Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
~98~
Pressure-chamber grinder
The present invention is concerned with a
pressl~re-c~amber grinder in which the maternal to be
ground, such as talc, bonus, titanium oxide, or soot,
is ground to ultra-ine-grain particles by mans of
grinding gas. The grinder comprises a grinder corollary
of substantially circular section, and the chat or is
provided with a feed opening for the material to be
ground, fed as a gas-tight plug, as well as with tangent
tidally directed nozzles for the grinding gas, pitted
as uniformly spaced on the mantle face or at least on a
part of same. At the opposite end of the grinder, there
is an outlet opening for the material ground, a classic
lien being connected to the said opening, from which classifier the coarse fraction can be returned into
the grinder. As the grinding gas is used compressed
air or water vapour, favorably superheated water vapour.
In an attempt to improve the energy economy
of jet grinders, the first operation has been to replace
the ejector feeder of a conventional grinder by a
so-called plug feeder, whereby energy economies of us
to 10 to 15 per cent have been achieved.
In practice, it has, however, been noticed
that a grinder constructed in view of the ejector feeder
does not operate fully satisfactorily when a plug
feeder is used. This is why, for example, a jet grinder
has been developed whose grinder chanter has the shape
of an oblong box through which the material to be ground
passes, the grinding-gas nozzles being arranged along
two opposite walls of the grinder chamber as directed
so that the grinding-gas jet coming from each nozzle
acts upon the material to be ground in a way both
grinding and changing the direction of flow. The
efficiency of the apparatus is relatively good, because
the material is subjected to the grinding effect at
each nozzle. However, there is the drawback that part
ok
of the material to be ground can flow past the nozzle without
being at all subjected to the grinding effect.
The object of -the present invention is also -to eliminate
this drawback by developing an apparatus in which -the entire
material flow is forced to pass through several grinding zones
without being Abel to by-pass them. The pressure-chamber grinder
in accordance with -the invention is characterized in that it
comprises: a housing defining a space and having a mantle face
extending around the space; a partition wall connected in the
housing dividing the housing space into a regrinding chamber
and a main grinding chamber and extending substantially transfer-
sly to the mantle face; the housing including a portion defining
a regrinding portion having a cross-sectional area larger than
the regrinding chamber, the regrinding portion being connected
to the regrinding chamfer; material feed means connected to
the housing and communicating with the regrinding portion for
feeding a gas-tight plug of material to the regrinding portion;
a plurality of tangentially directed nozzles, uniformly spaced
around the mantle face and connected to the housing for supplying
grinding gas under pressure to the regrinding portion of the
housing; a pair of concentric walls connected to the housing
for separating the regrinding portion from the regrinding
chamber, each of the concentric walls extending axially by at
least one-half an overall height of the regrinding portion;
the housing having an outlet communicating with the main grinding
chamber for discharging at least partially ground material from
the main grinding chamber; at least two level nozzles extending
through the partition wall extending toward a centerline of -the
. - 2 -
.,
main grinding chamber and forming an angle with each other, -the
level nozzles cornmunica-tiny with the regrinding chamber and
with -the main grinding chamber and structured to pass rrlate-rial
with grinding gas from the pre-yrinding chamber to the main
grinding chamber at- supersonic speed, the main grinding chamber
including a grinding zone adjacent an outlet of each of -the two
level nozzles at which material and grinding gas collide at
supersonic speed, the grinding zone spaced from the outlet; and
a classifier connected to the housing outlet and having a
classifier outlet for discharging material and grinding gas
into the grinding zone, the classifier separating a coarse
fraction from a fine fraction of material which has been ground
in the pro and main grinding chambers, supplying the coarse
fraction to the grinding zone and supplying the fine fraction
out of the housing.
The following is a description by way of example of
an embodiment of the invention, reference being had to the
accompanying drawings in which:-
Figure l shows a side view of the apparatus; and
Figure 2 shows a section along line A-A in Figure 1.
The pressure-chamber grinder shown comprises a grinder
chamber 1 of substantially circular section, which is provided
with a feed opening 3 for the material to be ground, fed as a
gaslight plug, and whose opposite end is provided with an outlet
opening 5 for the material ground. Tangentially directed
grinding-gas nozzles 7 are arranged as uniformly spaced around
-the entire circumference of the mantle face over at least a part
pa -
I
of the mantle face 6 of the! grinder chamber 1. The
oblong grinder chamber is, by means of a partition
wall 8, divided into a regrinding chamber 9 and a
grinding chamber 10 proper, which chambers are inter-
connected by means of at least two Level nozzles forming an angle with each other. The material-gas
jets rushing through the nozzles at a supersonic speed
intersect each other in the grinding chamber 10 placed
immediately at the outlet side of the Level nozzles 11,
at which point a zone of collision of the material
particles to be ground is formed. The coarse fraction
coming from the classifier 17 connected to the outlet
opening 5 of the grinding chamber 10 is returned to
this zone.
In view of efficient operation of the Papa-
fetus, it is essential that the collision zone is
formed immediately in the proximity of the outlet side
of the Level nozzles 11 in order that the speed of the
gas flows should not have time to be lowered. The
location of the collision point and the extent of the
collision zone can be affected by means of the angle
between the Level nozzles 11, which angle may vary
within the limits of about 60 Tao, whereat angles
within the range of about 90 to 120 have proved most
advantageous.
The feed opining 3 may be located at any
place near one end of the grinder chamber 1, preferably
close to the mantle face 6, so that the material to be
ground, fed into the grinder chamber by means of the
plug feeder, is immediately subjected -to the action of
the grinding-gas flows coming from the nozzles 7.
One should aim at the circumstance that the
inlet angle between the material-gas jets discharged
through the Level nozzles 11 is such that a favorable
material circulation is produced in the grinder.
If necessary, it is possible to connect two
or more grinder units in series. In such a case, a
.,
requirement is that a grinding gas of sufficiently high
pressure is available in order that the speed of the
material-gas jet passing through each Level nozzle 11
should become supersonic.
At least a part of the marltle face 6 of the
grinding chamber 10 provide with the outlet opening 5
is conical so that the cross-sectional area of the
grinding chamber 10 becomes smaller towards the outlet
opening 5, whereat the speed of the material-gas flow
rushing out of the grinder becomes higher.
In order to intensify the material-gas flow
taking place in the regrinding chamber 9, it is
advantageous to shape each partition wall 8, in the
direction of inlet of the flow either conical or convex,
whereat the feed openings of the Level nozzles 11 placed
in the partition wall 8 may be placed entirely at the
face of the partition wall 8. When the partition walls
8 are shaped in this way, unnecessary recesses and pro-
jetting portions are avoided at the same time, which
2Q recesses and projections would be subject to intensive
wear
According to a preferred embodiment, the end
of the grinder chamber 1 placed next to the feed opening
3 is provided with a regrinding portion 14, whose
cross-sectional area is larger than that of the rest of
` the grinder chamber 1 and whose mantle face is provided
with tangentially directed grinding gas nozzles 7. The
feed opening 3 of the grinder is placed at the proximity
of the mantle face of the regrinding portion 14. In
the solution shown in Fig. 1, the feed opening 3, to
which the feeder pipe coming from the plug feeder and
provided with a screw conveyor 4 is connected, is
located in the end wall 2. It is recommended that the
material to be ground is, before it is fed into the
regrinding portion 14, by means of a separate grind-
ing-gas jet, accelerated to the same speed as the speed
of the material-gas f low circulating in the regrinding
portion 14.
To each end wall 2, 15 of the regrinding
portion 14, at least one partition wall 6, 12 is attached
which is parallel to the circumference and which art
lion walls are concentric and have a height of at least
half the overall height of the regrinding portiorl 14
so that they are slightly overlapping each other. The
junction of these partition walls 6, 12 is to operate
as some sort of obstacle for the material flow fluidized
in the pre-grindirlg portion 14, whereat the regrinding
and classification taking place in this portion are
intensified.
In order to simplify the entire grinder Papa-
fetus, it is advantageously possible to place the
classifier 17 in the regrinding chamber 9 so that its
outlet end for the coarse fraction passes through the
partition wall 8 at the centre point of this wall and
extends to the zone of collision of the material-gas
jets rushing through the Level nozzles lo so that the
coarse fraction coming out of the classifier 17 is
immediately subjected to a new yrindiny action. The
classifier 17, which is preferably of the cyclone type,
is via a connecting pipe 16 connected to the outlet
opening 5 of the grinding chamber 10, from which the
round material-gas flow is passed into the classifier
` . 17 tangentially. In the classifier 17, the coarse
fraction is separated from the rest of the material
flow by means of the centrifugal force and returned
into the said collision or grinding zone. The fine
I fraction is passed through an outlet pipe 18 provided
at the other end of the classifies 17 possibly into a
subsequent pressure-chamber grinder 7 operating at a
lower pressure, or straight into a product tank.
By providing the tangentially directed
grinding-gas nozzles 7 only at the mantle face of the
regrinding portion 14, the said nozzles 7 being con
netted to the grinding-gas distributor beam 13 sun-
fj
rounding the regrinding portion 19, an advantageously
operating grinder is obtained into which high-pressure
grinding gas it fed exclusively through the said
nozzles 7.
The grinder chatter 1 may be positioned
either vertically or horizontally, depending on the
type of classifier 17 used and on the location of the
classifier.
In connection with a pressure-chamber grinder
yin accordance with Fig. 1, as the grinding gas is pro-
fireball used superheated water vapour at a pressure of
at least 7 bars, the vapour being fed into the prey
grinding portion 14 through the nozzles 7 and a post-
live pressure of at least 3 bars being maintained in the
regrinding portion 14 by means of the said vapour.
In the subsequent grinding chamber lo into which the
material-gas flow rushes at a supersonic speed through
the Level nozzles 11, appropriately a positive pressure
of about 0.05 to 0.1 bar is maintained, the material-gas
mixture being passed from the said chamber to the
classifier 17.
It is evident that the various details of
the pressure-chamber grinder may be designed in many
different ways within the scope of the invention.
