It is well known that during the filtration process the resistance of the filter medium varies markedly from cycle to cycle due to irreversible clogging of its pores by particles of the suspension [I-4]. Thereupon the resistance of the medium in batch filters rises upon transition to each successive operation cycle, but for continuous filters, for example, for drum vacuum filters, it varies as a function of the number of turnovers. In the process of operation of a fi!ter, its productivity gradually decreases, and finally becomes so small that the filtration process must be stopped and regeneration or replacement of the medium must be carried out.The procedure for calculating the filtration process under a changing resistance of the medium has been insufficiently developed. In [4,5] only the form of filtration at a constant pressure drop on the filter (p = const) has been examined. At the same time, batch filters often operate at a constant filtration velocity, v, or with feed of suspension by centrifugal pumps, where p and v are variable.Let us examine the calculation of the process for the following two cases:I. The volume of filtrate, V', obtained from a unit filter area is constant in each cycle; the values of the filtration time, T, and the cake washing time, Tw, are variable.II. In each cycle the filtration time is constant and is assigned, but the volume of the filtrate obtained continuously decreases due to a rise in the resistance of the filter medium, B.The overall productivity of filter operation when n cycles are performed, allowing for the time, Taux, for auxiliary operations, is determined from the formula T=(~ m~-~w.m@ ~a~) n.(1)Here and below, mean values of quantities are denoted by the subscript "no"In case I the total number of cycles per operating period can be determined from the condition of maximum filter productivity or minimum operational costs, as was done for the p = const process in [4]. Less well-founded is the proposal of [5] to calculate the number of cycles from an assigned ratio of the maximum (at the end of the operating period) to the minimum (during the first cycle) value of filtration time: L = Tf/Tmin; thereupon the value of Tmin is determined from the minimally allowable value of the cake layer thickness, ~mino T The minimum yield of filtrate, Vmin, is equal to 5min/U where u is the ratio of the cake volume to the volume of filtrate obtained; i.e., at assigned parameters of the suspension and cake, and at adopted L and ~min values, the value of Tf is theoretically assigned~ In case II, which is apparently most applicable for continuous filters, the number of v operation cycles can be determined from assigned values of Vmi n or ~min at the end of the operating period. The adoption of this condition for batch filters, as was done in [5], is insufficiently founded, since for them a minimum thickness of the cake layer can be considered only as an additional limitation in solving the optimization problem~ Let us examine methods of calculating process parameters in general form. St...
