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This study investigates the synthesized NiO- and CuO-based carriers supported by Al2O3, CeO2, ZrO2 and their combinations in chemical looping combustion (CLC). The oxygen carriers were tested in a thermogravimetric analyzer (TGA), where the results showed that the oxygen capacity increased using mixed support oxides in both NiO-based and CuO-based samples. The reducibility of CeO2 played a role in the increase of oxygen capacity and in the case of NiO-based samples, the reduction of NiAl2O4 phase as promoted by the formation of CeAlO3 played a role, as well. For NiO-based samples, a significant increase of carbon deposition occurred for mixed support oxides (Al2O3-ZrO2, Al2O3-CeO2 and Al2O3-ZrO2-CeO2) at 750 °C in comparison with the use of one support while the differences were negligible at 950 °C. To examine the structure and properties of the oxygen carriers, they were characterized by XRD, SEM/EDX and XPS. Comparison of fresh and used samples revealed sintering of active-sites particles on the surface of supports as evident of EDX mapping images and the decrease in active-site to support ratio in the XPS analysis. NiO/Al2O3-ZrO2-CeO2 was found to be a potential oxygen carrier for further CLC studies and scaleup.

A redox process combining propane dehydrogenation (PDH) with selective hydrogen combustion (SHC) is proposed, modeled, simulated, and optimized. In this process, PDH and SHC catalysts are physically mixed in a fixed-bed reactor, so that the two reactions proceed simultaneously. The redox process can be up to 177.0% higher in propylene yield than the conventional process where only PDH catalysts are packed in the reactor. The reason is twofold: firstly, SHC reaction consumes hydrogen and then shifts PDH reaction equilibrium towards propylene; secondly, SHC reaction provides much heat to drive the highly endothermic PDH reaction. Considering propylene yield, operating time, and other factors, the preferable operating conditions for the redox process are a feed temperature of 973 K, a feed pressure of 1 bar, and a mole ratio of H2 to C3H8 of 0.15, and the optimal mass fraction of PDH catalyst is 0.5. This work should provide some useful guidance for the development of redox processes for propane dehydrogenation.

The chemical looping hydrogen production (CLHP) process is a new approach for hydrogen ( H 2 ) 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.

Hydrogen is an indispensable energy carrier for the sustainable development of human society. Nevertheless, its storage, transportation, and in situ generation still face significant challenges. Methanol can be used as an intermediate carrier for hydrogen supplies, providing hydrogen energy through instant methanol conversion. In this study, a sorption-enhanced, chemical-looping, oxidative steam methanol-reforming (SECL-OSRM) process is proposed using CuO–MgO for the on-board hydrogen supply, which could be a promising method for safe and efficient hydrogen production. Aspen Plus software was used for feasibility verification and parameter optimization of the SECL-OSRM process. The effects of CuO/CH3OH, MgO/CH3OH, and H2O/CH3OH mole ratios and of temperature on H2 production rate, H utilization efficiency, CH3OH conversion, CO concentration, and system heat balance are discussed thoroughly. The results indicate that the system can be operated in auto-thermal conditions with high-purity hydrogen (99.50 vol%) and ultra-low-concentration CO (< 50 ppm) generation, which confirms the possibility of integrating low-temperature proton-exchange membrane fuel cells (LT-PEFMCs) with the SECL-OSRM process. The simulation results indicate that the CO can be modulated in a lower concentration by reducing the temperature and by improving the H2O/CH3OH and MgO/CH3OH mole ratios.

Calcium sulfate (CaSO4) has been verified as a promising oxygen carrier (OC) in the chemical looping combustion (CLC) for its high oxygen capacity, abundant reserve and low cost, but its low reactivity and deleterious sulfur species emission from the side reactions of CaSO4 should be well considered for its wide application in CLC. In order to promote the reactivity of CaSO4 and increase its potential to inhibit the gaseous sulfur emission, a CeO2-enhanced CaSO4 OC mixed OC of core-shell structure was prepared using the combined template synthesis method. Reaction characteristics of the prepared CaSO4-CeO2 mixed OC with a typical lignite was first conducted and systematically investigated, and an improved reactivity of the prepared CaSO4-CeO2 mixed OC was demonstrated than its single component CaSO4 or CeO2 due to the fast transfer and exchange of oxygen from the CaSO4 substrate to coal via the doped CeO2. Furthermore, the solid products formed from the mixed CaSO4-CeO2 OC with the selected coal were collected and analyzed. Especially, evolution and redistribution of the sulfur species of different forms were focused. At the latter reaction stage of YN reaction with the CaSO4-CeO2 mixed OC, the SO2 emitted from the side reactions of CaSO4 was greatly diminished and the doped CeO2 was proven effective to directionally fix the SO2 released to turn into different solid sulfur compounds, which were determined as Ce2O2S, Ce2S3 and Ce2(SO4)3·5H2O and formed through the different pathways. In addition, good regeneration of the reduced CaSO4-CeO2 mixed OC could be reached in spite of the unavoidable interaction between the included minerals in coal and the reduced mixed OC. Overall, the combined template method-made CaSO4-CeO2 mixed OC reported herein was not only endowed with enhanced reactivity for coal conversion, but also owned the potential to directionally fix the gaseous sulfur emission, which is quite applicable as OC for simultaneous decarbonatization and desulfurization in the real CLC process.

The chemical looping process, where an oxygen carrier is reduced and oxidized in a cyclic manner, offers a promising option for hydrogen production through splitting water because of the much higher water splitting efficiency than solar electrocatalytic and photocatalytic process. A typical oxygen carrier has to comprise a significant amount of inert support, to maintain stability in multiple redox cycles, thereby resulting in a trade-off between the reaction reactivity and stability. Herein, we proposed the use of ion-conductive yttria-stabilized zirconia (YSZ) support Fe2O3 to prepare oxygen carriers materials. The obtained Fe2O3/YSZ composites showed high reactivity and stability. Particularly, Fe2O3/YSZ-20 (oxygen storage capacity, 24.13%) exhibited high hydrogen yield of ∼10.30 mmol g−1 and hydrogen production rate of ∼0.66 mmol g−1 min−1 which was twice as high as that of Fe2O3/Al2O3. Further, the transient pulse test indicated that active oxygen diffusion was the rate-limiting step during the redox process. The electrochemical impedance spectroscopy (EIS) measurement revealed that the YSZ support addition facilitated oxygen diffusion of materials, which contributed to the improved hydrogen production performance. The support effect obtained in this work provides a potentially efficient route for the modification of oxygen carrier materials.

The experiments of chemical looping gasification of biomass based on Fe2O3–CaO oxygen carrier were studied in a fixed bed reactor using sawdust as a biomass feedstock. It was found that compared to the parent Fe2O3 and CaO, the combined oxygen carriers of iron oxide and calcium oxide demonstrated the best activity for chemical looping gasification of biomass. When the mass ratio of sawdust:Fe2O3:CaO was 2:2:1, the maximum syngas yield could reach 531.3 mL g−1 sawdust at the reaction temperature of 850 °C. Furthermore, from the results of cycle experiments, SEM and XRD characterizations, it was found that Fe2O3 could provide oxygen for sawdust gasification, while CaO played a dual role of absorbing CO2 and catalysis at mild temperatures and reforming tars to syngas at high temperature. Fe2O3–CaO oxygen carriers exhibited good cycling characteristics during chemical looping biomass gasification.

Chemical looping steam methane reforming (CL-SMR) is a promising and efficient method to produce hydrogen and syngas. However, oxygen carrier (OC) prepared by synthesis are complex, expensive and poor mechanical performance, while natural ore OCs are low activity and poor selectivity. In order to avoid these problems, Ni/Fe modification of natural ores were proposed to improve the reactivity and stability of OC to CL-SMR. The results indicated that the modified calcite recombined and improved the structural phase during the reaction, enhancing performance and inhibiting agglomeration. Moreover, high ratio of iron to nickel was easy to sinter and decline the OC performance. In addition, with the increase of steam flow, both CH4 conversion and carbon deposition decreased. Thereinto, the highest H2 concentration, CH4 conversion efficiency and H2 yield were obtained when the ratio of steam to OC was 0.05. Furthermore, CH4 flow rate had a great impact on CL-SMR performance. When the ratio of CH4 to OC was 0.04, it achieved the highest CH4 conversion efficiency of 98.96%, the highest H2 concentration of 98.83% and the lowest carbon deposition of 3.23%. However, the carbon deposition increased with the increase of CH4 flow rate. After a long-time chemical looping process, the Ni/Fe modified calcite showed a consistently stable performance with average H2 concentration of 93.08%, CH4 conversion efficiency of 88.03%, and carbon deposition of 2.15%.

Chemical looping combustion (CLC) is a next-generation combustion technology that uses an oxygen carrier in a metal oxide particulate form to supply oxygen that is necessary for combustion. This study analyzed the effect of pressure on the transport velocity with the aim of designing a pressurized CLC. The emptying time method was used to determine the transport velocity with a two interconnected pressurized fluidized bed system. This investigation also verified the feasibility of the existing correlations to predict the effect of pressure on the transport velocity in the gas fluidized bed. A modified correlation that considers the pressure and the particle properties was then proposed. This study demonstrated that the modified correlation led to a smaller difference between the measured transport velocity and calculated values under ambient and pressurized conditions so that the prediction of transport velocity in a pressurized circulating fluidized bed can be expected to be more accurate.

Oxygen carriers such as CuO/CeO2 and CuO/Nb2O5 were found to have very good selectivity to syngas products when used in chemical looping reforming. The oxygen carriers with 10% CuO has been applied in partially oxidizing liquefied petroleum gas in a chemical looping reforming process at 800 °C and the kinetic model of the processes were developed and then validated with the experimental data. The results show that first order kinetic, 3D contraction and third order kinetic models gave best fits for CuO/CeO2 powder, CuO/CeO2 pellets and CuO/Nb2O5. These resulted in rate constants of 0.0836 s−1, 0.0202 s−1, 0.1075 s−1 and 0.0682 s−1 for CuO/CeO2 powder, CuO/CeO2 pellets, CuO/Nb2O5 powder and CuO/Nb2O5 pellets. Using the rate constants, the model results were found to give good correlations when compared to experimental data.

Operating chemical looping process at mid-temperatures (550-750 oC) presents exciting potential for the stable production of hydrogen. However, the reactivity of oxygen carriers is compromised by the detrimental effect of the relatively low temperatures on the redox kinetics. Although the reactivity at mid-temperature can be improved by the addition of noble metals, the high cost of these noble metal containing materials significantly hindered their scalable application. In the current work, we propose to incorporate earth-abundant metals into the iron-based spinel for hydrogen production in a chemical looping scheme at mid-temperatures. Mn0.2Co0.4Fe2.4O4 shows a high hydrogen production rate at the average rate of ∼0.62 mmol.g-1.min-1 and a hydrogen yield of ∼9.29 mmol.g-1 with satisfactory stability over 20 cycles at 550 oC. The mechanism studies manifest that the enhanced hydrogen production performance is a result of the improved oxygen-ion conductivity to enhance reduction reaction and high reactivity of reduced samples with steam. The performance of the oxygen carriers in this work is comparable to those noble-metal containing materials, enabling their potential for industrial applications.

Chemical looping conversion of coal (CLCC), an innovative technology, is an efficient and clean way for the utilization of coal. Oxygen carrier (OC) reduction by the coal is the rate-limiting process for the CLCC with deep OC reduction. K-decorated Fe2O3/Al2O3 OC, found to be a promising OC, can increase the reaction rate of OC and char. Unfortunately, due to the complexity of the OC the preparation conditions on the performance of this composite OC were not clear. In this study, the effect of Al2O3 content and calcination temperature on the activity and stability of Fe-based OC were investigated by thermogravimetric analysis (TGA), H2 temperature-programmed reduction (TPR), N2 adsorption analyzer, X-ray diffraction (XRD) and scanning electron microscope (SEM). The impact of K2CO3 loadings on the reactivity and stability of OC was also studied in a fix-bed reactor. In addition, optimal preparation conditions were screened out. The results showed that Al2O3 could increase the specific surface area of OC and anti-sintering ability. However, the Al2O3 had an adverse impact on the mechanical strength and reactivity of OC. The increase of calcination temperature of OC could increase the mechanical strength but decrease the reactivity of OC. The loading of K2CO3 could significantly improve the reactivity of OC, and K2CO3 was favorable for the redox stability of OC. The optimal preparation conditions of the composite OC are as follows: the addition amount of Al2O3 was 30%, the addition amount of K2CO3 was 5%, and the calcination temperature of OC was 1030 °C.

Chemical looping reforming (CLR) is a recent trend for syngas production, which has several merits compared to the conventional manner. One of the most important issues for CLR is to find low-cost material as oxygen carriers, so iron is a promising candidate. This paper contributes to testing the thermodynamic ability of iron-based oxygen carrier for chemical looping reforming of ethanol (CLRE). Iron thermodynamically investigated in temperature 100–1300 °C and excess oxygen number (Φ) 0–4. It was found that the temperature and Φ have an apparent effect on the gaseous composition produced from the process. Increases in temperature within the range of 100–1300 °C enhanced syngas generated and reduced coke formation and CH4. Whereas, increased Φ, particularly at higher temperatures, had also enhanced syngas production as well as reduced coke formation. However, increasing Φ for values beyond one had decreased syngas and not significantly reduced coke deposition. Moreover, an experimental investigation was carried out in a fixed bed reactor for more in-depth verification of iron ability as an oxygen carrier through using magnetite ore (mainly Fe3O4). It found that the effect of temperature on syngas production was consistent with that calculated thermodynamically, as syngas increased with raising the temperature through the CLRE.

Chemical looping gasification (CLG) is a promising technology for high-quality syngas production. One key issue to successful CLG is the selection of high-performance oxygen carrier. In this study, several Ca- and Mg-rich steelmaking wastes from steel industry, such as blast furnace slag (BF slag), blast furnace dust (BF dust) and Linz-Donawitz converter slag (LD slag), were used as oxygen carriers in chemical looping gasification of biomass. The results showed that the reducibility of Ca- and Mg-rich waste, especially LD slag and BF dust, was superior to that of hematite. Considering long-term operation, the cyclic stability of steelmaking waste was tested. BF dust showed a poor stability, while the other carrier (hematite, BF slag or LD slag) presented an excellent stability during multiple redox cycles in spite of partial sintering and agglomeration. Moreover, the effects of supply oxygen coefficient (O/B ratio) and reaction temperature on CLG of biomass were investigated. The results revealed that Ca- and Mg-rich waste exhibited a higher syngas production compared to hematite. The higher performance could be attributed to the improved reduction rate of Fe2O3 and gasification rate of biomass by Ca or Mg in steelmaking waste. In addition, LD slag exhibited the higher gas value at the O/B ratio of 1 at 900 oC. As a consequence, LD slag was an appropriate oxygen carrier for CLG of biomass in terms of perfect reducibility, superior cyclic stability and high reactivity.

The chemical looping technology is an emerging technology for the efficient conversion of biomass to heat, power, fuel, and value-added chemicals. Chemical looping uses a metal oxide oxygen carrier to fully or partially oxidize the biomass feedstock, which avoids N2 dilution to the CO2 or syngas product. Thus, chemical looping technology can convert biomass to sequestration-ready CO2 or high purity syngas, which leads to the potential for negative carbon emission and enhanced energy efficiency in biomass conversions. Various chemical looping processes for biomass conversions, using different oxygen carrier materials and reactor designs, have been studied ranging from lab scale to pilot scale. This article reviews the current state of development in the scale-up of chemical looping technology for biomass conversions. It also provides perspectives on the chemical looping technology of relevance to various biomass conversion issues including CO2 capture, utilization and sequestration, biomass feedstock collection, handling and conversion enhancement, choice of reaction schemes, fuel and air reactor designs and operation, operational load variation, fate of pollutants and effect of ashes. Representative process configurations, reactor designs, oxygen carrier material selections, and the testing results are described along with the technology challenges, their potential solutions, and future research needs.

Liquid chemical looping technology is an innovation of chemical looping conversion technology. Using liquid metal oxide as the oxygen carrier during gasification process could prolong the service life of oxygen carrier and improve the process efficiency. In this paper, based on Gibbs minimum free energy method, the thermodynamic characteristics of biomass liquid chemical looping gasification were studied. Cellulose and lignin, the main components of biomass, were taken as the research objects. Bismuth oxide and antimony oxide were selected as liquid oxygen carriers. The results showed that when the temperature increased from 600 °C to 900 °C, the output of H2 and CO in the products of cellulose gasification increased from 0.5 and 0.3 kmol to 1.3 and 2.6 kmol respectively. Different ratios of oxygen carriers to gasification raw materials had the best molar ratio. The addition of steam in the system was beneficial to the increase of H2 content and the increase of H2/CO molar ratio. Bi2O3 and Sb2O3 with different mass ratios were used as mixed oxygen carriers. The simulation results showed that the gasification temperature of biomass with different mixed oxygen carriers had the same equilibrium trend products. It could be seen from the results of product distribution that the influence of the mixing ratio of Bi2O3 and Sb2O3 on gas product distribution could be neglected. These results could provide simulation reference and data basis for subsequent research on liquid chemical looping gasification.

In the chemical looping with oxygen uncoupling (CLOU) process, CuO is a promising material due to the high oxygen carrier capacity and exothermic reaction in fuel reactor but limited by the low melting point. The combustion rate of carbon is faster than the decoupling rate of oxygen carrier (OC). Hence, high temperature tolerance and rapid oxygen release rate of CuO modified by three different ores were investigated in this study. The kinetics analysis of oxygen decoupling with Cu-based oxygen carriers was also evaluated. Results showed that CuO modified by chrysolite had faster oxygen release rate than that of CuO. Limestone showed obvious positive effect on the oxidization process. The selected OCs could keep stable in at least 20 cycles, for about 1200 min. Shrinking core model (SCM) fitted well for the decoupling process in the temperature range of 1123–1223 K. Reduction rate kinetic information may aid in the development of chemical looping with oxygen uncoupling (CLOU) technologies during reactor design and process modeling. Ternary doped copper oxide with chrysolite and limestone could improve the reactivity of CuO in decoupling and coupling process and also improve the high temperature tolerance.

Under high-temperature batch fluidized bed conditions and by employing Juye coal as the raw material, the present study determined the effects of the bed material, temperature, OC/C ratio, steam flow and oxygen carrier cycle on the chemical looping combustion of coal. In addition, the variations taking place in the surface functional groups of coal under different reaction times were investigated, and the variations achieved by the gas released under the pyrolysis and combustion of Juye coal were analyzed. As revealed from the results, the carbon conversion ratio and rate were elevated significantly, and the volume fraction of the outlet CO2 remained more than 92% under the oxygen carriers. The optimized reaction conditions to achieve the chemical looping combustion of Juye coal consisted of a temperature of 900 °C, an OC/C ratio of 2, as well as a steam flow rate of 0.5 g·min−1. When the coal was undergoing the chemical looping combustion, volatiles primarily originated from the pyrolysis of aliphatic CH3 and CH2, and CO and H2 were largely generated from the gasification of aromatic carbon. In the CLC process, H2O and CO2 began to separate out at 270 °C, CH4 and tar began to precipitate at 370 °C, and the amount of CO2 was continuously elevated with the rise of the temperature.

An intensified hydrogen production steam reforming process named ‘Sorption-Enhanced Chemical Looping Steam Methane Reforming’ (SE-CL-SMR) was studied. Aspen Plus was used to carry out a thermodynamic investigation into the influence of various operating conditions on hydrogen production and process thermal efficiency. The steam to carbon molar ratio (S/C), the CaO to carbon molar ratio (CaO/C), the metal oxide to carbon molar ratio (MeO/C), the metal oxide composition (NiO:CuO), and the oxidising agent species were all shown to influence the process performance. The main findings were that; (1) the introduction of CaO reduces the potential for coke formation with predicted zero coke formation for CaO/C ratios > 0.4; (2) increasing amounts of metal oxide (MeO/C) and steam (S/C) enhance the hydrogen production yield and purity; (3) due to its involvement in an exothermic reaction, the presence of CuO allows for the reforming reactor to operate as an adiabatic reactor with an operating temperature within the range of 600 °C–700 °C; (4) an increase in the NiO:CuO ratio leads to an increase in methane conversion. With the operating conditions of S/C = 3, CaO/C = 1, MeO/C = 1, NiO:CuO = 0.9 and air as the oxidising agent, a hydrogen purity as high as 98% was predicted for the SE-CL-SMR process, along with the lowest observed CO2 production rate. Under the same conditions and using pinch analysis, the thermodynamic model prediction of the thermal process efficiency is reported as ca. 86%. This is significantly higher than the reported efficiency of 79% for the ‘Sorption-Enhanced Steam Methane Reforming’ (SE-SMR) process, predicted using similar thermodynamic models.

Chemical looping combustion (CLC) is a clean and efficient flame-free combustion technology, which combust the fuels by lattice oxygen from a solid oxygen carrier with inherent CO2 capture. The development of oxygen carriers with low cost and high redox performance is crucial to the whole efficiency of CLC process. As the solid by-product from the sulfuric acid production, pyrite cinder presented excellent redox performance as an oxygen carrier in CLC process. The main components in pyrite cinder are Fe2O3, CaSO4, Al2O3 and SiO2 in which Fe2O3 is the active component to provide lattice oxygen. In order to systematic investigate the functions of supports (CaSO4, Al2O3 and SiO2) in pyrite cinder, three oxygen carriers (Fe2O3-CaSO4, Fe2O3-Al2O3 and Fe2O3-SiO2) were prepared and evaluated in this study. The results showed that Fe2O3-CaSO4 displayed high redox activity and cycling stability in the multiple redox cycles. However, both Fe2O3-Al2O3 and Fe2O3-SiO2 experienced serious deactivation during redox reactions. It indicated that the inert Fe-Si solid solution (Fe2SiO4) was formed in the spent Fe2O3-SiO2 sample, which decreased the oxygen carrying capacity of this sample. The XPS results showed that the oxygen species on the surface of Fe2O3-CaSO4 could be fully recovered after the 20 redox cycles. It can be concluded that CaSO4 is the key to the high redox activity and cycling stability of pyrite cinder.

Fe-based oxygen carriers (OCs) are currently the crucial material basis for chemical looping technology to realize industrial applications. However, the relatively low reactivity of pure Fe-based OCs limits their extensive applications. One strategy to enhance reactivity in the chemical looping process is the introduction of another metallic element by doping. This study prepared a series of Fe-based OCs (Cu2xFe2(1-x)O3) with low concentration doping of Cu. The reaction mechanism and reactivity modulation of Cu2xFe2(1-x)O3 OCs in the chemical looping process were systematically investigated by means of experiments and density function theory (DFT) calculations. Activation energies for Cu2xFe2(1-x)O3 ranging between 72 and 37 kJ/mol were detected using H2 and the thermogravimetric analyzer (TGA) test, indicating enhanced reactivity in the chemical looping process as compared with that of pure Fe-based OCs of 84 kJ/mol. Thus, the low concentration doping of Cu can effectively improve the reactivity of Fe-based OCs. Furthermore, comprehensive DFT calculations upon the transition state indicated the reaction energy barrier for Cu2xFe2(1-x)O3 with different doping concentration and configurations to be in the range of 1.68–1.02 eV, lower than that of pure Fe2O3 of 2.30 eV. The Cu doping and the modulation of the reaction pathways are important reasons for the enhanced reactivity of Cu2xFe2(1-x)O3 OCs. Additionally, this study proposed a lattice oxygen release mechanism of Cu2xFe2(1-x)O3 OCs during chemical looping combustion.

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.

Oxygen carriers (OCs) with perovskite structure are attracting increasing interests due to their redox tunability by introducing various dopants in the structure. In this study, LaNixFe1-xO3 (x = 0, 0.1, 0.3, 0.5, 0.7, 1.0) perovskite OCs have been prepared by a citric acid–nitrate sol–gel method, characterized by means of X-ray diffraction (XRD) analysis and tested for algae chemical looping gasification in a fixed bed reactor. The effects of perovskite types, OC/biomass mass ratio (O/B), gasification temperature and water injection rate on the gasification performance were investigated. Lower Ni-doped (0 ≤ x ≤ 0.5) perovskites crystalized in the rhombohedra system which was isostructural with LaNiO3, while those with composition 0.5 ≤ x ≤ 1 crystalized in the orthorhombic system. Despite the high reactivity for LaNiO3, LaNi0.5Fe0.5O3 (LN5F5) was found to be more stable at a high temperature and give almost as good results as LaNiO3 in the formation of syngas. The relatively higher syngas yield of 0.833 m3⋯kg−1 biomass was obtained under the O/B of 0.4, water injection rate of 0.3 ml⋯min−1 and gasification temperature at 850 °C. Continuous high yield of syngas was achieved during the first 5 redox cycles, while a slight decrease in the reactivity for LN5F5 after 5 cycles was observed due to the adhesion of small grains occurring on the surface of OCs. However, an obvious improvement in the gasification performance was attained for LN5F5 compared to raw biomass direct gasification, indicating that LN5F5 is a promising functional OC for chemical looping catalytic gasification of biomass.

12 figures.-- This article is part of the 2021 Pioneers in Energy Research: Javier Bilbao special issue., Biomass chemical looping gasification (BCLG) uses lattice oxygen from an oxygen carrier instead of gaseous oxygen for high-quality syngas production without CO2 emissions. In this work, the effect of the main operating variables, such as oxygen/biomass ratio (λ), gasification temperature, and steam/biomass ratio (S/B), was investigated using two low-cost materials: a Fe ore and a Mn ore. Oxygen fed to the air reactor for oxidation was used as an effective method for controlling the amount of lattice oxygen used for syngas production. The main variable that affected the process performance and the syngas quality was λ, while the fuel reactor temperature and the S/B ratio had a minor effect. Small performance differences found between the ores can be attributed to different degrees of CH4 and light hydrocarbons reforming in the process. The CO2 content in the syngas was high (40 −43%) under autothermal conditions because the gasification reactions required the heat to be generated by combustion. CH4 contents of around 10% were found in syngas, coming from the unburned or unreformed volatiles. Syngas yields around 0.60 Nm3/kg of dry biomass were found for both ores. Additionally, high biomass conversions (Xb > 94%) and carbon conversion efficiencies (ηcc > 95%) were obtained in all cases, showing the capability of the process of avoiding CO2 emissions to the atmosphere. No agglomeration was found in the bed during the BCLG process, although attrition rates were high, leading to lifetimes of 160 and 300 h for the manganese and iron ores, respectively. Migration of Fe or Mn to the external part of the particle, generating a metal concentrated shell, was observed. Its detachment was responsible for the decrease in the oxygen transport capacity (ROC) of the material with the operating time and the reduced lifetime. The results obtained here allowed the iron ore to be considered as an oxygen carrier suitable for the BCLG process., This work has been supported by the European Union’s Horizon 2020 Research and Innovation Framework Programme under grant Agreement 817841 [Chemical Looping Gasification for Sustainable Production of Biofuels (CLARA)] and the AEI/FEDER, UE (ENE2017-89473R).

Alternative energy technologies at their current state cannot fully replace the existing fossil fuel-based energy production that has led to a rise in the atmospheric CO2 concentration. CO2 sequestration is a compelling solution to greatly reduce CO2 emissions from sources like fossil fuel-based power plants. Chemical-looping oxygen uncoupling process releases gaseous oxygen for combustion at high temperatures in the fuel reactor. The choice of oxygen carrier material (OCM) is pivotal to the chemical-looping process. In this study, citrate gel technique has been used to prepare the OCMs. A total of 5 (five) perovskites were prepared with varying degree of substitution of general formula La0.6A′0.4B′1-yFeyO3 where y = (0.8, 0.9) including the base LaFeO3. Calcined OCMs were characterized with XRD, SEM and BET analysis. OCMs showed an increase in surface area after oxygen release in a thermogravimetric experiment. Oxygen evolution rate ranged from 0.0043 to 0.0521 Kg O2/Kg OCM in a single cycle operation.

In order to produce high-quality bio-oils and syngas from biomass, a novel pyrolysis approach based on the chemical looping concept, namely chemical looping pyrolysis (CLPy), was proposed. In the current work, thermodynamic feasibility study and experimental investigations of the proposed CLPy with calcium-ferrite oxygen carriers and Nannochloropsis sp. microalgal biomass were conducted. The results suggested that the reduced calcium-ferrite oxygen carrier facilitated the denitrification, ketonization, and hydrodeoxygenation (HDO) of bio-oils during the pyrolysis stage. Since large amounts of oxygen in bio-oils were transferred to the reduced oxygen carrier, the heating value of bio-oils was remarkably increased up to 34.2 MJ/kg and 36.0 MJ/kg by employing the reduced CaFe2O4 and Ca2Fe2O5 oxygen carrier, respectively. In addition, a high H2 content of 50% in the pyrolysis gas was observed at the optimal pyrolysis temperature. In the gasification stage, the production of high-quality syngas was achieved. The content of H2 accounted for up to 70% of the gasification products when taking steam as gasifying agent, while that of CO was composed of 66% without the use of a gasifying agent. Moreover, the oxygen carrier was reduced to its reduction state, available for the next loop. In summary, CLPy proposed in this work involves the continuous transference of the oxygen from bio-oils to syngas by an oxygen carrier and provides a brand-new approach for the comprehensive utilization of biomass.

Hydrogen production by biogas conversion represent a promising solution for reduction of fossil CO2 emissions. In this work, a detailed techno-economic analysis was performed for decarbonized hydrogen production based on biogas conversion using calcium and chemical looping cycles. All evaluated concepts generate 100,000 Nm3/h high purity hydrogen. As reference cases, the biogas steam reforming design without decarbonization and with CO2 capture by gas-liquid chemical absorption were also considered. The results show that iron-based chemical looping design has higher energy efficiency compared with the gas-liquid absorption case by 2.3 net percentage points as well as a superior carbon capture rate (99% vs. 65%). The calcium looping case shows a lower efficiency than chemical scrubbing, with about 2.5 net percentage points, but the carbon capture rate is higher (95% vs. 65%). The hydrogen production cost increases with decarbonization, the calcium looping shows the most favourable situation (37.14 €/MWh) compared to the non-capture steam reforming case (33 €/MWh) and MDEA and iron looping cases (about 42 €/MWh). The calcium looping case has the lowest CO2 avoidance cost (10 €/t) followed by iron looping (20 €/t) and MDEA (31 €/t) cases.

Chemical looping gasification is an efficient technology to convert biomass into valuable syngas. The iron-based oxygen carriers are a promising option for large-scale commercial applications due to their low cost and environmentally-friendly properties. The present study aims at evaluating the performance of the syngas production from the chemical looping gasification of torrefied woodchips in a pilot-scale bubbling fluidized bed reactor using iron ore and ilmenite as oxygen carriers. The effects of the operating parameters were investigated in this study. The results show that an increase in operating parameters could favor the process performance. Carbon conversion efficiency and the yields accelerate at high operating conditions. Carbon conversion efficiency showed a maximum value of 91.42% for iron ore at the ratio of oxygen carrier-to-biomass of 6, while the gas yield reaches the peak at SBR of 1.4 for ilmenite. The addition of steam in biomass chemical looping gasification improves hydrogen production and syngas quality in the product gas. Despite ilmenite provides better performance for hydrogen production, it characterizes by a lower reactivity compared to iron ore. It is also found that iron ore performs better at lower values of steam-to-biomass ratios and temperatures, while ilmenite shows good results at higher those parameters.

Chemical looping combustion (CLC) is an energy conversion technology with high efficiency and inherent separation of CO2. The existence of sulfur in coal may affect the CO2 purity and the performance of oxygen carrier due to the interactions between sulfur contaminants and oxygen carrier. The migration of sulfur in Beisu coal during the in-situ gasification chemical looping combustion (iG-CLC) process using two oxygen carriers (iron ore and CuO/SiO2) was investigated respectively. The thermodynamic analysis results showed the formation of metal sulfides was thermodynamically favored at low temperatures and low oxygen excess coefficients, while they were obviously inhibited and the production of SO2 was significantly promoted with an increase in temperature and oxygen excess coefficient. Moreover, part of sulfur was captured and fixed in the forms of alkali/alkaline earth metal sulfate due to the high amount of alkali/alkaline earth metal oxides in the coal ash or/and oxygen carrier. The experimental results showed that the sulfur in coal mainly released in the form of SO2, and the sulfur conversion efficiency (XS) in the reduction stage were 51.04% and 48.24% when using iron ore and CuO/SiO2 respectively. The existence of metal sulfides was observed in the reduced oxygen carriers. The values of XS in the reoxidation process reached 3.80% and 7.64% when using iron ore and CuO/SiO2 respectively. The residue and accumulation of sulfur were also found on the surfaces of two oxygen carriers.

Chemical looping combustion of coal has attracted great attention due to its advantage in carbon capture. Sulfur in coal may have negative impacts on this process including deteriorating the reactivity of oxygen carrier and generating gaseous sulfur species. In this research, the release and migration characteristics of sulfur in the chemical looping combustion of Xinzhou coal with two synthetic oxygen carriers, CuO/SiO2 and NiO/Al2O3, were investigated by experiments and thermodynamic simulation. The thermodynamic analysis showed that sulfur in coal mainly migrated to metal sulfides at lower temperatures and peroxide coefficients, but the formation of SO2 was favored at higher temperatures and peroxide coefficients. Experimental results showed that the sulfur conversion efficiencies (XS,g) during the reduction stage reached 62.34 % and 61.25 % under Cu- and Ni-based oxygen carriers, respectively, and XS,g during the reoxidation stage were 6.25 % and 7.44 %, respectively. For both oxygen carriers, the share of H2S and SO2 in the sulfurous gases exceeded 96 % during the reduction stage, while SO2 was the only sulfurous gas when air was introduced. Even though the metal sulfides (Cu2S, Ni3S2 and NiS) were observed in the reduced samples, those two oxygen carriers showed satisfactory regeneration performance after one redox process.

Calcium‒based chemical looping gasification (calcium‒based CLG) shows promise for as a solution for waste problems. There has, however, been little discussion about dioxin emissions and heavy metal contamination in calcium‒based CLG. Herein, a thermodynamic equilibrium analysis was investigated to determine the characterization of copper (II) chemical forms (a main catalytic metal for the formation of dioxins) and heavy metal distribution in calcium‒based CLG of municipal solid waste (MSW). Results demonstrate that the high hydrogen concentration in calcium‒based CLG could promote the formation of HCl (g) instead of CuCl2 (g); therefore, it was beneficial in suppressing formation of dioxins. Furthermore, during the operating temperature of gasifier in calcium‒based CLG (600–750 °C), some heavy metals (Pb, Cr, Cu) could be stabilized as solid compounds except for Pb. The valences of heavy metals decreased in the calcium‒based CLG. If sulfur was present, some heavy metals, such as Pb, could convert into solid sulfides; sulfur, therefore, has a positive effect on the stabilization of heavy metals. Consequently, this study may provide information useful in restricting dioxin emissions and heavy metal contamination in calcium‒based CLG.

Coal is the dominant composition of fossil fuel but, with the accompanying gaseous products, causes environmental pollution. Here, we report a methodology to improve C conversion in co-gasification. The steam gasification and chemical looping gasification (CLG) of lignite and rice husk with oxygen uncoupling over 5% NiO/CuO oxygen carrier were conducted by non-isothermal kinetics method in a fixed-bed reactor. The gasification results showed that the yields of gas products in CLG of lignite or rice husk are higher than that in steam gasification. The yields of gases in chemical looping co-gasification (CLCG) are higher than that in steam co-gasification. In the co-gasification, the complementation of reactivity between fuels facilitated the C conversion rate, so the yields in co-gasification were higher than in individual gasification. The C conversion in CLCG of lignite and rice husk is 14.51% higher than that in steam co-gasification.

Novel self-supported Mgy(CuxNi0.6-xMn0.4)1-yFe2O4 with (y = 0, 0.05, 0.1, 0.15, and x = 0, 0.15, 0.3, 0.45, 0.6) oxygen carriers (OCs) are synthesized through the co-precipitation method. The synthesized OCs’ properties are characterized by X-ray powder diffraction (XRD), Raman spectra, transform infrared spectroscopy (FT-IR), Brunauer-Emmett-Teller (BET), transmission electron microscopy (TEM), field emission scanning electron microscopy (FESEM), energy-dispersive X-ray spectroscopy (EDX), and Thermogravimetric Analysis (TGA). The synthesized OCs are assessed in Chemical Looping Steam Methane Reforming (CL-SMR) process subject to different mesh sizes, reaction temperatures, Steam/Carbon (S/C) molar ratios, Mg concentrations, and Cu and Ni concentrations. The characterization of the OCs and process results indicate the contributive effect of Mg incorporation on the CuxNi0.6-xMn0.4Fe2O4 support structure. The redox results reveal that Mg0.1(Cu0.3Ni0.3Mn0.4)0.9Fe2O4 OC is of the highest activity, even at low reduction temperatures. This OC exhibits the highest activity and stability with lowest coke deposition during 24 redox cycles at 650 °C and S/C = 2.5. The highest CH4 conversion of about 99.4% and H2 yield of about 84.4% are obtained.

In this study, thermodynamic analysis of the syngas production using biodiesel derived from waste cooking oil is studied based on the chemical looping reforming (CLR) process. The NiO is used as the oxygen carrier to carry out the thermodynamic analysis. Syngas with various H2/CO ratios can be obtained by chemical looping dry reforming (CL-DR) or steam reforming (CL-SR). It is found that the syngas obtained from CL-DR is suitable for long-chain carbon fuel synthesis while syngas obtained from CL-SR is suitable for methanol synthesis. The carbon-free syngas production can be obtained when reforming temperature is higher than 700 °C for all processes. To convert the carbon resulted from biodiesel coking and operate the CLR with a lower oxygen carrier flow rate, a carbon reactor is introduced between the air and fuel reactors for removing the carbon using H2O or CO2 as the oxidizing agent. Because of the endothermic nature of both Boudouard and water-gas reactions, the carbon conversion in the carbon reactor increases with increased reaction temperature. High purity H2 or CO yield can be obtained when the carbon reactor is operated with high reaction temperature and oxidizing agent flow.

The chemical looping dry reforming of methane can be used to convert greenhouse gases into products with much desirable specification. However, developing an oxygen carrier with coke-tolerance and high oxygen exchange rate usually requires the use of rare-earth metals or lanthanides. In this study, by utilizing deposited surface carbon as a reaction intermediate rather than suppressing it, complete methane conversion was possible even with the earth-abundant metal oxide particles. To establish an optimized H2/CO ratio for the hydrocarbon synthesis, the CH4 feedstock was partially replaced with CO2. By itself, Ni-Al oxide exhibited deactivation due to the agglomeration arising from methane decomposition over the redox cycle. Fe-Al oxide had stable performance over cycles, but a sudden performance decline was observed when the amount of CO2 co-feeding exceeded a certain point. Incorporating Ni into the Fe-Al oxide was found to overcome these problems. The formation of a spinel phase with Fe alleviated the agglomeration, and enhanced CH4 activation under high CO2 partial pressure. The introduction of Ni also improved carbon gasification kinetics with CO2.

The earth-abundant transition metal manganese (Mn) has been shown to be useful to activate dinitrogen at atmospheric pressure and elevated temperature by forming bulk Mn nitrides. Mn nitrides could then be used, for example, for ammonia (NH3) synthesis in a chemical looping process by contacting nitride with gaseous hydrogen (H2). Here, we present an investigation of the morphology and local time-dependent composition of micrometer-scale Mn plates during nitridation in dinitrogen (N2) near atmospheric pressure at 700 °C. The main motivation was to obtain design data for chemical looping synthesis of NH3 and to add to the somewhat sparse literature on nitridation of Mn. The morphology and elemental compositional variation of the nitrided specimens were studied with scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDX), wide angle X-ray diffraction (WAXD), and mass balances. Three possible nitrogen (N) populations that may govern the Mn nitridation and later NH3 synthesis are identified. After four hours of nitridation, the N weight gain was found to be 9.4 ± 0.7 kgN to nMn−1 for the plates used here, resulting in a nitridation depth of 83 ± 8 μm.