System efficiency analysis of dual interconnected bubbling fluidized bed reactors for solar fuel production

Simulation of two-step redox recycling of non-stoichiometric ceria with thermochemical dissociation of CO2/H2O in moving bed reactors – Part I: Model development with redox kinetics and sensitivity analysis

Chemical looping combustion of Victorian brown coal using Fe-based oxygen carriers

Chemical Looping for Energy Technology: A Special Issue

Chemical looping air separation (CLAS), based on the chemical looping principle, is a novel and energy-efficient method to separate oxygen from air. The oxygen carriers used capture oxygen from air in an oxidation reactor and release oxygen in a reduction reactor. In this work, the adaptability of Cu/Zr oxygen carrier used for CLAS was investigated through thermodynamic analysis and experimental methods. X-ray diffraction (XRD) and scanning electron microscope (SEM) were used to measure the phases and surface morphology of oxygen carriers before and after experiments. The results show that CuO has the capability of releasing oxygen when the temperature is higher than 725 °C in the nitrogen atmosphere, and the minimum oxygen reduction temperatures increase with the increasing of oxygen concentrations. The Cu/Zr oxygen carrier has high oxygen reduction and oxidation rates when temperature is higher than a certain values. For reduction, the value is about 860 °C. For oxidation, the value is about 500 °C. The reactivity of oxygen carrier increases significantly with the temperature increasing. On overall, reactivity of oxygen carrier has little difference under different particle sizes. The oxygen carrier exhibits a stable oxygen reduction and oxidation behavior during reduction–oxidation cycles. XRD patterns show that the main phases in reduced samples are Cu2O and ZrO2. The main phases in fresh and oxidized samples are CuO and ZrO2. SEM images show that the fresh and reacted oxygen carriers are porous. The surface of reacted samples is smoother than fresh samples and no agglomeration has been found.

Process simulation and thermodynamic evaluation for chemical looping air separation using fluidized bed reactors

Chemical looping hydrogen production uses the oxidation and reduction of metal oxides, typically iron, to produce hydrogen. This work focuses on the modification of iron oxide with calcium oxide to form an oxygen carrier containing di-calcium ferrite (Ca2Fe2O5), which presents favourable thermodynamics for achieving higher conversions of steam to hydrogen compared to chemically unmodified iron oxide. Different methods of synthesis, viz. mechanochemical synthesis and co-precipitation, were used to produce Ca2Fe2O5, and their resulting performances were compared. Consistent with thermodynamic predictions, it was found that CO2, or steam, was sufficient to fully regenerate the reduced carriers to Ca2Fe2O5. The cyclic stability of the oxygen carriers were studied in fluidised bed reactors and by thermogravimetric analysis (TGA). Good stability of the materials was observed for up to 50 cycles, with no evidence of agglomeration even up to 950 oC. The rate of deactivation was found to correlate with the purity of Ca2Fe2O5 and the presence of impurity phases such as CaFe2O4, which tended to segregate into its constituent elemental oxides. Carbonation of the oxygen carriers was examined by TGA, and was found to occur appreciably only for the reduced carrier (a mixture of CaO and Fe) between temperatures of 500 – 700 oC and 0.1 – 0.5 atm of CO2, whereas the oxidised carrier (viz. Ca2Fe2O5) did not carbonate. Fresh and cycled materials were characterised by XRD, SEM and BET analysis. Ca2Fe2O5 is a potentially viable material as an oxygen carrier for hydrogen production, but owing to thermodynamic limitations cannot be used for complete fuel oxidation.

Attrition behavior and particle loss of a copper oxide-based oxygen carrier from a methane chemical looping combustion (CLC) process was investigated in a fluidized bed reactor. The aerodynamic diameters of most elutriated particulates, after passing through a horizontal settling duct, range between 2 and 5 μm. A notable number of submicrometer particulates are also identified. Oxygen carrier attrition was observed to lead to increased CuO loss resulting from the chemical looping reactions, i.e., Cu is enriched in small particles generated primarily from fragmentation in the size range of 10-75 μm. Cyclic reduction and oxidation reactions in CLC have been determined to weaken the oxygen carrier particles, resulting in increased particulate emission rates when compared to those of oxygen carriers without redox reactions. The generation rate for particulates <10 μm was found to decrease with progressive cycles over as-prepared oxygen carrier particles and then reach a steady state. The surface of the oxygen carrier is also found to be coarsened due to a Kirkendall effect, which also explains the enrichment of Cu on particle surfaces and in small particles.

Hydrodynamics and OCM reaction performance in a bubbling fluidized bed reactor and a riser reactor

Evaluation of iron based chemical looping for hydrogen and electricity co-production by gasification process with carbon capture and storage

Biogas combustion in a chemical looping fluidized bed reactor

Effective performance of ilmenite oxygen carrier for chemical looping combustion of carbon monoxide, hydrogen, and methane in a fluidized bed reactor

Reductive/oxidative sequential bioelectrochemical process for Perchloroethylene (PCE) removal: effect of the applied reductive potential and microbial community characterization

Chemical looping air separation is a new method to separate oxygen from air. In the process, oxygen carrier releases oxygen in the reduction reactor and absorbs oxygen in the oxidation reactor. The reduction is endothermic, and the oxidation is exothermic. The heat transfer from oxidation reactor to reduction reactor is essential to design the CLAS process with low energy consumption. In this paper, the optimization CLAS process of CuO/ZrO2 oxygen carrier was established based on thermal analysis and pressure analysis. In the system, the heat can achieve self-balance with little heat supplied from outside. The effects of the technological parameters on the system energy consumption were investigated using Aspen Plus software. The results show that the energy consumption decreases with reduction temperature increasing and oxidation temperature decreasing. Moreover, the smaller the difference of temperature between the two reactors is, the lower energy consumption is. Under negative pressure, with the decreasing reduction pressure, the energy consumption decreases. Under positive pressure, with the increasing oxidation pressure, the energy consumption decreases firstly and then increases. The optimization operating parameters are obtained. The lowest energy consumption of the system is 0.132 kWh m−3 at the conditions of 990 °C reduction and 1000 °C oxidation temperatures and 0.5 atm. reduction and 1.7 atm. oxidation pressures.

Carbon dioxide splitting and hydrogen production using a chemical looping concept: A review

Evaluation of dust and gas explosion potential in chemical looping processes