Abstract
M.Ing.
Fouling of suspended solids on piping and equipment causes severe operating and
maintenance problems in process, water treatment and miningrelated plants.
In the SASOL environment fouling related problems are mainly experienced on
equipment operating in process cooling water services. Suspended solids appear in the
form of activated sludge in the cooling water system and the solid particle sizes are
usually submicron in size. Conventional solid liquid separation techniques like
centrifuging, sedimentation, filtration, etc. could up to this stage not be applied
successfully to remove the finest solids from the process cooling water system.
The possibility to separate solid liquid suspensions by means of acoustic energy was
investigated. The theoretical principles of acoustic waves, especially standing waves,
were studied and explained. A theoretical model indicates that separation of solid/liquid
suspensions can be obtained virtually immediately after acoustic energy is applied.
Theoretically the size and frequency of a tipical acoustic transducer can be calculated
for a specific application.
Based on theoretical calculations and findings, an experimental setup was prepared to
carryout experiments on different suspensions. A control suspension made-up of water
and powder, of Yttlich the particle sizes were approximately 10 pm, was prepared and
exposed to a standing acoustic wave. Separation was achieved successfully. Follow-up
experiments were carried out to establish the optimum conditions to which separation
could be achieved. Different flow velocities were tested as well as different power
inputs.
The best separation was achieved with the lowest flow rate of 2.5 mils and the highest
available voltage of 12 Volt. These conditions were not only used to separate a control
suspension but also in a real situation where it was attempted to separate suspended
solids from the cooling water system. The attempts were unsuccessful. Additional
experiments were also done on ash water and cooling water blowdown which also
failed.
The failure of effective separation of the process cooling water suspensions is due to
the extremely small sizes of the solid partides in suspension. Greater energy input than
was available for this project, is required as the particle sizes decreases. Provision
needs to be made for all particle sizes to achieve effective results.
The separation of solid liquid suspensions is achievable with the aid of acoustic energy.
The physical properties of the suspension however determines the size and magnitude
of the separating equipment. A proposal for the implementation of a full scale acoustic
separation system is given. The proposal comprises of a parallel system to ensure
continuity of the cooling process.