The Study Of Carbon Dioxide Desorption Process In Hollow Fiber Membrane Contactors

As a new type of low-power CO₂desorption process，The CO₂desorption process in hollow fiber membrane contactors combined withboth the advantages of a hollow fiber membrane contactor as the masstransfer separation device and the thermal desorption process. The hollowfiber membrane contactor which has a large mass transfer area in pervolume can effectively improve the heat and mass transfer efficiency ofthe desorption process. In the CO₂desorption process in hollow fibermembrane contactors, respectively the gas phase and liquid phase flow oneach side of the membrane, It not only can avoided the operationalproblems such as entrainment, flooding which happened in the traditionaldesorption equipment, but also the gas phase and liquid phase can beadjusted independently, therefore the operation has larger elasticity. Inhollow fiber membrane contactors, liquid phase and gas phase can beadjusted independently, so it is feasible that adjusting the liquid conditionto improving the desorption efficiency and changing gas phase condition to reducing the energy consumption synchronously.In this paper, the PP and PTFE hydrophobic porous hollow fibermembrane contactors which have huge interfacial area per volume hasbeen used for carbon dioxide desorption. The effect of various parameterssuch as the absorbent types, the concentration of MDEA solution, flowrate of liquid phase and gas phase, temperature, the operating conditionsof gas phase, membrane materials and the device structure parameters ofmembrane contactors on CO₂desorption efficiency and energyconsumption were investigated, and high desorption ratio and masstransfer flux were obtained, the energy consumption reduced on the sametime. The mass transfer mechanism of the desorption process in hollowfiber membrane contactors has been investigated. The experimentalresults show that the carbon dioxide desorption efficiency was improvedby the increasing of the concentration of MDEA, the saturation level ofCO₂in absorbent, the temperature, liquid flow rate and mass transferarea. However, the gas phase condition had little effect on CO₂desorptionefficiency but obvious effect on energy consumption in membranecontactors. The reheating energy consumption of CO₂desorptionprocess in hollow fiber membrane contactors can be reduced byincreasing MDEA concentration and liquid flow rate. The evaporationheat of water can be reduced by increasing MDEA concentration andreducing gas phase flow rate when the tube side of contactor was taken sweeping with positive pressure, but it is useless by changing the liquidflow rate. The effect of desorption temperature on the desorption energyconsumption was restricted by the gas operating conditions.The performance of desorption efficiency and energy consumptionin membrane desorption process is excellent. In the optimal conditionswhich liquid flow rate was227.46cm·min^-1, the gas flow rate was14.0cm·s^-1, the desorption temperature of90°C, the desorption ratio increasedrapidly to over90%when CO₂was released from5.0mol·L^-1MDEAsolution in PP hollow fiber membrane contactor within began20minutesthe desorption rate has reached80%at6th minute, while the desorptionenergy consumption is only105.55KJ·mol^-1CO₂which was far lowerthan the conventional desorption180-200KJ·mol^-1CO₂.