysis by using the exceeding electrical energy resultant from alcohol and sugar plants that use sugar cane bagasse as fuel. The studies were carried out in cogeneration plants authorized by the Electrical Energy National Agency (ANEEL). The processing history of sugar cane considered was based on the 2006/2007 harvests. The total bagasse produced, electrical energy generated and exceeding electrical energy in a year were calculated. It was obtained an average energy consumption value of 5.2 kWh Nm⁻³ and the hydrogen production costs regarding the amount of sugar cane processed that ranged from US$ 0.50 to US$ 0.75 Nm⁻³. The results pointed that the costs for the production of hydrogen via the bagasse exceeding energy are close to the production costs that use other sources of energy. As the energy generated from the bagasse is a renewable one, this alternative for the production of hydrogen is economical and environmentally viable.     

On-board hydrogen storage and production: An application of ammonia electrolysis

On-board hydrogen storage and production via ammonia electrolysis was evaluated to determine whether the process was feasible using galvanostatic studies between an ammonia electrolytic cell (AEC) and a breathable proton exchange membrane fuel cell (PEMFC). Hydrogen-dense liquid ammonia stored at ambient temperature and pressure is an excellent source for hydrogen storage. This hydrogen is released from ammonia through electrolysis, which theoretically consumes 95% less energy than water electrolysis; 1.55 Wh g⁻¹ H₂ is required for ammonia electrolysis and 33 Wh g⁻¹ H₂ for water electrolysis. An ammonia electrolytic cell (AEC), comprised of carbon fiber paper (CFP) electrodes supported by Ti foil and deposited with Pt-Ir, was designed and constructed for electrolyzing an alkaline ammonia solution. Hydrogen from the cathode compartment of the AEC was fed to a polymer exchange membrane fuel cell (PEMFC). In terms of electric energy, input to the AEC was less than the output from the PEMFC yielding net electrical energies as high as 9.7 ± 1.1 Wh g⁻¹ H₂ while maintaining H₂ production equivalent to consumption.     

Hydrogen production of bio-oil steam reforming combining heat recovery of blast furnace slag: Thermodynamic analysis

Hydrogen production via steam reforming of bio-oil combining heat recovery of blast furnace slag was investigated via thermodynamic analysis in this paper. The addition of blast furnace slag just had a slight enhancement for hydrogen production from the steam reforming process of bio-oil at low temperature, and had almost no thermodynamic effect (either promotion or restraint) for the steam reforming reaction equilibrium at high temperature where higher H₂ yield were obtained, no matter how much blast furnace slag was added. However, different masses of blast furnace slag as heat carrier supply different amounts of heat, so the optimal blast furnace slag addition was performed via energy balance. If the sensible heats of the reformed gas and the slag after steam reforming reactions were unrecycled, the required mass of blast furnace slag was over 30 times of bio-oil mass, while the required slag mass was just 11.5 times of bio-oil mass if the sensible heats after the steam reforming reactions were recycled. For the latter, about 0.144 Nm³ H₂ per kg blast furnace slag was obtained at the reforming temperature of 700–750 °C and the steam/carbon mole ratio of 6.