| With the increasing of greenhouse gas emissions, the global warming becomes prominent, which has caused a great impact on the survival environment of our human beings. As the main source of greenhouse gases, carbon dioxide (CO2) is getting more and more attention. Currently, CO2emission control has become an important issue between the governments, CO2 capture is then extensively researched and developed.Among the existing technologies for CO2 capture, amine-based method, one of chemical absorption technologies, has been widely studied and developed because of its fast absorption rate and high capacity of CO2, but the high operation cost becomes the bottleneck. While the energy consumption for solvent regeneration usually accounts for more than 70% of the operating cost for the whole processes. Therefore, selection for high efficient absorbents turns to the key point of amine-based method for CO2 capture.For this work, an improved rate-based screening method, i.e. multiple fast screening method, was developed to quickly screen high efficiency solvents, which was according to the existing screening research work and the cyclic properties. The method is based on an integrated CO2 absorption-desorption process, where the absorption process is performed at 40℃ and desorption process is done at the temperature of 80℃. While the amine solutions obtained a certain initial lean loading by the pretreatment process, and the duration of each of the two processes was set to be 60 minutes.For the first part of the work:Firstly, the multiple fast screening method was applied for repeated and multiple screening experiments by 30wt% monoethanolamine (MEA) solutions. The results shows the loading curves with time of two repeated experiments are in close agreement with each other, and the value of the average relative tolerance is 1.52%. Results of the multiple circulation experiments shows that the cyclic capacities of two absorption-desorption screening processes are 0.158 and 0.159 mole CO2/mole amine respectively, and there is only little changes. While the reaction rate curves with loadings of three times absorption-desorption experiments, including the pretreatment process, are almost in coincidence. These results validated the repeatability as well as the reliability of the multiple fast screening method combined with the experimental setup, also show the stability of solvents for multiple circulation. Then the multiple fast screening method was used to screen MDEA, DEEA, AMP and DEA solutions of 30wt%, the cyclic capacities of amines show that the order of CO2 capture efficiency as follows:AMP>DEA>DEEA>MEA>MDEA, and this is obviously different from that of traditional equilibrium-based fast screening method. What’s more material balance of gas phase and liquid phase of all the single amines screening experiments was calculated, and the absolute average deviation (AAD) was 2.65%, which shows the results can be reliable. Finally, results of a traditional simulation process in pilot plant scale by Aspen plus present the CO2 capture performance of tested amines has the same order as the screening results, and it verified the results of the multiple fast screening method can give a guidance for further industrial application for CO2 capture.For the second part of the work:the multiple fast screening method was used for the optimal molar ratio screening of blended MEA and DEEA solutions with total concentration of 5 mole/L, and mole ratio of blended MEA/DEEA systems was 4:1, 3:2,2.5:2.5,2:3 and 1:4 respectively. The results show that the blended MEA/DEEA solutions with mole ratio of 2.5:2.5 has the fastest absorption rate, while the blended solutions with ratio of 1:4 has the fastest desorption rate, with the increasing of mole ratio of DEEA, absorption rate of blended solutions decreased, but the desorption rate increased. Also, the cyclic capacity of multiple fast screening experiment was increased first and then decreased, while that of the equilibrium-based screening method just increased with molar ratio of DEEA increasing. In addition, the blended MEA/DEEA solutions with mole ratio of 2.5:2.5 has the highest cyclic capacity of 0.233mol CO2/mol amine, and its CO2 capture performance is 45.6% higher than that of MEA solutions in 5 mole/L. Then, material balance of gas phase and liquid phase of all the blended screening experiments was calculated, and the absolute average deviation (AAD) was 2.80%, it supported the results of the screening experiment can be reliable. |
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