Geothermal energy use in hydrogen liquefaction

We propose the use of geothermal energy for hydrogen liquefaction, and investigate three possible cases for accomplishing such a task including (1) using geothermal output work as the input for a liquefaction cycle; (2) using geothermal heat in an absorption refrigeration process to precool the gas before the gas is liquefied in a liquefaction cycle; and (3) using part of the geothermal heat for absorption refrigeration to precool the gas and part of the geothermal heat to produce work and use it in a liquefaction cycle (i.e., cogeneration). A binary geothermal power plant is considered for power production while the precooled Linde–Hampson cycle is considered for hydrogen liquefaction. A liquid geothermal resource is considered and both ideal (i.e., reversible) and non-ideal (e.g., irreversible) system operations are analyzed. A procedure for such an investigation is developed and appropriate performance parameters are defined. Also, the effects of geothermal water temperature and gas precooling temperature on system performance parameters are studied. The results show that there is a significant amount of energy savings potential in the liquefaction work requirement as a result of precooling the gas in a geothermal absorption cooling system. Using geothermal energy in a cogeneration scheme (power production and absorption cooling) also provides significant advantages over the use of geothermal energy for power production only.     

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.     

Potential methods for geothermal-based hydrogen production

In this study, four potential methods are identified for geothermal-based hydrogen production, namely, (i) directly from the geothermal steam, (ii) through conventional water electrolysis using the electricity generated from geothermal power plant, (iii) using both geothermal heat and electricity for high temperature steam electrolysis and/or hybrid processes, (iv) using the heat available from geothermal resource in thermochemical processes to disassociate water into hydrogen and oxygen. Here we focus on relatively low-temperature thermochemical and hybrid cycles, due to their greater application possibility, and examine them as a potential option for hydrogen production using geothermal heat. We also present a brief thermodynamic analysis to assess their performance through energy and exergy efficiencies for comparison purposes. The results show that these cycles have good potential and become attractive due to the overall system efficiencies over 50%. The copper–chlorine cycle is identified as a highly promising cycle for geothermal hydrogen production. Furthermore, three types of industrial electrolysis methods, which are generally considered for hydrogen production currently, are also discussed and compared with the above mentioned cycles.     

Performance analysis and optimization of a hydrogen liquefaction system assisted by geothermal absorption precooling refrigeration cycle

The present paper deals with the hydrogen liquefaction with absorption precooling cycle assisted by geothermal water is modeled and analyzed. Uses geothermal heat in an absorption refrigeration process to precool the hydrogen gas is liquefied in a liquefaction cycle. High-temperature geothermal water using the absorption refrigeration cycle is used to decrease electricity work consumption in the gas liquefaction cycle. The thermoeconomic optimization procedure is applied using the genetic algorithm method to the hydrogen liquefaction system. The objective is to minimize the unit cost of hydrogen liquefaction of the composed system. Based on optimization calculations, hydrogen gas can be cooled down to ?30 °C in the precooling cycle. This allows the exergetic cost of hydrogen gas to be reduced to be 20.16 $/GJ (2.42 $/kg LH₂). The optimized exergetic cost of liquefied hydrogen is 4.905 $/GJ (1.349 $/kg LH₂), respectively.     

The performance assessment of a combined organic Rankine-vapor compression refrigeration cycle aided hydrogen liquefaction

In this study, the performance of the combined cooling cycle with the Organic Rankine power cycle, which provides cooling of the hydrogen at the compressor inlet which compresses the constant temperature in the Claude cycle used for hydrogen liquefaction, on the system is examined. The Organic Rankine combined cooling cycle was considered to be using a geothermal source with a flow rate of 120 kg/s at a temperature of 200 °C. The first and second law performance evaluations of the whole system were made depending on the heat energy at different levels taken from the geothermal source. The thermodynamic analysis of the equipment making up the system has been done in detail. The temperature values at which the hydrogen can be effectively cooled were determined in the presented combined system. The efficiency coefficient of the total system was calculated based on varying pre-cooling values. As a result of the study, it was determined that cold entry of hydrogen into the Claude cycle reduced the energy consumption required for liquefaction. Amount of hydrogen cooled to specified temperature increase by increase in mass flow of geothermal water and its temperature. Liquefaction cost is calculated to be 0.995 $/kg H₂ and electricity produced by itself is calculated to be 0.025 $/kWh by the new model of liquefaction system. Cost of the liquefaction in the proposed system is about 39.7% lower than direct value of hydrogen liquefaction of 1.650 $/kg given in the literature.     

Geothermal‐based hydrogen production using thermochemical and hybrid cycles: A review and analysis

Geothermal‐based hydrogen production, which basically uses geothermal energy for hydrogen production, appears to be an environmentally conscious and sustainable option for the countries with abundant geothermal energy resources. In this study, four potential methods are identified and proposed for geothermal‐based hydrogen production, namely: (i) direct production of hydrogen from the geothermal steam, (ii) through conventional water electrolysis using the electricity generated through geothermal power plant, (iii) by using both geothermal heat and electricity for high temperature steam electrolysis and/or hybrid processes, and (iv) by using the heat available from geothermal resource in thermochemical processes. Nowadays, most researches are focused on high‐temperature electrolysis and thermochemical processes. Here we essentially discuss some potential low‐temperature thermochemical and hybrid cycles for geothermal‐based hydrogen production, due to their wider practicality, and examine them as a sustainable option for hydrogen production using geothermal heat. We also assess their thermodynamic performance through energy and exergy efficiencies. The results show that these cycles have good potential and attractive overall system efficiencies over 50% based on a complete reaction approach. The copper‐chlorine cycle is identified as a highly promising cycle for geothermal‐hydrogen production. Copyright © 2009 John Wiley & Sons, Ltd.     

Assessment of geothermal energy use with thermoelectric generator for hydrogen production

In this work, a new model for producing hydrogen from a low enthalpy geothermal source was presented. Thermal energy from geothermal sources can be converted into electric power by using thermoelectric modules instead of Organic Rankine Cycle (ORC) machines, especially for low geothermal temperatures. This electrical energy uses the water electrolysis process to produce hydrogen. Simulation and experiments for the thermoelectric module in this system were undertaken to assess the efficiency of these models. TRNSYS software is used to simulate the system in Hammam Righa spa, the temperature of this spring is 70 °C. Obtained results reveal that in hammam righa spa in Algeria, 0.5652 Kg hydrogen per square meter of thermoelectric generator (TEG) can be produced in one year.     

Upgrading waste heat from a cement plant for thermochemical hydrogen production

A calcium oxide/steam chemical heat pump (CHP) is presented in the study as a means to upgrade waste heat from industrial processes for thermochemical hydrogen production. The CHP is used to upgrade waste heat for the decomposition of copper oxychloride (CuO.CuCl₂) in a copper–chlorine (Cu–Cl) thermochemical cycle. A formulation is presented for high temperature steam electrolysis and thermochemical splitting of water using waste heat of a cement plant. Numerical models are presented for verifying the availability of energy for potential waste heat upgrading in cement plants. The optimal hydration and decomposition temperatures for the calcium oxide/steam reversible reaction of 485 K and 565 K respectively are obtained for the combined heat pump and thermochemical cycle. The coefficient of performance and overall efficiency of 4.6 and 47.8% respectively are presented and discussed for the CHP and hydrogen production from the cement plant.     

The feasibility of using geothermal energy in hydrogen production

A feasibility study exploring the use of geothermal energy in hydrogen production is presented. It is possible to use a thermal energy to supply heat for high temperature electrolysis and thereby substitute a part of the relatively expensive electricity needed. A newly developed HOT ELLY high temperature steam electrolysis process operates at 800 – 1000°C. Geothermal fluid is used to heat fresh water up to 200°C steam. The steam is further heated to 900°C by utilising heat produced within the electrolyser. The electrical power of this process is reduced from 4.6 kWh per normalised cubic meter of hydrogen (kWh/Nm³ H₂) for conventional process to 3.2 kWh/Nm³ H₂ for the HOT ELLY process implying electrical energy reduction of 29.5%. The geothermal energy needed in the process is 0.5 kWh/Nm³ H₂. Price of geothermal energy is approximately 8–10% of electrical energy and therefore a substantial reduction of production cost of hydrogen can be achieved this way. It will be shown that using HOT ELLY process with geothermal steam at 200°C reduces the production cost by approximately 19%.     

Optimum energy evaluation and life cycle cost assessment of a hydrogen liquefaction system assisted by geothermal energy

In this study, analyses of the thermodynamic performance and life cycle cost of a geothermal energy-assisted hydrogen liquefaction system were performed in a computer environment. Geothermal water at a temperature of 200 °C and a flow rate of 100 kg/s was used to produce electricity. The produced electricity was used as a work input to liquefy the hydrogen in the advanced liquefaction cycle. The net work requirement for the liquefaction cycle was calculated as 8.6 kWh/kg LH₂. The geothermal power plant was considered as the work input in the liquefaction cycle. The hydrogen could be liquefied at a mass flow rate of 0.2334 kg/s as the produced electricity was used directly to produce liquid hydrogen in the liquefaction cycle. The unit costs of electricity and liquefied hydrogen were calculated as 0.012 $/kWh and 1.44 $/kg LH₂. As a result of the life cycle cost analysis of the system, the net present value (NPV) and levelized annual cost (LAC) were calculated as 123,100,000 and 14,450,000 $/yr. The simple payback period (N_spp) and discount payback period (N_dpp) of the system were calculated as 2.9 and 3.6 years, respectively.     

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.     

Advantages of integration with industry for electrolytic hydrogen production

This paper evaluates possible synergies with industry, such as heat and oxygen recovery from the hydrogen production. The hydrogen production technology used in this paper is electrolysis and the calculations include the cost and energy savings for integrated hydrogen production. Electrolysis with heat recovery leads to both cost reduction and higher total energy efficiencies of the hydrogen production. Today about 15–30% of the energy supplied for the production is lost and most of it can be recovered as heat. Utilization of the oxygen produced in electrolysis gives further advantages. The integration potential has been evaluated for a pulp and paper industry and the Swedish energy system, focusing on hydrogen for the transportation sector. The calculated example shows that the use of the by-product oxygen and heat greatly affects the possibility to sell hydrogen produced from electrolysis in Sweden. Most of the energy losses are recovered in the example; even gains in energy for not having to produce oxygen with cryogenic air separation are shown. When considering cost, the oxygen income is the most beneficial but when considering energy efficiency, the heat recovery stands for the greater part.     

Application of the fusion reactor to thermochemical-electrochemical hybrid cycles and electrolysis for hydrogen production from water

Current studies of hydrogen production from water by thermochemical-electrochemical hybrid cycles and electrolysis are being done with particular attention to their application to the use of fusion energy. Eight hybrid cycles are evaluated on the basis of the following criteria: (1) thermodynamics, (2) experimental performance, (3) process design, (4) applicability of fusion reactors, and (5) possibility of commercialization in about five years. Current commercial technologies are presented for low temperature electrolysis of water; research and development efforts on the advanced alkaline water electrolyzer and the solid polymer electrolyzer are discussed; and the possibility of water electrolysis by advanced power cycles using fusion reactor energy is examined.     

Analysis and performance assessment of a combined geothermal power-based hydrogen production and liquefaction system

In this paper, the thermodynamic study of a combined geothermal power-based hydrogen generation and liquefaction system is investigated for performance assessment. Because hydrogen is the energy of future, the purpose of this study is to produce hydrogen in a clear way. The results of study can be helpful for decision makers in terms of the integrated system efficiency. The presented integrated hydrogen production and liquefaction system consists of a combined geothermal power system, a PEM electrolyzer, and a hydrogen liquefaction and storage system. The exergy destruction rates, exergy destruction ratios and exergetic performance values of presented integrated system and its subsystems are determined by using the balance equations for mass, energy, entropy, energy and exergy and evaluated their performances by means of energetic and exergetic efficiencies. In this regard, the impact of some design parameters and operating conditions on the hydrogen production and liquefaction and its exergy destruction rates and exergetic performances are investigated parametrically. According to these parametric analysis results, the most influential parameter affecting system exergy efficiency is found to be geothermal source temperature in such a way that as geothermal fluid temperature increases from 130 °C to 200 °C which results in an increase of exergy efficiency from 38% to 64%. Results also show that, PEM electrolyzer temperature is more effective than reference temperature. As PEM electrolyzer temperature increases from 60 °C to 85 °C, the hydrogen production efficiency increases from nearly 39% to 44%.     

Thermodynamic analysis of a novel integrated geothermal based power generation-quadruple effect absorption cooling-hydrogen liquefaction system

In this paper, we propose a novel integrated geothermal absorption system for hydrogen liquefaction, power and cooling productions. The effect of geothermal, ambient temperature and concentration of ammonia-water vapor on the system outputs and efficiencies are studied through energy and exergy analyses. It is found that both energetic and exergetic coefficient of performances (COPs), and amounts of hydrogen gas pre-cooled and liquefied decrease with increase in the mass flow rate of geothermal water. Moreover, increasing the temperature of geothermal source degrades the performance of the quadruple effect absorption system (QEAS), but at the same time it affects the liquefaction production rate of hydrogen gas in a positive way. However, an increase in ambient temperature has a negative effect on the liquefaction rate of hydrogen gas produced as it decreases from 0.2 kg/s to 0.05 kg/s. Moreover, an increase in the concentration of the ammonia-water vapor results in an increase in the amount of hydrogen gas liquefied from 0.07 kg/s to 0.11 kg/s.     

Artificial Neural Networks based thermodynamic and economic analysis of a hydrogen production system assisted by geothermal energy on Field Programmable Gate Array

In this study, the thermodynamic and economic analysis of a geothermal energy assisted hydrogen production system was performed using real-time Artificial Neural Networks on Field Programmable Gate Array. During the modeling of the system in the computer environment, a liquid geothermal resource with a temperature of 200 °C and a flow rate of 100 kg/s was used for electricity generation, and this electricity was used as a work input in the electrolysis unit to split off water into the hydrogen and oxygen. In the designed system, the net work produced from the geothermal power cycle, the overall exergy efficiency of the system, the unit cost of the produced hydrogen and the simple payback period of the system were calculated as 7978 kW, 38.37%, 1.088 $/kg H₂ and 4.074 years, respectively. In the second stage of the study, Feed-Forward Artificial Neural Networks model with a single hidden layer was used for modeling the system. The activation functions of the hidden layer and output layer were Tangent Sigmoid and Linear functions, respectively. The system was implemented on Field Programmable Gate Array using the Matlab-based model of the system as a reference. The maximum operating frequency and chip statistics of the designed unit of Field Programmable Gate Array based geothermal energy assisted hydrogen production system were presented. The result can be used to gain better knowledge and optimize hydrogen production systems.     

Experimental study and development of an improved sulfur–iodine cycle integrated with HI electrolysis for hydrogen production

The sulfur–iodine (SI or IS) thermochemical cycle assembled with solar or nuclear energy has been proposed as a large-scale, clean and renewable hydrogen production method. In present work, an improved SI cycle integrated with HI electrolysis for hydrogen production was developed according to experiments and simulation. The mathematical models of HI electrolysis using proton exchange membrane (PEM) electrolytic cell was developed, and then the user-defined module of HI electrolysis was set up through Aspen Plus and verified by experimental data. After designing and simulating the new flowsheet of the SI cycle based on HI electrolysis, 10 L/h of H₂ and 5 L/h of O₂ were obtained. The theoretic thermal efficiency of flowsheet reached 25–42% in terms of the utilization of waste heat. An ideal thermal efficiency of 33.3% through the proper internal heat exchange in the flowsheet was determined. Sensitivity analyses of parameters in the system were conducted. Increasing proton transfer number of PEM electrolytic cell in HI section improved the thermal efficiency of SI cycle. The ratio of distillate to feed rate and the plate number of distillation column in H₂SO₄ section were the most sensitive factors to the heat duty of overall SI cycle. The proposed new flowsheet for SI cycle is competitive to the flowsheets previously proposed in the field of flowsheet simplification.     

Global warming potential of the sulfur–iodine process using life cycle assessment methodology

A life cycle assessment (LCA) of one proposed method of hydrogen production – thermochemical water-splitting using the sulfur–iodine cycle couple with a very high-temperature nuclear reactor – is presented in this paper. Thermochemical water-splitting theoretically offers a higher overall efficiency than high-temperature electrolysis of water because heat from the nuclear reactor is provided directly to the hydrogen generation process, instead of using the intermediate step of generating electricity. The primary heat source for the S–I cycle is an advanced nuclear reactor operating at temperatures corresponding to those required by the sulfur–iodine process. This LCA examines the environmental impact of the combined advanced nuclear and hydrogen generation plants and focuses on quantifying the emissions of carbon dioxide per kilogram of hydrogen produced. The results are presented in terms of global warming potential (GWP). The GWP of the system is 2500 g carbon dioxide-equivalent (CO₂-eq) per kilogram of hydrogen produced. The GWP of this process is approximately one-sixth of that for hydrogen production by steam reforming of natural gas, and is comparable to producing hydrogen from wind- or hydro-electric conventional electrolysis.     

Heat transfer problems for the production of hydrogen from geothermal energy

Electrolysis at low temperature is currently used to produce Hydrogen. From a thermodynamic point of view, it is possible to improve the performance of electrolysis while functioning at high temperature (high temperature electrolysis: HTE). That makes it possible to reduce energy consumption but requires a part of the energy necessary for the dissociation of water to be in the form of thermal energy.

A collaboration between France and Iceland aims at studying and then validating the possibilities of producing hydrogen with HTE coupled with a geothermal source. The influence of the exit temperature on the cost of energy consumption of the drilling well is detailed.

To vaporize the water to the electrolyser, it should be possible to use the same technology currently used in the Icelandic geothermal context for producing electricity by using a steam turbine cycle. For heating the steam up to the temperature needed at the entrance of the electrolyser three kinds of heat exchangers could be used, according to specific temperature intervals.     

Life cycle assessment of nuclear hydrogen production processes based on high temperature gas-cooled reactor

Conventional hydrogen production technologies mostly fossil fuels as energy and material basis. The rapid development of nuclear energy in recent years offers a new opportunity. Clean electricity and process heat generated by nuclear reactors can provide energy for hydrogen production, effectively reducing the environmental burden. This study used life cycle assessment (LCA) method to sort out the inputs and outputs of the nuclear hydrogen production processes and analyze the environmental impacts based on local data in China. In this study, we constructed frameworks for two nuclear energy-based processes and created four different scenarios to compare the effect of energy efficiency. Six indicators were used to quantify the environmental impact. The results showed that: (1) electrolysis cell manufacturing and spent fuel disposal generate the largest emissions in hydrogen production. (2) S–I cycle is sensitive to heat transfer efficiency, while high-temperature electrolysis is more sensitive to power generation efficiency; (3) The environmental impact of high-temperature electrolysis (without carrier gas) is slightly lower than that of S–I cycle, but the advantage will disappear as energy efficiency increases. At present, high-temperature electrolysis offers a clean alternative to conventional technologies for hydrogen energy and hydrogen economy. The S–I cycle might have a better prospect in the future. Our study results will provide a scientific assessment of the possibilities of developing nuclear energy for hydrogen production in China and help to make some decisions and policies.