Thesis-1992-Zhang.pdf (11.49 MB)
Crossflow microfiltration modelling and mechanical means to prevent membrane fouling
thesis
posted on 2017-06-30, 13:40 authored by Guan Mei ZhangThe definition, history and applications of Microfiltration (MP) are briefly
reviewed in Chapter 1. The physical mechanisms and mathematical models of the
filtration process including concentration polarization (CP), gel polarization (GP) and
pore blocking are given in Chapter 2.
Crossflow microfiltration membrane fouling and the deposition of solids onto the
filter surface have been investigated using a process fluid (seawater), latex and a ground
mineral. The performance of various membrane materials has also been studied,
including: acrylonitrile, polypropylene, PTFE, ceramic and stainless steel. The seawater
filtration work showed in Chapter 3 that good filtrate flux rates can be maintained if
material fouling or depositing on the membrane can be prevented from entering the
membrane structure. A surface deposit may be removed by mechanical means such as
backflushing with permeate or compressed air. This aspect of the work indicated that
a more comprehensive study of fouling was required. Existing crossflow filtration
membrane models did not adequately represent even the simplest filtration when
penetration of the membrane structure applied. Such conditions occurred during latex
filtration in Chapter 4.
Latex of varying sizes and density were manufactured and filtrations using
acrylonitrile membranes were performed. Considerable deposition of latex inside the
membrane pores occurred despite the nominal rating of the membrane being less than
the latex particle diameter. Thus the membranes relied on a depth filtration mechanism
rather than a surface straining mechanism for filtration effectiveness. A standard
filtration blocking model was modified for use in crossflow microfiltration, coupled
with a mass balance on the amount of material filtered. This mathematical model was
then used to predict and correlate the rate of filtration flux decay with respect to filtration
time during crossflow filtration. The model provided acceptable accuracy and is an
improvement on existing empirical models for the flux decay period.
Under the circumstances of membrane penetration it is advisable to minimise the
amount of material entering the membrane structure. Mechanical means to achieve
this were investigated and a novel anti-fouling method using a centrifugal field force
and enhanced shear stress at the membrane surface was developed. The filtration of
limestone slurries with three different tubular filters are presented in Chapter 5, in which
one filter was conventional, the other two novel ones were specially designed for the
separation of particles with a density different from that of the liquid, one used a helical
channel around the filter, and the other had tangential inlet and outlet endcaps. The
centrifugal force produced by the spinning flow around these two filters retarded the
approach of particles towards the membrane surface so that the particle deposition was
reduced. The results showed such a system was energy efficient, saving 20 % of the
energy required to effect a separation of mineral material compared with using the
membrane in a more conventional way.
History
School
- Aeronautical, Automotive, Chemical and Materials Engineering
Department
- Chemical Engineering
Publisher
© Guan Mei ZhangPublisher statement
This work is made available according to the conditions of the Creative Commons Attribution-NonCommercial-NoDerivatives 4.0 International (CC BY-NC-ND 4.0) licence. Full details of this licence are available at: https://creativecommons.org/licenses/by-nc-nd/4.0/Publication date
1992Notes
A Doctoral Thesis. Submitted in partial fulfilment of the requirements for the award of Doctor of Philosophy of Loughborough University.Language
- en