Chemical Looping Hydrogen Production Research Articles

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.

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.

Highly Efficient CO2 Capture and Utilization of Coal and Coke-Oven Gas Coupling for Urea Synthesis Process Integrated with Chemical Looping Technology: Modeling, Parameter Optimization, and Performance Analysis

The resource endowment structure of being coal-rich and oil-poor makes China’s production of coal-based ammonia and urea, with a low production cost and a good market, a competitive advantage. However, the process suffers from high CO2 emissions and low energy efficiency and carbon utilization efficiency due to the mismatch of hydrogen-to-carbon ratio between raw coal and chemicals. Based on the coal-to-urea (CTU) process and coal-based chemical looping technology for urea production processes (CTUCLAS&H), a novel urea synthesis process from a coal and coke-oven gas-based co-feed chemical looping system (COG-CTUCLAS&H) is proposed in this paper. By integrating chemical looping air separation and chemical looping hydrogen production technologies and the synergies between coal gasification, low-energy consumption CO2 capture and CO2 utilization are realized; the excess carbon emissions of the CTU process are avoided through coupling the pressure swing adsorption of COG, and the low carbon emissions of the proposed system are obtained. In this work, the novel process is studied from three aspects: key unit modeling, parameter optimization, and technical-economic evaluation. The results show that COG-CTUCLAS&H achieves the highest system energy efficiency (77.10%), which is much higher than that of the CTU and CTUCLAS&H processes by 40.03% and 32.80%, respectively, when the optimized ratio of COG to coal gasified gas is 1.2. The carbon utilization efficiency increases from 35.67% to 78.94%. The product cost of COG-CTUCLAS&H is increased compared to CTU and CTUCLAS&H, mainly because of the introduction of COG, but the technical performance advantages of COG-CTUCLAS&H make its economic benefits obvious, and the internal rate of return of COG-CTUCLAS&H is 26%, which is larger than the 14% and 16% of CTU and CTUCLAS&H, respectively. This analysis will enable a newly promising direction of coal and COG-based co-feed integrated chemical looping technology for urea production.

Chemical Looping Enhanced Oil Shale-to-Liquid Fuels Process: Modeling, Parameter Optimization, and Performance Analysis

The solid heat carrier moving bed with internals is an advanced oil shale retorting technology. However, the retorting gas produced by pyrolysis is generally used as fuel gas. The content of CO, H2, and CH4 in the retorting gas is high, and direct combustion leads to resource waste and environmental pollution. In addition, heteroatomic sulfur and nitrogen, as well as unsaturated hydrocarbons, reduce the quality of shale oil. To solve these problems, this paper proposed a chemical looping enhanced oil shale-to-liquid fuels (CLeSTL) process. The chemical looping hydrogen production technology is applied to convert retorting gas to hydrogen, and the hydrogen produced is used for shale oil hydrogenation to improve the oil quality. In this paper, the new process is modeled and simulated; then technoeconomic analysis is carried out. Technical analysis shows that shale oil yield is increased from 65% to 95.7% and the yield of light fraction is increased from 20% to 64%–83%. Economic analysis shows that the CLeSTL process with ligh fraction hydrogenation has the highest investment profit rate and large profit space. In addition, when the oil price is lower than 50 USD/bbl, the investment profit is 5%, which shows strong anti-risk ability.

The effect of microscopic phenomena on the performance of iron-based oxygen carriers of chemical looping hydrogen production

The scope of this work was to investigate and understand the microscopic effects on the performance of the active catalytic system in the chemical looping process. The inhibiting and accelerating effects of the different materials have been extensively studied. The ZrO2 doped with MgO and Y2O3 showed a chemical inertness and the formation of a porous morphology for an enhanced cyclic stability. Testing in large-scale application indicates that supporting material with higher yttrium content in ZrO2 has an excellent performance for 100 cycles. The HT-XRD and DSC analyzes clearly show microscopic phenomena play a fundamental role in the process and correspond to the phase transition. Stabilization of the cubic/tetragonal crystal structure leads to suppression of the phase transition and exhibits highest activity. The work reveals new fundamental principles for the design of OC in chemical looping hydrogen and understanding the influence of microscopic effects on the stability of oxygen carriers.

Polygeneration of Hydrogen and Power Using Chemical Looping Water Splitting with Dual Loops of Oxygen Carrier

The demand for hydrogen as a fuel, particularly in the transportation and power sectors, has recently been increasing due to its environmental benefit of clean combustion. However, the conventional technologies for hydrogen production involve an energy penalty in purification of hydrogen and the carbon dioxide capture, which reduce the process efficiency, whereas the technique of chemical looping hydrogen production (CLH) has an inherent capacity for CO2 capture and produces pure stream of hydrogen. This paper proposes modifications in the conventional three-reactor CLH setup, leading to elimination of the energy-intensive air separation unit and imparting flexibility in terms of polygeneration (hydrogen and power). The design modification for thermally integrating the air reactor, gasifier, and splitter for an oxygen carrier has facilitated two distinct oxygen carrier loops to meet the polygeneration objectives. The performance metrics based on efficiency have been utilized to assess the performance of the proposed process and demonstrate the flexibility in polygeneration. The effect of varying operational parameters such as split fraction, composition of metal oxide, and temperature of air reactor on the performance of the proposed process has also been evaluated.

Evaluation of oxygen vacancy and carbon deposition effect at the perovskite on methane adsorption

The perovskite with A-site doping can improve the reactivity of oxygen carrier and fuel so as to promote the performance of chemical looping hydrogen production (CLH). In this study, the effects of Sr doping in the A site of LaFeO3 perovskites on the adsorption of CH4, CH3, CH2 and CH are investigated and the oxidation reaction process on the perovskite surface is measured by means of the quantum chemistry calculation. The formation of oxygen vacancy and carbon deposition on the perovskite surface with A-site doping is evaluated. The results demonstrate that the increase of oxygen vacancy content can promote the charge transfer between the perovskite surface and CH4, CH3 and CH2. Whereas the formation of oxygen vacancy weakens the CH oxidation ability so as to reduce the adsorption energy of CH. Meanwhile, the carbon deposition does not only affect the charge transfer on the perovskite surface, but also alters the adsorption mode. The Sr doping lowers the energy barrier for the CH oxidation reaction, while the formation of carbon deposits makes the oxidation of CH difficult.

Dynamic model of isothermal moving bed reducer for chemical looping hydrogen production

This paper investigates process modelling and reactor design for the reducer in the chemical looping hydrogen production (CLHP) process. The CLHP process adopts a three-reactor technology that can provide an efficient and sustainable alternative to the current hydrogen production technology via steam methane reforming (SMR), which suffers from several limitations during industrial operation. CLHP can achieve higher thermal efficiency than SMR and provide a carbon capture and storage (CCS) system. So far, no report on the modelling analysis of the reducer despite its critical dependence on temperature. The modelling study adopts the modified pellet-grain model at the micro-scale and counter-current moving bed model reactor at the reactor level. Simulation results of the gas-solid behavior based on the multi-scale model agree with the literature evidence. Critical information from the model revealed that the oxygen carriers (solids) can attain a desired state, but the syngas remains underutilized. The model simulation further suggests that lowering the gas-solid velocity ratio (Vgs) can substantially promote the syngas conversion. However, the Vgs value must remain above a threshold value (170), defined through the limitation of gas-solid velocities in a moving bed reactor. Since a CCS system requires high purity (>95%) of the product gas, rigorous temperature-pellet size optimization is vital to achieving the target purity while maintaining desired solid state.

Deactivation of a steam reformer catalyst in chemical looping hydrogen systems: experiments and modeling

The utilization of real producer gases such as raw biogas or gasified wood for chemical looping hydrogen production implies the introduction of harmful contaminants into the process. Hydrogen sulfide represents one of the most challenging trace gases in the reformer steam iron cycle. The aim of the present work was an in-depth investigation of steam reforming with pure methane and synthetic biogas contaminated with selective concentrations of 1, 5 and 10 ppm of hydrogen sulfide. To validate the experimental data, the fixed-bed reactor system was modeled as one-dimensional pseudo-homogeneous plug flow reactor by an adapted Maxted model. In a preliminary thermodynamic study, the dry equilibrium composition was determined within a deviation of 4% for steam methane reforming (SMR) and 2% for synthetic biogas reforming compared to the experimental results. The impact of hydrogen sulfide on the reactivity of the catalyst was characterized by the residual methane conversion. The deactivation rate and extent is directly proportional to the concentration of H2S, as higher hydrogen sulfide concentrations lead to a faster deactivation and lower residual methane conversion. A comparison of the methane conversion as a function of sulfur coverage between experimental and simulated data showed good agreement. The predicted results are within <10% deviation for SMR and synthetic biogas reforming, except for sulfur coverages between 0.6 and 0.8. The temperature in the catalyst bed was monitored throughout the deactivation process to gather additional information about the reaction behavior. It was possible to visualize the shift of the reforming reaction front towards the bottom of the reactor caused by catalyst deactivation. The impact of sulfur chemisorption on the morphology of the steam reformer catalyst was analyzed by scanning electron microscope (SEM/EDS) and Brunnauer–Emmet–Teller techniques. SEM patterns clearly indicated the presence of sulfur as a sort of dust on the surface of the catalyst, which was confirmed by EDS analysis with a sulfur concentration of 0.04 wt%.

Sorption-enhanced chemical looping steam reforming of glycerol with CO2 in-situ capture and utilization

Hydrogen production from chemical looping steam reforming using an oxygen transport catalyst is definitely enhanced by CO2 in-situ capture, which shifts the chemical equilibrium and reduces the energy demands. The utilization of CO2 from this process as a reactant for chemicals and fuels could help to improve economic reasons and mitigate its impact on climate. In this study, we proposed a sorption-enhanced chemical looping steam reforming of glycerol to realize the synergetic capture and conversion of CO2 in one integrated chemical looping hydrogen production process. The process is characterized to usethe oxidized NiO/NiAl2O4 as a steam reforming catalyst, the reduced NiO/NiAl2O4 as a CO2-CH4 dry reforming catalyst, and the inexpensive dolomite as a CO2 sorbent. The surface carbon that would deactivate the catalyst is combusted by air after CO2-CH4 dry reforming and the Ni on the catalyst is re-oxidized. The coupling of these different processes of chemical looping steam reforming, CO2 in-situ capture, dolomite decomposition and CO2 in-situ utilization, results in simultaneous generation of high purity hydrogen and syngas. The results demonstrated that hydrogen of above 92.5% was one-step generated and CO2 was decreased to zero in the pre-CO2 breakthrough periods. The reduced NiO/NiAl2O4 catalysts favored the CO2-CH4 dry reforming at 850 °C. The syngas of H2-to-CO molar ratios of 0.8–1.1 through the conversion of CO2 from in-situ extraction of the absorbed CO2 dolomite, was produced. The NiO/Al2O4 with 15 wt% NiO gave the highest hydrogen and syngas yields, and maintained high performance for the proposed system. The catalysts and dolomite exhibited good stability with no obvious loss of activity in 10 cycles.

Hydrogen and ammonia production from low-grade agricultural waste adopting chemical looping process

Chemical looping hydrogen production (CLH2) is a new technology used to produce hydrogen (H2) from fuels while separating CO2 simultaneously. This research aims to build an integrated conversion system of rice husks, a high energy potential biomass, to H2 with high energy efficiency. The developed system mainly consists of superheated steam drying, steam gasification, chemical looping, and Haber-Bosch processes. Three different systems are developed and compared. The first and second systems employ direct chemical looping (DCL) using H2O and CO2 as gas enhancers for the reducer, respectively, while the third system adopts syngas chemical looping (SCL). Exergy recovery and process integration technologies are adopted to enhance energy and exergy efficiencies. A mixture of Fe2O3 and Al2O3 is used as oxygen and heat carriers in the CLH2 module. Process modeling, optimization, and evaluation of both energy and exergy efficiencies are conducted using Aspen Plus. Some crucial operating parameters, including reactor temperature, pressure, the oxygen carrier flow rate, and gas enhancer flow rate, are selected to evaluate the performance of the system, especially in terms of efficiency. The highest achievable H2, NH3, and net power efficiencies are 51.8%, 38.09%, 0.65%, respectively, when DCL is adopted with CO2 as a gas enhancer during the reduction.

A new scheme for ammonia and fertilizer generation by coal direct chemical looping hydrogen process: Concept design, parameter optimization, and performance analysis

Ammonia is a very important chemical industry product. It has a wide range of applications in refrigeration, energy, and fertilizers , and 80% of ammonia is used as a nitrogen fertilizer. China mainly produces ammonia and urea from coal gasification , which leads to difficult CO 2 capture and high energy consumption. This study proposed a new process for the production of ammonia and urea by coal direct chemical looping hydrogen production process (CDCLTU). The coal direct chemical looping hydrogen production replaces the air separation unit and water gas conversion unit of the traditional coal-to-urea process (CTU), which effectively separates and captures CO 2 and significantly reduces the energy consumption. A model of the CDCLTU was established using Aspen Plus. Parameter optimization, technoeconomic, and environmental analysis were conducted through simulations. The results showed that CDCLTU could completely replace the air separation system that the CTU relies on. Compared with the traditional process, the utilization rate of C increased from 53.46% to 67.95% in the new process. The energy consumption of CO 2 separation and capture was reduced by 97.04%. The CDCLH had a 79.7% energy efficiency in the hydrogen production process and 99% capture rate of CO 2 . The total capital investment was dropped by 41%, unit urea production cost dropped by 12.1%, and the payback period dropped from 7.5 to 3.5 years. This paper provides a new direction for clean and efficient utilization of coal resources. • Proposed a novel coal-to-urea process by chemical looping technology. • Conducted main parameters optimization and performance analysis for the new process. • The new process reduced 97.04% energy consumption of CO 2 separation and capture. • Production cost of the new process is 12.1% lower than that of the conventional process. • The new process achieved 67.95% C utilization rate and 1.39 t/t lower CO 2 emission.

Environmental evaluation of hydrogen production employing innovative chemical looping technologies – A Romanian case study

A cradle-to-gate life cycle assessment is carried out to evaluate the environmental impact of producing 1 kg of hydrogen implementing innovative chemical looping technologies: chemical looping hydrogen production (CLH), sorption enhanced reforming (SER), and sorption enhanced chemical looping reforming (SECLR). The performance of the looping technologies is compared against conventional hydrogen production without and with CO2 capture, as well as against green hydrogen production in order to determine the more environmentally-friendly option. Comparing the looping technologies with the reference blue hydrogen production it shows that CLH has a lower environmental burden, presenting smaller values in 9 out of 12 environmental impact indicators. If we confront the looping technologies against each other, CLH shows better performance in 11 out of 12 environmental indicators. As expected, green hydrogen has a much smaller overall environmental impact with the exception of human toxicity, terrestrial ecotoxicity and mineral depletion.

Thermodynamic modelling of hydrogen production in sorbent‐enhanced biochar‐direct chemical looping process

AbstractHydrogen (H2) has been widely considered the clean energy carrier of choice for emerging renewable energy generation technologies. However, H2 is a secondary fuel mainly derived from natural gas. Over the past decades, research on developing H2 production technology that reduces carbon emissions has gained momentum due to increasing atmospheric levels of carbon dioxide (CO2). This study proposed a new sorption‐enhanced (SE) and biochar‐direct (BD) integrated chemical looping system for hydrogen production from biomass gasification, using iron oxide as an oxygen carrier, calcium oxide (CaO) as a CO2 adsorbent, and biochar as a reducing agent. In this study, a thermodynamic model with the proposed sorbent‐enhanced biochar‐direct (SE‐BD) chemical looping hydrogen production (CLHP) process has been developed using an Aspen Plus simulator. The effect of important process parameters, including the reactor temperature, the syngas composition, and the molar feeding ratios of iron oxide/syngas, biochar/syngas, and CaO/syngas on the performance in terms of product gas composition, iron oxide conversion, H2 yield, H2 purity, and reactor heat demand has been evaluated. The simulation results show that the addition of biochar significantly enhances the overall hydrogen yield compared to the conventional CLHP process; whereas the addition of CaO‐sorbent was found to significantly improve the H2 purity. Moreover, the exothermic lime carbonation further reduced the thermal requirements of the process. In addition, this thermodynamic simulation demonstrates that the sorbent‐enhanced biochar‐direct chemical looping hydrogen production (SE‐BD‐CLHP) process can achieve a wide operating window for complete iron oxide (Fe3O4) reduction by adjusting the CaO and biochar feeding ratio.

Parameter optimization and exergy efficiency analysis of petroleum coke-to-hydrogen by chemical looping water splitting process with CO2 capture and self-heating

The petroleum coke-to-hydrogen process is promising since the output of high-sulfur petroleum coke is increasing year by year, the pollution emissions of its combustion for power generation are serious, and the refinery needs a lot of hydrogen. Therefore, this study establishes the process model and conduct the parameter optimization of the petroleum coke direct chemical looping hydrogen production process. The optimized mass ratios of oxygen carrier (Fe2O3), steam, and air to petroleum coke are 12.71, 2.98, and 2.18; however, that are 12.71, 1.79–2.08, and 4.53–5.32 when the proportion of the reduced oxygen carrier entering steam reactor is reduced from 100% to 60–70%, which can be operated in a self-heating mode with air preheating temperature of 278.54–816.80 ℃. When the proportion is increased from 60% to 65.32% and 70%, the product exergy of hydrogen is increased from 454.58 MW to 494.92–530.36 MW with about 100% CO2 capture and the exergy efficiency is therefore increased from 59.56 to 60.75% to 62.32–63.59% and 62.65–63.91%. This paper also studies the sulfur distribution and existing forms of sulfides. Finally, this study found that the exergy efficiency of the chemical looping hydrogen process with the proportion of 65–70% is significantly higher than that of the hydrogen production process by petroleum coke gasification.

Diffusion transport characteristic of carbon monoxide within calcium sulfate slit in chemical looping hydrogen production: Molecular dynamics simulation

Chemical looping hydrogen production is a kind of technology for high-carbon energy cleaning and low-carbon utilization with great development potential, which can realize H2 production and CO2 separation at low cost. CaSO4 oxygen carrier, as the non-metal oxide oxygen carrier, is not only cheap in price and friendly to the environment, but also high in amount of oxygen carried and excellent in the thermodynamic reaction property. For the key problem of its popularization and application – low reaction rate, this paper investigated the diffusion transport characteristics of the fuel gas molecule, which was one of key microprocesses affecting the reaction rate, in the channel of CaSO4 oxygen carrier. Based on the channel of CaSO4 oxygen carrier and the slit model, the influence of the slit width, reaction temperature and coverage rate of doped element Na or Fe of oxygen carrier on the internal diffusion behavior of CaSO4 oxygen carrier was investigated by the molecular dynamics simulation. The results show: CO molecules physical adsorb on CaSO4 slit surface; Increase of the slit width will reduce the binding of CaSO4 surface on single CO molecule, but CO molecular diffusion capacity will increase first and then decrease; The temperature rises will result in the growth of CO molecular diffusion capacity, because CO molecule to be easy to diffuse to the unoccupied reaction site; After Na and Fe is loaded on CaSO4 slit surface, CO molecular diffusion capacity is greatly improved, and the diffusion coefficients of CO molecule are 27 and 28 times of pure CaSO4 slit surface, respectively. The calculation results can provide theoretical basis for the structural design and channel optimization of calcium-based oxygen carrier for chemical looping hydrogen production.

Room-temperature chemical looping hydrogen production mediated by electrochemically induced heterogeneous Cu(I)/Cu(II) redox

The chemical looping process is a promising technology for high-purity hydrogen production. However, this process is operated at high temperature (e.g., >600°C), leading to rigorous requirements in the aspects of reactor design and oxygen carriers. Here, we develop a room-temperature electrocatalytic chemical looping hydrogen production system using Cu(OH) 2 as the oxygen carrier and ascorbate as the fuel. The electrolyzer is assembled by coupling cathodic hydrogen evolution and anodic Cu 2 O electro-oxidation. Ascorbate acts as the reducible fuel to reduce the resultant Cu(OH) 2 into Cu 2 O and completes the redox loop. The assembled electrolyzer achieves a current density of 100 mA cm −2 at 0.94 V. The required electricity input per cubic hydrogen produced is 2.57 kWh Nm −3 H 2 , almost half of that for conventional water electrolysis (4.83 kWh Nm −3 H 2 ). This work not only provides a new approach for hydrogen production but also facilitates the development of an innovative catalytic process. • A room-temperature electrocatalytic chemical looping H 2 production system was reported • Operando methods revealed that RTECL works on the basis of Cu(OH) 2 /Cu 2 O redox • The electricity input for hydrogen produced is merely 2.57 kWh Nm 3 H 2 for RTECL As an ideal hydrogen production method, water electrolysis is limited by its high energy consumption because of oxygen evolution reaction with sluggish kinetics. A room-temperature electrocatalytic chemical looping (RETCL) hydrogen production system using Cu(OH) 2 as the oxygen carrier was reported. A two-step indirect process was demonstrated, including an electrocatalytic-driven catalyst oxidation reaction from Cu 2 O to Cu(OH) 2 and spontaneous redox reaction between Cu(OH) 2 and ascorbate to form Cu 2 O and dehydroascorbic acid. The assembled RETCL hydrogen production system needs only 0.94 V to drive 100 mA cm −2 and realizes electricity consumption as low as 2.23 kWh Nm −3 H 2 (half of that of sole water electrolysis). Ultra-low electricity consumption for hydrogen production was achieved based on a room-temperature electrocatalytic chemical looping (RETCL) hydrogen production system. A two-step, Cu(OH) 2 -mediated indirect process was proved for the RETCL system that the pivotal specie Cu(OH) 2 is generated by the electrically driven oxidation of Cu 2 O and spontaneously undergoes redox reaction with ascorbate to reform Cu 2 O, achieving electricity consumption of 2.23 kWh Nm −3 H 2 .

CFD simulation of a cold flow model of inter-connected three fluidized reactors applied to chemical looping hydrogen production

The chemical looping hydrogen production (CLHP) process is a new approach for hydrogen (H2) fuel production. The proposed process consists of three reactors which are air reactor (AR), fuel reactor (FR) and steam reactor (SR). In this study, the gas solid flow behaviour in a cold model of the proposed CLHP process was simulated using computational fluid dynamics (CFD) with kinetic theory of granular flow. The effect of drag coefficient models on the pressure profile of each reactor was investigated and the results from the modified Syamlal–O’Brien drag model agreed well with the experimental data. The model was further used to investigate effects of the operating parameters on the hydrodynamics profiles of each reactor. The solid flux increased with the increasing of inlet velocity of AR and FR but decreased with the increasing of the inlet velocity of SR. At the same time, the solid flux increased with the increasing of the solid inventory.

Highly integrated system for ammonia and electricity production from biomass employing direct chemical looping: Exergy and exergoeconomic analyses

An integrated system was developed to simultaneously produce ammonia and power using biomass as feedstock. The proposed system has the following subsystems: (i) self-heat recuperation-based drying to significantly reduce energy consumption, (ii) direct chemical looping hydrogen production with two-stage combustion to obtain highly purified hydrogen and nitrogen, (iii) Haber-Bosch (H-B) process to produce ammonia, and (iv) Brayton-Rankine combined cycle to exploit the thermal energy of purged gas from the H-B process. In-depth exergy and exergoeconomic analyses were performed. Self-heat recuperation-based drying achieved an energy-saving ratio of up to 93.4% compared to traditional drying. Exergy analysis showed that the exergetic efficiencies of ammonia and net power production were 44.36% and 1.73%, respectively. The largest exergy destruction occurred in the fuel reactor, accounting for approximately 28% of the total exergy destruction. Exergoeconomic analysis revealed that refrigerator and some pressure-changing components (MComp1, Comp, MComp2, and EXP1) have higher cost reduction potential; a decrease in cost rates (ZK s) (as well as purchasing costs) of these components is necessary for system cost reduction. The final product cost allocation demonstrated that the unit costs of ammonia and electricity were 29 USD/GJ and 140 USD/GJ, respectively, under the initial input parameters.