Improved Method and Apparatus for Manufacturing Caustic Soda.
Year: 1894

page_text: Date of Application, 30th Mar., 1894-Accepted, 5th May, 1894
COMPLETE SPECIFICATION.
Improved Method and Apparatus for Manufacturing Caustic Soda.
I, THOMAS CRANEY, of 624 Harrison Street, Bay City, State of Michigan,
United States of America, Manufacturer, 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:-
My invention refers to the manufacture of caustic soda from salt brine on a
commercial scale and has for its object to cheapen the cost of manufacturing it
by electrolysis.
To this end my invention consists in the improved method and apparatus more
fully hereinafter described.
In the drawings, I have shown in diagram plan an apparatus designed for carrying
out my improved method.
A represents a number of electrolytic cells, adapted to be used on a commercial
scale for the electrolysis of common salt in solution. They may be of any known
form and construction, except that I prefer to use electrolytic cells of the kind in
which an electrolytic diaphragm divides the cell into separate compartments for
the electrodes.
B represents a receiver, into which the caustic soda solution from the cathode
compartments of the cells is collected.
C represents the electric generators which supply the electric current for
electrolysis through suitable conductors shown in dotted lines and marked with
asterisks.
D represent the steam engines which drive dynamos.
E represents the boilers which furnish the steam for the dynamos.
Frepresents evaporators preferably of the character known as vacuum pans,
such as are in use for manufacturing salt from brine by the use of exhaust steam.
G represents connections for conducting the exhaust steam from the engine to
the evaporators.
H represents the fusing kettles into which the concentrated solution of caustic
soda from the evaporators is discharged, and L represents a return pipe by means
of which the water of condensation from the evaporators may be used to supply
the cathode compartments of the cells with the necessary supply of water.
With an apparatus constructed on this general plan I carry out my improved
method as follows: I use salt brine such as it is pumped from the salt wells, in the
anode compartments of the cells and preferably the water of condensation from
the evaporators in the cathode compartments in the cells.
Instead of carrying the electrolytic decomposition in the cells to its full limit as
heretofore I only carry it out to the extent of producing a weak solution, say about
one to two per rent. of caustic soda, and this I draw off into the receiver, at the same
time I substantially maintain the salt brine on the anode side always up to its full
degree of strength.
With this weak solution of caustic soda produced by the electrolytic process I
then go on and produce the commercial article by drawing the solution off into the
evaporators and concentrate it therein by the use of exhaust steam drawn from the
very engines which furnish me the power for generating the current.
The concentration of the soda solution is carried on in the evaporators until a
strength of about thirty-five per cent. more or less is obtained when it is drawn off
into the fusing kettles from which it is received as the caustic soda of commerce.

page_text: In the commercial manufacture of caustic soda from salt brine by electrolysis
it was heretofore the aim of the manufacturer to produce a concentrated solution
of caustic soda by way of electrolysis and then proceed by boiling down.
My improved method is exactly on the reverse plan, I throw the expense and
burden of concentrating on the use of exhaust steam from the engine.
The philosophy of this will readily appear, when it is taken into consideration
that I can produce a great deal more caustic soda pound for pound in a one per cent.
solution than I can produce with the same amount of electric horse power in
a four per cent. solution, while on the other hand, the steam required to convert the
one per cent. solution into a four per cent. solution by evaporation would only require
a small fraction of the horse power (i.e. steam) which it would require to produce
a like amount of four per cent. solution by electrolysis.
My method aims to produce the maximum amount of soda in solution for a given
horse power irrespective of the degree of concentration. In carrying out this
plan in a commercial plant a safe limitation would be to produce an adequate
amount of solution of caustic soda commensurate with the economical use of steam
in the form of exhaust steam from the engines.
But my
method is capable of being carried out on a still more economical plan,
and to this end I produce a caustic soda solution by the electrolytic process of still
less concentration, and instead of putting it directly into the evaporators, I pass all
or a portion of it first into the boilers and then to the evaporators, using a portion
of it for making steam for the engines.
A feed pump (marked I) or any other device for feeding boilers may be used in
the ordinary manner, and a pipe J for carrying the surplus of the evaporating pans.
Thus if one half of the water in the solution for instance is converted into steam
while passing through the boilers, the rest which passes into the evaporators is then
doubled in strength.
In the practical application of my method it has to be taken into consideration
that the greatest economy is derived from a continuous operation of all the parts
of the plant. This imposes certain limits of my method but it is obvious that the
output from the electrolytic vats may be made commensurate to the capacity of
the evaporators.
To this end I can regulate the cut-off of my engines so as to produce a balance
between the output from the electrolytic vats and that of the evaporators, and if
necessary I can also decrease or increase the number of electrolytic tanks of the
relative strength of the solution within economical limits.
Having now particularly described and ascertained the nature of the said inven-
tion and in what manner the same is to be performed, I declare that what I
claim is
The method and apparatus herein described for manufacturing caustic soda.
DaLea
ny ov
THOMAS CRANEY.
Haseltine, Lake & Co.,
45, Southampton Buildings, London, W.C., Agents for the Applicant.