The chemical looping combustion (CLC) and chemical looping oxygen uncoupling (CLOU) processes are unique and efficient methods for the direct separation of carbon dioxide in combustion. In these processes, metal oxides are used under reducing atmosphere as an oxygen carrier to transfer oxygen between air and a fuel reactor. The fuel is converted by oxygen provided by the oxygen carrier. In the case of using coal or any ash-containing fuel, interaction between coal-derived ash and the oxygen carrier is likely to occur and can lead to deactivation and agglomeration of the oxygen carriers. As the amount of the possible compounds and compositions of ash can vary widely, thermodynamic equilibrium calculations can be used to represent the formed compounds during the CLC process to reveal the interaction between the oxygen carrier and the commonly present oxide compounds in ash. In this study, the interaction between the oxide compounds commonly present in ash and CuO oxygen carriers was studied both experimentally and thermodynamically. CuO is a widely used oxygen carrier with CLOU properties, the ability to release gaseous oxygen under inert atmosphere. Experiments were carried out at 900 °C under both oxidizing and inert atmosphere using CuO or Cu2O (CuO/Cu2O) as the oxygen carrier and SiO2, Al2O3, Fe2O3, CaO, and K2O to represent the oxide compounds present in ashes. To observe the interaction of the oxygen carriers with each oxide compound used, equal moles of copper oxide and oxide compound were mixed. Further, oxide compound fractions with the elemental composition relevant to coal ash were mixed with oxygen carriers to investigate the interaction under conditions approaching realistic operation. In all cases, a significant amount of copper oxides survived without any interaction. However, it was observed that silicate-based formations, especially potassium silicates, lead to strong agglomeration which most likely would decrease the lifetime and oxygen-releasing ability of the oxygen carriers. As the results showed that the thermodynamic equilibrium-based calculations were well in line with the experiments, these calculations can be a good first approach in these types of investigations.

As CO 2 emission is one of the most critical issues that causes global warming, methods have been developed for carbon capture and storage. Chemical looping combustion (CLC) and chemical looping oxygen uncoupling (CLOU) are unique and useful methods for direct separation of carbon dioxide in combustion. In CLC and CLOU, metal oxides are used as an oxygen carrier to transfer oxygen between an air and a fuel reactor. The fuel is oxidized with the released oxygen by the oxygen carrier used. When coal or any ash-containing fuels are used an interaction between ash-forming matters and oxygen carrier can occur which can cause to deactivation or agglomeration of the oxygen carriers. The composition of species in the ash and their amount can vary widely and also depend on the fuel used. Thermodynamic equilibrium calculations (TEC) can be used to predict the resulting compounds during in CLC and CLOU. This can help choosing the right fuel for the right oxygen carrier or vice versa. In this study, the interaction between common salt-based ash-forming matters present in ash and the widely used CuO oxygen carriers was studied both experimentally and thermodynamically. Experiments were carried out at 900 °C under both oxidizing and inert atmospheres using CuO or Cu 2 O (CuO/Cu 2 O) as the oxygen carrier and K-and Na-based carbonate, chloride, nitrate, phosphate, and sulfate to represent salt compounds present in the ashes. To observe the interaction of the oxygen carriers with each salt compound used, equal moles of copper oxide and a salt compound were mixed. In addition to this, the effect of salt compounds used for the interaction between oxygen carrier and a model ash was also investigated. NaSO 4 showed the harshest effect among the salts used since it caused a strong agglomeration. Generally, potassium-based salts did not affect the oxygen carriers directly and the results were consistent with the TEC. However, sodium-based salts showed significant effect on the system which differed from the TEC results.

No abstract

In this study, oxygen release/consumption behavior of calcium manganese-based oxides (CaMn1–x B x O3, where B: Cu, Fe, Mg and x = 0.1 or 0.2) used in a chemical looping oxygen uncoupling (CLOU) application was investigated. The effect of B-site dopants such as Fe, Mg, and Cu on the oxygen release behavior was also investigated with the aim to use these materials in thermal energy storage (TES). Previous literature studies about CLOU performance of doped calcium manganites were taken into consideration for dopants selection. Calcium manganite-based oxides have been used in chemical looping oxygen uncoupling (CLOU) applications owing to their oxygen release behavior to the gas phase. Studies have revealed that calcium manganite-based oxides show a promising nonstoichiometry over a range of temperatures and oxygen partial pressures, which makes them useful for thermochemical energy storage applications. However, the related literature studies have been mainly focused on their nonstoichiometric characteristics related to temperature and oxygen partial pressure and thermodynamic properties. In this work, thermal analysis and fluidized bed tests were carried out as complementary techniques. CaMn0.8Cu0.2O3 showed the highest oxygen release performance in fluidized bed tests, while CaMn0.9Mg0.1O3 had the best cyclic stability overall among the samples used in the study.

Perovskites are well-known oxides for thermochemical energy storage applications (TCES) since they show a great potential for spontaneous O2 release due to their non-stoichiometry. Transition-metal-based perovskites are particularly promising candidates for TCES owing to their different oxidation states. It is important to test the thermal behavior of the perovskites for TCES applications; however, the amount of sample that can be used in thermal analyses is limited. The use of redox cycles in fluidized bed tests can offer a more realistic approach, since a larger amount of sample can be used to test the cyclic behavior of the perovskites. In this study, the oxygen release/consumption behavior of Mn- or Cu-substituted SrFeO3 (SrFe0.5M0.5O3; M: Mn or Cu) under redox cycling was investigated via thermal analysis and fluidized bed tests. The reaction enthalpies of the perovskites were also calculated via differential scanning calorimetry (DSC). Cu substitution in SrFeO3 increased the performance significantly for both cyclic stability and oxygen release/uptake capacity. Mn substitution also increased the cyclic stability; however, the presence of Mn as a substitute for Fe did not improve the oxygen release/uptake performance of the perovskite.

No abstract