氨基酸离子液体混合工质吸收CO_2降膜流动及气液界面湍动研究

发布时间：2018-06-02 13:13

本文选题：CO_2吸收 + 离子液体　；参考：《重庆大学》2015年博士论文

【摘要】：随着经济的快速发展,化石能源的大量消耗,CO2的过量排放给人类环境与生存带来了严重威胁,因此CO2的捕集和封存在国内外引起了广泛关注。据统计,全球CO2排放量的40%以上是来自于电厂及其它化石燃料转化活动,联合国政府间气候变化专门委员会(IPCC)已将针对燃煤电厂的CO2捕集与封存技术作为2050年温室气体减排目标最重要的技术方向。在各种捕集CO2的方法中,降膜吸收法具有气液膜之间相互不贯透、设备压降小、降膜较薄、接触面积大、传质阻力小等优点,特别适合用在电厂烟气流量大,CO2分压低(燃煤电厂的烟气中CO2体积含量为12%15%)的场合。为深入分析新型绿色有机溶剂离子液体(IL)和有机胺混合溶液在降膜反应器内的流动特性及CO2吸收性能,本文采用四甲基铵甘氨酸离子液体([N1111][Gly])与乙醇胺(MEA)混合溶液作为吸收剂,针对其降膜吸收过程中涉及到的CO2吸收性能、液膜流动特性及传热传质过程中的液膜界面湍动现象等问题进行了研究。本文的主要研究内容和结论如下:①研究了竖直降膜反应器在均匀冷却条件下,5%IL+15%MEA混合溶液在竖直反应器内的流动特性,对比了液膜在竖直平板和竖直槽道内成膜的区别,讨论了液体流量和液膜与平板之间温差对液膜铺展宽度和铺展面积的影响。结果表明:随着液体流量及液膜与平板之间温差的增加,液膜的铺展宽度和面积增加;由于竖直槽道内角区处毛细力作用的影响,使液膜在降膜槽道内的铺展有别于液膜在竖直平板上的铺展,对液膜的铺展面积、液膜流型等有较大的影响;液膜在竖直平板上流动时具有较大的铺展面积;通过水和混合工质的降膜流动特性对比得出,液体物性影响液膜的扩展强度,进而影响液膜的铺展宽度和面积。②对比了四种吸收剂20%MEA、20%IL、5%IL+15%MEA、10%IL+10%MEA(质量比)的CO2吸收性能,从中选择一种性能较好的工质5%IL+15%MEA作为CO2吸收剂,研究了在逆流气体吹扫下,其在降膜反应器中的流型转换规律,给出了流型之间相互转换的临界液体流量,并分析了在不同流型下的CO2吸收速率、液体利用率和液相传质系数,最后探讨了液体温度、气体流量、气体进口CO2浓度对CO2吸收速率和脱除率的影响。实验结果表明:5%IL+15%MEA每摩尔胺吸收的CO2量达到最大,且相对其他三种吸收剂,5%IL+15%MEA吸收剂更易被完全利用;在降膜流动过程中,随液体流量的改变,液膜呈现溪流、片状流和完整流三种流型,逆流气体提高了液膜流型相互转换的临界液体流量;液膜流型对CO2吸收性能的影响很大,相对溪流和片状流,完整流具有较高的CO2吸收速率和液体利用率,而液相传质系数却在溪流和片状流下较大;由于接触角的滞后性,在液膜成膜过程中,先以较大的液体流量使液膜在反应器内形成完整流之后,再逐渐减小液体流量至完整流转换成片状流的临界流量,可以使液膜在较小的液体流量下维持完整流,从而达到较高的吸收速率和液体利用率;适当提高吸收剂温度可以提高CO2的吸收速率和脱除效率,而气体流量的改变需要均衡考虑CO2吸收速率和CO2脱除率两者的变化,气体进口CO2浓度的增加可以提高CO2吸收速率,但是对CO2脱除率并没有太大的影响③采用纹影仪观察了四种工质(H2O、20%MEA、20%IL、5%IL+15%MEA)的静止液膜中心,被单根或双根加热管局部加热时的界面湍动现象,分析了不同温度场对界面对流结构的影响。实验结果表明:在相同温度梯度下,四种工质界面均呈现清晰的与温度梯度方向一致的滚筒状暗条纹结构,条纹之间相互独立;与纯水相比,当加入乙醇胺MEA或离子液体IL时,局部界面对流结构发生改变;对于每一种工质,随着界面温度梯度的不同,其界面对流结构亦发生改变,当液膜整体温度升高时,由于溶剂的挥发,温度梯度和浓度梯度的共同作用会影响界面对流形态;相比液膜被单根加热管局部加热时的界面湍动形态,当液膜被双根加热管同时加热时,在两根加热管中心产生了一条分界线,此外,界面温度的非稳态变化导致两根加热管中心的分界线也是在逐渐变化,并不是一条稳定在两根加热管之间的直线。④采用纹影仪观察了三种CO2吸收剂(20%MEA、20%IL、5%IL+15%MEA)在吸收CO2过程中,由于传质不均引起的界面湍动现象,分析了液膜厚度和气体流量对界面对流形态及液相传质系数的影响。结果表明:界面局部浓度发生变化导致Marangoni对流可以强化液相传质,使实际液相传质系数远远大于理论的液相传质系数,且?值(实际测量得到的液相传质系数与理论计算得到的液相传质系数之比)与吸收过程紧密相关,随吸收时间的增加,?值先是呈上升趋势,到达峰值后,随之减小;在不同液膜厚度和气体流量下,界面对流形态不同,?值随液膜厚度和气相流量的变化没有呈现明显的规律。⑤界面处的微细对流可以强化液膜内的扩散传质,基于此,提出了在液膜表面构造非均匀温度场从而诱导液膜内产生微细对流的方法。采用红外热像仪研究了液膜在局部加热的竖直平板和竖直槽道内流动时的表面温度场分布,探讨了局部加热时液膜破裂的临界温度。结果表明:在竖直槽道内,随局部加热温度的增加,液膜会发生破裂,液膜破裂的临界温度随液体流量的增加而增加,相比在横向方向加热,在槽道纵向方向上加热时,液膜表面的温度场分布更加不均匀,且液膜破裂的临界温度大于在横向方向加热时的情况,布置三根加热片时的液膜破裂临界温度大于布置一根时的情况;而在竖直平板上,实验过程中并没有观察到液膜的破裂,而是发现了液膜在流动方向上逐渐收缩,随局部加热温度的增加,液膜收缩加剧,液膜铺展面积急剧减小。
[Abstract]:With the rapid development of the economy and the large consumption of fossil energy, the excessive emission of CO2 poses a serious threat to the human environment and survival. Therefore, the capture and sealing of CO2 has aroused widespread concern at home and abroad. According to statistics, more than 40% of the global CO2 emissions are derived from the power plant and its fossil fuel conversion activities, and the Intergovernmental climate of the United Nations The change special committee (IPCC) has taken the CO2 capture and storage technology for coal-fired power plants as the most important technical direction for the greenhouse gas emission reduction targets in 2050. In the various methods of collecting CO2, the falling film absorption method has the advantages of interpenetration between gas and liquid membranes, small pressure drop of equipment, thin film reduction, large contact area and small mass transfer resistance. It is suitable for the situation that the flue gas flow rate of the power plant is large and the CO2 partial pressure is low (the volume content of CO2 in the flue gas of the coal-fired power plant is 12%15%). In order to analyze the flow characteristics and CO2 absorption properties of the new green organic solvent ionic liquid (IL) and the organic amine mixed solution in the falling film reactor, the four methammonium glycine ionic liquid ([N1111][Gly]) is used in this paper. The mixed solution of ethanolamine (MEA) is used as an absorbent to study the CO2 absorption properties involved in the process of falling film absorption, the liquid film flow characteristics and the turbulent phenomenon of the liquid film interface during the heat and mass transfer process. The main contents and conclusions of this paper are as follows: (1) the vertical drop film reactor was studied under uniform cooling condition, 5 The flow characteristics of%IL+15%MEA mixed solution in a vertical reactor were compared. The difference between the film formation in the vertical plate and the vertical channel was compared. The effect of the temperature difference between the liquid flow and the liquid film and the flat plate on the spreading width and spread area of the liquid film was discussed. The results showed that the liquid film was increased with the temperature difference between the liquid film and the flat plate. The spreading width and area increase; the spreading of the liquid film in the falling film channel is different from the spreading of the liquid film on the vertical plate because of the influence of the capillary force at the inner corner of the vertical channel. It has a great influence on the spreading area of the liquid film and the flow pattern of the liquid film; the liquid film has a larger spreading area when the liquid film is flowing on the vertical plate; through water and the water, the liquid film has a large spreading area. The comparison of the flow characteristics of the mixed refrigerants shows that the liquid property affects the expansion strength of the liquid film, and then affects the spreading width and area of the liquid film. Secondly, the CO2 absorbability of four absorbents, 20%MEA, 20%IL, 5%IL+15%MEA, 10%IL+10%MEA (mass ratio), is compared, and a better refrigerant 5%IL+15%MEA is selected as a CO2 absorbent from it. The flow pattern conversion law in the falling film reactor was carried out under the flow of countercurrent gas. The critical liquid flow rate between the flow patterns was given. The CO2 absorption rate, the liquid utilization rate and the liquid mass transfer coefficient under different flow patterns were analyzed. Finally, the liquid temperature, the gas flow rate, the gas inlet CO2 concentration and the CO2 absorption rate were discussed. The experimental results show that the CO2 amount per mole of 5%IL+15%MEA is maximum, and the 5%IL+15%MEA absorbents are more easily utilized relative to the other three absorbents. In the process of falling film flow, the liquid film presents stream, flake flow and complete flow pattern with the change of liquid flow, and the countercurrent gas improves the flow pattern of the liquid film. The liquid film flow pattern has a great influence on the absorption properties of CO2, relative stream and flake flow, the complete flow has higher CO2 absorption rate and liquid utilization ratio, while the liquid mass transfer coefficient is larger under the stream and flake flow. After the complete flow of the liquid film is formed in the reactor, the critical flow of the liquid flow to the complete flow is gradually reduced, and the liquid film can maintain a complete flow under the smaller liquid flow, thus achieving a higher absorption rate and liquid utilization. The absorption rate and removal efficiency of CO2 can be improved by increasing the absorbant temperature properly. The change of gas flow rate and CO2 absorption rate and CO2 removal rate need to be balanced. The increase of CO2 concentration in gas inlet can increase the absorption rate of CO2, but there is no significant effect on the CO2 removal rate. (3) the static liquid membrane center of four types of refrigerants (H2O, 20%MEA, 20%IL, 5%IL+15%MEA) is observed by the schlierer. The effects of different temperature fields on the interfacial convection structure are analyzed. The experimental results show that under the same temperature gradient, the four types of working fluids have a clear structure of roller like dark stripes that are consistent with the direction of the temperature gradient, and the lines are independent of each other. Compared with pure water, when ethanol is added to the ethanol, it is added to the ethanol. At the time of amine MEA or ionic liquid IL, the convective structure of the local interface changes; for each material, the interfacial convection structure changes with the temperature gradient of the interface. When the overall temperature of the liquid film increases, the common action of the temperature gradient and the concentration gradient will affect the interfacial convection morphology because of the evaporation of the liquid film. When the root heating tube is heated locally, the boundary of the two heating tubes is heated at the same time when the liquid film is heated at the same time. In addition, the non steady state change of the interface temperature leads to the gradual change in the dividing line between the two heating tubes, which is not a straight line stable between the two heating tubes. The effect of three CO2 absorbents (20%MEA, 20%IL, 5%IL+15%MEA) on the interfacial turbulence caused by uneven mass transfer during the absorption of CO2 was observed by schlieren. The effect of the thickness of the liquid film and the flow of gas on the interfacial convection morphology and the mass transfer coefficient were analyzed. The results showed that the change of the local concentration of the boundary caused the strong convection of Marangoni to be strong. The mass transfer in liquid phase makes the mass transfer coefficient of the actual liquid phase far outweigh the theoretical liquid mass transfer coefficient, and the value (the ratio of the liquid phase mass transfer coefficient obtained by the actual measurement and the theoretical calculation of the mass transfer coefficient) is closely related to the absorption process. With the increase of the absorption time, the value of the liquid phase is on the rise first, and then decreases after the peak, and in the different liquid. Under the film thickness and gas flow, the convection morphology of the interface varies with the thickness of the liquid film and the change of the gas flow rate. 5. The micro convection at the interface can strengthen the diffusion and mass transfer in the liquid film. Based on this, an inhomogeneous temperature field on the surface of the liquid film is proposed to induce the micro convection in the liquid film. The temperature distribution of the surface temperature field of the liquid film in a vertical plate and a vertical channel with local heating is studied by infrared thermography. The critical temperature of the rupture of the liquid film is discussed when the local heating is heated. The results show that the liquid film will break up with the increase of the local heating temperature in the vertical channel, and the critical temperature of the rupture of the liquid film follows the liquid flow. When heating in the transverse direction and heating in the longitudinal direction of the channel, the temperature distribution on the surface of the liquid film is more uneven than in the longitudinal direction of the channel, and the critical temperature of the rupture of the liquid film is greater than that in the transverse direction. The critical temperature of the rupture of the liquid film when the three heated sheets is arranged is greater than that of the arrangement of one time; but on the vertical plate, In the course of the experiment, the rupture of the liquid film was not observed, but it was found that the liquid film gradually contracted in the flow direction. With the increase of the local heating temperature, the shrinkage of the liquid film increased and the spreading area of the liquid film decreased sharply.
【学位授予单位】：重庆大学
【学位级别】：博士
【学位授予年份】：2015
【分类号】：X773

【参考文献】