Classifying – separating – and assorting solids – Fluid suspension – Gaseous
Reexamination Certificate
1999-03-23
2001-03-20
Nguyen, Tuan N. (Department: 3653)
Classifying, separating, and assorting solids
Fluid suspension
Gaseous
C209S143000, C209S149000
Reexamination Certificate
active
06202854
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention generally relates to classifiers used for separating relatively fine particles from a particulate material, such as sand used in the road construction industry. More particularly, this invention is directed to an air classifier having a compact construction with reduced energy requirements.
2. Description of the Prior Art
Sand used in the construction of asphalt and concrete roads is sized to provide an appropriate particle size distribution which excludes extremely fine particles (dust) that are undesirable for the final asphalt or concrete mix. Removal of the fine particles is often performed after the sand has been processed through a crusher and then sized. Typical methods for removing fine particles from sand and other particulate matter include placing the sand on a wash screen, and then flowing water over the screen to carry finer particles, e.g., −200 mesh (less than 75 &mgr;m) through the screen. The resulting sand slurry is then pumped to a settling pond. The sand remaining on the screen typically has a moisture content of about 8%, and therefore requires drying before being added to an aggregate mixture for use in the production of asphalt or concrete.
Though widely used, wet screening processes have several disadvantages. The use of water can pose a problem if the construction site is in an arid area, and the necessity to dry the processed sand adds undesirable equipment and fuel costs. The environmental impact of settling ponds is also undesirable. Therefore, what is needed is a process and apparatus for removing fine particles from sand that is suitable for use in such applications as asphalt and concrete road construction. In addition to eliminating the requirement for water, a suitable apparatus would also preferably have minimal energy requirements and provide a compact operating unit for ease of transportation.
SUMMARY OF THE INVENTION
The present invention provides an apparatus and process for removing fine particles from sand and other particulate material. The apparatus is generally an air classifier that combines gravitational and aerodynamic forces to classify sand at 10 mesh and finer. According to this invention, the classifier is configured to have a vertical passage centrally located at the vertical axis of an annular-shaped passage. The vertical passage is defined by a plurality of inclined vanes that are vertically separated by gaps. The sand or other particulate matter to be sized is introduced through an inlet at or near the top of the annular-shaped passage, and then flows downwardly through the annular-shaped passage around the vertical passage. Air is flowed substantially horizontally into the annular-shaped passage and radially inward toward the vertical passage and the vanes thereof so that, as the particulate matter flows downwardly through the annular-shaped passage, the air separates a relatively finer constituent of the particulate matter from a relatively coarser constituent of the particulate matter. More specifically, the airflow is regulated so that the coarser constituent is allowed to continue to flow downward out of the annular-shaped passage, but at least a portion of the air causes the finer constituent of the particulate matter to flow upwardly through the gaps between the vanes into the vertical passage, and then downwardly through the vertical passage and eventually out of the vertical passage. Thereafter, the finer constituent can undergo any further separation processing, such as with cyclones and/or fabric filter collectors.
According to the above, the efficiency of the process of this invention is promoted as a result of air being introduced into the annular-shaped passage from essentially the entire perimeter of the passage, and flowed radially inward toward the vertical passage. With this arrangement, a relatively large area is provided for processing the sand for a given vertical drop of the sand. Another advantage is a relatively low energy requirement for expelling the finer constituent from the classifier, which is achieved because the finer particles are immediately redirected downward through the classifier after passage through the vanes, such that their flow out of the classifier is assisted by gravity. Additional benefits of the invention are derived from eliminating the prior art use of water, which may not be available at the processing location, would necessitate the use of a settling pond, and yields an aggregate that requires drying. Finally, the classifier is able to remove dust and other fine constituents of a particulate matter immediately downstream from a crusher, without any intervening sizing operation of a type conventionally required by the prior art. As a result, particulate emissions are reduced and subsequent sizing and dust suppression is simplified.
Other objects and advantages of this invention will be better appreciated from the following detailed description.
REFERENCES:
patent: 4038178 (1977-07-01), Hukki
patent: 4055487 (1977-10-01), Moori
patent: 4151074 (1979-04-01), Mohri
patent: 4252642 (1981-02-01), Mohri
patent: 4307242 (1981-12-01), Shah et al.
patent: 4885832 (1989-12-01), English
patent: 5024754 (1991-06-01), Patzelt et al.
patent: 5511668 (1996-04-01), Keuschnigg
patent: 3730382 (1989-03-01), None
P.W. Atkins,Physical Chemistry, Third Edition (1986), pp. 770-772, 784-785.
Krieser Clarence
Miller James
Marsulex Environmental Technologies, LLC
Nguyen Tuan N.
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