Improvements in Apparatus for Use in the Decomposition of Common Salt in the Production of Sulphate of Soda, or for analogous purposes.
Year: 1894

page_text: Date of Application, 13th Nov., 1894
Complete Specification Left. 13th Aug., 1895-Accepted, 13th Nov., 1895
PROVISIONAL SPECIFICATION.
Improvements in Apparatus for Use in the Decomposition of
Common Salt in the Production of Sulphate of Soda, or for
analogous purposes.
We, WILLIAM THOMSON Engineer of The United Alkali Company Limited
and PHILIP JOHN WORSLEY a Director of the said Company both of Netham
Chemical Works, Bristol do hereby declare the nature of this invention to be as
follows:-
Hitherto sulphate of soda has been produced by mixing and causing to react
with each other, equivalent quantities or nearly equivalent quantities of sulphuric
acid and common salt (sodium chloride). The reaction has been usually carried
out in two separate stages. In the first stage about 65 per cent. of the salt has been
decomposed and the gaseous hydrochloric acid evolved has been associated with a
large amount of vapour of water since a large portion of the water contained in
the sulphuric acid and the moisture of the salt are driven off in this stage of the
process which has been carried out in an iron pot. The residual mass consisting of
undecomposed salt, bisulphate of soda, and free sulphuric acid as well as some
water has then been transferred to a calcining furnace where the reaction is
completed.
"
The furnaces hitherto used for carrying out the second part of the process
have been either "closed
66
or open "and the necessary turning, or stirring, of
the material has been accomplished by manual labour, or circular furnaces have
been employed provided with mechanical means for stirring the sulphate of soda
during the calcination.
"
These mechanical furnaces have been either closed (i.e. the products of
combustion have not come into contact with the charge in the furnace) in which
case the heat has been applied below the bed of the furnace as well as above the
arch and the agitation has been accomplished by means of revolving arms carrying
stirrers or ploughs. Or the furnace has been an
66 open one in which case the
fuel gases have been applied above the bed only, but beneath the arch thus coming in
contact with the charge, which has in this case been agitated by means by
revolving arms provided with stirrers or ploughs, or the furnace bed has been
made to revolve, the stirrer frame being fixed. This last class of furnace was
often used to carry out the whole process of manufacture of sulphate of soda in
a single operation.
Our invention has for its object to provide means whereby in the first stage of
the process hydrochloric acid gas is produced as free from vapour of water as
possible so that the gas may be employed without previous drying in the manu-
facture of chlorine by such processes as the Deacon process.
Another object of our invention is to provide means whereby the process can
be carried out in a perfectly continuous manner so as to obtain a steady stream of
bydrochloric acid gas but without sacrificing the benefits to be derived from the
two stages of the reaction and to combine the advantages of a closed furnace with
those of a mechanical stirrer.
According to our invention we employ in the first stage of the manufacture of
sulphate of soda a pot or pan of cast iron provided with a mechanical stirrer into
which we charge by a suitable pipe or passage sulphuric acid in a steady stream.

page_text: Through another pipe or passage provided with a worm or screw we propel
common salt into the pot. Both these pipes or passages are provided with means
for regulating the rate of supply so that the relative quantities of sulphuric acid
and salt cau be maintained in the requisite proportions. The quantity of sulphuric
acid should be adjusted to the feed of the salt so that there is an excess of
sulphuric acid. If the mixture in the pot be kept at a suitable temperature there
is formed a solution of bisulphate of soda and hydrochloric acid gas is given
off in a steady stream. The charge in the pot remains sufficiently liquid to
flow in a constant stream out of the pot through a suitable pipe or passage
into the furnace, the rate of flow corresponding automatically to the rate of
feed. The put is covered with a lid or dome provided with an exit for the
gaseous products of the reaction. It is advantageous to combine several pots with
one furnace.
The furnace is a closed furnace preferably heated both below the bed and
above the arch which closes the furnace muffle. The furnace consists of a circular
or annular bed hounded by side walls. The bed and the side walls may be
constructed of tiles and bricks or of iron, cast iron or steel plates preferably
curved to give direction to strains. This bed is supported by brick walls which
serve also as flues for the fuel gases by means of which the bed is heated.
Above this bed we arrange an arch or cover capable of revolving, and carrying
a stirrer frame which travels with the arch or cover. This roof or cover consists
of two arches supported by a circular cast iron curb ring. The lower arch
immediately above the bed may either be made of steel plates curved to give
direction to the strains or it may be made of brick work or other suitable material.
Between these two arches the fuel gases are admitted.
The curb rings are suitably suspended from a frame work of girders fastened to
and carried by an iron or steel circular way plate supported by and travelling on
bearing wheels. If the furnace bed be made annular we prefer to make the
roof annular also and to place within the central space an inner set of
bearing wheels supporting an innerway plate to give additional support to the
girders.
Below the lower arch the curb ring is provided both on the outer circumference
and in the annular space if the furnace bed be annular with a vertical flange,
which dips into and travels in a circular trough placed upon the vertical sides of
the furnace bed. This trough is filled with finished pulverulent sulphate of soda or
other suitable material so that the trough and the flange form a seal sufficiently
tight to prevent the escape of hydrochloric acid gas or other vapours between the
furnace bed and its roof. When the furnace bed is annular we place a similar
trough inside the central space and provide the inner curb ring with a similar
vertical flange so that the central space may be sealed likewise. For the purpose
of stirring the charge upon the bed we attach to the girders or curb rings which
carry the roof or to both a frame supporting a number of vertical stirrers to which
rotation is given by means of suitable gearing. The stirrers reach down to the
bed of the furnace passing through a kind of wall box built in the arches so as to
prevent access of the fuel gases. Where the stirrers pass through the lower arch
they are suitably luted or packed to prevent the escape of hydrochloric acid gas
into the atmosphere or into the fuel gases. In addition to the rotating stirrers we
fix another frame or other frames which carry or carries ploughs set at an angle
such that in travelling over the bed the material on the bed is turned over or moved
from the circumference to the centre or vice versa. These ploughs pass through a
box or slot in the arches and are luted or sealed where they pass through the lower
arch as described with regard to the rotating stirrers.
In order to heat the space between the two arches of the travelling roof, we build
on the roof a fire place or fire places. The fuel gases from this fire place or these
fire places pass through apertures in the upper arch into the space between the two
arches, and are withdrawn through apertures by means of flues or pipes which lead
to a chimney. The connections of these outlet flues to the chimuey are made by

page_text: means of a suitable sand lute or the like which permits the rotatory motion of the
flues. Or the flues may be connected to an iron chimney which is fast to the roof
of the furnace and rotating with it. Or the space between the two arches may have
producer or other gas conveyed into it by means of pipes provided with sand
lutes and the beat may be produce 1 by admitting atmospheric air into the space
and burning the gas between the arches, the products of combustion passing into a
chimney as described.
The furnace receives its charge from the pot, together with a certain amount of
fresh sait, corresponding to the excess of sulphuric acid which had been used in
the pot. The salt is delivered regularly and continuously by means of a screw or
worn. The charge whilst being calcined or roasted is kept in agitation and
prevented from sticking to the bed by means of the revolving stirrers, whilst the
ploughs, turning the charge over, cause it to travel gradually across the bed till it
is in a position to be pushed into the outlet provided for that purpose and thence
into waggons or any other receptacle placed beneath the furnace to receive
it. This discharging of the finished material is also continuous and automatic.
We have described the apparatus as being used for decomposing common salt in
making sulphate of soda but it may be used for other analogous purposes to which
it is or may be applicable.
Dated this 13th day of November 1894.
JOHNSONS & WILLCOX,
47 Lincoln's Inn Fields, Agents.
Improvements in Apparatus for Use in the Decomposition of
Common Salt in the Production of Sulphate of Soda, or for
analogous purposes.
We, WILLIAM THOMSON, Engineer to The United Alkali Company Limited,
and PHILIP JOHN WORSLEY, a Director of the said Company, both of Netham
Chemical Works, Bristol, 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:-
Hitherto sulphate of soda has been produced by mixing, and causing to re-act
with each other, equivalent quantities, or nearly equivalent quantities, of sulphuric
acid and common salt (sodium chloride). The re-action has been usually carried
out in two separate stages. In the first stage about 65 per cent. of the salt has
been decomposed and the gaseous hydrochloric acid evolved has been associated
with a large amount of vapour of water since a large portion of the water
contained in the sulphuric acid, and the moisture of the salt, are driven off in this
stage of the process which has been carried out in an iron pot. The residual mass,
consisting of undecomposed salt, bisulphate of soda, and free sulphuric acid, as
well as some water, has then been transferred to a calcining furnace, or roaster,
where the second part of the process is carried out, and the reaction is completed
and the necessary turning, or stirring, of the material has either been accomplished
by manual labour, or mechanical means have been employed.
These mechanical furnaces, or roasters, have been either closed, (i.e. the products
of combustion have not come into contact with the charge in the furnace), in which
case the heat has been applied below the bed of the furnace as well as above the
arch, the agitation being accomplished by means of revolving arms carrying stirrers
or ploughs, or the furnace has been an open one, in which case the fuel gases
have been applied above the bed only but beneath the arch thus coming in contact
with the charge, which has in this case beeu stirred by means of revolving arms
"
22

page_text: provided with stirrers, or ploughs, or the furnace bed has been made to revolve, the
stirrer frame being fixed. This last class of furnace was often used to carry out
the whole process of manufacture of sulphate of soda in a single operation.
Our invention has for its object to provide improved apparatus for use more
especially in the decomposition of common salt, for the production of sulphate of
soda, whereby in the first stage of the process hydrochloric acid gas is produced in
a continuous stream and nearly free from vapour of water, so that the gas may be
employed without previous drying in processes where a dry hydrochloric acid gas
is required as for instance in the manufacture of chlorine by the Deacon process,
and whereby the second stage can be carried out in a continuous manner thus
yielding a steady stream of bydrochloric acid gas.
According to our invention we provide a pot, or pots, having an automatic feed
for the salt and mechanical stirrers, in which pot or pots the first stage of the
decomposition of salt is effected; and we further provide in combination with such
pot or pots, a closed furnace or roaster, in which the second stage of the decom-
position of salt is effected. This furnace is provided with a fixed bed and with a
roof, which rotates and carries with it the stirring devices, and heat can be applied
both below the fixed bed, and above the rotating roof.
In order that our invention may be clearly understood we have annexed hereto
drawings illustrating our improved apparatus which we will describe as applied to
the manufacture of sulphate of soda.
Figure 1 is a section and Figure 2 is a plan shewing the combination of two
"pots" with a furnace, or roaster.
According to our invention we employ in the first stage of the manufacture of
sulphate of soda, a pot, or pots, 1, (or pans, but we will refer to them as pots),
preferably made of cast iron provided with a mechanical stirrer 3 driven from any
suitable prime mover geared to the vertical shaft of the stirrer. Into these pots
we charge sulphuric acid by a suitable pipe or pipes 4. Through another passage 5,
provided with a feeding worm or screw, we supply common salt into each pot.
Both these pipes or passages 4 and 5 are provided with means for regulating the
rate of supply so that the relative quantities of sulphuric acid and salt can be
maintained in the requisite proportions. The quantity of sulphuric acid should be
adjusted to the feed of the salt, so that there is an excess of sulphuric acid. If
the mixture in the pots be kept at a suitable temperature and the supply of the
salt and sulphuric acid be maintained steadily, there is formed a solution of
bisulphate of soda and hydrochloric acid gas is given off in a steady stream.
The charge in each pot remains sufficiently liquid to flow, in a fairly constant
stream out of the pot through a suitable pipe or passage 6 into the furnace or
roaster A, the rate of flow corresponding automatically to the rate of feed. The
pot is covered with a lid or dome 7 provided with an exit 8 for the gaseous
products of the reaction. A combination of two pots is shewn in Figures 1 and 2
but although, in order to equalize any irregularities of working, it is advantageous
to combine two or more pots with one furnace, it is to be understood that we may
use one pot, or two or more pots, as may be desired.
The furnace or roaster is a "closed furnace," preferably heated both below the
bed and above the arch which closes the furnace muffle the openings 6 passing
through the side walls thereof.
The furnace shewn is constructed as described with reference to Figures 1 to 7
in the Specification of our application for Letters Patent 21946 of even date
herewith, and we have marked the various parts of the furnace with the same
letters of reference as are used in the said Specification 21946, so that there is
no need to repeat the description of the furnace here. The furnace may be
constructed as shewn, or in accordance with any of the modifications described in
the said Specification 21946.
The furnace receives its charge from the pot or pots 1, together with a certain
amount of fresh salt, corresponding to the excess of sulphuric acid which has been
used in the pot. This fresh salt is delivered regularly and continuously by means

page_text: of the screw (1), or worm, supplying the furnace. The charge whilst being
calcined, or roasted, is kept in agitation and prevented from sticking to the bed by
means of the revolving stirrers S whilst the ploughs T turning the charge over,
cause it to travel gradually across the bed, till it is in a position to be pushed into
the outlet (Z) provided for that purpose and thence into wagons or any other
receptacle placed beneath the outlet to receive it. This discharging of the finished
material is also continuous and automatic.
The exit or exits for gaseous products (Z³) evolved during the process of
calcination in the furnace, the heating arrangements and the other accessories of
the furnace may be like those described in our aforesaid Specification 2191694, or
the heating of the roasting bed may be effected, or in part effected, by waste heat
from the pot or pots 1.
We have described the apparatus as being used for decomposing common salt in
making sulphate of soda, but it may be used for other analogous purposes to which
it is, or may be, applicable.
Having now particularly described and ascertained the nature of our said inven-
tion and in what manner the same is to be performed we declare that what we
claim is :-
1. The improved apparatus for use in the decomposition of common salt in the
production of sulphate of soda in a continuous manner or for analogous purposes,
the said apparatus consisting in the combination of a furnace or roaster and a pot
or pots such as are herein before described and illustrated in the accompanying
drawings.
2. The combination of a pot or pots (into which part of the salt is charged) with
a furnace or roaster (into which the remainder of the salt is charged) whereby in
the manufacture of sulphate of soda a uniform stream or streams of dry or nearly
dry bydrochloric acid gas is or are obtained from the pot or pots, and a uniforin
stream or streams of hydrochloric acid gas is or are obtained from the furnace
substantially as herein before described.
Dated this 13th day of August 1895.
JOHNSONS & WILLCOX,
47 Lincoln's Inn Fields, London, W.C., Agents.