Numerical Simulation Study Of CO₂ Capture From Dry Flue Gas By Pressure Swing Adsorption And Temperature Swing Adsorption

At present,issues such as sea level rise caused by global warming have attracted worldwide concern.Carbon dioxide is one of the greenhouse gases causing global warming,thus reducing carbon dioxide emissions has become one of the top goals of the world.Techniques for separation and purification of CO2 have been extensively studied,and there are four main technologies for the separation and purification of CO2:adsorption,cryogenic distillation,membranes,absorption.Due to its low energy consumption,simple process and highly automated,adsorption has become one of the most concerned technologies.Depending on regeneration method employed for adsorbent,adsorption separation processes can be mainly divided into two categories:pressure swing adsorption(PSA)and temperature swing adsorption(TSA).To the best of our knowledge,multi-column VPSA,TSA and TVSA processes have not been reported for in-depth study and comparison.Based on the research background,advantages and disadvantages of pressure swing adsorption and temperature swing adsorption in carbon capture were investigated in this paper.Firstly,with zeolite 13X as the adsorbent,adsorption equilibrium data of pure CO2 and N2 between 25℃-150℃ on 13X were determined by static volume method and then fitted by Extended Langmuir model.Then,two-stage vacuum swing adsorption(VPSA),temperature swing adsorption(TSA),and temperature/vacuum swing adsorption(TVSA)were designed to capture CO2 from dry flue gas(15%CO2/85%N2).To obtain the optimal operating conditions,the influence of key operating parameters including feed flowrate,purge to feed ratio,vacuum level,time of recycle step on process performance were studied.Furthermore,the separation and purification behavior of the three processes were systematically analyzed by studying the pressure,temperature and concentration distribution inside the column.Results show that the CO2 products produced by the three processes under optimized conditions have achieved the target of 95%purity and 90%recovery,which meets the requirements of carbon capture and storage(CCS).Finally,a detailed comparison of the three processes was made in this study.VPSA was capable to achieve a great advantage in productivity and energy consumption with the value of 3.8 molCO2/kgads/h and 0.79 MJ/kgCO2 respectively,and it seemed to be the most effective CO2 capture process compared with TSA and TVSA.TVSA performed best in CO2 purity and recovery with the value of 97.27%and 97.66%respectively,meanwhile the productivity was up to 1.63 mol/kgads/h with the energy consumption of 3.22 MJ/kgCO2.Moreover,it is worth noting that TVSA would be an energy saving adsorption process that can produce CO2 product with high CO2 purity and CO2 recovery if a suitable low-grade waste heat source was available.Nevertheless,TSA was suggested to be an inefficient way for CO2 capture due to its poor performance of productivity and energy consumption,as well as no advantage in terms of CO2 purity and recovery.