AN IMPROVED PROCESS FOR ABSORBING AND UTILIZING THE SULPHUROUS ACID CONTAINED IN GASES FROM FURNACES AND CALCINING KILNS
Year: 1881

page_text: LETTERS PATENT to Charles Denton Abel, of No. 28, Southampton
Buildings, Chancery Lane, in the County of Middlesex, for an Invention of
"AN IMPROVED PROCESS FOR ABSORBING AND UTILIZING THE SULPHUROUS
ACID CONTAINED IN GASES FROM FURNACES AND CALCINING KILNS."
communication from abroad by Heinrich Precht, of Stassfurt, in the German
Empire
A
PROVISIONAL SPECIFICATION left by the said Charles Denton Abel at
the Office of the Commissioners of Patents on the 9th August 1881.
CHARLES DENTON ABEL, of No. 28, Southampton Buildings, Chancery Lane,
in the County of Middlesex. "AN IMPROVED PROCESS FOR ABSORBING AND
UTILIZING THE SULPHUROUS ACID CONTAINED IN GASES FROM FURNACES AND
CALCINING KILNS." [A communication from abroad by Heinrich Precht, of
Stassfurt, in the German Empire.]
For absorbing and utilising the sulphurous acid contained in the gases from
furnaces and calcining kilns of industrial establishments hydrate of magnesia and
hydrate of alumina are employed; both metallic oxides absorb with great energy
sulphurous acid from such gases, formning sulphites, which on heating to a red heat
are converted into pure sulphurous acid and magnesia or alumina. Instead of
hydrate of magnesia carbonate of magnesia can be employed, from which carbonic
acid is driven off while absorbing sulphuric acid from the said gases.
The technical carrying out of this process requires, firstly, that the gases or
fumes should be cooled down to about 212° Fahr.; it' is also desirable to free them
previously as much as possible from sulphuric acid and to submit the gases in a
moist condition to the action of the said hydrates. The hydrate of magnesia is
also either moistened with water and spread on hurdles in hermetically closed
chambers through which the gases pass, or it is brought in contact with the gases
in the form of milk of magnesia inside receptacles provided with stirring apparatus.
The gaseous current may be so regulated that it is first brought in contact with

page_text: the most exhausted absorbing medium, and the gases that have been nearly freed
from sulphurous acid are eventually led over pure hydrate of magnesia. The
resulting sulphite of magnesia forms a crystalline salt of the formula Mg O SO³ 6H³O,
which contains small quantities of hydrate of magnesia, and about 30 to 33 per
cent. of sulphurous acid.
With the use of milk of magnesia the sulphite of magnesia is obtained as an
almost insoluble crystalline deposit, while the sulphate of magnesia formed at the
same time remains in solution. The solution containing sulphate of magnesia
can either be utilised by itself or be used for moistening the regenerated magnesia.
On heating the sulphite of magnesia, freed as much as possible from the
adhering lye, the magnesia is regenerated, the sulphurous acid escapes partly with
the water of crystallisation at 392° Fahr. and partly at a higher temperature, and
about three per cent. remains as sulphate of magnesium in the residue.
The sulphate of magnesia formed during the absorption of the sulphurous acid
and the heating of the sulphite of magnesia can be converted into magnesia,
sulphurous acid, and carbonic acid, by heating it to redness with charcoal powder;
the escaping gas, which contains 2 volumes of sulphurous acid to 1 volume of
carbonic acid = 66 per cent. of the former, is employed for the manufacture of
sulphuric acid, like the pure sulphurous acid. It is preferable to mix the charcoal
with the magnesia before the absorption of the sulphurous acid, from one to two
per cent. is sufficient, but an excess of charcoal is not injurious, and comes into
operation at the next process. The magnesia is almost entirely recovered by this
process, only a small loss requiring to be made good with new material.
Hydrate of alumina operates in the same way as hydrate of magnesia,
absorbing the sulphurous acid from the gases until basic sulphite of alumina
Al2O3 SO² + 4 H2O is formed. As the basic sulphite of alumina only contains
from 24 to 26 per cent. of sulphurous acid, the regeneration of the alumina is less
remunerative than that of the magnesia.
Also the heated magnesia takes up water of hydration rapidly and absorbs the
sulphurous acid easier than alumina.

page_text: SPECIFICATION in pursuance of the conditions of the Letters Patent filed
by the said Charles Denton Abel in the Great Seal Patent Office on the
8th February 1882.
CHARLES DENTON ABEL, of No. 28, Southampton Buildings, Chancery Lane,
in the County of Middlesex. "AN IMPROVED PROCESS FOR ABSORBING AND
UTILISING THE SULPHUROUS ACID CONTAINED IN GASES FROM FURNACES AND
CALCINING KILNS." A communication from abroad by Heinrich Precht, of
Stassfurt, in the German Empire.
For absorbing and utilising the sulphurous acid contained in the gases from
furnaces and calcining kilos, or other apparatus evolving sulphurous acid, lime has
been employed, but its use is not advantageous, as not only does it also absorb
carbonic acid, but the sulphurous acid which is simultaneously absorbed is not
easily recoverable. I employ hydrate of magnesia or hydrate of alumina; both
these metallic oxides aborb with great energy the sulphurous acid from such gases,
forming sulphites, which on being heated to redness are decomposed and re-converted
into pure sulphurous acid on the one hand, and magnesia or alumina on the other.
Instead of hydrate of magnesia, carbonate of magnesia can be employed, from
which the carbonic acid becomes driven off while the absorption of the sulphurous
acid from the said gases takes place. Or hydrate of magnesia and carbonate of
magnesia may be used in combination.
The technical carrying out of this process requires, firstly, that the gases or
fumes should be cooled down to about 100° centigrade (212° Fahr), it is also
desirable to free them previously as much as possible from sulphuric acid, and to
submit the gases in a moist condition to the action of the said hydrates. The hydrate
of magnesia is either moistened with water and spread on hurdles in chambers,
towers, or other suitable apparatus through which the gases pass, or it is brought in
contact with the gases in the form of milk of magnesia within receptacles or
chambers provided with stirring apparatus. The gaseous current may be so
regulated as first to come in contact with some of the magnesia or alumina already
more or less saturated, and the absorbing powers of which have become more or less
exhausted, while the gases that have been thus partially freed from sulphurous acid are
eventually led over fresh hydrate of magnesia. The resulting sulphite of magnesia
forms a crystalline salt of the formula Mg O SO² 6 H*O, usually containing however
small quantities of hydrate of magnesia. It should contain about 30 to 33 per cent.
of sulphurous acid.
With the use of milk of magnesia, the sulphite of magnesia is obtained as an
almost insoluble crystalline deposit, while a small portion of sulphate of magnesia
formed at the same time remains in solution. The solution containing sulphate of
magnesia can either be utilised by itself, or be employed for moistening the
regenerated magnesia.
On heating the suphite of magnesia, freed as much as possible from the adhering
lye, the magnesia is regenerated, the sulphurous acid escapes partly with the water
of crystallisation at 392° Fahr, and partly at a higher temperature, and about 3 per
cent remains as sulphate of magnesia in the residue.
The sulphate of magnesia formed during the absorption of the sulphurous acid
and the heating of the sulphite of magnesia, can be also converted into magnesia,
sulphurous acid, and carbonic acid, by treating it according to Clemm's process,
that is, by heating it to redness with charcoal powder, the escaping gas which
contaius 2 volumes of sulphurous acid to 1 volume of carbonic acid,= 66 per cent.
of the former, and can be employed for the manufacture of sulphuric acid, like the
pure sulphurous acid. It may also be heated in a current of hydrogen sulphide or

page_text: of the vapour of sulphur, or even in a current of hydrogen or a hydrocarbon or any
other suitable volatile or solid reducing agent for the purpose of decomposing the
combined sulphuric acid, disengaging sulphurous acid, and regenerating the
magnesia. If charcoal or powdered coal be employed, it is preferable to mix.it
with the magnesia before the absorption of the sulphurous acid (from one to two
per cent is sufficient), but an excess is not injurious, and comes into operation
at the next process. The magnesia is almost entirely recovered, only a small loss
requiring to be made good with new material.
The heated gases from the furnaces, calciners, or other apparatus evolving gases
mixed with sulphurous acid, may be cooled, either by passing them through iron or
metal pipes exposed to the air, or by spraying water into them in suitable chambers
placed in the flue, or by passing them over the surface of water placed in a
suitable pan in the bed of the flue, which water may or may not be kept in a state of
agitation to promote its evaporation and consequently its cooling power, and in
this latter case the said water may be mixed with finely powdered magnesia so as
to form a milk of magnesia, and thus not only to act as a cooler but to take more
or less part in the absorption.
The same water may be used over and over again where the cooling is performed in
the flue, if any loss of sulphurous or sulphuric acid be feared from the solvent
properties of water for these acids.
•
Hydrate of alumina operates in the same way as hydrate of magnesia, absorbing
the sulphurous acid from the gases until basic sulphite of alumina Al³ OS SO² + 4
HO is formed, but the basic sulphite of alumina only contains from 24 to 26 per
cent. of sulphurous acid; the regeneration of the alumina is less remunerative than
that of the magnesia.
Also after having been heated, magesia takes up water of hydration rapidly, and
regains its power of absorbing the sulphurous acid easier than alumina does.
Having thus described the nature of this Invention, and in what manner the
same is to be performed, as communicated to me by my foreign correspondent,
I claim,―
First. The use of hydrate of magnesia and carbonate of magnesia for the absorption
of sulphurous acid from the gases of furnaces and calcining kilns.
Second. In combination with the process of absorbing sulphurous acid from gases
by means of hydrate of magnesia and carbonate of magnesia, the regeneration of
the magnesia by heating to redness the sulphite of magnesia.
Third. The use of hydrate of alumina or of a mixture of this with hydrate of
magnesia or carbonate of magnesia, for absorbing the sulphurous acid from the
gases of furnaces and calcining kilns.
Fourth. In combination with the process of absorbing sulphurous acid from gases
by means of bydrate of alumina, the regeneration of the alumina or mixture thereof
with magnesia by heating the sulphites to redness.
In witness whereof, I, the said Charles Denton Abel, have hereunto set my
hand and seal, this Eighth day of February, in the year of our Lord One
thousand eight hundred and eighty two.