【作者】 陈迁乔；

【导师】 钟秦；

【作者基本信息】 南京理工大学 ， 化学工程与技术， 2012， 博士

【摘要】 微孔中空纤维膜接触器用于烟气脱硫引起广泛关注。本文采用实验室模拟烟气,对疏水性中空纤维膜接触器用于烟气脱硫的工艺进行了实验研究并建立了脱硫率计算模型；对对流传质的物理机制进行研究,从场协同的角度对螺旋管强化管内传质进行了定量计算,对实际烟气中可能存在的颗粒物的沉积情况进行了模拟研究。以Na2SO3溶液为吸收剂,模拟烟气走膜管内侧,进行脱硫实验研究。结果表明当Na2SO3溶液浓度大于5%,液相阻力可以忽略；脱硫率随气速的增大而减小,而随膜组件长度、膜传质系数的增大而增大。该工艺脱硫率高且稳定。忽略液相传质阻力,用传质速率与物料衡算法及传质经验式,建立脱硫率计算模型,与实验值误差小于9.5%。用自制螺旋状膜管组装膜吸收器,进行脱硫实验研究。结果表明相对于传统的直管膜,螺旋管可以较大程度地促进SO2的传递,提高脱硫率。随着管内流速的增加,强化传质效果明显,气体停留时间和吸收液流速对脱硫率影响不大。从微分方程出发,归纳了对流传质的局部、2D和3D的场协同方程。从对流传质的机理着手,对平板边界层低速率传质以及吹喷和抽吸三种边界条件的速度场和浓度场进行模拟研究。提出cosβ>0,即速度和浓度梯度矢量的夹角β<90°,扩散消弱宏观强制对流传质,cosβ<0,即β>90°,扩散强化宏观强制对流传质。抽吸时,边界层内β为锐角,边界层底层cosβ最大,浓度梯度也最大,所以传质速率高。吹喷时,由于边界层底层区域β>90°,上部区域β<90°,溶质出现了返混,致使传质速率低,边界层厚度增大。补充了经典传递理论对三种边界条件传质速率差异的解释。证实了对流传质速率不仅决定于流速、物质的浓度差以及流体物性,还依赖于浓度场和速度场的协同。采用计算流体力学方法,对层流直管和螺旋管内传质进行模拟研究。发现直管内大部分区域径向比轴向浓度梯度高2个数量级。为了强化传质,应降低浓度梯度矢量和速度矢量的夹角,在径向产生一定的流动。而螺旋管内的二次流横穿浓度等值线,即部分流体沿着浓度梯度方向(或其反方向)流动,极大地提高了两场的协同。二次流随着Re的增大而增强,传质增强效果也越显著,正是二次流显著提高了速度场和浓度场的协同。所研究的螺旋结构中,在Re=1000～2400时,最大平均二次流速度达到主流速度的6.8%-6.5%,Sh增大了4.99-6.43倍。场协同原理可以很好地解释螺旋管对流传质强化的机理。采用计算流体力学方法,对直径为0.05μm-3μm的烟尘颗粒在中空纤维直管和螺旋管内的沉积特性进行模拟。直管内0.1μm和1μm的颗粒的沉积率都小于1%,而螺旋管内的沉积率在90%左右。螺旋管内沉积率随着颗粒直径和气速的增大而增大,惯性离心力是颗粒在螺旋管中沉积的主要因素。建议采用螺旋型除尘器对粉尘颗粒进行收集。更多还原

【Abstract】 Removing acidic gas by using microporous hollow fiber membrane contactor (HFMC) has attracted extensive attention. Using the hydrophobic hollow fiber membrane contactor, the experiment study of flue gas desulfurization has been carried on and the desulphurization rate calculation model has been established. The physical mechanism of convective mass transfer has been studied, the quantitative calculation of helical tube strengthening mass transfer has been carried out from the viewpoint of field synergy, the particle deposition was simulated which is possible presence in the actual flue gas.An experimental research of flue gas desulfurization (FGD) by HFMC was carried out and corresponding model of calculating desulfurization rate was developed. The results show that the desulfurization rate are high and stable, the mass-transfer resistance of the liquid phase can be neglected when the concentration of Na2SO3absorbent is more than5%, the desulfurization rate will be increasing with the rising of the module length, the membrane’s mass coefficient and it will be reducing with the rising of the gas velocity. The calculated data of desulfurization rate in HFMC from the model which had been developed by using of the mass transfer rate, material balance method and empirical correlative equation are in good agreement with the experimental date; the errors between them are within9.5%.FGD character was studied with membrane contactor assembled with self-made helical membrane tube. The experiment research results show that helical structure can promote SO2mass transfer greatly compared with straight tube membrane. Strengthen mass transfer effect is obvious with the increase of gas velocity in tube, gas residence time and absorption liquid velocity has a little influence on desulfurization rate.From the convective mass transfer differential equation, local,2D and3D field synergy equation have been summed up.The plate boundary layer convective mass transfer under three kinds different boundary conditions were studied by numerical simulation method and put forward that the diffusion strengthen macroscopic forced convective mass transfer when the concentration field and velocity field angle β>90°, whereas the diffusion weaken macroscopic forced convective mass transfer when β<90°.The results of the study show that the angle β<90°, concentration gradient and cos β reach maximum at the same time in lower boundary layer for suction boundary, so mass transfer rate is high. But for injection boundary, due to some regional β>90°, and some regional β<90°, result in the diffusion and the convective mass transfer mutually reinforcing in the lower and offset each other in the upper of the boundary, so the mass transfer efficiency is low, the boundary layer thickness increases. It is the difference of the velocity field and concentration gradient field that led to the mass transfer rate differences in three boundary conditions. Additional explanation of mass transfer rate differences was given under three kinds of boundary conditions in the classical transfer theory.The results validated that the convective mass transfer Sherwood number depends not only on the Reynolds number and the Schmidt number but also on the synergy of concentration field and velocity field.Using numerical simulations, laminar convective mass transfer in in the straight tube and helical tube have been studied. the results show that concentration gradient in radial is larger than that in axial2magnitude orders when Sc is1.2. In order to strengthen the mass transfer, the angle of velocity and concentration gradient should be decreased, in an another words, fluid flow along radial should be generated. The secondary flow crosses the equi-concentration line, namely, some fluid flow along the direction of concentration gradient (or its reverse direction), greatly improves the synergy of the two fields in helical tube. The secondary flow is more intense with the increase of Re, the effect of mass transfer is more significant. The secondary flows promote the synergy of concentration and velocity fields, which is the reason of enhancement the mass transfer for helical tube. The maximum of area-average secondary velocity reaches6.8%-6.5%of bulk velocity, and Sh increases4.99～6.43folds when Re=1000～2400for helical structure in the paper. It is shown that the field synergy principle explains well the mechanism of mass transfer enhancement in the helical tube.The deposition performance of the particles in straight and helical hollow fibre membrane tube were simulated by calculation fluid dynamic with the particles diameter0.05μm～3μm. The result shows that the deposition rate is low in straight tube and is high in helical tube. The deposition rate is below1%for0.μm and1μm particles in straight tube when the gas velocity is10m/s, but the deposition rate is about90%in helical tube under the same operation conditions. The deposition rate increase with the diameter increasing of particles and enlarging of De number in helical tube. Inertial centrifugal force is the main factors of effecting particles deposition in helical tube. Using spiral type precipitator collect the fine dust is proposed.更多还原