Process and Apparatus for Obtaining Common Salt by the Refrigeration of Brine.
Year: 1893

page_text: COMPLETE SPECIFICATION.
[Communicated from abroad by CONRAD HIRZEL, of Winterthur, Switzerland,
Engineer.]
Process and Apparatus for Obtaining Common Salt by the
Refrigeration of Brine.
I, CHARLES DENTON ABEL, of No. 28 Southampton Buildings, Chancery Lane,
the County of London, 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 :-
This invention relates to a process and apparatus for producing common salt by
the refrigeration of brine, and is based on the fact that the curve of solubility of
salt, which is about horizontal above -15° C. descends considerably at temperatures
below this, and that at such low temperature large quantities of hydrated salt of the
formula NaCl 2 H₂O are separated. If the solution be still further cooled, say to
the point of congelation of the saturated brine, that is, to -22° C., there will be
produced in addition to the above mentioned hydrate NaCl 2 H₂O another hydrated
sodium chloride of the formula NaCl 10 H,O."
The first named hydrate liquefies in the atmosphere with formation of a saturated
brine and leaves a residue of non-hydrated salt. The last named hydrate on the
other hand is dissolved to a clear brine without residue.
According to the present invention the above known facts are made to form the
basis of the hereinafter described process for the commercial production of common
salt.
-
Saturated brine is cooled by refrigerating apparatus to form - 15 to
20° C.,
that is to say, to the lowest temperature possible at which a notable formation of
the hydrate rich in water: NaCl 10 HO does not yet take place, but only the
hydrate poorer in water: NaCl 2 H,O is separated. The separated hydrate is
removed from the brine and dried, and the latter is again saturated by solution of
salt. This can be effected either by causing the exhausted brine to flow into a
bore hole leading to the brine or rock salt beds, in order to be again drawn out of
the bore hole as saturated brine, or rock salt that has been raised from the mine
can be dissolved in the exhausted brine.
As the exhausted brine flowing off from the refrigerating machine has, on account
of the refrigerating action to which it has been subjected, a considerably lower
temperature than the saturated or approximately saturated brine which is introduced
into the refrigerating machine, it is advisable to cause both liquids to pass through
an apparatus for the interchange of heat in such manner that the inflowing warmer
saturated brine will be subject to a preliminary cooling by the outflowing colder
exhausted brine, before entering the refrigerating machine.
This invention furthermore relates to a process for dehydrating the doubly
hydrated salt obtained in the above described manner by artificial refrigeration.
Instead of allowing this hydrate NaCl 2 H,O to liquefy in the open air or by
heating, and by separating the brine produced from the residues, to obtain solid
table salt, the hydrated sodium chloride, poor in water, after passing from the
refrigerating machine is made to pass directly into a drying apparatus through
which hot air or other hot gases are made to pass. There is thus combined with
the refrigerating process an evaporating process whereby the water contained in
the sodium chloride is driven off before it can dissolve a part of the salt.
This treatment of the salt with hot air or hot gases is particularly advantageous
on the ground that, on the one hand the drying of porous solid bodies (in this case
the crystalline magma) by means of the intimate contact with the hot gases, is
TDi Q77

page_text: effected much more rapidly than by evaporating a solution by indirect transmission
of heat, and because, on the other hand, this evaporating process combined with the
refrigerating process affords a greatly increased yield of salt. If the hydrated
sodium chloride were allowed to liquefy in the air, the 40 p.c. of water contained
therein would dissolve nearly one fourth of the total amount of salt, so that
only ths of the salt obtained by the refrigerating process could be obtained as
anhydrous table salt. If on the other hand the hydrate is subjected in the above
described manner to an evaporating process, then in consequence of the direct
contact of the hot gases with the crystalline magma the other 25 p.c. of salt which
would otherwise be separated as hydrate, will be gained, with a very small
expenditure of fuel.
On the accompanying drawing is shewn the construction of an apparatus suitable
for carrying out the above described process;
Fig. 1 shews a vertical section of the cooling cylinder with the supply and
discharge pipes for the brine,
Fig. 2 shews a vertical section of the drying apparatus for the separated salt.
A is the brine reservoir into which the brine is forced by the brine pump, and
from which it is supplied as required to the apparatus. For regulating the supply
a cock is provided in the supply pipe a. The latter communicates with the
apparatus B for effecting the interchange of heat, which consists of a tubular casing
containing a bundle of pipes through the sides of which the interchange of heat
between the inflowing fresh brine and the outflowing exhausted brine is effected, the
fresh saturated brine which has the temperature of the bore hole from which it
comes being made to enter the upper end of the space between the casing and the
bundle of tubes, and to flow downwards therein, while the cold, more or less
exhausted brine enters at bottom at 61 into the interior of the bundle of tubes and
flows upward therein, taking up heat transmitted through the sides of the tubes
from the outer fresh brine. The cooled fresh brine passes from the apparatus at a'
and enters at a into the salt separator C, in which it is distributed as uniformly as
possible by issuing through the finely perforated end of the pipe a". The warmed
exhausted brine flows off at 611 and may be conducted back to the bore hole in
order to be again saturated.
The salt separator C consists of a casing formed conical at its lower end and a
vaporizing coil D of a refrigerating machine which is surrounded by a partition D'
open at top and bottom. 6 is the overflow pipe for the exhausted brine, in which
a pump can be introduced for maintaining a uniform circulation. c is the discharge
pipe for the separated salt in which a pump F is introduced for propelling the
latter. The cooled saturated brine is refrigerated by contact with the vaporizing
coil D until its temperature sinks to about
20°. A portion of the salt is by
this means separated in the form of the hydrate NaCl 2 H₂O and is deposited in
the form of fine crystals in the collecting conc E. The partially exhausted brine
rises slowly between the partition D' and the outer casing and flows off through
pipe into the heat interchanging apparatus B. The salt collecting in the
cone E is drawn off periodically by the pump F and discharged into the straining
vessel G.
―
The latter is arranged with a tumbling device for readily discharging the
hydrated salt into trucks for conveying it to an ordinary drying hearth, or it is
discharged directly into the hopper H of the drying machine shewn at Fig. 2.
M is a rotary stirrer by the periodical rapid rotation of which the brine has a
corresponding rotary motion imparted to it whereby the salt which deposits upon
the coil D is washed off so as to keep the surface of this clean for the effective
interchange of heat.
The vaporising coil must for this purpose be so connected with the compresser
and the condenser of the refrigerating machine, that by a simple reversal of a
reversing valve the vaporising coil may for a time be made to act as condenser,
whereupon the adhering salt crystals are at once melted off and are washed away
by the rotary motion of the brine imparted by the stirrer M, the crystals falling

page_text: into the funnel E whence they are removed to the strainer G together with the
other crystals.
The drying apparatus consists of the feeding hopper H with distributing rollers,
and the drying apparatus proper, in which there are arranged superposed endless
travelling aprons in such a manner that in travelling round the rollers on which
they are stretched, they convey the salt to be dried slowly from the one end to the
other and cause it to fall on to the next apron below.
While the hydrated salt is thus being conveyed along in a distributed manner by
the aprons, it is subjected to the action of currents of hot air or other hot gases
made to travel in the contrary direction by being drawn through the apparatus by
a fan L at top.
The fresh air entering the apparatus at bottom is caused to pass in contact with
suitable heating apparatus at K in order to be heated to the requisite degree for
effecting the drying of the salt.
Having now particularly described and ascertained the nature of this inven-
tion and in what manner the same is to be performed, I declare that what I
claim is :-
1. A process for obtaining common salt consisting in separating doubly hydrated
salt from a more or less saturated brine by partially freezing the same in a
refrigerating apparatus, the remaining brine being then again saturated with crude
salt, substantially as described.
2. A process for obtaining common salt consisting in separating doubly hydrated
salt from a more or less saturated brine by partially freezing the same in a
refrigerating apparatus, the remaining brine being again saturated with raw salt,
while the separated hydrated salt is dried by the action of hot gases, substantially
as described.
3. An apparatus for carrying out the process referred to in Claim 1 consisting of
a cylindrical vessel C open at top and preferably made conical at the lower end,
in which a refrigerating medium is made to act upon the brine within a vessel Di
open at both ends, into which the brine enters at top, while the exhausted brine
rises up in the space between the vessels D' and D and is discharged from the top
of such space, whereby a mixing of the exhausted and saturated brine is prevented
as much as possible.
Dated this 11th day of September 1893.
ABEL & IMRAY,
Agents for the Applicant.