Classifying – separating – and assorting solids – Fluid suspension – Liquid
Patent
1998-07-30
2000-12-05
Walsh, Donald P.
Classifying, separating, and assorting solids
Fluid suspension
Liquid
209 3, 209724, B03B 528, B03B 100
Patent
active
061554294
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention concerns a process for centrifugal separation of materials contained in a liquid slurry. More specifically, the invention concerns such a process wherein the slurry includes a light material having a specific gravity that is less than the liquid carrier and a heavy material having a specific gravity that is greater than the liquid carrier. A gas, preferably air, is injected into the slurry prior to feeding the slurry to a hydrocyclone, resulting in an enhanced degree of separation of the light and heavy materials.
2. Description of Related Art
Hydrocyclones have been employed for many years to separate solid materials of differing specific gravity from liquid slurries. Separation of light particles from slurries has been enhanced in the past by adjusting the specific gravity of the liquid carrier by addition of salts. However, this results in increased cost and environmental concerns.
In the paper industry, a variety of reverse centrifugal cleaning methods have been used to remove good paper fibers from contaminants of closely similar or lower specific gravities. A discussion of reverse centrifugal cleaning is provided in Seifert et al., U.S. Pat. No. 4,155,839 and Bliss U.S. Pat. No. 4,565,443.
It has been found that enhanced separation of light and heavy particles from a slurry containing light particles having a specific gravity that is less than the liquid carrier and heavy particles having a specific gravity that is greater than the liquid carrier is achieved by injection of air into the slurry upstream of the hydrocyclone. The process does not require modification of the hydrocyclone apparatus and, as a result of the increased efficiency of separation of the heavy and light components, reduces the number of passes required to achieve a high degree of separation.
SUMMARY OF THE INVENTION
The process of this invention relates to separating a first material from a second material in a hydrocyclone, comprising the steps of: a) providing a slurry of the first and second materials in a liquid carrier, wherein the liquid carrier has a specific gravity less than the specific carrier of the first material and greater than the specific gravity of the second material; b) injecting a gas into the slurry to aerate the slurry prior to feeding the slurry into the hydrocyclone; c) feeding the aerated slurry into the hydrocyclone to separate the first material from the second material; and d) collecting the separated first material and second material.
Preferably, air is used as the gas which is injected into the slurry and the liquid carrier is water. In one embodiment, the first material comprises a polyamide and the second material comprises polypropylene. Preferably, the polyamide is either nylon 66 or nylon 6.
DESCRIPTION OF THE INVENTION
The process of the current invention is useful in the separation of solid materials contained in a liquid slurry wherein one of the materials has a specific gravity that is less than that of the liquid carrier and another of the materials has a specific gravity that is greater than that of the liquid carrier. The process involves injection of a gas into the slurry prior to feeding the slurry to a hydrocyclone.
Any gas may be used which does not react with the slurry components. A preferred gas is air, which is generally inert and readily available at low cost. The gas is introduced into the slurry upstream of the hydrocyclone. Air may be conveniently introduced via a pump that is used to pump the slurry to the hydrocyclone. However, the resulting cavitation generally causes premature deterioration in pump performance. Alternate methods for introducing air into the slurry include use of static or dynamic mixers upstream of the hydrocyclone.
The air should be introduced at sufficient flow rate to aerate the slurry. It is important that the air is well dispersed in the liquid stream in very small bubbles when the slurry enters the hydrocyclone, hence the need to inject into the pump or the use of in
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E. I. Du Pont de Nemours and Company
Schlak Daniel
Walsh Donald P.
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