【作者】 李江；

【导师】 张卫东；

【作者基本信息】 北京化工大学 ， 化学工程与技术， 2010， 博士

【摘要】 膜吸收技术是脱除C02等温室气体最有前途的方法之一。然而,多孔膜的存在导致近膜壁面处溶质浓度分布不均(微观层面)以及中空纤维膜接触器壳程流体流动状态的非理想性(宏观层面),给膜吸收传质过程带来了不利的影响。本文针对这两类问题系统地进行了膜吸收过程的传质强化研究。通过理论分析,提出了膜吸收过程的传质强化方法,建立数学模型对传质强化过程进行了描述和预测。利用添加固相微粒扰动液相边界层,改善了近膜壁面处溶质浓度分布的不均性；在壳程吸收剂中添加细微粒子或引入外源振荡,加强了中空纤维膜接触器内壳程流体的径向混合,改善了壳程流体的非理想性。具体阐述如下：基于表面更新理论并通过传质区域的划分,建立了固相粒子强化膜吸收过程的传质模型。考察了固相粒子固含率、多孔膜孔隙率、吸收剂pH值、粒子粒径等因素对强化过程的影响,使用实验数据对模型结果进行验证,二者吻合良好。所建立的传质模型,可较好地对固相粒子强化膜吸收传质过程进行描述和预测。研究了吸收剂中固相粒子的引入对膜吸收过程近膜壁面处传质行为的影响。为屏蔽膜器结构以及壳程非理想性对过程的影响,采用板式膜接触器进行相关研究。固相粒子沿膜壁面的切向运动使得膜壁面处溶质浓度分布趋于均匀,垂直于膜壁面的法向运动扰动边界层,减小了传质阻力。固相粒子的加入在一定程度上减小了不同孔隙率膜之间的传质效果差异,同时还强化了传质,且孔隙率越小固相粒子的强化效果越大。为改善壳程流体流动的非理想性,提出了一种通过向吸收剂中引入细微粒子强化中空纤维膜吸收传质过程的技术。吸收过程中,采用超声将固相粒子悬浮在液相吸收剂中。粒子的加入使传质系数提高40%以上,对装填因子较大的膜器强化效果更佳。通过示踪实验获得了固相粒子的传质强化机理：固相粒子的加入减弱了示踪曲线的拖尾现象,加强了壳程流体在径向上的混合,有效地改善了壳程流体的流动状态,进而强化了传质过程。采用振荡器带动膜接触器发生振荡的方式,将传质实验与示踪实验相结合,研究了振荡对中空纤维膜器壳程流体流动状态以及传质性能的影响。结果表明,振荡可使膜吸收过程传质系数增加50%以上。当振荡方向与吸收剂流动方向平行时,振荡使得液相边界层与液相主体的混合程度变大,但会带来一定程度的轴向返混；而对于垂直操作模式,膜器的振荡不仅可以增大液相边界层与液相主体的混合程度,还加大了壳程流体在径向的混合,同时在一定程度上减弱了流体在壳程轴向的返混。更多还原

【Abstract】 Membrane gas absorption technology is one of the most promising alternatives to conventional technologies in carbon dioxide (CO2) capture. However, the heterogenous concentration profile near the membrane surface caused by inducing the microporous membrane decrease the mass transfer rate, and the non-ideal flow condition in the hollow fiber module shell-side also deteriorate the overall mass transfer. For the purpose of overcoming theses issues, experimental and modeling study on intensification of mass transfer in the membrane gas absorption process has been carried out in this work.Mathematical model considering the effect of porosity and mathematical model for the intensification process based on surface renewal theory are developed. The effects of solid loading, membrane porosity, absorbent pH value and particle diameter have been investigated. The calculated results have a good agreement with the experimental results.Pure CO2 was absorbed by de-ionized water or NaOH aqeous solution using membranes with different porosities in the flat-sheet membrane contactor. In order to improve the distribution of the concentration of solute near the membrane surface, solid particles are added into the absorbent liquid to enhance the turbulence in the boundary layer. The difference of mass transfer coefficient obtained by varied porosities declined by adding solid particles into the absorbent liquid. The higher enhancement factor is obtained at lower porosity.A method of improving the absorption performance in hollow fiber contactor by adding the third solid phase into the shell-side absorbent is proposed. Ultrasound is used in this work as an approach to make the solid particles suspending in the absorbent. The mass transfer rate is enhanced above 40% by adding solid particles into the absorbent, and the enhancement factors increase with an increase of the packing density. The residence time distributions (RTD) curves are measured, which demonstrate that the addition of the solid particles can improve the flow conditions in the shell-side.The influence of shaking on the flow condition in the shell-side of the module and the mass transfer of hollow fiber membrane gas absorption process has been investigated. The results of absorption experiments indicate that the shaking of module raises the mass transfer coefficient above 50%. The mass transfer improvement is higher when the shaking direction vertical to the liquid velocity direction. The shaking of the module can improve the flow status in the shell side of the hollow fiber modules.更多还原