Study On The Capture And Separation Of CO₂Using Hollow Fiber Membrane Contactors

Carbon dioxide is the most emitted anthropogenic greenhouse gas,is responsible for increasing the earth’s surface temperature.Capture and separation of CO2have important significance.There are many processes that carbon dioxide can be selectively removed from fuel gases.However,industrialized gas absorption device is basically a traditional gas absorber facility. Large volumn of equipment,greater investment, restricted operating conditions and the low absorption efficiency stop it from large-scale application.Membrane contacting process,which is a hybrid membrane gas absorption process,is extensively studied in recent years.The hollow fiber membrane contactor is a gas absorption equipment combining the advantages of membrane separation process(modularity,small size) and gas absorption technology(high selectivity). It is ideal for the absorption and separation of CO2.In this thesis, the modified hydrophobic microporous hollow fiber membrane contactor was designed.The experimental setup is built for separating CO2from the actual fuel gas and simulated fuel gas (CO2, N2, O2gas mixture). Seven kinds of aqueous absorbent, such as methylethanolamine(MDEA),diethanolamine(DEA), monoethanolamine(MEA),diethylenetriamine(DETA),triethylenetetramine(TETA), potassium glycinate(PG),piperazine(PZ),were applied.And the absorbent solution is made of the seven kinds of aqueous absorbent by different content.The CO2absorption experiments are carried out under different conditions of gas flux,liquid flow rate and concentration.The influence factors of CO2removal efficiency are analyzed comprehensively by detecting the CO2content in the fuel gas.Experimental results show that the CO2removal efficiency increased with the increases of liquid flow rate and the concentration of absorbent.But it decreased with the increases of gas flux and the CO2concentration in the mixture gas.As the same operating conditions,the carbon dioxide removal rate is5%higher by using self-designed membrane contactor than the original membrane contactor.The fuel gas SO2affects hardly the absorption liquid after desulfurization treatment.In the same environment,the absorption effects of seven different absorbers are compared.The absorption rate is as follows:TETA> DETA> PG> PZ> MEA> DEA> MDEA.According to desorption experiments and recycling absorption experiments, desorption regeneration capacity of seven absorbers as follows:MDEA>DEA>TETA>DETA>PG>PZ>MEA.Absorption effect was gradually weaken.Five absorption solutions(TETA、DETA、PG、PZ、MEA) mixed with MDEA in different proportions.The experimental data show that regeneration efficiency is getting better and better with the increase of content of MDEA,but the removal efficiency of CO2will gradually reduce.When PG and MEA mixed with MDEA in different proportions, the optimum ratio was3:2.The absorption solution had higher absorption rate and longer running time.However,when TETA、DETA and PZ mixed with MDEA in different proportions,it will be able to achieve high absorption efficiency of99%.Experiments studied the tube side,shell side,membrane mass transfer and analyzed on the influencing factors of total mass transfer codfficient.The simulated and experimental of overall mass transfer coefficient are compared.Results are quite similar.The conclusion is that with the increases of liquid flow rate,the concentration of absorbent,gas flux and the CO2concentration in the mixture gas,the total mass transfer codfficient will increase gradually.To capture and separation of CO2using modified membrane contactors,the thesis made economic accounting.The main factors of affecting CO2recycling costs have price of membrane,steam price and lifetime of membrane.