The Flow Characteristics And Gas-liquid Interfacial Turbulence Phenomenon Study Of The Falling Amino Acid Ionic Liquid And MEA Mixed Solution Film For Co₂ Absorption

With the rapid economy development and the large amount consumption of fossil energy, excessive emissions of CO2 has brought serious threat to the human environment, therefore, CO2 capture and storage has caused widespread attention domestic and overseas. According to statistics, CO2 emissions from the thermal power plants and in the transformation of other fuel account for more than 40% in the world. The UN’s intergovernmental panel on climate change(IPCC) has selected the technology of CO2 capture and storage emitted from the coal fired power plants as one of the most important technical direction, in order to realize the target regarding to the reduction of greenhouse gas emissions in 2050. In all kinds of methods for CO2 capture, falling film reactor features lower pressure drop,higher interfacial area, lower gas flow resistance over the film, the thin liquid film driven by gravity along the solid surface. It is particularly suitable for capturing the CO2 emitted from the coal fired power plants which is in large amount and with lower partial pressure of CO2(the volume ratio of CO2 in coal fired power plant flue gas is 12% 15%).For further analyse the flow characteristic and CO2 absorption performance of the new green organic Ionic liquid and amine mixed solution in a falling film reactor, this study is based on the falling film absorption of CO2 capture using the mixed solution of tetramethyl ammonium glycine ionic liquid([N1111][Gly]) and amine(MEA) as absorbent, and the liquid film flow characteristics, the CO2 absorption performance and the interface phenomena associated with the process of absorption were studied. In this paper, the main studies and conclusions are as follows:① The flow characteristics for the heated falling liquid film of 5%IL+15%MEA mixed solution on a uniformly cooled vertical reactor is studied. A comparision study of the film flow between the vertical plate and channel was carried out. The effect of the wall liquid temperature difference and the liquid flow rate on the film width and film area were analyzed. The results showed that: the capillary force in the vertical channel brought quite different flow patterns and film area. The film width and film area were larger with increasing wall liquid temperature difference and liquid flow rate. The film spreading area was larger when the film flowing on the vertical plate. Through a comparision study between the water and mixed solution, it can be concluded that, the physical properties of the fluid can great affect the expansion of the liquid film thus resulting in different spreading film width and area.② The comparision study of the absorption performance of CO2 with the four absorbents(20%MEA, 20%IL, 5%IL+15%MEA, 10%IL+10%MEA) were carried out, and the solution of 5%IL+15%MEA with good absorption performance was select as the CO2 absorbent. The effect of counter current gas flow rates on the flow pattern transitions and CO2 absorption performance(absorption rate, liquid utilization rate and liquid phase mass transfer coefficient) under different flow patterns were studied. Finally, the effect of liquid temperature, gas flow rate, CO2 inlet concentration on the CO2 absorption rate and the removal efficiency were discussed. The results showed that: the mixed solution of 5%IL+15%MEA has the maximum CO2 absorption amount per mole amine, and is more likely to be fully utilized relatived to the other three kinds of absorbent. The falling film was observed to take the form of “corner rivulet flow”, “falling ?lm flow with dry patches” or “complete falling ?lm flow” with the increasing liquid flow rate. The critical liquid flow rates between the flow patterns were higher with a contercurrent gas flow rate. The absorption performance was dramatically different under different flow patterns. The CO2 absorption rate and liquid utilization rate were higher under the “complete falling film flow” compared to the performance in the “corner rivulet flow”, “falling ?lm flow with dry patches” folw pattern. Due to the contact angle hysteresis, a high absorption rate and utilization rate can be achieved at the critical liquid flow rate between the transition of the “complete falling film flow” to the “falling ?lm flow with dry patches”. Improve liquid temperature appropriately can improve the CO2 absorption rate and the removal efficiency, and the change of gas flow rate needs to take a balance between the CO2 absorption rate and removal efficiency, the increase of the gas inlet concentration can improve the CO2 absorption rate, but it has little effect on the CO2 removal efficiency.③ Schlieren apparatus was adopted to observe the interfacial turbulence phenomena of the static liquid film with a single and two local heaters for four different solutions(H2O, 20%MEA, 20%IL, 20%IL+15%MEA). The influence of temperature field on the interfacial convection structure was analyzed. The experimental results showed that: when at the same temperature field, the interface of the four solutions all presented roll convection structures in the same direction of the temperature gradient. Compared to the pure water, when the solute of MEA and IL were added, the convection structures changed due to their different physical properties. For each of working medium, the interface convection structure was also different with different temperature field. When the static liquid film was heated by two heating tudes with a certain distance, a dividing line was appeared between the zone of the two heating tubes. Also, the dividing line was not straight and was changing all the time because of the unsteady temperature changes at the film interface.④ The interfacial turbulence phenomena, which was caused by interface concentration gradient due to uneven mass transfer in the CO2 absorption process, was observed using the Schlieren. Three working mediums(20%MEA, 20%IL, 5%IL+15% MEA) were considered. The influence of the liquid film thickness and the gas flow rate on the interface convection structure and liquid phase mass transfer coefficient were analyzed. The results showed that: the Marangoni convection resulted by the local concentration fluctuation at the interface can enhance mass transfer in the liquid. Therefore, the actual liquid phase mass transfer coefficient is much greater than the theoretical mass transfer coefficient. The ? factor(the ratio of the actual mass transfer coefficient and the theoretical mass transfer coefficient) is closely related to absorption process. ? factor gradually increased to a peak value and then decreased gradually. The interface convection structures were different under different liquid film thickness and gas flow rate. There is no obvious regularity of ? factor with the variation of the liquid film thickness and gas flow rate.⑤ The method of generating microconvection in the liquid film was put forward by realizing the ununiform temperature distribution field at the film interface. The liquid phase mass transfer can be enhanced by the microconvection at the liquid interface. The temperature distribution of the liquid film on the locally heated vertical plate and channel was studied using the infrared camera. The heater was arranged in the transverse and longitudinal direction, respectively. The critical temperature of the liquid film rupture was provided. The results showed that: the rupture of the liquid film would happen with the increase of the heating temperature in the locally heated vertical channel. The critical temperature of the liquid film rupture increased with increasing liquid flow rate. Compared to heating in the transverse direction, the film surface temperature field is more nonuniform when heating in the longitudinal direction, and the critical temperature of the liquid film rupture is greater than that when heating in the transverse direction. The rupture critical temperature with three heating sheet is larger than that with one heating sheet. For the film flowing on the vertical plate, the film rupture was not observed in the experiment, however, the shrinkage of the film was found in the flow direction leading to a sharp decrease in the film spreading area.