| Summary: | 碩士 === 國立成功大學 === 環境工程學系 === 102 === After industrial revolution, the increases of CO2 concentration in the atmosphere are resulted from the consumption of huge amounts of fossil fuels, and CO2 accumulating in the atmosphere will cause global climate changes including temperature increasing and ocean level rising. Hence, the effective control of CO2 emission is imperative. Oxyfuel combustion system is a CO2 concentrated technology, contributing to increasing capture efficiency, decreasing processing cost, and constructing easily. Recently, it is considered a new option for power generation. In CO2 capture technologies, the high temperature carbonation by dry techniques is a trend for related field. Calcium-based slags not only are used to absorb carbon dioxide but also reduce the cost of sorbents. In this study, the calcium-based slags (desulfurization slag, EAF oxidizing slag, EAF reductive slag and bottom ash) were used to absorb carbon dioxide in the simulated oxy-fuel combusted flue gas.
Results of this study are described as follows：
1.According to the results by using ICP and XRD analysis, the calcium oxide content of desulfurization slag (73.08%) is much higher than those of EAF furnace oxidizing slag (28.70%), EAF reductive slag (39.34%), and bottom ash (2.00%). Furthermore, the Ca form in desulfurization slag is Ca(OH)2, hence has a great potential on the carbonation. According to the results by using TGA analysis, desulfurization slag is the best choice in those slags for the removal of CO2, and the utilizaton is a function of calcium content of the slags.
2.In a fixed-bed reactor, the optimal operating temperature was about 600oC for the CO2 removal with desulfurization slag; the utilization ratio of the sorbent increased as the space velocity decreased before it was lower than 4,000 mL hr-1 g-1; the effects of adding water vapor on the carbonation of desulfurization slag were performed. The results indicate that the water vapor concentration can enhance the carbonation reaction and the optimal condition is 5%. However, the utilization decreases as the water vapor concentration increases over 5%, resulting from blocking of carbonation by extreme water vapor concentration. The effect of sulfur-containing flue gas shows that the overall utilization of the slag goes down, and the results are speculated that desulfurization slag could not provide more effective active sites to sulfurization.
3.The sorbents were examined for the better understanding of structure change, element composition and crystal transformation by XRD, SEM, FTIR. From the XPS and FTIR patterns, when the water vaper and SO2 existing simultaneously, the carbonated products contain not only CaCO3 but also CaSO4 because of the sulfurization.
4.For the kinetic study for the carbonation of desulfurization slag with experiment data at various temperatures, the first type of deactivation model is suitable to describe results.
5.In the study, carbon dioxide separation technology was also coupled with a oxy-coal combustion system, by using GGBF slag and the pilot plant located in NCKU Kuei-Len campus to demonstrate its feasibility in carbon dioxide sorption and look for the optimal operating conditions. Results of this study are described as follows (1)The optimal operating temperature is about 500°C for the carbon dioxide removal with GGBF slag. (2) The water vapor concentration and the higher degree of combustion completion can enhance the carbonation reaction.
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