Chemical Looping Hydrogen Generation Research Articles

Coal-direct chemical looping hydrogen generation with BaMnO3 perovskite oxygen carrier

Coal-direct chemical looping hydrogen generation (CDCLHG) is a novel process that uses coal to directly produce H2 with inherent CO2 capture. A key issue is to find out suitable oxygen carriers for this process. In this study, perovskite was proposed as the oxygen carrier for CDCLHG, and a series of Mn-based and Fe-based perovskite oxides were synthesized by a sol-gel method for CDCLHG reactions in a fixed-bed reactor. The results showed that BaMnO3 was an optimal oxygen carrier for CDCLHG, which could obtain H2-rich gas (>85%) with a high H2 gas production rate, about 13 times higher than that in char steam gasification. Further tests showed that the optimal reaction temperature and O/C ratio were 850 °C and 1: 0.05, respectively. XRD and XPS patterns indicated that part of the lattice oxygen in BaMnO3 could convert to the carbonate oxygen in BaCO3 during the fuel oxidation stage (FO stage) and obtained BaMnO3-δ with plentiful oxygen vacancies in it. The BaMnO3-δ could partially restore its lattice oxygen in the reduction of steam stage (RS stage) and completely recover its initial structure in the air calcining stage (AC stage). SEM images showed that the decrease of BaMnO3 reaction performance after 9 cycles was mainly due to ash accumulation.

Thermodynamic performance study of a new diesel-fueled CLHG/SOFC/STIG cogeneration system with CO2 recovery

A new type of diesel-fueled cogeneration system is proposed in this study. The system mainly includes solid oxide fuel cell, chemical looping hydrogen generation and steam injection gas turbine cycle. The system can effectively avoid the carbon deposition of solid oxide fuel cell, recovering CO2 without separation energy consumption. Additionally, it adopts the way of centralized supply of steam and air, thus reducing the complexity and loss of the system. On this basis, the system is comprehensively evaluated by sensitivity analysis, exergy analysis, energy utilization diagram analysis and exergoeconomic analysis. It is found that the total power efficiency, exergy efficiency and fuel energy saving ratio of the new system can reach 64%, 60% and 60% respectively. Meanwhile, the power production cost of the new system is 51.25 $/GJ, and the optimization suggestion of the system is given according to the result of exergoconomic analysis. The proposed system provides a theoretical basis and new idea for the design and construction of diesel-fueled energy supply system.

Study on the redox performance of Cu and Ce‐doped CoFe 2 O 4 as oxygen carriers for chemical looping hydrogen generation

Study on the redox performance of Cu and <scp> Ce‐doped CoFe ₂ O ₄ </scp> as oxygen carriers for chemical looping hydrogen generation

Enhanced performance of hematite oxygen carrier by CeO2 for chemical looping hydrogen generation

Natural hematite is a promising oxygen carrier for chemical looping hydrogen generation (CLHG) owing to its abundance and low price. However, the reactivity of hematite is poor compared with the artificial oxygen carriers. To solve this problem, modified hematite with different CeO2 loading amounts were prepared, and the redox reactivity, cyclic stability, sintering and carbon deposition resistance were investigated with the original hematite (0%CeO2) as the control group. It was found that the CeO2-modified hematite presented far higher H2 yield and purity than 0%CeO2, and the hematite with CeO2 loading amount of 20 wt % (20%CeO2) displayed the highest reactivity, carbon deposition resistance, and satisfactory cyclic stability. The H2 yield of 20%CeO2 was 110% higher than that of 0%CeO2, and the H2 purity of the former was 99.71% vs 98.36% for the latter. The desirable performance of 20%CeO2 could be ascribed to the promotion effects of CeO2 on the lattice oxygen mobility. Specifically, the cubic fluorite CeO2 and the generated perovskite CeFeO3 provided channels for the lattice oxygen transport, enhancing the redox reactivity. The CeO2 modification could also inhibit the Fe outward migration to particle surface and thus increase the sintering resistance. The generation of cerium silicate could be inimical to the oxygen mobility, however, it could restrain the growth of CeO2 crystallite. Moreover, the interaction between CeO2 and Fe2O3 could decrease their crystallite sizes and further promote the sintering resistance.

Evolution of Sm‐Doped Fe2O3/CeO2 Oxygen Carriers in Chemical Looping Hydrogen Generation

The Sm‐doped Fe2O3/CeO2 is desirable for chemical looping hydrogen generation (CLHG) owing to its satisfactory oxygen ion conductivity, and the reactivity of Fe2O3/Ce0.8Sm0.2O1.9 (FSDC20) is the highest among the Sm‐doped Fe2O3/CeO2 oxygen carriers with different Sm‐doping amounts. This work is focused on the performance evolution of FSDC20 in CLHG with Fe2O3/CeO2 (FSDC0) as comparison, and the related mechanisms are explored. The results show that the evolution of H2 yield with redox cycles for both samples contain an activation and an attenuation process, and the fourth cycle acts as the demarcation point for FSDC20 before the H2 yield stabilizes. Specifically, the activation mainly lie in the phase transition from Fe3O4 to FeO, and the activation and attenuation processes can be ascribed to the particle microstructure evolution. For the activation process in the first four cycles, the grains on the particle aggregate together, however, with porous structure, and the improved reactivity can be attributed to the enhanced interaction between Fe2O3 and CeO2 as well as the generation of CeFeO3. However, the grains continue to aggregate on a large scale after the fourth cycle, leading to serious sintering and thus the attenuation process.

Thermodynamic analysis of fuel-cell-based combined cooling, heating, and power system integrated solar energy and chemical looping hydrogen generation

A novel solid-oxide-fuel-cell-based cooling, heating, and power (CCHP) system integrated chemical looping hydrogen generation is proposed, in which the chemical looping hydrogen generation realizes the high-efficiency CO2 capture and provides hydrogen to fuel cell, avoiding carbon deposition caused by the direct reaction of methane. The high-temperature solar heat collector is integrated to assist the fuel cell subsystem in achieving high-efficiency power generation and energy cascade utilization. The thermodynamic models of components are constructed, and the energy and exergy performances under the design conditions with or without solar energy are compared and analyzed. Through validating the thermodynamic models, the simulation results indicate that the energy and exergy efficiencies in cooling mode are 78.02% and 45.92%, respectively. The energy efficiency in heating mode reduces by 5.08%, while the exergy efficiency increases by 0.67%. The CO2 capture rate of the proposed system reaches 99.96% and the CO2 purity is about 99.59%. The energy consumption of CO2 capture in the proposed system reduces by 69.37% compared to the conventional system. The sensitivity analysis of key parameters such as fuel cell operating temperature and direct normal irradiance on system performances are performed. The results show the total energy and exergy efficiencies can be improved by properly increasing the SOFC operating temperature. Although the energy and exergy efficiencies slowly drop with the increasing direct normal irradiation, the energy output increases by 6.10% and 4.95% in cooling and heating mode from 500 W/m2 to 1000 W/m2, respectively.

Renewable hydrogen production from biogas using iron-based chemical looping technology

An integrated recycling waste bioenergy and manufacturing low-carbon hydrogen by a method to convert biogas to hydrogen based on the chemical looping concepts was proposed in this study. Biogas from biomass anaerobic digestion and pyrolysis was employed in the reduction step as the feedstock of fuel gas. Simulated marsh gas (CH4 and CO2) and pyrolysis gas (CO and H2) were used to validate the feasibility of the reduction performance with iron (III) oxide at different reaction temperatures. The experiments were conducted by using a thermogravimetric analyzer and a tandem packed-bed reactor. As for marsh gas, the reaction behavior was completely different under different CO2 concentrations and converting temperatures. The reduction reaction with CH4 would be divided into three stages, including complete combustion, competition reaction, and partial oxidation stage. Furthermore, the syngas with a tailored ratio of 1:1 can be produced without CH4 breakthrough by adjusting CO2 concentration. Besides, the total H2 production achieved 241.9 mL per gram of oxygen carrier with a purity of 98.29%. Regarding the pyrolysis gas, the solid conversion and CO breakthrough curve were investigated. Compared to a single reactor, seven reactors were required to increase the average solid conversion from 34.1% to 42% and reduced the total redox time from 705.6 min to 437.7 min. Overall, this study provided a link between waste bioenergy recycling and H2 generation with a novel chemical looping hydrogen generation (CLHG) system and supplied theoretical support for scaling up the packed-bed reactor to improve H2 production efficiency.

Ni, Co and Cu-promoted iron-based oxygen carriers in methane-fueled chemical looping hydrogen generation process

Oxygen carrier (OC) is essential in methane based chemical looping hydrogen generation (CLHG) process. Fe-based oxygen carriers have attracted lots of attention and attempts have been made to improve the CH4 conversion and hydrogen productivity. However, the influence of different promoters has yet to be compared. In this work, the interaction of promoters (Ni, Co and Cu) with Fe and the feasibility of tiny doping were investigated. Results showed that the oxygen activity and CH4 conversion increased after the addition of Ni, Co and Cu. Ni-promoted oxygen carriers presented the highest CH4 conversion and H2 yield. Co dopant benefitted the oxygen capacity, but Cu dopant restricted the deep reduction of Fe-based oxygen carriers. H2-TPR results revealed the oxygen activity was improved significantly at the intermediate temperature. A low concentration of Ni addition worked on hydrogen productivity as Mg-Fe-Al-O spinel with 1.7 wt% of Ni produced 1.3 mmol/gOC comparing with 1 mmol/gOC for Mg-Fe-Al-O. The promoters also facilitated the Fe segregation from the spinel phase. And the surface sintering of the promoted OCs was more serious, possibly resulting from the impregnation method. These findings could provide guidance for selection of promoters in chemical looping hydrogen generation process fueled by CH4.

Thermodynamic performance study of a new SOFC–CCHP system with diesel reforming by CLHG to produce hydrogen as fuel

In this paper, a combined cooling, heating and power system based on diesel-fueled chemical looping hydrogen generation and solid oxide fuel cell, and with CO2 capture was established. The system can achieve efficient power generation while separating CO2 without energy consumption, and effectively avoid the carbon deposition problem. Aspen software is used to simulate the process of the system, and FORTRAN program is used to calculate, through the thermodynamic analysis model, the unique performance change law of the new system using diesel is obtained, and thermodynamic analysis is performed on the system at last. The results show that the power efficiency of the new system is 54.1%, while the exergy efficiency and fuel energy saving ratio can reach 53%. At the same time, the influence of fuel flow and fuel utilization factor on the system performance does not continue to increase or decrease, and the system performance parameters will have a peak value with the change of pressure. The results not only provide a theoretical basis for the future construction of new diesel-fueled energy supply system, but also provide a new idea for the optimization scheme of energy-saving system and carbon recovery.

Study on Hydrogen Production of ZhunDong Coal Using Chemical Looping with Cu-Fe as Oxygen Carrier

ABSTRACT The main problem of coal direct chemical looping hydrogen generation (CLHG) is that coal ash and oxygen carrier (OC) cannot be effectively separated, which makes the OC activity is reduced after multiple cycles. In this study, a double plate-fixed bed reactor is adopted. The gasification of coal and the reduction reaction of oxygen carrier were integrated in the same furnace, and the hydrogen production characteristics of ZhunDong coal by chemical looping were studied. Cu-Fe composite oxygen carrier was prepared by chemical synthesis method. The results show that the higher the copper oxide content and the smaller the coal particle size, the better the effect of hydrogen yield. The potassium can promote the rate of coal gasification and increase oxygen carrier reduction rate, but faster reduction reaction rate will aggravate the formation of carbon deposition. The oxygen consumed in reduction of OC is preferentially from CuO, while Fe/FeO reacts with H2O prior to Cu/Cu2O in the hydrogen production stage. Compared with Cu-Fe OC, the implantation of MgAl2O3 plays an important role in stabilizing the redox ability and mechanical properties of OC.

Effect of support on hydrogen generation over iron oxides in the chemical looping process.

Fe2O3 is recognized as an excellent oxygen carrier for its low cost and high oxygen capacity. However, pure Fe2O3 must be deposited on supports to ensure high reactivity and durability. Here, we proposed several Fe2O3-based oxygen carriers using MgAl2O4, Ce0.8Gd0.2O1.9, and Zr0.8Y0.2O1.9 as supports and investigated their performance for chemical looping hydrogen generation. The support effect on chemical looping hydrogen generation performance was evaluated, and the fundamental insights were investigated in depth. Fe2O3/Ce0.8Gd0.2O1.9 exhibited a superior performance regarding high hydrogen yield and stable trend over 20 cycles at 750 °C. However, hydrogen yield of Fe2O3/Zr0.8Y0.2O1.9 exceeded that of Fe2O3/Ce0.8Gd0.2O1.9 at higher temperatures (850 °C). Characterizations show that Ce0.8Gd0.2O1.9 exhibits the highest oxygen vacancy concentration, which significantly improves the reduction and reoxidation reactions of Fe2O3, thus leading to an enhanced hydrogen yield. However, the interaction between Fe2O3 and Ce0.8Gd0.2O1.9 contributed to the increase in Fe2+ concentration, thus decreasing the oxygen capacity during the redox cycle and contributing to the declined hydrogen yield at higher temperatures. This work highlights the potential of Ce0.8Gd0.2O1.9 to be used as an effective support for Fe2O3 at mid-temperatures. We hope that the support effect in this work can be extended to design and select more active and durable oxygen carriers.

Fabrication of Iron-based Oxygen Carriers on Various Supports for Chemical Looping Hydrogen Generation

Fe2O3/Al2O3 and Fe2O3/TiO2/Al2O3 oxygen carriers were fabricated and evaluated for chemical looping hydrogen generation (CLHG) using a TGA system and a fixed-bed reactor. Oxygen carriers were converted to around 33% in a fixed-bed reactor to ensure uniform reduction. The reduced oxygen carrier was tested for steam generation, where in all cases Fe2O3/Al2O3 displayed a better conversion than Fe2O3/TiO2/Al2O3. It was found that increasing the reaction temperature from 800 to 850 °C had little effect for either oxygen carrier, but a further increase to 900°C resulted in an increased steam conversion. A higher steam flow rate caused a lower overall steam conversion but a higher H2 production. A higher feed rate of reduced oxygen carrier let to a higher steam conversion up to a rate of 18.4 and 14.9 g min–1 for Fe2O3/Al2O3 and Fe2O3/TiO2/Al2O3, respectively. A final comparison was performed with up to 50 redox cycles, where Fe2O3/Al2O3 showed superior reactivity in the first cycles but ended at a conversion of 54.6% with Fe2O3/TiO2/Al2O3 ending at a conversion of 64.6%.

Exergy Analysis of a Novel Chemical Looping Hydrogen Generation System Integrated with SOFC

In this paper, a novel system integrating chemical-looping hydrogen generation (CLH) system and solid oxide fuel cell (SOFC) has been proposed. This new methane-fuelled energy system was investigated with energy balance and exergy analysis. CLH produces the hydrogen as the fuel of the SOFC, and the FeO and Fe3O4 are selected as the looping material. Waste heat from the SOFC is absorbed by the CLH and converted to chemical energy through the reduction reaction of CLH. Owing to the cascade utilization of the fuel between the CLH and SOFC, the net efficiency of this novel system can achieve 62.8% considering CO2 separation, more than 10 percentage points higher than a methane reforming fuelled SOFC system. Meanwhile, by using the CLH to produce the hydrogen, the CO2 can be recovered without an energy penalty. Through the analysis of the graphical exergy, the cascade utilization of waste heat and the high-efficiency hydrogen production is the main reason of high performance. This novel system also has the advantage of CO2 capture without energy penalty, so this combined system is an advantaged method to accomplish the efficient utilization of methane.

Energy and economic analysis of a hydrogen and ammonia co-generation system based on double chemical looping

In this work, a model of hydrogen production by double chemical looping is introduced. The efficiency benefit obtained was investigated. The chemical looping hydrogen generation unit is connected in series to the downstream of a chemical looping gasification unit as an additional system for 100 MW·h coal gasification, with the function of supplementary combustion to produce hydrogen. Using Aspen Plus software for process simulation, the production of H2 and N2 in the series system is higher than that in the independent Chemical looping gasification and Chemical looping hydrogen generation systems, and the production of hydrogen is approximately 25.63% and 12.90% higher, respectively; The study found that when the gasification temperature is 900 °C, steam-carbon ratio is 0.84 and oxygen-carbon ratio is 1.5, the hydrogen production rate of the system was the maximum. At the same time, through heat exchange between logistics, high-pressure steam at 8.010 × 104 kg·h−1 and medium-pressure steam at 1.101 × 104 kg·h−1 are generated, and utility consumption is reduced by 61.58%, with utility costs decreasing by 48.69%. An economic estimation study found that the production cost of ammonia is 108.66 USD·(t NH3)−1. Finally, cost of equipment is the main factors influencing ammonia production cost were proposed by sensitivity analysis.

Energy quality factor and exergy destruction processes analysis for chemical looping hydrogen generation by coal

SummaryChemical looping hydrogen generation (CLHG) is a hydrogen production process with broad prospects for its advantages of not requiring H2 purification process and direct CO2 capture. Presently, the research on the integrated system of CLHG focuses on the impact of integrated processes and operating variables on the overall energy efficiency and exergy efficiency of the system. However, the research on the matching relationship between quantity and quality in the process of energy conversion is insufficient, and the flow direction of exergy and the specific exergy destruction process for equipment are not clear. The integrated system of coal gasification (CG) and three reactors CLHG was established in this paper with a hydrogen production efficiency of 42.55% and system exergy efficiency of 52.98%. This paper studied the exergy flow direction and efficiency of the equipment in the system, providing the improved direction for the amelioration of the system; a detailed description was present on the change process of energy quality in each equipment with energy quality factor, and the concept of energy quality factor ratio was proposed as an evaluation tool for matching the quantity and quality of energy in the system. It is calculated that the ratio of energy quality factor of the integrated system of CG and CLHG is 0.944. By comparing with the energy quality ratio of the traditional CG hydrogen production system (0.896), it can be concluded that the integrated system of CG and CLHG has a better energy matching relationship.

Research of coal‐direct chemical looping hydrogen generation with iron‐based oxygen carrier modified by NaAlO2

AbstractThis study reports a high‐performance modified oxygen carrier (OC) in a three‐cycle chemical looping process in which coal is used as the raw feedstock to produce hydrogen. A series of experiments of coal‐direct chemical looping hydrogen generation (CLHG) were conducted in a batch fluidized bed reactor, in the absence or presence of the NaAlO2. The experimental results indicated that the carbon conversion and hydrogen yield reached 87.0% and 1.30 L · g−1, respectively, when the coal/oxygen carrier (Fe4Al6) mass ratio was 1:20. However, FeO was the main product of the reduction process with Fe4Al6, which limits the production of hydrogen during steam oxidation. Therefore, NaAlO2 was used to improve the reaction performance of the OC. The carbon conversion and hydrogen production of NaAlO2‐loaded oxygen carriers were 10.7% and 9.6% higher than Fe4Al6, respectively. X‐ray diffraction (XRD), scanning electron microscopy (SEM), Brunauer‐Emmett‐Teller (BET), and temperature‐programmed reduction (TPR) techniques were used to characterize the oxygen carriers. According to the XRD analysis results, the addition of 5 wt% NaAlO2 can generate NaFeO2. The unique layer structure of NaFeO2 can loosen the structure between Fe2O3 and Al2O3. Thus, the surface morphology and pore structure of the oxygen carrier were improved, which are responsible for the enhancement in reactivity rather than the catalytic effects of the alkali metal. The cycle performance of the Na0.5Fe4Al6 remained stable after multi‐redox cycles, and no serious sintering phenomena were observed; in addition, the carbon conversion and hydrogen yield remained above 86% and 1.40 L · g−1, respectively.

Modified CeO2 as active support for iron oxides to enhance chemical looping hydrogen generation performance

Chemical looping hydrogen generation (CLG) is a promising pathway that can offer both the high purity hydrogen as well as the efficient CO2 capture capability. However, this process was significantly hindered by the lack of active oxygen carriers at relatively low temperatures. Mixed ionic-electronic (MIEC) supported iron oxides exhibit desirable redox performance for the improved oxygen-ion conductivity. In this work, we prepared several AxCe1-xO2-δ (A = Gd, La; x = 0, 0.1, 0.3) supported Fe2O3 for hydrogen production at 750 °C. It was shown that Fe2O3/Gd0.3Ce0.7O2-δ shows the highest hydrogen generation performance and stability over 50 redox cycles. The reactivity follows the sequence of: Fe2O3/Gd0.3Ce0.7O2-δ > Fe2O3/La0.1Ce0.9O2-δ > Fe2O3/Gd0.1Ce0.9O2-δ > Fe2O3/La0.3Ce0.7O2-δ. The fundamental investigation shows that the doping of rare earth (Gd, La) into CeO2 contributes to the formation of oxygen vacancies, thus improving the lattice oxygen diffusion. The enhanced hydrogen generation performance attributes to the high lattice oxygen diffusion to improve the reactivity and inhibiting outward diffusion of Fe. The roughly linear relation between the oxygen vacancy concentration and chemical looping performance can be extended to predict the performance of oxygen carriers for other chemical looping applications, methane reforming, combustion, and ethane dehydrogenation, etc.

Thermodynamic performance study of the CLHG/SOFC combined cycle system with CO2 recovery

In this paper, the chemical looping hydrogen generation (CLHG) and solid oxide fuel cell (SOFC) are combined to achieve efficient power generation and CO2 separation and capture without energy consumption. The system can realize the utilization of H2 produced by CLHG in SOFC to avoid carbon deposition in it. The anode of the SOFC is completely refluxed into the steam reactor (SR) of CLHG without the need to install an afterburner, which avoids the direct combustion of fuel and greatly reduces the generation of NOx. High temperature air at SOFC cathode outlet and high temperature gas at fuel reactor (FR) outlet enter GT to do work. The transcritical carbon dioxide cycle (TRCC) is used to recover waste heat, making the system compact and efficient. The new CLHG/SOFC combined cycle system proposed in this paper has high performance, which can recover CO2 and prevent NOx generation, and also prevent carbon deposition in SOFC. In addition, the anode of SOFC is completely refluxed to SR to further improve the system performance. This paper discusses the effects of fuel flow, fuel utilization, SOFC operating temperature, system operating pressure, and CO2 turbine inlet pressure on system performance. The calculation results show that the total efficiency of the system can reach more than 80%, the power generation efficiency can reach more than 65%, and the exergy efficiency is more than 60%.

Comparative exergy and exergoeconomic analysis between liquid fuels production through chemical looping hydrogen generation and methane reforming with CO2

Recently, the concept of carbon utilization has been widely investigated to reduce greenhouse gas emissions and mitigate dependence on fossil fuels. For this purpose, two different carbon capture and utilization processes to produce liquid fuels, carbon looping cyclic reforming (CCR) and carbon dioxide hydrogenation based on chemical looping hydrogen generation (CH-CLHG), are introduced. This article aims to identify which utilization method holds more potential for future technical development. To achieve it, comprehensive thermodynamic, economic and exergoeconomic assessments are implemented. The results indicate that the exergy efficiency of CH-CLHG system is 3.84% more than that of CCR system, and the cost of liquid fuels production is 36.64% less. It is also suggested that CCR system is superior to CH-CLHG system in terms of the liquid fuels output. When the electricity price is below 0.068 $/kWh, the cost of liquid fuels of CCR system is more competitive than that of CH-CLHG system. Since the higher fuel cost and larger exergy destruction, CCR system’s exergy destruction cost is more significant. In addition, the exergy destruction and exergy efficiency as well as exergoeconomic performance of each main component are presented in detail to reveal the cost formation process, and to find out the measure that would improve system efficiency and cost-effectiveness.

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%.