| dc.description.abstract | In recent years, most industrial countries come to realize the important environmental effect by greenhouse gas, especially massively discharged carbon dioxide. The greenhouse gas was generally recognized the main cause of annual average temperature rise on earth year by year. For this serious issue, many countries promote carbon capture, storage and utilization (CCSU) to lower the carbon dioxide emission.
In order to capture carbon dioxide, pressure swing adsorption (PSA) is one of gas separation methods which features low energy consumption, lower capital investment, and simple operating process.
This study provides a vacuum pressure swing adsorption process for the capture of carbon dioxide for pretreated flue gas from coal-fired power plants. The research purpose is to get the bottom product with a carbon dioxide purity of over 85% for a long time (100 hours) operation. We selected zeolite 13X molecular sieve as the adsorbent, used Thermo Cahn D-200 Digital Recording Balance to measure the isotherm of CO2 and N2 at different temperatures to describe the behavior of adsorption equilibrium. Then we put the adsorbent into the adsorption bed to do the breakthrough experiments with different feed concentration and flow rate, and discussed the effects of feed concentration and flow rate on adsorption bed and breakthrough time.
In this study, a 3-bed-9-step VPSA process was utilized to capture CO2 from the flue gas of the coal-fired power plant with a bench-scale adsorption bed of 0.16 m diameter and 0.6 m length and the basic operating circumstance was set at feed pressure 3.2 bar, cocurrent depressurization pressure 0.4 bar, and vacuum pressure 0.1 bar. The experimental study showed a result of bottom product with 91.01 % purity and 58.46 % recovery of CO2, and the total mechanical energy consumption including water pumping motor of the scrubber, air dryer, air compressor, and two vacuum pumps for cocuurrent and countercurrent depressurization was 7.89 GJ / tonne CO2 for the 280th cycle, and two vacuum pumps only accounted for 1.39 GJ / tonne CO2. We also took out some particles of the adsorbent from the adsorption bed every 24 hours during long time (100 hours) operation and measured the change of its adsorption capacity with time.
Then we used pure CO2 and N2 to make appropriate control to mix 5% CO2 + 95% N2 and 20% CO2 + 80% N2 as feed concentration and the bottom product could be obtained 50.28% and 96.42% under the same 3-bed-9-step operation process. The operation time was modified for different feed concentration to improve the CO2 purity or recovery of the bottom product. When the feed was the flue gas, the purity of the bottom product dropped from 92.04% to 82.26%, the recovery increased from 59.01% to 60.58%, and the mechanical energy consumption decreased from 7.64 to 7.56 GJ /tonne CO2. When feed was 5% CO2 + 95% N2, the purity of the bottom product increased from 50.28% to 82.89%, the recovery decreased from 49.04% to 40.24%, and the mechanical energy consumption increased from 5.09 to 5.31 GJ /tonne CO2. When feed was 20% CO2 + 80% N2, the purity of the bottom product decreased from 96.42% to 96.09% a, the recovery increase from 48.33% to 50.31%, and the mechanical energy consumption decreased from 1.54 to 1.48 GJ /tonne CO2.
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