Modelling of the tubular filter press process.
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Date
2000
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Abstract
The objective of this project was to develop a suitable procedure for the design, control and optimisation
of the Tubular Filter Press. To this end, the following objectives were defined for this study:
• To extend or improve upon the constant pressure compressible cake filtration model, predictive
solution procedure, and standard laboratory characterisation techniques requlred to obtain the empirical
model parameters, presented in Rencken (1992).
A new generalised area contact constant pressure compressible cake filtration model was
developed for both the internal cylindrical and planar filtration geometries. The model utilises a
heuristically developed area contact function which relates the interparticle contact area to the
solids compressive pressure within the cake. If the area contact is zero, the model reduces to
the conventional point contact model as presented in Rencken ( 1992). The sludge used in this
investigation was found to exhibit a negligible degree of area contact.
A new pseudo variable pressure solution procedure was developed, that is an extension of the
constant pressure solution procedure, to account for the initial variable pressure stage of the
Tubular Filter Press operation. The pseudo variable pressure solution procedure was found to
account accurately for the initial filtration behaviour observed during the pressurisation period
of the Tubular Filter Press. However for the normal operation of the Tubular Filter Press. the
difference between the output of the pseudo variable pressure and constant pressure solution
procedures, was found to be insignificant.
Wall friction in compression-permeability (C-P) cell tests was identified as a main source of
error. The significance of wall friction was investigated using a specially constructed C-P cell.
that enabled the transmitted pressure through the cake sample to be measured. The accuracy of
the characterisation which had been corrected for the effects of wall friction, was found to
improve the prediction of the filtration behaviour of the sludge significantly.
The direct shear test was identified and documented as a feasible experimental procedure to
determine the coefficient of earth pressure at rest. The coefficient of earth pressure is unique to
the non-planar filtration geometries. The coefficient of earth pressure at rest was determined
for the sludge used in this investigation.
• To incorporate the constant pressure compressible cake filtration model and the associated predictive
solution procedures into a user-friendly computer programme that will facilitate the design and
optimisation of full-scale plants. The predictive solution procedures were incorporated into the Windows 95 computer
programme, COMPRESS, that can be used for any constant pressure compressible cake
dead-end filtration application where the filtration geometry is planar or internal cylindrical.
A control and optimisation strategy for the continuous operation of the Tubular Filter Press has
been proposed.
To develop a regressive solution procedure, and incorporate this procedure into a user-friendly
computer progranune, that will enable the empirical model parameters. normally obtained from standard
laboratory-scale tests, to be obtained from actual filtration data.
A regressive solution procedure was developed that utilises a direct search optimisation
technique that is an extension of the COMPLEX method. The regressive solution procedure
was incorporated into the Windows 95 program, REGRESS. The program utilises filtration
data from any dead-end constant pressure filtration application of either planar or internal
cylindrical geometry. REGRESS provides an effective means for determining the true physical
or plant specific filtration characteristics of the sludge. The regressive solution procedure also
enables the parameters specific to the new area contact model to be determined. The sludge
characterisation obtained from regressing on filtration data was found to be a significant
improvement in predicting the filtration behaviour, than the characterisation obtained from the
standard non-filtration laboratory-scale methods, even after the C-P cell data had been
corrected for the effects of wall friction.
The programs COMPRESS and REGRESS should greatly assist in the design. control and optimisation of
the Tubular Filter Press process.
Description
Thesis (M.Sc.Eng.)-University of Natal, Durban, 2000.
Keywords
Filter presses--Mathematical models., Filters and filtration--Data processing., Filter presses., Water--Purification--Filtration., Theses--Chemical engineering.