Chemical and Biomolecular Engineering - Theses
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ItemSimplified computational models for adsorbent screening and cycle design for cyclic adsorption cycles for post-combustion CO2 capture applications( 2014)Cyclic adsorption processes are a promising technology for CO2 capture from large emissions point sources. Thousands of adsorption materials have been developed for CO2 capture, but there is no accepted method of determining which adsorbents are truly promising for use in an industrial process. Detailed adsorption simulation software is available, but it requires significant computational time and expert users. Therefore, most researchers resort to crude isotherm analysis when evaluating materials, which can be misleading in many cases. In order to rapidly screen adsorbent materials, we have developed a novel simple pressure/vacuum swing adsorption (PSA/VSA) model which can be solved in less than one second using MATLAB while still approximating experimental data. We have used this model to rapidly screen different classes of adsorbents for post-combustion CO2 capture, determine the ideal operating conditions, and identify optimal adsorbent properties. Our study suggests that zeolite 13X is still the best material available for post-combustion CO2 capture from dry flue gas. However, purity, recovery, and specific power results can be much improved if materials are developed with ideal, yet reasonably achievable, properties. Our results also showed that thermal effects and selectivity are much more important to VSA performance than is CO2 adsorption capacity and that the ideal CO2 heat of adsorption for this process is between 35KJ/mol and 45KJ/mol. Temperature swing adsorption (TSA) has also gained much attention recently as a CO2 capture technology because of its low energy penalty. The main drawback of TSA is long cycle times which can take several hours to complete. In order the overcome this challenge, we have developed a hot product purge TSA cycle using structured supported amine adsorbents which can be used to capture CO2 at high throughput with purities and recoveries over 90%. We analyzed several configurations of this cycle in attempt to reduce the associated thermal energy requirement. We also found the ideal adsorbent isotherm parameters for this process from a range of feasible adsorbent capacities, heats of adsorption, and entropies of adsorption. Using these ideal isotherms, we were able to simulate a process with a thermal energy requirement as low as 2.9 GJ/ton CO2 for a 90°C feed and 2.3 GJ/ton CO2 for a 30°C feed. We also performed a case study on the integration of our process into a Victorian brown coal-fired power station based on thermal efficiency data from the Loy Yang B power station. Our calculations suggest that for this process, the parasitic energy can be as low as .5GJ/ton CO2 which is much lower than that which can be achieved using VSA. We also estimated the bed size factor for this process to be approximately 500 kg/TPD CO2 which is on the same order of magnitude as VSA.