Study On Mass Transfer Process Of Flue Gas Moisture Recovery In Coal Fired Boiler Using Membrane

In the future, the proportion of lignite in our country will increase continuously, and its water vapor amount can be as high as 16%, and the natural gas combustion does as level 18%. There are a lot of researches on the use of membrane technology to recover the water vapor from wet flue gas, which involving the model calculation, CFD numerical simulation and experimental verification. But the transport mechanism and the fine description of the mass transfer process of the wet flue gas in the membrane module are less involved.According to whether there are pores in the membrane, the dissolved penetration of the membrane can be divided into two ways which are micro pore diffusion and dissolved permeability. At the same time, because of the wide application of composite membrane and asymmetric membrane, the concept of resistance model is also applied to analyze the mass transfer process of membrane. Many scholars in the past used Fick equation to explain the mass transfer process, on the basis of summarizing the use conditions and theoretical results of the model of the micro diffusion, dissolved permeability and composite resistance model of the micro hole. Considering the non ideal electric gradient and concentration gradient, Stefan Maxwell can be better described in this paper.Taking third kinds of composite films as an example, the membrane structure is divided into coating, connecting layer and supporting layer to Calculate. The coating part can be regarded as the non porous membrane, and its penetration mode is dissolution penetration. The transition layer is the connection part of the supporting layer and the coating, and its diffusion mode is dissolution penetration and Knudsen diffusion. The support layer has complex structure, and the penetrating mode of this part are viscous flow and Knudsen diffusion. After using the experimental data and the simulation method, to verify the theoretical model, it is found the difference between the physical model and the experimental data and the simulation results is small, and model can be used for calculating the flow rate of water vapor membrane.Using this theory model, this article discuss the influence of material permeability, pressure difference, porosity, thickness of transition layer, and temperature on the performance of water recovery. The results show that the material with high Henry coefficient and high selectivity to water vapor has a great advantage in the application, And the increase of the porosity, the pressure difference and the thickness of the transition layer are helpful to increase the water vapor flux. In this paper, we use the multiple attribute decision theory and the results of model calculation to sort several materials for decision analysis. Cellulose acetate can better meet engineering application in the calculation condition and consider range.