Improvements in or relating to Evaporators for Obtaining Common Salt, and for analogous purposes.
Year: 1895

page_text: Date of Application, 13th Aug. 1895-Accepted, 14th Dec., 1895
COMPLETE SPECIFICATION.
Improvements in or relating to Evaporators for Obtaining
Common Salt, and for analogous purposes.
I, THOMAS SCOTT, of 9 St. Vincent Street, Edinburgh, in the County of Mid-
Lothian, North Britain, Engineer, 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:-
The object of my invention is to construct an apparatus heated by steam to
evaporate saline solutions, and more especially brine, at their boiling temperature,
and to separate the salt directly in the heating vessel.
This has been found to be difficult or impracticable as a continued operation
on account of salt-scale "adhering to the heating surfaces and interfering
with their capacity to transmit heat. By "salt scale" I mean a dense crust
consisting essentially of chloride of sodium in which may be entangled particles
of insoluble lime-salts, mud etc.
My invention consists in an improved general construction and combination of
parts as hereinafter described, and also in a special manner of operating and
cleansing the apparatus as hereinafter explained.
Contrary to the form of tall upright steam drum set on a deep liquor pot
hitherto employed, I employ a low steam chest which may be of rectangular,
circular, or other form in horizontal section, the horizontal being generally in
excess of the vertical measurement.
But in order that my said invention may be more readily understood and easily
carried into effect I will proceed to describe the same with reference to the
accompanying drawings.
Figures 1, 2 and 3 are elevation, end elevation and plan respectively of one
form of my improvements in which the apparatus is stationary.
Figures 4 and 5 are elevation and plan of a moveable or telescopic apparatus
constructed in accordance with my invention; and
Figures 6 and 7 are elevation and end elevation of a modification.
Referring to Figures 1, 2 and 3, I construct a steam chest A which is heated by
steam, under pressure, from the boiler B by means of the pipe b: the condensed
steam and water passing away through the pipe c into the condenser C from
whence it passes through the pipe c' to the boiler B as required: said pipes b, c
and being provided with suitable valves or cocks. The said steam chest A has
mounted within it a series of short heating and stay tubes D, or divisions, which
are preferably placed and mounted vertically as shewn. The steam chest A is
suspended and immersed in liquor contained in a shallow tank or salt pan E, which
may be partly steam-jacketed, and a low space is left between the said chest A
and the bottom of the pan E. The steam chest A while occupying as large a
proportion of the cubical contents of the salt-pan E as possible, will yet have on
one or more sides a space or spaces e for the downward circulation of liquor and
for introducing tools or mechanical arrangements under the steam-chest A and
along the bottom of the pan E, to remove the separated salt at intervals or
continuously, into the side pockets or receptacles E' from which it is lifted and
spread on suitable drying or draining tables X.
A close hood, F, which may be made so as to be removable when desired,
covers the space over the steam-chest A but leaves the extending pockets E¹ of
pan E free. This hood F is attached to the pan E and on the free side or
the

page_text: sides dips slightly into the liquor contained in the said pan E, thus forming a
hydraulic lute, under which the salt may be drawn ont, and the said hood F also
captures the steam over the chest A and so enables it to pass away in pipes G for
other uses hereafter referred to.
Having made an apparatus as above described which combines extensive heating
surface, ie, evaporating capacity (the horizontal area of the steam chest being
structurally capable of great extension) with relatively small liquor contents,
proceed to operate the same, and to keep the heating surfaces free from such
incrustations of "salt scale as would unduly hinder the transmission of heat, in
the following manner :-
27
I use a constant feed of liquor, preferably pre-heated in the double-bottomed
pans H by means of the steam which arises from the boiling brine or liquor in the
pan E said feed being supplied through the medium of the pipes and cocks L, L' :
there being one, two or more of such pans used. so as to suit the speed of
working.
.
When desired to withdraw the salt from the salt pan E I stop the feed and
open a valve J in the bottom of the salt-pan E, when the liquor content:
Instantaneously diop into one, two or more. lower tanks K provided to receive
them. Having shut the discharge valve and removed any loose salt remaining in
the pan EI quickly discharge fresh water,-boiling if possible-from an overhead
tank though preferably from the lower parts h of the pans H by means of the
pipes L and into the salt-pan E in such quantity as may be required to cover the
salt-encrusted surfaces of the same. This water from the underside of the pans H
being immediately put into viclent ebullition by the transmitted heat of the steam
in the steam-rhest A circulates furiously along the heating surfaces and dissolves
the salt scale" with great rapidity. It may then be run off into the settling
tanks K by opening the valve J and so be converted into saturated liquor or
retained to be evaporated down according te the degree of salinity which it has
acquired.
I am aware that in certain salt works it is not unusual to occasionally add fresh
or sea water to the brine in ordinary salt-pans, with the object of bringing it
temporarily below the point of full saturation and ao causing it to dissolve the
"salt seale" adhering to the pan bottom. The proportionate quantity of water
used in these circumstances is considerable and its dissolving power slow on
account of the previous presence of a quantity of saturated brine which no
provision has been made to remove. It is consequently an expedient which is
only adopted under exceptional circumstances.
The special design and relative accessories of my improved apparatus have been
contrived by me to allow of this water-cleaning or flushing operation being introduced
without practical inconvenience as a systematic part of the process of salt-
making with steam-pans which contain heating tubes and of its being carried out
with a restricted use of water and of steam for boiling or circulating the water,
and in so short a time that the useful operation of the plant is nearly continuous.
In certain cases, as for example when it is not desired to remove continuously the
fine salt formed, but to allow it to rest for some time in the brine with the view
of obtaining larger crystals, or for other purposes, I modify the construction
and make what is my second form of apparatus as follows, and as is shewn in
Figures 4 and 5 :-
1 fix or suspend the steam-chest M to or from two or more girders M¹ which
carry the hood M2 and I mount the pan P in such a manner as to be movable in 5
both a vertical and horizontal direction, so that the space under the steam chest M
may be regulated in accordance with the bulk of salt accumulating between the
periods of drawing: and before introducing fresh water, said space may be reduced
to any desired extent.
The said raising and lowering of the salt pan P, which slides up and down the 5
outside of the hood M³, may be effected by means of a travelling winch N running
along the girders M', said winch being travelled backwards and forwards by means

page_text: of an endless band arrangement Q, in such a manner, as to enable the pan P and
its contents to be lowered into the pit R, travelled along, raised, and brought into
contact with the stoppers S, where, owing to the forward movement of the winch N,
the pan P is turned over and its contents emptied into the space or. drying
bench T, the rest of the apparatus remaining practically the same as already
described.
Or as a modification I may construct the apparatus as shown in Figures 6 and 7,
in which B¹ is the boiler, P the salt pan, P* the raising & lowering arrangement,
M³ the steam-chest, M the hood, H the double pans & G the pipes; the other
parts being practically the same as already described. The raising and lowering
arrangement in this case, preferably consisting of screws P' which enable the pan Pi
to be raised or lowered telescope fashion around the hood M' and so be enabled to
empty its contents into the drying chamber. The top ends of screws P' being
carried by a cross stay P³, which also carries the hood M. In this case the liquor
contents will be relatively small in comparison with the development of heating
surface, whereas in the case where the steam chest M is fixed as stationary the
liquor contents may periodically be made relatively as small or even smaller by
adjustment.
My improved apparatus may be worked by single effect as hercinbefore
described, but I may also if desired, work it to greater advantage in either of
the following ways:
Firstly By double effect, the escaping steam passing through a feed heater
and under supplementary pans where it will produce a second smaller crop of salt.
These pans may be open so as to expose the liquor to the air, or if closed, vacuum
may be applied to lower the boiling point of the liquor.
Secondly-By multiple effect us a regenerative evaporator, the escaping steam
being compressed and pumped into the interior of the steam chest at such increased
pressure and temperature as may practically be necessary to obtain a satisfactory
rate of evaporation per square foot of heating surface.
And Thirdly-Indirectly, for boiling and reboiling of liquors circulated between
it and auxiliary tanks when salts will separate at a lower temperature from the
solutions which leave the heating vessel saturated at their boiling point.
Also in accordance with my invention I may use the surplus hot water from the
secondary pans for the purpose of dissolving rock salt into brine said salt being
dissolved in suitable tanks and the surplus water led to such tanks by means of
suitable pipes and cocks, the special advantages of the foregoing being a consider-
able saving of time and also obtaining a much clearer solution containing a smaller
percentage of sulphate of lime than has hitherto been obtainable when cold spring
or natural waters have been used.
Having now particularly described and ascertained the nature of my said inven-
tion and in what manuer the same is to be performed, I declare that what I
claim is :-
1. The method of operating and cleansing evaporating vessels for concentrated
saline solutions when worked with steam-heat by regular and frequent flushing with
fresh or partly fresh water to dissolve or disintegrate and remove the "salt scale
substantially as hereinbefore described.
"
2. The general arrangement, construction and combination of parts forming ny
improvements in or relating to evaporators for obtaining common salt and other
analogous purposes, substantially as hereinbefore described and shewn in
Figures 1, 2 and 3 of the accompanying drawings.
3. The general arrangement, construction and combination of parts formning my
improvements in or relating to evaporators for obtaining common salt and other
analogous purposes, substantially as hereinbefore described and shewn in
Figures 4 and 5 of the accompanying drawings.
4. The general arrangement, construction and combination of parts forming my
improvements in or relating to evaporators for obtaining common salt and other

page_text: analogous purposes, substantially as here before described and shewn in
Figures 6 and 7 of the accompanying drawings.
5. The method of omplexing hot distilled water from the secondary pans of salt
evaporators for the purpose of dissolving rock salt into brine, substantially as
herein before described.
Dated this 6th day of Ananet 1895
JOHNSONS,
115 St. Vincent. Street, Glasgow, Applicant's Agents.