Integration of chemical looping oxygen production and chemical looping combustion in integrated gasification combined cycles

Abstract Energy penalty is the primary economic challenge facing CO2 capture technology. This work aims to address this challenge through a novel power plant configuration, capable of achieving 45.4% electric efficiency from coal with a 95% CO2 capture efficiency. The COMPOSITE concept integrates chemical looping oxygen production (CLOP) and packed bed chemical looping combustion (PBCLC) reactors into an integrated gasification combined cycle (IGCC) power plant. Hot gas clean-up technology is implemented to boost plant efficiency. When commercially available cold gas clean-up technology is used, the plant efficiency reduces by 2%-points, but remains 2.3%-points higher than a comparative PBCLC-IGCC power plant and 8.1%-points higher than an IGCC power plant with pre-combustion CO2 capture. It was also shown that the COMPOSITE power plant performance was not sensitive to changes in the performance of the CLOP reactors, implying that uncertainties related to this novel process component do not reduce the potential of the COMPOSITE concept. The outstanding efficiency obtained for this concept is made possible by a complex and highly integrated plant configuration, whose operability and techno-economic feasibility must be demonstrated

Oxygen production at intermediate temperatures using Ca2AlMnO5+δ double perovskite-type oxides

Double-perovskite Ca2AlMnO5+δ exhibits promising oxygen uptake and release capacity at intermediate temperatures (400–700 °C), which makes it an interesting candidate for in situ oxygen production in an integrated gasification combined cycle (IGCC) process. Experiments were conducted at 10 bars by alternating gas feeds of air and various sweep gases to a packed bed filled with 300 g of granular oxygen carrier materials. These realistic operating conditions demonstrated that 15–20% oxygen can be introduced to the sweep gas, which is sufficient for autothermal gasification of solid fuels in IGCC. Argon performed slightly better than CO2 as a sweep gas, presumably because of some CO2 absorption or the higher O2 partial pressure of CO2 that inhibited O2 release. Further O2 concentration increases can be expected from increasing the temperature under reduction by feeding a fuel gas to combust with the released O2, but experiments with H2 did not produce the desired effect because the combustion reaction was too slow at the optimal reactor temperature (~ 600 °C). In general, the reduction stage was more prone to kinetic limitations, as illustrated by a significant decrease in O2 concentration when the sweep flowrate was increased. A longer oxidation stage to fully charge the oxygen carrier also increased O2 concentrations in the sweep, but this requires a process integration such as IGCC where the large quantity of warm depleted air can be effectively utilized. Furthermore, the enthalpy of oxidation of Ca2AlMnO5+δ was obtained from density functional theory modeling, equilibrium conditions in thermogravimetric analysis, packed bed experiments and directly from differential scanning calorimetry. The enthalpy of oxidation obtained by these techniques range from − 166 to − 196 kJ mol−1 O2.publishedVersio

A numerical homogenisation strategy for micromorphic continua

Cellular materials are of special interest according to their peculiar mechanical properties. In this paper, special attention is paid to the simulation of size-dependent microtopological effects. We introduce a numerical homogenisation scheme for a two-scale problem dealing with a micromorphic continuum theory on the macroscale and a classical Cauchy continuum on the microscale. The transitions between both scales are obtained by projection and homogenisation rules derived from an equivalence criterion for the strain energy, also known as the Hill-Mandel condition

Redox energetics of novel perovskite-type oxygen carriers for chemical looping reforming

The present work focuses on the redox energetics of novel perovskite-type oxygen carriers for chemical looping reforming. The aim of this study is to increase the level of knowledge on the redox characteristics of materials for possible applications as the oxygen carriers for the chemical looping processes. Here we focus on the perovskite-type oxides (ABO3) with lanthanum on the A-site and first row transition metals on the B-site since first row transition metals normally have more than one oxidation sate, non-stoichiometry in the perovskite oxides with such metals on the B-site is common while keeping the same structure. The partial substitution of the cation on the Bsublattice is studied as a measure to adjust the redox energetics. In the present study partial substitution of cobalt in LaCoO3 with Mn and Fe is chosen. The redox behavior of nonstoichiometric compounds may be assessed from the variation of the oxygen nonstoichiometry with temperature and oxygen partial pressure. Thermogravimetric analyses (TGA) is used for most of the systems but in order to reach higher accuracy, specialized instruments are needed. One of the most accurate techniques to measure the oxygen nonstoichiometry is coulometric titration (CT). A novel CT setup was designed, constructed and validated. This setup was subsequently used to study the oxygen non-stoichiometry of the LaMn1-xCoxO3-δ system at 1223, 1273, and 1373 K. For the LaMn1-xCoxO3-δ system it is found that the observed oxygen non-stoichiometry curve is due to the simultaneous reduction of both manganese and cobalt on the B-sublattice and the enthalpy of oxidation values show a linear dependence by x (portion of Co). The oxygen non-stoichiometry and redox energetics of the second studied system, LaFe1-xCoxO3-δ, just similar to the previous system show no indication of the sequential reduction of the cations occupying the B-sublattice. The absolute value of the enthalpy of oxidation increases as the iron portion on the B-sublattice increases, which approves this finding. In contrast to the experimental approaches, DFT calculations might provide a cost effective tool to examine complex systems and obtain an approximation for the redox thermodynamic properties; according to the following reaction: 4LaBO2.5 + O2 = 4LaBO3. It is however necessary to examine the sources of error and the accuracy of the calculations. Therefore a benchmark study was conducted on the formation energetics of lanthanide first row transition metal perovskite-type oxides (LaBO3). The benchmark shows that although fundamental errors in the GGA affect the energetics, still with addition of ad hoc corrections, it is possible to obtain values which are in good agreement with the experiment. The benchmark also confirms that as long as the calculations are spin polarized (with any magnetic structure) and performed with the relaxation of the experimental crystal structure, the total energies are reproduced within 15 kJ/(mol B). Turning to the reduced phases, LaBO2.5, the calculations proved to be much more difficult than the oxidized phases. In contrast with LaBO3 phases, a bigger fraction of total energy of the reduced phases is attributed to the magnetic configuration, meaning that a simple magnetic structure (e.g. ferromagnetic) does not predict the ground state reasonably. Still, the biggest challenge is due to the configuration of oxygen vacancies on the oxygen sublattice. Simultaneous presence of oxygen vacancy and spin configurations necessitates a computational algorithm based on statistics, e.g. Monte Carlo method, which was out of the scope of this study given the three year time frame. This however opens up an opportunity for the future works

Influence of Ce3+ polarons on grain boundary space-charge in proton conducting Y-doped BaCeO3

Defect segregation and space-charge formation were investigated for a (0 2 1)[1 0 0] symmetric tilt grain boundary in Y-doped BaCeO3. Density functional theory calculations according to the PBE+U formalism were used to calculate segregation energies for protons, oxygen vacancies and Y-acceptor dopants from the bulk to the grain boundary core. Defect concentration and potential profiles across the grain boundary were obtained from thermodynamic space-charge models. Oxygen vacancies were found to exhibit a particularly exothermic segregation energy of up to −1.66 eV while protons exhibited segregation energies in the range of −0.47 eV to −0.93 eV. The grain boundary was determined to be predominated by protons below 800 K in 3% H2O and the corresponding space-charge potential was 0.4–0.7 V under the Mott–Schottky approximation. The role of electronic defects in the space-charge properties was evaluated, and it was substantiated that electron conduction along the grain boundary could become evident under reducing conditions.publishedVersio

Influence of Ce3+ polarons on grain boundary space-charge in proton conducting Y-doped BaCeO3

Defect segregation and space-charge formation were investigated for a (0 2 1)[1 0 0] symmetric tilt grain boundary in Y-doped BaCeO3. Density functional theory calculations according to the PBE+U formalism were used to calculate segregation energies for protons, oxygen vacancies and Y-acceptor dopants from the bulk to the grain boundary core. Defect concentration and potential profiles across the grain boundary were obtained from thermodynamic space-charge models. Oxygen vacancies were found to exhibit a particularly exothermic segregation energy of up to −1.66 eV while protons exhibited segregation energies in the range of −0.47 eV to −0.93 eV. The grain boundary was determined to be predominated by protons below 800 K in 3% H2O and the corresponding space-charge potential was 0.4–0.7 V under the Mott–Schottky approximation. The role of electronic defects in the space-charge properties was evaluated, and it was substantiated that electron conduction along the grain boundary could become evident under reducing conditions

Simplified model description of a CLOP reactor for system simulation and analysis

In order to perform overall system simulations and optimization at the flowsheet level, simplified models of process units are required. We present a simplified model of the CLOP reactor (chemical looping for oxygen production) and compare it against a rigorous dynamic fixed bed model, which uses a 1D phenomenological approach. The model is validated towards the detailed model to verify that the performance is captured correctly. In this way, after model validation, system simulations can be performed and optimized both based on process flow configuration, and temperature/pressure ranges. When combined in a process simulation, the model can give an understanding of the potential of a given oxygen carrier material (OCM) for usage in power plants utilizing the novel COMPOSITE concept, which is a concept for energy production with CO2 capture. Both the rigorous and the simplified models are based on using fuel burning to maintain the desired operating reactor temperature. The model can be used for finding equilibrium points in the air and fuel reactors, and thus identify what is the limiting factor for the reactor performance.publishedVersio

Microstructural Stability of Tailored CaMn0.875−xFexTi0.125O3−δ Perovskite Oxygen Carrier Materials for Chemical Looping Combustion

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Manufacturing of perovskite oxygen carriers by spray granulation for chemical looping combustion

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Fe2O3–Al2O3 oxygen carrier materials for chemical looping combustion, a redox thermodynamic and thermogravimetric evaluation in the presence of H2S

9 FigurasAlumina-supported Fe2O3 oxygen carrier material (OCM) system is among the most promising OCM systems for solid and gaseous fuel CLC. This work utilizes a comprehensive thermogravimetric and thermodynamic equilibrium approach to redox and CLOU performance, oxygen transfer capacity, reduction rate and sulfur tolerance of the Fe2O3 impregnated on Al2O3 OCM. Thermodynamic evaluations reveal that the beneficial composition range lies in a wide range of 7.5–34% molar Fe2O3 ratios. This is the range at which aluminum-rich corundum phase, i.e., (Al, Fe)2O3, remains stable throughout the oxidizing to very reducing oxygen partial pressures in fuel reactor. The experimental system in this study contains 20 mass% Fe2O3, i.e., XFe = 13.8% molar which lies well within this interval. Deep redox cycle experiments confirm the thermodynamic modeling and during the long residence time of this experiment, the sample is almost fully reduced and exhibits its thermodynamic redox oxygen capacity of close to 1.5 mass%. Extension of the deep redox cycles to 15 cycles induces no performance deterioration in terms of capacity, rate of reduction or morphological failure. The redox experiment under sour reducing gas indicates no H2S poisoning for the 20 mass% Fe2O3 supported on Al2O3 OCM. The findings that this system is not affected with the H2S content of the gas, and the prediction of the SO2 release from the fuel reactor is in good agreement with our recent reactor testing findings available in the literature.The work presented in this article is conducted as part of the European Union Seventh Framework Programme (FP7/2007-2013) under Grant Agreement No. 608571 (Project acronym SUCCESS).Peer reviewe