Metal sulfide-based process analysis for hydrogen generation from hydrogen sulfide conversion

Fossil fuel power plants often generate sulfur species such as hydrogen sulfide or sulfur dioxide due to the sulfur content of the raw feedstocks. To combat the associated environmental, processing, and corrosion issues, facilities commonly utilize a Claus process to convert hydrogen sulfide (H₂S) to elemental sulfur. Unfortunately, the potential for H₂ production from H₂S is lost in the Claus process. In this study, two chemical looping process configurations utilizing metal sulfides as chemical intermediates for sulfur recovery are investigated: (1) sulfur recovery (SR) system for sulfur production; (2) sulfur and hydrogen (H₂) recovery (SHR) system for sulfur and H₂ and production utilizing staged H₂ separation. Since, H₂ yield and sulfur recovery in a single thermal decomposition reactor is limited by low H₂S equilibrium conversion, a staged H₂ separation approach is used to increase H₂S conversion to H₂ using the SHR system. Steady-state simulations and optimization of process conditions are conducted in Aspen Plus (v10) simulation software for the chemical looping process configurations and the Claus process. An energy and exergy analysis are done for the Claus and chemical looping processes to demonstrate the relative contribution to exergy destruction from different unit operations as well as overall exergy and energy efficiency. The two chemical looping process configurations are compared against the conventional Claus process for similar sulfur recovery in a 629 MW_e integrated gasification combined cycle power plant. The SHR system is found to be the most efficient option due to a 97.11% exergy efficiency with 99.31% H₂ recovery. The overall energy and exergy efficiencies of this chemical looping system are 14.74% and 21.54% points higher than the Claus process, respectively, suggesting more efficient use of total input energy.     

Performance of hydrogen and power co-generation system based on chemical looping hydrogen generation of coal

An integrated hydrogen and power co-generation system based on slurry-feed coal gasification and chemical looping hydrogen generation (CLH) was proposed with Shenhua coal as fuel and Fe₂O₃/MgAl₂O₄ as an oxygen carrier. The sensitivity analyses of the main units of the system were carried out respectively to optimize the parameters. The syngas can be converted completely in the fuel reactor, and both of the fuel reactor and steam reactor can maintain heat balance. The purity of hydrogen produced after water condensation is 100%. The energy and exergy analyses of the proposed system were studied. Pinch technology was adopted to get a reasonable design of the heat transfer network, and it is found pinch point appears at the hot side temperature of 224.7 °C. At the given status of the proposed system, the hydrogen yield is 1040.11 kg·h⁻¹ and the CO₂ capture rate is 94.56%. At the same time, its energy and exergy efficiencies are 46.21% and 47.22%, respectively. According to exergy analysis, the degree of exergy destruction is ranked. The gasifier unit has the most serious exergy destruction, followed by chemical looping hydrogen generation unit and the heat recovery steam generator unit.     

Thermodynamic assessments of a novel integrated process for producing liquid helium and hydrogen simultaneously

Liquid helium and hydrogen are two precious cryogens with advanced applications in various energy research fields. However, producing these cryogens generally come with high-cost processes. In this research, Liquid hydrogen is obtained in two stages with the aid of a mixed refrigeration subprocess and helium cryogen. Also, liquid helium is obtained in three stages with the aid of helium upgrader, pressure swing adsorption, and helium liquefier subprocesses. The liquid helium is produced at 19.42 K, 195 kPa, and 6161 kgmole/h. Also, the liquid hydrogen is produced at 3.69 K, 110.3 kPa, and 17,970 kgmole/h. The novelties of this research can be described as the production of liquid helium and hydrogen simultaneously, low SEC, novel configuration, and production of liquid helium and hydrogen at near ambient pressure. Thermodynamic analyses show that the specific energy consumption, coefficient of performance, and figure of merit are equal to 18.96 kW h/kg, 0.03, and 0.37, respectively. Also, the exergy analysis shows that the exergy efficiency and exergy destruction in the whole process are equal to 67% and 4471 MW, respectively. Also, sensitivity analysis shows that increasing the PSA process efficiency positively impacts all process parameters like SEC, COP, FOM, and exergy efficiency.     

Exergy analysis on the process for three reactors chemical looping hydrogen generation

Three reactors chemical looping (TRCL) is a promising hydrogen production process without needing H₂ purification and capturing CO₂ directly. Based on the deficient research on the energy conversion mechanism in TRCL and the role of external heat sources in the TRCL process, this paper studied the thermodynamic characteristics of energy conversion in methane-TRCL and syngas-TRCL and water-gas shift (WGS) systems, and established the mathematical model of the related parameters through the concept of energy grade. Meanwhile, in this system the energy grade effects of input heat, heat quantity, hydrogen concentration in syngas and steam quantity on the thermodynamic performance are studied. The results show that the TRCL system of methane and syngas has the highest exergy efficiency with 89% and 88.3% respectively, while the energy grade of external input heat is 0.694. Under mentioned above, methane-TRCL is suitable for the case where the heat input value is greater than 310.52 kJ/mol, and the syngas-TRCL system is more efficient than WGS system with 4.8%.     

Renewable hydrogen production concepts from bioethanol reforming with carbon capture

This paper is assessing the hydrogen production from bioethanol at industrial scale (100000 Nm³/h hydrogen equivalent to 300 MW thermal) with carbon capture. Three carbon capture designs were investigated, one based on pre-combustion capture using chemical gas–liquid absorption and two based on chemical looping (one based on syngas and one using direct bioethanol looping). The carbon capture options were compared with the similar designs without carbon capture. The designs were simulated to produce mass and energy balances for quantification of key performance indicators. A particular accent is put on assessment of reforming technologies (steam and oxygen-blown autothermal reforming) and chemical looping units, process integration issues of carbon capture step within the plant, modelling and simulation of whole plant, thermal and power integration of various plant sub-systems by pinch analysis. The results for chemical looping designs (either syngas-based or direct bioethanol) show promising energy efficiency coupled with total carbon capture rate.     

Exergy study of hydrogen cogeneration and seawater desalination coupled to the HTR-PM nuclear reactor

This work presents a novel integration system of the high-temperature gas-cooled reactor-pebble bed module project to a hydrogen production process using the iodine-sulfur cycle in cogeneration with seawater desalination. The current approach includes a Rankine cycle, a sulfur-iodine thermochemical cycle for hydrogen production and a multi-stage flash desalination process. The use of a catalyst that allows the H₂SO₄ decomposition reaction to being carried out at temperatures compatible with the nuclear reactor project is considered. The residual heat from the acid decomposition reactions is used to desalinate seawater through the multi-stage flash process. A chemical process simulator is used to create a computational model that allows estimates of global and local efficiencies of the proposed flow diagram. Some operating parameters were sized, and their influence on the efficiency is also reported. The proposed model for the sulfur-iodine cycle can produce 0.41 kg/s of hydrogen with partial energy and exergetic efficiency of 37.35% and 38.64%. The desalination process can process 40.70 kg/s with energy and exergy efficiencies of 58.78% and 82.66%, respectively. The higher exergy destruction share is obtained in the heat exchangers (36.55%), chemical reactors (16.56%) and separators (12.80%). The global system showed efficiencies of 40.13% and 52.04%, respectively.     

Performance assessment of an integrated PV/T and triple effect cooling system for hydrogen and cooling production

In this paper we study an integrated PV/T absorption system for cooling and hydrogen production based on U.A.E weather data. Effect of average solar radiation for different months, operating time of the electrolyzer, air inlet temperature and area of the PV module on power and rate of heat production, energy and exergy efficiencies, hydrogen production and energetic and exergetic COPs are studied. It is found that the overall energy and exergy efficiency varies greatly from month to month because of the variation of solar radiation and the time for which it is available. The highest energy and exergy efficiencies are obtained for the month of March and their value is 15.6% and 7.9%, respectively. However, the hydrogen production is maximum for the month of August and its value is 9.7 kg because in august, the solar radiation is high and is available for almost 13 h daily. The maximum energetic and exergetic COPs are calculated to be 2.28 and 2.145, respectively and they are obtained in the month of June when solar radiation is high for the specified cooling load of 15 kW.     

A new solar and geothermal based integrated ammonia fuel cell system for multigeneration

In this study, a new solar and geothermal based integrated system is developed for multigeneration of electricity, fresh water, hydrogen and cooling. The system also entails a solar integrated ammonia fuel cell subsystem. Furthermore, a reverse osmosis desalination system is used for fresh water production and a proton exchange membrane based hydrogen production system is employed. Moreover, an absorption cooling system is utilized for district cooling via available system waste heat. The system designed is assessed thermodynamically through approaches of energy and exergy analyses. The overall energy efficiency is determined to be 42.3%. Also, the overall exergy efficiency is assessed, and it is found to be 21.3%. The exergy destruction rates in system components are also analysed and the absorption cooling system generator as well as geothermal flash chamber are found to have comparatively higher exergy destruction rates of 2370.2 kW and 643.3 kW, respectively. In addition, the effects of varying system parameters on the system performance are studied through a parametric analyses of the overall system and associated subsystems.     

Thermodynamic evaluation of hydrogen and electricity cogeneration coupled with very high temperature gas-cooled reactors

Hydrogen production using thermal energy, derived from nuclear reactor, can achieve large-scale hydrogen production and solve various energy problems. The concept of hydrogen and electricity cogeneration can realize the cascade and efficient utilization of high-temperature heat derive for very high temperature gas-cooled reactors (VHTRs). High-quality heat is used for the high-temperature processes of hydrogen production, and low-quality heat is used for the low-temperature processes of hydrogen production and power generation. In this study, two hydrogen and electricity cogeneration schemes (S1 and S2), based on the iodine-sulfur process, were proposed for a VHTR with the reactor outlet temperature of 950 °C. The thermodynamic analysis model was established for the hydrogen and electricity cogeneration. The energy and exergy analysis were conducted on two cogeneration systems. The energy analysis can reflect the overall performance of the systems, and the exergy analysis can reveal the weak parts of the systems. The analysis results show that the overall hydrogen and electricity efficiency of S1 is higher than that of S2, which are 43.6% and 39.2% at the hydrogen production rate of 100 mol/s, respectively. The steam generators is the components with the highest exergy loss coefficient, which are the key components for improving the system performance. This study presents a theoretical foundation for the subsequent optimization of hydrogen and electricity cogeneration coupled with VHTRs.     

Experimental based comparative exergy analysis of a multi-cylinder spark ignition engine fuelled with different gaseous (CNG,HCNG, and hydrogen) fuels

The experimental investigation was carried out on a multi-cylinder spark ignition (SI) engine fuelled with compressed natural gas (CNG), hydrogen blended CNG (HCNG) and hydrogen with varying load at 1500 rpm in order to perform comparative exergy analysis. The exergy analysis indicates that work exergy, heat transfer exergy and exhaust exergy were the highest with hydrogen at all loads due to its high flame temperature, low quenching distance, and high flame speed. The engine's exergy efficiency was the highest with hydrogen (34.23%), and it was about 24.23% and 24.08% with CNG and HCNG respectively at high load (20.25 kW). This indicates a higher potential of hydrogen to convert chemical energy input of fuel into heat and then power output. The exergy destruction was observed minimum with hydrogen at all loads, and it was drastically reduced at high loads. The combustion irreversibility which was calculated using species present during combustion, was the main contributor to exergy destruction, and it decreased with hydrogen. The minimum combustion irreversibility was 11.75% with hydrogen, followed by HCNG and CNG with 16.46% and 18.88% respectively at high load. The high quality of heat due to high in-cylinder temperature and low entropy generation during combustion caused by less number of chemical species in hydrogen combustion are the main reasons for lower combustion irreversibility with hydrogen.     

A renewable energy based waste-to-energy system with hydrogen options

A pressurized gasification combined system is studied in a novel integration with geothermal energy to produce hydrogen-enriched syngas. This system utilizes dewatered sludge, which leaves the biological wastewater treatment facility during the wastewater treatment process and is used as a feedstock to produce hydrogen as a useful output. The hydrogen produced is transformed in a proton-exchange fuel cell to electricity for community use. This system also incorporates a wind farm with a hydrogen storage system to meet societies’ energy need when the energy demand fluctuates. The integrated system is then analyzed with thermodynamic-based energy and exergy approaches. The Greater Toronto area is chosen as the case study location and comprehensive thermodynamic analysis and simulation are completed on the Aspen Plus and Engineering Equation Solver softwares while the annual wind speed data are obtained from the RETScreen software. The daily total energy delivered to the community from this proposed system is recorded to be 2.1 GWh. In addition, the hydrogen production ratio at the gasification system is observed to be 0.12 through the sludge utilization where the energy and exergy efficiencies of the integrated gasification combined cycle were calculated to be 24% and 28%, in this order. The highest energy and exergy efficiency with 38.6% and 42.2%, respectively, are observed in January where the wind farm operated at a capacity of 41.7% and the average wind speed was 6.3 m/s for Greater Toronto Area. The overall energy and exergy efficiencies of this waste-to-energy system are calculated as 32.7% and 36.6%, respectively.     

A novel hydrogen production system based on the three-step coal gasification technology thermally coupled with the chemical looping combustion process

Coal gasification technology is a significant process for the coal-based hydrogen production system and is considered as a key technology in the transition to “Hydrogen Economy”. To decrease the exergy destruction and enhance the cold gas efficiency of the coal gasification process, a novel three-step gasification technology thermally coupled with the chemical looping combustion process is proposed. And the hydrogen production system with CO₂ recovery is integrated based on the three-step gasification technology. Results indicated that the cold gas efficiency of the three-step coal gasification technology is 86.9%, which is 10.1% points enhanced compared with GE gasification technology. Besides, the novel system has an energy efficiency of 62.3%, which is 3.1% higher than that of the reference system. Exergy analysis presented that the employment of the three-step gasification technology contributed to the reduction of system exergy destruction by 4.2%. Furthermore, the energy utilization diagram (EUD) suggested that matching between endothermic reactions and exothermic reactions plays important role in the enhancement of cold gas efficiency.     

Sustainable hydrogen production options and the role of IAHE

In this paper, some potential sustainable hydrogen production options are identified and discussed. There are natural resources from which hydrogen can be extracted such as water, fossil hydrocarbons, biomass and hydrogen sulphide. In addition, hydrogen can be extracted from a large palette of anthropogenic wastes starting with biomass residuals, municipal wastes, plastics, sewage waters etc. In order to extract hydrogen from these resources one needs to use sustainable energy sources like renewables and nuclear. A total of 24 options for sustainable hydrogen production are then identified. Sustainable water splitting is the most important method of hydrogen production. Five sustainable options are discussed to split water, which include electrolysis, high temperature electrolysis, pure and hybrid thermochemical cycles, and photochemical/radiochemical methods. Other 19 methods refer to extraction of hydrogen from other materials than water or in conjunction with water (e.g., coal gasification with CO₂ capture and sequestration). For each case the achievable energy and exergy efficiency of the method were estimated based on state of the art literature screening for each involved process. In addition, a range of hydrogen production capacity is determined for each of the option. For a transition period to hydrogen economy nuclear or solar assisted coal gasification and fossil fuel reforming technologies – with efficiencies of 10–55% including CO₂ sequestration – should be considered as a viable option. Other “ready to be implemented” technology is hydro-power coupled to alkaline electrolysers which shows the highest hydrogen generation efficiency amongst all electrical driven options with 60–65%. Next generation nuclear reactors as to be coupled with thermochemical cycles have the potential to generate hydrogen with 40–43% energy efficiency (based on LHV of hydrogen) and 35–37% exergy efficiency (based on chemical exergy of hydrogen). Furthermore, recycling anthropogenic waste, including waste heat, waste plastic materials, waste biomass and sewage waters, shows also good potential as a sustainable option for hydrogen production. Biomass conversion to hydrogen is found as potentially the most efficient amongst all studied options in this paper with up to 70% energy efficiency and 65% exergy efficiency.     

Transient thermodynamic analysis of a novel integrated ammonia production,storage and hydrogen production system

A transient thermodynamic analysis is reported of a novel chemical hydrogen storage system using energy and exergy approaches. The hydrogen is stored chemically in ammonia using the proposed hydrogen storage system and recovered via the electrochemical decomposition of ammonia through an ammonia electrolyzer. The proposed hydrogen storage system is based on a novel subzero ammonia production reactor. A single stage refrigeration system maintains the ammonia production reactor at a temperature of −10 °C. The energy and exergy efficiencies of the proposed system are 85.6% and 85.3% respectively. The proposed system consumes 34.0 kJ of work through the process of storing 1 mol of hydrogen and recovering it using the ammonia electrolyzer. The system is simulated for filling 30,000 L of ammonia at a pressure of 5 bar, and the system was able to store 7500 kg of ammonia in a liquid state (1% vapor) in 1500 s. The system consumes nearly 45.3 GJ of energy to store the 7500 kg of ammonia and to decompose it to reproduce the stored hydrogen during the discharge phase.     

Energy and exergy analyses of thin layer drying of mulberry in a forced solar dryer

This paper is concerned with the energy and exergy analyses of the thin layer drying process of mulberry via forced solar dryer. Using the first law of thermodynamics, energy analysis was carried out to estimate the ratios of energy utilization and the amounts of energy gain from the solar air collector. However, exergy analysis was accomplished to determine exergy losses during the drying process by applying the second law of thermodynamics. The drying experiments were conducted at different five drying mass flow rate varied between 0.014 kg/s and 0.036 kg/s. The effects of inlet air velocity and drying time on both energy and exergy were studied. The main values of energy utilization ratio were found to be as 55.2%, 32.19%, 29.2%, 21.5% and 20.5% for the five different drying mass flow rate ranged between 0.014 kg/s and 0.036 kg/s. The main values of exergy loss were found to be as 10.82 W, 6.41 W, 4.92 W, 4.06 W and 2.65 W with the drying mass flow rate varied between 0.014 kg/s and 0.036 kg/s. It was concluded that both energy utilization ratio and exergy loss decreased with increasing drying mass flow rate while the exergetic efficiency increased.     

Optimization of hydrogen production from three reforming approaches of glycerol via using supercritical water with in situ CO2 separation

A pathway for hydrogen production from supercritical water reforming of glycerol integrated with in situ CO₂ removal was proposed and analyzed. The thermodynamic analysis carried out by the minimizing Gibbs free energy method of three glycerol reforming processes for hydrogen production was investigated in terms of equilibrium compositions and energy consumption using AspenPlus™ simulator. The effect of operating condition, i.e., temperature, pressure, steam to glycerol (S/G) ratio, calcium oxide to glycerol (CaO/G) ratio, air to glycerol (A/G) ratio, and nickel oxide to glycerol (NiO/G) ratio on the hydrogen production was investigated. The optimum operating conditions under maximum H₂ production were predicted at 450 °C (only steam reforming), 400 °C (for autothermal reforming and chemical looping reforming), 240 atm, S/G ratio of 40, CaO/G ratio of 2.5, A/G ratio of 1 (for autothermal reforming), and NiO/G ratio of 1 (for chemical looping reforming). Compared to three reforming processes, the steam reforming obtained the highest hydrogen purity and yield. Moreover, it was found that only autothermal reforming and chemical looping reforming were possible to operate under the thermal self-sufficient condition, which the hydrogen purity of chemical looping reforming (92.14%) was higher than that of autothermal reforming (52.98%). Under both the maximum H₂ production and thermal self-sufficient conditions, the amount of CO was found below 50 ppm for all reforming processes.     

Performance assessment and optimization of industrial pasta drying

Drying is a high‐energy‐intensive operation and an important step in the pasta production. In this study, exergy analysis of a four‐step drying system in a farfalle pasta production line using actual operational data obtained from a plant located in Izmir, Turkey, was performed. Exergy loss rates, evaporation rates, exergy efficiencies, and improvement in potential rates for each dryer section were determined in this drying system. The exergy efficiency values varied between 0.25% and 5.27% from the predrying to the final drying section. The exergy efficiency value for the entire drying system was calculated to be 2.96%, and the highest exergetic improvement in potential rate was 165.54 kW for the first dryer section. Copyright © 2013 John Wiley & Sons, Ltd.     

Performance comparison among different multifunctional reactors operated under energy self-sufficiency for sustainable hydrogen production from ethanol

Four ethanol-derived hydrogen production processes including conventional ethanol steam reforming (ESR), sorption enhanced steam reforming (SESR), chemical looping reforming (CLR) and sorption enhanced chemical looping reforming (SECLR) were simulated on the basis of energy self-sufficiency, i.e. process energy requirement supplied by burning some of the produced hydrogen. The process performances in terms of hydrogen productivity, hydrogen purity, ethanol conversion, CO₂ capture ability and thermal efficiency were compared at their maximized net hydrogen. The simulation results showed that the sorption enhanced processes yield better performances than the conventional ESR and CLR because their in situ CO₂ sorption increases hydrogen production and provides heat from the sorption reaction. SECLR is the most promising process as it offers the highest net hydrogen with high-purity hydrogen at low energy requirement. Only 12.5% of the produced hydrogen was diverted into combustion to fulfill the process's energy requirement. The thermal efficiency of SECLR was evaluated at 86% at its optimal condition.     

Thermodynamic and thermoeconomic assessment of hydrogen production employing an efficient multigeneration system based on rich fuel combustion

The recent development of distributed multigeneration energy systems is changing the focus of producing different energy vectors from large centralized plants to local energy systems. A novel multigeneration system is designed in the present work to supply domestic energy demands of power, hydrogen and heating. The proposed system mainly consists of a supercritical CO₂ cycle, a gas turbine equipped with a rich-fueled combustion chamber, a membrane for hydrogen separation and a water-gas shift reactor. Feeding the combustion chamber with a rich fuel mixture leads to the availability of a significant hydrogen amount in the products, which can be separated and stored. Thermodynamic analysis revealed that the highest irreversibility belongs to the combustion chamber, which is responsible for almost half of total exergy destruction. The cost of the produced hydrogen is estimated to be 2.2–6.8 $/kg for a natural gas price of 9.51 $/GJ and equivalence ratios of 2.9–1.65. The overall energy and exergy efficiencies, hydrogen production rate, total system cost rate, and cost of produced electricity are found to be 75.1%, 58.9%, 40.6 kg/h, 222 $/h and 51 $/MWh, respectively, assuming an equivalence ratio of 2.     

Thermodynamic assessment of a lab-scale experimental copper-chlorine cycle for sustainable hydrogen production

An integrated lab-scale copper-chlorine (Cu-Cl) thermochemical cycle for hydrogen production at the University of Ontario Institute of Technology (UOIT) is presented and analyzed in this paper. In a practical operation of the Cu-Cl cycle, besides the main steps of hydrolysis, thermolysis, electrolysis and drying, the oxidized anolyte (consumed anolyte at the electrolyzer cell) needs to be recycled to be concentrated sufficiently for the electro-chemical process. Recycling of the oxidized anolyte through the separation processes is achieved by distillation of anolyte, drying unit, separation cell, pressure swing distillation and CuCl₂ concentrator. This study examines the thermodynamic performance of all unit operations in the lab-scale Cu-Cl cycle. A process simulation model with Aspen Plus is used to assess the system by energy and exergy analyses. For the specific system design characteristics, the cycle is capable of producing 100 L/h of hydrogen. From the simulation results, the overall energy and exergy efficiencies of the lab-scale Cu-Cl cycle are determined to be 11.6% and 34.9%, respectively. Furthermore, after the thermolysis and hydrolysis reactors, the quench cell and CuCl₂ concentrator have the highest exergy losses with thermal energy transferred through CuCl solidification and water vaporization phase-change processes at relatively high temperature. Additional results of the processes are presented and discussed.