Improvements in or relating to Filter Presses.
Year: 1899

page_text: Date of Application, 27th Mar., 1889-Accepted, 13th May, 1899
Improvements in or relating to Filter Presses.
I, MAX ZAHN, Manufactory Director, of Artern, in Thuringia, Germany, do
hereby declare the nature of this invention and in what manner the same is to be
performed, to be particularly described and ascertained in and by the following
statement:
It is well known that the cakes or compact deposit formed by precipitates or
solid matter are apt to be rent and cracked during the process of filtering in
filter-presses. Besides, the cakes separate from the sides of the containing
vessel, thus producing free spaces between the cake and the sides of the vessel. It
is therefore, very difficult to deprive such precipitates of the accompanying liquor
or ley as the rinsing liquid rapidly passes through the said rents, fissures and free
spaces without producing the desired effect.
To avoid this drawback, compressed air or gas is, according to the present inven-
tion caused to strike or act upon the precipitated cake from one side before its
treatment with the rinsing liquid. This sudden air shock acts as a piston on the
whole surface of the cake, compresses the strata of the precipitate and drives the
cake or deposit against the sides of the chamber thus closing up all fissures and
empty spaces in it or between it and the sides of the frame.
The inner sides of the frame or chamber are so constructed as to become narrower
conically in the direction of the air current, whereby the cake or deposit becomes
pressed or compacted into a narrower space.
The accompanying drawing of a filtering device illustrates this process,
Figures I and II are horizontal sections on the line CD and A B respectively of
Figures III and IV of several frames and plates as arranged in a filter press.
Figure III shows a frame, and
Figure IV a plate in plan of the press in question.
The frames and plates are arranged alternately in the press and are provided
with orifices or passages S¹ S and L (Figs. III and IV) which passages when the
press is fitted up, form conduits which are likewise lettered Sand L (Figs. I
and II).
The passages S and S2 contmunicate with the interior spaces of the
frames R R R R by means of passages s¹²yyü yʊ gỉ så.
The alternate plates are provided with taps and nozzles respectively. Thus
the plates PP3 are provided as shown in the drawing, with taps h¹h and the
plates P P with nozzles t¹². These plates which are provided with taps-accord-
ing to the drawing the plates PP3 communicate with the passage L by means
of the passages. The plates and frames are separated from each other by the
filter cloths 136 27.
The operation of the press is as follows: -The liquid to be filtered enters by
means of the conduits S1 S2 and passages s¹³ ³ ³ ³ ³ ³ ³ into the interior of the
frames R R R³ R. The precipitate or solid matter is deposited or retained there,
while the liquid free from the solid matter, passes through the several filtering
cloths into the free spaces of the plates P¹ P³ ³ P¹ leaving the apparatus by way
of the taps and nozzles.
33

page_text: the liquid to be filtered is closed, as also are the passages S'S. The taps are
also closed and a valve in the passage which communicates with the conduit L is
opened through which valve compressed air or compressed gas enters into said
conduit L. The air, passing through the passages into the interior free space
of the plates P1 P2 presses on the cakes contained in the frames R¹ R² R³ R* in the
direction shown by the arrows, packing or condensing the same more closely and
against the inner sides of the frames, which are so constructed that the spaces grow
narrower in the direction of the current of air, with a view of increasing the effect
of the pressure.
The cakes having thus been prepared for the subsequent rinsing or lixiviation the
rinsing liquid is caused to operate on them. This may be effected by introducing
the liquid through the conduit L and the passages into the interior of the
plates PP3 whence the liquid is caused to pass through the cakes in the direction
of the arrows, into the free spaces of the plates PP leaving the latter by way of
the nozzles. In this case the rinsing liquid must be a clear liquid inasmuch
as otherwise the filtering cloths would have to be changed after every filtering
operation.
The use of clear liquids, however, in often accompanied by very serious draw-
backs as for instance when the precipitate or deposit is somewhat soluble in the
liquid employed which in such a case is apt to dissolve away or form holes in the
cakes. In such a case the use of a clear liquid is avoided and a liquid is employed
which holds suspended in it the solid particles of a substance the same as that of
which the precipitate or deposit consists or of a substance having no effect on
the cakes.
Such a liquid is not introduced through the conduit L but through the
conduits SS and passages &³¹³ directly into the frames. The cakes
having been separated from the respective filtering cloths through which the com-
pressed air was applied, i.c., from the filtering clothes as represented in the
drawing a free space is formed between the cakes and the said filter
cloths which free space is now occupied by the rinsing liquid, whence it is pressed
through the cakes, as indicated by the arrows. The solid matter, suspended in
the rinsing liquid serves to fill up any holes caused by removal of portions of the
deposit produced by the dissolving nature of the liquid and consequently the use
of such a rinsing liquid containing solid matter in suspension in the treatment of
cakes of a corresponding nature is sometimes alone sufficient without the previous
application of compressed air to secure the required result.
The process just described is of special use in cases when the cakes contain, two
or more substances, of which it is desirable to eliminate one or more by means of a
solvent during the filtering process itself.
Let us assume there are two substances A and B in the precipitate or deposit of
which substance A is to be eliminated. If a clear liquid which is a solvent of A
is passed through the cakes, it forms holes or fissures, by the dissolution of the
body A, through which holes and fissures the liquid would rapidly pass without
having an opportunity of dissolving the body A contained in the other portions
of the cake.
According to the present invention, however, the solvent for the substance A is
mixed with an appropriate quantity of the body B which is kept in suspension, and
the liquid so charged is passed through the frames of the apparatus. In places
from which the body A has been removed through the solvent action of the liquid
particles of the body B are deposited. Thus no holes and fissures are formed, or
are filled up as soon as formed: the cakes remaining in a solid unbroken mass,
which is thus evenly permeated by the liquid with the result that the whole of the
substance A is removed from the precipitate.
Having now particularly described and ascertained the nature of my said
invention, and in what manner the same is to be performed, I declare that what
I claim is:-
1 A process for the production of uniformly comunadal
1

page_text: press in which compressed air or gas is applied to the cakes in the press, previous to
lixiviation, followed, if desired, by the application of a lixiviating liquid containing
solid matter in suspension substantially as described.
2. A filter press for use in carrying out the process described characterized by the
inner surfaces of the frames of the filter press being conically formed in the direction
of the air inlet for the purpose of compacting the cake substantially as described.
3. A modification of the process described for the purpose of separating two or
more substances contained in the fluid to be filtered, in which a liquid, consisting
of a solvent of the body that is to be eliminated having particles of the substance
which is to be retained in the press, suspended in it, is introduced into the filter
press and passed through the deposit, substantially as described.
4. A filter press substantially as described or illustrated in the accompanying
drawings.