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Item type:Publication, Access status: without files , Gasification kinetics of lignite char in a fluidized bed of reactive oxygen carrier particles(2019-01-15); ; ; ; Werther, JoachimThe conversion of lignite under Chemical Looping Combustion conditions differs sharply from air-fired combustion as high volumetric gas concentrations of CO2 and steam prevail in the reactor and the oxygen for the fuel conversion is provided by a solid oxygen carrier. In this work a lab scale fluidized bed reactor (ID = 53 mm) was used to measure the conversion behavior of German Rhenish lignite under Chemical Looping Combustion conditions. The carrier used was 14 wt-% copper oxide on γ-alumina. Special focus was laid on the particle size of the char during gasification, hence 3–6 different size fractions, in the range of 150–1500 μm were converted during each test series, respectively. The gasification experiments showed that gasification of lignite in a fluidized bed of inert sand particles is slightly faster for steam compared to CO2 gasification. In the inert sand bed, chemical reaction limitation of the kinetics could be seen for all lignite size fractions below 850 μm diameter. Gasification rates were in the range of literature findings for fluidized bed gasification in inert sand beds. The inhibition effects of both CO and H2 were reproduced by applying CO and H2 as fluidization gases during gasification. Gasification experiments in a fluidized bed of a completely oxidized oxygen carrier showed for both CO2 and steam gasification an enhancement of the char conversion, even more for smaller particle sizes of the lignite. Simultaneous gasification with CO2 and steam showed only slight increases in the measured gasification rates compared to steam only gasification. The Shrinking Core Model was generally able to describe the experiments. A resistance approach was used to describe the strong mass transfer limitations seen in the reactive bed for larger char particles particularly at higher temperatures. Kinetic parameters were extracted for the simultaneous steam and CO2 gasification under in-situ Gasification Chemical Looping Combustion conditions.Publicationtype: Journal Article213 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , Reaction kinetics for flowsheet modeling of chemical looping combustion in fluidized bed reactors(2017-05); ; ; ; Werther, JoachimChemical Looping Combustion (CLC) is an alternative combustion process for the separation of carbon dioxide during the conversion of fuels. The process itself may be carried out in a system of interconnected fluidized bed reactors with a solid oxygen carrying material is circulated between them. CLC reaction kinetics differ sharply from regular air-fired combustion in terms of gas concentrations inside the two reactors and that the oxygen is transported between those reactors by a solid oxygen carrier. Further, they are strongly dependent on the hydrodynamics inside the fluidized bed reactors. For a predictive simulation of CLC, reaction kinetics of the oxygen carrier's reduction and oxidation, as well the conversion of solid fuels has to be known. To keep complexity low, overall reactions schemes are mostly used to describe chemical reactions. Various research groups measured the reactivity of the oxygen carrier with TGA, neglecting the effects of fluidization on the chemical conversion. In this work, the lab scale bubbling bed facility (diameter = 53mm) at Hamburg University of Technology was used for experiments on the behavior of copper oxide carriers on the basis of Al2O3. The conversion behavior was modeled with solid reaction models proposed in the literature and checked which one fits best to the experimental data from the plant. Additionally, the solid fuel lignite was investigated with regard to the conversion behavior under CLC conditions inside the lab scale fluidized bed. The oxygen carrier's gas-phase reactions are hard to capture with the typical Arrhenius type reaction rates inside the fluidized bed reactor. It is shown that several competing reactions take place, which does not lead to steadily increasing reaction rates with higher temperatures. Devolatilization of lignite is fast compared to its gasification. The gasification of lignite could be tracked over a broad temperature and particle size spectrum and modeled with particle reaction models and Arrhenius type reaction rates.Publicationtype: Conference Paper82