Variable flow rate in compactible filter cakes

Traditional formulas used for design of fitters and interpretation of exper imental data depend upon a number of simplifications including negligible s olid velocity u(s) and a superficial liquid flow rate q(L) which is assumed to be a function of time and independent of distance x through a filter ca ke. The extent of variation of u(s) and q(L) for highly compactible biosoli ds is discussed in this article. An approximate method based on well-known equations which rest on the assumption the q(L) is constant throughout a co mpressible cake at a given time is presented. Using previously available fo rmulas, the assumption of constancy of q(L) is abandoned; and approximate e quations yielding q(L) as a function of x are developed. Comparisons are ma de of the variation with distance of q(L), u(s), and relative velocities fo r cakes of different degrees of compactibility and slurries of varying conc entrations, problems related to verification of a given model are discussed . (C) 1998 Elsevier Science Ltd. All rights reserved.