Research into the influence of vertical drainage elements on the operational efficiency of rapid filters

Abstract

To improve the efficiency of removal of suspended solids at rapid filters, we designed improved structure of the device. The improvement is based on the application, simultaneously with a granular filter layer, of vertical drainage elements with porous fibrous shells. Such a solution makes it possible to shift part of the load to the shells of drainage elements, reduce colmatation and head losses in a granular filter layer, as well as to more evenly distribute contaminants along its height. This increases the duration of operation of the filter under filtering mode and brings down the cost of regeneration of a filter layer. A filtration equation was derived to describe parallel filtration of a low-concentrated suspension through a granular medium and a fibrous medium. The mathematical model also includes equations of mass transfer, mass exchange and dependences to account for the impact of colmatation and parameters of filtering media. For a granular filter layer, we considered filtering with a gradual blocking of pores; for a porous shell - the formation of a sediment layer at its surface. Using a mathematical model, we conducted numerical experiments. The following significant parameters for the filter with improved design were determined: equivalent diameter of particles in a filter layer, working height of the vertical drainage element, duration of washing a porous fibrous shell. We give examples of calculations for determining the values of basic parameters at which the effectiveness of application of vertical drainage elements is maximal.