Research Information System
Thesis Type: Doctorate
Institution Of The Thesis: Gazi University, Turkey
Approval Date: 2016
Thesis Language: Turkish
Student: Duygu Uysal
Supervisor: ÖZKAN MURAT DOĞAN
Abstract:In our day, the climate change refers to global warming and the primary cause of global warming is the increment in the concentration of carbon dioxide which is the most important greenhouse gas. There are natural causes of carbon dioxide emissions but the actual reason of this dangerous increment is because of anthropogenic emissions. The greatest production of anthropogenic emissions belongs to thermal power plants in which energy and heat are produced. Currently there are many researches about decreasing the concentration of carbon dioxide in the atmosphere or reducing the emissions of carbon dioxide. The most efficient way is to capture carbon dioxide in flue gases into a solution at the source of emission. Despite the fact that there is not many industrial applications of carbon dioxide absorption in full scale, doing researches about this global threat is a common current concern. Alternative solutions are being sought because of the high cost of energy in operating and regeneration units of the existing conventional absorption systems, resulting in decreasing the overall efficiency of the plant by 1% and the sensitivity of solutions to degradation, resulting in loss of solution. So the researches have been focused on finding a new and efficient solution that eliminates the disadvantages of the current systems. In this thesis, it is proposed to use calcium acetate solution as that new and efficient solution and necessary information about using it in absorption systems has been searched. Calcium acetate is a benign and eco-friendly chemical which is simple and inexpensive to produce and it does not have any problem in degradation. It is generally used as de-icer on the roads or as food preservative. Moreover, the fact that similar chemicals are being used to capture acid gases gave the inspiration of using it in the absorption of carbon dioxide. In literature, there is little information about calcium acetate and no information on calcium acetate-carbon dioxide system. So, to start with this thesis, it was first necessary to obtain the thermophysical properties of calcium acetate solutions with different concentrations at different temperatures and at atmospheric pressure. Besides, the thermophysical properties and the total absorption capacities of these solutions at higher pressures were also obtained. Then, determination of diffusion coefficients of carbon dioxide and calcium acetate in the solution has been carried out as the first step of mass transfer study. This research for diffusion coefficients was done both theoretically and experimentally by using a diaphragm cell and the results obtained from both approaches matched quite reasonably. The absorption of carbon dioxide into calcium acetate solution is absorption with chemical reaction. Thus it is not possible to determine the solubility of carbon dioxide in calcium acetate solution experimentally. So the Henry constants for carbon dioxide in calcium acetate solutions were calculated theoretically. The reaction kinetics was also investigated since the absorption is with chemical reaction. In order to achieve this, a stirred-cell reactor was used and a parametric study was performed. In kinetics study, the reaction between calcium acetate and carbon dioxide was performed at different solution concentrations, carbon dioxide concentrations and temperatures. As a result, the reaction rate expression was obtained. It was found that the rate of reaction between carbon dioxide and calcium acetate is dependent on both component concentrations by first order. The values of activation energy and preexponential factor were also obtained. In the last stage of the thesis, mass transfer study was performed using a stirred cell and a wetted wall column, which are the two equipments mostly used in similar researches. As a result of the experiments performed with these two different equipments, physical and chemical mass transfer coefficients were determined. Furthermore, the enhancement factors for chemical absorption with respect to the physical absorption were calculated for both systems and found to be very close to each other. It was understood that chemical absorption of carbon dioxide by calcium acetate solution is in the transition range of fast reaction to the intermediate reaction regimes.