Improvements in Apparatus for Filtering, Washing, and Drying, suitable for the Treatment of Bicarbonate of Soda.
Year: 1896

page_text: Improvements in Apparatus for Filtering, Washing, and Drying,
suitable for the Treatment of Bicarbonate of Soda.
A communication from abroad from SOLVAY ET CIE., of No. 25 Rue du Prince
Albert, Brussels, Belgium, Manufacturers.
I, WILLIAM LLOYD WISE of 46 Lincoln's Inn Fields in the County of London,
Consulting Engineer and Chartered Patent Agent, do hereby declare the nature of this
invention to be as follows:-
The filtering, washing, and drying of chemical products is an operation which
requires apparatus adapted to each kind of material. Thus, a granular or crystalline
precipitate can be very well treated in an apparatus which would be quite unsuitable
for filtering a gelatinous material, and vice versa.
Now, the apparatus hereinafter described is specially designed for the treatment of
bicarbonate of soda resulting from the ammonia-process, but it is obvious that its use
may be extended to all substances having similar physical properties.
The apparatus comprises a trough in which the substance to be filtered is main-
tained in aqueous suspension. In this trough a drum revolves about a horizontal
axis. The periphery of the drum is formed of a perforated metal sheet or plate,
covered with a fine metallic cloth on which a piece of flannel, which constitutes the
filtering surface, is fastened by suitable means. Inside the filtering drum suction is
produced, by means of which the solid substance in suspension in the trough is caused
to collect on the flannel and the liquid is drawn therethrongh. But with this degree
of simplicity the apparatus operates very imperfectly. After a very short time of
working, the filtering surface (flannel, etc.) becomes obstructed by the particles
attracted to it, and thus the filtering and the drying of the material are rendered
insufficient and irregular.
In order to obviate this drawback, the principle of counter-currents is employed
that is to say, by means of an automatic or other device the production of suction
inside the filtering drum is discontinued, or the suction is prevented from acting
freely, and the liquid contained in the said drum, which is kept intentionally at a
higher level than the external liquid to be filtered, flows back in the opposite
direction through the filtering surface and sweeps away the obstructions.
When this operation of washing by counter-current is automatic, the filtering
surface is maintained at its highest possible degree of purity, and the maximum
results are achieved as regards the quantity filtered and also as regards the drying;
but for this automatic action a more complicated construction of apparatus is
necessary. If, however, the more simple construction is thought sufficiently satis-
factory, it is advisable to promote the drying by another arrangement. The filtered
material is removed from the filter by the operation of a knife, which removes in a
continuous manner a layer of greater or less thickness. The action of this knife
produces a certain hardness of the underlying layer which is unfavourable to
efficient drying. To avoid this, instead of leaving the knife in a fixed position,
it is mounted on a movable arm which imparts a constant motion to the knife.

page_text: Instead of removing a layer of fixed thickness, the knife then scrapes off varying
thicknesses of the Inyer of deposit on the filter, and removes the surface that has
hardened during a preceding rotation.
To obtain the maximum drying effect, more than one scraping knife can bo
employed. Now, the surfaco of the filtered material dries under the action of the
vacuum more rapidly than the internal portion. After a partial revolution, the said
surface is already suitable for removal; but if it is left in place, it prevents the
underlying layer from drying. A first knife, therefore removes the thin dry skin
and a second knife arranged more in the rear removes further on a second and
deeper skin. Several knives may be arranged in this way one behind another.
A second equalizing knife is necessary to give to the layer filtered or to be
filtered a uniform thickness at the moment when it passes out of the trough.
When it is necessary to wash the filtered material, this is done by means of a pipe
arranged parallel to the axis of rotation of the filter and provided with extremely
fine perforations which cause a very uniform rain or spray of water to be discharged
upon tho filtered material.
When the apparatus is arranged for applying the principle of counter-currents in
an automatic manner to the washing of the filtering layer, the interior of the drum
is divided into compartments by means of partitions. These compartments have their
openings arranged side by side in a ring, which rotates in front of a fixed part or
hollow slide face. lis function is to remove or cut off each compartment in succession
from the action of the vacuum during the time that its orifice is situated opposite to
that of the slide face. This slide face communicates through a pipe either with the
atmosphero or with a supply of water under pressure. Therefore each time that an
opening in the ring comes in front of the slit in the slide face, there is produced
in the corresponding compartment a current flowing from the interior towards the
exterior and having the result of defnching the obstructions from the filtering
material.
Dated this 2nd day of March 1896
W. LLOYD WISE,
46 Lincoln's Inn Fields, London, W.C., Charterod Patent Agent.
Improvements in Apparatus for Filtering, Washing, and Drying,
suitable for the Treatment of Bi-carbonate of Soda.
A communication from abroad from SOLVAY ET CIE., of No. 25, Rue du l'rince
Albert, Brussels, Belgium, Manufacturers.
1. WILLIAM LLOYD WISE, of 46 Lincoln's Inn Fields, in the County of London,
Consulting Engineer and Chartered Patent Agent, 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:-
The filtering, washing, and drying of chemical products is an operation which
requires apparatus adapted to each kind of material to be treated. Thus, a granular
or crystalline precipitate can be very well treated in an apparatus which would be
quite unsuitable for filtering a gelatinous material, and vice versa.
Now, apparatus according to this invention as hereinafter described is specially
designed for the treatment of bicarbonate of soda resulting from the ammonia-process,
but it will be obvious that its use may be extended to all substances having similar
physical properties.

page_text: In the accompanying drawings,
Fig. 1 shows a filtering, washing, and drying apparatus partly in end clevation and
partly in cross section and Fig. 2 shows it partly in side elevation and partly in
fongitudinal section.
Figs. 3, 4, 5, and 6 illustrate a modification.
Referring to Figs. 1 and 2, the apparatus comprises a trough A in which the
substance to be filtered is maintained in suspension by an agitator K which is
carried by a pivotted frame G and is oscillated mechanically by any suitable means
such as by an eccentric G' and rod G2 as shown. In the trough is a dram C mountod
to revolve about a horizontal axis B and carried by a hollow axle upon which the
frame G is mounted. The periphery of the drum is formed of a perforated metal
sheet or plate or grid, covered with a fine metallic or wire cloth on which an annular
layer of flannel or other filtering medium which constitutes the filtering surface, is
fastened by suitable means. Within the filtering drum there is set up through
pipes V Vextending through the hollow axle a partial vacuum or suction under the
influence of which the solid substance in suspension in the trough A is caused to
collect on the flannel whilst the liquid is drawn therethrough. But with this degree
of simplicity the apparatus operates very imperfectly. After a very short time of
working, the filtering surface (flannel, etc.) becomes obstructed by the particles
collected thereon and thus the filtering as well as the drying of the material are
rendered insufficient and irregular.
In order to obviate this drawback there is employed according to this invention,
the principle of counter-current-that is to say, by means of an automatic or other
device the suction inside the filtering drum is periodically discontinued and the liquid
contained therein which is kept intentionally at a higher level than the external liquid
to be filtered, is allowed to flow back in the opposite direction through the filtering
surface so as to remove therefrom the particles of obstructing matter. The suction
pipe inlet at X is at a sufficient height above the liquid level in the trough to afford in
the drum the requisite head of liquid for the washing of the filtering medium when
the sucking action is interrupted in the drum. The suction may be interrupted by
closing by a valve or valves the communication between the drum and the pump or
equivalent used to withdraw air from the interior of the drum, as sufficient air will
enter the drun through the exposed surface thereof to then destroy the vacuum
within the drum. When this operation of washing by a counter-current is effected
automatically, the filtering surface is maintained at its highest possible degree of
efficiency, and the maximum results are attained as regards the quantity of material
filtered and also as regards the degree of drying of the material, but for this
automatic, action a more complicated construction of apparatus is necessary, as will
hereinafter be seen from Figs. 3 and 4. In cases where the more simple construction
illustrated in Figs. 1 and 2, is deemed sufficiently satisfactory, it is advisable to
promote the drying of the material by an arrangement of knife or knives, as herein-
after described. The filtered material may be removed from the filter by the action
of a fixed knife E which removes in a continuous manner a layer of material of
greater or less thickness. The action of this knife, if fixed, would, however, produce
a certain degree of hardness of the underlying layer which would be unfavourable to
efficient drying. To avoid this, instead of fixing the knife in position, it may be so
mounted as to have imparted to it by any suitable means a constant motion such that
the knife edge is caused to approach and recede from the filtering surface so as to
remove at different times different thicknesses of material. Figs. 7 and 8 illustrate
one way of operating the movable knife. The frame G which receives oscillatory
motion as before described carries a pivot N that is connected by a rod N' to the
knife E which is able to oscillate about an axis O.
Instead of removing a layer of fixed thickness, it then
thicknesses of the layer of material deposited on the filter, and
that has hardened during a preceding rotation.
scrapes off varying
reinoves the surface
To obtain the maximum drying action the number of scraping knives is increased
in the arrangement shown in Figs. 3 and 4. In fact, the surface of the filtered

page_text: material dries under the action of the partial vacuum more rapidly than the
internal portion. Aller a partial revolution, it is already suitable for removal; but
if it is left in place, it prevents the underlying hayor from drying. A first or
forward knife E is therefore provided to remove the thin skin which is dry, and a
second knife E, arranged in the rear of the first one, subsequently removes a second
and duper skin. Several knives may be arranged in this way one behind another.
In the drawings there is also shown at H an additional or equalizing knife, which
is necessary to give to the layer of material to be tiltorol a uniform thickness at the
inument when it passes out of the trough A.
When it is necessary to wash the littered material, this is done as follows:-
There is arranged parallel to the axis of rotation of the filter a pipe L (Fig. 1)
provided with extremely fine holes through which a very uniform rain or spray of
water is discharged continuously upon the filtered material.
I will now describe the means used for applying the principle of the counter-
current in an automatic manner to the washing of the layer of the filtering material.
The interior of the drum (Figs. 3 and 4) is divided into compartments by menus of
partitions M. There coinpartaments have their openings M' arranged side by side in
a circlu so as to rotate in front of a fixed part or hollow slide face (see Fig. 5)
which serves to remove or cut off each compartment in succession from the influence
of the partial vacuum that obtains within the drum during the time that the
opening Mis opposite to that of the slide face and to phare the particular com-
partment of the drum in communication through a pipe Weither with the external
atmosphere or with a reservoir containing a supply of water under pressure. As
will be seen the arrangement is such that each time that an opening M comes in
front of the opening in the slide face J, there will be produced in the corresponding
compartment a water current flowing from the interior towards the exterior of the
drum and thence into the trough and having for object to detach the particles of
obstructing matter from the filtering material.
In each arrangement. Y is the inlet to the trough A for the liquid to be filtered
and Z is an overflow from the trough.
Having now particularly described and ascertained the nature of the said inven-
tion and in what manner the same is to be performed 1 declare that what I
claim is :-
L. In apparatus of the kind referred to, constructed with a drum wherein a
partial vacuum is applied for filtering and drying purposes, providing for periodical
washing of the filtering meiimm by causing liquid to how fruin the interior of the
drum through the filtering medium.
2. In apparatus of the kind referred to in the preceding claim providing for the
purpose there mentioned a higher water level within the filtering drum than in
the trough into which the drum dips, substantially as described.
3. Apparatus of the kind referral to in Claim I adapted to cause the interior of
the drum or portion thereaf which is partially exhausted of air so as to cansu
filtration and entry of liquid from the trough into the drum to be in an automatic
Banner periodically disconnected from the exhaust. mechanism and charged with
water in such wise that then water will flow out of the drum through the filtering
medium to wash the same substantially as described.
4. The arrangement described and shown in Figs. 3 to 6 inclusive, for washing
automatically successiva portions of the surface of the dram during each rotation.
5. In apparatus of the kind referred to a movable scraping-knife applied
substantially as described for the purpose of obviating excessive hardening of the
filiered layer and the consequent fouling of the filtering surface as set forth.
6. In apparatus of the kind herein referred to the arrangement substantially as
described of two or more scraping-knives so applied as to remove from the filtering
surface successive portions or thicknesses of material deposited thercon as
set forth.
7. In apparatus of the kind refurrel to an equalizing knife adapted to reduce to

page_text: uniform thickness the layer of material on the drum as it passes out of the trough,
substantially as described.
8. The improved filtering, washing, and drying apparatus constructed arranged
and operating substantially as herein before described with reference respectively to-
and shown in Figs. 1 and 2, and in Figs. 3 to 6 inclusive of the drawings annexed.
Dated this 2nd day of January 1897.
W. LLOYD WISE,
46 Lincoln's Inn Fields, London, W.C., Chartered Patent Agent.