Investigation Of Membrane Absorption Flue Gas Desulphurization And Convective Mass Transfer Strengthen

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.