| Air pollution is quite serious in China today due to high total particle pollution exhaust emission level. Actually, the inhalable particulates are mainly composed of industrial smoke and fly dust. General speaking, the principal particle pollution emission sources mainly come from coal-fired power plants, industrial coal-fired boilers, and coal-fired furnaces. As the coal consumption is growing rapidly, the ultrafine dust and carbonblack particles hard to deposit are increasingly polluting the atmosphere. In the present work, several numerical models on the purification of industrial black smoke with porous ceramic filter were conducted to investigate the effect of dust deposit on filtration process, which is of great importance for smoke purification in high-temperature condition.The major focuses and research findings of this paper are as follows:(1) The physicochemical properties of ceramic material and carbonblack dust were investigated and their microstructures were characterized correspondingly. The particle size ceramic material was expressed by the deduced formulas and the size distribution of carbonblack particles was fitted to acquire the equivalent mean diameter. Simultaneously, the chemical compositions of those materials were tested by the X-ray diffractometer.(2) The CFD simulation and experimental investigation were performed for the ceramic filter in high temperature. The Pro/Engineering software was employed to establish the3-dimensional model of ceramic filter, and the corresponding model mesh was created by the Gambit software. In order to validate the model mesh, the grid independent validation was conducted by Richardson interpolation method. Finally,5specifications of porosities were applied to calculate the relationship between inlet flow velocity and filtration pressure drop. The results show that the simulated curves are in agreement with the experimental data, indicating that the CFD simulation can well predict the filtration process with clean ceramic filter.(3) A cake collapse model was proposed to investigate the effect of fractal compression on cake porosity by taking the combined effect of relaxation ratio, fractal dimension, aggregate size, and coordination number into account. Subsequently, the effect of those variables on cake pressure drop was derived using the porosity function. Furthermore, a novel inversion method was designed to acquire the real coordination number and the corresponding relaxation ratios for the model. Through the analysis of binary images of field emission scanning electron micrographics (FE-SEMs), the fractal dimension was calculated with the fitting logarithmic pixel values by a box-counting dimension method. The aggregate size was obtained by Rosin-Rammler fitting of the statistical aggregate size in the FE-SEMs. Hence, the independence of inter-and intra-aggregate porosity, cake porosity and cake pressure drop on the fractal dimension and relaxation ratio for the reverse-calculated coordination number. By comparison, it is found that the model predictions with consideration of cake collapse are more close to the experimental data than the model without considering the cake collapse. Due to high-accuracy and simple computation, this model displays a great application potential in the prediction of cake pressure drop.(4) An unsteady model on dust deposit was established to predict the change of pressure drop with the specific deposit. Thus, the effect of dust deposit and detachment on the pressure drop was predicted. By calculation, it is evident that the basic parameters (such as primary porosity, diameter of ceramic granular, and vessel thickness), and operation conditions (operation flow rate and ambient concentration) have great influence in the dust deposit, resulting in the effect on pressure drop. To further study the dynamic process during filtration with cleaning, the changes of specific deposit and pressure drop in many cleaning-filtration cycles were researched, and the corresponding cleaning efficiencies of ceramic filters with different specifications of ceramic vessels were analyzed for assessing the cleaning profiles in the early and steady stages.(5) To study the collection performance of ceramic filter, a filtration model with application of cake surface theory was established. By analyzing the dust accumulation process, the time-independent collection efficiency, and the primary and steady collection efficiency under different ambient concentration and filtration filow rate were investigated.(6) A pulse-jet cleaning and filtration model was proposed by using the weighted area fraction assumption. With the utilization of Matlab software, the pulse-jet cleaning and filtration procedure was calculated by a program to acquire the relationship between area fractions and cleaning-filtration cycle. The results show that as the cycle number increases, the capture capability of filtration media increasingly becomes weaker and the increment of dust deposit in the next cycle become smaller, resulting in the decrease of the increment of area fraction. For different dust area fractions, the analysis of instantaneous weighted filtration velocity with time was conducted. It is found that the smaller mass per unit area caused the sharp decrease of filtration, and vice versa. |
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