Study On Filtering Performance Of Bag Filter

In the field of bag filter research, it is always the focus question to decrease the pressure drop and increase the filtration efficiency. The high filtration efficiency means the good filtration results, however high pressure drop will cause the waste of energy. In practice, It is the key point for evaluation of bag filter's performance that how to resolve contradictory between the high filtration efficiency and high pressure drop and how to optimize the construction of bag filter. Moreover the efficiency formula of classical filtration theory is expressed as implicit function and is inconvenient to be used, however it only can be used under stationary filtration condition and can not work under non-stationary filtration condition. Except these problems how to predict the pressure drop under non-stationary condition is another problem.In order to resolve these problems mentioned above, firstly the author analyzed the change law of filtration efficiency when each factor which affects filtration efficiency changed solely. In the base of this, the testing set of bag filtration was set up. The experiment has been done under stationary filtration condition and non-stationary filtration condition respectively.Under stationary filtration condition, firstly the author took the study about the effect of filtration velocity on filtration efficiency. The research shows that there exists a critical velocity. When the filtration velocity is under the critical velocity, decreasing the pressure drop and increasing the filtration efficiency can be realized by reducing the filtration velocity. Secondly the study on distribution of pressure drop was taken. From the test data it can be shown that pressure drop of filter cylinder exceed 90% of total pressure drop of bag filter. So the point of construction optimization should be concentrated on the filter cylinder. At last from the multianalysis, the regression relation of filtration efficiency was obtained. After comparing this formula with the test data and theoretical calculation, the author drawed a conclusion that this formula could be used to predict the filtration efficiency.Under non-stationary filtration condition, firstly the study about the effect of particle concentration, filtration velocity and filtration time on pressure drop was taken. The key of study was the effect of filtration time on pressure drop. Through analysis of the test data, it has been found that the earlier the dust cake formed, the smaller the number of particle would be which invaded the layer of fibers. So it can decrease the pressure drop effectively to accelerate the form of dust cake under non-stationary filtration condition. Secondly through the regression of test data, the regression relation about the pressure drop under non-stationary condition was obtained, which can not only be used to predict the pressure drop of bag filter under testing condition , but also provide some reference for evaluation of bag filter's performance. At last the author made a theoretical derivation of filtration efficiency under non-stationary condition. Based on classical filtration theory, according the characteristic of non-stationary filtration the author set up the mathematical model and obtained a efficiency formula through deduction. According this formula when thefiltration begins, the filtration time t is very little and can be approximatively looked as 0, under this condition this formula is the same as classical efficiency formula, the stationary filtration can be looked as one special course of this formula, and with the increase of filtration time the efficiency caculated by this formula will reach 1 quickly, it is coincidence with real process .At the end of the dissertation, according to the test data the author analyzed the merit and defect of membrane filter. Respectively under stationary and non-stationary filtration conditions the drag characteristics was compared between the ordinary filter and membrane filter. The analysis shows that: Because the film has the same effect as particle layer, so the d...