Chemical Looping Hydrogen Research Articles

Bi-metallic Ni–Fe LSF perovskite for chemical looping hydrogen application

This work introduces a novel composite bimetallic perovskite Fe2O3-NiO/La0.6Sr0.4FeO3 as an oxygen carrier for chemical looping hydrogen production. The materials were tested in a2-g packed bed reactor at different temperatures ranging from 500 to 900 °C and atmospheric pressure by alternating three-stage chemical looping hydrogen reactions. FeNi bimetallic interactions and La0.6Sr0.4FeO3 (LSF-641) resistance to carbon deposition resulted in a stable material with only a 2% oxygen capacity drop over 20 redox cycles. The modified LSF exhibited a 20 increase in H2 generation compared to LSF-641. These results demonstrate the effectiveness of doping Fe with Ni to generate more stable OC and the low H2 generation of LSF coupled with its greater redox cycling. Pre- and post-experimental (SEM-EDX) characteristics showed a homogenous distribution of Ni and Fe on the surface, thus confirming high stability to metal oxide cluster formation or sign of sintering.

Investigations on oxygen carriers derived from natural ores or industrial solid wastes for chemical looping hydrogen generation using biomass pyrolysis gas

Chemical looping process based on multiple-step redox reactions of oxygen carriers (OCs) holds great promise for producing high purity hydrogen with inherent CO2 separation, however, there is a challenge to prepare environmental-friendly OCs with low-cost. Herein, a series of natural ores and industrial solid wastes were screened and made into Fe-based OCs for chemical looping hydrogen generation (CLHG). The results show that OCs prepared by pyrite cinder (OC-PC) feature 94.8% biomass pyrolysis gas (BPG) conversion and 94.5% CO2 concentration in OCs reduction stage. In hydrogen production stage, OC-PC achieves maximum H2 yield, 3.04 mmol g−1, which is 2∼9 times high than other OCs. The highest H2 purity is approximately 99.99%. Long term testing results indicate that OC-PC has excellent stable activity and anti-sinter ability. OCs prepared by red mud correspond to better BPG conversion (96.0%), however, the H2 yield (0.83 mmol g−1) is much lower than that of OC-PC. For OCs prepared from natural ores, they show unsatisfactory H2 production and BPG conversion compared with OC-PC. OCs prepared by ilmenite are with low specific surface area which restrains the heterogeneous reaction. The content of metal element (Mg, K, Ca) also influences the behavior of OC, which is beneficial for the fuel conversion. Moreover, the distribution of inert, anti-coking ability, oxygen vacancy also influence the sinter, H2 purity and H2 yield. Comprehensively evaluating the OCs performance, pyrite cinder is considered to be the most suitable OC raw material for CLHG.

Design, optimization, and technical evaluation of coking dry gas chemical looping hydrogen generation systems coupled with solid oxide fuel cell

Coking dry gas from delayed coking processes is rich in light hydrocarbons, making it a comparative ideal feedstock for hydrogen production. Current steam reforming processes have the disadvantages of high energy consumption and carbon emissions, whereas chemical looping hydrogen generation produces high-purity hydrogen with inherent carbon capture and a low energy penalty. Therefore, this study proposes a coking dry gas chemical looping process for hydrogen production, considering two schemes (external-heating and self-heating) and optimizes key parameters of the systems in detail. The optimal molar ratios of the oxygen carrier, steam, and air to coking dry gas for the externally heated and self-heated schemes were 8.62, 4.90, 2.27 and 8.62, 3.78, 4.07, respectively. The energy efficiencies of the two systems can reach 76.55% and 77.93% with carbon capture rates of 76.29% and 100%, 3.26% and 5.13% higher than efficiency of the steam reforming system. The self-heated system had the highest hydrogen production of 2.67 kmol/kmol coking dry gas. Based on a self-heated hydrogen system, a chemical looping hydrogen generation system was coupled with a solid oxide fuel cell. This integrated system achieved the better power generation performance with an anode recycling ratio of about 0.7. The net electrical efficiency of the system was 58.79%, which is 3.34% higher than that of a steam reforming system coupled with a solid oxide fuel cell. The results reveal that the chemical looping systems are suitable for the clean utilization of dry gas and provide a strategy for efficient hydrogen production and power generation.

A ternary Fe-based oxygen carrier with ZrO2-LaFeO3 as support for chemical looping hydrogen generation

Fe2O3 is usually supported by inert materials to improve the sintering resistance and redox stability in chemical looping hydrogen generation (CLHG). It is reasonable to apply inert together with perovskite as a composite support for Fe-based oxygen carrier in CLHG. In this work, the Fe2O3/ZrO2/LaFeO3 ternary oxygen carriers were synthesized, and the synergistic effects of ZrO2 and LaFeO3 on the reactivity and redox stability and the intrinsic mechanisms were investigated. The results showed that the 3LF (the mass ratio of LaFeO3 and ZrO2 was 30:10 with Fe2O3 loading at 60 wt %) demonstrated the best hydrogen generation performance with an average H2 yield of 8.3 mmol g-1 and H2 purity of over 99.5%. The LaFeO3 reacted with ZrO2 to form pyrochlore La2Zr2O7 with high melting point, which could be beneficial to the sintering resistance, though it led to the decline of the LaFeO3 quantity. All the cycled samples exhibited a core-shell structure in view of Fe element distribution, owing to the outward migration of Fe cations. The ternary Fe-based oxygen carrier 3LF displayed the most desirable performance in hindering the Fe migration, resulting in enhanced sintering resistance. Furthermore, the high oxygen vacancy concentration in the 3LF facilitated the lattice oxygen transport and hence promoted the reactivity and redox stability in CLHG.

Evaluation of Oxygen Carrier Performance in a Packed‐Bed Reactor during Chemical Looping Hydrogen Generation

AbstractChemical looping hydrogen generation (CLHG) has attracted much attention owing to its simple operation, low carbon capture cost, and high hydrogen purity. The performance of oxygen carrier plays an important role in the CLHG. In this work, considering the variation of internal reaction and coke deposition inside the oxygen carrier during the CLHG process, a packed‐bed reactor model is established. The temperature, gas composition, and coke deposition distribution inside the particle and reactor are explored. The results indicate that the reaction progress of the oxygen carrier near the wall is slightly faster than that at the center. The overall conversion rate and coke accumulation of the oxygen carrier near the wall are greater than those at the center.

Hydrodynamic study on the riser of chemical looping hydrogen production system with multiple fluidized bed reactors

Chemical looping technology is an available way for hydrogen production with low penalty energy for improving gas purity and CO2 is captured simultaneously. Understanding the operation and flow behavior is crucial for development of chemical looping hydrogen production. Experimental investigations of the system with dual interconnected fluidized bed reactors were carried out and presented in this work. The results indicated the system reached stable operation with current design. Influence of superficial gas velocity on the pressure distribution was examined and the corresponding mass inventory in the reactor was also analyzed. It showed that the relative pressure decreases with the increase of riser fluidization velocity and more particles will be transported to the fuel reactor from riser. The pressure curve fluctuated in sinusoidal shape as expected. It was better to make a large fuel reactor which holds most of solids and contributed to the stability. A tanks-in-sires model was utilized for analyzing the pressure evolution in the riser, which was less time consumed compared with computational fluid dynamic method. It showed the obvious phase shift of pressure drop along height. Also, the force balance of a particles was analyzed for predicting the mass inventory of riser and this method overcame the insufficient of measurement technology. The influences of solid circulating rate and gas velocity were obtained and be investigated further. This is a feasible way for quick prediction of flow behavior in the riser for both the design and operation under a certain operating condition.

A comparative study of the reaction mechanism for deep reduction hydrogen production using two special steel solid wastes and a chemical looping hydrogen production scheme

Pickling sludge (PS) and presintered waste (PW) are two special steel solid wastes that have potential as oxygen carriers due to their Fe content. Using these raw materials to produce hydrogen allows for the resource utilization of solid waste, which has good environmental effects. Here, we studied the deep reduction-hydrogen production characteristics. Specifically, the effects of temperature, papermaking sludge (PMS) blended ratio, and reaction time on the deep reduction characteristics of Fe in pickling sludge and presintered waste were studied. On this basis, the study also aimed to investigate the effects of temperature and PMS blended ratio on hydrogen production. The results indicated that when exposed to high temperature, PMS shows the ability to effectively reduce pickling sludge and presintered waste. The maximum Fe recovery rate can reach 65.63 and 96.94 % in a fixed bed reactor operating at 700 °C and a blended ratio of approximately 10 %. Under the conditions of 900 °C and 15 %/50 % papermaking sludge addition, the Fe content within pickling sludge and presintered waste was reduced to FeCr2O4 and FeO, respectively. Subsequently, during the reaction with steam, Fe2O3 and Fe3O4 were generated in PS and PW, respectively. The hydrogen production per unit mass of Fe2O3 in pickling sludge is higher due to the existence of the FeCr2O4 spinel structure in the reduction product of pickling sludge. According to the above results, two hydrogen production strategies of PS and PW through different deep reduction paths are proposed.

Integrated process for simulation of gasification and chemical looping hydrogen production using Artificial Neural Network and machine learning validation

A significant driver of global warming is fast growth in greenhouse gas (GHG) generated by energy-producing areas. Converting biomass into useful products, chemical looping gasification is an appropriate route. Using integrated steam gasification technology that utilizes a chemical looping method to produce hydrogen. Mn-, Ni-, and Ca-based materials are the three types of oxygen carriers (OC), and they are utilized. This process offers the syngas, in the greatest quality and quantity, which is a key factor. We consider that the optimum gasifier temperature is 1100 °C. The steam-to-biomass ratio is 0.95, if the steam is further increased then the char gasification reaction starts moving in the reverse direction. In this process, 736.629 MW of power is produced when only natural gas and air are used in the combustion chamber and if we add hydrogen, power is increased up to 16 MW. To predict syngas composition and the S/B ratio, machine learning modeling using Artificial Neural Networks (ANN) algorithms are applied and compared, Bayesian Regularization and Scaled Conjugate gradient proves to be the best ANN model for validating and comparing with process model, demonstrating its accuracy and potential for optimizing biomass gasification processes as high as up-to 0.99 R2 value.

Enhanced morphological maintenance and redox stability by dispersing nickel ferrite into silica matrix for chemical looping hydrogen production via water splitting

Chemical looping hydrogen production (CLHP) is widely regarded as a clean and efficient route for high purity hydrogen production. However, a huge barrier is how to avoid serious deactivation caused by sintering and agglomeration of oxygen carriers. A novel fabrication process of highly dispersing NiFe2O4 into silica matrix is proposed. The oxygen carriers of NiFe2O4 completely dispersed over silica matrix (NFSM) are successfully synthesized. The characterizations, hydrogen production capacity and cycle redox performance of oxygen carriers are further investigated. The results illustrate that NiFe2O4 active components are homogeneously dispersed on the silica matrix without any impurities. NFSM demonstrates the highest reactivity with CO as well as the greatest hydrogen production of 296 mL/g due to the strong confinement effect of silica matrix and good particle dispersion. The porous silica matrix offers large amounts of channels for the lattice oxygen transport and effectively prevents Fe and Ni cations outward migration to particle surface, which actually inhibits the larger clusters and sintering. NFSM can keep stable hydrogen production of approximately 290 mL/g during the cyclic experiments. Briefly, the innovation method of embedding active component into well-established silica matrix supports contributes to the enhanced anti-sintering properties and redox stability of oxygen carriers.

Comparative Analysis of Energy and CO2 Emission for the Integration of Biomass Gasification with a Dual-Reactor Chemical Looping Hydrogen Production Process

Comparative Analysis of Energy and CO₂ Emission for the Integration of Biomass Gasification with a Dual-Reactor Chemical Looping Hydrogen Production Process

CoxFe1-xFeAlO4-δ as highly active oxygen carriers for enhanced chemical looping hydrogen production

The oxygen carrier is a key factor to enable efficient and high-quality chemical looping hydrogen production. Here, we prepared several oxygen vacancies engineered CoxFe1-xFeAlO4-δ spinel by tuning Co loading of and investigated the performance for hydrogen production through chemical looping. The results show that Co0.4Fe0.6FeAlO4-δ displays a high hydrogen yield of 10.56 mmol.g−1 with a stable trend for 100 cycles at 600 °C. Mechanism studies demonstrate that doping Co decreases the energy barriers for oxygen vacancy formation, resulting in a high oxygen vacancy concentration on the surface. The high oxygen vacancy concentration accelerates the bulk oxygen diffusion, which is the rate-limiting step of the redox reaction. The enhanced bulk oxygen diffusion improves the oxygen release and redeposition of the lattice oxygen during redox cycles, thus promoting the chemical looping hydrogen production performance. No obvious phase separation can be found for Co0.4Fe0.6FeAlO4-δ during 100 cycles. The observed doping effect can pave way to developing more advanced oxygen carriers with high reactivity and stability for chemical looping applications.

Numerical Study on the Process of Chemical Looping Hydrogen Production with Multiple Circulating Fluidized Bed Reactors

Numerical Study on the Process of Chemical Looping Hydrogen Production with Multiple Circulating Fluidized Bed Reactors

Techno-economic analysis of sustainable methanol and ammonia production by chemical looping hydrogen generation from waste plastic

In this work, a techno-economic analysis on a novel plant configuration achieving the combined production of ammonia and methanol through chemical looping has been carried out. The innovative process presents advantages in terms of reduced dependency on market price fluctuations, thanks to the combined production of two chemicals, and optimal utilization of the chemical looping gases. The chemical looping plant is fed with recycled high density polyethylene to enhance the carbon circularity of the process. In this case, part of the captured CO2 is employed for methanol production along with hydrogen from chemical looping, while hydrogen from electrolysis is used for ammonia production by reaction with nitrogen from the air reactor. Renewable electric energy supply ensures a carbon free power to fuel conversion. Several sensitivity analyses were carried out to assess the optimum process parameters combination, i.e. fuel flow rate, steam flow rate, oxygen carrier inlet temperature. The final production rate is divided between 174 kg/h of methanol and 910 kg/h of ammonia. An economic analysis was then carried out. A capital cost of 27 M€ and an operating cost of 3 M€/y were computed. Sensitivity analyses on the impact of the electricity input cost, the electrolytic oxygen selling price, the electrolyser capital cost and the internal rate of return were carried out. The electricity demand was discovered to impact for the 68% of the total operating costs. For an electricity cost of 0.03 €/kWh, oxygen selling price of 0.07 €/kgO2 and internal rate of return of 8%, a final products cost of 0.76 €/kg was then determined. The process achieves specific CO2 emissions of 0.017 kgCO2/kgprd, which is significantly lower than the traditional processes (0.24 kgCO2/kgCH3OH and 1.66 kgCO2/kgNH3), and an energy intensity of 36 GJ/tprd. The final selling price of the products is still not competitive with the traditional processes but is comparable with ammonia production from electrolysis and air separation and methanol production from electrolysis and direct air capture.

Technoeconomics and carbon footprint of hydrogen production

Decarbonization of the global economy needs not only carbon-free electricity but also a fuel that is free of greenhouse gas emissions. Hydrogen is a prime candidate, with colors such as gray, blue and green production methods receiving attention. Generally missing from this discourse, however, is a quantitative comparison on the cost, scale, carbon footprint and infrastructure requirements for each of these technologies. Here we present a detailed technoeconomic comparison of five hydrogen production technologies: thermochemical water splitting, methane pyrolysis, water electrolysis, steam methane reforming, and chemical looping hydrogen production. Steam or autothermal methane reforming with carbon capture (SMR + CC) at large scale sets the benchmark for costs, but at small scales, electrochemical technologies appear more suitable. Potentially competitive with and sometimes more affordable than SMR + CC are chemical looping hydrogen production and methane pyrolysis. The impacts of the CO2 footprint of the electricity grid and a price on CO2 are also quantitatively evaluated. A qualitative consideration of the ability to leverage existing infrastructure is also offered with a view towards rapid scalability. Finally, the key research needs are identified for each technology.

Techno-economic analysis of a glycerol to methanol, ethylene glycol and 1,2-propanediol cogeneration process integrated with biomass chemical looping hydrogen generation

Glycerol hydrogenolysis to alcohols such as methanol, ethylene glycol and 1,2-propanediol is regarded as a promising technology. Nevertheless, conversion of fossil fuels to H2 suffers high CO2 emissions. Therefore, a new glycerol to methanol, ethylene glycol and 1,2-propanediol process integrated with biomass chemical looping hydrogen generation was designed and simulated via Aspen Plus. The prediction results demonstrated that under the flow rate of glycerol 20 t/h and H2 feed 2.4 t/h, the output of methanol, ethylene glycol and 1,2-propanediol was 11095, 1142 and 5000 kg/h, respectively. It also demonstrated that the total efficiency of energy for the proposed process was 53.8%. Additionally, under the condition of glycerol price 725 $/t and corn straw price 59 $/t, the production cost of methanol, ethylene glycol and 1,2-propanediol was 310, 523 and 1100 $/t, respectively. Moreover, the return on investment as well as payback period were 93% and 0.85 years, respectively. Additionally, sensitivities analysis results showed that glycerol price was responsible for the largest impact factor, whereas the influence of oxygen carrier price was relatively small.

Particle-resolved simulation of Fe-based oxygen carrier in chemical looping hydrogen generation

Oxygen carrier capability plays an important role in the performance of chemical looping hydrogen generation (CLHG). In this work, particle-scale simulation of oxygen carriers during the CLHG process is carried out, where the coke deposition effect on pore structures is taken into consideration. Meanwhile, the impacts of porosity and active component distribution of oxygen carriers on the CLHG performance are also analyzed. The results demonstrate that the CLHG performance is sensitive to particle porosity and active component distribution, especially for fuel reactor (FR). The increase of particle porosity can promote the carbon formation rate and hydrogen production rate. The flow direction and the diffusion will lead to the discrepancy of temperature between Egg-shell and Egg-yolk particles.

Efficient utilization of Al2O3 as structural promoter of Fe into 2 and 3 steps chemical looping hydrogen process: Pure H2 production from ethanol

Chemical Looping Hydrogen (CLH) allows the direct production of pure hydrogen exploiting the redox properties of Fe, with high flexibility on the type of reductant used. In this work, a highly pure hydrogen stream suitable for the direct use into Proton Exchange membrane Fuel Cells was produced, using bioethanol as renewable fuel. The influence of both redox temperature (675°C–750 °C) and chemical composition of the Fe-based particles (2 wt% and 40 wt% of alumina added) on the carbon formation rate during reduction step was also deeply analyzed. Al2O3 changed both FexOy redox kinetics and equilibrium phases, leading to a complete iron deactivation at high Al2O3 concentration. The addition of an air oxidation step (3 steps CLH) is fundamental to restore the redox activity, with a constant efficiency of about 30% at 750 °C for 10 cycles. Furthermore, Al2O3 promotes the ethanol conversion into carbon, undermining the hydrogen purity.

Experimental and theoretical studies of natural mineral attapulgite supported iron-based oxygen carriers in chemical looping hydrogen production

The low-priced and efficient oxygen carrier is the key to the successful operation of chemical looping hydrogen production (CLH) technology, and also the premise and foundation of its large-scale application. In this study, a novel iron-based oxygen carrier based on natural mineral attapulgite (ATP) was first applied to CLH. The effects of support on the performance of iron-based oxygen carrier and its mechanism in the CLH process were investigated. The results showed the Fe2O3 with ATP as support had more superior activity and stability than those supported by expanded perlite, kaolin or Al2O3. In particular, Fe6ATP4 exhibited a high hydrogen yield at 850 °C which was twice as high as that of Fe2O3/Al2O3. The excellent reaction performance of Fe2O3/ATP was validated by both experimental and theoretical methods. Density functional theory (DFT) calculations revealed that the electrons in Fe2O3/ATP system have stronger delocalization than those of Fe2O3/Al2O3. Moreover, XPS showed there were more defect oxides or hydroxyl groups on the surface of ATP-supported Fe2O3, which further facilitated the reduction reaction.

Performance of red mud oxygen carriers in chemical-looping hydrogen production using different components of plastic waste pyrolytic gas

This study proposed plastic waste-fueled Chemical-looping Hydrogen Production (CLHP) based on the concept of three-reactor chemical-looping process for the purposes of sustainable treatment of plastic wastes while producing high purity H2 and separating CO2. Oxygen carrier prepared from red mud wastes (Bauxite residues) was suggested to be circulating materials to improve combustion efficiency and H2 yield. The feasibility of using pelletized oxygen carrier prepared from red mud wastes was experimentally investigated with major components (H2, CH4 and C2H4) of plastics pyrolysis gases as fuels. The red mud oxygen carrier composed of around 38 wt% Fe2O3 and 50 wt% inert materials, and CuO-promoted oxygen carriers composed of 8.0 wt% CuO and 92 wt% red mud wastes were used. The two oxygen carriers were examined by parallel experiments, focusing on the aspects of oxygen transport, stability, hydrogen productivity and carbon deposition. Temperature and different components of plastic pyrolysis gases had significant impacts on oxygen transport behaviors; reduction tests using CH4 or C2H4 fuels suggested that the operation temperature of Fuel Reactor should be higher than 800 °C for deep reduction and high H2 productivity. CuO addition significantly promoted oxygen carrier's reactivity and oxygen transport capacity with various fuel components. The cyclic CLHP experiments, performed over 10 redox cycles with C2H4 as fuels, showed that there was only a limited degradation in oxygen carriers caused by carbon deposition and element migration. The developed oxygen carriers can meet the requirements of long-term operation for CLHP process. Carbon deposition on the oxygen carriers derived from hydrocarbon fuel cracking seemed to be inevitable, which experimentally determined in the range of 0.01–0.043 g g−1 oxygen carriers as C2H4 was used as fuels. However, the reactivity of these carbon deposits was extremely low; their initial steam-gasification temperatures were around 750 °C, much higher than the temperature used for water splitting reaction. This provides the potential opportunities for an industrial CLHP process to produce high purity H2 (>97%) despite of carbon deposits presents in Fuel Reactor.

Insight into the biomass pyrolysis volatiles reaction with an iron-based oxygen carrier in a two-stage fixed-bed reactor

The reaction between biomass pyrolysis volatiles and oxygen carrier (OC) is a non-negligible issue in the chemical looping combustion or chemical looping reforming of pyrolysis gas. This study systematically investigated the reaction characteristic of biomass pyrolysis volatiles with iron-based oxygen carriers, aiming to produce hydrogen by chemical looping reforming of pyrolysis gas. This work also examined the evolution of three-phase product distribution (carbon deposition, tar, and gas), which was generated through the reaction between biomass pyrolysis volatiles and an iron-based oxygen carrier. The results indicate that increasing the amount of oxygen carrier and temperature facilitated the tar conversion into more gas and less deposited carbon. The low valent state of Fe promotes tar cracking, decreasing tar content while increasing carbon deposition. Moreover, an increase in OC usage formed more naphthalene in tar, which gets much more pronounced with the low valent state of iron oxides. The consumption of CO in the biomass volatile matter (VM) reforming reaction is significant, and the carbon in tar is mainly transformed into CO2. The tar conversion with biomass VM produces less carbon deposition and higher gas yield than coal VM due to large amounts of light tar. The concentration of reducing gas is sufficient to reduce Fe2O3 to FeO, which is essential for the chemical looping hydrogen generation.