Liquid purification or separation – Processes – Making an insoluble substance or accreting suspended...
Patent
1989-11-20
1992-11-17
Silverman, Stanley S.
Liquid purification or separation
Processes
Making an insoluble substance or accreting suspended...
210738, 210748, 209 1, 209155, 422 20, 422128, 20415715, 204193, C02F 136
Patent
active
051640945
DESCRIPTION:
BRIEF SUMMARY
The invention relates to a process for the flocculation, precipitation, agglomeration or coagulation of substances or microorganisms present in a liquid in a dissolved, colloidally dissolved, suspended or emulsified state and for separating said substances or microorganisms from said liquid, wherein the liquid charged with the substances or microorganisms to be separated is subjected to the field effect of ultrasonic waves which cause an accumulation of particles to be separated in the vibration node regions or vibration bulge regions of the ultrasonic wave and the particles thus accumulated are separated from the liquid, such separation being effected particularly by sedimentation.
In order to separate suspended particles or microorganisms, which may be of submicroscopic dimensions, from liquids by means of sedimentation or filtration within a reasonably short time, these particles or microorganisms have to be combined into larger particles or agglomerated with larger particles. Coagulation processes are made possible in a disperse system by reduction of the electrostatic surface charge of the particles (destabilization) and by supplying kinetic energy (transport).
A process of the type initially mentioned is known wherein particles suspended in liquids are flocculated by subjecting the respective liquid to an ultrasonic wave field and the flocculated material is then separated from the liquid (U.S. Pat. No. 4,055,491).
It is an object of the present invention to provide a process of the type initially mentioned wherein liquids, in particular water, for the purpose of purification, as well as suspensions for the extraction and recovery of raw materials and microorganisms, are treated in the most effective manner in a simple and energy-saving process. Another possibility is the recovery of fine-grained carbon from carbon-containing suspensions, even if said suspensions also contain other substances.
It is known that sound radiation pressure conveys the particles to the velocity bulge surfaces of the ultrasonic field, meaning those sites where the deflection of the water molecules is highest. If the ultrasonic frequency exceeds a determined cutoff frequency fo, the particles follow the vibration of the water only minimally. This means that there is maximum relative movement between the particles and the oscillating water. The water in molecules periodically pass the velocity bulge surfaces at right angles at maximum sound velocity. The particles collecting in the velocity bulge surfaces follow the vibrations of the water only minimally and thus cause a reduction of the cross section of the flow path. The velocity of the vibrating water thus has to increase between the particles, forcibly resulting in a local reduction of pressure between the particles at retention of total energy. This relative low pressure between the particles causes their mutual attraction which is used according to the invention for the coagulation of the particles.
The process according to the invention of the type initially mentioned is characterized in that the liquid charged with substances or microorganisms is subjected to one or several fields of stationary ultrasonic waves, the ultrasonic frequency f being greater than one seventh of the cutoff frequency fo, the range above half of the cutoff frequency fo being preferred and fo being defined as follows: and R is the effective particle radius in m; in spherical particles, the effective particle radius R is equal to their radii; for particles of other shapes, R is the radius of that sphere of the same material countering the oscillating liquid with the same flow resistance. These measures are well suited for achieving the aforementioned object. A rapid coagulation or agglomeration of the substances contained in the liquid is achieved with low energy requirement. As a result, the provided selection of ultrasonic frequency and exposure to ultrasonic waves in a stationary wave field exert a very favorable influence.
The formation of stationary ultrasonic wave fields can be effected by
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McCarthy Neil M.
Silverman Stanley S.
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