| Summary: | 碩士 === 國立成功大學 === 環境工程學系 === 103 === In recent years, human being rely on the fossil fuel due to the booming economy. A great amount of carbon dioxide releasing from fossil fuel combustion cause the global warming. As a result, it is a serious issue to capture carbon dioxide for global citizens today. Oxy-fuel combustion system is a carbon dioxide capture technology, contributing to higher capture efficiency due to concentrated CO2, decreasing processing cost, and constructing easily. Recently, it is considered as a new option for power generation. In fluidized bed system, it has high heat transfer and mass transfer coefficient and it is easy to reach isothermal condition which fits the high temperature carbonation by dry techniques. Utilizing desulfurization slag as sorbent not only reuses the waste but also reduces cost. In this study, desulfurization slag was used to absorb carbon dioxide from oxy-fuel combustion in a fluidized bed reactor.
Results of this study are described as follows：
1. The minimum fluidized velocity decreases along with the increasing temperature both for empirical model prediction and experimental results. However, the minimum fluidized velocity at 700oC is slight higher than at 600 oC due to slag sintering. Besides, the assumption of Ergun equation neglects the interparticle force causing that the experimental results are higher than empirical results.
2. According to the results of ICP and XRD analysis, the contents of calcium hydroxide in desulfurization slag of 150-300 μm and 75-106 μm are 15.76% and 18.86%, respectively. From TGA analysis, the desulfurization slags of both 150-300 μm and 75-106 μm have a considerable slag utilization (24.5-34.09%) from 450oC to 580oC.
3. When the gas velocity reaches minimum fluidized velocity, the utilization of the slag with size 150-300 μm will increase from 28.7% of a fixed bed mode to 41.2%. Fluidized bed reactor is better than a fixed bed reactor due to the high heat transfer and mass transfer rate. In a fluidized bed reactor, as the weight hourly space velocity becomes higher, the slag utilization decreases as a result of the short residence time. Besides, the smaller size of the desulfurization slag, the higher of the utilization.
4. The optimal operating temperature is about 600oC for the CO2 removal with desulfurization slag of 150-300 μm. Furthermore, the effects of adding water vapor on the carbonation of desulfurization slag were conducted. The results illustrate that the water vapor content can enhance the carbonation reaction and its optimal content is 5% which the slag utilization is 42.2% with 1.5 Umf. However, the slag utilization decreases as the water vapor content is greater than 5%, resulting from competitive sorption and sintering.
5. The results of XRD, SEM, EDS, Mapping and FTIR analyses indicate the structure and bonding for desulfurization slags before and after carbonation. It confirms the appearance of CaCO3 after carbonation reaction.
6. The deactivation model regressions of the experimental breakthrough curves have been conducted and the results show that the model is in good agreement with the experimental data. The activation energies for the reaction and deactivation are 58.9 and 8.7 kJ mol−1, respectively.
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