Process for Treating Blast Furnace Gases for the Extraction of Alkaline and Ammonium Compounds, Iodides, and Iodine therefrom.
Year: 1894

page_text: Date of Application, 31st May, 1894--Accepted, 7th July, 1894
[Communicated from abroad by PAUL GREDT, of Esch-sur-A bzette, Luxemburg,
Belgium, Engineer.]
Process for Treating Blast Furnace Gases for the Extraction of
Alkaline and Ammonium Compounds, Iodides, and Iodine
therefrom.
I, OLIVER IMRAY, of No. 28, Southampton Buildings, Chancery Lane in 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 :-
My foreign correspondent has found, that the particles of dust, carried along by
the gases of blast-furnaces, contain besides the cyanides of alkalies, ammonia and
other useful salts considerable quantities of iodic salts; so that it would be a very
profitable business to extract them; provided that without sensibly increasing the
costs of manufacture, the following could be devised:
a. A method of separating from those gases all the particles of dust they carry ;
collecting them, at the same time, in such a state and form as would allow of
utilising them advantageously.
°
b. A method of separating the mass of the dust extracted from the furnace-gases
into its component parts by such means as are offered within the working of any
foundry.
Up to the present time trials have been made in order to extract tar and ammonia
from the gases of the blast-furnaces using raw coal.
Tar and ammonia have been obtained by condensation, and the gases having
passed through the condensers have been used for heating the boilers and hot-blast-
ovens.
As to the coke-blast-furnaces, which are by far the most numerous nowadays,
there is but very little tar in the gases, and the ammonia exists in too small a
quantity to be extracted with any profit. The gases of the furnaces have therefore
been utilised, up to now, only in respect of their heating power.
In order to prevent the solid substances which the said gases carry along with
them in large quantities (dust, fine ashes etc.) from obstructing the channels, in
several foundries, purifiers are put into the gas-pipes. The purification however
has always been incomplete, because, the size of the purifiers not corresponding
with the large volume of the gases, conducted through them, the gases pass with
too great a speed, considerable quantities of dust which is carried along with them
is deposited at short intervals in the channels, and, in obstructing these, cause a very
expensive and difficult cleaning of the channels and apparatus.
The same inconveniences also exist in the blast-furnaces for raw coal, where the
extraction of tar and ammonia has been tried.
In order to obtain the most considerable quantity of ammonia and tar by the
condensation of the vapours, the volume of the gases has been subdivided by con-
ducting them through a great many small pipes, but, owing to the enormous
volume of the gases, the passage of the latter through these pipes has been very
rapid. In order to avoid this acceleration it would be necessary to enlarge the
pipes considerably, but this would increase the cost of the ammonia and tar,
produced by this way to such an extent that it would be entirely out of proportion
to the expenses of the installation and of keeping in repair the apparatus; besides,
the swifter the current is, the less the gases are purified.
It is almost impossible to obviate the above mentioned inconveniences by

page_text: inserting larger chambers into the set of pipes and by sprinkling water or acids into
these chambers from various sides and in a direction contrary to that of the gas
current. In fact, it is entirely erroneous to imagine that an abrupt enlargement of
the pipes would cause a diminution of the swiftness of the current, as there are
formed in the said enlargements bodies of gas, through which the current traverses
with the same speed, with which it passes through the pipes. The jets of the liquids
alone, in opposing themselves to the current and dividing it, diminish that swiftness
a little.
It is moreover to be observed that, as these jets pass constantly in the same
direction, there remain vacuous spaces between them, through which the particles
of dust make their escape.
In short, speaking from a practical point of view, I may say, that the condensation
apparatus have not answered the expectations, and that the above mentioned
inconveniences still exist; the hot-blast stoves are rapidly destroyed by the dust
which is deposited in the channels, and the cleaning of the latter demands frequent
stoppages.
My correspondent has succeeded in finding not only a practical method of
completely separating all the various descriptions of dust carried along by the
blast furnace-gases from each other, but also a very profitable method of extracting
from the above mentioned gases the cyanides of alkalies, ammonia and other salts,
and of disintegrating at the same time the mass formed by the various dusts into its
component parts.
The mode of working is the following:
--
a. A lye is formed, which is saturated with all the soluble dusts, cyanides, iodides
of ammonia, alkalies and other salts carried along by the gases, whereby the latter
is simultaneously purified from all insoluble bodies.
b. This lye is evaporated.
c. The mass is heated and concentrated by evaporation, in a distilling furnace, to
such a degree that, the cyanides and ammonium-compounds being changed into
gases and disengaged, there remains an incandescent liquid mass, which is drawn
off; this mass contains iodine in the form of iodide of potassium, it contains more-
over chloride of calcium and chloride of potassium; these three substances can
easily be separated from each other by fractional crystallisation.
The practical working of this method is as follows:
The gases saturated more or less with dust according to the pressure and quantity
of the blast, are, as soon as they have left the furnace-top, conducted into a set of
pipes, constructed in such a manner that an acceleration of the current is impossible,
and there most of the dusts are separated, through their own weight from the
gases.
In the first of the purifiers the gases rise and descend; in the second they pass
horizontally through the pipes.
In both sets the interior diameter of each pipe is the same for the whole length
of the pipe, and it is so proportioned to the size of the mouth of the furnace that
the swiftness of the current is the same in any part of the pipe, rendering possible
the separation of the dusts through their own weight.
The specific weight of the blast furnace gases is on average 0.0075, that of the
dust 3:59.
Taking these specific weights, the average velocity of the gas current at the
moment it leaves the furnace throat and the average length of the purifiers, it will
be easy to find the diameter the pipes must have.
My correspondent has calculated that the pipes being from 22 to 27 yards long.
their diameter must measure between 2 and 3 yards for obtaining an entirely
satisfactory result.
The furnace gases enter into the first pipe at its top. Owing to their specific
weight which is by far greater than that of the gases, the velocity with which the
dusts move, becomes greater than that of the gas current; and in consequence the
greater part of the dusts being carried down by their own weight, leave the gas

page_text: 1
current at the bottom of the first pipe, where the direction of the current is changed,.
and drop down into a basin.
The gases, leaving the furnace top at 100°, are naturally cooled in the pipes,.
which are installed in the open air; so, that already in the first pipe, the water
vapour leaving the furnace together with the gases, are condensed; the drops of
water thus formed, fall just like the dusts in consequence of their greater specific
weight, into the basin into which the pipes are placed by couples.
The soluble particles of the dusts ie. the salts above mentioned, are dissolved
into this water resulting from the condensed steam (this happening already in some
measure during the descent) and, dropping together with the soluble substances into
the lye that accumulates in the basin they form a certain quantity of mud, which.
must be removed from time to time.
If the quantity of steam, carried along by the furnace gases is not sufficiently-
large to serve as an hydraulic closure of the purifiers, the basin can be filled up to
a certain height, with water or any other liquid.
In order to aid the condensation of the water and ammoniacal vapours and to
effect simultaneously the separation of the dusts, an artificial rain is produced in
one or several pipes; to this end the liquid of the basin is pumped into a receiver
constructed in the upper part of the pipes and provided with a perforated bottom;.
from this receiver the liquid falls down in the form of a fine rain which covers
the whole interior surface of the pipes and naturally carries down all the dusts,.
which may still have remained in the gases passing through the pipes.
In the set of pipes placed horizontally, the dusts are in the same manner
partially dissolved already in the first pipe by the condensed steam, or fall together
with the latter, on account of their greater specific weight into the basin and in this.
set, just as in the first, only the lightest dusts are carried along with the gas current.
into the second and third pipe. The separation of the dusts in the first pipe will be
a complete one, if as above mentioned a receiver with sieve is put into the upper
part of the pipe and the lye is pumped into the said receiver from the basin so that
an abundant rain is produced in the purifier. The gases, thus washed in the whole
set of the pipes, are purified from all the dusts, even from the lightest, which may
have been carried as far as the second and third pipe. The lye is used repeatedly.
for producing this artificial rain, until it is sufficiently concentrated. As soon as a
certain quantity of light dusts is mixed with the liquid, that is pumped into the
sieve and is naturally thrown into the latter together with the liquid; the sieve will
consequently become silted from time to time and must be cleaned by means of
brushes made to pass over it in different directions.
The gases delivered from all the dusts and vapours are utilized, as before, in
heating the boilers and hot blast furnaces.
A complete purification of the gases as just described, is very important in the
manufacture, because the pipes and apparatus are not only not obstructed, but the
heating power of the gases, thus cleaned, increases also in proportion to their degree.
of purity.
The lye is drawn off from time to time or continually. It is first evaporated in
basins, which are heated by the same purified gases, and may for instance be
established above the opening which leads from the boiler to the chimney, and in
which the heat of the burned gases is still sufficiently intense to produce a quick.
evaporation.
The concentrated lye, containing on average 0.75 per cent. of iodine, is
conducted through a funnel into an alembic suspended in a stove. Into the lower
part of this stove, refractory bricks are placed in such a manner, that there remain
open spaces between them, forming channels, the gas enters the stove through a set
of channels and the air through a number of openings, in order by their combustion
to heat the bricks and alembic to a white heat.
The opening of the alembic is closed during the distilling operation. The
purified gases above mentioned can also be used for heating the bricks and alembic;
the combustion gases escape by a flue.

page_text: In heating the alembic, partial decomposition and evaporation of its contents is
produced, especially of the ammonium-compounds and cyanides. The vapours and
gases formed in this way are conducted through the compartments of the receiver
in which there is a certain quantity of sulphuric acid, the chloride of ammonium is
changed there into sulphate of ammonia and hydrochloric acid. In the first
compartments the condensed matters and the matters carried away by the current
of the vapours are retained.
The gases, which leave the receiver are purified again in a "Glover" tower in
order to condense the gaseous hydrochloric acid and the cyanides. The gases,
which are not utilised, leave by the chimney.
The distillation being finished, there remains in the alembic an incandescent
mass, which is drawn off after having removed the stopper.
This mass being composed of iodide and chloride of potassium and of chloride of
calcium, can be dissolved in water and decomposed into its elements by fractional
crystallisation. From the iodide of potassium the metallic iodine is extracted by
the well known methods.
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. The herein described method of collecting the dust from blast furnace gases
by passing the gases at moderate velocity through large exposed pipes, along with
showers of liquid pumped up from receptacles in which the dust and liquid of
condensation are deposited as a mud.
2. The herein described process for extracting alkaline and ammonium
compounds, iodides, and iodine from the mud obtained as above set forth by
evaporating and afterwards condensing and collecting the liquid ingredients of the
mud, fusing the residue, and, after cooling, dissolving it in water, and finally
separating the said substances by fractional crystallisation.
Dated this 31st day of May 1894.
ABEL & IMRAY,
Agents for the Applicant.