Solid material comminution or disintegration – Apparatus – Including means applying fluid to material
Reexamination Certificate
1999-12-15
2002-09-03
Ostrager, Allen (Department: 3725)
Solid material comminution or disintegration
Apparatus
Including means applying fluid to material
C241S056000, C241S061000, C241S080000, C241S082000
Reexamination Certificate
active
06443376
ABSTRACT:
TECHNICAL FIELD
This invention relates generally to improvements in pulverizers, including the separation of coarse particles from fine particles, an improved free air purging mechanical seal assembly provided between the classifier and housing, free air cooling of the drive shaft, and a feed distributer which facilitates the drying of wet particulate material.
BACKGROUND
Pulverizing of dry materials is practiced today using hammer mills, impact attrition mills, ball mills, and others outfitted with internal classifiers that separate the coarse and the fine particle fractions. Problems with these mills include inadequate internal circulation of material flow thereby causing excessive grinding, reduced classifier efficiency, lower throughput, and wearing of certain parts of the mill.
A typical impact attrition pulverizer, shown in
FIG. 1
, comprises vertically oriented cylindrical housing
2
provided with air inlet
3
, feed inlet
4
, and product outlet
6
—coordinated with a suction device (not shown), coarse particle exit tube
8
, and classifier
10
. Conventional classifiers typically comprise a vaned wheel that generates a centrifugal air flow. A problem with the type of classifier shown in
FIG. 1
is inefficient particle separation. More sophisticated classifiers capable of higher particle separation efficiency have been developed, but with these, particle buildup between the classifier and the housing necessitates frequent disassembly and cleaning and can cause mechanical failure.
Housing
2
has inner liner
28
that is preferably provided with a surface that facilitates pulverization, such as a plurality of ridges that extend parallel to the center line of housing
2
. A drive shaft
24
is vertically oriented along the center line of housing
2
. Drive shaft
24
coaxially supports rotor
30
and classifier
10
. Rotor
30
preferably comprises a plurality of rotor segments
32
. A plurality of spaced beater plates
34
reside around the circumference of rotor segments
32
, such that the foremost edges of beater plates
34
extend radially toward inner liner
28
and align vertically with drive shaft
24
. The rotor segments
32
may be separated from each other by partition disks
36
. A particle pulverizing domain
38
is defined between beater plates
34
, inner liner
28
, as well as in the pocket formed by the beater plates and the partition disks.
During operation, a rotating device (not shown) rotates drive shaft
24
at high speed and the suction device at product outlet
6
pulls external air through the apparatus from air inlet
3
and feed inlet
4
. The material to be processed is introduced at feed inlet
4
and is wafted through particle pulverizing domain
38
. Within particle pulverizing domain
38
, the periphery of rotor
30
(i.e., the edges of beater plates
34
) and inner liner
28
, cooperate to grind and pulverize the substrate material. The material is ground by impact with beater plates
34
and inner liner
28
, as well as attrition between particles.
Classifier
10
allows the finer particles to pass through toward product outlet
6
and the coarse particles are rejected and directed toward the inner liner
28
by the centrifugal force generated by the classifier and thrown out from the coarse particle exit tube
8
.
It is undesirable to permit over-sized particles to be discharged with the desired fine particle material at the product outlet. Such particles are regarded as contaminants and lower the quality of the product. It is common practice to remove coarse particles from the classifying zone and recycle them as tailings for further reduction, for example, via the coarse particle exit tube
8
shown in FIG.
1
. But this arrangement is insufficient, especially for ultra-fine grinding. In the conventional device described above, removal of the coarse particles relies solely on the momentum of the coarse particle induced by the centrifugal force from the classifier. Thus, the coarse particles, rejected by the classifier, tend to accumulate around the classification zone and eventually leads to clogging and malfunction.
It is especially important to reliably discharge the coarse particle fraction if it includes a contaminant that is harder than the material being ground. It is well known that a small percentage of hard abrasive contaminants can greatly reduce the capacity of the pulverizing apparatus. Such contaminants also make it difficult achieve stringent top-size requirement. For example, limestone, depending on its source, may have a small percentage of alumina or magnesia scale. Since these particles are very hard, they cannot be fully pulverized and they will either continuously re-circulate through the pulverizer or be discharged with the fine particle fraction. Thus, improvements in extraction and grinding of the coarse particles are needed.
It is well known in the art that conventional pulverizers can be used to dry wet particulate matter slurries. In the adaptation of a pulverizer for drying applications, a wet material suspension is dispersed in the pulverization domain and mixed with hot turbulent air. The hot air is introduced into the pulverizer from air inlet
3
.
Like other drying processes, under a given capacity, the higher the air temperature, the less air flow required. A problem with adapting conventional pulverizers for drying is overheating of the area where the drive shaft meets the lower bearing member. The overheating is caused by rotational friction and the hot inlet air. Thus, with conventional pulverizers in drying applications, there is a limitation on inlet air temperature and extra oil-cooling arrangements are required to prevent overheating of the area where the drive shaft meets the lower bearing member.
In a drying application, the wet substrate suspension should be introduced directly onto the rotor. This is necessary because a high degree of initial dispersion—provided by the action of the high speed rotor
30
—is required for drying. However, the drying efficiency can further be enhanced by a proper design of the feed intake nozzle.
The present invention is directed to an improved device that alleviates these problems and provides features herebefore unknown in the art.
SUMMARY OF THE INVENTION
The invention generally relates to a particle pulverizing apparatus having a cylindrical housing oriented along a vertical axis. This housing is typically provided with an inner liner, an inlet, an outlet, and a rotatable drive shaft oriented along the vertical axis. The drive shaft supports a rotor having an outer diameter such that a particle pulverizing domain exists between the inner liner and the rotor, as well as in the pocket formed by the beater plates and the partition disks.
In one embodiment, a coarse particle extraction assembly is provided. This assembly includes an extraction port in the housing, a pipe positioned adjacent the extraction port and including an air nozzle therein. During operation, the air nozzle discharges an air jet into the pipe to generate a vacuum at the extraction port to extract the coarse particles from the housing through the extraction port. This coarse particle extraction system efficiently removes the coarse particle fraction of the particulate material for collection or further pulverization.
Advantageously, the pipe is configured and dimensioned to provide a non-linear path for the coarse particles, and the air nozzle is positioned such that the air jet can convey and accelerate the coarse particles. Preferably, an impact plate is positioned downstream of the air nozzle for directing the extracted coarse particles back into the housing. If desired, a venturi can be positioned between the air nozzle and the impact plate to guide return of the extracted coarse particles. As used herein, a venturi comprises a tube with a convergent section, a venturi throat, and a divergent section.
In another embodiment, the coarse particle extraction system may include an acceleration chute, positioned between the air nozzle and the impact plate for further accelerating and direc
Huang Ching-Chung
Lin Qingsheng
Voorhees Robin T.
Hong William
Hosokawa Micron Powder Systems
Ostrager Allen
Winston & Strawn
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