IMPROVEMENTS IN THE MANUFACTURE OF COMMON SALT AND IN THE APPARATUS EMPLOYED THEREIN."
Year: 1876

page_text: PROVISIONAL SPECIFICATION left by Hugh Warth at the Office of the
Commissioners of Patents on the 13th October 1876.
HUGH WARTII, of Forbes Road, Penge, in the County of Surrey. "IMPROVEMENTS IN
THE MANUFACTURE OF COMMON SALT AND IN THE APPARATUS EMPLOYED THEREIN."
This Invention is based upon the known fact that solutions of common salt
(chloride of sodium) in the form of brine, when saturated at different temperatures
differ in strength or density (although the difference is not very great), and that
currents are created in fluids to which heat is applied, that portion of the fluid
which possesses the greater amount of heat rising to the surface, and thus creating a
rapid circulation.
By means of the methods of treatment and of the apparatus embraced by this
Invention a saving of fuel is effected, and the manufacture or extraction of salt
from brine considerably accelerated, as compared with the methods and apparatus
previously employed for such purpose.
In the manufacture of salt from brine as it has hitherto been carried on large
shallow evaporating pans or other vessels are employed, which are heated from
below either by means of open fires or by steam, or by both. The salt separates
and collects chiefly at the cooler end of the pan or other vessel, that is to say, at the
part furthest removed from the source of heat.
In accordance with this Invention the fresh brine is introduced into a vessel and
heated therein separately from the vessel in which the salt is allowed to crystallise,
the first-mentioned vessel being connected with a large shallow evaporating pan,
which latter may be left entirely open, or a portion thereof partitioned off and
covered in, the brine being made, by preference, to flow over a low partition in
such a manner as to set up a circulation from the nearest or hottest to the further-
most or coldest part of the pan, and from thence to the vessel through a pipe or
pipes. In this manner the colder brine, which is of about the temperature of
60° to 60° cent. and which is still saturated, although at a lower temperature and
containing about 27 per cent. of salt, is brought together and mixed with the hotter
fresh brine with which the first-mentioned vessel is fed, and no salt crystallises out,

page_text: as the brine always remains under saturated at the temperature to which it becomes
heated in the said last-mentioned vessel. The brine is next caused to circulate
through a connecting pipe or pipes from the first-mentioned vessel to another separate
vessel or boiler which is heated by direct heat from an open fire-place, and which
vessel may be in the form of a tubular boiler or may be an ordinary iron boiler; the
same being in either case provided with a moveable lid and heated from the outside.
The steam which is generated in the last-mentioned close vessel, in which the brine
attains a density of about 29 per cent. owing to the rapid evaporation which is
going on, is at the greatest point of heat, and is used for heating the first-mentioned
vessel either by being carried through a coil of pipes placed within the brine in the
said vessel, or by being applied to the outside of the vessel by means of a steam
jacket, or by both methods combined.
The concentration and evaporation of the brine is mainly effected in the said
boiler, and in which the brine reaches its highest temperature, but it is necessary
that the same should be left in a somewhat under saturated condition. It is then
allowed to flow into that part of the pan which by preference is covered in by means
of a moveable lid, and the steam mixed with air which is given off, is drawn away
and utilized for heating the brine in the first-mentioned vessel, either by being
conveyed through a separate coil of steam pipes or by being admitted and mixed
with the steam coming from the boiler into which the brine is admitted, as before-
mentioned, in a part of the steam coil or steam jacket in which the temperature of
the steam has sunk down to that of the steam from the evaporating pan. The fresh
brine as well as the brine coming from the evaporating pan is heated in the first-
mentioned vessel by being passed in a direction opposite to that of the hottest
steam in the steam coils.
Instead of employing the whole body of steam mixed with air at one and
the same operation, as herein-before mentioned, the same may be drawn off in
successive portions of gradually increasing temperature, so as to act most advan-
tageously upon the brine with which it is brought into contact.
In the case of a portion of the evaporating pan being left uncovered a partition is
placed through the middle thereof from the nearest end to almost the furthest end
of the pan, allowing for the circulation of the brine from the part at which the hot
liquor enters towards the colder portion thereof, at the temperature of about
50° to 60° cent. and brought back by its own natural flow into the first-mentioned
vessel.
The before-mentioned vessel and boiler and evaporating pan are respectively
connected in such a manner as to allow the brine to circulate freely and con-
tinuously. This is effected by connecting the boiler with the evaporating pan by
means of a pipe or pipes, by which the heated brine is carried off from near the
surface in the said vessel and delivered on a level on to the surface of the liquor in
the evaporating pan in the hottest part thereof nearest the boiler. The brine cools
down as it circulates slowly to the furthermost end of the pan, and the deposition
of the salt proceeds rapidly and regularly.
The cooling may also be assisted by air currents being passed over the surface of
the liquor contained in the open part of the pan. Having thus become reduced in
temperature to about 500 to 6000 cent. the liquor naturally flows from thence into
the first-mentioned vessel through a connecting tube or tubes, by which it is
delivered in a continuous slow stream close to the bottom of the said vessel. This
vessel raises the temperature of the comparatively cold and dilute brine which
has deposited the greater portion of its salt in the evaporating pan to a temperature
approaching that of the brine in the boiler. From the said vessel the brine passes
to the boiler containing the hottest brine by means of a connecting tube or tubes
by which the brine is taken from near the surface of the vessel and delivered near
the bottom of the boiler. The natural flow of the brine through the first-mentioned
vessel, the evaporating pan, and boiler, must be checked and regulated by means
of throttle valves, as will be well understood,

page_text: A saving of fuel is effected by utilising the steam from the boiler as well as that
from the evaporating pan to heat the liquor in the first-mentioned vessel, as also
the fresh brine with which the same is fed, to as high a temperature as the steam
will allow of. The waste gases from the fire-place are by preference passed under-
neath the first-mentioned vessel, and from thence along the bottom of the
evaporating pan to the chimney stack.