IMPROVEMENTS IN THE METHOD OF EFFECTING CONCENTRATION AND CRYSTALLISATION OF SODA SOLUTIONS, AND APPARATUS FOR THAT PURPOSE
Year: 1881

page_text: LETTERS PATENT to John Imray, of No. 28, Southampton Buildings, in the
County of Middlesex, for an Invention of "IMPROVEMENTS IN THE METHOD
OF EFFECTING CONCENTRATION AND CRYSTALLISATION OF SODA SOLUTIONS,
AND APPARATUS FOR THAT PURPOSE." A communication from abroad by
Jules Buffet, Engineer, of Paris, France.
PROVISIONAL SPECIFICATION left by the said John Imray at the Office
of the Commissioners of Patents on the 7th April 1881.
JOHN IMRAY, of No. 28, Southampton Buildings, in the County of Middlesex.
"IMPROVEMENTS IN THE METHOD OF EFFECTING CONCENTRATION AND CRYSTAL-
LISATION OF SODA SOLUTIONS, AND APPARATUS FOR THAT PURPOSE." [A com-
munication from abroad by Jules Buffet, Engineer, of Paris, France.]
This Invention relates to the concentration of soda solutions by evaporating in
vacuo in successive stages so as to separate the carbonate from the caustic alkali,
and to effect crystallisation of the former by means of apparatus arranged to
operate continuously without requiring the calcination and second solution and
concentration that are usually employed. For this purpose weak solutions of
carbonate having a strength of from 16° to 20° Beaumé after purification are treated
in close vessels in which is maintained such reduction of pressure that the solution
evaporates at a temperature not exceeding 130° Fahrenheit, till it is concentrated to
36° Beaumé, which is about the limit of its possible concentration, the liquor is
then run off and crystallised. When caustic solutions are dealt with at a strength
of about 28° Beaumé they are concentrated in vacuo to about 33° Beaumé, up to
which point they do not deposit carbonate. They are then run into evaporating
vessels provided with extensions downwards, forming wells in which the carbonate
is deposited, and whence it is from time to time withdrawn by openings at the
bottom and delivered into trucks run under these openings. The liquor remaining
is a solution of caustic soda, which can then be concentrated and treated as usual.
The concentrating apparatus for continuous working consists of four vessels, all
subject to steam-heat and vacuum. The first two are employed alternately to
receive the solutions, which after sufficient concentration are run into either of the
other two which have wells for the carbonate, these also being employed alternately
for the farther concentration and deposit of the carbonate. The vessels are provided
with the necessary pipe connections and gauges, all the parts being made of iron,
so as not to be acted on by the alkali.

page_text: SPECIFICATION in pursuance of the conditions of the Letters Patent filed
by the said John Imray in the Great Seal Patent Office on the 7th October
1881.
JOHN IMRAY, of No. 28, Southampton Buildings, in the County of Middlesex.
"IMPROVEMENTS IN THE METHOD OF EFFECTING CONCENTRATION AND CRYSTAL-
LISATION OF SODA SOLUTIONS, AND APPARATUS FOR THAT PURPOSE." A com-
munication from abroad by Jules Buffet, Engineer, of Paris, France.
The evaporation of soda solutions, whether for the production of soda crystals
or of soda, is at present effected in the open air with heating to a greater or less
extent.
This Invention relates to the concentration of these solutions by evaporation
in vacuo, whereby this part of the manufacture of soda is greatly simplified and
⚫ improved.
The processes actually in use for the manufacture of soda crystals include the
use of either weak or strong solutions.
The weak solutions only have about 18° Beaumé; they have to be partially
evaporated, and the salts obtained calcined in order to oxidize the sulphurets;
they are then again dissolved, producing liquors of a maximum of 34° Beaumé, and
on cooling crystals of soda are produced.
These operations are greatly simplified by evaporation in vacuo; this new mode
of evaporation permits of the immediate concentration of the weak liquors into
liquors of 36° Beaumé for crystals, thereby avoiding the calcination. Moreover,
and this is a very important point, the liquors are only heated to a temperature
considerably under 212° Fahr., namely, a temperature approaching 100°, with
which the maximum degree of solubility of carbonate of soda corresponds. The
liquors are therefore near their maximum degree of concentration, for with a
vacuum of 27.5 inches of mercury in the evaporating pan, ebullition takes place at
about 122° to 130°. By the evaporation in the open air on the other hand the
temperature of the liquors is always near 212°, and the maximum of concentration
is not approached to any near degree.
When strong liquors are used, having from 27° to 28° Beaumé, they are
submitted to suitable carbonisation and desulphurisation, after which they are
concentrated to from 33° to 34° Beaumé, either by direct heating or by addition of
carbonate. In any case, owing to the relatively high temperature of evaporation,
the liquors do not attain the possible maximum of concentration.
According to the present process, weak liquors of from 16° to 20° Beaumé are
submitted to carbonisation and desulphurisation, and then charged into vessels
where they subside. After decanting they are charged into the vacuum pans,
where a vacuum is maintained, such that the temperature of evaporation does not
exceed 130° Fahr., so that the liquor is concentrated to 36° Beaumé, that is, near
to its possible maximum. The concentrated liquor is then transferred to crystal-
lising pans. Thus, the use of the vacuum pans has the double advantage of effecting
economy in fuel, and of preventing the temperature from being exceeded which
corresponds to the maximum solubility of the carbonate of soda. This method is
equally applicable to the treatment of caustic liquors for the manufacture of caustic
soda. One of the existing processes for this purpose consists in diluting the liquors
till they have about 8° or 9° Beaumé, and then rendering them caustic with lime,
after which they are decanted and concentrated to about 42° to 43° Beaumé
forming caustic liquors, which are then further evaporated and fused in special cast
iron boilers.

page_text: The second existing process is based on the fact that if a solution containing
carbonate of soda and caustic soda be concentrated, the carbonate will be pre-
cipitated when the solution attains 34° or 35° Beaumé, the salt being removed as
it is produced the mother liquor is then treated as in the first process. In either
case the concentration is effected by heating over a naked fire. The present
improved process is applicable to either of the above methods.
.
The construction and mode of operation of the apparatus for the carrying out of
the improved process will be understood on reference to the accompanying
Drawings, in which Fig. 1 shows a front elevation, Fig. 2 an end elevation, and
Fig. 3 a plan. It consists of two pans A and B, and of two other pans C, C¹,
which are shewn in vertical section in Figs. 4 and 5. D, D', are the intermediate
safety columns, and E is the condenser, both provided with purge pipes p, p', p², p³.
The pans are constructed as ordinary pans, triple acting, but they are made of cast
or wrought iron; the circulation of the heating steam is effected in a series of iron
pipes X, X', and Y.
When the apparatus is intended for the manufacture of soda crystals as described
it only has three pans, and it is arranged as ordinary apparatus of triple action.
But for the preparation of the red lyes for the manufacture of caustic soda the
apparatus must be arranged for the reception of the deposits of carbonate of soda
that are formed during the process. For this purpose the second and third pans
are extended below the tubular heater so as to form a lower cylindrical body,.
which is provided with a manhole and sight-holes. Also the two pans C, C¹, are
made to intercommunicate by a pipe M, and can, if necessary, be isolated from the
other apparatus in order to serve as simple concentrating boiler in cases where
their concentration has not been effected sufficiently by the evaporation. In this
case the steam is admitted through cocks L or L¹ into the one or other of the pans.
As usual the pans are provided with pipes I, I, I, for discharging the gases from
the tubular parts; these pipes communicate with the main exhaust pipe K. of the
air pump; the valves K1, K2, K³, permit of the separation of the pans from the
exhaust. Lastly, the Drawing shews the accessory arrangements, such as the sight-
holes g, the pressure gauges m, cocks for adımission of air, purge pipes a of the
tubular parts, the air pipes d, manholes T; Z is the pipe for conveying the water
to the condenser, and provided with a cock S; U is the pipe connecting the con-
denser with the air pump. For evaporating the caustic liquors with this apparatus
the proceeding is as follows:-The caustic liquors having 8° or 9° are conveyed
into the first pan A of the apparatus by the pipe G, and issue by the pipe G' when
they have 19° Beaumé, passing to the second pan B, where they are concentrated
to 28° Beaumé; thence they pass through pipe G2 or G3 into one of the two pans
C, C¹, where they are concentrated to 38° or 39°. If the caustifying has not been
complete the small amount of carbonate of soda contained in the liquor is pre-
cipitated at this degree, it is separated as follows:-The cock G2 is closed while
allowing the steam from the safety column D to enter the tubular part of the
pan C; the admission of the steam from the column D¹ into each of the two third
pans is regulated by means of valves H, H¹. The pan C continuing to receive the
steam, the caustic liquor passes rapidly from 38° to 43° Beaumé; the steam supply
to the pan C is then stopped, and the pan C¹ is brought into action in order not to
interrupt the process. When the pan C is stopped, the liquor not being any longer
agitated by the ebullition, any traces of carbonate of soda become deposited into
the lower cylindrical chamber, from which it is removed through the register Q,
which is closed by a screw R. The red lyes are drawn off through the cock V²;
O, V, V1, V2, are the discharge cocks of the three pans. The red lyes are then
conveyed into the cast iron boilers as in the existing process.
For carrying out the second above mentioned process the mode of proceeding is
as follows:-The raw soda liquors proceeding from the levigation, and having a
mean of 28° Beaumé, are conveyed by the pipe G to the first pan A. The liquor
is concentrated in this pan till it has about 33° Beaumé, till then no precipitate of

page_text: carbonate of soda will have been formed. The liquor is then passed from A into
B, where it is further concentrated under separation of carbonate of soda, which is
however kept in suspension by the considerable agitation of the mass through the
ebullition. The liquor remains in this pan until the proportion of caustic soda in a
sample taken from the mass proves sufficient; the communication with the pan C
is then opened. This pan is filled as full as possible, and is then cut off from the
others, the concentration being continued in the two first pans simultaneously
with the third, but the passage of the liquor from the second to the third pan
being intercepted. The volume of the liquor in this pan C consequently diminishes,
and the carbonate of soda continues to be precipitated. When the level of the
liquor approaches the upper tube plate, or when its degree of causticity is sufficient,
the pan C is filled by putting it in communication with the air pump, the pan B,
and the safety colume D'. The action of the air pump and of the steam from the
safety column D¹ are then stopped in C, and the ebullition being stopped the salts
in suspension can deposit in the cylindrical chamber placed below the lower tube
plate while the deposit is taking place. The apparatus is now worked with the
third pan C, in which the same operations take place as described with reference
to C. When the deposit of salts in C has been completed, which is readily
ascertained by means of the sight holes, it is ascertained whether the supernatant
liquor is pure caustic soda lye or whether it still contains a sensible quantity of
carbonate. If it is sufficiently caustic it is conveyed direct to the boilers for
effecting the final concentration where the caustic soda is fused, but should it still
contain too much carbonate it is passed into the pan C₁ when the operation in the
latter is nearly completed. The liquor being withdrawn the register Q and closing
screw R are opened, so as to let the salt fall into trucks that take it to the
works, where it is subjected to the necessary treatments for rendering it suitable
for commerce. The apparatus being again closed it is again put in operation as
described.
It will be seen from the foregoing that at each operation there is a certain
quantity of lye that passes from one third pan to the other reciprocally. This
quantity naturally increases at each operation, when it becomes sufficient to fill a
pan; this pan is entirely cut off from the rest of the apparatus and the process of
evaporation is then carried on in a single pan by means of the air pump and of a
current of steam coming from the generator through the pipe L. The volume is
reduced until a perfectly caustic lye is obtained, as in this evaporation the small
amount of carbonate in solution becomes precipitated. The operation being
completed, that is to say, when the lye contains no more carbonate in solution, the
action is stopped, and after subsidence the lye is withdrawn through the pipe V¹
and the salt is taken out through the doors Q, R.
Having thus described the nature of the said Invention and in what manner
the same is to be performed, as communicated to me by my foreign correspondent,
I claim,―
First. The method of concentrating soda solutions, whether for the production
of carbonate of soda or caustic soda by evaporation in vacuo, substantially as
herein described.
Second. The application of evaporation in vacuo to the concentration of solutions
for the production of soda crystals at a temperature approaching as nearly as
possible that which corresponds to the maximum solubility of the carbonate of soda,
substantially as herein described.
Third. The application of the evaporation in vacuo for the production of red
lyes for the manufacture of caustic soda, the carbonate of soda being deposited
from the lye when brought to a sufficient degree of concentration, substantially as
herein described.
Fourth. The use for effecting the concentration of soda solutions referred to in
the preceding claims of vacuum evaporating apparatus, arranged and operating
substantially as herein described.

page_text: Fifth. The construction of iron evaporating pans for the concentration of soda
solutions with lower extensions for the reception of the deposits of carbonate of
soda and provision of means for the discharge thereof, substantially as herein
described.
In witness whereof, I, the said John Imray, have hereunto set my hand
and seal, this Seventh day of October, in the year of our Lord One thousand
eight hundred and eighty one.
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