Investigation of Solid Fuel Conversion in the Chemical Looping Process
coal direct chemical looping
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Publisher:The Ohio State University
Series/Report no.:The Ohio State University. Department of Chemical and Biomolecular Engineering Honors Theses; 2010
The high energy density and abundance of coal along with the sustainability of biomass make them favorable fuels for energy production. However, the combustion of carbon-based fuels inevitably results in the production of the greenhouse gas carbon dioxide (CO2). To avert climate change and comply with likely future regulations for greenhouse gas emissions, the CO2 byproduct must be efficiently captured. Unfortunately, existing carbon capture methods result in significant decreases in plant efficiency and significant increases in capital and operating costs. The Coal-Direct Chemical Looping (CDCL) is an energy conversion process for coal/biomass that can separate the CO2 stream in-situ by utilizing iron oxide composite particles as oxygen carriers. Using this method, the iron oxide particles provide crucial oxygen to the coal instead of air, which is the key strategy to the process. The cycling of the iron oxide particles allows for efficient and total carbon capture, therefore ensuring the sustainability and economic viability of carbon-fueled power. Although biomass also produces CO2 upon combustion, it also absorbs CO2 as it is grown. Therefore, biomass can be utilized as a replacement for coal and further improve the sustainability of the process by making it carbon negative. The objective of this study is to investigate the enhancement of char and iron particle conversion with CO2, design a mechanism for particle transfer from the reducer to the combustor, and perform a preliminary assessment of the potential of biomass in the CDCL process. The main obstacle for CDCL is the conversion of coal char because the reaction between the metal oxide and the char is a slow solid-solid reaction. CO2 was found to help gasify the char and significantly increase the rate of reaction. In fact, in the experiments performed in this study, the addition of CO2 increased the amount of char reacted twofold. Furthermore, mixtures between 50% and 70% metal oxide with char were found to increase the char conversion the most compared to other mixtures. These mixtures increased the amount of char reacted 2-5 times, depending on the type of coal used. Ease of coal fluidization was found to be independent of the amount of metal oxide particles; however addition of 80-100% by mass of an inert particle was required in order to fluidize the biomass. A cold model of the reactor was constructed in order to study the gas-solid hydrodynamics and to design the most controllable method of handling solid fuels and oxygen carriers in the system. A design with high resistance and constant flow was selected based on experiments performed on the cold model. The results obtained by this study prove the capabilities of the CDCL process and will allow it to continue towards the scale up to a sub-pilot demonstration.
Department of Chemical and Biomolecular Engineering: Outstanding Undergraduate Research
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