IMPROVEMENTS IN THE MANUFACTURE OF SODA BY MEANS OF AMMONIA AND CARBONIC ACID, AND IN THE APPARATUSES APPLIED THEREFOR "
Year: 1878

page_text: LETTERS PATENT to Hermann Unger, of Leipsic, in the Kingdom of Saxony,
for the Invention of IMPROVEMENTS IN THE MANUFACTURE OF SODA BY
MEANS OF AMMONIA AND CARBONIC ACID, AND IN THE APPARATUSES APPLIED
THEREFOR
"
COMPLETE SPECIFICATION filed by the said Hermann Unger at the Office
of the Commissioners of Patents on the 19th June 1878.
HERMANN UNGER, of Leipsic, in the Kingdom of Saxony.
"IMPROVEMENTS IN
THE MANUFACTURE OF SODA BY MEANS OF AMMONIA AND CARBONIC ACID, AND
IN THE APPARATUSES APPLIED THEREFOR."
This Invention relates to improvements in the manufacture of soda from common
salt (chloride of sodium) by the ammonia process. In this process as conducted at
present, the whole amount of carbonic acid gas is pressed through a high column of
a solution of common salt satured with ammonia.
The carbonic acid required for the conversion of the salt is taken from two
sources, one part of the quantity being obtained from a limekiln or from the com-
bustion of fuel, the other part from the calcination of the bicarbonate of soda
produced in the first stage of the process. The former part of the carbonic acid is
however mixed with a prepondering quantity of nitrogen and other gases, which
have hitherto been forced through the column of saline solution together with the
carbonic acid, a very considerable and useless expenditure of power being necessarily
required therefor.
The object of my Invention is now to divide the process relating to the absorption
of carbonic acid into two partial processes.
In the first part the ammoniacal solution of salt is exposed in thin but extensive
films and in form of fine spray to contact with the gases obtained from kilns or by
combustion, these gases simply passing without pressure over the surface of the
liquid. By these means one equivalent of carbonic acid is caused to be taken up by
the liquid.

page_text: In the second part of the process, the puro gas re-obtained by calcination of the
bicarbonate of soda produced is applied substantially as hitherto.
The apparatus which I employ for my improved process is represented on the
annexed Sheet of Drawings, The same consists of a series of vertical cylinders or
absorbing vessels which have been consecutively marked by the letters A-H, in
succession as the liquid traverses them. The letters a, b, c, d, denote the course of
thic gases obtained from a limekiln, &c.; the letters e, f, g, g', g, show the course of
the pure carbonic acid; and i, k, l, m, n, that of the ammonia gas,
The main absorbing apparatus for the first equivalent of carbonic acid is the
apparatus E. The limekiln gas or combustion gas is conducted into the same by
tube a, whilst the prepared ammoniacal solution of salt enters by tube 8'.
In the centre of the cylinder constituting the shell of the apparatus, a shaft M
revolves provided with a considerable number of disks K, K, smaller in diameter
than the cylinder. To the sides of the latter annular disks L, L, are fixed
intervening between the former. The liquid entering at 8¹ and running on the
first rotating disk K is spread out by centrifugal force and flies off from its edge in
a fine spray, it thereupon flows over the surface of the first annular or fixed disk,
and drips from its inner edge on the second rotating disk, and so on. The
liquid is thus caused to present a very large surface to the gases, and in consequence
speedily absorbs the carbonic acid contained therein. During this absorbing process
considerable heat is developed, the cylinder is therefore provided with a water
jacket for refrigeration. On account of the absorption of carbonic acid by the
liquid a part of its ammonia becomes free and is mixed with the said gases. For
the purpose of utilizing this ammonia the gases are caused to pass from E through
tubo b into the apparatus B, which is in all respects similar to E, except that it has
a single shell, no water cooling being in this case required. At the top through
tube p¹ a solution of salt of a certain standard enters, which already contains a
small amount of ammonia, and which absorbs an additional amount from the gas
passing upward through B.
It will be observed that in the apparatus E gas and liquid flow both in the same
direction. This arrangement has the effect that the ammonia carried over from E
into B is not pure ammonia, but carbonate of ammonia; in consequence the quantity
of ammonia entering into B is not as great as would be the case if the gases in E
were conducted from the bottom towards the top, and contrary to the flow of the
liquid.
If the process is carried out in such a manner as to allow a small quantity of
carbonic acid to pass over from E into B, the monocarbonate of ammonia is
converted into bicarbonate, which is yet with more facility absorbed by the solution
of salt in B.
The gas after having passed the apparatus B yet contains a certain quantity of
ammonia; it is therefore finally conducted by a tube c into the cylinder A, where
this ammonia is washed out by pure water entering at the top by tube o. (Instead
of water a solution of chloride of calcium or a diluted acid may also be used.)
For the purpose of spreading the water out over a large surface, I fill this
cylinder with short and narrow tubes of clay or other suitable material placed
vertically close to each other, and in numerous tiers one above the other. The
ammoniacal water running off at p is subsequently used for dissolving salt; d is
the tube through which the residual nitrogen, &c., is drawn off by a fan or an
ejector.
The saline solution from B is conducted by tube q into the absorbing cylinder C,
where it is finally impregnated with the necessary quantity of ammonia entering
by tube n. The mode of obtaining this ammonia will be described hereafter.
The interior arrangement of the cylinder or apparatus C is analogous to that of
the described cylinder A. From C the liquid, which has become hot by the process,
is passed through a refrigerator D and subsequently drawn off through tube s
by a pump (not shown in the Drawing) and discharged through tube 8' into the
cylinder E.

page_text: In the first part of this description it was the course of the gases which served as
a basis for a systematic arrangement of the same. If however the course of the
liquid is taken into special consideration it will be seen that the water, which has
absorbed a small quantity of ammonia in A, after having been used for dissolving
salt, is pumped as saline solution into B for being impregnated with more ammonia
(respectively of carbonate or bicarbonate of aninonia), thence runs into C for final
impregnation with the same gas, is subsequently cooled in D, and at last pumped
into E for absorption of the first equivalent of carbonic acid.
The second part of the process is carried out in the cylindrical vessels F¹, F², F³,
&c., which are arranged in a circle or in a row beneath the vessel E. By a system
of tubes t, 1, 2, &c., and suitable cocks, any one of the former vessels may be made
to communicate with the latter, and they are filled successively.
Supposing F to be in communication with E, pure carbonic acid gas is pumped
into F by tube g, g²; the gas which is not absorbed in F2 passes through tube g³
into F, thence through g¹ into F, &c., and the remainder through g' into F'. If
the liquid in F should not completely absorb the remaining gas, the residue may
pass through tube t into the vessel E, so that the ammonia which the carbonic acid
necessarily carries with it may be re-absorbed by the liquor in B.
For the purpose of causing the carbonic acid to be more equally distributed in
the liquor contained in the vessels F¹, F, &c., closely wound spirals N are fixed
within them, and by preference to the tubes g', g, &c. The vibrations to which
these spirals are subject prevent them from becoming incrusted by the bicarbonate
of soda in course of precipitation, any small quantity of this salt which may adhere
to them being detached when the vessel is filled anew.
After the liquor in F has been saturated with carbonic acid it is drawn off
together with the bicarbonate of soda formed, and the carbonic acid is conducted
from tube g through gs into F by suitably opening and respectively closing the
corresponding stop valves shown in the Drawing. Thereupon the cock in tube t' is
closed and the cock in t³ opened, gas being at the same time allowed to pass from F
into . Thus the process in these cylinders goes on continuously, the cylinder'
which is being filled with liquor being the one into which the gas enters last.
The precipitated bicarbonate of soda is separated from the adhering liquor by a
centrifugal machine, a press, or other suitable means.
The third part of the process comprises the treatment of the liquor separated from
the bicarbonate of soda, and consisting of a solution of chloride of ammonium with
a certain quantity of bicarbonate of ammonia, the object being to re-obtain the
ammonia for repeated use. For this purpose the liquor is pumped into the
apparatus G, which is in principle similar to B and E. The cylindrical shell of the
same is double, so as to form a hollow jacket, which is divided by a horizontal
partition wall into two parts, the upper part G¹ being filled with water for cooling,
while the lower part k is filled with hot ammonia gas from H.
The carbonic acid derived from the calcination of bicarbonate of soda, after
having been cooled in a suitable condenser, enters into G by tube c, and the fluid
obtained by condensation may enter with the gas. This gas contains a quantity of
ammonia, the greater part of which is absorbed in the upper part of G by the liquor
entering at v.
The carbonic acid on leaving G by tube fpasses into the apparatus I, similar in
design to A and C, where the residual ammonia is washed out by means of water
or of acidulated ammoniacal liquor, for the purpose of preventing any obstruction in
the tubes by the formation of bicarbonate of ammonia. The pure carbonic acid is
thereupon conducted into a gas holder and finally pumped into the vessels F1, F2,
&c., as has been described.
In the lower part of G the bicarbonate of ammonia is decomposed for re-obtaining
its carbonic acid. The heat required therefor is supplied by the hot ammonia gas
rising from the apparatus H into the space k.
The liquor arriving at the bottom of G, and consisting substantially of a solution
of chloride of ammonium, runs through tube w into apparatus H, where it is;

page_text: decomposed by means of lime milk entering by tube x, the limo neutralizing at the
same time any residue of carbonic acid, which would be of prejudicial influence on
the further process. The products of the said decomposition are a solution of
chloride of calcium which runs off at y, and ammonia gas which rises through tube i
into (for the purpose stated above), thence passes by tube 7 into the refrigerator m,
and finally by tube n to vessel C for being absorbed by the solution of salt, as has
also been already described. Whatever fluid condenses in m flows back into H by
a small syphon tube.
The requisite heat for the decomposing process in apparatus H is obtained
by admitting steam through pipes s. Moreover this apparatus is or may be heated
from the outside by admitting into its jacket either steam or the hot solution of
chloride of calcium running off at y.
With regard to the apparatuses A, C, and I, it may be observed that the tubes
with which they are filled may be very small, and in fact I prefer to use tubes
which are smaller in proportion to the cylinders than those shown in the Drawing.
Moreover instead of applying but one of these apparatuses in every special case two
or more may be used.
The described arrangement of absorbing apparatuses containing numerous small
tubes may also be made use of in other cases where a gas is to be absorbed by a
liquid, such as the purification of coal gas, the absorption of acid vapours, &c. It
also presonts advantages in a suitably modified form for obtaining ammonia out of
the ammoniacal liquor from gas works and from other sources, as the lime with
which the liquor has to be mixed beforehand cannot accumulate in the apparatus
on account of the vertical arrangement of the tubes, and as in case steam is
admitted from below, its heat is utilized in an efficient manner.
The requisite pumps, hydraulic joints, safety valves and other details have
been omitted in the Drawing, as they do not belong to the substance of the
Invention.
Having thus described the nature and object of this Invention, and the manner
in which it is to be or may be carried out in practico, I claim as new and essential
features of the same,―
1. The improved method of manufacture of soda by the ammonia process,
according to which the first equivalent of carbonic acid obtained from combustion
or limekiln gases is taken up by the ammoniacal solution of salt by surface
absorption without application of pressure, while the second equivalent of carbonic
acid resulting from the calcination of bicarbonate of soda is introduced under
pressure, substantially as described.
2. An absorbing or decomposing apparatus B, C, G, or H, consisting of a vertical
cylinder having a number of annular horizontal or inclined disks L, in combination
with a rotating shaft M, to which are fixed tho disks K intervening between the
former, as and for the purpose specified.
3. An absorbing or decomposing apparatus A, C, or I, consisting of a vessel filled
with small vertical tubes, as and for the purpose described.
4. The absorbing apparatus E into which gases containing carbonic acid are
admitted by tube a, and an ammoniacal solution of salt by tube 8', both tubes a
and s¹ being at or near the top of the apparatus, as set forth and for the purpose
specified.
5. The two absorbing apparatuses B and E combined with each other and with
the tubes a, b, c, s², and p¹, substantially as described and for the purpose set
forth.
6. The two absorbing apparatuses B and E in combination with one or more
absorbing apparatuses A, for the purpose stated.
7. In combination with the cylinder F¹ or F, &c., the spirals N, substantially as
set forth and for the purpose specified.
8. The cylinders F, F, &c., communicating with each other by pipes g¹, g², &c.,
and with a supply pipe for compressed carbonic acid gas, combined with the
absorbing apparatus E, as described and for the purpose stated.

page_text: 9. The apparatus G having a double shell with horizontally divided space, in
combination with a supply pipe e for carbonic acid obtained from the calcination of
bicarbonate of soda, and with a supply pipe v for the liquor resulting from the
production of bicarbonate of soda, substantially as herein described and for the
purpose set forth.
10. The apparatus H provided with double shell, in which apparatus the liquor
from G is decomposed by lime, as herein described.
11. The apparatuses G and H combined with each other and with one or more
apparatuses C for the absorption of ammonia by solution of salt, substantially as set
forth.
12. The combination of the apparatuses A, B, C, E, F, F, &c., G, H, and I,
with each other, and with the refrigerators D and m, as and for the purpose
specified.
In witness whereof, I, the said Hermann Unger, have hereunto sot my hand
and seal, this Seventh day of June, in the year of our Lord One thousand
eight hundred and seventy-eight.
HERMANN UNGER.
(L.S.)